Assessing Seawater Intake
Systems for Desalination Plants
Subject Area: Water Resources and Environmental Sustainability
Assessing Seawater Intake
Systems for Desalination Plants
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Assessing Seawater Intake
Systems for Desalination Plants
Prepared by:
Erin D. Mackey, Nicki Pozos, Wendie James, and Tom Seacord
Carollo Engineers, P.C., Boise, ID 83713
Henry Hunt
Collector Wells International, Inc., Columbus, OH 43229
and
David L. Mayer
Tenera Environmental, Lafayette, CA 94549
Jointly sponsored by:
Water Research Foundation
6666 West Quincy Avenue, Denver, CO 80235-3098
WateReuse Research Foundation
4021 Liggett Drive, San Diego, CA 92106
U.S. Bureau of Reclamation
1849 C Street NW, Washington DC 20240-0001
and
California Department of Water Resources
P.O. Box 942836, Sacramento, CA 94236-0001
Published by:
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
DISCLAIMER
his study was jointly funded by the Water Research Foundation (Foundation), WateReuse
Research Foundation (WateReuse), U.S. Bureau of Reclamation (Reclamation), and California
Department of Water Resources (DWR). he Foundation, WateReuse, Reclamation, and DWR
assume no responsibility for the content of the research study reported in this publication or for the
opinions or statements of fact expressed in the report. he mention of trade names for commercial
products does not represent or imply the approval or endorsement of the Foundation, WateReuse,
Reclamation, or DWR. his report is presented solely for informational purposes.
Copyright © 2011
by Water Research Foundation
ALL RIGHTS RESERVED.
No part of this publication may be copied, reproduced
or otherwise utilized without permission.
ISBN 978-1-60573-124-7
Printed in the U.S.A.
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
CONTENTS
LIST OF TABLES ����������������������������������������������������������������������������������������������������������������������� ix
LIST OF FIGURES ��������������������������������������������������������������������������������������������������������������������� xi
FOREWORD ������������������������������������������������������������������������������������������������������������������������������� xv
ACKNOWLEDGMENTS �������������������������������������������������������������������������������������������������������� xvii
EXECUTIVE SUMMARY�������������������������������������������������������������������������������������������������������� xix
CHAPTER 1: INTRODUCTION ��������������������������������������������������������������������������������������������������
Intake Selection Requires Consideration of Multiple Issues ���������������������������������������������
Technology Options �����������������������������������������������������������������������������������������������
Permitting Requirements ���������������������������������������������������������������������������������������
Environmental Impacts ������������������������������������������������������������������������������������������
Stakeholder Values �������������������������������������������������������������������������������������������������
Utility Constraints and Interests�����������������������������������������������������������������������������
Project Objectives ��������������������������������������������������������������������������������������������������������������
Project Approach ����������������������������������������������������������������������������������������������������������������
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CHAPTER 2: STATE-OF-THE-SCIENCE IN OCEAN INTAKE DESIGN AND
PERMITTING FOR SEAWATER DESALINATION ������������������������������������������������������������� 7
Overview ���������������������������������������������������������������������������������������������������������������������������� 7
Controlling Parameters in the Intake Selection Process ���������������������������������������������������� 8
Capacity ��������������������������������������������������������������������������������������������������������������� 10
Geology ���������������������������������������������������������������������������������������������������������������� 10
Cost ���������������������������������������������������������������������������������������������������������������������� 10
Water Quality ������������������������������������������������������������������������������������������������������� 11
Environmental Impacts ���������������������������������������������������������������������������������������� 11
Permitting������������������������������������������������������������������������������������������������������������� 11
Sustainability�������������������������������������������������������������������������������������������������������� 12
Intake Technologies ��������������������������������������������������������������������������������������������������������� 12
Open Intakes �������������������������������������������������������������������������������������������������������� 12
Subsurface Intakes ����������������������������������������������������������������������������������������������� 17
Co-Location of Seawater Intakes ������������������������������������������������������������������������� 30
Potential Alternative Approaches to Well Drilling����������������������������������������������� 31
Environmental Impacts From Intake Construction and Operation ���������������������������������� 33
Overview of Ocean Biota of Concern ������������������������������������������������������������������ 34
Impact of Intake Operation—Impingement and Entrainment ����������������������������� 34
Impact and Mitigation Measures for Open Intakes���������������������������������������������� 37
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©2011 Water Research Foundation. ALL RIGHTS RESERVED.
vi | Assessing Seawater Intake Systems for Desalination Plants
Impact and Mitigation Measures for Seawater Intake Wells �������������������������������
Impact and Mitigation Measures for Subsurface Intakes ������������������������������������
Permitting and Regulations ����������������������������������������������������������������������������������������������
Overview of the Permitting Process ��������������������������������������������������������������������
Federal Permitting Requirements ������������������������������������������������������������������������
Select State Permitting Requirements������������������������������������������������������������������
Public and Stakeholder Involvement �������������������������������������������������������������������������������
Stakeholders Are Intrinsic to the Decision-Making Process��������������������������������
Relative Values of Trade-Offs ������������������������������������������������������������������������������
Tips for Successful Stakeholder Involvement �����������������������������������������������������
Guidance on Using Stakeholder Communications Tools ������������������������������������
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CHAPTER 3: UTILITY SEAWATER INTAKE EXPERIENCE SURVEY �������������������������������
Introduction ����������������������������������������������������������������������������������������������������������������������
Methodology ��������������������������������������������������������������������������������������������������������������������
Report Format ������������������������������������������������������������������������������������������������������������������
General Utility Characteristics�����������������������������������������������������������������������������������������
Population Served, Desalination Capacity, and Intake Capacity �������������������������
Planned and Installed Desalination Capacity �������������������������������������������������������
Desalination Market Drivers ��������������������������������������������������������������������������������
Inluence of Global Warming Regulations on Treatment Planning ���������������������
Seawater Intake Design Characteristics ���������������������������������������������������������������������������
Intake Type and Technologies ������������������������������������������������������������������������������
Intake Design Features �����������������������������������������������������������������������������������������
Screening Technologies ���������������������������������������������������������������������������������������
Capital and Operating Costs ��������������������������������������������������������������������������������
Intake Operations �������������������������������������������������������������������������������������������������
Environmental Impacts and Mitigation ���������������������������������������������������������������������������
Assessment of the Entrainment and Impingement Effects of Intake Systems�����
Loss of Habitat and Environmental Evaluation of Screen Designs ���������������������
Permitting Experience������������������������������������������������������������������������������������������������������
Permitting Requirements �������������������������������������������������������������������������������������
Permitting Timelines ��������������������������������������������������������������������������������������������
The Stakeholder Process ��������������������������������������������������������������������������������������������������
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CHAPTER 4: CONTROLLING PARAMETERS IN SEAWATER INTAKE
DEVELOPMENT ������������������������������������������������������������������������������������������������������������������
Deining a Seawater Intake Scenario �������������������������������������������������������������������������������
Information Needed for Evaluating the Intake Design Options ��������������������������
Controlling Parameters in the Decision-Making Process ������������������������������������������������
Incorporating the Decision-Controlling Elements Into a Decision Framework ��������������
Part 1� Deine the Options ������������������������������������������������������������������������������������
Part 2� Evaluate the Options���������������������������������������������������������������������������������
Part 3� Compare the Options ��������������������������������������������������������������������������������
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©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Contents | vii
CHAPTER 5: USING THE DESALINATION INTAKE DECISION TOOL����������������������������� 95
Step 1: Deine Intake Design Scenario ���������������������������������������������������������������������������� 95
Step 2: Assess Technical and Logistical Feasibility of Options��������������������������������������� 95
Step 3: Identify Permitting Needs and Assess Permitting Feasibility������������������������������ 97
Step 4: Estimate Planning-Level Costs for Each Technology ��������������������������������������� 100
General Guidelines for Estimating Intake Development Costs ������������������������� 101
Step 5: Evaluate Pertinent Stakeholder Issues ��������������������������������������������������������������� 101
Step 6: Grade and Rank the Viable Options ������������������������������������������������������������������ 105
Grade the Options ���������������������������������������������������������������������������������������������� 105
Rank the Options������������������������������������������������������������������������������������������������ 107
Final Step: Generate Project Reports ����������������������������������������������������������������������������� 108
CHAPTER 6: CASE STUDIES������������������������������������������������������������������������������������������������� 111
Case Study 1: Carlsbad Desalination Plant�������������������������������������������������������������������� 111
Case Study 2: City of Santa Cruz/Soquel Creek Water District ������������������������������������ 129
APPENDIX A: SEAWATER INTAKE SYSTEMS FOR DESALINATION PLANTS
UTILITY QUESTIONNAIRE SUPPLEMENTAL DATA �������������������������������������������������� 151
APPENDIX B: COST ESTIMATES FOR THE CARLSBAD CASE STUDY ������������������������ 159
REFERENCES �������������������������������������������������������������������������������������������������������������������������� 165
ABBREVIATIONS �������������������������������������������������������������������������������������������������������������������� 171
DESALINATION INTAKE DECISION TOOL
(AVAILABLE ON CD-ROM PACKAGED WITH PRINTED REPORT AND WATERRF
WEBSITE)
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
TABLES
2�1
Partial list of existing seawater desalination plants and their respective intake types ������� 9
2�2
Studies required for seawater open intakes ���������������������������������������������������������������������� 16
2�3
Studies required for seawater intake wells����������������������������������������������������������������������� 25
2�4
Applicability of the various active and passive intake technologies to different
seawater intake locations ������������������������������������������������������������������������������������������������� 39
2�5
Major regulations and permits pertaining to seawater intake construction and
operation in California ����������������������������������������������������������������������������������������������������� 59
2�6
Major regulations and permits pertaining to seawater intake construction and
operation in Florida ���������������������������������������������������������������������������������������������������������� 62
2�7
Major regulations and permits pertaining to seawater intake construction and
operation in Texas ������������������������������������������������������������������������������������������������������������ 64
3�1
Populations served by seawater desalination plant survey respondents �������������������������� 75
3�2
Summary of desalination capacities, intake capacities, and average intake lows for
reporting plants ���������������������������������������������������������������������������������������������������������������� 75
3�3
Environmental impacts and mitigation study results ������������������������������������������������������� 85
4�1
Elements of a deined intake planning scenario ��������������������������������������������������������������� 90
4�2
Structural design options for seawater intakes����������������������������������������������������������������� 90
4�3
Controlling parameters in seawater intake planning and design ������������������������������������� 92
5�1
Deinitions of overview scenario description parameters ������������������������������������������������ 97
5�2
Deinitions of implementation feasibility scenario description parameters ��������������������� 99
5�3
Deinitions of permitting assessment parameters ���������������������������������������������������������� 101
5�4
Deinitions of cost estimation parameters and calculations ������������������������������������������� 103
5�5
Deinitions of stakeholder assessment parameters ��������������������������������������������������������� 105
5�6
Deinitions of weighting parameters ������������������������������������������������������������������������������ 106
ix
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x | Assessing Seawater Intake Systems for Desalination Plants
5�7
Deinitions of ranking parameters���������������������������������������������������������������������������������� 108
5�8
Deinitions of reporting options ������������������������������������������������������������������������������������� 109
A�1
Purpose of desalination plant ����������������������������������������������������������������������������������������� 151
A�2
Intake types and technologies ���������������������������������������������������������������������������������������� 152
A�3
Preferred screening technologies ����������������������������������������������������������������������������������� 153
A�4
Type and location of screens ������������������������������������������������������������������������������������������ 154
A�5
Capital, mitigation, O&M costs ������������������������������������������������������������������������������������� 155
A�6
Environmental impacts and mitigation �������������������������������������������������������������������������� 156
A�7
Utilities rationales for recommendation or non-recommendation of a stakeholder
process���������������������������������������������������������������������������������������������������������������������������� 157
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
FIGURES
1�1
Selecting an ocean intake design is complex ��������������������������������������������������������������������� 4
2�1
Typical on-shore (lagoon and channels) and off-shore (pipe) open wet-well intake,
line, and screen conigurations����������������������������������������������������������������������������������������� 13
2�2
Vertical seawater intake well ������������������������������������������������������������������������������������������� 19
2�3
Horizontal (Ranney) seawater intake well ����������������������������������������������������������������������� 19
2�4
Slant seawater intake well ������������������������������������������������������������������������������������������������ 21
2�5
HDD seawater intake well ����������������������������������������������������������������������������������������������� 22
2�6
Schematic of a seabed iltration intake system ���������������������������������������������������������������� 27
2�7
Conceptual drawing of the seabed iltration intake system for the Fukuoka District,
Japan, SWRO Facility������������������������������������������������������������������������������������������������������ 28
2�8
Comparison of through-low and dual-low traveling water screen arrangements ���������� 43
2�9
Schematic of a through-low vertical traveling screen ���������������������������������������������������� 45
2�10
Schematic of a ine-mesh vertical traveling screen system ��������������������������������������������� 46
2�11
Chalk Point Generating Station, Maryland, barrier net coniguration ����������������������������� 50
2�12
Illustration of an off-shore narrow-slot wedgewire screen intake system ����������������������� 52
2�13
Example of a stakeholder process designed to lead to a recommendation in the form
of a group “opinion statement” ���������������������������������������������������������������������������������������� 67
3�1a
Instructions page of the Utility Seawater Intake Experience Survey ������������������������������ 70
3�1b
Page 1 of the Utility Seawater Intake Experience Survey ����������������������������������������������� 71
3�1c
Page 2 of the Utility Seawater Intake Experience Survey ����������������������������������������������� 72
3�1d
Page 3 of the Utility Seawater Intake Experience Survey ����������������������������������������������� 73
3�1e
Additional information page of the Utility Seawater Intake Experience Survey ������������ 74
3�2
Planned and installed desalination capacity of the responding utilities ��������������������������� 76
xi
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
xii | Assessing Seawater Intake Systems for Desalination Plants
3�3
Assessment of seawater desalination market drivers by survey respondents ������������������ 77
3�4
Number of survey plant respondents considering carbon offsets ������������������������������������ 77
3�5
Seawater intake locations of survey respondents������������������������������������������������������������� 78
3�6
Intake technologies in relation to seawater intake type (surface/subsurface) of
survey respondents ����������������������������������������������������������������������������������������������������������� 79
3�7
Design features of reporting surface intakes �������������������������������������������������������������������� 79
3�8
Design features of reporting subsurface intakes �������������������������������������������������������������� 80
3�9
Screening technologies used by responding seawater desalination plants ���������������������� 81
3�10
Capital and O&M costs reported by the responding seawater desalination plants ���������� 81
3�11
Mitigation costs as a function of overall desalination plant costs reported by the
survey respondents ����������������������������������������������������������������������������������������������������������� 82
3�12
Summary of critical intake operational problems reported by the survey respondents ��� 83
3�13
Summary of non-critical intake operational problems reported by the survey
respondents ���������������������������������������������������������������������������������������������������������������������� 83
3�14
Impingement and entrainment studies among reporting plants ��������������������������������������� 84
3�15
Loss of habitat and screen design evaluations reported by survey respondents �������������� 85
3�16
Permitting requirements reported by survey respondents ������������������������������������������������ 86
3�17
Permitting timelines reported by survey respondents ������������������������������������������������������ 87
3�18
Stakeholder communication strategies reported by the survey respondents ������������������� 88
3�19
Rationales for supporting the stakeholder process reported by survey respondents ������� 88
4�1
The global intake planning decision process ������������������������������������������������������������������� 93
5�1
Flowchart describing the overview scenario deinition process (Step 1 in the
Desalination Intake Decision Tool)���������������������������������������������������������������������������������� 96
5�2
Flowchart of describing the feasibility assessment process (Step 2 in the
Desalination Intake Decision Tool)���������������������������������������������������������������������������������� 98
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Figures | xiii
5�3
Flowchart describing the permitability assessment process (Step 3 in the
Desalination Intake Decision Tool)�������������������������������������������������������������������������������� 100
5�4
Flowchart of cost estimation process (Step 4 in the Desalination Intake Decision
Tool) ������������������������������������������������������������������������������������������������������������������������������� 102
5�5
Flowchart of the stakeholder assessment process (Step 5 in the Desalination Intake
Decision Tool) ���������������������������������������������������������������������������������������������������������������� 104
5�6
Flowchart of the grading process (Part 1 of Step 6 in the Desalination Intake
Decision Tool) ���������������������������������������������������������������������������������������������������������������� 106
5�7
Flowchart of the ranking process (Part 2 of Step 6 in the Desalination Intake
Decision Tool) ���������������������������������������������������������������������������������������������������������������� 107
6�1
Overview of the intake scenario for Carlsbad���������������������������������������������������������������� 113
6�2
Screening evaluation of vertical wells for Carlsbad ������������������������������������������������������ 114
6�3
Screening evaluation of an on-shore open intake for Carlsbad ������������������������������������� 115
6�4
Screening evaluation of an off-shore open intake for Carlsbad ������������������������������������� 116
6�5
Screening evaluation of an iniltration gallery for Carlsbad ������������������������������������������ 117
6�6
Screening evaluation of a co-located intake for Carlsbad ��������������������������������������������� 118
6�7
Screening evaluation of HDD wells for Carlsbad���������������������������������������������������������� 119
6�8
Screening evaluation of slant wells for Carlsbad ����������������������������������������������������������� 120
6�9
Screening evaluation of horizontal wells for Carlsbad �������������������������������������������������� 121
6�10
Permitting evaluation for an on-shore open intake for Carlsbad ����������������������������������� 122
6�11
Permitting evaluation for a co-located intake for Carlsbad ������������������������������������������� 123
6�12
Cost evaluation for an on-shore open intake for Carlsbad ��������������������������������������������� 124
6�13
Cost evaluation for a co-located intake for Carlsbad ����������������������������������������������������� 125
6�14
Stakeholder evaluation for an on-shore open intake for Carlsbad ��������������������������������� 126
6�15
Stakeholder evaluation for a co-located intake for Carlsbad ����������������������������������������� 127
6�16
Ranking of alternatives for Carlsbad ����������������������������������������������������������������������������� 128
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
xiv | Assessing Seawater Intake Systems for Desalination Plants
6�17
Overview of the intake scenario for Santa Cruz ������������������������������������������������������������ 131
6�18
Screening evaluation of vertical wells for Santa Cruz ��������������������������������������������������� 132
6�19
Screening evaluation of an on-shore open intake for Santa Cruz ���������������������������������� 133
6�20
Screening evaluation of an off-shore open intake for Santa Cruz ��������������������������������� 134
6�21
Screening evaluation of an iniltration gallery for Santa Cruz �������������������������������������� 135
6�22
Screening evaluation of HDD wells for Santa Cruz ������������������������������������������������������ 136
6�23
Screening evaluation of slant wells for Santa Cruz ������������������������������������������������������� 137
6�24
Screening evaluation of horizontal wells for Santa Cruz����������������������������������������������� 138
6�25
Permitting evaluation of an iniltration gallery for Santa Cruz�������������������������������������� 139
6�26
Permitting evaluation of an off-shore open intake for Santa Cruz �������������������������������� 140
6�27
Permitting evaluation of slant wells for Santa Cruz ������������������������������������������������������ 141
6�28
Cost evaluation of an iniltration gallery for Santa Cruz ����������������������������������������������� 142
6�29
Cost evaluation of an off-shore open intake for Santa Cruz ������������������������������������������ 143
6�30
Cost evaluation of slant wells for Santa Cruz ���������������������������������������������������������������� 144
6�31
Stakeholder evaluation of an iniltration gallery for Santa Cruz ����������������������������������� 145
6�32
Stakeholder evaluation of an off-shore open intake for Santa Cruz ������������������������������ 147
6�33
Stakeholder evaluation of slant wells for Santa Cruz ���������������������������������������������������� 149
6�34
Ranking of alternatives for Santa Cruz �������������������������������������������������������������������������� 150
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
FOREWORD
The Water Research Foundation (Foundation) is a nonproit corporation that is dedicated
to the implementation of a research effort to help utilities respond to regulatory requirements
and traditional high-priority concerns of the industry� The research agenda is developed through
a process of consultation with subscribers and drinking water professionals� Under the umbrella
of a Strategic Research Plan, the Research Advisory Council prioritizes the suggested projects
based upon current and future needs, applicability, and past work; the recommendations are forwarded to the Board of Trustees for inal selection� The Foundation also sponsors research projects
through the unsolicited proposal process; the Collaborative Research, Research Applications, and
Tailored Collaboration programs; and various joint research efforts with organizations such as the
U�S� Environmental Protection Agency, the U�S� Bureau of Reclamation, and the Association of
California Water Agencies�
This publication is a result of one of these sponsored studies, and it is hoped that its indings will be applied in communities throughout the world� The following report serves not only as
a means of communicating the results of the water industry’s centralized research program but also
as a tool to enlist the further support of the nonmember utilities and individuals�
Projects are managed closely from their inception to the inal report by the Foundation’s
staff and large cadre of volunteers who willingly contribute their time and expertise� The Foundation
serves a planning and management function and awards contracts to other institutions such as water
utilities, universities, and engineering irms� The funding for this research effort comes primarily
from the Subscription Program, through which water utilities subscribe to the research program
and make an annual payment proportionate to the volume of water they deliver and consultants and
manufacturers subscribe based on their annual billings� The program offers a cost-effective and
fair method for funding research in the public interest�
A broad spectrum of water supply issues is addressed by the Foundation’s research agenda:
resources, treatment and operations, distribution and storage, water quality and analysis, toxicology, economics, and management� The ultimate purpose of the coordinated effort is to assist water
suppliers to provide the highest possible quality of water economically and reliably� The true beneits are realized when the results are implemented at the utility level� The Foundation’s trustees
are pleased to offer this publication as a contribution toward that end�
Roy L� Wolfe, Ph�D�
Chair, Board of Trustees
Water Research Foundation
Robert C� Renner, P�E�
Executive Director
Water Research Foundation
xv
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
ACKNOWLEDGMENTS
Carollo Engineers gratefully recognizes that the Water Research Foundation is the joint
owner of the technical information upon which the report is based� Carollo Engineers thanks the
Foundation for the inancial, technical, and administrative assistance in funding and managing the
project through which this information was discovered�
This study would not have been possible without the dedication of the following individuals and organizations:
Principal Investigators
Erin D� Mackey, Ph�D�, P�E�, Carollo Engineers, P.C.
Tom Seacord, P�E�, Carollo Engineers, P.C.
Project Team
Henry Hunt, Collector Wells International, Inc.
David Mayer, Ph�D�, Tenera Environmental
Nicki Pozos, Ph�D, P�E�, Carollo Engineers, P.C.
Wendie James, Carollo Engineers, P.C.
Susan Peterson, Carollo Engineers, P.C.
Stacy Fuller, Carollo Engineers, P.C.
Co-Sponsoring Organizations
Water Research Foundation
WateReuse Research Foundation
U�S� Bureau of Reclamation
California Department of Water Resources
Participating Utilities
City of Santa Cruz, Santa Cruz, California
Poseidon Resources, Stamford, Connecticut
Tampa Bay Water, Clearwater, Florida
Cambria Community Services District, Cambria, California
City of Corpus Christi, Corpus Christi, Texas
Long Beach Water Department, Long Beach, California
Marin Municipal Water District, Corte Madera, California
Marina Coast Water District, Marina, California
Texas Water Development Board, Austin, Texas
Water Research Foundation Project Manager
Kenan Ozekin, Ph�D�
xvii
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
xviii | Assessing Seawater Intake Systems for Desalination Plants
Project Advisory Committee
Chandra Mysore, Ph�D�, HNTB
Shahid Chaudhry, Ph�D�, California Energy Commission
Jennifer Wong, California Department of Water Resources
Robert Huehmer, P�E�, CH2M HILL
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
EXECUTIVE SUMMARY
As coastal populations grow, traditional drinking water sources are struggling to keep up
with new demands� Tapping the ocean for potable water via seawater desalination is gaining popularity as a potential water supply source� However, it can only be used where the associated regulatory, ecological, and public relations challenges can be overcome� Of the three components of
seawater desalination (intake, treatment, and concentrate discharge), intake location and design
is often the most challenging aspect of the system in terms of technical strategy, regulatory challenges, and public perception�
OBJECTIVES
The goal of this project is to take a detailed, integrated view of the seawater intake planning
and implementation process through: (1) the presentation of an overview of the seawater intake
planning and implementation process, and (2) the provision of a methodology that walks the user
through the decision-making process�
BACKGROUND
The applicability of different intake types depends upon siting options, geology, local ecology, cost, regulations, and stakeholder considerations� In many cases, implementing ocean desalination requires a broad, integrated view of the hurdles and impacts associated with each intake
type as all the elements of the decision process are interrelated� An integrated approach is needed
to best navigate intake project planning�
While it is important to have a clear understanding of what intake alternatives are technically feasible, it does not always mean that these options can be implemented� Ocean desalination
projects often fail to become reality because ocean intake alternatives:
1�
2�
May adversely affect the environment (e�g�, entrainment, impingement, sustainability,
safety of other water sources); and/or
May not adequately address stakeholder values (e�g�, water rates, water quality speciications, ecological issues)�
The intake design determines the quantity and quality of the feed water available for
treatment and must balance the needs and values of the local community and the ecosystem�
Consequently, selecting the appropriate technology for developing a seawater supply typically
considers a variety of information from many technical and non-technical sources� These include:
•
•
•
•
•
•
Site conditions,
Technology options,
Permitting requirements,
Environmental impacts,
Stakeholder values, and
Utility constraints and interests�
xix
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
xx | Assessing Seawater Intake Systems for Desalination Plants
Effective, eficient development of water management plans that may include seawater
desalination (with associated intake structure and operating plan) requires consideration of all
these elements in an integrated, structured fashion�
APPROACH
The research goal, to develop a detailed presentation of the seawater intake planning and
implementation process, was met through four primary objectives:
1�
2�
3�
4�
Development of a user-friendly technical report summarizing the state-of-the-science
on seawater desalination intake structures and methods and the costs and beneits
associated with different intake approaches (Chapter 2)�
Characterization of utility experience with the ocean intake planning, design, and
implementation process (Chapter 3)�
Creation of an ocean intake planning and decision-making tool that takes the information in the report and makes sense of the planning process for the user (Chapters 4 and
5 and a Microsoft Access-based Tool, DesalIntakeTool�mdb, included on the attached
CD-ROM)�
Illustrate the desalination intake planning and implementation process (and use
of the Tool) through two case studies (Chapter 6 and example data input to the
DesalIntakeTool�mdb ile)�
RESULTS/CONCLUSIONS
The Current State-of-the-Science in Seawater Intake Design and Implementation
Ocean intake alternatives include both surface and subsurface options; described simply:
•
•
•
Open intakes are located above the sealoor and are the most common type of intake
for large (>10 mgd, or >38,000 m3/d, production) plants�
Subsurface intakes are buried pipes and/or wells dug beneath the shoreline or ocean
loor� Seawater is drawn through the subsurface into the intake pipe� The subsurface
geology typically limits capacity and performance (as compared to open intakes)�
These can be either wells or iniltration galleries�
Co-location with an existing intake makes use of an existing intake system for a new
(desalination) application� Seawater is withdrawn from an existing intake or outfall
for another facility system (almost always a power plant)�
Each option is best-suited to different types of subsurface geology and has associated positive and negative impacts on the environment and aesthetic values� To date, wells are the most
common types of intake in use� This may change as the number of seawater desalination plants
grows; current new locations under consideration are much more diverse than in the past�
The applicability of different intake types depends upon the project-speciic siting options,
site geology, local ecology, cost, regulations, and stakeholder considerations� Environmental
impacts (and associated permitting), especially impingement and entrainment concerns, are
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Executive Summary | xxi
typically the most challenging (and costly) inluence on the intake design selected and the manner
in which it is constructed and operated�
Seawater intake wells have proven to be quite economical for desalination plants with
production capacities smaller than 10 mgd (38,000 m3/d), while open ocean intakes have found
wider application for large seawater desalination plants� In general, United States (U�S�) regulatory
agencies have indicated a preference to subsurface intake technologies (where feasible) as opposed
to direct, open-water intakes due to the reduced environmental impacts associated with these systems� Sometimes this preference can curtail the development of a seawater source or treatment
site� Generally, it will greatly increase the unit cost for producing water� Clearly, the consideration
of multiple engineering, cost, and stakeholder issues are an integrated part of the planning and
design process�
Facilitating Navigation of the Decision-Making Process
The essential planning elements, technical limitations, and controlling parameters identiied in the state-of-the science work was used to guide the development of a decision framework
for assessing the relative feasibility and merits of different intake design options for a given intake
scenario (as deined by the user)� The structure of the decision process is as follows:
Part 1. Deine the Options
Step 1. D
eine the Scenario� Describe the capacity, potential location(s), and cost factors
for the scenario under consideration�
Step 2� Do Preliminary Assessment of Technical Feasibility. The range of technical options
is identiied for each location type selected (e�g�, a cliff installation precludes the
option of a vertical well)� Some of the data will likely need to be collected before
the full analysis can be done (e�g�, geologic surveying)� In the interim, the user can
assume the option(s) are viable if (s)he prefers, inish the preliminary analysis,
and then come back and update the scenario with the needed information when its
available� This step is intended, in part, to help users identify data gaps�
Step 3� Capture Constraints and Concerns with Stakeholders (optional)� Users are encouraged to identify the stakeholders and their respective concerns that will inluence
the decision-making process� The user is encouraged to consider meeting with
stakeholder groups to: 1) educate them about the technical limitations and pros and
cons of the possible options; and (2) capture their comments, concerns and preferences about the various options�
Part 2. Evaluate the Options
Step 4. C
omplete Feasibility Analysis� Evaluate technical, permitting and stakeholder
issues� Prompt the user, in part, to collect needed data� This four-step process (technical, permitting, costs, and stakeholders) is recommended, although the last step is
not strictly needed and so is optional (though strongly recommended by the Team)�
Step 5� Estimate Cost� Identify and quantify cost elements� Each technology will have
“studies,” “permitting,” and “construction” cost lists� Calculations and default data
will be provided as feasible (this is an on-going effort)�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
xxii | Assessing Seawater Intake Systems for Desalination Plants
Part 3. Compare the Options
Step 6. G
rade and Rank Options� Assign grading criteria with weighting values and rank
the options�
Next Steps� The user is then prompted to consider a range of options to pursue next�
Please note: This tool is intended to facilitate the planning process, but is not intended
to replace a detailed Pre-Design and/or Master Plan� It is assumed that if the user were to pursue
development of a seawater intake and desalting plant following use of this tool (s)he would commission a detailed process design before any irm, concrete decisions were made�
APPLICATIONS/RECOMMENDATIONS
As seawater desalination becomes an increasingly attractive tool in the world’s struggle
to provide water for a growing population, it is the responsibility of those with the right expertise
to help make desalination a realistic option for public agencies and their customers� This project
delivers a user-friendly resource and decision methodology to help water utility managers navigate
the ocean intake selection process�
Public agencies, particularly those who are relatively unfamiliar with seawater desalination, can use this report to:
1�
2�
3�
Learn about the state-of-the science in seawater intake technology and implementation issues,
Learn what other utilities considering and using seawater intakes for desalination are
doing, and
Use the Desalination Intake Decision Tool to analyze potential scenarios for their own
situation, compare it with similar efforts, and weigh the beneits of desalination versus
the effort of implementation with respect to ocean intakes�
MULTIMEDIA
This decision process was turned into the Desalination Intake Decision Tool on the attached
CD-ROM (Microsoft Access™ program DesalIntakeTool�mdb)� This software walks the reader
through step-by-step (tab-by-tab) through the evaluation process� The user is prompted to answer a
series of questions� Most queries have “Note” sections where the user can add additional documentation related to the questions as desired� As the decision tool is targeted at developing an intake
development plan, it is assumed that the user has already determined the desalting process scenario
to the extent that he/she knows the volume of feed water the process will need�
If intake design options are deemed unfeasible at any point in the process, they are eliminated from further consideration� This process delivers technically defensible options that help a
user evaluate his/her option(s) and select which options is/are best for the application�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Executive Summary | xxiii
PARTICIPANTS
The participating utilities for this project included:
•
•
•
•
•
•
•
•
•
Cambria Community Services District, Cambria, California
City of Corpus Christi, Texas
City of Santa Cruz, California
Long Beach Water Department, Long Beach, California
Marin Municipal Water District, Corte Madera, California
Marina Coast Water District, Marina, California
Poseidon Resources, Stamford, Connecticut
Tampa Bay Water, Clearwater, Florida
Texas Water Development Board, Austin, Texas
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
CHAPTER 1
INTRODUCTION
As coastal populations grow, traditional drinking water sources are struggling to keep up
with new demands� Water agencies are turning to alternative sources to keep the taps running and
their communities satisied� Tapping the ocean for drinkable water—that is to say—seawater
desalination, is gaining popularity as a potential water supply source, but can only be used where
the associated regulatory, ecological, and public relations challenges can be overcome�
Of the three components of seawater desalination (intake, treatment, and concentrate discharge), intake location and design is often the most challenging aspect of the system in terms of
technical strategy, regulatory challenges, and public perception� These challenges are due, in part,
to the relatively limited experience many managers and other decision-makers have with desalination technology, the uncommon nature of using ocean intakes for traditional water agencies, and
the lack of a methodology to share knowledge from water utilities experienced in the desalination
implementation process�
INTAKE SELECTION REQUIRES CONSIDERATION OF MULTIPLE ISSUES
The intake design determines the quantity and quality of the feed water and must balance
the needs and values of the local community and ecosystem� Consequently, selecting the appropriate technologies for developing a seawater supply typically considers a variety of information
from several sources to determine feasibility� These include:
•
•
•
•
•
•
Site conditions,
Technology options,
Permitting requirements,
Environmental impacts,
Stakeholder values, and
Utility constraints and interests�
Technology Options
Intake alternatives include both surface and subsurface options� Each can be described
rather simply:
•
•
Surface intakes. Surface intakes are located above the sealoor and are the most common type of intake for large (>10 mgd) plants� They are typically concrete pipes that
include trash racks and screens to respectively remove debris and particulate matter
(both organic and inorganic)� Surface intakes also require additional pre-treatment
due to the presence of marine life and small particles that must be removed before the
desalination process�
Subsurface intakes. Subsurface intakes are buried pipes and/or wells buried beneath
the beach/ocean loor� Compared to surface intakes, subsurface intakes are typically
limited in capacity due to local geology; however, the extensive pretreatment required
1
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
2 | Assessing Seawater Intake Systems for Desalination Plants
for surface intakes is either eliminated or greatly reduced� Because of their limited
capacity, subsurface intakes are less common than open intakes for large plants�
Rather than designing and constructing a new surface or subsurface intake, it is sometimes
possible to use existing infrastructure� The opportunities are very limited, but other “reuse” options
include:
•
•
Shared existing intake. Co-locate a new, or share an existing intake (typically a
power plant intake)�
Converted existing intake. Convert an existing (e�g�, abandoned) intake or outfall
line into an intake for the desalination system� One example of this alternative was the
conversion of an existing wastewater outfall in Santa Barbara into an intake for the
city’s (now decommissioned) ocean desalination plant�
Permitting Requirements
The permitting environment for ocean intakes is highly complex� It involves consideration
of the environmental and social impacts associated with both the operation of the structure itself
and the construction process� It incorporates numerous State and Federal regulations (e�g�,
Section 316(b) of the Clean Water Act (CWA), the California Coastal Act, Section 10 Approval for
Construction within Dredge and Fill Permits) and almost as many regulatory agencies�
For example, the construction of a new open water intake is typically a lengthy process
involving a wide array of resource and regulatory agencies� Applicable regulations usually require
permits from:
•
•
•
•
•
The Army Corps of Engineers,
The United States Environmental Protection Agency (EPA),
The National Marine Fisheries Service,
U�S� Fish and Wildlife, and
State resource and environmental agencies through some combination of:
– Environmental Impact Report (EIR),
– Environmental Impact Statement (EIS),
– Environmental Assessment (EA),
– Biological Assessment, or
– Categorical Exclusion (CatEx),
– Endangered Species Act (ESA) Take Permit(s),
– Essential Fish Habitat, marine mammal and other wildlife protection acts, and
– National Pollutant Discharge Elimination System (NPDES) permit�
The State of California Task Force on Desalination has recommended that any new open
water intake for desalination would need to conduct 316(b) permitting and impact assessment
studies of the proposed intake’s location, design, capacity and operations, as well as the EPA’s
316(b) Phase II rule performance standards�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 1: Introduction | 3
Environmental Impacts
The construction process and operation of the intake structure can adversely impact the
