Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Prepared for Tasman District Council
March 2013
Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
This document has been prepared for the benefit of Tasman District Council. No liability is accepted by
this company or any employee or sub-consultant of this company with respect to its use by any other
person.
This disclaimer shall apply notwithstanding that the report may be made available to other persons for
an application for permission or approval to fulfil a legal requirement.
This document has been prepared for the benefit of Tasman District Council. No liability is accepted by
this company or any employee or sub-consultant of this company with respect to its use by any other
person.
This disclaimer shall apply notwithstanding that the report may be made available to other persons for
an application for permission or approval to fulfil a legal requirement.
QUALITY STATEMENT
PROJECT MANAGER
PROJECT TECHNICAL LEAD
Jeannie Homesley
Paul Jacobson
PREPARED BY
Kirsten Norquay, Paul Jacobson
CHECKED BY
Paul Jacobson, Kirsten Norquay
REVIEWED BY
Rainer Hoffmann
APPROVED FOR ISSUE BY
………………………………...............
Don Young
……/……/……
NELSON
Level 1, 66 Oxford Street, Richmond, Nelson 7020
PO Box 3455, Richmond, Nelson 7050
TEL +64 3 546 8728, FAX +64 3 548 2016
REVISION SCHEDULE
Signature or Typed Name (documentation on file).
Rev
No
Date
1
8/2/2013
2
12/3/13
Description
Prepared by
Checked by
Reviewed by
Approved by
Working Draft issued to
Working Party
KN
PJ
RH
PJ
Final with Working Party
Recommendation and
Executive Summary
PJ
KN
RH
PJ
Status: Final
Project number: 80501061
March 2013
Our ref: R_Motueka Treatment Options Final for RS.docx
Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Executive Summary
Introduction
The Tasman District Council (the Council) owns and operates the Motueka Wastewater Treatment Plant
(Motueka WWTP). From the late 1980s treated wastewater from the Motueka WWTP has been
discharged to land via sand soakage beds and, more recently, via wetlands. Solids carried over the
Motueka WWTP has progressively clogged the soil beneath the soakage beds and wetlands to the point
that there is now little if any soakage occurring. Since 2011 the treated wastewater has been largely
discharged via overflow from the wetland into the south channel of the Motueka River.
Accordingly, the Motueka Wastewater Working Party (Working Party) has been investigating options to
upgrade the WWTP to avoid, remedy and mitigate environmental effects associated with the current
discharge. The Working Party’s draft Project Objectives, including land based disposal provided it is
sustainable, practicable and cost affordable, are in the report.
The design horizon for the Motueka WWTP used in this report is 35 years (ie. ~ 2050), as there is
uncertainty around the longer term use of the low lying WWTP site due to the impact from sea level rise .
The purpose of this report is to present the Representative Options for treatment and discharge at the
Motueka WWTP. The intended audience of this report are primarily members of the Working Party and
Council Engineering Services Committee. It is also intended this report is used as supporting
documentation for public consultation as required.
Representative Options for Motueka WWTP Upgrade
The Working Party has considered six Representative Options for treatment and discharge at Motueka
WWTP. These Representative Options comprise:






Option A: Decentralised Wastewater Schemes, where wastewater from one individual property
or clusters or properties is treated and disposed of near the point of generation.
Option B: Discharge to Land, where wastewater is treated to a sufficient level prior to discharge
to rapid infiltration basins (RIBs). Treated wastewater then percolates down through the soil to the
underlying groundwater.
Option C: Discharge to Surface Water, where wastewater is treated to a sufficient level prior to
discharge to the south channel of the Motueka River, which drains to Tasman Bay.
Option D: Discharge to Groundwater, where wastewater is treated to a sufficient level prior to
injection via a bore into the groundwater. The treated wastewater then ultimately drains to
Tasman Bay and may intersect the south channel of the Motueka River.
Option E: Mix and Match of Options B and C, where wastewater is treated to a sufficient level
and is discharged to land when conditions allow and discharged to water at other times.
Option F: Long Term Option, Off-site (ie. not on the current Motueka WWTP site), where
wastewater is either pumped off-site (with or without treatment) or the reticulation in the catchment
is re-routed and the WWTP is located elsewhere.
A detailed assessment of the six options, including indicative costs for four of these options, and key
project risks is provided in the report.
Status: Final
Project number: 80501061
March 2013
Our ref: R_Motueka Treatment Options Final for RS.docx
Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Key conclusions about each option are as follows:





Option A: Decentralised Wastewater Schemes and Option F: Long Term Option, Off-site are
not feasible in the short to medium term due to both the likely timeframe for implementation and
the cost to the community of establishing an entirely new treatment and disposal system .
Option B: Discharge to Land was the Working Party’s initial preferred objective, however
hydrogeology investigation indicates that land disposal is only feasible during drier periods with
3
average flows of approximately 3,000 m3 per day and not feasible with high inflows of 7,000 m
per day when groundwater levels are high at the disposal site at Motueka.
Option C: Discharge to Surface Water is contrary to iwi and the Working Party’s objective of
land disposal.
Option D: Discharge to Groundwater after tertiary treatment and membrane filtration had
significantly higher capital and operating costs.
Option E: Mix and Match of Options B and C is the preferred option that maximises land
disposal when ground conditions allow but with a discharge to surface waters at other times.
Further consultation with iwi is required to examine this option, including ways to further address
Maori cultural issues, such as additional treatment or land passage for the discharge to surface
waters.
Strategy for Implementing Upgrade
Implementing the preferred option (ie. Option E: Mix and Match) in a staged, adaptive management
based approach based on the Working Party’s priorities and overall objective of land disposal would be
beneficial. Benefits of this approach include.




Ensuring investment is targeted on immediate areas of need (eg. odour mitigation and public
health protection), making it more affordable for the community whilst progressively working
towards land disposal.
Gaining an understanding of the ability of RIBs to accommodate average and sustained peak
wastewater flows in a full-scale prototype prior to commitment to 100% discharge to land.
Providing time for on-going monitoring of the treated wastewater quality and targeted
environmental monitoring, which will provide greater certainty around whether or no t treatment
modules to reduce ammonia or nitrogen are required.
Minimising over-capitalising at Motueka site in the short to medium term by maximising use of the
existing WWTP assets and selecting new portable treatment modules that could be relocated if a
new site is selected in the future.
Status: Final
Project number: 80501061
March 2013
Our ref: R_Motueka Treatment Options Final for RS.docx
Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Working Party Recommendation
After consideration, the Working Party recommends the following actions to the Tasman District Council;
1. That the Council accepts in principle Option E “Mix and Match of Options B and C” treatment and
discharge initially, with staged construction of land disposal.
2. That the Council budgets for staging of the upgrades as outlined in Table 1 below.
Table 1: Staging of Upgrade to Maximise Discharge to Land via RIB
Stage
Scope
Discharge
Indicative
Constructi
1
on Cost
Timing
1
Desludge oxidation pond
Existing discharge
$2.6M
2013-2014
2
Modify oxidation pond, install solids
removal and UV
Existing discharge
$4.1M
2014
3
Install prototype RIB
RIB + Existing discharge
~$0.6M
2015
4
Observe prototype RIB performance
and environmental effects
RIB + Existing discharge
TBC
2015-2016
Decision point
5
Install additional RIBs. Observe RIB
performance and environmental effects
RIB +Existing discharge
$4.3M
(~$0.6M per
RIB)
2017-2018
6
Install storage pond and tidal discharge
RIB + tidal
>$1.3M
2016
3. That the Council considers the necessity for further upgrades to the treatment and discharge of treated
wastewater, once Stages 1 to 4 above have been implemented.
4. That the Council implement a consultation strategy as detailed below:
 Preferred option and strategy recommended by Working Party 19 February 2013 .