environment� Construction-related concerns include erosion, disturbance of the local ecology, habitat destruction, impact of construction materials (e�g�, drilling lubricants), and the potential for
disturbance of pollutants from the soil/ocean bed� Construction impacts are primarily mitigated
using “Best Management Practices�”
Operation of the intake structure has two major impacts on the biological organisms in the
source water body: impingement and entrainment� Ocean intakes employ screening devices to
block large objects from entering the cooling water system (impingement)� Fish and other aquatic
organisms large enough to be blocked by the screens may become impinged if the intake velocity
exceeds their ability to move away�
Other mitigation measures include selecting a sub-surface well technology with low
entrainment potential, reducing the intake velocity, using ine meshed screens to exclude smaller
organisms, and siting the intake location in a less sensitive area�
Stakeholder Values
Stakeholder involvement is now an important component of many water and wastewater
public agency decisions� This is clearly evident in the process of siting an ocean intake, where
coastal watchdog groups may look suspiciously at any project that could negatively impact the
marine environment� For any project of this type to have a chance for success, managers must
involve stakeholders� Some of these methods include:
•
•
•
•
Integrating technical and policy or value discussions in open forums,
Respecting formal regulatory processes (e�g�, EIRs) while using a stakeholder process
to overcome their limitations,
Providing meaningful stakeholder roles and responding to their values while maintaining technical rigor and defensibility, and
Directing stakeholders to focus on water quality, environmental, and inancial outcomes rather than the means used to achieve them�
Analytical Tools (e�g�, ranking and grading alternatives) help organize complex choices,
while public participation methods (e�g�, workshops) are essential to interact with stakeholders
effectively about these choices� Using both sets of “tools” can facilitate successful integration of
stakeholders into the decision-making process�
Utility Constraints and Interests
Simply put, not every agency that wants to implement desalination will be able to do so�
Nor will every agency want to put in the time, resources, and effort required to implement desalination� Limitations on funding, adverse (hydro) geologic conditions, inability to eficiently overcome stakeholder challenges, or simply the lack of a proper site can derail the most enthusiastic
desalination effort�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
4 | Assessing Seawater Intake Systems for Desalination Plants
Figure 1.1 Selecting an ocean intake design is complex
PROJECT OBJECTIVES
The goal of this project is to take a detailed, integrated view of the seawater intake planning
and implementation process� As discussed above, the applicability of different intake types depends
upon the siting options, geology, local ecology, cost, regulations, and stakeholder considerations�
In many cases, implementing ocean desalination requires a broad, integrated view of the hurdles
and impacts associated with each intake type� Each element of the decision process is interrelated
to the others (Figure 1�1)� An integrated approach is needed to best navigate an intake project’s
planning approach�
While it is important to have a clear understanding of what intake alternatives are technically feasible, it does not always mean that these options can be implemented� Ocean desalination
projects often fail to become reality because ocean intake alternatives:
1�
May adversely affect the environment (e�g�, entrainment, impingement, sustainability,
safety of other water sources); and/or
2� May not adequately address stakeholder values (e�g�, water rates, water quality speciications, ecological issues)�
The project goals were met through two main deliverables: (1) presentation of an overview
of the seawater intake planning and implementation process; and, (2) provision of a methodology
that walks the user through the decision-making process�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 1: Introduction | 5
PROJECT APPROACH
This research project integrated consideration of all the above-mentioned inluences on the
decision-making process and developed four key deliverables:
1�
2�
3�
4�
A centralized state-of-the-science report on the technical, logistical, and social aspects
of intake selection (Chapter 2)�
A summary of utility experience with the ocean intake planning, design, and implementation process (Chapter 3)�
An easy-to-navigate decision tool that walks the user through the thought process of
understanding the beneits and limits of available options and selecting the best choice
from among them (a Microsoft Access-based version of this Tool is included on the
attached CD-ROM and described in Chapters 4 and 5)�
Case studies that illustrate use of the Tool and execution of the decision-making process (embedded in the software Tool on the attached CD-ROM and summarized in
Chapter 6)�
Through this project, public agencies will have a methodology to help them analyze their
own situation, compare it with similar efforts, and weigh the beneits of desalination versus the
effort of implementation with respect to ocean intakes�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
CHAPTER 2
STATE-OF-THE-SCIENCE IN OCEAN INTAKE DESIGN AND
PERMITTING FOR SEAWATER DESALINATION
In seawater desalination, salt water is irst pumped into the desalination plant from an
ocean intake structure� From there it passes through the desalination system (generally reverse
osmosis membranes) or a distillation process� The permeate (product) is re-mineralized (for drinking water this is typically to a minimum hardness of ~40 mg/L as CaCO3 and a minimum alkalinity
of ~40 mg/L as CaCO3) either through lime addition or blending with another source� Finally, it is
chlorinated/chloraminated and sent into the distribution system� The concentrate (reject) is usually
disposed of through an outfall back into the ocean� Of these three system components (intake,
treatment, and concentrate discharge), the intake is often the most challenging aspect of the system
in terms of technical strategy, regulatory approvals, and public acceptance�
This document captures the state-of-the-science in ocean intake permitting and design as
of April 2010� The intake technologies, associated environmental and permitting requirements,
and stakeholder issues considered in the Desalination Intake Decision Tool (the Microsoft Access
version of this tool, DesalIntakeTool�mdb, is included on the attached CD-ROM) are reviewed�
Supplemental information on potential new and emerging technologies, regulatory activities, and
some state-speciic regulatory information is also provided�
OVERVIEW
Ocean intake alternatives include both surface and subsurface options; described simply:
•
•
Open intakes are located above the sealoor and are the most common type of intake
for large (>10 mgd, or >38,000 m3/d, production) plants� They are typically concrete,
high-density polyethylene (HDPE), or iber-reinforced polymer (FRP) pipes with
concrete collars that include trash racks and screens to remove debris and particulate
matter (both organic and inorganic), respectively� Surface intakes require addition of
a pre-treatment system prior to the desalination process to remove marine life and
small particles in the feed water�
Subsurface intakes are buried pipes and/or wells dug beneath the shoreline or ocean
loor� Seawater is drawn through the subsurface into the intake pipe� The subsurface
geology typically limits capacity and performance (as compared to open intakes);
however, the extensive pretreatment required for surface intakes is either eliminated
or greatly reduced because the subsurface acts as a natural ilter� Because of their limited capacity and the need (in some cases) to construct a ilter bed around the screens,
subsurface intakes are less common than open intakes for large plants�
The most popular type of subsurface intake is a series of wells drilled on or
beneath the shore� The orientation can be vertical, angled, or horizontal� Seawater is
drawn through the natural sand deposits into the wells� (Although they are technically
“subsurface wells,” the geology and locations into which they are installed varies
signiicantly from all other subsurface options and thus these are often classiied separately�) Vertical wells are usually located some distance (setback) from the source
water and thus tend to produce a blended groundwater-seawater mix� Certain well
7
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
8 | Assessing Seawater Intake Systems for Desalination Plants
•
designs can be used to optimize the percentage of seawater by locating screened sections further off-shore, under the ocean, using angled or horizontal well technologies�
As with other types of subsurface intakes, wells typically greatly reduce or eliminate
the need for pretreatment prior to the desalination process; their practicality is dictated
by the local geology and groundwater quality� Any impacts to local fresh groundwater
and well day lighting from surface (e�g�, sand) erosion must be mitigated�
Co-location with an existing intake makes use of an existing intake system for a new
(desalination) application� Seawater is withdrawn from an existing intake or outfall
for another facility system (almost always a power plant)� Typically, operational coordination and ground rules are negotiated with the intake co-owner up front so both the
intake operator and the site owner can operate eficiently� Co-location solves the source
of water issue, however there are a number of issues related to changing the “existing
use” classiications for the water stream in the facility that would require design and
use changes (and possibly re-permitting) of the existing intake� This includes addressing questions about prolonging the life of the power plants and impacts from future
changes in ownership�
To date, wells are the most common types of intake in use (Table 2�1)� This may change as
the number of seawater desalination plants grows; current new locations under consideration are
much more diverse than in the past�
Seawater intake wells have proven to be quite economical for desalination plants with a
capacity smaller than 10 mgd (production), while open ocean intakes have found wider application
for large seawater desalination plants� In general, regulatory agencies have indicated a preference
to subsurface intake technologies (where feasible) as opposed to direct, open-water intakes due to
the reduced environmental impacts associated with these systems� Sometimes this preference can
curtail the development of a seawater source or treatment site� Generally, it will greatly increase
the unit cost for producing water� Clearly, the consideration of multiple engineering, cost, and
stakeholder issues are an integrated part of the planning and design process�
If a source of raw water from an existing system (e�g�, through co-location) is not readily
available, then the designer will consider whether it is best to take water from a direct seawater
intake or through a process of induced iniltration using seawater intake wells or other type of
submerged intake system� Each method has advantages and disadvantages related to the sitespeciic requirements� The overall feasibility and cost-to-beneit analysis of these issues are used
to determine which approach is the most effective for each application�
In some cases, this will be an obvious choice relating to the site characteristics, the volume
of water required, and the geology at the project location� However, at many sites there will be
multiple feasible alternatives that will need to be evaluated in order to select the approach that
makes the most sense from both a cost and an operational standpoint�
CONTROLLING PARAMETERS IN THE INTAKE SELECTION PROCESS
A number of factors, including the required capacity, geology, cost, water quality, environmental or permitting issues, and sustainability will be important considerations when evaluating
water supply/source options and selecting the most effective alternative for a particular application� Conditions will differ from site-to-site� Each parameter will affect the operation and
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Table 2.1
Partial list of existing seawater desalination plants and their respective intake types
Location
Intake type
Capacity
Golden Gate State Park
San Francisco, California, USA
Beach collector well
0�1 mgd (380 m3/d)
Santa Catalina Island
California, USA
Beach wells
0�15 mgd (570 m3/d)
Marin Municipal Water District
Corte Madera, California�, USA
Screened intake—pilot
0�2 mgd (760 m3/d)
Sand City
Sand City, California, USA
Beach well—pilot
0�26 mgd(980 m3/d)
Hyatt Regency Hotel
Grand Cayman Island
Beach wells
0�5 mgd (1,900 m3/d)
Municipal Water District of Orange County
Dana Point, California, USA
Beach slant well—pilot
0�5 mgd (1,900 m3/d)
Blue Hills
Nassau, Bahamas
Beach wells
0�6 mgd (2,300 m3/d)
Diablo Canyon Power Plant
Avila Beach, California, USA
Open intake
0�7 mgd (2,600 m3/d)
Marina Coast Water District
Marina, California, USA
Beach well
0�7 mgd(2,650 m3/d)
United Arab Emirates
U�A�E�
Floating intake on barge
1 mgd (3,800 m3/d)
Morro Bay
Morro Bay, California, USA
Beach wells
1�4 mgd (5,300 m3/d)
Antigua
Antigua
Open sea intake
2�5 mgd (9,500 m3/d)
N�V� Energie en Watervoorziening Rijnland
Leiden, Netherlands
Beach collector wells
2�6 mgd (9,800 m3/d)
U�S� Naval Base
Guantanamo Bay, Cuba
Open intake with ish trap
5 mgd (19,000 m3/d)
Ghar Lapsi
Malta
Beach wells
6�3 mgd (24,000 m3/d)
Veolia
Kindasa, Saudi Arabia
Open intake
7 mgd (26,500 m3/d)
Bay of Palma
Mallorca, Spain
Beach wells
11 mgd (42,000 m3/d)
Pemex Reinery
Salina Cruz, Mexico
Beach collector wells
12 mgd(45,500 m3/d)
Fukouka District Waterworks Agency
Fukuoka, Japan
Seabed iniltration gallery
13�2 mgd (50,000 m3/d)
Pembroke
Malta
Beach wells
14�3 mgd (54,000 m3/d)
Veolia
Sur, Oman
Open intake and beach wells
21 mgd (79,500 m3/d)
Aqualectra Production
Santa Barbara, Curacao
Permeable pit intake
22 mgd (83,000 m3/d)
Tampa Bay Water
Tampa, Florida, USA
Shared power plant intake
25 mgd (95,000 m3/d)
Desalcott
Point Lisas, Trinidad & Tobago
Bar screen intake
28�8 mgd (109,000 m3/d)
San Pedro del Pinatar
Cartagena, Spain
Horizontal bedrock wells
35 mgd (132,000 m3/d)
Public Utilities Board
Tuas, Singapore
Open intake
36 mgd (136,000 m3/d)
Sydney Water
Kurnell, Australia
Passive intake screen risers
66 mgd (250,000 m3/d)
Veolia
Ashkelon, Israel
Multiple-head open intakes
222 mgd (840,000 m3/d)
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 9
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Owner
10 | Assessing Seawater Intake Systems for Desalination Plants
maintenance for any water supply system to be employed; so each factor needs to be evaluated to
direct selection of the most effective alternative� One of a few key factors alone may simply eliminate, or conversely, nominate a particular technology as the most feasible�
Capacity
The desired capacity of the desalination plant may direct which options will be the most
feasible� Small systems (<5 mgd, or 19,000 m3/d) may be able to use a simple well as a costeffective alternative, while large systems (>20 mgd, or 76,000 m3/d) may ind that an open intake
will be the simplest, most practical, most cost-effective solution� For other, mid-range capacity
sites (5 to 20 mgd), planners often consider multiple alternatives�
Geology
Geology is perhaps the most critical issue to consider� Geologic and hydrogeologic conditions readily dictate whether a submerged intake is at all feasible� If the coastal deposits consist of
low permeability silts and clays, or low permeability consolidated (rock) formations, it may be
dificult or impossible to construct a submerged intake or iniltration gallery� For submerged intakes
to be practical, it is recommended that the transmissivity be >0�088 mgd/ft (1,100 m3/d/m)
(Schwartz 2000, cited in Voutchkov and Bergman 2007) for a depth of ≥45 ft (≥14 m) (Voutchkov
and Bergman 2007)�
If the coastal geology indicates that one or more porous geologic systems are present, these
water-bearing zones will need to be evaluated through a detailed hydrogeologic investigation to
further quantify and qualify their potential for developing the necessary capacity� Other issues,
such as seasonal erosion patterns (to ensure suficient coastal aquifer deposits exist year-round),
groundwater contamination, local groundwater use, impacts on seawater intrusion, potential
impacts and interferences on nearby users, and recharge/iniltration characteristics would also
need to be evaluated during this stage� In many cases, favorable soils/coastal aquifers exist at a
prospective site; however, the hydraulic properties (e�g�, hydraulic conductivity and transmissivity) may limit the capacity of each well, necessitating a large number of caissons that may not all
it within the project site boundaries or within a reasonable acreage that would have to be
purchased�
Cost
As the public, local government, and water utility managers evaluate the feasibility of seawater desalination, its cost is often compared with other alternatives (which often includes not
adding or losing system capacity)� This comparison is a signiicant issue when determining whether
or not the project is viable� Since there are few full-scale desalination installations in the U�S�, little
is known about the costs for constructing these intake systems within the U�S�, especially where
sensitive environmental areas along the coast are concerned, since additional costs will be incurred
during investigative, design and construction phases� However, as a general rule, open intakes
have signiicantly higher capital costs than well systems� For example, Wright and Missimer estimated a capital cost ratio (open intakes versus well systems) of approximately 1�8 to 2�0 for small
(≤2�0 mgd, or ≤7,600 m3/d) installations (Wright and Missimer 1997)� Operation and maintenance
(O&M) costs can vary signiicantly depending upon site-speciic conditions (e�g�, well depth)�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 11
Water Quality
The design of the treatment train for a desalination facility will depend on the quality of the
proposed source water; therefore, this will inluence what type of intake is preferred� Water from
an open intake requires signiicant pretreatment to remove particles, dissolved natural organic matter (NOM), aquatic organisms, loating or suspended debris, oil and grease-in short, anything that
could foul or affect the membranes within the main treatment system� Pretreatment costs should be
included in this alternative when comparing its costs to submerged and seawater intake well alternatives� Typically, well systems and properly designed submerged intakes provide satisfactory
pretreatment using the natural geologic deposits to pre-ilter the raw water before it enters the treatment plant� Results from testing at facilities using well and gallery systems typically show that raw
water turbidity and silt density index (SDI) values are maintained below membrane manufacturers’
recommendations (e�g�, Rovell 2001)� There are also instances where the salinity of the raw feed
water can vary according to the point of withdrawal� This also affects the treatment train design�
When wells are considered, elevated concentrations of certain inorganic minerals like iron and
manganese can also necessitate pretreatment prior to the desalination process�
Environmental Impacts
The nature of the location of seawater intakes–in the coastal zone–places them in environmentally sensitive areas, where public perception can play a key role in acceptance of the project;
regulatory approval can be dificult and costly� Environmental concerns include aesthetics, protection of ish and game, disturbance to local ecosystems (e�g�, wetlands or other local lora and
fauna), impacts upon existing land use, impacts to local water users, inluences on local freshwater
aquifers, and contamination from the construction process� Environmental restrictions may preclude one alternative or another from further consideration due to potential construction impacts,
ecologic degradation from long-term operation of the system, or permitting dificulty� Conversely,
on-shore sources of contamination that could be drawn hydraulically into the intake and impact the
treatment process and/or concentrate disposal (e�g�, anthropogenic hydrocarbons) should also be
considered�
Permitting
The age-old question “can this be permitted?” relects the critical nature of successfully
navigating the regulatory process� In many instances, it is a matter of conducting the proper studies, completing the requisite forms, and otherwise satisfying the requirements of the myriad agencies that hold permitting controls over an activity or facility to be approved� Identifying the
appropriate agencies and the speciic interests of the various agencies is pivotal to ensuring that all
foreseeable regulatory contingencies and situations are considered and potential roadblocks are
identiied early on in the planning and design process� In addition, where the source water may be
a blend of seawater and freshwater from local sources, water rights issues may also be involved�
(Tide-inluenced rivers can provide the opportunity to develop seawater supplies in some areas by
taking advantage of tidal cycles to obtain better quality water, less particles and/or organic material, and higher columns, timing intake operation to match the tidal cycle�) Groundwater rights can
also be an issue in some states�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
12 | Assessing Seawater Intake Systems for Desalination Plants
Sustainability
In addition to determining if a certain system can be physically designed, permitted, and
constructed at a given location, there needs to be suficient conidence that the desired lowrate can
be obtained over the lifespan of the installation� This includes consideration of both demand and
expected conditions (e�g�, recharge, tidal inluences, fouling, etc�)� This issue also factors into
design changes as pilot or demonstration systems are expanded or replaced by full-scale systems�
INTAKE TECHNOLOGIES
Open Intakes
An open (or direct) surface intake can range in design complexity from simply attaching an
intake pipe and screen assembly to an existing structure, to modifying an existing intake or outfall
line that may have been inactive, to constructing a dedicated, stand-alone structure� A typical open
intake design includes intake screens, conveyance piping, and a wet well or other mechanism for
housing the system pumps� Common intake design alternatives include the following:
•
•
•
•
•
•
•
Dock-, pier- or bulkhead- (i�e�, existing structure) mounted screens,
Wet well intake sumps with subsurface intake lines that extend to off-shore screens,
Wet well intake sumps with exposed intake lines anchored on the seabed extending to
off-shore screens,
Wet wells constructed into rock bluffs/cliffs with an intake line drilled through the
rock into the seawater with or without an attached screen,
Shoreline structures with open bay and bar rack screens,
Directionally drilled lines under and through the seabed with screens, and/or
Forebay/pump stations in sheltered settings (e�g�, sloughs or coves)�
The pump station is usually a wet well or sump structure in which pumps are mounted� It
is located on-shore at a site that allows easy access and connection to the desalination plant� These
structures can be quite large, as they usually include pumps, controls, chemical feed equipment (if
necessary), large primary screening devices like bar rack screens, secondary traveling screen
assemblies, multiple chambers, and a backwashing (sparging) system�
In some older facilities, the intake point-of-withdrawal is located at the shoreline� However,
more recent regulations typically prefer that the point-of-withdrawal is further off-shore, away
from near-shore habitats and areas where loating debris may accumulate� Figure 2�1 illustrates the
common on-shore and off-shore design conigurations�
The intake line and screen are extended to a preferred (in terms of capacity and water quality) off-shore location� The conveyance piping can be installed in several ways: (1) from an open
trench/open cut in which the pipe is laid out to the screens; (2) a trenchless approach where the
piping is installed below-grade by augering, microtunneling, or directionally drilling the borehole
from the pump station to the screens; (3) a simple above-grade layout where the pipe is laid on and
anchored to the seabed; or (4) some combination of these options� If the pump station (sump) is
located close to the screens the conveyance pipe may be very short, or not required�
Intake screens can include multiple components (e�g�, primary bar racks followed by ineropening traveling screen assemblies) or they can be simple, ixed, passive screens installed away
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 13
Figure 2.1 Typical on-shore (lagoon and channels) and off-shore (pipe) open wet-well intake,
line, and screen conigurations
from areas likely to have a lot of debris or aquatic life present within the water column� The intake
screen openings are typically sized for regulatory compliance with regard to ish and aquatic life
protection and itted with backwash capabilities to help keep screen surfaces free from debris to
maintain suitable open area to meet design entrance velocities� The design should provide the ability to inspect and maintain/clean the screens periodically, especially in areas where a high-growth
environment is expected� In some cases, it may be necessary to incorporate standby, or backup,
screens so that system performance can be maintained if one screen needs to be removed from
service for maintenance�
Depending upon the screen design, a ish trap or diversion/avoidance feature may also be
required� While some intakes draw water in through an open pipe, operating problems have been
reported with the entry of plants, marine organisms, and debris where no screens are used�
No matter which conceptual design is followed, the intake screening assembly will need to
conform with various agencies’ design guidelines regarding the protection of ish� These are principally concerned with the velocity of the water as it enters the screen itself and the size of the
screen openings� These agencies include, but may not be limited to, the National Marine Fisheries
Service (NMFS), a division of the National Oceanic and Atmospheric Administration (NOAA),
and the appropriate state Department of Fish and Game (DFG) and Fish & Wildlife (DFW) agencies� Permitting agencies will also likely consider intake design with regard to screen placement
such that it avoids areas of near-shore habitat for local aquatic life, and will require entrainment
and impingement studies�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
14 | Assessing Seawater Intake Systems for Desalination Plants
The hydraulic design of the intake will relect features that: provide suficient water depth
to maintain suitable head above the screen under normal conditions, avoid taking in loating debris,
provide suitable height above the seabed to avoid intake of saltation or bed load debris, and provide suitable height to be above seabed vegetation� Finally, intake siting may target a selected zone
within the water column for optimum water quality where stratiication occurs (if this option is
available)�
Water quality and biological issues also will affect the operation and maintenance of an
open intake� Typical factors include the presence of sea grass or eel grass, oil and grease (and other
ship trafic inluences), wastewater and stormwater discharges, biologically active environments
(where algae, mussels, barnacles, etc� are prevalent) and areas subject to algal blooms such as red
tides� These factors can physically foul the screens and membranes and can increase treatment
needs within the pretreatment and inished membrane treatment equipment through changes in
water quality�
Open intakes will require regular underwater inspection and periodic cleaning and maintenance (possibly as frequently as every 2 to 3 months) to maintain system eficiency and ensure the
needed supply can be provided on a sustained basis�
Cost
The cost of an open intake varies as widely as the types of designs that can be employed,
ranging from tens of thousands to tens of millions of dollars for even relatively small systems
(<10 mgd, or <38,000 m3/d)� While the cost for a pumping station and intake screens can be
roughly estimated from other inland/fresh water-type applications, one should keep in mind that
seawater intakes require (more expensive) corrosion-resistant materials� The length, and hence the
cost, of the conveyance piping can vary greatly, from a near-shore location (e�g�, in a slough setting) to an intake point several hundred to several thousand feet off-shore� This can incur expensive marine construction and related environmental restrictions�
Because an open intake will include some common components (e�g�, wet well pumping
station) across a wide range of capacities, costs are not proportional to capacity (i�e�, a 10-mgd
intake will not cost 10 times the cost of a 1-mgd intake)� Obviously, total cost will vary with the
required number and diameter of intake lines, and the number and size of intake screens; however,
the incremental costs for larger intake lines and screens will not be directly proportional when the
total intake system is considered�
Further complicating site-to-site cost comparisons is the fact that permitting and stakeholder negotiations can contribute substantially to project costs (over $10 million in some cases
where intake construction has been controversial)� The level of effort required for these activities
will vary greatly depending upon the local regulations, the level of stakeholder interest and concern, and the site-speciic technical conditions (e�g�, amount of surveying needed to determine if
endangered species are present or the amount of land that would need to be acquired from private
landowners)�
To date, there have been no new open intakes built in the U�S� for supplying water for
desalination facilities, so there is not a great deal of readily available data to identify what would
constitute typical costs for such an approach� However, there are many operating open intakes for
electric power plants� Data from these facilities can be used to estimate the cost and impacts of
water supply intakes for desalination�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 15
In summary, cost will always increase with capacity, but estimating expenses needs, in
large part, to be done on a case-by-case basis� Much less-costly solutions can be followed if there
are existing structures in the area to which the intake screen and conveyance piping can be attached,
such as bridge piers, bulkheads, or if existing infrastructure (e�g�, existing or abandoned intake or
outfall lines) can be modiied for use� Since a pretreatment system will need to be used with an
open intake, the cost for the pretreatment must be considered with the open intake cost when compared with submerged alternative� Pretreatment systems can cost from several hundred thousand
dollars to several millions of dollars� The cost of required entrainment and impingement studies
should also be included�
Recent Innovations
Intake screening systems are fairly well deined and are regularly improved to comply with
current and anticipated environmental regulations with regard to ish protection� The principal
innovations relating to intake design applies to the methods used for installation of the conveyance
piping from the pumping station to the screen location� While conventional open-trenching or
anchored/exposed piping approaches are still employed, the technologies for more environmentally friendly trenchless methods are being advanced to minimize impacts on the local environment during pipe installation, including the increased use of microtunneling and modiications to
horizontal directionally drilled (HDD) techniques�
Required Studies
As intake-screening devices are not designed to remove all organisms within the water
source, a number of studies relating to entrainment and impingement of biota are typically required
to support the permitting process� Some of the common studies that may be required to satisfy
regulatory and permitting bodies are presented in Table 2�2� The type of studies required will
depend on intake location and the ability of the selected screening technology to minimize entrainment and impingement�
Summary
The advantages and disadvantages of open intakes can be summarized as follows:
Pros
•
•
In most cases, provided adequate biological fouling mitigation and control measures
are employed (i�e�, prevention of biological growth on intake screens and pipelines),
an open intake should be able to meet any required capacity since the ability to deliver
the needed supply is dictated by the diameter of the conveyance piping and the size
and number of intake screens�
Intake sizing is very lexible; it should be possible to design an open intake to produce
capacities ranging from several hundred gallons per minute to several hundred million
gallons per day in virtually any geology, from a bluff or cliff setting to a shallow beach
setting to an intake in a sheltered position such as within a harbor or slough�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
16 | Assessing Seawater Intake Systems for Desalination Plants
Table 2.2
Studies required for seawater open intakes
Intake location Study type
Shoreline intake • Entrainment and source water
ichthyoplankton/selected
meroplankton�
• Hydrodynamic study of local,
ambient currents�
• Terrestrial surveys of biological
resources required at greenield
site�
Cost
$0�5 to 1�5
million
Off-shore open
water intake
$0�75
to 1�75
million
•
•
•
•
Shoreline
screened intake
•
•
•
•
Off-shore
screened open
water intake
•
•
•
•
Duration
• Year-long monthly (sometimes
bi-monthly) plankton surveys
and seasonal to continuous
hydrodynamic studies�
• Year-long quarterly surveys of
terrestrial plants and animals,
and intertidal/subtidal shoreline
communities that might be
disturbed by construction�
Entrainment and source water
• Year-long monthly (sometimes
ichthyoplankton/selected
bi-monthly) plankton surveys
meroplankton�
and seasonal to continuous
Hydrodynamic study of local,
hydrodynamic studies�
ambient currents�
• One time bathymetric survey�
Bathymetric survey�
• Year-long quarterly benthic
Benthic surveys of bottom
surveys of benthic and demersal
communities in areas pipeline and communities that might be
intake construction disturbances�
disturbed by construction�
Entrainment and source water
• Year-long monthly (sometimes
ichthyoplankton/selected
bi-monthly) plankton surveys
meroplankton�
and seasonal to continuous
Hydrodynamic study of local,
hydrodynamic studies�
ambient currents�
• Year-long quarterly surveys of
Terrestrial surveys of biological
terrestrial plants and animals,
resources required at a greenield
and intertidal/subtidal shoreline
site�
communities that might be
Screen performance testing,
disturbed by construction�
• Quarterly (or monthly) screenusually in concert with
entrainment survey�
performance tests�
Entrainment and source water
• Year-long monthly (sometimes
ichthyoplankton/ selected
bi-monthly) plankton surveys
meroplankton�
and seasonal-to-continuous
Hydrodynamic study of local,
hydrodynamic studies�
ambient currents�
• Year-long quarterly surveys of
Underwater surveys of benthic
benthic and demersal communities
and demersal biological resources along pipeline route and intake
required at a greenield site�
construction area and intertidal/
Screen performance testing,
subtidal shoreline communities that
might be disturbed by construction�
usually in concert with
entrainment survey�
• Quarterly (or monthly) screenperformance tests�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
$0�75
to 1�75
million
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 17
•
The basic framework of hydraulic designs for open intakes is well documented, and
thus can be applied relatively simply in most settings�
Cons
•
•
•
If an open intake is used, the raw water usually must be pretreated prior to entering the
membrane desalination system; this adds signiicantly to both capital and on-going
O&M costs�
Since the intake is constructed in open water, the appurtenances of the intake system
will be subject to corrosion, plugging, biological growth, erosion, wave activity, and
storm effects that can affect performance, service life, Operations and Maintenance
(O&M) requirements, and sustainability�
There will be an increased focus on the environmental protection aspects of the intake
operation as the intake screening devices are not designed to remove all the organisms
within the water source during the intake process� This will likely increase the reporting and permitting needs for the project relating to entrainment and impingement of
biota (and can prove quite costly and time-consuming)�
Subsurface Intakes
Wells
Desalination intake wells are water wells drilled in a coastal aquifer� Horizontal collector
wells are most common, but wells can also be drilled vertically (“vertical wells”) or at an angle
(“slant/angle wells” and “horizontal directionally drilled wells”)� The well concept is used where
geologic conditions are favorable to develop a water supply by pre-iltering the seawater through
natural aquifer deposits to provide low-turbidity, low-SDI water to the desalination system� This
process of natural iltration typically eliminates the need for pretreatment to remove suspended
particles from the source water� Wells can be sunk into suitable consolidated (rock) formations as
well as unconsolidated sand and gravel formations along coastal areas�
The key requirement for intake wells is the presence of a coastal aquifer formation that is
adequately permeable and hydraulically connected to the ocean so that seawater can iniltrate
through the formation and be pumped out through wells drilled near the shoreline� While many
coastal areas have sandy beaches, the underlying conditions may not be suitable; therefore, a thorough hydrogeological investigation is necessary to quantify the subsurface characteristics so that
realistic potential well yields and system design requirements can be estimated as part of determining feasibility� The yield of an intake well is typically dependent upon three principal factors:
1�
2�
3�
The hydraulic conductivity (permeability) of the formation,
The depth and aerial extent of the formation, and
The ability of the formation to receive recharge to support the intended well yield�
All of these are typically addressed during pre-design testing�
Impact on Shoreline Habitat/Aesthetics. Construction of vertical or horizontal well facilities requires disruption of a signiicant length of shoreline per unit capacity� The exact amount
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
18 | Assessing Seawater Intake Systems for Desalination Plants
needed (i�e�, how many wells are required to meet a speciic design capacity) cannot be known
until the coastal aquifer is characterized� Because of the presence of sensitive ecosystems and/or
their popularity for recreational use, obtaining construction permits and easements for coastal construction can be a formidable task� Construction activities have the potential to affect shore birds,
marine mammals, and intertidal organisms� The pipeline network necessary to link the wells with
the desalination facility may require trenching and subsequent backill of the system� Construction
would also temporarily disrupt public access to the beach�
Unsubmerged wells are constructed as large-diameter caissons with tall aboveground concrete structures that have a visual and aesthetic impact on the shoreline (Voutchkov 2005b)�
However, if the wells can be installed below-grade, long-term visual impacts will be minimized� A
buried well can be inished with a lush-grade top slab or buried in a concrete vault and backilled
with sand (Pankratz 2006)�
Potential Impacts on Freshwater Aquifers. Shoreline wells can negatively or positively
impact freshwater aquifers by either aiding or mitigating saltwater intrusion� In some situations, a
subsurface intake system (wells, iniltration galleries or seabed ilters) may draw water from existing freshwater aquifers as well as the ocean, potentially compromising seawater intrusion protection (Pantell 1993)� While wells will draw seawater toward the collection point(s), if they are
placed in close proximity to the shoreline they will not draw seawater past that point and push it
inland� In some locations, seawater intake wells can actually draw salt-water intrusion that has
moved inland back toward the shoreline as the wells are pumped and water lows toward the wells
from more than one direction� If these aquifers have been or could be contaminated, this contamination could affect the water quality available for treatment� In any case, the impact on local
groundwater sources is a factor to be evaluated in the pre-design phase�
Intake Well Types. Vertical Wells. A “vertical” well, as the name implies, is a well-drilled
straight down into the underlying rock or unconsolidated coastal aquifer system� A vertical seawater intake well consists of a non-metallic casing (typically iberglass or reinforced pipe), a well
screen, and a stainless steel submersible or vertical turbine pump� Well diameter and depth is a
function of the aquifer characteristics and potential yields� The well casing will likely be between
6 and 24 inches (15 and 61 cm) in diameter� The well depth usually does not exceed 250 ft (76 m)�
The yield from a vertical well can range up to approximately 1 mgd (3,800 m3/d) (Pankratz 2006)�
There are numerous drilling methods for installing vertical wells� The method selected for
any given project is dependent upon the formation type, required depth, well diameter, target formation for screening, and equipment availability� Standard drilling techniques include cable-tool
(percussion), air rotary, reverse circulation, air-hammer, bucket-auger, dual-tube rotary, dualrotary, and rotasonic drilling�
A vertical well can be drilled in a relatively short period of time (usually in a matter of days
or weeks); however, it is common that multiple wells will be required, increasing the time frame
for construction� These wells are typically placed near the shoreline to facilitate maintenance� As
depicted in Figure 2�2, vertical wells experience radial inlow from both seaward and landward
directions� This will likely decrease the salinity of the intake water and can inluence local groundwater sources (see previous section for discussion of potential groundwater impacts)� Vertical
wells have been used for desalination at locations around the world�
Horizontal Wells. Often referred to as radial or “Ranney” collector wells after their inventor, a horizontal well consists of a reinforced concrete caisson sunk down into the coastal aquifer
and well screens that extend out laterally into the formation from inside the caisson (Figure 2�3)�
The laterals can project radially or in a pattern oriented toward a surface water source if the intended
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 19
Figure 2.2 Vertical seawater intake well
Figure 2.3 Horizontal (Ranney) seawater intake well
water supply is to come from induced iniltration or some preferential direction, such as in a
coastal well application� The primary beneits to using a horizontal well (as opposed to a vertical
well) are:
1�
2�
It can be drilled from a central location with a long lateral reach (particularly advantageous for sites with limited above-ground access), and
The borehole is exposed to a greater surface area within the geologic formation, so
capacity is typically enhanced (Delhomme et al� 2005)�
The caisson is sunk using the open-end caisson method—each circular section of the caisson
is formed and poured on-site, at grade, and then sunk by excavating soil from inside the caisson� As
the soil is removed, the caisson sinks into the ground under its own weight� As each section sinks to
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
20 | Assessing Seawater Intake Systems for Desalination Plants
ground level, the subsequent section is tied-in, poured, and sunk� This process continues until the
lowest section (which contains the ports for jacking the well screens) reaches the design elevation
selected for screen placement� At this time, a concrete sealing plug is placed in the bottom of the
caisson so it can be dewatered and entered� The lateral well screens are then extended out through
the port assemblies cast into the walls of the lower caisson sections� Since the well screens are projected out near the base of the formation, maximum drawdown can be used and all the screens can
be installed within the most hydraulically eficient aquifer zone, optimizing well screen
eficiencies�
Since the screens in these wells are placed horizontally, a higher rate of water withdrawal
is possible than with vertical wells� As a result, fewer horizontal wells (than vertical wells) are
required to pump the same volume of water� Horizontal collector wells are typically designed to
withdraw from 0�5 mgd to 5�0 mgd (1,900 to 19,000 m3/d) of raw water each� The caisson is constructed of reinforced concrete with an inside diameter of 10 to 30 ft (3 to 9 m) and a wall thickness
of 1�5 to 3 ft (46 to 91 cm)� The caisson depth varies according to site-speciic geologic conditions,
ranging from approximately 30 to over 150 ft (9 to >46 m)� The number, length, and location of
the horizontal lateral screens are determined based on a detailed hydrogeological investigation�
Typically, the diameter of the laterals ranges from 8 to 12 in (20 to 30 cm) and their length extends
up to 300 ft (91 m)� The size of the slot opening on the lateral screens is selected to accommodate
the grain-size of the underground soil formation� If necessary, an artiicial gravel-pack ilter is
installed around the screen to prevent sand iniltration in iner-grained aquifer deposits�
As with vertical wells, horizontal wells can be located near the shoreline and unlike vertical
wells, the well screens can be projected out away from near-shore inluences� This allows the percentage of seawater being withdrawn to be maximized (i�e�, minimizes the use of on-shore groundwater sources)�
Since the well screens are installed horizontally, they can be placed within the most advantageous zone within the aquifer with respect to hydraulic eficiency and for selective water quality
withdrawal where stratiied conditions exist� Blank sections of casing can be increased near the
caisson to further concentrate the screened portion of the well (withdrawal point) off-shore to optimize the intake of seawater� Horizontal wells have been installed at hundreds of sites around the
world for induced iniltration, including a number for desalination applications�
Slant/Angle Wells and Horizontal Directionally Drilled Wells. Slant wells and HDD wells
are drilled at an angle so that the pump house and access roads can be built some distance from the
shore, minimizing loss of shoreline habitat, recreation access, and aesthetic value� Furthermore,
with the use of extensive piping, multiple slant wells and HDD wells can be connected together to
branch out and cover a large area of shoreline from a single pumping facility�
Slant/Angle Wells. As shown in Figure 2�4, to optimize the well screen distance from shore
these wells are typically drilled using rotary drilling equipment set at an angle of up to 25° from
horizontal� The primary intent of using this design is to extend the screened area of the well away
from the wellhead/pump location out toward the sea� This allows the well to be drilled in-shore but
withdraw water from a point off-shore, similar to how a horizontal well can move the point of
withdrawal off-shore while facilitating access to the well base and pumping equipment�
Because the well casing and screens are installed at an angle, the well screens will likely
transect multiple geologic layers within the coastal aquifer, drawing water of different qualities
from different layers/levels� Few slant wells have been installed for seawater desalination applications so very little data are available regarding these wells construction, performance and maintenance� In the U�S�, the Municipal Water District of Orange County (MWDOC) is pilot testing a
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 21
Figure 2.4 Slant seawater intake well
2�9-mgd (11,000 m3/d) slant well intake system in Dana Point, Calif� (Williams McCaron 2007)�
The proposed future full-scale system would produce 10 to 15 mgd (38,000 to 57,000 m3/d) of
desalinated seawater� The reported cost for this test intake was on the order of $1 to 1�5 million in
U�S� 2007 dollars�
Horizontal Directionally Drilled Wells. HDD wells are non-linear slant wells that are
installed using a specialized drilling technology that has been used extensively in the petroleum
and power industries� The equipment typically consists of a rotary drill with a custom-designed
drilling luid program to return drill cuttings, cool the drill bit, and maintain hole integrity during
boring, especially in unconsolidated deposits� As shown in Figure 2�5, drilling begins with a pilot
hole drilled at a low angle from the horizontal from an on-shore location� For a seawater application, the drilling would follow a designed proile below ground and out under the seabed to exit at
on the sea loor, typically in a large-radius arc� Once the borehole reaches its target location, the
pilot hole is reamed to a diameter suficiently large enough to accept the selected pipeline or conduit size� The pipeline or conduit is then pulled into place within the enlarged hole�
During drilling, the drilling luid is typically under signiicant pressure, so a careful mudmanagement program must be developed to ensure that this luid does not blow out (“frac-out”)
through the seabed as the drilling head approaches the surface, where the contaminated mud could
adversely impact aquatic life�
To date, this type of drilling has been used on a very limited basis for water supply wells,
largely due to the dificulty of installing a hydraulically eficient screen within an unconsolidated,
permeable coastal aquifer formation� However, HDD technology has been successfully used for a
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
22 | Assessing Seawater Intake Systems for Desalination Plants
Figure 2.5 HDD seawater intake well
few installations exceeding 10 mgd (38,000 m3/d)� For example, San Pedro del Pinatar, Spain has
a 144,000-m3/d (38-mgd) HDD ocean intake system (total production capacity 65,000 m3/d, or
17 mgd)� Nine wells deliver an average of 16,000 m3/d (4�2 mgd)� After 1 year of operation they
reported that the system was successfully delivering feed water within speciications (SDI <4,
turbidity <1�5 NTU) (Malfeito 2006)�
Recent advances in horizontal directional drilling have focused on developing ways to drill
using water in lieu of drilling luids to enable more eficient well screens to be installed and to
avoid problems such as smearing of formation soils during screen installation that would clog
screen slot openings�
Technical Issues for Construction of Seawater Intake Wells
While open intakes can be applied in almost any setting, a number of technical issues can
affect the applicability or feasibility of using intake wells�
Geology. First and foremost, the geologic and hydrogeologic conditions at a given site
dictate whether or not wells can practically meet the design capacity for a planned facility� Aquifer
conditions such as depth, hydraulic conductivity (permeability), recharge rate, and water quality
must to be suitable for developing a high enough yield per well to provide the needed capacity
within the space available for siting the facility� As stated previously, a hydrogeologic investigation is needed to identify the site’s geologic conditions and determine the hydraulic characteristics
of the coastal aquifer before well yields and design requirements can be adequately estimated� This
investigation typically includes exploratory test drilling and aquifer pumping tests� In some cases,
geophysical investigations can be used to screen and rank potential well sites along the shoreline
to minimize the test drilling phase� Computer low modeling can be useful where multiple well
systems may be required or where evaluation of hydraulic inluences and interferences between
nearby wells is needed� Soil and aquifer proiles in coastal areas are typically stratiied; identiication and selection of the most appropriate zone within the aquifer can enhance the well’s
performance�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 23
Sustainability. The aquifer must be able to meet the capacity of the planned facility during
both the pilot/demonstration phase and over the expected life of the full-scale system� In general
terms, it is appropriate to consider vertical wells for systems that would require a raw water supply
of 1 to 2 mgd (3,800 to 7,600 m3/d), slant wells for supplies of 1 to 5 mgd (3,800 to 19,000 m3/d),
and horizontal wells for supplies ranging from 5 to 20 mgd (19,000 to 76,000 m3/d) or more,
although each site will have their own aquifer conditions, which could be outside these general
ranges�
Aesthetics. Since seawater intake wells are typically in close proximity to the coastline,
addressing aesthetics is often an issue with public acceptance of the project� As stated at the beginning of this section, seawater intake wells have been completed below grade (and buried), lush
with grade, and above grade with a pump house structure, which can often be architecturally
designed to reduce visual impacts and/or blend in with existing structures in the facility setting�
Pumping Equipment. The pumps to be installed in a vertical well or in the caisson of a
collector well can be either standard vertical turbine or submersible pumps since they are typically
installed in a conventional vertical arrangement� Pumps installed in slant or HDD wells, that do not
intersect a wet well or caisson, will often need to be submersible so that they can be installed
within the angled well casing� The pumping equipment must be constructed of special corrosionresistant materials to prolong service life�
Maintenance. As well, performance declines (as the screen openings gradually become
plugged through a variety of physical, chemical, and biological mechanisms), periodic well screen
cleaning and redevelopment will be required to maintain production eficiency and meet production capacity� Well maintenance on vertical wells and collector wells follows industry standards,
however, well screen maintenance in slant and HDD wells may require specialized maintenance
techniques in order to access and rehabilitate the full length of the screened interval effectively�
Construction Area and Time. Construction in coastal areas will undoubtedly require some
activities on or near beaches or other public-use areas� In many cases, there will be limitations on
when construction activities can occur based on seasonal uses for the location, environmental
restrictions during certain breeding times, and other limited-access situations�
It is also necessary to evaluate how much shoreline frontage is (potentially) available to the
project to determine if suficient property exists to it in the requisite well system with appropriate
spacing� The physical dimensions for the area required for installation of seawater intake wells will
vary according to the method selected, with a vertical well requiring the smallest working area and
HDD drilling likely requiring the largest area�
The construction area for horizontal wells and slant wells is similar� The duration of construction will vary according to the method selected, again with a vertical well requiring the least
amount of time and a horizontal well requiring the longest time for construction due to its multiplestage assembly needs� In general, a vertical well can typically be completed with several weeks, a
slant or HDD well within several months, and a horizontal well within a number of months up to
a year for the larger wells�
Cost. The cost for seawater intake well systems is quite variable� For accurate cost comparisons, the cost for each respective system should include all facility components, including the
well(s), pumping equipment and controls, mechanical piping, wellhouse, security fencing, electrical service and water main to connect the wells together, access roads, property acquisition and
other related expenses� The costs for any necessary investigations and pre-construction testing for
each alternative should also be included�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
24 | Assessing Seawater Intake Systems for Desalination Plants
The number of wells required for each well type will depend upon the aquifer hydraulics at
each site� A general rule of thumb for comparison is that a slant well has about 1�5 times the yield
of a vertical well, and a horizontal well has a yield of about 5 to 10 times (average of 7) that of a
vertical well� These comparisons have not been compared to yield expected from a HDD well
since there is extremely limited data available on this topic�
General cost estimates for installing seawater intake wells (unequipped) range from
$200,000–500,000 for a vertical well, $3,000,000–5,000,000 for a collector well, $1,500,000 for a
slant well, and about $3,000,000 for an HDD well� Obviously, site-speciic conditions will signiicantly affect construction costs for these alternatives� Cost estimates for deeper vertical wells
(several thousand feet deep), which may be appropriate at some sites, can exceed $1,000,000�
Drilling With Fluids. For any well drilled using a viscous drilling luid (e�g�, drilling mud),
a common practice with rotary drilling, special procedures are required to reduce potential negative impacts (e�g�, plugging) on the permeability of the formation� The drilling luid must be controlled to limit penetration into the formation, and development programs must be able to effectively
remove and dispose of residual mud to optimize well eficiency� The drilling luid program should
avoid the use of biologically active muds that may exacerbate bacterial growth within the aquifer�
In addition, the drilling program for HDD wells needs to protect against the drilling luid fracing
out through the seabed as drilling pressures exceed those balanced by the soil cover�
Recent Innovations. As mentioned above, slant wells and HDD well technologies are relatively new, and as such, are in a state of continuing development for the environmental setting
under consideration here� Continuing research is focused on materials of construction, striving to
identify cost-effective materials that can be used in a saline environment for longevity of service
and that may resist biological growth� In addition, horizontal and slant well technologies are continuing to identify improved construction methods that will allow longer well screens to be
installed, enabling well placement further back from environmentally sensitive near-shore areas
while maintaining the point-of-withdrawal off-shore� HDD well drilling technologies are continuing to improve methods for constructing wells in unconsolidated deposits while maintaining the
integrity of the aquifer pore space openness and permeability�
Required Studies
In order to assess the impact of seawater intake wells and subsurface intake systems, a
number of studies are often required to support the regulatory and permitting process (Table 2�3)�
Since both intake types provide natural pre-iltration of the raw seawater, impingement, and
entrainment is minimized and the studies focus on hydrogeological impacts, sediment erosion, and
low modeling� In addition, potential or existing contamination from on-shore sources may need to
be evaluated�
Summary
Seawater intake wells have proven to be quite economical for small desalination plants
(<10 mgd, or <38,000 m3/d), while open ocean intakes have found signiicantly wider application
for large seawater reverse osmosis (SWRO) desalination plants� In general, regulatory agencies
have indicated a preference for subsurface intake technologies as opposed to direct, open water
intakes due to the reduced environmental impacts associated with these systems�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 25
Table 2.3
Studies required for seawater intake wells
Type of study
Hydrogeological study
Groundwater low
modeling
Erosion study
Off-shore geophysical
survey
Endangered species
survey
Type of data collected
• Data review�
• Test drilling�
• Aquifer testing and
analysis�
Investigate:
• Salt-water intrusion�
• Well interferences�
• Impact on local fresh
water sources�
• Evaluate projected
erosion over a period of
time�
Duration of study
• Seasonal (monthly or
quarterly) evaluation of
groundwater conditions�
• Using existing
data developed in
hydrogeological study
—modeling effort of
~4 months�
• Using existing data—
modeling effort of
~1 month�
• Locate old trenches and • One time study requiring
valleys under the seabed�
~1 to 2 months�
• Seasonal inventory
• Identify on-shore
and mapping surveys,
and off-shoregenerally done on a
endangered species
monthly or quarterly
that may be affected
basis�
by well construction or
operation�
Range of costs
required to complete the study
$100,000–
$500,000*
$50,0000–
$250, 000
~$50,000
$400, 000
$5,000–$100,000
* Wide range relect consideration for stringent regulatory environments where permitting and local site controls
may require special procedures be followed to minimize impacts on drilling sites�
As of September 2009, there were only four operational SWRO facilities with capacities
larger than 5�3 mgd (20,000 m3/d) using seawater intake wells worldwide� The largest SWRO
facility with intake wells is the 38-mgd (144,000 m3/d) San Pedro del Pinatar installation in Spain�
The second-largest is the 14�3-mgd (54,000 m3/d) Pembroke plant in Malta (Aboelela 1997,
Andrews 1985)� The 11-mgd (42,000 m3/d) Bay of Palma SWRO plant in Mallorca, Spain uses
intake wells with capacity of 1�5 mgd (5,700 m3/d) each� The fourth largest is the 7�2-mgd
(27,000 m3/d) plant in Blue Hills, Bahamas�
The advantages and disadvantages of seawater intake wells can be summarized as
follows:
Pros
•
•
The raw water produced from seawater intake wells typically has been pre-iltered
through the rock formation, greatly reducing or eliminating the need for pretreatment
prior to the desalination process�
Since the well systems are not physically in contact with the open water, the potential
for entrainment and impingement is eliminated, making this approach attractive from
a regulatory standpoint, as it optimizes protection of ish and aquatic life�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
26 | Assessing Seawater Intake Systems for Desalination Plants
•
The natural iltration typically provides a fairly consistent raw water quality and with
narrower temperature ranges than generally found with surface water sources�
Cons
•
•
•
•
•
For large-capacity systems, aquifer conditions may limit the yield available from individual wells, thus requiring that many wells be installed to meet the project water
needs�
There may be insuficient property available to properly space and locate the necessary wells for a given project, or additional property may be needed, raising the project costs�
If the well system is too large and unwieldy or if additional property is required, the
costs and O&M requirements may become prohibitive�
Depending upon what water sources are within the hydraulic inluence of the well(s),
local groundwater aquifers may be inluenced by pumping, or the water quality may
contain excessive concentrations of certain inorganic minerals, such as iron and manganese, which may require specialized pretreatment prior to the desalination process�
Production of drilling mud can have adverse environmental impacts and disposal
issues� However, in some cases, this can be mitigated by using alternate drilling
techniques�
Iniltration Galleries/Seabed Filtration
An iniltration gallery uses induced iniltration to develop a pre-iltered water supply from
a seawater source (Figure 2�6)� Iniltration galleries are typically constructed in marine environments within excavated areas and in areas adjacent to seawater, such as in beach sands parallel to
the shoreline or consolidated formations, like coral limestone, that abut the source water� Seawater
iniltrates through the porous rock formation and into the intake�
These systems are typically constructed by excavating native soils or rock, placing a screen
or network of screens within the excavated area, and then backilling with a porous media (of a size
and depth similar to that of granular media ilters used for conventional water treatment plants) to
form an artiicial ilter around the screens� Heavy armor stone is sometimes required for erosion
protection� These excavations need to be located beyond surf zones, in areas with suficient water
depth and at an appropriate burial depth to protect the integrity of the structure�
The intake screens are typically connected to a pump station/sump by a pipe� By pumping
the system, water is drawn into the excavation and iltered through the media, undergoing some
pretreatment in the process (large particle removal)� If the ilter media cannot suficiently remove
suspended particles, marine organisms, organic matter, and other debris alone it may be necessary
to install pretreatment equipment in conjunction with this type of intake� As wave action, currents,
and sedimentation occur with time, impacts on this type of intake will likely require periodic
removal of suricial silts and debris and ultimately replacement of the entire ilter media to maintain performance�
Filter beds are sized and conigured using the same design criteria as slow sand ilters� The
design surface-loading rate of the ilter media is usually about 0�2 to 0�3 gpm/ft2 (8�0×10–3 to
12�0×10–3 m3/min-m2)� Approximately 1 inch (2�5 cm) of sand is typically removed from the surface
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 27
Source: Adapted from Poseidon Resources Corporation 2004�
Figure 2.6 Schematic of a seabed iltration intake system
of the ilter bed every 6 to 12 months� After about three years, the eroded sand must be replaced with
new sand to its original depth�
Currently, there are few existing large seawater desalination plants (with capacity >5 mgd,
or 19,000 m3/d) using seabed intake systems� The largest seawater desalination plant with a seabed
intake system is the 13�2 mgd (production capacity) Fukuoka District SWRO Facility in Japan
(Figure 2�7)� The Fukuoka seawater desalination plant seabed intake area is 312,000 ft2 (7�2 ac� or
29,000 m2)�
Technical Issues
Filter Media Maintenance. Maintaining iniltration eficiency depends upon the needed
iniltration rate (water velocity at the interface between the seawater and the ilter media) to limit
ilter clogging of layers near the interface� As the pore spaces within the ilter media become
plugged over time, it becomes necessary to either reduce the pumping rate or perform periodic
rehabilitation to remove particles and biological growth (to restore porosity)� Submerged intake
designs need to incorporate backwash, or sparging, capability (although operating data suggest this
action to have limited effectiveness) and provide the means to collect operating data (e�g�, pumping rate, water level differentials, and turbidity) and periodically inspect interior portions of the
gallery system� If ilter media openness cannot be maintained, ilter eficiency will decline over
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
28 | Assessing Seawater Intake Systems for Desalination Plants
Source: Adapted from Vautchkov and Bergman 2007�
Figure 2.7 Conceptual drawing of the seabed iltration intake system for the Fukuoka
District, Japan, SWRO Facility
time, reducing the performance and yield of the intake, requiring a substantial degree of invasive
maintenance of the intake bed to restore adequate performance�
Erosion. Near-shore submerged intakes can be subject to periodic erosion during storm
events, seasonal sand migration, bottom wave surges, tidal action, etc� that impact the thickness
and presence of the ilter media over time� For example, if there is suficient seasonal erosion, the
entire ilter media may be periodically removed during winter months and then replaced during
summer months as sand cyclically migrates away from and subsequently re-deposits on the sea
loor� This erosion/re-deposition pattern often alters the grain-size gradation of the ilter media
over time, changing the iniltration characteristics and thus the yield� Portions of the gallery system
itself can also be damaged or removed by such activity�
Water Quality. Since submerged intakes typically incorporate a thinner layer of ilter media
than is used in conventional ilter plants or at sites where seawater intake wells use natural formations for iltration, a lesser degree of iltration storage capacity is available, allowing easier breakthrough of particles and/or organic matter� The quality of the source water can also be a factor
when siting an intake or deciding on the most effective intake type and design� Selecting a location
for the point-of-intake where the water quality is better can signiicantly improve system
performance�
Cost
The cost for construction of submerged intakes depends upon a number of factors including the length of conveyance piping, design and location of the sump/pump station, intake screen
design, intake location (i�e�, distance from the shoreline), and site-speciic requirements to satisfy
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 29
environmental and permitting conditions� In terms of overall water cost (including both the capital
and O&M components), seabed iltration systems are usually more costly than any of the other
type of subsurface intakes� At this time, there are no submerged intakes in place at desalination
plants in the U�S�, so no applicable example cost data are available�
Summary
Iniltration galleries tend to be used where seawater intake wells are not feasible due to
geologic conditions and where very low capacity is desired� For example, iniltration galleries are
suitable for sites where the permeability of the underground soil formation is relatively low and for
bank iltration where the width of the coastline or the on-shore sediments is insuficient to develop
conventional seawater intake wells�
These intakes are problematic with regard to the accurate prediction and sustenance of
pumping rates, maintenance of suitable iniltration eficiencies, and maintenance of gallery screens
and ilter media� Since these systems are typically constructed with a relatively thin layer of media,
they may not achieve an optimum degree of iltration of suspended particles�
Because submerged intake construction is typically disruptive, permitting and environmental restrictions may preclude their approval at some sites� As these intakes become plugged,
rehabilitation may require re-excavation within the marine environment, which would likely be
both costly and problematic from an environmental and permitting standpoint�
The advantages and disadvantages of submerged intakes can be summarized as follows:
Pros
•
•
Affords some preiltration of the source water before it reaches the desalination membranes, which reduces pretreatment needs�
Since a submerged intake is basically a constructed ilter around an intake screen, it
can be applied virtually anywhere, in a wide range of geologic settings�
Cons
•
•
•
Since the ilter media is typically artiicially placed in an excavation, it is dificult to
determine what the system capacity will be as pre-construction coastal aquifer testing
is often limited or impractical� The capacity may be estimated using theoretical calculations or using conservative estimates based on similar operational experience in
similar settings�
The design of a submerged intake typically includes relatively thin ilter media layers
and limited grading of media sizes such that the intake of particles and organic materials that plug interstitial pores and accumulate within the screening and conveyance
portions of the intake is expected� Erosion or wave action may also alter the hydraulic
properties of the ilter media, which could affect performance and capacity� This
necessitates maintenance to remove plugging debris to maintain suitable capacity�
Environmental restrictions can make such maintenance problematic and/or costly�
Since this type of intake is often constructed fairly close to the shoreline, it is expected
to be subject to erosion forces during storm events and to seasonal erosion/replacement sequences such that the system may become exposed, damaged, or signiicantly
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
30 | Assessing Seawater Intake Systems for Desalination Plants
altered� These changes will undoubtedly change the intake performance over time,
potentially affecting yield, eficiency, maintenance frequency, and even interrupting
service if damage or impacts are severe�
Co-Location of Seawater Intakes
In some situations, it may be possible to co-locate a new seawater desalination plant adjacent to an existing industrial ocean intake or outfall� In most cases, the “existing infrastructure” is
the cooling water intake or outfall of a coastal power plant� As with open intakes, microscreens
(<0�5-mm, or <0�02 in� openings) are typically used to remove any remaining marine organisms
and particles (Voutchkov 2005a)� To mitigate the environmental impact of entraining marine life,
the organisms collected on the microscreen hoppers can be conveyed to a wet well and pumped
back into the cooling water outfall for release back into the ocean� Such “reuse” options include:
•
•
Sharing an Existing Intake. It is typically very advantageous to share an existing
intake� The infrastructure is already in place, as is a withdrawal permit� Power plants
with once-through cooling systems are typically the most beneicial, although other
attractive options exist� A example of this alternative is the recent permitting of the
Carlsbad Desalination Plant in the City of Carlsbad, California� This installation is
presented as a Case Study in a later chapter�
Converting an Existing Intake. It is also often advantageous to convert an existing
abandoned or soon to be abandoned intake or outfall pipeline into an intake for a new
desalination system� One example of this alternative was the conversion of an existing
wastewater outfall in Santa Barbara, California into an intake for the City’s desalination plant (currently not in operation)�
If the facility is to be co-operated with a power plant or other installation, operational
agreements that address communications, low scheduling, functional constraints, and costsharing arrangements should be negotiated and agreed to as a part of the pre-design process�
The opportunities for co-location are very limited (i�e�, there are not many existing intakes
and outfalls that would be available for such a purpose), but from a cost and logistics standpoint,
co-location is generally preferred to new construction� However, this approach can be controversial where there is a strong desire by stakeholders to decommission the existing structure�
Summary
The advantages and disadvantages of using an existing intake can be summarized as
follows:
Pros
•
•
Potentially large capital cost savings due to elimination of infrastructure capital
expenses and some O&M expenses�
Many of the permits are already in place, so only modiication of an existing permit
would be needed, saving both time and money�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 31
•
If water is obtained from a power plant cooling process, the elevated temperature
could reduce energy requirements for the desalination process, reducing O&M costs�
Cons
•
•
•
•
Permitting can be dificult and costly where public opposition exists to maintaining
long-term use of an intake structure�
Any environmental concerns associated with the existing pipeline would still have to
be addressed (this is typically concerns surrounding an extension of its operational
life past the power plant decommissioning)�
If water is obtained from a power plant cooling process, the elevated temperature will
often lower permeate water quality from the SWRO process possibly requiring a
higher level of treatment�
The water quality at the existing location would have to be accepted, regardless of
whether an intake at an alternative location would provide advantages in the design
and operation of the desalination plant�
Potential Alternative Approaches to Well Drilling
In the U�S�, seawater desalination is still considered an emerging or developing technology�
As such, there are continuing improvements being made to the design and construction of seawater
desalination intake structures� As with all technologies, there are other approaches/modiications
to the standard approaches described above that are either: (1) used in other industries, or (2) emerging new technologies� Depending upon the size of the project and the potential beneits design and/
or construction modiications could offer, utilities and consultants may want to consider investigating new approaches to subsurface drilling� This section lists some such innovative technologies
and techniques in subsurface drilling, culled primarily from waste management and oil-and-gas
drilling� Such operations similarly must drill into the local geology, be concerned with keeping the
drilling luids separate, and try to minimally disturb the surrounding area�
Casing While Drilling
Conventional oil drilling uses short lengths of rigid pipe, but in casing while drilling, this
has been replaced by coiled steel or composite tubing� In such systems, drilling equipment is
deployed down a borehole at the end of a long string of composite tubing or hose, which is uncoiled
from a large spool on a specialty rig or truck located at the surface� When a planned section of the
borehole is drilled, the drill bit is retrieved and the casing is pulled into place� Increasingly small
sections of the well are drilled and the pipe is pulled into place�
A recent invention (U�S� Patent No� 6,722,451) presents “a method to deliver an expandable casing string to an uncased borehole coaxially upon a composite coiled tubing drilling string…�
Once the drilling operation is completed, the casing string is expanded by supplying pressure
between the coaxially positioned strings to expand the casing string to the borehole” (Saugier
2004)� Essentially, the casing is put in place while the hole is drilled, then it is expanded to the
outer wall of the boring after being pulled in by the drilling head� Some signiicant pros and cons
of using this new drilling method are summarized below:
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
32 | Assessing Seawater Intake Systems for Desalination Plants
Pros
•
•
•
•
It eliminates the need for a pit at the bottom end (so the pipe can be pulled through the
borehole)�
It allows deeper drilling�
It allows more directional capability than the standard approach (using rigid sections
of pipe)�
It prevents leakage of drilling luids into the surrounding geology�
Cons
•
•
It is a patented technology�
Conventional casings are not easily deployed into such a well� Standard steel casings
are not lexible enough to follow the contours of tortuous drill paths�
Environmentally Contained Mud Annulus
Drilling in surf and near maritime zones will often use a mud-powered drill� Pressurized
mud is channeled to the drill bit� As the drill cuts into the geology, the mud sweeps the cuttings and
tailings up out of the hole along the outside of the casing� If the local geology is fractured or weak,
the mud-cuttings-tailings mix can escape into the surrounding area� While mud drilling is an effective technique, a number of environmental concerns can complicate or preclude its use:
•
•
Drilling mud leaking from the drilling annulus is contaminated with drilling luids and
so will contaminate the surrounding area�
Geology along surf and maritime zones is vulnerable to wave-induced erosion and is
often fractured, which provides more routes for drilling luid to leak into the surrounding area�
A recent invention (U�S� Patent No� 6,851,490) presents a system that allows the drill “pressure [to] be controlled in the vicinity of the drill head not to exceed either the ambient hydrostatic
pressure at the drill head and/or the ability of the geologic formation to prevent polluting leakage
into the overlying body of water” (Cherrington 2005)� If proven, this approach could substantially
lower the pressure of the drilling mud and avoid mud cracking out through the ocean loor� Some
signiicant pros and cons of using this new drilling method are summarized below:
Pros
•
It would prevent leakage of drilling luids into the surrounding geology�
Cons
•
•
•
It is a patented technology�
It is a relatively new technology�
Drilling mud poses a problem for SWRO operation and disposal of development
water�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 33
Gravel Screening of Drill Cuttings
A major concern in underground horizontal drilling (as is the case in drilling into the seabed) is the removal of the reamed mud� These cuttings are often heavier than the transport (drilling) luid and can settle to the bottom of the hole, forming a compacted mass� Often, a porous well/
intake casing surrounded by a iltering medium (often gravel) will be used� If insuficient ilter
media is used the hole will clog and may also contaminate the media, reducing its effectiveness�
Another invention from the oil-and-gas industry (U�S� Patent No� 5,209,625) presents a
“method and apparatus for installing a horizontal porous pipe surrounded by a iltering medium”
(an engineered gravel pack) to improve integrity of the borehole (Cherrington 1993)� This method
mitigates sand iniltration into horizontal water walls, compaction at the bottom of the well, and
problems associated with locating well intakes in materials that could vary and be iner than anticipated (Cherrington 1993)� Some signiicant pros and cons of using this drilling method are summarized below:
Pros
•
•
•
Being able to install a well from a single blind hole would allow the work to be conducted from on-shore�
Costs could be signiicantly lower-working in the marine environment is usually
much more costly than drilling from land�
It could make permitting more feasible in sensitive areas�
Cons
•
•
It is a patented technology�
Conventional casings are not easily deployed into such a well� Standard steel casings
are not lexible enough to follow the contours of tortuous drill paths�
Microtunneling
Microtunneling is being used for installation of water and sewer piping in a wide range of
settings� Typically, this technology involves an entry and exit shaft/pit� It may be impossible to
complete this type of installation in a sensitive environment such as the ocean bed where access to
an off-shore point for the exit point may not be possible� Advancements in this technology are
focusing on developing retraction capability to allow blind hole drilling so that the microtunneling
bore can be made off-shore� The boring equipment could then be retracted through the projection
pipe and a well constructed within the projection pipe that could eficiently withdraw a raw water
supply�
ENVIRONMENTAL IMPACTS FROM INTAKE CONSTRUCTION AND OPERATION
The effect of intake construction and operation on the marine environment is of signiicant
concern in the design, permitting, and implementation of seawater intakes� Construction impacts
can include disturbance of coastal land and of the marine environment and contamination of the
marine environment with drilling luids during intake installation� During operation, impingement
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
34 | Assessing Seawater Intake Systems for Desalination Plants
and entrainment of marine life is of primary concern� The environmental issues and impacts surrounding intake construction and operation are summarized in the following discussion�
Overview of Ocean Biota of Concern
The type of ocean biota that is affected by the construction and operation of a seawater
intake is a function of the intake’s location, the nature of the source water body, the local lora and
fauna, and the design and operating characteristics of the intake�
Tides and currents, including currents induced by operation of the intake itself, transport
planktonic organisms that have little or no swimming ability into the intake� Their passage through
the intake system can be fatal depending upon the species� The concentration of plankton in the
ocean water is highly variable both spatially and temporally� Bays and estuaries with high levels of
nutrients can have correspondingly high concentrations of both phytoplankton (plants) and zooplankton (animals), while open coastal areas with nutrient-poor waters may support very limited
planktonic communities� Seasonal luctuations in nutrient levels, sunlight, and temperature can
produce luctuations in the composition and overall concentration of the plankton� The reproductive cycles of larger plants and animals (invertebrates and ish) can add eggs, larvae, and juvenile
offspring to the plankton�
The effects of intake operation on planktonic species at a population level are very limited
with the possible exception of sensitive, localized species that might normally occur in very low
numbers� Larger, non-planktonic, invertebrates and ish are better able to walk, crawl, or swim
away from intake-induced currents and thus can better avoid subsequent entrainment or impingement� As with plankton, species composition and abundance is highly site-speciic� Demersal species (those living on or near the bottom) tend to be less susceptible to entrapment than species
occupying the midwater depths�
The position of the intake in the water column, its location relative to the shoreline, and the
intake’s approach velocity all have an inluence on the relative impact of intake operation on individual species�
Impact of Intake Operation—Impingement and Entrainment
The withdrawal of seawater affects the biological resources of the source water body
through two processes: impingement and entrainment� Impingement refers to biota, typically ish,
becoming physically trapped on the intake screens� Entrainment refers to biota getting drawn into
the intake with the seawater inlow� Impingement and entrainment mortality associated with the
operation of open intake systems has historically been one of the drivers behind the use of intake
wells and iniltration galleries�
Most circulating water systems employ some type of primary screening device (bar rack)
to block larger objects from entering the seawater intake system� Smaller secondary screening
systems generally consist of an array of mesh or slot screens that can be stationary or rotating�
Mesh sizes of approximately 0�95 cm (3⁄8 in�) to 1�6 cm (5⁄8 in�) are commonly used in the steam
electric power industry to screen cooling water intake structures� Fish and other aquatic organisms
large enough to be blocked by these screens may become impinged if the intake velocity exceeds
their ability to move away, or if they become entangled in debris that may be present in front of the
intake system� These organisms will remain impinged against the screens until the intake velocity
is reduced so they can move away or until the screen is rotated and backwashed to remove them
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 35
into a collection basket for release� The loss of these organisms (normally both juvenile and adult
sizes) can directly impact the intakes source water populations (standing stocks) and a loss of
future population, typically calculated as production foregone�
A number of facilities employ intake systems that collect ish and other organisms removed
by intake screens and return them to the source water� The effectiveness of such systems to return
the organisms is relatively easy to measure, but the survival and ecological success of the returned
organisms is dificult to observe or quantify� It is a commonplace occurrence for the return point to
become a ish feeding station for larger ish and birds� Generally, the best practice is to use intake
locations and designs that avoid entrapping ish, such as shoreline locations rather than on deadend channels or sloughs, and to use louvers and passive screens such as narrow-slot low-velocity
screens to allow organisms to be swept away from the intake area�
Small planktonic organisms, including the early life-stages of larger organisms, pass
through the screen mesh and are entrained in the circulating water low� These organisms are
exposed to velocity and pressure changes from the circulating water pumps and, in some cases, to
chlorine or other antifouling practices� The ilter feeding of fouling organisms such as mussels and
barnacles that line marine intake conduits and pipes consume large quantities of the organisms
entrained in the intake low (up to 95 percent); biofouling is typically a primary source of entrainment mortality�
Since passage through the intake system is assumed to kill most entrained organisms,
intake design and performance studies are conducted to determine if the entrainment mortality rate
would be signiicant at the population level for the affected species� The additional mortality rates
imposed by the intake system on the high natural mortality rates of early life stages in most species
typically cannot be measured directly due to the high natural variability of the populations in the
marine environment�
Relatively few seawater intake facilities employ systems that eliminate entrainment of ish
and other organisms� Passive ine mesh and narrow slot screens have proven effective at reducing
entrainment, but examples of such screening systems to perform in the marine environment effectively are limited to fouling and maintenance issues� However, the survival and ecological success
of the screened organisms are generally without question� Best practice is to locate the passive
screen intake in locations with strong ambient currents (sweeping lows) to maximize ine mesh
screen performance� The effectiveness of ine mesh and narrow slot screen to reduce entrainment
and eliminate impingement is a function of the ratio of intake through screen velocity-to-ambient
current velocity�
A number of seawater intake facilities have signiicantly reduced the biofouling of both
intake screens and system conduits through the use of antifouling coatings� Though the antifouling
coatings materials and application methods are still experimental, they have proven effective in
their earlier stages of service�
Loss of Habitat
Loss of habitat is always incurred, to a greater or lesser degree, with the use of any type of
intake technology� In the case of open intakes, the impact is relatively low� Construction involves
the removal or covering of the existing shoreline or near-shore benthic habitats with the man-made
structures that form the intake� However, over a period of time, these structures themselves are
colonized by marine organisms and become new habitats� The type of habitat involved may be
dissimilar, a concrete pipe substituting for a sandy seabed, but overall there is little net loss of
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
36 | Assessing Seawater Intake Systems for Desalination Plants
habitat, and there is even a possible increase in the biomass and diversity supported by the presence of the intake structure�
Seawater intake wells and other subsurface, iniltration-type structures can have a much
greater impact on the existing habitat if they require the excavation of large coastal areas in close
proximity to the ocean� After construction, the well pumps, piping, electrical equipment, and their
protective enclosures, all necessary for the operation of the system, will occupy a portion of the
beach zone�
Discharge
The environmental concerns associated with the discharge from any desalination facility
revolve around the brine that is produced as a byproduct of the desalination process and its potential effects on receiving water organisms� The hypersaline discharge tends to be of a higher density
than the receiving water and can, therefore, sink to the bottom and negatively impact benthic and
demersal organisms in the vicinity of the discharge� Diluting the brine to reduce its salinity prior
to discharge can minimize negative effects� If this is accomplished by increasing the intake volume, then the reduced discharge effects may be offset by the increased impacts associated with the
elevated intake lowrate (e�g�, increased impingement and entrainment, habitat loss due to the need
for an enlarged intake structure)�
Inluence of Source Water Characteristics on Intake Impacts
The characteristics of the source water body used by the intake can have a large impact on
the design and operation of a desalination facility as it inluences both performance and environmental impacts� Physical factors such as temperature, salinity, and turbidity may be relatively
stable in one location but luctuate widely on a seasonal or even daily basis at another spot within
the same water body� Ship trafic, storm water, river lows, currents, waves, tides, and shoreline
characteristics at different locales determine which intake technology will perform well and which
will be unsuitable from place-to-place�
The eficacy of an off-shore intake in reducing entrainment depends, to a large degree, on
the vertical stratiication of entrainable organisms in the water column at the point of withdrawal�
In such a system, entrainment reduced by locating the submerged intake at a depth where the concentration of entrainable organisms is less (than at other depths)� Off-shore intakes typically terminate at a vertical riser of the inlet conduit in 30 to 50 ft (9 to 15 m) of water� Since the same volume
of intake water must pass through an off-shore inlet with an opening much smaller (commonly 15
to 20 ft, or 4�6 to 6�1 m) than the existing shoreline intake, the low rate would need to be reduced
to maintain the intake velocity design standard of 0�5 ft/s (0�15 m/s)�
While it is readily apparent that the physical and biological characteristics of a source
water body at any given location are site-speciic, some general characteristics typical of the
broader classiications of different types of seawater (i�e�, open ocean, bays and estuaries, or even
existing power plant outfall water) are summarized in the following sections�
Ocean. When attempting to characterize the open ocean as a potential water source, one
must irst recognize the wide range of conditions encompassed within this classiication� At a given
location, the ocean may be a very high-energy water mass or may be relatively calm� The shoreline
can range from rocky vertical cliffs to gently sloping sandy beaches� Temperature, salinity, and
other physical and chemical variables may be relatively constant or vary widely over time�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 37
Biologically, the ocean at a speciic location may be relatively sterile or rich in plant and animal
life�
In general, the ocean represents a very large water mass and, as such, it has the ability to
absorb or buffer natural and manmade inluences with little or no noticeable effect� A facility using
the ocean as its water source and, most likely, as the receiving water body for its discharge, will
have little physical, chemical, or biological inluence on the ocean outside of the immediate area
surrounding the facility, so environmental concerns are typically conined to the vicinity of the
potential intake location�
Bay/Estuary. Bays and estuaries differ from the open ocean primarily in terms of scale�
Their water volume is much smaller, they tend to be shallower, and they are protected from the
high-energy waves and storm surges that regularly act upon open coastal waters� Biologically, they
are usually very productive and often function as spawning grounds and nurseries for a variety of
ish and invertebrate species� Many of the larvae and early life stages of these species are small,
fragile, and very weak swimmers; as such they are easily entrained and/or impinged by an operating intake system� In comparison with the ocean, bays and estuaries have a lower capacity for
absorbing the environmental impacts associated with intake operation and maintenance�
Environmental concerns may be conined to the vicinity of the potential intake location or may
extend to the overall health of the water body�
Power Plant Discharge Water. Using the discharge water from an existing coastal power
plant (which uses seawater for cooling) as the feed water for a desalination facility eliminates construction impacts and typically will not introduce any new operational impacts� Shunting water
through a desalination facility does nothing to increase the impingement and entrainment already
associated with the operating power plant’s circulating water system and routing the membrane
concentrate into the existing discharge pipe helps to dilute and disperse it� Environmental concerns
are typically associated with the impact on local biota of potentially for extending the operating
life of the intake after the power plant has been decommissioned�
Impact and Mitigation Measures for Open Intakes
Open intakes divert water directly from the ocean� As discussed previously, marine life can
be negatively affected when they either are held against the screens (impinged) or pass through the
screens and into the intake pipe (entrained)� The extent of this impact is related to the source water
characteristics, type of technologies used, and the intake location�
The major components that make up most open intake systems are similar but their sitespeciic arrangement, construction, and operation can greatly inluence the individual contribution
to entrainment and impingement impacts that is made by each component at a given facility� They
are as follows:
•
•
•
Intake location—Open coastline, bays, harbors, estuaries�
Primary screening—Usually very coarse screenings, large-sized mesh or gaps in bar
rack systems located at or near the intake entrance(s)� These systems are usually stationary screens or bars, but some have debris removal (raking) systems�
Secondary/ine screening—Traveling water screens used to catch smaller organisms
and particles not removed by the primary screens� The mesh size varies from about
25 mm (1 in�) down to 1 mm (0�04 in�)� These screens can be equipped with Ristrophstyle baskets and ish-return systems�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
38 | Assessing Seawater Intake Systems for Desalination Plants
Other important design variables include:
•
•
•
•
Intake approach velocity—Impingement increases with an increase in intake approach
velocity�
Overall length of the intake system—The longer the intake (length of conduits and
piping), the greater the available surface area for macrofouling settlement� This affects
the number of fouling organisms preying on entrained animals, debris management
concerns, and the type of biofoulant-control strategy needed�
Placement of the screening systems within the intake system—This primarily concerns the positioning of the screening equipment relative to the intake entrance� Most
off-shore intakes have both their primary and secondary screens located on-shore at a
considerable distance from the intake entrance� This allows both aquatic animals and
non-buoyant debris to enter the system� The only size-limiting feature is the area of
the entrance itself� Fish and other aquatic animals can become resident within the
system between the inlet and the primary or secondary screens� If the inlet approach
velocity is low enough, ish can swim out, but they may opt to remain in the system
feeding on other entrained organisms or the attached biogrowth� Biofouling control
measures such as heat treatment can be lethal for the resident organisms, resulting in
large ish kills�
Shoreline intake systems can also promote large resident ish populations if
their screens are located downstream of the intake entrance� Many such systems have
passive bar racks located at the intake while the secondary, iner mesh, active screens
are located a considerable distance downstream, usually just in front of the intake
water pumps� As with an off-shore intake, ish that can it through the spacing in the
bar racks (usually 2 to 3 in� or 5 to 8 cm) can take up residence within the intake water
system upstream of the secondary screens� Systems with both their primary and secondary screens located in close proximity to the inlet do not have to deal with resident
ish mortality�
Site-speciic biofouling species and biofouling control strategies—Most macrofouling species are ilter feeders that remove their prey from the intake water as it lows
over them� Prey can include planktonic organisms, ish, and invertebrate larvae, juvenile and small adult aquatic organisms� The walls of the intake water system conduits
and piping provide an extensive substrate for macrofouling attachment and growth� A
well-developed macrofouling layer contributes to entrainment mortality and becomes
a source of debris (e�g�, barnacle and mussel shells) that can reduce the performance
of the intake system�
In response to the problems associated with biofouling, most facilities have developed control strategies to inhibit, control, or eliminate biofouling settlement and growth�
These strategies may include (alone or in combination) chemical treatment, thermal
treatment, mechanical cleaning, and the use of anti-fouling or foul-release coatings�
Screen Application Sites
The screening mechanisms discussed here can be used for both on-shore and off-shore
intakes as both types locate their screens on-shore� The only major difference between on-shore
and off-shore screening, in most cases, is that the inlet to an off-shore the system is located upstream
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 39
Table 2.4
Applicability of the various active and passive intake
technologies to different seawater intake locations
Intake technology
Active screening technologies
Adjustable vertical barriers
Angled screens
Center-low/dual-low screens
Fish return conveyance systems
Modular inclined screens
Vertical traveling screens
Standard through-low vertical traveling screens
Fine-mesh modiied traveling screens
Other modiied traveling screens
Passive screening technologies
Aquatic ilter barriers
Barrier nets
Light and acoustical deterrents
Louvers
Narrow slot/wedgewire screens
Porous dikes
Velocity caps
Variable frequency drive (VFD) pump seasonal/
diurnal low management
Ocean
On-shore Off-shore
Bay/Estuary
On-shore Off-shore
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
(off-shore) and connected to the shoreline or in-shore structures by an intake pipe, tunnel or
conduit�
Different mitigation technologies are preferred for different intake locations (Table 2�4)�
The majority of off-shore inlets are unscreened and ish can readily enter the system� If the approach
velocity to the inlet is relatively low (<~0�5 ft/s, or <~15 cm/s) and a low velocity is maintained
throughout the intake piping, ish can swim in and out of the system at will� At higher velocities,
ish entering the system cannot escape, but may remain resident within the system without becoming impinged on the in-shore screens� Biofouling is a concern with off-shore systems since the
inlet and piping provides an abundant surface area for macrofouling settlement and growth� Filter
feeding macrofouling organisms prey on the entrained larvae and smaller organisms and can contribute greatly to entrainment mortality�
Active Screening Technologies
A wide variety of active screening devices are currently available� In active screening,
water passes through a sieve and the impinged debris is physically removed� The size of the
removed material is a function of the screen’s mesh size� Since the debris can include impinged
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
40 | Assessing Seawater Intake Systems for Desalination Plants
organisms, some of these screening systems incorporate mechanisms to gently detach the impinged
material and return it to the water body from which it was taken�
Organisms that are small enough to pass through the screen mesh are entrained with the
intake water and may or may not survive their passage through the remainder of the system�
Screens with a relatively large mesh size will entrain more organisms than those with a small mesh
size, but since many of the small organisms (including ish larvae and ichthyoplankton) are fragile,
changing to a ine-mesh screen may only exchange entrainment mortality for impingement mortality� Fine-mesh screens also impinge more debris that can physically damage, smother, or entangle
impinged organisms�
In general, the following active (often referred to as “traveling”) screen features will tend
to increase the survival of impinged organisms:
•
•
•
•
•
•
•
•
Low approach velocity (ideally ≤0�5 ft/s [≤0�15 m/s])�
Escape or diversion channels upstream of the screen that allow actively swimming
organisms a way out prior to impingement�
Lifting baskets or trays that provide ample volume for water and the removed aquatic
organisms�
Fine-mesh screens�
Continuous operation of the screen system to minimize the amount of time the organisms spend impinged�
A gentle but effective spray system for washing organisms from the screen surface�
As short a return system as possible to minimize physical damage during the return
process�
An effective biofouling control strategy for the traveling screens and the return
piping�
Adjustable Vertical Barriers. An adjustable vertical barrier is used to redirect the present
inlet lows of the intake from the lower portion of the water column to other depths between the
loor and the surface� For some locations, this device can reduce entrainment rates by selecting a
level of the water column for withdrawal that has relatively lower concentrations of larvae or other
organisms than at other levels of the water column� In other cases, it may be a detriment� The effect
is site-speciic and should be evaluated case-by-case�
This type of barrier is better suited to stably stratiied areas� Fish larvae and other forms of
plankton in deep bays, such as San Francisco Bay and the San Francisco Bay Delta, have exhibited
strong patterns of stratiication that luctuated vertically with tidal velocity, direction, and daylight/
nighttime conditions� It would be impractical to try to track the position of a vertical barrier to
match the complex variation in planktonic larvae concentrations in water bodies like these�
There is a similar likelihood that raising the elevation of the intake withdrawal higher in the
water column could, in some cases, increase the rate of entrainment mortality� For example, a
study by Brothers (1975) found that the larvae of Clevelandia ios were positively phototactic for
the irst ten days of their larval stage, the stage most susceptible to entrainment� Since these goby
larvae are found at the surface during this period, redirecting the intake withdrawal from the bottom to the top of the water column could signiicantly increase entrainment mortality� For a similar
reason, adult anchovy that commonly school in the surface water might be more susceptible to
impingement if an intake structure’s withdrawal point was moved higher in the water column� The
presence of a physical barrier surrounding the intake area might reduce the number of crabs that
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Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 41
are impinged by directing their bottom movements out and around the intake structure and its traveling screens�
Angled Screens. Angled screen installations are composed of a series of vertical traveling
screens arranged strategically at an angle to maximize diversion of ish and other marine animals
to a primary bypass line� The organisms captured in the primary bypass line will typically be led
to a secondary bypass line, holding tank, or released back to the natural habitat� Most angled screen
installations have been added to protect young salmonids� Angled screens have been studied for
possible use at intake structures to protect a variety of ish in freshwater, riverine, estuarine, and
marine environments (Electric Power Research Institute [EPRI] 1999)� They also have been used
in hydroelectric and irrigation intake facilities� Installations of angled screens in combination with
diversion and ish return systems are effective at removing entrapped and/or impinged organisms
with varying degrees of return survival� It can protect the young-of-the-year and older ish, and is
an effective device for preventing impingement� The combined experience gained from past studies indicates that angled screen systems can be very effective for diverting ish into a bypass line
if given the proper physical and hydraulic conditions� There have been various studies on angled
screen performance at different facilities around the U�S�
At Brayton Point Station Unit 4 in Mt� Hope Bay, Massachusetts, an 18-month biological
effectiveness evaluation was conducted to determine the species type, number and initial/extended
survival life of ish diverted in the bypass line (Davis et al� 1988)� This intake structure has eight
openings that extend to the bottom of a skimmer wall� There are trash racks at the inlet and behind
this is a screenwell� A center wall divides the structure into two halves� Each half is equipped with
three lush-mounted vertical traveling screens set 25° normal to the low� The ish are guided to a
rectangular opening and are then sluiced back to Lee River� The diversion eficiency of the angled
screen was determined by the comparison of the proportion of ish entering the bypass to the number of ish entering the screenwell� The number of ish that entered the screenwell was calculated
by adding the ish impinged on the angled screens to the estimated number of ish diverted during
the impingement period� The survival rates at the Brayton facility varied from 25 percent for fragile species to 65 percent for hardy species� The overall diversion eficiency of all species was 76�3
percent (Davis et al� 1988)� The study noted that the diversion eficiency increased to 89�7 percent
when young-of-the-year bay anchovy were excluded� In sum, there were a total of 79,206 ish collected from the angled screens and diversion low during the experimental period and the system
was not very effective for young bay anchovy but was suficient to adequately protect the other
species�
A full-scale experiment was conducted in the Danskammer Point Generating Station on the
Hudson River in 1981 (EPRI 1999)� The angled screen system was installed in a cooling water
intake canal� The coniguration of the system consisted of two vertical traveling screens set at an
angle 25° to the direction of low� The angled channel led to a 0�5-ft (15-cm) -wide bypass line�
This line then connected to ish collection and larval collection tanks� The diversion effectiveness
study was conducted over a three-year period, and divided into two sections: a study of young/
older ish, and a study of ichthyoplankton (EPRI 1999)� Both the young and older ish were collected on a seasonal basis from the ish pump discharge using nets and from the collection tanks
for which the ish has a 96-hour mortality expectancy� A total of 59,309 ish comprised of 38 species were collected from February 18, 1981 to October 27, 1983� The diversion eficiency ranged
from 95�4 to 100 percent with a mean of 99�4 percent� The species affected on the river were the
bay anchovy, blueback herring, white perch, spottail shiner, alewife, Atlantic tomcod, pumpkinseed, and American shad� The study determined that the overall eficiency (diversion eficiency ×
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
42 | Assessing Seawater Intake Systems for Desalination Plants
initial survival × latent (96 hr) survival) ranged from 67�9 percent for alewife to 98�7 percent for
spottail shiner, with an overall mean of 84�4 percent (EPRI 1999)�
As noted above, an angled screen system requires an area leading up to the pumps in which
the screens are installed at an angle to the low� This would take up additional area from the harbor
or from land inshore of the existing intake structure building, possibly reducing bottom habitat�
Center-Flow/Dual-Flow Screens. The center-low/dual-low traveling screen system
(Figure 2�8) is designed to reduce the loss of aquatic and marine life resulting principally from
impingement� Center-low screens eliminate debris carry-over� The screen baskets are half cylinders or are “V” shaped, which provide up to 60 percent more screening area compared to similarly
sized dual-low or through-low screens� However, these screens may create adverse low conditions that could impact intake water pump performance� Dual-low screens use Ristroph-style
screen baskets and ine-mesh screens, these eliminate debris carry-over, but can have high, localized velocities that could adversely impact intake water pump performance�
The center-low screen design concept passes the water through the center and exiting on
both sides of the screen conveyor� The dual-low screen design concept is the same as a center-low
except that the water entry is from both screens into the center passage (Figure 2�8)� These two
designs have allowed the use of a iner mesh material without increasing through-screen velocity�
Both concepts are used in connection with ish return conveyance systems� The screen is
positioned so the ish and debris are trapped in the direction of the low� There are wall-mounted
structural components that guide the screen trays and baskets� In the debris/ish removal area
above the screens, low-pressure spray nozzles are positioned to dislodge debris into the removal
trays� The ish and other marine life are transferred to a ish trough or holding tank to be released
back to their natural environment� The application of the system is typical for limited space constraints on the entry channel�
Center-low screens itted with ine mesh screens have demonstrated relatively high survival rates for impinged organisms when coupled with appropriate return conveyance systems�
Although center-low screens may increase impingement survival, it would need to be coupled
with an effective ish return� The installation of center-low screens would not be expected to
reduce entrainment losses, and depending upon the species entrained could theoretically reduce
survival rates�
The biological effectiveness of both systems has been evaluated� An experiment was conducted on the center-low screen system at the Barney M� Davis Power Station located on the
shoreline of the upper Laguna Madre near Corpus Christi, Texas (Murray and Jinnette 1978)� The
low velocities going through the ine-mesh screens ranged from 1�7 to 3�1 ft/s (0�5 to 0�9 m/s)� The
samples were collected on a month-to-month basis from January to December 1977� A total of
12,060 individual marine organisms comprised of 15 species of invertebrates and 37 species of
vertebrates were collected� The overall survival rate was 86 percent�
The study also examined the inluence of debris loading on survival of the impinged organisms� Debris loading and survival were related� During the months of January, February, and March
the debris weight luctuated and the mortality rate followed the same pattern�
A study was also done on the Roseton Generating Station’s dual-low screen system at
Central Hudson Gas and Electric Corporation (LMS 1991)� The dual-low screens were designed
to improve ish survival through implementation of water retaining lifting buckets, a dual-pressure
spray cleaning system, lattened woven wire mesh screens and faster operational speeds� The low
velocity approaching the screens was 0�75 ft/s (0�23 m/s)� The system used both the low-pressure
(organism removal) and high-pressure (debris removal) overhead sprays to clean the screens� The
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 43
Source: Adapted from Tom Pankratz 2006�
Figure 2.8 Comparison of through-low and dual-low traveling water screen arrangements
Roseton post-impingement survival program was conducted during the seasonal periods of May 9
through August 30, 1990 and September 30 through November 29, 1990� The study collected
48,729 ish comprised of 30 species; 12,668 ish were evaluated for extended survival� The postimpingement survival for the dual-screen low was found to be higher than the conventional traveling screens that were simultaneously studied�
If an intake is located in a bay or estuary, these screen types can be located directly on the
shoreline� However, if an intake is located on the open coast several complicating modiications
must be made� Due to tidal change and wave action, the intake must be located some distance offshore� Marine organisms may enter the connecting pipe, which may lead to increased entrainment
and impingement� Fish in particular are prone to see such structures as desirable habitat� Biofouling
control practices aimed at keeping the structure clear may further harm marine life� Furthermore,
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
44 | Assessing Seawater Intake Systems for Desalination Plants
any ish return system is likely to be less successful due to the extended distance, increased abrasion and associated stress the organisms would be subjected to with this design�
Other environmental impacts from center-low and dual-low screens are the additional
space requirements which can be constrained by available landward space at the site, and the
impacts associated with the necessary construction activities for the facility that reduce bottom
habitat seaward of the plant�
Fish Return Conveyance Systems. Fish return conveyance systems are required with any
ish diversion and collection system� There are two basic types of conveyance systems for the
return of entrapped or impinged organisms and debris to the water body: (1) a trash pump to transport material away from the intake, and (2) gravity low� These systems have standard traveling
screens with Ristroph-style screen baskets and ine-mesh, a low-pressure spray system, and ishreturn piping�
Both pump-augmented and gravity-low return systems have the advantage of minimizing
recirculation and re-impingement of debris and organisms on intake screens due to their relatively
large transport distance capability, but pump-augmented systems often result in mechanical abrasion and high organism mortality� The gravity sluiceway return system reduces mechanical abrasion, but may result in a higher rate of re-impingement due to the relatively limited transport
distances� Returned ish would be susceptible to disease and predation at the ish return discharge
point due the stress of passage through the pumped ish return system�
Previous studies have concluded that the potential magnitude of reduction in impingement
losses attributable to a gravity ish conveyance system is uncertain (PG&E 1983)� However, the
combination of a modiication to the screens and their operation and the installation of a modiied
screen wash gravity sluiceway return system for an intake may improve impingement survival at
locations where impingement losses are problematic�
Modular Inclined Screens. Modular incline screens (MIS) reduce impingement mortality
and entrainment by diverting organisms to a return system� A MIS is designed with a slot width of
2�0 mm, which will reduce impingement, and to some degree, entrainment� A MIS module consists
of an entrance with trash racks, de-watering stoplogs in slots, an inclined wedgewire screen set at
a shallow angle (10 to 20°) to the low, and a bypass for directing diverted ish to a transport pipe�
The module is completely enclosed and is designed to operate at relatively high through-slot
velocities (2 to 10 ft/s (0�6 to 3�0 m/s)) to assure effective ish guidance to the bypass� The velocity
selected is determined by the species and life stages to be protected at the site�
If located in a bay or estuary, the intake for the traveling screens can be installed directly
on the shoreline� However, like center-low and dual-low screens, if located on the open coast
several complicating modiications must be made� Due to tidal change and wave action, the intake
must be located some distance off-shore� Marine organisms may enter the connecting pipe, which
may lead to increased entrainment and impingement� Fish in particular are prone to see such structures as desirable habitats� Biofouling control practices aimed at keeping the structure clear may
also harm marine life� Furthermore, any ish return system is likely to be less successful due to the
extended distance, increased abrasion, and associated stress organisms would be subjected to�
Additionally, installation of an MIS would require disturbance and removal of bottom sediments�
Vertical Traveling Screens. Vertical traveling screens are physical barriers designed to
prevent passage of ish and debris into the water intake system� It is a standard feature at most
power plant intake structures in the U�S� The ability of traveling screens to act as a barrier to ish
without impinging depends on many site-speciic factors, such as the size of the impinging ish,
location of the screens, and presence of escape routes� It is considered advantageous to locate
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 45
Source: Adapted from Pankratz 2004�
Figure 2.9 Schematic of a through-low vertical traveling screen
intake screens on the shoreline� The vertical traveling screen system coniguration consists of large
vertical meshed screen panels (commonly 3⁄8-in�, or 10-mm opening) mounted on two parallel
chains and motor operated from the upper sprocket� Figure 2�9 shows a conventional vertical traveling screen� The screen rotates periodically for cleaning with a direct spray nozzle; the debris is
collected in a trough and carried to a refuse basin�
As with modular inclined screens, if located in a bay or estuary, the intake for the traveling
screens can be placed directly on the shoreline� However, if located on the open coast, the intake
must be located some distance off-shore due to near-shore tidal change and wave action� Marine
organisms may enter the connecting pipe, which may lead to increased entrainment and impingement� Fishes in particular are prone to see such structures as desirable habitats� Biofouling control
practices aimed at keeping the structure clear may further harm marine life� Any ish return system
would likely be less successful due to the extended distance, increased abrasion, and associated
stress on the entrained or impinged organisms�
Standard Through-Flow Vertical Traveling Screens. In this type of system the raw water
passes through ascending (upstream) and descending (downstream) screen mesh panels or baskets�
Debris and aquatic organisms are removed by high-pressure water spray prior to the screen panel’s
descent on the downstream side� The screen mesh size usually ranges from 1⁄2 to 3⁄4 in� (1�3 to
1�9 cm)� Debris is lushed to retention containers for disposal or returned to the source water without special provisions for ish survival�
Vertical traveling screens are the industry standard for intake structures� With relatively
minor variation and modiication, their design and operation varies little with location or facility�
Two biologically important features of these active screening systems are: proven reliability and
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
46 | Assessing Seawater Intake Systems for Desalination Plants
Figure 2.10 Schematic of a ine-mesh vertical traveling screen system
the ability to effectively maintain debris-free conditions in the intake area� Both of these operating
features serve to lower impingement rates by maintaining consistent intake lows and velocities
and reduced amounts of entangling material in the intake forebay�
Fine-Mesh Modiied Traveling Screens. Fine-mesh modiied traveling screens incorporate
components that improve survival of impinged ish� These typically use 0�5- to 1�0-mm (0�02 to
0�04 in�) mesh openings� However, depending on the size and shape of ish eggs and larvae being
protected, a smaller or larger mesh may be appropriate� A through-slot velocity of 0�5 ft/s (0�15 m/s)
for this technology would constitute default compliance with the impingement mortality performance standard in EPA’s Phase II Rule� An example of a ine-mesh traveling screen is shown in
Figure 2�10�
Fine-mesh traveling screens have been installed at a few large-scale steam electric power
plant cooling water intakes� Each screen basket is equipped with a water-illed lifting bucket that
safely retains collected organisms as they are carried upward with the rotation of the screen� The
screens are designed to operate continuously to minimize impingement exposure time� As each
bucket passes over the top of the screen ish are rinsed into a collection trough by a low-pressure
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 47
spray wash system� Once collected, the ish are transported back to a safe release location� These
types of features have been incorporated into the through-low, dual-low, and center-low type
screens� The most well known screens are the Ristroph screens, and several new screen types are
now available: multi-disc screens, plastic belt-screens, and water intake protection screens�
Installation of the ine-mesh modiied traveling screens would not have any signiicant
adverse environmental impacts�
Other Modiied Traveling Screens. Without the addition of various ish handling (e�g�, ish
lifting buckets) and operating features (e�g�, continuous screen operation), traveling screen systems generally result in high mortality to all but the hardiest species that become impinged� These
screens have no capacity for protecting entrainable-sized organisms� However, if traveling screens
are placed relatively lush with the face of the intake structures, they can offer protection to juvenile and adult ish that have the swimming capability to avoid impingement�
Vertical Traveling Screens With Fish-Handling Features. For some species of ish, impingement mortality can be reduced through structural modiications to conventional vertical traveling
screens and a change in intake screen operation from intermittent to continuous rotation� The
needed structural modiications include installation of watertight ish collection baskets along the
screen, both low-pressure and high-pressure wash systems, and a ish return sluiceway� A differential control and two-speed motor are also included, so that when the screen is operated continuously it turns slowly, and as the number ishes and/or debris loads increase, the screen rotation rate
can be automatically increased� In general, the same 3⁄8-in� (10-mm) screen mesh size would be
used on modiied vertical traveling screens�
Screens modiied to reduce impingement mortality need to be accompanied by ish pumps
and/or a sluiceway designed to return impinged organisms to the receiving water body� Most installations of modiied traveling screens use a dual sluiceway return system, a gravity sluiceway return
system for impinged organisms removed from the screens by the low-pressure spray wash, and
another sluiceway for debris removed by the high-pressure spray wash�
Other examples of commonly used active screening equipment include:
•
•
•
•
Geiger multi-disc traveling water screens—A modular screen design that incorporates a series of sickle-shaped screen panels designed to eliminate debris carry-over�
Drum screens—A series of wire mesh panels are mounted around the periphery of a
cylinder, forming a drum� The cylinder rotates on a horizontal axis� Water enters
through the open ends of the drum and passes through the mesh panels to enter the
intake water system�
Beaudrey water intake protection (WIP) screens—A modular screen design; a screen
is mounted on a wheel that rotates around a hub and is cleaned by a suction scoop� A
ish pump provides suction� Biological eficacy not known but it is currently being
tested in the Midwest�
Hydrolox—Plastic through-low belt screen with ish protection features� Biological
eficacy not known but it is currently being tested at a facility on Long Island, New
York�
Modiications of vertical traveling screens that include ish buckets, a low-pressure wash
system, provisions for continuous rotation, and a ish return system represent an alternative technology with the potential for reducing impingement losses of several of the common species of ish
and invertebrates impinged at intake structures�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
48 | Assessing Seawater Intake Systems for Desalination Plants
Several modiications to increase the biological effectiveness of conventional vertical traveling screens have been attempted in recent years� The biological effectiveness of varying the
frequency of traveling screen rotation was assessed at the Moss Landing Power Plant (MLPP;
PG&E 1983)� Information is also available on the impingement survival of Chinook salmon from
the Columbia River (Page et al� 1976 and 1978) and of striped bass from the Hudson River (EA
1979, Texas Instruments 1977)� Data from these and other studies are used to examine the potential
effectiveness of modiied vertical screens at new intake structures�
In addition, consideration has recently been given to the potential effectiveness of a screen
mesh smaller than the standard 3⁄8-in� (10-mm) but larger than 0�04-inch (1-mm) to reduce the
combined losses of entrainment and impingement� In addition to the ish handling provisions noted
above, traveling screens have been further modiied to incorporate screens with mesh openings as
small as 0�5 mm to collect ish eggs and larvae and return them to the source water body� For many
species and early life stages, mesh sizes of 0�5 to 1�0 mm (0�02 to 0�04 in�) are required for effective screening� Various types of traveling screens, such as through-low, dual-low, and center-low
screens, can be itted with small-mesh screens�
It should be noted that impingement survival of fragile species, such as northern anchovy,
Paciic herring, smelt, and silversides would probably not be improved substantially by increased
screen rotation frequency� It is expected that the addition of ish buckets, low-pressure spray washers, and continuous rotation of screening surfaces would increase survival of fragile species such
as surfperch and rockish, assuming the ish could be safely returned to the source water body� The
safe return of impinged organisms has proven to be a dificult and generally unsolved problem at
most ish return locations�
As with ine-mesh modiied traveling screens, if the intake is located in a bay or estuary the
traveling screens can be located directly on the shoreline� However, if located on the open coast it
must be located off-shore and again, several complicating modiications must be made to address
tidal changes and wave action� In this case, marine organisms may enter the connecting pipe,
which may lead to increased entrainment and impingement� Fish in particular are prone to see such
structures as desirable habitats� Biofouling control practices aimed at keeping the structure clear
may further harm marine life� Any ish return system is likely to be less successful due to the
extend distance, increased abrasion, and associated stress organisms would be subject to�
Other than consideration of the space requirements and construction-related effects of
installing ish return conduits along the shoreline, no other signiicant environmental effects associated with installing and operating modiied traveling water screens are anticipated�
Passive Screening Technologies
Passive screen types include bar racks, grizzly bars, stationary screens, wedgewire screens,
and aquatic ilter barriers� Most bar rack, grizzly bar, and stationary screen systems incorporate
some form of debris removal rake system, so they are not strictly passive� Similarly, wedgewire
screen intakes and aquatic ilter barriers incorporate an airburst system to dislodge debris and rely
on local water currents to carry the debris away�
The disadvantage of a truly passive screening system is that it will clog with debris and
macrofouling growth� The narrower the bar spacing or screen mesh, and the higher the water
velocity, the more quickly occlusion will occur� Higher approach velocities also translate to
increased impingement and entrainment� A low-velocity passive system with large openings will
allow ish to pass back and forth through the barrier while still excluding large debris� As the
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 49
passive barrier becomes occluded, however, the water velocity through the remaining open areas
will increase and impingement will increase, as some ish are no longer able to swim out of the
system� The higher water velocity will also speed the occlusion of the remaining open areas�
Passive screens are most effective if incorporated into intakes with low velocities in waters with
low debris loads� The most common passive screening technologies are discussed below�
Aquatic Filter Barrier. The aquatic ilter barrier (AFB) is a physical barrier system consisting of two layers of material with an airburst system installed in between to allow automatic
cleaning of accumulated silt and debris� The system is anchored to the seabed and has loats on the
top to keep it suspended in the water column� The AFB could be designed to reduce entrainment
and virtually eliminate impingement by reducing approach velocities to ≤0�02 ft/s (0�6 cm/s),
which would constitute default compliance with the impingement mortality performance standard
in EPA’s Phase II Rule�
Aquatic ilter barriers combine a very ine mesh size with low water velocity by extending
over a very large area relative to the low� Even with very low approach velocities this system will
eventually clog if not periodically cleaned� Aquatic ilter barriers rely on periodic bursts of compressed air to dislodge debris from their openings and naturally occurring water currents to carry
the dislodged material away from the screens� While such consistent currents can be found in rivers, they do not normally occur in the marine environment� As a result, the use of passive screens
in seawater intakes has been limited to large mesh debris screening systems� Concern about the
susceptibility to marine biofouling and the resulting occlusion of ine mesh passive systems like
wedgewire screen intakes has also restricted their use in seawater intakes�
The installation of an AFB would signiicantly disturb the sediment, as many bottom
anchors are required� The AFB itself would result in the loss of a large amount of aquatic habitat
due to its length� The installation of support pilings would disturb sediments, eliminate some benthic habitat, and might introduce a navigation hazard�
Barrier Nets. Coarse-mesh barrier nets function by expanding the surface area of the intake
to reduce the through-screen (i�e�, net) velocity� All low to the intake passes through the net, so all
aquatic life forms (based on the mesh size) are blocked from entering the intake� An example of a
barrier net installation is provided in Figure 2�11�
The barrier net can be sized large enough to achieve through-net velocities of 0�5 ft/s
(0�15 m/s) or less, a rate that would have constituted default compliance with the impingement
mortality performance standard in EPA’s Phase II Rule� This mesh size also has the potential to
provide some beneit for larger entrainable life stages�
Barriers are physical devices that block an aquatic organism’s access to the intake water
system� These have had some success in diverting some species away from the intake and may also
incorporate behavioral mechanisms (bubbles or turbulence) to further direct the motion of active
swimmers� Barriers are not effective in preventing the entrainment or impingement of weakswimming or planktonic species�
The design and location of barrier nets are site-speciic and take into consideration the
characteristics of local ish populations and concentrations of debris� Given the proper hydraulic
conditions (primarily low velocity) and positioning in areas without heavy debris loading, barrier
nets have been effective in preventing ish from entering seawater intakes�
Installation of a barrier net would cover acres of aquatic habitat and installation of support
pilings would disturb sediments and benthic communities and would eliminate some benthic and
open water habitats� Although enclosing this open water habitat may adversely impact larger ish,
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
50 | Assessing Seawater Intake Systems for Desalination Plants
Source: Adapted from EPRI 1999�
Figure 2.11 Chalk Point Generating Station, Maryland, barrier net coniguration
which are excluded by the net, the space is not lost to smaller ish and shellish� This structure
would also impact navigation�
Light and Acoustical Deterrents. Behavioral sound/light system components include
sound generators and strobe lights� The use of these behavioral devices only has the potential to
reduce impingement� “Hybrid” sound/strobe light conigurations provide a “wall” of light and
sound to deter ish from entering the intake� As with physical barriers and louvers, these systems
have had some success with some species, but are not effective in preventing the entrainment or
impingement of weak-swimming or planktonic species�
For installation of the behavioral system, the supports occupy minimal area and should not
disrupt sediments or impact navigation� However, operationally, there is the potential for negative
impacts to other marine species�
Louvers. A louver diversion system consists of an array of evenly spaced, vertical slats
(like venetian blinds) aligned across an entry channel at an angle speciied to allow ish bypass�
The design of the diversion system is based on the approach low velocity and swimming speed of
the indigenous ish� The concept behind the system is that it will create a stimulus in the water to
divert the ish to a safer (lower-velocity) area� The design may also incorporate behavioral mechanisms (bubbles or turbulence) to further direct the motion of active swimmers away from the
entrance� The effectiveness of the system is based on species characteristics, life stage, and site
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 51
speciics� These are not effective in preventing the entrainment or impingement of weakswimming or planktonic species�
As noted above, louver systems require a channel leading up to the screen in which the
louvers are installed at an angle to the direction of low� Such a channel would have to be built
seaward, causing contaminant effects associated with the necessary construction activities and
reducing bottom habitat�
Louvers generally are not considered acceptable by most U�S� environmental regulatory
agencies because they have been less effective compared to other ish protection systems� However,
they have been applied to riverine environments with migratory species� There are studies that
demonstrated the louvers to be 80 to 95 percent effective in diverting a wide variety of species over
a wide range of conditions (EPRI 1986 and 1994)� For example, Southern California Edison’s
Redondo Beach station conducted experiments on 18 species of ish including northern anchovy,
queenish, white croaker, walleye, surfperch, and shiner perch in a test lume (Schuler 1973)� They
tested in velocities ranging 0�5 to 4 ft/s (0�15 to 1�2 m/s)� The louvers were placed at angles ranging
from 20 to 90° to the direction of low� The maximum guidance of 96 to 100 percent happened with
the louvers spaced 1-in� (2�5 cm) apart, set at a 20° orientation to the low, with low vanes normal
(90°) to the frame, and an approach velocity of 2 ft/s (0�6 m/s)� Schuler (1973) determined that the
coniguration of the bypass channel was as important to the effectiveness as the louver and the
velocity settings� Additionally, it was determined that the system worked equally well in light and
darkness (Schuler 1973)�
Based on the results from the Redondo Beach experiment, California Edison’s San Onofre
Nuclear Generating Station developed and installed a traveling louver system in its ocean intake�
The plant’s once-through cooling system includes intake structures situated approximately 0�6 mi�
(1 km) from the shore at depths of 29�5 ft (9 m)� The intake has a wide lower lip and velocity cap
and the facility depends on a ish return system to mitigate ish entrapment� The diversion system
uses the guiding vanes and louvers to direct the ish away from the banks of traveling screens into
a safe collection area� Velocity through the screens was between 2 and 3 ft/s (0�6 and 0�9 m/s)� The
data for biological effectiveness of this particular system could not be found�
Northeast Utilities Service Company also conducted a research to evaluate the use of louvers for diverting juvenile and adult clupeids and Atlantic salmon smolts in the Holyoke Canal on
the Connecticut River (Harza and RMC 1992; Harza and RMC 1993; Stira and Robinson 1997)�
The effectiveness of louvers was evaluated on the juvenile clupeids (American shad and blueback
herring) at various canal lows� This experiment found that 76 percent of marked and recaptured
test ish and 86 percent of the naturally migrating ish were guided to a bypass channel that safely
returned them to the river (Harza and RMC 1993)� A separate experiment was performed with
Atlantic salmon smolts measured a similar guidance effectiveness of 85 to 90 percent (Harza and
RMC 1992)�
Since louver arrays are necessarily set at an angle to the low, they require a length of intake
channel or canal to work effectively� They are not applied to shoreline intake locations, but have
been applied to on-shore intake screen wells used in conjunction with off-shore-submerged intakes,
which entrap ish�
Narrow-Slot Wedgewire Screens. Wedgewire screens are designed to reduce entrainment
and impingement mortality by preventing passage of organisms into the intake water low�
Biological effectiveness is enhanced with the presence of an ambient low past the screens to transport non-motile or early life stages with weak swimming capabilities away from the intake
structures�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
52 | Assessing Seawater Intake Systems for Desalination Plants
Figure 2.12 Illustration of an off-shore narrow-slot wedgewire screen intake system
Wedgewire screens are typically designed to minimize entrainment by using 0�5-mm slots�
The industry standard design for wedgewire screens is a maximum through-slot velocity of 0�5 ft/s
(0�15 m/s), which would constitute default compliance with the impingement mortality performance standard in EPA’s Phase II Rule� A schematic of the narrow-slot cylindrical wedgewire
screen technology representing an off-shore setting is shown in Figure 2�12� Another option is to
mount the modules on a bulkhead along the shoreline�
Wedgewire screen intakes combine very ine mesh size with low water velocity by extending over a very large area relative to the lowrate� Even with very low approach velocities this
system will eventually clog if not periodically cleaned� Periodic bursts of compressed air are used
to dislodge debris from its openings� Naturally occurring water currents carry the dislodged material away�
While such consistent currents can be found in river applications, they do not normally
occur in the marine environment� Concern about the susceptibility to marine biofouling and the
resulting occlusion of ine-mesh passive systems like wedgewire screen intakes has also restricted
their use� As a result, the use of passive screens in the marine environment has been limited to
large-mesh debris screening systems�
The ability of narrow-slot wedgewire screens to reduce the number of impinged organisms
in a submerged off-shore intake depends on locating the intake in an area with a low quantity of
impingeable organisms� Many of the dominant groups of ish and invertebrates (e�g�, lounder,
sole, rockish, white croaker, surfperch, crab, and shrimp) are typically found in association with
off-shore bottom habitat� Pelagic ish species, such as smelt, northern anchovy, and Paciic herring,
are commonly found in large schools moving through the water column; they often concentrate
near bottom features during the daytime� Submerged off-shore intakes have higher approach
velocities than on-shore systems and use conduits within which ish can become entrapped, resulting in an increase in the number of organisms impinged� Furthermore, there is a distinct possibility
that the physical presence and nature of an off-shore intake would attract ish and invertebrates,
and so increase the probability of entrapment and subsequent impingement� Thus, use of a submerged off-shore intake system with narrow-slot wedgewire screens can result in entrapment and
impingement rates signiicantly higher than is seen with shoreline intakes�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 53
Implementation of this alternative would involve environmental impacts associated with
dredging and with installing the sheetpile bulkheads and piping� Environmental impacts of installing the off-shore option would involve some disturbance of potentially contaminated sediments
and some displacement of aquatic habitat due to placement of the pipes� The off-shore option
would impact the benthic habitat during construction and would result in some permanent loss
(though the pipe may act as an artiicial reef)�
Porous Dikes. Porous dikes are barriers surrounding a shoreline intake that exclude marine
life but allow the passage of water� The size of the openings can be adjusted during design and
construction to suit the local marine life� The dike must be properly sized to allow suficient low
while maintaining a very low approach velocity� As it is a passive system it is susceptible to occlusion by siltation, debris clogging and macrofoulant growth� The smaller the openings the more
likely and the more rapidly occlusion occurs� Since larval organisms will likely be able to pass
through the dike, the area it encloses may in time, support populations of the same species that are
excluded as adults on the outside�
Porous dikes constructed around ocean intakes must be able to withstand the force of waves
and currents� The large size of a porous dike can make it impractical for bays and estuaries due to
concerns over loss of habitat and/or intrusion into navigable channels�
Velocity Cap. A velocity cap is a behavioral-based technology that is applied only to offshore-submerged intakes� The velocity cap intake minimizes capture of ish by converting the low
of ocean water into the intake pipe from primarily a vertical direction to a horizontal one, and distributing the low over a larger area, so that low velocities are reduced to speeds avoidable by
many ish� The general theory is that ish are more sensitive to horizontal rather than vertical low
and will generally more readily avoid horizontal changes in velocity (EPA 1977)�
The use of a velocity cap on a submerged off-shore vertical riser intake signiicantly reduces
the entrapment and impingement of many forms of pelagic marine life including ish, invertebrates
and wildlife such as turtles, seals, sea lions, and birds� Retroitting existing off-shore vertical intake
risers with velocity caps has been proven so effective at reducing intake effects that a new offshore intake riser would not be constructed without a velocity cap� In spite of the effectiveness of
velocity caps at reducing the impingement rates of off-shore-sited intakes, entrapment and impingement rates of these intake structures remain much higher than at shoreline intake facilities�
Other than the construction-related impacts associated with installing an off-shore intake
system, there are no other signiicant environmental impacts associated with the velocity cap
option�
VFD Pump Seasonal/Diurnal Flow Management. Reduction or elimination of diversion
operation during sensitive periods can, in some locations, signiicantly reduce the number of organisms lost by entrainment and impingement� The amount of the reduction depends on the length of
time the intake system is out of operation or curtailed, and the concentration of organisms during
the period of outage or curtailment� Water would either have to be stored in advance or alternative
sources of water would have to be used for this period�
Bubble Curtains. Air bubble curtains generally have been ineffective in blocking or diverting ish in a variety of ield applications� Air bubble curtains have been evaluated at a number of
sites on the Great Lakes with a variety of species� At those sites, the curtains have all been removed
from service� In no case have air bubble curtains been shown to effectively and consistently repel
any species (EPRI 1999)�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
54 | Assessing Seawater Intake Systems for Desalination Plants
Impact and Mitigation Measures for Seawater Intake Wells
Impingement and Entrainment
Seawater intake well intake systems extract the seawater supply necessary for the operation
of the desalination plant by slowly withdrawing water from below the water level at the coastline�
Water velocity at the seawater–sand interface is negligible� As such, impingement of larger marine
organisms like those retained on bar racks and traveling screens of a power plant does not occur�
Since the seawater is iltered through the surrounding sand, entrainment of smaller marine organisms such as larval ish, invertebrates, and zooplankton would also be eliminated�
Loss of Coastal Habitat
Seawater intake wells have a relatively small yield (≤3�6 mgd or 14,000 m3/d) so that
desalination facilities with large capacities would require many wells� Large stretches of shoreline
could therefore be disrupted by the construction of large-capacity systems� HDD and slant well
structures and access roads can be built further from the water’s edge, minimizing both loss of near
coast habitat and aesthetic impact to the beach zone�
Impact and Mitigation Measures for Subsurface Intakes
Entrainment and Impingement
Subsurface intakes have the same potential biological beneits as seawater intake well systems� This type of intake system extracts seawater by slowly withdrawing the water from the surrounding sand� Water velocity at the seawater–sand interface would be negligible� As such,
impingement of larger marine organisms like those retained on bar racks and traveling screens of
power plants would not occur� Since the seawater is iltered through granular media, entrainment
of smaller marine organisms is also eliminated�
Loss of Benthic Habitat
Due to the expanse of shoreline that needs to be disturbed and excavated, the impact of the
installation of an iniltration gallery would be signiicant� This massive excavation work would
yield large amounts of beach sand excavation debris, a portion of which (10 to 20 percent) would
have to be transported and disposed of off-site� For some locations, this may be a challenging task�
The extensive beach excavation required has the potential to impact shore birds, marine mammals,
and intertidal organisms in the area of construction� Construction activities would cause temporary
disruptions to tourists and public use of the beach� The pipeline network necessary to link the wells
with the desalination facility would require extensive trenching and subsequent burial of the
system�
The entire benthic ecosystem in the area covered by the seabed ilter would be removed as
part of the excavation process� The material removed would pose an enormous dredge spoil disposal problem� The dredging of the sea loor, establishment of a layer ilter bed, and the periodic
replacement of the layered ilter media would disrupt normal public use of the beach and surf zone
in this area during construction� In addition, the construction of the seawater intake wells that
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 55
would be needed to convey the source water from the seabed iltration system to the desalination
plant would also have all of the impacts that have previously been cited for the seawater intake
well and iniltration gallery systems�
After construction had been completed, the presence of structures necessary to house
pumps and other equipment needed for the iniltration gallery would likely cause additional impacts
(primarily visual and aesthetic)� In addition, the use of this system may also require installation of
seawater intake wells that collect the intake water from the iniltration gallery prior to transferring
it to the desalination plant for treatment�
PERMITTING AND REGULATIONS
Standard, universal construction permits and regulations, like those related to zoning, rightof-way, building permits, etc�, are well known and documented throughout the industry in numerous water treatment projects� Thus, those topics are not covered here� Instead, this section focuses
on the construction and operational issues requirements speciic to seawater intakes�
Overview of the Permitting Process
Each coastal state has a regulatory procedure and designated agencies to review and process applications for coastal development� For example, in California, an application for a new
desalination facility is reviewed and approved by a lead governmental agency implementing
California’s Environmental Quality Act (CEQA)� For coastal intakes, this is the California Coastal
Commission (CCC)� The permitting process takes the general form of an environmental impact
analysis and reporting procedure that can lead to a variety of outcomes from a declaration of “no
signiicant impact” to a fully developed EIR and certiied Environmental Impact Statement (EIS)�
It is incumbent upon the applicant to propose a project that conforms to all of the applicable local
ordinances, regulations, and statutes (LORS)� In most circumstances, the applicant is required to
have acquired all of the necessary permits and approvals for the proposed project prior to inal
certiication of the project EIR/EIS� Permits for the withdrawal and diversion of seawater for
desalination are also required in the EIR/EIS certiication process�
Federal Permitting Requirements
Development of Ocean Intake Regulations
There are no existing Federal laws or statutes regulating open water intakes speciically for
desalination facilities� A number of states that are seeking to establish a regulation protocol for
open water intakes have looked to Section 316(b) of the 1972 CWA� This section of the CWA,
along with its sister Section 316(a), was enacted by Congress to regulate the steam electric industry’s cooling water intake and discharge to navigable waterways� These Federal regulations are
incorporated into water quality regulations by many individual states� For those states that have not
promulgated their own set of NPDES-related water quality regulations on cooling water intakes,
the Federal 316(b) rule has traditionally regulated the power industry’s cooling water intakes�
The 1972 version Section 316(b) of the CWA is noticeably brief in its language� It rather
simply requires that the location, design, and capacity of the intake should minimize the adverse
environmental impacts of impingement and entrainment to the degree that the cost of intake
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
56 | Assessing Seawater Intake Systems for Desalination Plants
technology was not wholly disproportionate to its beneit� Over the next three decades, many court
cases were fought over the interpretation and implementation of Section 316(b)’s spare language�
In response, the EPA published 316(b) guidance to assist the industry in their efforts to comply
with 316(b) requirements for their cooling water intake facilities� This guidance was challenged by
Riverkeepers of New York in Federal Court on the grounds that the plain language of the Act
required the installation of the best technology available and did not allow the use of mitigation to
compensate for entrainment and impingement effects� The Court ordered EPA to propose new
rules to remedy the problem of 316(b) regulation and compliance�
The EPA responded with a set of new rules that bifurcated the regulation between new and
existing power plants� The new Rule imposed entrainment and impingement mortality compliance
standards equivalent to that achievable by closed-cycle cooling for new power plant intakes (316[b]
Phase I Rule promulgated in 2001), and 60 to 90 percent reduction in entrainment and 80 to 95 percent reduction in impingement for existing once-through-cooling power plants (316[b] Phase II
Rule promulgated in 2004)� In both rules, EPA allowed the use of restoration and other forms of
mitigation to achieve regulatory compliance� Again, Riverkeepers challenged the new rules, mostly
on the grounds that the plain language of the Act required technology-based compliance�
In November 2006, the Court ruled in favor of the Riverkeepers complaint, remanding the
Phase II Rule to EPA and disallowing the use of mitigation for compliance (consistent with the
Court’s previous inding on the Phase I Rule)� In addition, the Court disallowed the use of a costbeneit test to determine the feasibility of alternative intake technologies� In January 2007, the EPA
suspended the new Phase II Rule until further notice, reverting to the use of Best Professional
Judgment to determine 316(b) compliance on a case-by-case basis�
The intent and substance of the remanded rule is commonly referenced, in part, during
regulatory proceedings, as the compliance standard for impingement and entrainment reduction
targets for new desalination open water intakes� The studies and analyses required to assess these
potential effects of new open water intakes for desalination facilities are often described as needing
to be “316(b)-like�”
As described above, federal regulations and programs that need to be considered across the
United States include:
•
•
•
•
•
•
•
•
•
•
Clean Water Act Section 316(b)�
Clean Water Act Sections 401 and 404�
Coastal Zone Management Act�
Environmental Justice Program�
Endangered Species Act�
Fish and Wildlife Coordination Act�
Marine Mammal Protection Act�
National Environmental Policy Act�
National Estuary Program�
Section 10 of the Rivers and Harbors Act�
Given that these requirements are enforced largely by state agencies, speciic details regarding compliance with each regulation/program are included in the following section on select state
requirements� Compliance and permitting in states that are not covered in this report would be
enforced by the analogous agency in that location� E�g�, compliance with the Coastal Zone
Management Act would be enforced by the agency that develops and executes the state’s Coastal
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 57
Management Plan� For example, in Florida this is the Florida Department of Environmental
Protection’s (FDEP’s) Coastal Management Program�
Select State Permitting Requirements
Seawater desalination is still a new concept for many coastal states and their preparedness
for permitting seawater desalination plant intakes varies greatly� This section provides guidance on
the permitting agencies and processes for states that have either engaged in the development of
seawater desalination plants (California, Florida, and Texas) or anticipate doing so (Massachusetts),
and so have developed some preliminary protocols and guidance on this topic� As the most experience to date exists in California, that state is covered in more detail than the other three reviewed
here�
Overview
A key element of any successful desalination project is the ability to site and design an
intake that: (1) produces a reliable supply of water suitable for desalination, and (2) minimizes the
environmental effects of intake diversion and withdrawal� It is also the key to the ease and success
of receiving regulatory approval for the project�
The protection of ish, shellish, and other wildlife are commonly the key issues that concern both the general public and the representatives and scientists of regulatory and resources
agencies when reviewing and permitting a proposed desalination project� The strength of the concerns over these issues, and the regulatory procedures and processes triggered by these concerns,
are nearly always in direct relationship to the location of the proposed intake with respect to valuable or sensitive species or habitat� These environmental and regulatory permitting concerns also
drive planning and development decision-making with regard to the location, design, capacity, and
operation of the proposed facility’s feed water intake� In most cases, signiicant scientiic and engineering effort will need to be expended to characterize the biological, physical, and chemical
oceanography of the intake source water currents, salinity, and the ish and shellish populations
that could be affected by their impingement on intake screens or entrained into the desalination
process�
Contemporary information on populations of ish and shellish at risk of impingement or
entrainment by the facility’s proposed intake and feed water supply (source water) will nearly
always be one of the leading regulatory and permitting requirements and tasks� In some circumstances, available information that is less than ive years old can be used in place of contemporary
data to assess potential intake effects; this possibility can considerably shorten the regulatory and
permitting process timeline� Otherwise, source water and entrainment studies supporting the
design, location, capacity, and operation of new open water intakes will generally require a period
of 18 to 24 months to acquire an approved study plan, collect a year’s worth of samples, process
these, and perform the impact analyses� Source water studies, which are typically patterned along
the lines of EPA guidance for Section 316(b) demonstrations, are relatively prescriptive in scope
and vary according to the seasonality of the species of concern at risk to entrainment and impingement� Hydrographic/oceanographic studies of source water currents and water quality in the area
of the proposed intake typically occur in concert with source water studies of larval, juvenile, and
adult ishes and shellish at risk to entrainment and impingement at the facility’s intake� The results
of these source water studies are used to inform the design, capacity, and operation of the intake to
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
58 | Assessing Seawater Intake Systems for Desalination Plants
minimize entrainment and impingement effects� In the case of open water intake screens (passive
or active), other behavioral devices would be required to minimize impingement effects on ish
and shellish by avoidance or return to the source water�
Intakes are generally not allowed at the end of channels, which tend to trap ish and interfere with their safe return to the source water body� Source water study results may indicate that
impacts could be lessened if the lowrate into the facility’s intake were reduced to match patterns
of seasonally or diurnally occurring abundances of important species or particular life stages�
Although open water intakes can impact local navigation and permanently displace existing habitat, these impacts are minor in comparison to the potential effects of entrainment and
impingement� The assessment and mitigation of these ecological impacts are key factors in the
success and timeliness of permitting a desalination plant open water intake�
The use of a subsurface intake avoids essentially all the negative effects (entrainment and
impingement) associated with operating an open water intake� This may shorten the timeline to
permit an intake, as no source water studies are needed� The use of subsurface intakes for desalination apparently has wide support among environmental groups and some resource and regulatory
agencies, depending on the actual design� However, constructing seabed iniltration intakes would
permanently destroy and displace existing bottom habitat and ish populations, the effect of which
might be viewed as more damaging than an open water intake with properly designed screens to
minimize entrainment and impingement effects� Seabed iniltration intakes as well as beach galleries can require a high degree of maintenance that would repeatedly disturb the recolonized areas
initially disrupted by the installation of these intake devices�
California
A large number of desalination projects in the planning and development stage are proposed for location along California’s coastline, coastal harbors, bays, and estuaries� The largest of
these projects, a 100-mgd intake capacity (379,000 m3/d) facility located in Carlsbad, received
inal regulatory approval in November 2007� The various proposed locations involve a wide range
of source water types and habitats including brackish freshwater in the Sacramento-San Joaquin
Delta, San Francisco Bay, Monterey Bay, Santa Monica Bay, Long Beach Harbor, Agua Hedionda
Lagoon, and along Southern California’s open coastline� This wide range of locales crosses several
areas of jurisdiction with respect to shoreline development, source water withdrawal, and waste
discharge� Populations of fully protected endangered species, both aquatic and terrestrial, found at
some of the state’s proposed sites, involve an even wider range of resource and regulatory jurisdictions, each with their separate review and approval procedures and processes� Key regulations and
permitting activities needed for a new seawater intake are summarized in Table 2�5 and discussed
in detail below�
Development along the state’s coastline is under the regulatory jurisdiction of CCC� The
CCC was established by voter initiative in 1972 (Proposition 20) and later made permanent by the
Legislature through adoption of the California Coastal Act of 1976� The coastal zone, which was
speciically mapped by the Legislature, covers an area larger than the State of Rhode Island� On
land, the coastal zone varies in width from several hundred feet in highly urbanized areas up to
ive miles in some rural locations� Off-shore, the coastal zone includes a three-mile-wide band of
ocean� The coastal zone established by the Coastal Act does not include San Francisco Bay, where
the BCDC regulates development� Along with the BCDC, the CCC is one of California’s two
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 59
Table 2.5
Major regulations and permits pertaining to seawater intake construction and
operation in California
Regulatory/permitting activity
Responsible federal/
state agency
Description/applicability
Lease for coastal and/or offshore land
California State
Lands Commission
(CSLC)
Lease coastal and off-shore lands for private or municipal use�
Permit evaluation includes the biological review of entrainment,
impingement, and discharge effects of intake and discharge
facilities operating on state-leased lands�
Coastal Development Permit
CCC
Required by Section 307 of the Coastal Zone Management Act
and by the California Coastal Act� Applies to development in
and on the California Coastal Zone� Must also be in compliance
with the Local Coastal Program (LCP) if one is in place for the
intended location�
Bay Conservation
and Development
Commission (BCDC)
Required by Section 307 of the Coastal Zone Management Act
and by the California Coastal Act� Applies to development in and
on San Francisco Bay� Must also be in compliance with the LCP
if one is in place for the intended location�
Environmental Impact
Assessment /Environmental
Impact Report
LCP, CCC/BCDC
and CSLC
Describe the impact of site preparation, construction, and
operation on navigation, ish and wildlife resources, water
quality, water supply, and aesthetics� Describe mitigation and
repair plans� EIA is required by NEPA (National Environmental
Policy Act)� EIR is required by the California Environmental
Quality Act� These are typically submitted as one document�
Endangered Species Act
consultation
U�S� Fish and
Wildlife Service
(USFWS)
Assess habitat for the presence of endangered and/or threatened
species; this includes migratory animals�
California
Department of Fish
and Game (CDFG)
The state agency that manages terrestrial, marine, estuarine, and
freshwater habitats and associated endangered, threatened, and
exotic species�
NOAA
Issue permits for “taking species incidental to (not the purpose
of) an otherwise lawful activity (ESA Section 10(a)(1)(B))�” A
Habitat Conservation Plan must accompany it�
NMFS
Enforce federal marine resources and habitats laws (e�g�, ESA,
Marine Mammal Protection Act)�
Section 10 of the Rivers and
Harbors Act permit
U�S� Army Corps of
Engineers
Applies to construction of any structure in or over any
“navigable water” of the United States, the excavation/dredging
or deposition of material in these waters or any obstruction or
alteration in a “navigable water�”
Section 316(b) of the Clean
Water Act
State or Regional
Water Quality
Control Board and
CSLC
Requires that the location, design, construction, and capacity
of intake structures minimize adverse environmental impacts;
e�g�, screens to mitigate entrainment and enmeshment, an intake
velocity of ≤0�5 ft/s (0�15 m/s)�
Section 401/404 of the Clean
Water Act
U�S� Army Corps of
Engineers and CSLC
Needed for the discharge of dredge or ill materials into navigable
waters�
Revised National Pollutant
Discharge Elimination System
(NPDES) permit
State and Regional
Water Quality
Control Board
A provision of the Clean Water Act that prohibits discharge of
pollutants into waters of the United States unless a special permit
is issued�
Marine habitat consultation
The NPDES permit for an existing ocean intake/outfall must
be revised and approved if it is to be used as an intake for a
desalination facility�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
60 | Assessing Seawater Intake Systems for Desalination Plants
designated coastal management agencies for the purpose of administering the federal Coastal
Zone Management Act (CZMA) in California (OOCRM/NOAA 2007)�
The most signiicant provisions of the federal CZMA give state coastal management agencies regulatory control (federal consistency review authority) over all federal activities and federally licensed, permitted, or assisted activities� Federal consistency is an important coastal
management tool because it is often the only review authority over federal activities affecting
coastal resources given to any state agency� For issues and concerns related to seawater intakes, the
CCC is assisted in their consistency reviews by various federal and state resource and regulatory
agencies and services such as the NMFS, USFWS, the CDFG, and the State and Regional Water
Quality Control Boards�
Development within California’s coastal zone may not commence until either the CCC or
a local government with a CCC-certiied local coastal program has issued a coastal development
permit� California’s coastal management program is carried out through a partnership between
state and local governments� Implementation of Coastal Act policies is accomplished primarily
through the preparation of LCPs that must be completed by each of the 15 counties and 59 cities
located in whole or in part in the coastal zone of interest�
In recent practice during the CCC’s November 2007 review and approval of Poseidon’s
Carlsbad desalination facility, the CCC staff carefully reviewed the 316(b)-type studies and assessment of the entrainment and impingement effects predicted for the facility’s co-located feed water
intake� The CCC staff then continued to work closely with the applicant to validate potential
effects of biological models and the mitigation of these effects through habitat restoration design�
The CCC commonly oversees the development and inal performance of mitigation efforts for
their permitted projects�
The CSLC, which leases coastal and off-shore lands, recently expanded their mission to
include the biological review of entrainment, impingement, and discharge effects of shoreline and
off-shore seawater intake and discharge facilities operating on state-leased lands� The CSLC has
indicated that after 2026 the CSLC will no longer renew leases for once-through-cooling water
intakes� The CSLC’s earlier position has been modiied in deference to the regulatory authority
granted to California’s State and Regional Water Quality Control Boards under federal CWA and
state water codes� The CSLC recognizes that a once-through cooling water intake with a NPDES
permit that is in compliance with Section 316(b) will be qualiied for lease approval or renewal�
In the case of a desalination facility proposing to withdraw feed water from an existing
seawater intake with a valid NPDES permit, the altered permitted use (e�g�, changed from cooling
water to process feed water) of the facility’s intake or discharge low requires a new and separate
facility NPDES permit� Such was the case in California’s most recently issued NPDES permit for
a co-located desalination facility’s feed water intake (100-mgd Carlsbad desalination facility)� In
this case, the San Diego Regional Water Quality Board required the applicant to assess the facility’s potential entrainment, impingement, and hypersaline discharge effects, assuming that the site’s
existing cooling water intake and discharge were no longer permitted� Under such a scenario, the
desalination facility would be required to withdraw an additional 200 mgd (757,000 m3/d) of seawater to maintain discharge salinity no greater than 40 g/L� The analyses assessed the resulting
impingement and entrainment effects of feed water withdrawal associated with desalination-only
operations� The impact analyses also took into account the entrainment and impingement effects
associated with the need to increase seawater lows to meet the facility’s discharge limits for salinity� The analyses also assumed that the entrainment and impingement effects and any associated
requirement to minimize or mitigate these effects to meet future regulations would become the sole
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 61
responsibility of the Carlsbad project� It is reasonable to expect that in future cases involving colocated desalination projects, the applicant will be required to analyze the environmental effects of
its seawater intake both in conjunction with and separate from the existing operations of the colocated facility (i�e�, consider a shutdown scenario of the host facility’s operations)�
The use of a seawater intake or discharge from an existing facility to supply feed water to
the desalination facility would require a separate NPDES permit for the desalination facility’s new
purpose for the use of intake low and discharge� However, if the desalination facility is only
diverting power plant discharge water for feed water, there is a case to be made that in circumstances when the entrainment mortality is nearly 100 percent prior to reaching the desalination
facility’s withdrawal point, any additional entrainment effects resulting from the desalination operation are of a de mininus nature� From the standpoint of entrainment and impingement effects, the
use of a primary host facility’s discharged seawater represents a high level of recycling technology,
as well as avoiding new entrainment and impingement impacts associated with a new seawater
intake�
Florida
As of April 2010, no new open ocean seawater intakes for desalination plants had been
constructed in Florida, although SWRO projects were being considered (e�g�, Flagler County and
South Florida Water Management District)� The largest SWRO plant in the United States, the
Tampa Bay Water desalination facility, is located in Florida, but it uses an existing intake at a
power plant, where it diverts approximately 44 mgd (167,000 m3/d) of cooling water outlow into
its intake structure�
While no speciic guidance for seawater intakes has been developed by the state, their
structure and operation is essentially identical to that of power plant intakes—seawater is pumped
through intake pipes into the plant� Thus, the guidance developed in this section is based primarily
on electrical power plant (seawater) intake permitting guidance (FDEP 2007) and a search of the
databases for a variety of state and federal agencies and related sections of the Florida Administrative
Code (FAC; State of Florida 2001 and 2007)�
The FDEP is the primary agency responsible for permitting seawater intakes, although, as
with any other state, numerous other agencies are involved in different aspects of the project� The
procedures for permitting electrical power plants (including their seawater intakes) are described
in sections 403�501–403�539, FS (State of Florida 1997)� FDEP’s companion rules can be found in
Chapter 62-17, Parts I and II, FAC (State of Florida 2001 and 2007)� Key regulations and permitting activities needed for a new seawater intake are summarized in Table 2�6�
Massachusetts
In July 2007, the Commonwealth of Massachusetts published draft guidance on “The Siting
and Monitoring Protocols for Desalination Plants” (EOEEA 2007)� This document includes the
following recommendations with respect to seawater intakes:
•
•
Mitigate environmental impacts according to Massachusetts Environmental Policy
Act (MEPA) requirements,
Collect enough data to document what and how impacts to the environment will be
avoided or mitigated during construction and operation,
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
62 | Assessing Seawater Intake Systems for Desalination Plants
Table 2.6
Major regulations and permits pertaining to seawater intake
construction and operation in Florida
Regulatory/permitting activity
Responsible federal/state agency Description/applicability
Coastal Zone Management
Certiication (Coastal Permit)
FDEP
Required by Section 307 of the Coastal Zone
Management Act; the design must be consistent with
the Florida Coastal Management Program (FCMP)�
Environmental Impact Assessment
FDEP
Describe the impact of site preparation, construction,
and operation on navigation, ish and wildlife
resources, water quality, water supply, and aesthetics�
Describe mitigation and repair plans� Required by
NEPA�
Environmental Resource Permit &
Authorization to use State owned
submerged lands
Local water management district/ Required before beginning any construction activity
Internal Improvement Trust
that would affect wetlands, change surface water
Fund*
lows, or contribute to water pollution�
ESA consultation
USFWS
Assess habitat for the presence of endangered and/or
threatened species; this includes migratory animals�
Florida Fish and Wildlife
Conservation Comm� (FWC) †
Division of Habitat and Species
Conservation
The Division of Habitat and Species Conservation
manages terrestrial, marine, estuarine and freshwater
habitats and associated endangered, threatened, and
exotic species�
Protected Wildlife Permits
FWC2 Ofice of Licensing and
Permitting
Permits the handling of “protected wildlife�”
Marine habitat consultation
NMFS
Issue permits for “taking species incidental to (not
the purpose of) an otherwise lawful activity (ESA
Section 10(a)(1)(B))‡�” A Habitat Conservation Plan
must accompany it�
Enforce federal marine resources and habitats laws
(e�g�, ESA, Marine Mammal Protection Act)�
FWC2 Division of Marine
Fisheries Management
Assesses the status of important marine species and
makes regulatory and management recommendations
to the FWC Commissioners�
Section 10 of the Rivers and Harbors
Act permit
U�S� Army Corps of Engineers
Applies to construction of any structure in or
over any navigable water of the United States, the
excavation/dredging or deposition of material in
these waters or any obstruction or alteration in a
“navigable water�”
Section 316(b) of the Clean Water
Act
FDEP (include in design
package)
Requires that the location, design, construction
and capacity of intake structures minimize adverse
environmental impacts; e�g�, screens to mitigate
entrainment and enmeshment, an intake velocity of
≤0�5 ft/s (0�15 m/s)�
Section 401/404 of the Clean Water
Act
U�S� Army Corps of Engineers
and FDEP
Needed for the discharge of dredge or ill materials
into navigable waters�
Revised NPDES permit
FDEP
A provision of the Clean Water Act, which prohibits
discharge of pollutants into waters of the United
States unless a special permit is issued�
The NPDES permit for an existing ocean intake/
outfall must be revised and approved if it is to be
used as an intake for a desalination facility�
*The Board of Trustees of the Internal Improvement Trust Fund acts as the proprietor of Florida state-owned submerged lands�
The Board itself reviews very large projects, but FDEP and the local water management districts are responsible for reviewing
and approving most authorizations�
†Complete rules for the Fish and Wildlife Conservation Commission are listed in Chapter 68 of the Florida Administrative Code�
‡Endangered Species Permits and Conservation Plans page: http://www�nmfs�noaa�gov/pr/permits/esa_permits�htm�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 63
•
•
•
•
•
Locate the intake outside areas of critical natural resource value (e�g�, estuaries, Areas
of Critical Environmental Concern, and Outstanding Resource Waters),
Intake operation “should not affect the hydrological regime of the area where the
intake occurs,”
Withdrawal should not affect ish habitats, wetlands, benthic isheries, endangered or
threatened species, adjacent freshwaters, and natural salinity structures (e�g�, salt
wedge),
Submerged intakes are preferred, and
Co-location and regionalization are encouraged�
Texas
As with Florida, as of April 2010, no seawater intakes for desalination plants had been
constructed in Texas, although a number of SWRO projects were being considered� These include
large projects in the Cities of Corpus Christi (25 mgd, or 95,000 m3/d) and Brownsville (25 mgd,
or 95,000 m3/d)� Feasibility studies have been conducted for both cities (Turner Collie & Braden
et al� 2004 and Dannenbaum et al� 2004, respectively) and a large-scale SWRO demonstration
plant has been tested at the City of Brownsville�
Some initial guidance for permitting seawater intakes has been developed for the Texas
Water Development Board (R�W� Beck Inc� 2004); however, this effort was hampered in part by
the lack of existing precedents (operating facilities) and resultant limited stakeholder guidance�
The demonstration test at the City of Brownsville is intended to help establish “a clear regulatory
path to facilitate the permitting process for future large-scale seawater desalination projects”
(TWDB 2006, pg� 23)� As with Florida, the guidance developed in this section is based primarily
on electrical power plant (seawater) intake permitting guidance (FDEP 2007), existing feasibility
studies (Turner Collie & Braden et al� 2004 and Dannenbaum et al� 2004), and a search of the
databases for a variety of state and federal agencies�
The Texas Commission on Environmental Quality (TCEQ) is the primary agency responsible for permitting seawater intakes, although as with any other state numerous other agencies
would be involved with some aspects of the project� Key regulations and permitting activities
needed for a new seawater intake are summarized in Table 2�7�
PUBLIC AND STAKEHOLDER INVOLVEMENT
Ever-increasing water demands plus declining supplies imply that some communities will
have to weigh dificult trade-offs among agricultural, urban, ecological, industrial, and recreational
water uses against developing new sources of water (with their associated environmental, property
value, and water rate impacts)� This decision-making process is a joint effort between the water
utility, state regulators, and local municipal and private stakeholders�
Stakeholders Are Intrinsic to the Decision-Making Process
Engineering is not just deining a technical problem and developing a technical solution to
it a given agency’s need� It often incorporates consideration of stakeholder concerns with respect
to environmental impacts, watershed effects, carbon footprint, etc� Many times these stakeholders
extend beyond county or state boundaries�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
64 | Assessing Seawater Intake Systems for Desalination Plants
Table 2.7
Major regulations and permits pertaining to seawater intake
construction and operation in Texas
Regulatory/permitting
activity
Responsible federal/
state agency
Coastal Zone Management
Certiication (Coastal
Permit)
Texas Coastal Coordination Required by Section 307 of the Coastal Zone Management Act;
Council, Texas General Land the design must be consistent with the Texas Coastal Management
Ofice*
Plan�
Dune Protection Permit
Local government
Established by the Texas Coastal Management Program,
construction along the coast requires a permit and associated Dune
Protection Plan (application requirements are listed in TAC §15�3)�
Environmental Impact
Statement
TCEQ
Describe the impact of site preparation, construction, and operation
on navigation, ish and wildlife resources, water quality, water
supply, and aesthetics� Describe mitigation and repair plans�
Required by NEPA�
Endangered Species Act
consultation
Texas Parks and Wildlife
Department (TPWD)*
Review endangered and threatened animals list (maintained by
TPWD) and compare to organisms identiied in the EIS� The
Department’s Wildlife Permitting Section permits the handling of
listed species�
U�S� Fish and Wildlife
Service
Assess habitat for the presence of endangered and/or threatened
species; this includes migratory animals�
NOAA
Issue permits for “taking species incidental to (not the purpose of)
an otherwise lawful activity (ESA Section 10(a)(1)(B))�”† Must
have a Habitat Conservation Plan�
NMFS
Enforce federal marine resources and habitats laws (e�g�, ESA,
Marine Mammal Protection Act)�
Marine habitat consultation
Description/applicability
Section 10 of the Rivers and U�S� Army Corps of
Harbors Act
Engineers
Applies to construction of any structure in or over any navigable
water of the U�S�, the excavation/dredging or deposition of material
in these waters or any obstruction or alteration in a “navigable
water�”
Section 316(b) of the Clean
Water Act
TCEQ (include in design
package)
Requires that the location, design, construction and capacity of
intake structures minimize adverse environmental impacts; e�g�,
screens to mitigate entrainment and enmeshment, an intake velocity
of ≤0�5 ft/s (0�15 m/s)�
Section 401/404 of the
Clean Water Act
U�S� Army Corps of
Engineers1
Needed for the discharge of dredge or ill materials into navigable
waters�
Water Rights Permit
TCEQ
Permit to withdraw water from the Gulf of Mexico inside the
territorial limits of the state�
Revised Texas Pollutant
Discharge Elimination
System (TPDES) permit
TCEQ
NPDES, a provision of the Clean Water Act, which prohibits
discharge of pollutants into waters of the United States unless a
special permit is issued� TCEQ has federal regulatory authority over
discharges of pollutants to Texas surface water that it administers
through its TPDES program�
The NPDES permit for an existing ocean intake/outfall must
be revised and approved if it is to be used as an intake for a
desalination facility�
*The Permit Service Center of the Texas General Land Ofice can provide a consolidated joint permit application form for these
permit types for locations on the Texas lower coast�
† Endangered Species Permits and Conservation Plans page: http://www�nmfs�noaa�gov/pr/permits/esa_permits�htm�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 65
“Stakeholders” are organizations and individuals with a vested interest in the outcome of
an action or decision� “Inside stakeholders” include city government leaders (mayor, regulatory
agencies, water board, etc�), who need to be regularly updated and consulted throughout the process to enable them to make informed decisions� “Outside stakeholders” can be civic groups, environmental groups, neighbours, etc� Stakeholder involvement is now an important piece of many
water and wastewater decisions� Nowhere is this more in evidence than in the development of new
water sources�
A good formal stakeholder process is almost always an improvement over “decideannounce-defend” decision-making� It is more transparent and helps minimize confrontations�
This does not mean turn over the decision making power to the stakeholders, it means include their
input in the decision-making process so a more balanced, defensible solution can be achieved�
Relative Values of Trade-Offs
The value of both the various technological (e�g�, developing a new water source) and
social (e�g�, modifying consumption patterns) options a community can use to address potable
water shortfalls depend upon what can technologically be achieved for local or regional water
quality and the comparative importance of competing stakeholder interests� Some of the key tradeoffs managers need to address involving the “what and how” of stakeholder involvement include:
•
•
•
•
Integrating technical and policy or value discussions in open forums�
Supplementing formal regulatory procedures (e�g�, the permitting process) with a parallel stakeholder process to negotiate and build consensus on the inal plan�
Responding to groups or individuals’ needs while maintaining technical rigor and
defensibility�
Using sound science and engineering practices to balance effort versus accuracy in
sampling, modeling, and assessment�
These trade-offs incorporate consideration of stakeholder values (e�g�, ecological quality,
costs, drinking water quality) into solving technical problems (e�g�, effectiveness of chemical treatment, feasibility of reuse options, and mitigation of environmental impacts)� It combines formal
decision-making actions with a more open-ended process whose design is up to the water utility
working with regulators and decision-makers�
Tips for Successful Stakeholder Involvement
If a single axiom could be ascribed to the process of involving stakeholders in decisionmaking, it would be: “engage stakeholders early and give them a meaningful role�” Controversy
arises when the legitimacy of the decision-making process is questioned� Projects must include a
means of assuring adequate roles for stakeholders from the start� No process can guarantee better
outcomes, but some role for public participation is often essential for many public works decisions� The following seven strategies are recommended for facilitating successful stakeholder
discussions:
1�
Begin stakeholder involvement early� Organize the stakeholder process into manageable steps that deine progress and lead to a completed stakeholder product� Stakeholder
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
66 | Assessing Seawater Intake Systems for Desalination Plants
2�
3�
4�
5�
6�
7�
involvement is a “front-end” activity, so the facilitator needs a strategic plan of the
steps needed to create a stakeholder product (ranking of options, recommendation,
vote/survey,���) and deine how it will be used by the decision-makers (City Council,
regulators, district board, etc�)�
Deine clear and meaningful roles and goals� Make stakeholder roles and project
goals consistent with decision-making responsibilities and the level of input or control
appropriate for the given decision� A range of options (e�g�, “consult,” “recommend,”
“decide”) is possible� In any case, participants generally need to be able to compare
alternatives, understand consequences, and express their preferences in a meaningful
way�
Keep the process “values” focused, not “alternatives” focused� Orient participants to
the ends, not the means� A common problem in decision-making is focusing too early
and too much on decision options� From a policy perspective, it makes more sense to
“work backwards” from water quality, environmental, and inancial goals to the
options that can achieve them�
Use decision analysis methods to understand and characterize stakeholder values�
Decision analysis aids the decision-making process by deining a decision methodology that facilitates formally evaluating the various alternatives based on sound science, measurable consequences, and clear trade-offs� Decision analysis tools can help
planners structure the decision making process to balance effort and accuracy, and to
fairly quantify uncertainty�
Know your stakeholders and their issues well� Look out for issues and information
appearing outside the stakeholder process�
Keep close attention to how engineering, regulatory, legal, scientiic, political, and
inancial issues interact and change� By identifying questions and issues as part of the
decision framework, stakeholders can inluence their resolution� Attention to critical
framing issues is essential for a manager gauging progress of the stakeholder
process�
Maintain trust and credibility� Participants need to know that their views will be
respected and heard, that they will be treated equitably, that critical decisions have not
been made prematurely, that commitments will be met, and that information will be
unbiased�
Guidance on Using Stakeholder Communications Tools
Analytic tools help organize complex choices, while public participation methods are
essential to interact with stakeholders effectively about these choices� Using both sets of “tools”
can help facilitate integration of stakeholders into the decision-making process� The following section provides guidance on one popular stakeholder involvement tool, workshops�
Stakeholder Workshops
The stakeholder workshop process involves using public involvement tools to include the
public in water and wastewater decisions� Techniques used included open-ended whole-group discussion, small work groups focusing on different technology choices, presentations from specialists on water quality comparisons, ranking of options, and real-time development of a inal group
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 67
Source: Adapted from Kadvany and Clinton 2002�
Figure 2.13 Example of a stakeholder process designed to lead to a recommendation in the
form of a group “opinion statement”
opinion statement with “majority” and “minority” views� Figure 2�13 illustrates the steps in an
“opinion statement” workshop�
The irst step in the workshop process is to collectively (with the stakeholders) identify
what the issues and problem(s) are that the agency must solve� To do this, the agency must make it
clear to the stakeholders that they are the responsible organization that must solve this problem� In
turn, the problem must be a real, not a perceived problem� The desired outcome of the irst step is
an understanding of the problem and key issues by all stakeholders�
The second step is to identify the values, in other words, “what’s at stake�” “Values” deine
what is important to an individual stakeholder� Some examples of values include river water quantity, neighborhood impacts, cost, and drinking water quality� Once the stakeholder values are
deined and understood, the process can move on to deining various alternatives and their associated trade-offs� The beneit of irst understanding the problem and the stakeholder values is that a
basis is set in which acceptable alternatives can now be identiied�
Step three, deining alternatives, is the irst stage where technical input may be required�
The alternatives could include implementing seawater desalination, deining various types of recycled water projects, or acceptable levels of water conservation� The alternatives can be compared to
identify what trade-offs might need to be made to meet the values identiied in step two of the workshop process� For example, a preferred alternative may be to implement a submerged iniltration
gallery for a new seawater desalination plant intake� However, a trade-off may be that signiicant
disturbance of the seabed would be required and signiicantly, higher costs would be incurred for
its maintenance� This trade-off would need to be identiied so the stakeholders could consider it�
Step four involves combining the preferred alternatives into scenarios and conducting a
comparison� The scenarios represent actual combined projects that would form a full solution to
the problem� Steps three and four could be combined into one workshop or could be expanded into
several workshops as needed�
Step ive allows the agency and the stakeholders to deine and ‘frame’ the policy direction
of the scenarios� For example, should an agency go beyond their permitted discharge limit or
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
68 | Assessing Seawater Intake Systems for Desalination Plants
should they just continue to meet their discharge requirements? This type of policy selection should
be made before the recommendations are formulated (step six)�
The inal step, step six, is to provide a recommendation� The recommendation could be in
the form of an Opinion Summary in which the stakeholder can identify both majority and minority
opinions or it can take other forms as desired�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
CHAPTER 3
UTILITY SEAWATER INTAKE EXPERIENCE SURVEY
INTRODUCTION
As part of the overall strategy to assist utilities in planning for the design of seawater intake
systems, the Research Team developed a 54-question survey to capture information summarizing
the experiences of participating utilities with the ocean intake planning, design, and implementation process�
METHODOLOGY
Forty-four utility managers with existing or planned seawater desalination facilities from
across the United States and abroad were contacted and invited to participate by completing and
returning the electronic intake experience survey� These managers were queried on their existing
or planned intake’s size, design characteristics, costs, and operation as well as their experiences
with environmental impacts and mitigation, permitting, and the stakeholder process� Twenty-four
utilities submitted surveys� Not all questions were answered in every case� Where possible, gaps
were illed with the aid of information available in the public domain (internet searches, journal
articles, conference proceedings, etc�)� Anonymity was promised to the respondents in order to
promote openness and participation�
The survey structure was broken into ive sections, General Utility Overview, Seawater
Intake Systems Design Characteristics, Environmental Impacts and Mitigation, Permitting
Experience, and Stakeholder Process� A simple check box and quick-ill format was used to make
the completion process as quick and easy for the respondents as possible� A copy of the survey is
presented in Figures 3�1a through 3�1e� Twenty-four of the utilities completed the questionnaire, a
response rate of 55 percent� The collected information was entered into an online survey tool,
Survey Monkey (www�surveymonkey�com), to facilitate data analysis and presentation�
REPORT FORMAT
This utility survey report follows the ive-section structure of the questionnaire:
1�
2�
3�
4�
5�
General Utility Overview�
Seawater Intake Systems Design Characteristics�
Environmental Impacts and Mitigation�
Permitting Experience�
The Stakeholder Process�
Each section summarizes the utility responses either in graphical or tabular form� Where it
is considered appropriate, responses to some questions are combined into a single igure or table�
To assure promised anonymity, information is grouped primarily by categories rather than listing
the plants individually� In instances where plants are mentioned individually, numbers are used in
place of names (Plant 1, Plant 2, and so forth)� This numbering sequence is used only for
69
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
70 | Assessing Seawater Intake Systems for Desalination Plants
AwwaRF Project #4080: Seawater Intake Systems for Desalination Plants
Utility Qu estionnaire
B ackg rou nd
Intake location and design is a challenging part of seawater desalination in terms of technical
strategy, regulatory challenges, and public perception. This is due, in part, to the relatively limited
experience many managers and other decision-makers have with desalination technology. The
objective of this project is to develop a user-friendly decision methodology for ocean intake project
implementation. Part of this effort is to learn what is happening in the field with utilities who are
considering, are in the process of installing and who have installed desalination systems with ocean
intakes.
Instru ctions for C omp leting th e Su rv ey
1 ) . The survey is located on the following worksheet and is composed of five parts. It uses checkboxes
and blue-tagged filled in boxes _ _ _ _ _ _ _ _ _ _ _ _ _ to allow q uick completion.
2 ) . It can be filled out and returned electronically or printed and mailed/ faxed back.
3 ) . To fill it out, simply scroll down the instrument ( it prints out as 3 pages) and fill in the req uested
data as appropriate for your site. C heck the correct box where appropriate, or fill in data. If you wish to
provide more detailed information that is most welcome – you can include it on the sheet or we can
collect it by phone.
4 ) . M ore detailed information on any topic can be added on the “A dditional Information” sheet.
H ow th e Data W ill B e Used
All u tility d ata will b e rep orted anonymou
U tility
sly. names are only being used to organiz e
information internally. The data will not be reported in a way that allows easy identification of a specific
utility ( i.e., it will be grouped by topic) . If you have any concerns about any specific sensitive issues in
your area, please let us know at your earliest convenience. It is standard policy for both A wwaR F and
C arollo to not publish utility data until that organiz ation has had the opportunity to review and approve
its use in the F inal R eport.
C
D
C
1
B
omp lete Su rv eys C an B e Retu rned T o:
r. E rin M ackey
arollo E ngineers
2 5 9 2 W E xplorer D r., S uite 2 0 0
oise, ID 8 3 7 1 3
TH A N K Y O U
–Y O U R
H E L P IS A PPR E C IA TE D !
Figure 3.1a Instructions page of the Utility Seawater Intake Experience Survey
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 3: Utility Seawater Intake Experience Survey | 71
Aw w aRF Project #4080: Seaw ater Intake Systems for Desalination Plants
Utility Questionnaire
Check (click on) the appropriate box in each section.
Fill in the shaded boxes
Pg. 1 of 3
where applicable NOTE: All utility data will be
SECTION 1. UTILITY OVERVIEW
Facility Name:
Either current, planned, or potential future installation.
Facility Size
Population
Desal. Capacity
Intake Capacity
Avg. Flow Rate
<10,000
<5 mgd
<5 mgd
mgd
m3/d
10k-49,999
5-10 mgd
5-10 mgd
11-25 mgd
11-25 mgd
50k-99,999
26-50 mgd
26-50 mgd
>100,000
>50 mgd
>50 mgd
>1,000,000
Purpose of Seaw ater Desalination Plant
Status of Seaw ater Desalination Plant
Operating
Drought-proof supply
Installed, but not yet on-line
Meet increased demand
In Construction
Meet reduced supply shortfall
In Design
Other (please specify)
Demo-Testing/Planning
Pilot-testing/Planning
Did/do/will you need to consider
Yes No
"Carbon Footprint" offsets?
Initial Planning
Potential Future Project
reported anonymously. Utility
names are only being used to
organize information internally. The
data will not be reported in a way that
allows easy identification of a specific
utility (i.e., it will be grouped by topic).
If you have any concerns about any
specific sensitive issues in your area,
please let us know at your earliest
convenience. It is standard policy for
both AwwaRF and Carollo to not
publish utility data until that
organization has had the opportunity
to review and approve its use in the
Final Report.
SECTION 2. SEAWATER INTAKE DESIGN CHARACTERISTICS
Check all that apply. Intake Characteristics
Intake Type
For Surface Intakes
# of intake pipes
Shared Converted
Pipe diameter
Pipe capacity
If so, shared or converted?
If so, what type of shared intake?
Average flow
Surface Intake
Length of intake
Open Ocean
For Subsurface Intakes
Combined
Shoreline
Surface/Subsurface
# of wells
Other (please specify)
Well diameter
Subsurface Intake
Well capacity
Infiltration Gallery
Average flow
Well(s)
Length of intake
Horizontal (Ranney)
Beach
Other details you'd like to add:
Horiz. Directionally Drilled
Slant
Other (please specify)
Vertical
Co-located/replaced existing
intake?
Yes
No
Screening Technology/ies Used
Vertical Traveling Screen
Modified Traveling Water Screens
Fish Return System
Adjustable Vertical Barrier
Centerflow/Dual Flow Screen
Narrow Slot/Wedgewire Screen
Fine Mesh Modified Traveling Screens
Light and Acoustical Deterrents
VFD Pump Seasonal/Diurnal Flow Mg'mt
Location of Primary Screens
Type(s) of Screens Used
Primary
Secondary
Location of Secondary Screens
ft
m
mgd
m3/d
mgd
m3/d
ft
m
ft
m
mgd
m3/d
mgd
m3/d
ft
m
Check all that apply.
Velocity Cap
Angled Screens
Barrier Net
Aquatic Filter Barrier
Louvers
Modular Inclined Screens
Bubble Curtain
Porous Dikes
Figure 3.1b Page 1 of the Utility Seawater Intake Experience Survey
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
72 | Assessing Seawater Intake Systems for Desalination Plants
Aw w aRF Project #4080: Seaw ater Intake Systems for Desalination Plants
Pg. 2 of 3
Utility Questionnaire
Select one
If multiple estimates were completed.
Costs
Conceptual estimate
I have more than one estimate (i.e ., we
What type of cost numbers do
considered multiple scenarios).
you have?
Design estimate
The costs here are for:
As-built cost
Units (currency & volumetric units)
None
What was the capital cost? $
e.g. , $U.S., per gal. capacity
If done, what was mitigation cost? $
e.g. , $U.S.
What is the O&M cost? $
e.g. , per 1,000 gal.
Yes No
Was this in line with expectations?
If not, please explain:
Intake Operations
For operating systems only, others should sk ip down to the next section
How many months per year does the system operate?
Yes No
Have you experienced operational problems?
Loss of capacity
If so, did they include:
Silting of the intake
Primary screens clogging with marine life
Pump operations
Primary screens clogging with silt or mud
Corrosion
Secondary screens clogging with marine life
Intake pipe (please describe problem below)
Secondary screens clogging with silt or mud
Yes No
Did It interrupt production?
If so, does this happen regularly?
If so, please describe the recurrence pattern:
If so, for how long?
SECTION 3. ENVIRONMENTAL IMPACTS AND MITIGATION
For completed/in design systems only, others should sk ip down to the next section.
Was/will a biological assessment of the entrainment and Yes No
impingement effects performed?
If so, what was the lead time for study?
months
How long did it take to get the plan approved?
months
What was the study duration?
months
currency
What was the estimated cost? $
Yes No
Was there concern about loss of habitat?
If so, for what types of species?
In general terms, what was the scope of the analysis?
Was an environmental evaluation performed for the screen design?
If so, were the findings:
No negative impact
A negative impact
If a negative impact was found, what mitigation steps were taken?
Figure 3.1c Page 2 of the Utility Seawater Intake Experience Survey
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 3: Utility Seawater Intake Experience Survey | 73
Aw w aRF Project #4080: Seaw ater Intake Systems for Desalination Plants
Utility Questionnaire
Pg. 3 of 3
SECTION 4. PERMITTING EXPERIENCE
Please provide as much information as possible based on your k nowledge and project status.
Permitting Requirements
What permits & studies are/were/will be required?
Check all that apply
Env'l Res. Permit & Auth. to Use State Owned Submerged Lands (Fla.)
Endangered Species Act consultation
Section 10 of the Rivers and Harbors Act permit
Section 316(b) of the Clean Water Act permit
Section 401/404 of the Clean Water Act permit
I don't know what
permits will be required.
NPDES Permit
Protected Wildlife Permits
Water Rights Permit (Tex.)
Protected Wildlife Permits
Marine Habitat Consultation
Dune Protection Permit (Tex.)
Coastal/Offshore Land Lease (Cal.)
Coastal Construction Permit
Env'l Impact Assessment (or EIS)
For utilities with completed installations.
Permitting Timeline
years
months
How long was the permitting process?
Yes No
Did a particular permit drive the overall timeline?
What was it?
If so,
How long did it take?
years
If you would like to provide details,
you can do so here.
months
SECTION 5. STAKEHOLDER PROCESS
Stakeholder Process Used
If you have a completed installation, complete this section.
Yes No
Did your utility use a stakeholder process as part of the implementation process?
If you are planning to complete a seawater intak e installation, complete this section.
Does your utility plan to use a stakeholder process as part of the implementation process?
If you are considering a seawater intak e installation, complete this section.
Is it likely, if your plan goes forward, that your utility will use a stakeholder process?
Stakeholder Communications Strategies Used as Part of the Implementation Process
If you have a completed/planned a stak eholder process, complete this section.
Meetings with public officials during the planning process
Meetings with public officials during the design process
Involving public officials in the intake selection process
Involving non-governmental organizations in the intake selection process
Public hearings
Public comment periods
Stakeholder workshops
Check all that apply.
“Stakeholders” are organizations
and individuals with a vested interest
in the outcome of an action or
decision. “Inside stakeholders”
include the city government leaders
(mayor, city council, water boards,
etc.), who need to be regularly
updated and consulted throughout
the process to enable them to make
informed decisions. “Outside
stakeholders” can be regulatory
agencies, civic or environmental
groups, neighbours, etc.
Stakeholder involvement is now an
important piece of many water and
wastewater decisions.
Add other event types as
needed.
Yes No
Would you recommend the same stakeholder process to others?
Why?
Figure 3.1d Page 3 of the Utility Seawater Intake Experience Survey
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
74 | Assessing Seawater Intake Systems for Desalination Plants
AwwaRF Project #4080: Seawater Intake Systems for Desalination Plants
Utility Qu estionnaire
If you wish to provide additional information, we can either collect it in a one-on-one conversation with you,
or you can provide details below, as you prefer.
Click inside this box to type.
Figure 3.1e Additional information page of the Utility Seawater Intake Experience Survey
quantiication purposes and not as a unique identiier; i�e�, Plant 1 in Table 3�3 is not the same
Plant 1 used in the appendix tables� Supplemental information is included in Appendix A where it
was thought that the full narrative responses provided would aid understanding the intake design
process without violating conidentiality�
GENERAL UTILITY CHARACTERISTICS
Ten U�S� facilities and 14 international facilities submitted substantially completed surveys� The range of utility types is summarized below� Fourteen plants listed their status as operating, with the remaining 10 in some phase of design and/or testing� Consistent with the status of
installed desalination capacity worldwide, nearly 90 percent of the 14 operating plants were located
outside of the U�S�
Population Served, Desalination Capacity, and Intake Capacity
Table 3�1 and Table 3�2 present the reported population sizes served by the plants, desalination capacity, intake capacity and average low rates� Broadly speaking, intakes were sized to
provide considerable redundancy, with an (intake) design capacity of approximately twice that of
the designed desalination capacity� In addition, intakes were also generally oversized—13 utilities
had intakes where average low rates were less than the lower end of the design capacity�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 3: Utility Seawater Intake Experience Survey | 75
Table 3.1
Populations served by seawater desalination plant survey respondents
Population range
<10,000
10,000–49,999
50,000–99,999
100,000–1,000,000
>1,000,000
Total
Number of plants
1
2
2
13
5
23*
*Twenty-three of the 24 participating plants provided population data�
Table 3.2
Summary of desalination capacities, intake capacities, and
average intake lows for reporting plants
Range, mgd
<5
5–10
11–25
16–50
>50
Total
Desalination capacity
5
5
6
7
1
24
Intake capacity
4
0
6
7
6
23*
Average intake low
within reported range,
mgd
0�7
—
8�0
15�5
78
*Twenty-three of 24 participating plants provided intake capacity data�
Planned and Installed Desalination Capacity
Figure 3�2 presents a graphical overview of the planned and installed desalination capacity
by plant location—U�S� or international� Installed capacity includes three categories of plants: “online,” “installed but not on-line,” and “previously on-line but currently not in operation�” Two
plants fall in the latter two categories� “Planned capacity” includes plants in the initial planning
phase and those that are undergoing some measure of technology validation (i�e�, demonstrationand pilot-scale testing)� Twenty-three utilities reported their capacities (presented in log-normal
formats)�
International plants occupied the mid capacity range (5–30 mgd or 19,000–114,000 m3/d),
while U�S� plants dominated the lower- (<5 mgd or 19000 m3/d) and higher-capacity (>30 mgd or
114,000 m3/d) ranges�
Desalination Market Drivers
To assess the reasons for the construction of a seawater desalination plant, utilities were
asked to select responses from a prepared list� Twenty utility managers provided responses; all
identiied more than one rationale for the inclusion of seawater desalination in their drinking water
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
76 | Assessing Seawater Intake Systems for Desalination Plants
100
Capacity (mgd)
10
1
US Installed
US Planned
International Installed
International Planned
0.1
0
5
10
Utility ID
15
20
Figure 3.2 Planned and installed desalination capacity of the responding utilities
portfolio� Their responses are summarized in Figure 3�3� A comprehensive list of responses by utility is provided in Appendix A�
Desalination plant construction was inluenced equally by a utility’s desire to have a
drought-proof supply (10 respondents) as to meet increased demand (12 respondents)� To a lesser
extent, plants were constructed to ill a supply gap caused by a reduction in the availability of water
from conventional supplies—imported and locally generated (8 respondents)� Other reasons (provided by one utility each) were the need for supply reliability, diversiication of supply, and to
blend desalinated seawater with well water to improve water quality�
Inluence of Global Warming Regulations on Treatment Planning
To assess the responsiveness of the governing/permitting bodies towards the growing
awareness of the impact of desalination systems on greenhouse gas emissions, participants were
asked to indicate whether or not consideration of carbon footprint offset was (completed facilities)
or would be (facilities in progress) given�
Twenty of the 24 utilities responded to this question (summarized in Figure 3�4)� The need
for greenhouse gas-mitigation plans was sharply divided by location� Seven of the ten responding
U�S� facilities reported they are considering carbon footprint offsets while only three of the ten
responding international facilities reported that they either considered or planned to consider carbon footprint offsets for their facilities�
At irst glance, this disparity would seem to indicate a greater responsiveness on the part of
U�S� facilities toward global warming issues, however, this divide is likely more historical than
geographical� Many of the existing facilities were constructed prior to the recent surge in interest
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 3: Utility Seawater Intake Experience Survey | 77
Drought Proof
Supply
Increased
Demand
2
2
6
3
3
1
1
Reduced
Supply
Other:
• Supply reliability
• Supply diversification (emergency outages of import system)
• Blend with well water to improve water quality
Figure 3.3 Assessment of seawater desalination market drivers by survey respondents
14
12
Skipped
No
Yes
Number of Facilities
10
8
6
4
2
0
US
International
Facility Location
Figure 3.4 Number of survey plant respondents considering carbon offsets
in global warming issues� The Middle East and Europe were among the earliest entrants into the
seawater desalination market� Plants have been built in the Middle East since the 1970’s� As a
result, international facilities adopted the technology in a less stringent permitting climate than
prevails today� In contrast, the irst seawater desalination plant commissioned in the U�S� was a
0�6-mgd (2,300 m3/d) plant in the early 2000s; of the 10 responding U�S� facilities, seven of these
were still only in the planning and/or technology validation phase at the time of survey
completion�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
78 | Assessing Seawater Intake Systems for Desalination Plants
Number of Plants
20
16
12
8
4
0
Isolated
Co-located
Converted Existing
Figure 3.5 Seawater intake locations of survey respondents
SEAWATER INTAKE DESIGN CHARACTERISTICS
Intake Type and Technologies
Intake designs were characterized by basic type—surface or subsurface� Each basic type
was further differentiated by subsurface/surface intake design coniguration� Of the twenty-three
plants that responded to this question, over 80 percent use isolated intakes (Figure 3�5)� Three
plants were co-located with power plants and use their cooling tower outfalls as seawater intakes
and one plant had converted an existing outfall� Twelve plants relied on surface intakes, ten
employed subsurface intakes and an additional two plants used both intakes�
The particular intake technology types, and their prevalence are illustrated in Figure 3�6;
the most frequently used surface intake technology was open ocean and the most frequently used
subsurface technologies were vertical and beach wells� Complete responses on the intake systems
are provided in Table A�2 in Appendix A�
Intake Design Features
Design features of the intakes of eleven plants reporting the use of surface intakes are illustrated in Figure 3�7� Similar features for eight subsurface intake systems are illustrated in Figure 3�8�
These graphs show average number of pipes/wells, diameters, low and capacity for all reporting
surface and subsurface systems� Data are plotted on logarithmic scale, with error bars used to illustrate the range of values reported� In general, wells and pipes were of similar dimensions (approximately 3�5 ft�/6�1 m in diameter for each), but the capacity of pipes far exceeded that of the wells
(39 mgd/148,000 m3/d per pipe used in surface intakes compared to 1�7 mgd/6,400 m3/d per well
used in subsurface intakes)�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 3: Utility Seawater Intake Experience Survey | 79
Surface
Other
Shoreline
Open Ocean
Total
0
2
4
6
8
10
12
14
Subsurface
Slant Wells
Ranney Wells
Infiltration Gallery
HDD Wells
Vertical Wells
Beach Wells
Total
0
2
4
6
8
10
12
Number of Plants
Figure 3.6 Intake technologies in relation to seawater intake type (surface/subsurface) of
survey respondents
10,000
1,000
39.29
100
10
3377.27
# of pipes
Pipe Diameter (ft)
Pipe Capacity (mgd)
Avg. Flow (mgd)
Intake Length(ft)
32.89
2.55
3.28
1
Surface Intakes
Figure 3.7 Design features of reporting surface intakes
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
80 | Assessing Seawater Intake Systems for Desalination Plants
10,000
# of Wells
Well Diameter (ft)
Well Capacity (mgd)
Intake Length (ft)
Avg. Flow (mgd)
1,000
2195.14
100
5.87
10.71
3.44
10
1.67
1
Subsurface Intakes
Figure 3.8 Design features of reporting subsurface intakes
Screening Technologies
Of the seventeen screening technology options (for entrainment and impingement mitigation) presented in the survey, only nine were used by the utilities surveyed (Figure 3�9)� Most of
the twenty utilities who responded to this question used a combination of screen types� Vertical
traveling screens and velocity caps were most common (used by eleven and fourteen utilities,
respectively)� Least common were aquatic ilter barriers, angled screens, and adjustable vertical
barrier, each used by only one utility� Tables A�3 and A�4 in Appendix A present preferred screening technologies and types and locations of screens�
Capital and Operating Costs
On the whole, utilities were reluctant to provide system costs� Ten of the twenty-four utility
respondents provided capital costs and seven provided O&M costs� Unit costs are presented in
Figure 3�10 and plotted with respect to the plant capacity� These data are intended to aid assessment of the impact of capacity on capital and O&M costs� Capital costs are presented in dollars per
gallon ($/gal�) and O&M costs in dollars per thousand gallons ($/1,000 gal�)� Costs were submitted
in the currency of the reporting utility, and converted to $US using December 16, 2008 exchange
rates� A complete summary of the submitted costs are presented in Table A�5 in Appendix A�
In general, there was an inverse relationship between plant capacity and unit capital O&M
costs—as with many aspects of drinking water plant design, higher unit costs were associated with
lower capacity� The igure shows a wide spread in the cost of developing a seawater intake; capital
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 3: Utility Seawater Intake Experience Survey | 81
Aquatic Filter Barrier
Angled Screens
Adjustable Vertical Barrier
Fine Mesh Modified Traveling Screens
Fish Return System
Narrow Slot/Wedgewire Screen
VFD Pump Seasonal/Diurnal Flow Mg'mt
Velocity Cap
Vertical Travelling Screen
0
2
4
6
8
10
12
14
Number of Plants
Figure 3.9 Screening technologies used by responding seawater desalination plants
$10
$25
Capital Cost ($/gal)
$20
Capital Cost
$8
O&M Cost
$7
$6
$15
$5
$4
$10
$3
O&M Cost ($/1000 gal)
$9
$2
$5
$1
$0
$0
0
5
10
15
20
25
30
Capacity (mgd)
35
40
45
50
Figure 3.10 Capital and O&M costs reported by the responding seawater desalination plants
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
82 | Assessing Seawater Intake Systems for Desalination Plants
100%
90%
80%
70%
60%
50%
40%
30%
20%
Mitigation Costs
Capital Costs
10%
0%
Mitigation Costs
Capital Costs
Plant 1 (0.6 mgd)
Plant 2 (104 mgd)
Plant 3 (0.5 mgd)
Plant 4 (88 mgd)
$125,515
$3,500,000
$75,000
$11,150,600
$2,700,000
$16,000,000
$2,900,000
$223,012,000
Figure 3.11 Mitigation costs as a function of overall desalination plant costs reported by the
survey respondents
costs ranged from $0�32 to $20/gallon (median ~$5�83/gal) and O&M costs from $0�31 to
$8�66/1,000 gallons (median ~$2�50/1,000 gal)� This underscores the highly site-speciic nature of
seawater intake development costs� Cost igures from one plant are of little value in predicting
expenditures for another plant, even at similar capacity� The reader should use caution in adopting
existing cost numbers without careful comparison of the physical and social characteristics of the
two sites�
This is true not only for capital and O&M costs, but for mitigation costs as well� Only four
plants provided both capital and mitigation costs (Figure 3�11)� For the two small plants (<1 mgd
capacity), mitigation efforts represented less than 5 percent of overall plant costs� For the two
larger plants (with intake capacities of 88 and 104 mgd), mitigation costs represented 5 and 18 percent, respectively, of overall plant costs� Since mitigation costs are often dictated by the technology
deemed necessary by the affected communities/bodies, this sizeable difference illustrates the
extent to which stakeholder values can inluence overall intake design costs�
Intake Operations
Critical and non-critical operating issues experienced at the plants are presented in
Figure 3�12 and Figure 3�13� Critical and non-critical operational problems were differentiated by
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 3: Utility Seawater Intake Experience Survey | 83
Corrosion
Intake Pipe
Pump Operations
Secondary filters clogged by marine life
Primary filters clogged by marine life
Operational problems are a regular occurrence
Operational problems result in loss of capacity
Operational problems interrupt production
Plant experienced operatonal problems
0
1
2
3
4
Number of Plants
Figure 3.12 Summary of critical intake operational problems reported by the survey
respondents
Problems solved by other means
Problems solved by regular maintenance
Operational problems occur regularly
Operational problems result in loss of capacity
Operational problems interrupt production
Plant experienced (non-critical) operation problems
0
5
10
15
Number of Plants
Figure 3.13 Summary of non-critical intake operational problems reported by the survey
respondents
their ability to reduce plant capacity� With the exception of two, all of the operating plants (14)
reported that their intakes are used 12 months of the year, with allowances for regular maintenance� One plant reported operating for 11 months per year and another operates its intake for
1 month per year� This latter plant has been shut down due to high operating costs and the 1-month
operation is intended to keep the plant functional so that it may be quickly brought on-line when
the operating issues are resolved�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
84 | Assessing Seawater Intake Systems for Desalination Plants
12
Installed or Operating
Number of Plants
10
In Design or Testing
8
6
4
2
0
Reporting
Yes Study
No Study
Figure 3.14 Impingement and entrainment studies among reporting plants
Most of the operating issues were considered non-critical (Figure 3�13) with six reporting
an interruption in production� This stoppage was resolved by regularly scheduled maintenance
(5 plants) and annual cleaning of primary screens to remove mussels that attach themselves
throughout the year� Four plants reported critical operating challenges� These challenges, and their
impact on plant capacity, are summarized in Figure 3�12� The nature of the recurrence pattern
included: iron clogging pre-ilters of the reverse osmosis (RO) membranes (1 plant), pump bearing
issues during high turbidity events (1 plant), and mussels and other marine life attaching to intake
pipes (2 plants)�
ENVIRONMENTAL IMPACTS AND MITIGATION
Assessment of the Entrainment and Impingement Effects of Intake Systems
Fifty percent of the responding utilities provided answers to this section of the survey and
their responses are summarized in Figure 3�14� All plants in the design and testing phase intended
to conduct a study of the biological and impingement effects of the intake system� Among plants
that were either installed and/or operating, nearly all had conducted a study of the intake system�
Six provided some speciics regarding study lead time, approval time, study duration and cost�
These data are presented in Table 3�3� Costs are in U�S� dollars and are based on the exchange rate
of December 16, 2008� Duration of the impingement and entrainment mitigation studies ranged
widely, from 15 to 39 months�
Loss of Habitat and Environmental Evaluation of Screen Designs
As shown in Figure 3�15 only eight plants (less than 50 percent) were concerned about loss
of habitat resulting from the construction of their respective intake systems� Screen design evaluations were conducted by four plants, with three suggesting that the screens would have a negative
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 3: Utility Seawater Intake Experience Survey | 85
Table 3.3
Environmental impacts and mitigation study results
Study lead time
Approval time
Duration
Total duration
of process
Cost of study
Plant 1
Plant 2
12–18 months
—
3
—
—
6 months
15–21 months
$800 K
Plant 3
24 months
24 months
12 months
60 months
Plant 4
>6 months
—
>12 months
>18 months
Plant 5
24 months
6 months
On-going
>30 months
Plant 6
12
15 months
12 months
39 months
$4�2 M
—
$500K
(annual)
—
—
Screen design shown to have negative
impact
Evaluation of screen design conducted
Concern about loss of habitat
0
2
4
6
8
10
Number of Plants
Figure 3.15 Loss of habitat and screen design evaluations reported by survey respondents
impact on the affected area� Narrative responses regarding scope of analysis, species affected and
mitigation steps taken are presented in Table A�6 in Appendix A�
PERMITTING EXPERIENCE
Permitting Requirements
To assess the extent to which utilities were familiar with the permitting process of seawater
desalination plants and associated facilities, survey participants were asked to indicate the permits
that are applicable to their planned/constructed plants� Fourteen utilities responded to this section of
the survey and the results are presented in Figure 3�16� The survey results indicate that most of the
respondents have some awareness of the permitting requirements for seawater desalination plants�
In addition to the permits selected from the provided list (Figure 3�16), respondents contributed a list of other permits that were required:
•
•
Coastal Development Permit (California)�
California Environmental Quality Act (California)�
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86 | Assessing Seawater Intake Systems for Desalination Plants
Other
Dune Protection Permit (TX)
Protected Wildlife Permit
Water Rights Permit (TX)
Uncertain of Applicable Permits
Section 316(b) of the Clean Water Act
Section 10 of the Rivers and Harbors Act
Env. Res. Permit & Auth. To Use State Owned Submerged
Lands (FL)
Endangered Species Act Consultation
Section 401/404 of the Clean Water Act
Coastal/Offshore Land Lease (CA)
Coastal Construction Permit
Marine Habitat Consultation
Environmental Impact Assessment
NPDES Permit
0
2
4
6
8
10
12
Number of Plants
Figure 3.16 Permitting requirements reported by survey respondents
•
•
•
•
•
•
•
General Construction Permit (California)�
California Department of Fish and Game (California)�
WRD Low Threat 2003-003DWQ (California)�
NOAA Construction Authorization Permit (California)�
California Department of Parks and Regulation�
Streambed Alteration Agreement/Permit (California)�
Clean Water Act equivalent (International)�
Between the list provided on the survey and that contributed by the respondents, seawater
intake desalination systems in California posed the most formidable permitting climate� Eight of
the combined fourteen permits identiied applied to that state alone�
Permitting Timelines
Figure 3�17 presents the permitting timelines and the extent to which a critical permit contributed to the overall permitting timeline� Eight plants with completed installations provided
information� As with mitigation studies, plants reported a wide spread in permitting duration and
the lack of a relationship between plant capacity and permit timeline indicates that duration was
more closely tied to location than capacity� Three plants indicated that the permitting process was
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 3: Utility Seawater Intake Experience Survey | 87
120
Total Permit Time
Time to Permit (months)
100
Critical Permit
80
60
40
20
0
0.3
0.6
30
10
33
38
50
50
Plant Capacity (mgd)
Figure 3.17 Permitting timelines reported by survey respondents
driven by a particular authorization: a Coastal Development Permit (U�S� plant), a Dissolved
Oxygen Permit, or a local ordinance regarding licensing and monitoring of water service provision
(international plants)�
THE STAKEHOLDER PROCESS
Twenty-two plants indicated that they had either involved or planned to involve stakeholders in the intake implementation process� A range of communication strategies were used
(Figure 3�18)� Twenty-one plants contributed information on the elements of the process used to
engage the public in decision-making� With the exception of two, all respondents indicated their
satisfaction with their stakeholder involvement plan and would recommend it to others� One
detractor indicated that the stakeholder process obligated them to spend an exorbitant sum
($15�4 million) on permitting alone� Another utility currently engaged in the stakeholder process
expressed ambivalence about the value of the effort; although early input may assist in the planning process, the utility is concerned that the efforts might be wasted on attempting to convert
adversaries who will never agree to compromise�
Narrative responses for the utilities recommending their respective stakeholder process are
presented in Table A�7 in Appendix A and summarized in Figure 3�19� An overwhelming percentage of the utilities (66%) considered that the stakeholder process was valuable because it facilitated public acceptance� A signiicant fraction (17%) recommend the process because it expedited
implementation (of seawater desalination) and enabled them to both control the information disseminated to the public and lead the public discourse�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
88 | Assessing Seawater Intake Systems for Desalination Plants
Stakeholder workshops
Public comment periods
Public hearings
Involving NGOs in the intake
selection process
Involving public officials in the
intake selection process
Meetings with public officials
during design process
Meetings with public officials
during planning process
0
5
10
15
20
25
Number of Plants
Figure 3.18 Stakeholder communication strategies reported by the survey respondents
Control
Information
17%
Expedite Process
17%
Public Acceptance
and Ownership
66%
Figure 3.19 Rationales for supporting the stakeholder process reported by survey respondents
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
CHAPTER 4
CONTROLLING PARAMETERS IN SEAWATER
INTAKE DEVELOPMENT
The irst step in developing a decision methodology is to identify the key issues and decisions that guide the decision-making process� This chapter deines the assumptions and controlling
parameters used to develop the Desalination Intake Decision Tool (DesalIntakeTool�mdb) on the
attached CD-ROM and described in Chapters 5 and 6�
Seawater Intake design and implementation is guided by two central questions:
1�
2�
What deines an “intake scenario?”
What issues control the decision-making process?
The answers to these two questions determine what shape the intake planning decision
process should take�
DEFINING A SEAWATER INTAKE SCENARIO
The irst step in deining an eficient, successful seawater intake planning process was to
deine the needs and constraints that deine the intake scenario� (Note: Each intake strategy the user
develops for assessment is referred to here as an “intake scenario�”)�
In this decision methodology, it is assumed that the physical and social constraints for the
installation location options have been deined in advance and the quantity of feed water to be
withdrawn is known� If this is not the case, the user is advised to irst deine their seawater treatment needs to the extent that they can deine the approximate size of the intake needed as early in
the planning process as possible� The elements that comprise an intake-planning scenario in the
DesalIntakeTool�mdb ile are listed in Table 4�1�
Information Needed for Evaluating the Intake Design Options
The required information needed to walk through the planning and design process (i�e�, how
the Decision Tool should prompt the user to deine their intake scenario) for a seawater intake
scenario as deined here is as follows:
1�
2�
Required intake capacity—The user must know what capacity the intake would need
to be�
Regulatory region—The three states where there are seawater intakes in the planning,
development, and/or implementation stage can have more detailed regulatory guidance, although other locations may also be considered� Regulatory guidance for these
locations is restricted to the Federal level�
• California�
• Texas�
• Florida�
• Other�
89
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90 | Assessing Seawater Intake Systems for Desalination Plants
Table 4.1
Elements of a deined intake planning scenario
Planning element
Installation size
Regulatory region
Potential location(s)
Information needed
• Required intake capacity�
• Regulatory jurisdiction(s)�
• Geography and geology�
• Site access�
• Potential use issues�
• Partnering options�
• Potential stakeholders�
• Environmental considerations�
• Technically feasible structural design options�
• Design, permitting, construction, and operating costs�
• Availability of capital�
• Repayment assumptions�
Design alternatives
Economic considerations
Table 4.2
Structural design options for seawater intakes
Beach
Open Intake
On-shore
Off-shore
Vertical Wells
Horizontal Wells
Slant Wells
HDD Wells
Iniltration
Gallery
Co-location
Bay
Open Intake
On-shore
Off-shore
Horizontal Wells
Slant Wells
HDD Wells
Iniltration
Gallery
Estuary
Open Intake
On-shore
Off-shore
Horizontal Wells
Slant Wells
HDD Wells
Iniltration
Gallery
Cliffs
Open Intake
On-shore
Off-shore
Horizontal Wells
Slant Wells
HDD Wells
Iniltration
Gallery
Rocky
Coastline
Open Intake
On-shore
Off-shore
Horizontal Wells
Slant Wells
HDD Wells
Iniltration
Gallery
Co-location
Co-location
Site location types under consideration—the geology and geography of the potential
intake location(s) under consideration�
• Beach�
• Bay�
• Estuary�
• Cliffs�
• Rocky Coastline�
• Co-location with an existing intake�
4� Technical options as a function of installation location—the geology and geography
of the potential intake location determines what types of intakes may be feasible�
Table 4�2 lists the intake structure options that are technically feasible for the different
types of site locations�
5� Economic considerations—if the user wishes to consider cost and inancing in the
decision process basic economic assumptions need to be deined up front�
3�
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Chapter 4: Controlling Parameters in Seawater Intake Development | 91
•
•
•
Availability of inancing�
Repayment terms�
Regional and temporal cost adjustment factors�
CONTROLLING PARAMETERS IN THE DECISION-MAKING PROCESS
Once the technical and non-technical elements of planning and implementing a seawater
intake project were deined, the second part of preparing to construct the decision methodology is
to identify all the parameters that control how and what kind of decisions are made�
Table 4�3 lists the parameters that control the feasibility and practicality of the various options for
withdrawing seawater for drinking water treatment�
INCORPORATING THE DECISION-CONTROLLING ELEMENTS INTO A DECISION
FRAMEWORK
The essential planning elements, technical limitations, and controlling parameters identiied and described above were used to guide the development of a decision framework for assessing the relative feasibility and merits of different intake design options for a given intake scenario�
The structure of the decision process is illustrated in Figure 4�1� A description of each step
follows�
Part 1. Deine the Options
Step 1� Deine Scenario� Describe the capacity, potential location(s), and cost factors for
the scenario under consideration�
Step 2� Make Preliminary Assessment of Technical Feasibility� The range of technical
options is identiied for each location type selected (e�g�, a cliff installation precludes the option of a vertical well)� Some of the data will likely need to be collected before the full analysis can be done (e�g�, geologic surveying)� In the interim,
the user can assume viability if (s)he likes and take the analysis to its conclusion
and then come back and update the scenario with the needed information� This step
is intended, in part, to prompt the user to collect needed data�
Step 3� Capture Constraints and Concerns with Stakeholders (optional)� Users are encouraged to identify the stakeholders and their respective concerns that will inluence
the decision-making process� The user is encouraged to consider meeting with the
stakeholder groups to: (1) educate them about the technical limitations and pros
and cons of the possible options; and (2) capture their comments, concerns and
preferences about the various options�
Part 2. Evaluate the Options
Step 4� Complete Feasibility Analysis� Evaluate technical, permitting and stakeholder
issues� Prompt the user, in part, to collect needed data� This four-step process (technical, permitting, costs, and stakeholders) is recommended, although the last step
is not strictly needed and so is optional (though strongly recommended by the
Team)�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
92 | Assessing Seawater Intake Systems for Desalination Plants
Table 4.3
Controlling parameters in seawater intake planning and design
Topic
Intake-speciic
General construction
Permitting
Site access
Stakeholder* issues
Controlling factors
• Water quality (impact on pre-treatment requirements)�
• Geology�
• Erosion concerns�
• Construction-related pollution�
• Entrainment & impingement effects�
• Existent pollution�
• Sewage�
• Red tide�
• Contaminated soil/sediments�
• Capacity (both current and future)�
• Seasonal variation in low�
• Local ecology�
• Timeline for implementation�
• Water temperature�
• Right-of-way�
• Timeline for access�
• Risk�
• Neighborhood impacts�
• Protected species, other environmental impacts�
• Water/inland location�
• Construction/O&M effects�
• Location with respect to the high water mark�
• State jurisdiction�
• Water body type�
• Ecology�
• Water quality standards (effect of discharge limits on needed capacity)�
• Water rights�
• Navigation limits (e�g�, shipping channels)�
• Land availability�
• Ownership�
• Procurement�
• Fisheries�
• Aesthetics (visual, audio, odor)�
• Fishing and recreation�
• Growth�
• Cost�
• Reliability�
• Sustainability�
• Long-term production�
• Global warming impact (closely tied to energy use)�
• Partnerships for construction and/or use�
• Co-location�
• Effect on once-through cooling operation timeline (prolongs)�
• Effect of change in ownership�
• Maintenance biota�
*Deined as owners, regulators, and local consumers and consumer groups�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 4: Controlling Parameters in Seawater Intake Development | 93
Define
Scenario
Part 1. Define the Options
Make Preliminary Assessment
of Technical Feasibility
Capture
Constraints and Concerns
with Stakeholders
Part 2. Evaluate the Options
Complete
Feasibility Analysis
Estimate
Cost
Grade and
Rank Options
Part 3. Compare the Options
Figure 4.1 The global intake planning decision process
Parameters to
quantify
Geology
Vertical
wells

Open
intake
—
Footprint req�
Land
Subsurface
Sustainability

—
Water rights
E&I mitigation
Capacity
Permitting req’mts
Protected species
Aquatic
Terrestrial
Protected area
Aquatic
Terrestrial
Existing pollution
Maint� access
Intake options
Iniltration
Co-location
gallery
HDD
wells
Slant
wells
Horizontal
wells



—

—

?

?

?

?

—
*
*
*
*
—


*
—



*
—










—

—



—









—




—

—

—

—


—






—




—
?Under state law for some locations—need to verify�
*Water Rights for ocean takes are required in Texas�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.


—


—
94 | Assessing Seawater Intake Systems for Desalination Plants
The data topics to be queried are listed in the following table� The user may
not have all the data or choose to enter all the data (s)he has, but providing the
master list will ensure that (s)he is at least aware of all the topics that need to be
considered�
Step 5� Estimate Cost� Identify and quantify cost elements� Each technology will have
“studies,” “permitting,” and “construction” cost lists� Calculations and default data
will be provided as feasible (this is an on-going effort)�
Part 3. Compare the Options
Step 6� Grade and Rank Options� Assign grading criteria with weighting values and rank
the options� The user can then consider his/her next steps�
Please note: This Tool is intended to facilitate the planning process, but is not intended to
replace a detailed Pre-Design and/or Master Plan� It is assumed that if the user were to pursue
development of a seawater intake and desalting plant following use of this Tool would commission
a detailed process design before any irm, concrete decisions were made�
The decision tree described here was turned into a software-based Decision Tool, which is
included on the attached CD-ROM, titled “DesalIntakeTool�mdb�” The user can use this Tool to
develop as many different intake scenarios as desired� Chapter 2 presents an overview of the current state-of-the-science in intake planning, permitting and design, and the role of stakeholders in
the planning process; this text is intended to serve as a reference for the user as he/she works
through the Tool� Chapter 5 describes how to navigate the Decision Tool� Chapter 6 presents two
Case Studies to illustrate what information is typically gathered, how the Tool is used, and how
some of the key drivers for process selection come into play�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
CHAPTER 5
USING THE DESALINATION INTAKE DECISION TOOL
This chapter walks the reader step-by-step (tab-by-tab) through using the Desalination
Intake Decision Tool (“Tool”) on the attached CD-ROM (Microsoft Access™ program
DesalIntakeTool�mdb)� In the Tool, the user is prompted to answer a series of questions� Most
queries have “Note” sections where the user can add additional documentation related to the questions, as desired� As the decision Tool is targeted at developing an intake design plan, it is assumed
that the user has already determined the desalting process scenario to the extent that he/she knows
the volume of feed water the process will need�
STEP 1: DEFINE INTAKE DESIGN SCENARIO
Before any intake options can be considered, the intake design scenario must be deined�
The irst step (the “Overview” tab of the DesalIntakeTool�mdb) is to title your scenario (“Project
Name,” “Description,” “Prepared By,” and “Date”)� The user must then answer the following four
questions:
1�
2�
3�
4�
What is the required intake capacity?
What geographical region are you in (i�e�, what state regulations apply)?
What type of site options are you considering?
What is the local economic climate?
The user may enter as much, or as little, information as he/she desires� The minimum information needed to use the Tool is:
•
•
•
•
•
Project name�
Date�
Required intake capacity�
Region�
Site location�
The user may also add additional documentation related to the questions in the “Note” sections as desired� This logic and the associated parameters are further described in Figure 5�1 and
Table 5�1�
STEP 2: ASSESS TECHNICAL AND LOGISTICAL FEASIBILITY OF OPTIONS
Once the scenario has been described in the “Overview” tab the user is ready for Step 2,
assessing the technical feasibility of the various potentially feasible options� (Note: the potentially
feasible options for each potential intake “Site Location” are listed in Table 4�2)� When the user
selects a potential Site Location (Beach, Bay, Estuary, Cliffs, Rocky Coastline, and Co-location),
the Tool will add a corresponding tab to the right of the Overview tab (between it and the
“Permitting” tab)� In each Site Location tab, the user is offered the range of potentially feasible
technology options� The user can then work through each option and answer the feasibility
95
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
96 | Assessing Seawater Intake Systems for Desalination Plants
Figure 5.1 Flowchart describing the overview scenario deinition process (Step 1 in the
Desalination Intake Decision Tool)
questions� Technical feasibility topics include consideration of environmental, geological, and
logistical issues� If the user does not know the answer to a question, he/she can mark it “Maybe”
and note in the option that more information is needed determine the feasibility for that technologylocation combination�
The questions all default to “Maybe” unless otherwise speciied (“Yes” or “No”) by the
user� Any option where all questions are rated “Yes” or “Maybe” in the top section, and “No” or
“Maybe” in the bottom section, will be retained� If the user rates any question in the top section a
“No,” or any question in the bottom section a “Yes,” that option will be deemed unfeasible and will
be eliminated from further consideration� The user may also add additional documentation related
to the questions in the “Note” sections as desired�
This logic and the associated parameters are further described in Figure 5�2 and Table 5�2�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 5: Using the Desalination Intake Decision Tool | 97
Table 5.1
Deinitions of overview scenario description parameters
Parameter
Required intake
capacity
Region
Description
• The design volume of seawater needed for the desalination system, in units of mgd�
• The state in which the intake project will be located; California, Florida, Texas
and “Other” are the options provided� The region selection will determine the
associated permitting section (additional, state-speciic permitting information is
provided for “California,” “Florida,” and “Texas”)�
California
• Denotes the State of California�
Florida
• Denotes the State of Florida�
Texas
• Denotes the State of Texas�
Other
• Denotes a location other than California, Florida, or Texas�
Site location
• The type of geology and geography where the intake may be located�
Beach
• The intake facility may be located on a sandy beach�
Bay
• The intake facility may be located on a bay (as opposed to the open ocean)�
Estuary
• The intake facility may be located on an estuary (as opposed to the open ocean)�
Cliffs
• The intake facility may be located on a cliff�
Rocky coastline • The intake facility may be located on a rocky beach�
Co-location
• The intake facility may be co-located with an existing facility (i�e�, use an existing
intake)�
Local economic
• Describe the local economic climate in which the intake structure will be
developed� This section prompts the user to consider what economic issues might
climate
inluence the development of the seawater intake� Answering these questions is
not essential to use the Tool, but are important parts of the planning process�
Capital
• Identify whether or not (or at what level) capital will be available to fund the
intake project, indicate if you need to look for new sources of capital�
availability
Tax base
• Is there a suficient tax base to support the project? Or what size project can the
tax base reasonably support?
Need for bond • Will a bond need to be issued?
issue
Public interest • Is there public support, and suficient demand, to justify seawater desalination?
in growth
Economic
• Are there any potential or on-going economic concerns that might impact project
concerns
funding?
STEP 3: IDENTIFY PERMITTING NEEDS AND ASSESS PERMITTING FEASIBILITY
Once the technically feasible potential intake options have been identiied in the Site
Location tabs, the user is ready for Step 3, assessing whether or not required permits can be
obtained in the “Permitting” tab of the Tool� All of the feasible Site Location-Technology combinations are listed in a menu on the left-hand side of the page� The user can click on each option in
turn� This activates the permitability assessment page, which will appear to the right� The permits
needed correspond to those major permits identiied for the region selected (California, Florida,
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
98 | Assessing Seawater Intake Systems for Desalination Plants
Figure 5.2 Flowchart of describing the feasibility assessment process (Step 2 in the
Desalination Intake Decision Tool)
Texas, and Other)� The “Other” option only shows standard federal permitting requirements; statespeciic or out of U�S� permitting requirements will have to be identiied on a case-by-case basis�
As in Step 2, the user can then work through the list of permits for each option and answer
whether or not a type of permit is needed for the application and whether or not the permit is attainable� If the user does not know the answer to the question he/she can mark it “Maybe” and note in
the option that more information is needed on this particular permit�
As in Step 2, the questions all default to “Maybe” unless otherwise speciied (“Yes” or
“No”) by the user� Any option where all needed permits are rated “Yes” or “Maybe” will be
retained� If the user rates any needed permit a “No” (not attainable) that option will be deemed
unfeasible and will be eliminated from further consideration� The user may also add additional
documentation related to the questions in the “Notes” sections as desired�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 5: Using the Desalination Intake Decision Tool | 99
Table 5.2
Deinitions of implementation feasibility scenario description parameters
Parameter
Intake tab
Description
• A tab for each site location type selected on the “overview” page is offered for
assessing the technical feasibility of various intake options for that location� The
user can then scroll through each sub-tab and answer the questions for each option�
Beach
• This site location includes consideration of the on-shore open intake, off-shore
open intake, vertical wells, horizontal wells, slant wells, HDD wells, iniltration
gallery, and co-location technology options�
Bay
• This site location includes consideration of the on-shore open intake, off-shore
open intake, horizontal wells, slant wells, HDD wells, and iniltration gallery
technology options�
Estuary
• This site location includes consideration of the on-shore open intake, off-shore
open intake, horizontal wells, slant wells, HDD wells, and iniltration gallery
technology options�
Cliffs
• This site location includes consideration of the on-shore open intake, off-shore
open intake, horizontal wells, slant wells, HDD wells, and iniltration gallery
technology options�
Rocky coastline • This site location includes consideration of the on-shore open intake, off-shore
open intake, horizontal wells, slant wells, HDD wells, and iniltration gallery
technology options�
Co-location
• This site location includes consideration of the co-location technology option�
Intake sub-tab
• Each technology option is offered for the site location type of interest� The user can
scroll through each sub-tab and answer the feasibility questions for each option�
options
Vertical wells
• This option is offered for the beach site location option�
On-shore open
• This option is offered for the beach, bay, estuary, cliffs, and rocky coastline site
location options�
intake
Off-shore open
• This option is offered for the beach, bay, estuary, cliffs, and rocky coastline site
location options�
intake
Iniltration gallery • This option is offered for the beach, bay, estuary, cliffs, and rocky coastline site
location options�
HDD wells
• This option is offered for the beach, bay, estuary, cliffs, and rocky coastline site
location options�
Slant wells
• This option is offered for the beach, bay, estuary, cliffs, and rocky coastline site
location options�
Horizontal wells • This option is offered for the beach, bay, estuary, cliffs, and rocky coastline site
location options�
Option considered • Reports the feasibility of the option based on the assessment provided by the
user� “Yes,” or “maybe” in the top section, and “no” or “maybe” in the bottom
feasible
section, indicate the option should be further considered� “No” in the top section
or “yes” in the bottom section eliminates the option from further consideration�
Questions within
• The user is offered a series of questions on a range of issues that often preclude
the consideration of an intake option (e�g, environmental concerns)� The user
each sub-tab
may answer “yes,” “no,” or “maybe�” If no answer is selected the tool defaults
to “maybe�” If “no” is selected for any question in the top section, or “yes” is
selected for any question in the bottom section, the option is labeled “unfeasible”
and precluded from further consideration�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
100 | Assessing Seawater Intake Systems for Desalination Plants
Figure 5.3 Flowchart describing the permitability assessment process (Step 3 in the
Desalination Intake Decision Tool)
This logic and the associated parameters are further described in Figure 5�3 and Table 5�3�
STEP 4: ESTIMATE PLANNING-LEVEL COSTS FOR EACH TECHNOLOGY
In seawater intake development, three primary cost centers are typically incurred sequentially: required studies, permitting, and construction (which includes design engineering work)�
For each intake option remaining from Step 3, the user can now estimate the required studies, permitting, and construction costs for the viable options� This corresponds to the tab “Cost” in the
Tool� As with the “Permitting” tab, each feasible technology will have its own sub-tab (accessible
from the click box on the left)�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 5: Using the Desalination Intake Decision Tool | 101
Table 5.3
Deinitions of permitting assessment parameters
Parameter
Site location:
technology box
(on left)
Permitting for
region: x
Option
considered
feasible
Permit list
for each site
location:
technology
option
Description
• All feasible (from Step 2 evaluation) site location-technology combination (e�g�,
beach:horizontal wells) are listed� The user can click on each option to pull up the
related permitting assessment in the box on the right�
• Indicates the state the user selected on the “overview” page� The permits listed
below this box are determined by the region selected by the user�
• Reports the feasibility of the option based on the assessment provided by the
user� “Yes,” or “maybe” indicates the option should be further considered� “No”
eliminates the option from further consideration�
• The user is offered a list of permits to rate: (1) if required (if so, check the box
under the “req” column; and (2) if attainable (if so, mark the circle under “yes”
column, if not mark the circle under “no” column, if uncertain mark the circle
under “maybe” column)� If no answer is selected the tool defaults to “maybe” and
permitability of the option is rated “maybe�” If “no” is selected for any permit type
the option is labeled “unfeasible” and precluded from further consideration�
The user is prompted to enter site-speciic information on each of the three primary cost
centers (required studies, permitting, and construction) and cost-estimation factors (e�g�,
“Contingency” percent mark-up)� The user may enter as much, or as little, information as he/she
desires� Blue boxes indicate automatic calculations� Background on the cost assumptions can be
reviewed by clicking on the “Cost Info” box in the “Cost” tab�
This logic and the associated cost calculations are further described in Figure 5�4 and
Table 5�4�
General Guidelines for Estimating Intake Development Costs
This cost-estimating step was added to prompt the user to develop comparative, order-ofmagnitude costs for implementing any of the intake designs they are considering for the scenario
of interest� Since intake costing is highly site-speciic and there are few full-scale desalination
installations in the U�S�, little is known about the costs for constructing these intake systems within
the U�S�, especially where sensitive environmental areas along the coast are concerned� Provision
of detailed guidance on intake cost-estimation is outside the scope of this report.
However, as a general rule, open intakes have signiicantly higher capital costs than well
systems� For example, Wright and Missimer estimated a capital cost ratio (open intakes versus
well systems) of approximately 1�8 to 2�0 for small (≤2�0 mgd, or ≤7,600 m3/d) installations
(Wright and Missimer 1997)� O&M costs can vary signiicantly depending upon site-speciic conditions (e�g�, well depth)� Examples of recent real-world costs for implementing seawater intakes
for desalination in the U�S� are summarized in Chapter 6�
STEP 5: EVALUATE PERTINENT STAKEHOLDER ISSUES
The inal feasibility assessment is Step 5, the evaluation of stakeholder issues in the
“Stakeholders” tab (in the DesalIntakeTool�mdb on the attached CD-ROM)� In this step, the user
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102 | Assessing Seawater Intake Systems for Desalination Plants
Figure 5.4 Flowchart of cost estimation process (Step 4 in the Desalination Intake Decision
Tool)
can input the pertinent stakeholder groups (e�g�, interested environmental groups, sporting groups,
business interests, regulators) that could be inluential in the decision-making process� These entities can be either supportive or unsupportive of the project� The critical criteria for inclusion here
is whether or not they would likely be involved signiicantly in the planning process� Although this
step is not required, the user is encouraged to start considering potential stakeholders and stakeholder values at this early stage of the planning and implementation process as these groups can
often be very inluential in whether or not a project comes to fruition�
As with the “Permitting” page, all of the feasible Site Location-Technology combinations
are listed in a menu on the left-hand side of the page� The user can click on each option in turn�
This activates the stakeholder assessment page, which will appear to the right� The user can enter
and describe as many different stakeholder groups (and categories of groups) as he or she desires�
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Chapter 5: Using the Desalination Intake Decision Tool | 103
Table 5.4
Deinitions of cost estimation parameters and calculations
Parameter
Required studies
Description
• The major environmental and geological studies considered necessary for the
application� The user can list the studies he/she has identiied as needed and the
estimated cost associated with each� The blue box at the bottom of this section
sums the cost of all the studies listed in this section�
Permitting costs
• The major permits required for the application� The user can list the permits he/
she has identiied as needed and the estimated cost associated with each� The
blue box at the bottom of this section sums the cost of all the permits listed in
this section�
Construction costs
• The major costs associated with the construction phase of the project, including
the following: direct construction cost, contingency, contractor overhead,
escalation-to-midpoint, sales tax, bid market allowance, engineering and legal,
and change orders�
Direct construction
• The major construction elements required for the application� The user can list
the construction items he/she has identiied as needed and the estimated cost
costs
associated with each�
Contingency
• A multiplier on the direct construction cost� This factor is added on to account
for unlisted items and site speciic conditions that are not evident during the
planning phase�
Contractor overhead • A multiplier on the direct construction cost plus the contingency cost� This
factor accounts for the contractor fees�
Escalation to
• A multiplier on the direct construction cost plus the contingency cost plus the
contractor overhead� This factor accounts for cost inlation over the course of
mid-point
the project� This factor is used when projects are of multi-year duration�
Sales tax rate
• A multiplier (the local applicable sales tax) on the sum of the following: direct
construction cost, contingency, contractor overhead, and escalation-to-midpoint�
Applicable in states where such a tax is in effect�
Bid market allowance • A multiplier on the sum of the following: direct construction cost, contingency,
contractor overhead, escalation-to-midpoint, and sales tax� This factor accounts
for anticipated higher costs if few bidders are expected�
Total estimated
• The total estimated cost for the construction phase of the project� This is
the sum of the following: direct construction cost, contingency, contractor
construction cost
overhead, escalation-to-midpoint, sales tax, bid market allowance, engineering
and legal, and change orders�
Engineering + legal • A multiplier on the sum of the following: direct construction cost, contingency,
contractor overhead, escalation-to-midpoint, sales tax, and bid market
allowance� This factor accounts for the engineering and legal fees�
Change orders
• A multiplier on the sum of the following: direct construction cost, contingency,
contractor overhead, escalation-to-midpoint, sales tax, and bid market
allowance� This factor accounts for change orders that might be needed in the
middle of construction�
Total estimated
• The total estimated cost of the project� This is a sum of: preliminary study
costs, permitting costs, and total construction costs�
project costs
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104 | Assessing Seawater Intake Systems for Desalination Plants
Figure 5.5 Flowchart of the stakeholder assessment process (Step 5 in the Desalination
Intake Decision Tool)
The Stakeholder is characterized both by type (selected from the “Category” drop down box),
stakeholder title, and “value” (i�e�, what they rate as important that inluences the intake development process, such as beach access or aesthetic concerns)� Also as in Steps 2 and 3, the user can
then rate whether or not the stakeholder value can be accommodated� If the user does not know the
answer to the question he/she can mark it “Maybe” and note in the option that more information is
needed on this particular stakeholder issue�
Again, this question defaults to “Maybe” unless otherwise speciied (“Yes” or “No”) by the
user� Any option where all identiied stakeholder values are is rated “Yes” or “Maybe” will be
retained� If the user rates any stakeholder value accommodation as “No” (not attainable) that option
will be deemed unfeasible and will be eliminated from further consideration� The user may also
add additional documentation related to the questions in the “Notes” sections as desired�
This logic and the associated parameters are further described in Figure 5�5 and Table 5�5�
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Chapter 5: Using the Desalination Intake Decision Tool | 105
Table 5.5
Deinitions of stakeholder assessment parameters
Parameter
Description
• All feasible (from Step 4 evaluation) site location-technology combination (e�g�,
Site location:
Beach:horizontal wells) are listed� The user can click on each option to pull up the
technology box
(on left)
related permitting assessment in the box on the right�
Option considered • Reports the feasibility of the option based on the assessment of stakeholder
accommodation provided by the user� “Yes,” or “maybe” indicates the
feasible
option should be further considered� “No” eliminates the option from further
consideration�
Category
• A class of stakeholder concerns� The options presented include “aesthetics,”
“public use/access,” “expandability,” “cost,” “reliability,” “sustainability,”
“maintenance,” “ancillary beneits,” “migration beneits,” “schedule,” and “other�”
Stakeholder
• The name of the stakeholder group in question—may be described with a speciic
group name or as a general category (e�g�, “Beach goers,” or “rate payers”)�
STEP 6: GRADE AND RANK THE VIABLE OPTIONS
Once the options for each site location in the deined scenario (Step 1) have been assessed
(Steps 2 through 5), the user is ready to evaluate the relative attractiveness of each viable alternative� A standard method is to deine a set of grading criteria and then rate how well each option
under consideration (e�g�, Beach—Iniltration Gallery) meets each criterion characteristic (e�g�,
practicality)� The composite score for each option produces a ranking that indicates how the options
compare for the speciied project values�
Grade the Options
The “Grading Criteria” tab allows the user to deine a rating scale for comparing the relative attractiveness of the feasible intake options for the associated intake scenario� Eight common
evaluation criteria have been included that consider cost, practicality, technical attractiveness and
stakeholder acceptability� The Tool also offers the option of adding up to ive others of the user’s
choosing�
The user should choose evaluation criteria important to the scenario under consideration�
Any pre-programmed criterion the user does not want considered should be given a “Weight”
value of zero (0)� Then the criteria of interest should be ranked for relative importance on a scale
of 1 (not important) to 5 (highly important)� Multiple locations are provided for the user to add his/
her notes to document assumptions, ideas, questions, etc� as desired� This sets the stage for the user
to walk through the remaining pages to complete the seawater intake scenario�
Users are encouraged to weight the grading criteria prior to evaluating the individual
options� Users should avoid later adjusting the weighting to inluence the outcome of the
evaluation�
If only one intake scenario option has been identiied in the evaluation process, the user
may want to consider grading and ranking that scenario against alternative treatment/
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106 | Assessing Seawater Intake Systems for Desalination Plants
Figure 5.6 Flowchart of the grading process (Part 1 of Step 6 in the Desalination Intake
Decision Tool)
Table 5.6
Deinitions of weighting parameters
Parameter
Consideration
Grade
Description
• Grading criterion�
• Value assigned to the corresponding consideration, on a scale of 1 (not important) to
5 (very important)�
water management plans (e�g�, limiting growth, developing a reclaimed water supply, enhancing
conservation, etc�) if such options are feasible� However, such a comparison would need to be
completed outside of the Tool, as the Tool only allows for ranking of the speciic desalination
intake options deined in the Tool�
This logic and the associated parameters are further described in Figure 5�6 and Table 5�6�
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Chapter 5: Using the Desalination Intake Decision Tool | 107
Figure 5.7 Flowchart of the ranking process (Part 2 of Step 6 in the Desalination Intake
Decision Tool)
Rank the Options
The “Ranking” tab allows the user to grade how well each intake option meets each of the
grading criteria on a scale of 1 (not favorable) to 5 (very favorable)� All of the feasible Site
Location-Technology combinations are listed in a menu on the left-hand side of the page� The user
can click on each option in turn� This activates the feasibility assessment page, which will appear
to the right� For each intake option the user should:
1�
2�
3�
Document the grading date in “Date Graded,”
Click on the intake option under consideration from the “Feasible Option List,” and
Grade each intake option for each evaluation criterion identiied�
The rated score for each option is shown at the bottom� The “perfect score” (if an option
was a “5” for every criterion) is also provided for comparison� If only one intake scenario option
has been identiied in the evaluation process, the user may want to consider ranking that scenario
against alternative treatment/water management plans (e�g�, limiting growth, developing a
reclaimed water supply, enhancing conservation, etc�) if such options are feasible� However, such
a comparison would need to be completed outside of the Tool, as the Tool only allows for ranking
of the speciic desalination intake options deined in the Tool�
This logic and the associated parameters are further described in Figure 5�7 and Table 5�7�
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108 | Assessing Seawater Intake Systems for Desalination Plants
Table 5.7
Deinitions of ranking parameters
Parameter
Site location
technology box
(on left)
Date graded
Consideration
Grading
Technology input
columns
Description
• The Site Location-Technology combinations that were not eliminated through
the feasibility assessment process in steps 2, 3, and 5� The user can click on each
option to pull up the related ranking data on the right�
• Date the assessment was done�
• Grading criterion�
• Values assigned to the corresponding Considerations in the “Grading Criteria”
tab , on a scale of 1 (not important) to 5 (very important)�
• User input of the grades he/she has assigned for each grading criterion on a scale
of 1 (not favorable) to 5 (very favorable)�
FINAL STEP: GENERATE PROJECT REPORTS
Once the user has completed whatever portion of the six assessment steps (s)he desires to
do, the user can go to the “Generating Reports” tab in the Tool and generate a range of report types
by clicking on the corresponding box� If some types of data are not input, some of the summary
reports will not be available (e�g�, if no data are input “Summary Cost” reports cannot be generated)� The report types are further described in Table 5�8�
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Chapter 5: Using the Desalination Intake Decision Tool | 109
Table 5.8
Deinitions of reporting options
Parameter
Summary analysis
reports
Summary
overview
Summary cost
Summary
permitting
Summary
stakeholder
Summary
ranking
Option reports
Vertical well
On-shore open
intake
Off-shore open
intake
Co-location
Iniltration
gallery
Hdd wells
Slant wells
Horizontal wells
Feasibility reports
Overall
evaluation
Permit
evaluation
Stakeholder
evaluation
Description
• Generates a printable summary page of the information input in a speciic tab in
the tool�
• Output from the “overview” tab�
• Output from the “costs” tab�
• Output from the “permitting” tab�
• Output from the “stakeholders” tab�
• Output from the “weighting criteria” and “ranking” tabs�
• Generates a printable summary page of the (Step 2) technical feasibility
assessments done for a speciic intake technology, this includes the assessments
for all site locations where the technology was considered�
• Output from the “vertical well” subtabs�
• Output from the “on-shore open intake” subtabs�
• Output from the “off-shore open intake” subtabs�
• Output from the “co-location” subtabs�
• Output from the “iniltration gallery” subtabs�
•
•
•
•
Output from the “hdd wells” subtabs�
Output from the “slant wells” subtabs�
Output from the “horizontal wells” subtabs�
Generates a printable summary page of the feasibility assessments done for the
various site location-technology combinations evaluated�
• Output of the overall feasibility assessment for the site location-technology
combinations evaluated, including consideration of technical assessment
feasibility, permitting, and stakeholder assessments� The results are grouped by
site location type�
• Output of the permitting assessment (whether or not the options were rated
feasible) of the site location-technology combinations evaluated� The results are
grouped by site location type�
• Output of the stakeholder accommodation assessment (whether or not the options
were rated feasible) of the site location-technology combinations evaluated� The
results are grouped by site location type�
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©2011 Water Research Foundation. ALL RIGHTS RESERVED.
CHAPTER 6
CASE STUDIES
CASE STUDY 1: CARLSBAD DESALINATION PLANT
Note: This case study illustrates the use of the Desalination Intake Decision Tool
(DesalIntakeTool�mdb on the attached CD-ROM) for a case where there is a high degree of known
conditions and a inal intake design selection has been made�
The Carlsbad Desalination Public Agency Partners (Partners) are a consortium of nine
agencies located in San Diego County, consisting of: the City of Carlsbad Municipal Water District
(CMWD), Valley Center Municipal Water District, Rincon del Diablo Municipal Water District,
Sweetwater Authority, Rainbow Municipal Water District, Vallecitos Water District, Santa Fe
Irrigation District, Olivenhain Municipal Water District, and the City of Oceanside� With an average rainfall of ten inches per year, San Diego County has essentially a desert environment� In the
early days of its history, the region relied on locally available groundwater to satisfy its water
needs� This changed in the mid 1900’s when a booming population and increasing agricultural use
put great pressure on the groundwater basins� This led increasingly to a shift to (then) more reliable
imported water� Today, over 90 percent of water used in the region is brought in from Northern
California and the Colorado River� Water is imported by Metropolitan Water District (MWD),
which sells this water under negotiated agreements to 26 cities and wholesalers� Included among
the MWD wholesalers is the San Diego County Water Authority (SDCWA); as a water purveyor
intermediary it completes the transaction by selling water to its own 24 member agencies� Many
of the Partners are among these end-of-the-pipeline agencies provided water by SDCWA�
While most of the region’s member agencies rely to varying degree on this imported water,
the positions of some purveyors, such as CMWD, are even more precarious due to an exclusive
dependence on imported water� Today this supply is threatened� Recurring drought, environmental
problems, and legally enforced regulations have placed restrictions on the pumping of water from
the Colorado River and the Northern California San-Joaquin Delta� In response to the anticipated
long-term shortfall, MWD has sought to manage water use by imposing water allocations for the
irst time in its 81-year history� Member agencies have in turn implemented mandatory conservation measures on their customers� Recognizing the unsustainability of the region’s reliance on
imported water, the Partners have initiated plans to develop their own local water supply by tapping an unlimited local source—the Paciic Ocean�
In a landmark public-private partnership deal, the Partners negotiated water-purchasing
contracts with Poseidon Resources—a private enterprise that develops and inances water infrastructure projects� Under the terms of these contracts, Poseidon would assume the developmental
and inancial risks associated with constructing and operating a seawater desalination plant and the
Partners would be guaranteed a reliable drought-proof water supply�
The proposed plant will be co-located with the Encina Power Plant in Carlsbad� The Encina
plant has an 857-mgd (3�2 million m3/d) open intake that provides seawater to the plant’s oncethrough cooling system� The heated water is then returned to the ocean� The Carlsbad Desalination
Plant will use 104 mgd (394,000 m3/d) of this water when the power plant is in operation and
304 mgd (1�2 million m3/d) of the power plant cooling water, if the plant discontinues oncethrough cooling in the future� Approximately 100 mgd (379,000 m3/d) will be used as inluent to
111
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112 | Assessing Seawater Intake Systems for Desalination Plants
the RO membranes which, operating at ~50% recovery, will generate 50 mgd (189,000 m3/d) of
concentrate� This concentrate will be blended with the remaining power plant cooling water (a
minimum of 204 mgd, or 770,000 m3/d) to dilute the concentrate before it is discharged back to the
ocean� The dilution capacity is establish in such manner that the discharge salinity of the blend is
lower than or equal to 40 g/L�
The plant broke ground in November 2009 and upon completion in 2012 will provide
50 mgd (189,000 m3/d) of water to 300,000 households within the region, meeting 10% of the San
Diego region’s water needs�
On the surface, the decision to add desalinated seawater to its water supply portfolio might
seem like an obvious decision by the region� However, this decision has been fraught with numerous challenges and contentious debates that underscore the dificulties involved in achieving widescale adoption of seawater desalination in the U�S� In many ways, the Carlsbad Desalination Plant
presents an ideal case study and a learning opportunity for all utilities seeking to include seawater
desalination in its water supply portfolio� The plant was conceived of 11 years ago and to date has
gone through 14 public hearings covering 120 hours of public testimony and deliberation, two plan
revisions, at least ive lawsuits, and an escalation in costs brought on primarily by mitigation
requirements� At the heart of much of this debate has been the intake system�
The proposed intake will consist of a connection to the existing cooling water discharge
canal of the Encina Power Plant� As a result, the RO plant intake facility is pre-screened by the
power plant intake facilities� This intake consists of 3-inch bar screen racks followed by 3⁄8-inch
ine screens� Unlike typical co-located desalination plants, where the permitted power plant intake
eliminates the need for a desalination intake permit, the Carlsbad Desalination plant was required
to obtain a separate open-intake permit, which will allow the plant to operate whether or not the
power plant is in operation� As a condition of the Environmental Impact Report (EIR; Dudek and
Associates et al� 2005), the Partners were required to investigate the feasibility of alternative intake
systems�
Since the proposed intake is an open intake, the following alternatives investigated were
common subsurface intake systems: vertical (beach) wells, slant wells, HDD wells, horizontal collector wells, and iniltration galleries� The results of Carlsbad Desalination Plant’s intake alternatives evaluation were input into the Desalination Intake Tool and are presented in the following
pages� Highlights include:
•
•
Non-viability of all beach well options due primarily to: coastal impacts from the
number of wells required being unacceptable, lack of precedence of using wells for
intake for plants of similar capacity (vertical wells), and unfavorable geology�
Non-viability of iniltration galleries due to: the large area required, impacts to protected kelp beds and other environmental impacts during construction and maintenance, uncertainty of long-term performance at this scale, and (while not stated in the
Desalination Intake Tool output) the undesirable aesthetic impacts that would occur
during construction and routine maintenance of the off-shore galleries�
Given the landmark nature of this project—the plant will be the largest desalination plant
in the U�S�—it has attracted the interest of numerous interest groups whose role in the planning/
permitting phase led to a number of the implemented mitigation measures� These groups are
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Chapter 6: Case Studies | 113
Figure 6.1 Overview of the intake scenario for Carlsbad
categorized and their respective values outlined in the Stakeholder Report in the Tool (also
presented)�
In addition to an investigation of alternative intake systems, the project also included a
comprehensive cost analysis of an on-shore open intake and the proposed co-located facility� The
results are captured in the Tool and included below�
It is worth mentioning again, that the Desalination Intake Tool did not solicit the permitting, stakeholder or costs for the options that were determined “Not Feasible” during the initial
screening� For those interested in cost estimates for the alternate intakes not presented by the
Desalination Intake Tool, we have included the cost estimates from the Carlsbad Desalination
Project EIR (Dudek and Associates et al� 2005) as Appendix B to this report�
Outputs from the Tool for the Carlsbad case study are in the following igures� Outputs
include the following: the scenario overview (Figure 6�1), screening evaluation of available intake
types for beach and Co-location siting options (Figures 6�2 through 6�9), permitting evaluation
(Figures 6�10 and 6�11), cost summary (Figures 6�12 and 6�13), stakeholder evaluation (Figures 6�14
and 6�15), and ranking of alternatives (Figure 6�16)�
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114 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.2 Screening evaluation of vertical wells for Carlsbad
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Chapter 6: Case Studies | 115
Figure 6.3 Screening evaluation of an on-shore open intake for Carlsbad
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116 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.4 Screening evaluation of an off-shore open intake for Carlsbad
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Chapter 6: Case Studies | 117
Figure 6.5 Screening evaluation of an iniltration gallery for Carlsbad
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118 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.6 Screening evaluation of a co-located intake for Carlsbad
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Chapter 6: Case Studies | 119
Figure 6.7 Screening evaluation of HDD wells for Carlsbad
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120 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.8 Screening evaluation of slant wells for Carlsbad
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Chapter 6: Case Studies | 121
Figure 6.9 Screening evaluation of horizontal wells for Carlsbad
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122 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.10 Permitting evaluation for an on-shore open intake for Carlsbad
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Chapter 6: Case Studies | 123
Figure 6.11 Permitting evaluation for a co-located intake for Carlsbad
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124 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.12 Cost evaluation for an on-shore open intake for Carlsbad
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Chapter 6: Case Studies | 125
Figure 6.13 Cost evaluation for a co-located intake for Carlsbad
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126 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.14 Stakeholder evaluation for an on-shore open intake for Carlsbad
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Chapter 6: Case Studies | 127
Figure 6.15 Stakeholder evaluation for a co-located intake for Carlsbad
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128 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.16 Ranking of alternatives for Carlsbad
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Chapter 6: Case Studies | 129
Figure 6.16 Ranking of alternatives for Carlsbad (continued)
CASE STUDY 2: CITY OF SANTA CRUZ/SOQUEL CREEK WATER DISTRICT
Note: This case study illustrates use of the Desalination Intake Decision Tool for a case
where there are a lot of unknowns and additional studies remaining to be completed before a inal
intake design selection is made�
The City of Santa Cruz (City) is located along the northern California coastline, about
80 miles south of San Francisco� The City relies solely on rainfall and meets its potable water
needs via surface and groundwater resources� Historically, the City has faced periods of drought�
Fearing a recurrence of the region’s 1976–’77 drought (the worst on record), the City embarked on
a multi-year process of background studies, which resulted in the formation and adoption of an
Integrated Water Plan (2005)� The plan includes a combination of programs including conservation, curtailment and seawater desalination as the preferred strategy that will help the City address
its drought-related water supply challenges� Soquel Creek Water District (District) is a neighboring
water agency just south of the City’s water service area� Similar to the City, the District also does
not receive any imported water and, contrary to its name, does not receive any surface water� Its
sole source of supply is groundwater that is extracted from two aquifers� The operation of these
aquifers by all public and private users is unsustainable; they are in overdraft and the potential for
seawater intrusion is high�
The proposed SWRO desalination project would be located within the city and have a
design capacity of 2�5 mgd (9,500 m3/d) to meet drought needs for the City� In non-drought
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130 | Assessing Seawater Intake Systems for Desalination Plants
conditions, the facility may provide water to the District at a lower capacity (approx� 1-1�5 mgd)�
The City’s IWP identiied potential expansion to 4�5 mgd (17,000 m3/d)� Additional capacity would
require additional environmental review that is outside the scope of the current project�
For the purposes of evaluating costs, a 2�5 mgd (9,500 m3/d) project would require a
6�3 mgd (24,000 m3/d) intake system; and 4�5 mgd (17,000 m3/d) project would require 11�3 mgd
(43,000 m3/d) intake� As proposed, RO concentrate from the plant would be blended with efluent
from the Santa Cruz Wastewater Treatment Plant, bringing the combined efluent nearer to ocean
salinity�
In preparation for the proposed SWRO desalination plant, a one-year pilot plant was operated� Testing ended in April 2009� A consultant has recently been hired to evaluate environmental
impacts of an SWRO facility� In the interim, a preliminary overview of intake systems was completed and the indings are provided below� Notable observations included:
•
•
•
•
Although subsurface intakes may be favored by the regulatory agencies, a 2001 report
concluded that the local nearshore geology may not support such intakes�
If beach wells are to be planned, the only one that may be viable is the slant well� The
other types of beach wells are being eliminated from consideration because of poor
soil conductivity and maintenance concerns�
An alluvial channel located off-shore may support subsurface slant wells or an iniltration gallery� Slant wells may be more favorable because of the ability to locate them
further from the shore� However, neither of these options may be acceptable since
sediments from the nearby San Lorenzo River are likely to cause plugging� However,
these options are currently being evaluated�
A likely intake approach, and the one evaluated in the EIR for the IWP, is to convert
an abandoned outfall into a screened open intake� The intake would use cylindrical
wedgewire screens to minimize impingement and entrainment�
Preliminary cost estimates are presented for three intake types: iniltration galleries, offshore open intake (HDPE sliplining of an existing pipeline) and slant wells� These estimates, along
with this study’s preliminary indings, are presented in the Desalination Intake Decision Tool’s
output in the included DesalIntakeTool�mdb software�
Outputs from the Tool for the Santa Cruz case study are in the following igures� Outputs
include the following: the scenario overview (Figure 6�17), screening evaluation of available
intake types for beach siting options (Figures 6�18 through 6�24), permitting evaluation (Figures 6�25
through 6�27), cost summary (Figures 6�28 and 6�30), stakeholder evaluation (Figures 6�31 and
6�33), and ranking of alternatives (Figure 6�34)�
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Chapter 6: Case Studies | 131
Figure 6.17 Overview of the intake scenario for Santa Cruz
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132 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.18 Screening evaluation of vertical wells for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 6: Case Studies | 133
Figure 6.19 Screening evaluation of an on-shore open intake for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
134 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.20 Screening evaluation of an off-shore open intake for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 6: Case Studies | 135
Figure 6.21 Screening evaluation of an iniltration gallery for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
136 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.22 Screening evaluation of HDD wells for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 6: Case Studies | 137
Figure 6.23 Screening evaluation of slant wells for Santa Cruz
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138 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.24 Screening evaluation of horizontal wells for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 6: Case Studies | 139
Figure 6.25 Permitting evaluation of an iniltration gallery for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
140 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.26 Permitting evaluation of an off-shore open intake for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 6: Case Studies | 141
Figure 6.27 Permitting evaluation of slant wells for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
142 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.28 Cost evaluation of an iniltration gallery for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 6: Case Studies | 143
Figure 6.29 Cost evaluation of an off-shore open intake for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
144 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.30 Cost evaluation of slant wells for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 6: Case Studies | 145
Figure 6.31 Stakeholder evaluation of an iniltration gallery for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
146 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.31 Stakeholder evaluation of an iniltration gallery for Santa Cruz (continued)
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 6: Case Studies | 147
Figure 6.32 Stakeholder evaluation of an off-shore open intake for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
148 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.32 Stakeholder evaluation of an off-shore open intake for Santa Cruz (continued)
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Chapter 6: Case Studies | 149
Figure 6.33 Stakeholder evaluation of slant wells for Santa Cruz
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150 | Assessing Seawater Intake Systems for Desalination Plants
Figure 6.34 Ranking of alternatives for Santa Cruz
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
APPENDIX A
SEAWATER INTAKE SYSTEMS FOR DESALINATION PLANTS UTILITY
QUESTIONNAIRE SUPPLEMENTAL DATA
Table A.1
Purpose of desalination plant
Plant number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Totals
Average
low rate
(mgd)
0�6
Droughtproof
supply
Meet
increased
demand
Meet reduced
supply shortfall
Other
Blend with well water
to improve water
quality
x
1�06
17�2
31�7
104
17�2
17�2
31�7
104
6�9
9�5
10
5
0�3
88
4�5
3�5
8�7
25
7�6
63�4
30
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Supply diversiication
x
x
x
x
x
x
x
x
x
x
x
x
10
12
x
x
8
151
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Supply reliability
3
Intake type
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Plant
No�
Isolated
1
x
2
x
3
x
4
x
5
x
6
Surface intakes
Co-located
Co-located (converted
existing)
(shared)
Open ocean Shoreline
x
8
x
9
x
10
x
12
x
Iniltration
gallery
Horizontal*
DD†
Beach
Plant
Vertical
x
x
x
x
x
x
x
x
x
x
x
x
x
x
11
Other
x
x
7
Combined
Subsurface intakes
x
x
x
13*
14
x
15
x
16
x
x
x
x
17
x
18
x
19
x
20
x
x
x
x
x
x
x
x
x
x
x
x
x
x
21
x
22
x
x
23
x
x
24
x
Totals
9
x
x
x
x
3
*Horizontal Ranney well
†Horizontal directionally drilled wells
1
10
2
0
3
2
3
4
6
3
6
152 | Assessing Seawater Intake Systems for Desalination Plants
Table A.2
Intake types and technologies
Appendix A: Seawater Intake Systems for Desalination Plants Utility Questionnaire Supplemental Data | 153
Table A.3
Preferred screening technologies
Plant
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Totals
A
B
C
x
x
x
x
x
x
x
x
x
x
D
x
x
E
F
G
H
I
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
4
x
x
x
x
x
x
x
x
x
x
1
1
x
x
4
1
x
Non-reporting
6
2
9
A: Vertical travelling screen
B: Fish return system
C: Adjustable vertical barrier
D: Narrow slot/wedgewire screen
E: Fine mesh modiied traveling screen
F: VFD pump seasonal/diurnal low management
G: Velocity cap
H: Angled screens
I: Barrier net
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
1
154 | Assessing Seawater Intake Systems for Desalination Plants
Table A.4
Type and location of screens
Plant
number
Type of screen
Location
1
Primary
Secondary
Located near bottom of well
Two of the 6 intake wells have secondary screens at
59 ft depth
2
Primary
Secondary
At intake windows
Around pump impellers
3
Primary
Secondary
Two inch coarse screens
Three 3⁄8" mechanical ine screens
4
Primary
Secondary
Location not provided
Location not provided
5
Primary
Underwater screens in intake bay
6
Primary
Secondary
Vertically drilled beach well with screens
Cartridge ilter at head of plant
7
Primary
Secondary
At intake, bars spaced at 100 mm
On land in submerged wet well 7 m deep
8
Primary
Secondary
Location not provided
Location not provided
9
Primary
Location not provided
10
Primary
Secondary
At power plant intake
At inluent of water treatment plant
11
Primary
Vertical surface intake structure
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Appendix A: Seawater Intake Systems for Desalination Plants Utility Questionnaire Supplemental Data | 155
Table A.5
Capital, mitigation, O&M costs
Plant
ID
Type of
cost
numbers
1
2
Estimated
3
4
Capital
cost*
Capital unit
cost ($/gal)
$2�7 million
$4�50
$16 million
$0�32
$268 million
$20�29
$0�31
$10�00
$1�56
As built
5
$10�2 million
$0�68
O&M
costs*
O&M cost
($/1000 gal)
Mitigation
cost
$8�66
$125,515
$3�5 million
6
Conceptual
$2�9 million
$5�80
$650,857
$6�02
$75,000
7
As built
$223 million
$5�87
$13,938
$0�37
$11�15 million
8
As built
$145 million
$2�90
9
Conceptual
$195�1 million
$5�91
$136 million
$9�07
10
$3�35
$4�75M
$4�17
*Capital and O&M costs cost igures were supplied in their respective country currencies� Conversions are based on
exchange rates for December 16, 2008: 1$US =88�8 Yen = AU$1�4349 = EU$0�7116�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Features of biological assessment of entrainment and impingement study
Lead
Approval
Study
Estimated
Habitat
Plant number
Study?
time
time
duration
cost
concern*
1
No
Yes*
2
No
†
Yes
12–18 months 3 months
12 months
$800,000
Yes
3
‡
Yes
4
5
Non reporting
§
Yes
6 months
No
6
7
Yes
Yes
8
No
9
Yes
**
10
Yes
24 months
24 months
12 months
$4�2 M
Yes
11
Yes
> 6 months
>12 months
Yes
12
No
No
††
Yes
24 months
6 months
On-going
$500k
Yes
13
(annual)
14‡‡
Yes
12 months
15 months
12 months
Screen design
Env� evaluation
of screen
Impact
Yes
Yes
Yes
No neg� impact
No neg� impact
Yes
No neg� impact
*No species speciied by this respondent�
†There was concern about loss of habitat for gobies and blennies and the scope of analysis looked at bioproductivity in the lagoon�
‡Concern about loss of habitat for Posidonia sea grass; client wanted intake and discharge areas clear of near-surface Posidonia beds�
§Scope of analysis for Plant 9 included water quality, sediment quality, and planktonic organisms�
**Initial concern about loss of habitat proved unfounded, as the diffusers were shown to provide a medium for the attachment and growth of some species�
††Loss of habitat concerns were for sea grasses, manatees, ish, etc� Scope of analysis relates to ongoing hydrological assessment of water quality,
population censuses, sea grass survey, etc�
‡‡Scope of analysis included water quality, existing oceanographic conditions, existing fauna and benthic marine species assessment and existing marine
sediment quality analysis�
156 | Assessing Seawater Intake Systems for Desalination Plants
Table A.6
Environmental impacts and mitigation
Table A.7
Utilities rationales for recommendation or non-recommendation of a stakeholder process
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
1
Yes
Ownership of the permitting process by a non-governmental organization is necessary for the process to be speedy�
2
Yes
It is crucial for public acceptance and client requirement completion to highly involve the stakeholders form an early stage in the project�
3
Yes
It is crucial for public acceptance and client requirement completion to highly involve the stakeholders form an early stage in the project�
4
No
Permitting—$15�4 million/ project
5
Yes
It is crucial for public acceptance and client requirement completion to highly involve the stakeholders form an early stage in the project�
6
Yes
It is crucial for public acceptance and client requirement completion to highly involve the stakeholders form an early stage in the project�
7
Yes
It is necessary for success� The education process is needed to build the required public support and cognition�
8
Yes
It is crucial for public acceptance and client requirement completion to highly involve the stakeholders form an early stage in the project�
9
Yes
It is crucial for public acceptance and client requirement completion to highly involve the stakeholders form an early stage in the project�
10
Yes
Involving stakeholders is the best way to provide science-based information and minimize myths and erroneous fears� For our project,
concern about intake is far lower than concerns about energy, water quality, and brine discharge�
11
Yes
12
Yes
It is robust and the experiences of other facilities show the value�
13
Not sure
It could turn out ine that we involved others in the planning effort and got early input� It may also turn out that we are opening ourselves
up to a great deal of wasted effort trying to bring stakeholders on board who will never get on board�
14
Yes
It is crucial for public acceptance and client requirement completion to highly involve the stakeholders form an early stage in the project�
15
Yes
Recognize/acknowledge public concern; potential opportunity to abate concerns; identify and understand project opponents�
16
Yes
It is crucial for public acceptance and client requirement completion to highly involve the stakeholders form an early stage in the project�
17
Yes
It is crucial for public acceptance and client requirement completion to highly involve the stakeholders form an early stage in the project�
18
Yes
Much better to involve the public in the process to engage them and give them ownership of the outcome�
19
Yes
More open, transparent, more engaged and participatory process leads to successful projects�
Appendix A: Seawater Intake Systems for Desalination Plants Utility Questionnaire Supplemental Data | 157
Would
recommend
Plant process?
Reason provided
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
APPENDIX B
COST ESTIMATES FOR THE CARLSBAD CASE STUDY
As part of their evaluation of desalination, the City of Carlsbad developed cost estimates
for several types of desalination intakes, including vertical beach wells, slant wells, horizontal
wells, an iniltration gallery, and a new open intake� These cost estimates are summarized herein�
Estimated costs are in October 2007 dollars with an associated Engineering News Record 20-Cities
Average Construction Cost Index of 8045�
ESTIMATE 1—VERTICAL BEACH WELLS
Design Criteria
Total capacity
Individual intake well capacity
Number of intake duty wells needed
Number of standby intake wells needed (25% redundancy)
Total number of intake wells needed
Best-case minimum distance between wells
Length of beach needed for all wells
Land area needed to install wells & support facilities
304 MGD
1�5 MGD
203
51
253
150 ft�
7�2 mi�
8�6 acres
Cost Estimates
Direct costs
Installation of a well
Total well installation (253 wells)
Conveyance pipeline @ $500/ft (7�2 mi�)
Intake booster pump station
Well pump electrical power supply
Total construction costs
Indirect costs
Acquire land for wells & support structures
Engineering, design & procurement (25% of direct cost)
Environmental mitigation (15% of direct cost)
Contingency (20% of direct cost)
Total indirect costs
Total estimated project cost
$1,200,000
$304,000,000
$18,925,000
$30,400,000
$50,160,000
$403,485,000
$4,304,408
$100,871,250
$60,522,750
$80,697,000
$246,395,408
$649,880,408
159
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160 | Assessing Seawater Intake Systems for Desalination Plants
ESTIMATE 2—SLANT WELLS
Design Criteria*
Total capacity
Individual intake well capacity
Number of intake duty wells needed
Number of standby intake wells needed (25% redundancy)
Total number of intake wells needed
Best-case minimum distance between wells
Length of beach needed for all wells
Land area needed to install wells & support facilities
304 MGD
5 MGD
61
15
76
300 ft�
4�3 mi�
17�4 acres
Cost Estimates
Direct costs
Installation of a well
Total well installation (76 wells)
Conveyance pipeline @ $500/ft (7�2 mi�)
Intake booster pump station
Well pump electrical power supply
Total construction costs
Indirect costs
Acquire land for wells & support structures
Engineering, design & procurement (25% of direct cost)
Environmental mitigation (15% of direct cost)
Contingency (20% of direct cost)
Total indirect costs
Total estimated project cost
$ 2,400,000
$ 182,400,000
$ 11,250,000
$ 30,400,000
$ 31,920,000
$ 255,970,000
$ 8,723,600
$ 63,992,500
$ 38,395,500
$ 51,194,000
$ 162,305,600
$ 418,275,600
*Design based on Dana Point (California) Desalination Plant�
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Appendix B: Cost Estimates for the Carlsbad Case Study | 161
ESTIMATE 3—HORIZONTAL (RANNEY) WELLS
Design Criteria
Total capacity
Individual intake well capacity
Number of intake duty wells needed
Number of standby intake wells needed (25% redundancy)
Total number of intake wells needed
Best-case minimum distance between wells
Length of beach needed for all wells
Land area needed to install wells & support facilities
304 MGD
5 MGD
61
15
76
400 ft�
5�7 mi�
17�4 acres
Cost Estimates
Direct costs
Installation of a well
Total well installation (76 wells)
Conveyance pipeline @ $500/ft (7�2 mi�)
Intake booster pump station
Well pump electrical power supply
Total construction costs
Indirect costs
Acquire land for wells & support structures
Engineering, design & procurement (25% of direct cost)
Environmental mitigation (15% of direct cost)
Contingency (20% of direct cost)
Total indirect costs
Total estimated project cost
$ 2,500,000
$ 190,000,000
$ 15,000,000
$ 30,400,000
$ 33,060,000
$ 268,460,000
$ 8,723,600
$ 67,115,000
$ 40,269,000
$ 53,692,000
$ 169,799,600
$ 438,259,600
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
162 | Assessing Seawater Intake Systems for Desalination Plants
ESTIMATE 4—INFILTRATION GALLERY
Design Criteria
Total capacity
304 MGD
101�3 MGD
Individual intake gallery capacity
Number of intake duty galleries needed
3
Number of standby intake galleries needed (0% redundancy)
0
Total number of intake galleries needed
3
5,280 × 400 × 15 ft�
Length × width × depth of gallery
Length of intake system
3�0 mi�
Land area needed to install galleries & support facilities
17�9 acres
Cost Estimates
Direct costs
Installation of a gallery
Total gallery installation (3)
Conveyance pipeline cost @ $500/ft (7�2 mi�)
Intake booster pump station
Intake pump electrical power supply
Total construction costs
Indirect costs
Acquire land for galleries & support structures
Engineering, design & procurement (25% of direct cost)
Environmental mitigation (15% of direct cost)
Contingency (20% of direct cost)
Total indirect costs
Total estimated project cost
$120,000,000
$360,000,000
$7,922,606
$12,160,000
$18,608,000
$398,690,606
$8,956,114
$99,672,652
$59,803,591
$79,738,121
$248,170,478
$646,861,084
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
Appendix B: Cost Estimates for the Carlsbad Case Study | 163
ESTIMATE 4—NEW OPEN INTAKE
Design Criteria
Total capacity
Length of intake pipe
Land area needed to install piping & support facilities
304 MGD
1,000 ft�
2�3 acres
Cost Estimates
Direct costs
Installation of piping @ $45,000/ft�
Construction of intake structure
Intake screens
Intake pump station
Intake pump electrical power supply
Total construction costs
Indirect costs
Acquire land for intake & support structures
Engineering, design & procurement (25% of direct cost)
Environmental mitigation (15% of direct cost)
Contingency (20% of direct cost)
Total indirect costs
Total estimated project cost
$45,000,000
$10,500,000
$8,000,000
$24,320,000
$5,223,000
$93,043,000
$1,147,842
$23,260,750
$13,956,450
$18,608,600
$56,973,642
$150,016,642
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
©2011 Water Research Foundation. ALL RIGHTS RESERVED.
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ABBREVIATIONS
ac
AFB
acre
aquatic ilter barrier
BCDC
Bay Conservation and Development Commission
CatEx
CCC
CDFG
CD-ROM
CEQA
cm
CMWD
CSLC
CWA
CZMA
Categorical Exclusion
California Coastal Commission
California Department of Fish and Game
compact disc–read only memory
California’s Environmental Quality Act
centimeter
Carlsbad Municipal Water District
California State Lands Commission
Clean Water Act
Coastal Zone Management Act
DFG
DFW
$/gal
Department of Fish and Game
Department of Fish and Wildlife
dollars per gallon
EA
EIA
EIR
EIS
EPA
EPRI
ESA
Environmental Assessment
Environmental Impact Assessment
Environmental Impact Report
Environmental Impact Statement
Environmental Protection Agency
Electric Power Research Institute
Endangered Species Act
FAC
FDEP
FRP
ft
ft2
ft/s
FWC
Florida Administrative Code
Florida Department of Environmental Protection
iber-reinforced polymer
foot or feet
square feet
feet per second
Florida Fish & Wildlife Conservation Comm�
g/L
gpm
gpm/ft2
grams per liter
gallons per minute
gallons per minute per square foot
HDD
HDPE
horizontal directionally drilled
high-density polyethylene
171
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172 | Assessing Seawater Intake Systems for Desalination Plants
in
inch
km
kilometer
LCP
LORS
Local Coastal Program
local ordinances, regulations, and statutes
m
m2
m3/d
m3/d/m
MEPA
mg/L
mgd
mgd/ft
mi
MIS
MLPP
mm
m/s
MWDOC
meter or meters
square meters
cubic meters per day
cubic meters per day per meter
Massachusetts Environmental Policy Act
milligrams per liter
million gallons per day
million gallons per day per foot
mile
modular incline screens
Mass Landing Power Plant
millimeter
meters per second
Municipal Water District of Orange County
NEPA
NMFS
NOAA
NOM
NPDES
National Environmental Policy Act
National Marine Fisheries Service
National Oceanic and Atmospheric Administration
natural organic matter
National Pollutant Discharge Elimination System
O&M
operation and maintenance
RO
reverse osmosis
SDCWA
SDI
SWRO
San Diego County Water Authority
Silt Density Index
Seawater Reverse Osmosis
TCEQ
TPWD
Texas Commission on Environmental Quality
Texas Parks and Wildlife Department
U�S�
USFWS
United States
United States Fish and Wildlife Service
VFW
variable frequency drive
WIP
water intake protection
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Assessing Seawater Intake Systems for Desalination Plants
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