 Council Engineering Services Committee issue the Council Summary document for public
feedback 28 March 2013.
 Site inspection by public early May 2013.
 Open/Information day in Memorial Hall (or other) early May 2013 .
 Three weeks for feedback and follow up 1 June 2013.
 Report back to Working Party on feedback 11 June 2013.
 Working Party to recommend preferred option for upgrade to the Council to start formal
consent process.
 Present Working Party’s recommendation to Council Engineering Service Committee
1 August 2013 for approval to proceed with consenting.
1
Costs are indicative, prepared for consenting purposes. These costs have NOT been developed using the Council
budgeting template normally used for estimating budgets in the Annual Plan or LTP, and will need further
evaluation before being included as budgets in these plans. See basis of indicative costs in Se ction 3.5.2.
Status: Final
Project number: 80501061
March 2013
Our ref: R_Motueka Treatment Options Final for RS.docx
Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Tasman District Council
Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
CONTENTS
Executive Summary ................................................................................................................................... i
Introduction ............................................................................................................................................... i
Representative Options for Motueka WWTP Upgrade ............................................................................. i
Strategy for Implementing Upgrade ......................................................................................................... ii
Working Party Recommendation ............................................................................................................ iii
1
Introduction ......................................................................................................................................... 1
1.1
Background .................................................................................................................................... 1
1.2
Working Party Draft Project Objectives ......................................................................................... 1
1.3
Purpose ......................................................................................................................................... 2
1.4
Structure ........................................................................................................................................ 2
2
Existing Situation ................................................................................................................................ 3
2.1
Overview ........................................................................................................................................ 3
2.2
Inlet Works ..................................................................................................................................... 4
2.3
Odour Control ................................................................................................................................ 4
2.4
Aeration Basin ............................................................................................................................... 4
2.5
Oxidation Pond .............................................................................................................................. 4
2.6
Polishing Ponds (former Sand Soakage Beds) and Wetlands ....................................................... 4
2.7
Discharge....................................................................................................................................... 4
3
Representative Options ...................................................................................................................... 5
3.1
Overview ........................................................................................................................................ 5
3.2
Basis of Concept Design ............................................................................................................... 6
3.2.1
Wastewater Influent Flow and Loads ...................................................................................... 6
3.2.2
Indicative Treated Wastewater Levels .................................................................................... 6
3.2.3
Solids Treatment and Disposal Requirements ........................................................................ 7
3.3
Wastewater Treatment Options (for Options B to E) ..................................................................... 7
3.3.1
Overview of Treatment Options .............................................................................................. 7
3.3.2
Oxidation Pond Based Treatment Options (Pond Options) .................................................... 8
3.3.2.1
Pond Option – Treatment Level T2 (Base) ...................................................................... 8
3.3.2.2
Pond Option – Treatment Level T3 (Base with Nitrification) ........................................... 8
3.3.2.3
Pond Option – Treatment Level T4 (Base with Nitrification and Denitrification) .............. 8
3.3.2.4
Pond Option – Treatment Level T5 (T4 with Membrane Filtration) ................................. 8
3.3.3
Activated Sludge Based Treatment Options (AS Options) ...................................................... 9
3.3.3.1
Status: Final
Project No.: 80501061
AS Option – Treatment Level T4 (Base) ......................................................................... 9
March 2013
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Treatment and Discharge Options
3.3.3.2
3.4
AS Option – Treatment Level T5 (T4 with Membrane Filtration) ..................................... 9
Treated Wastewater Discharge Options (for Options B to E) ........................................................ 9
3.4.1
Overview ................................................................................................................................. 9
3.4.2
Rapid Basin Infiltration or Tidal Discharge ............................................................................ 10
3.4.3
RIB Discharge (Representative Options B and E) ................................................................ 10
3.4.4
Tidal Discharge (Representative Options C and E) .............................................................. 11
3.4.5
Bore Injection (Representative Option D) ............................................................................. 11
3.5
Indicative Cost Estimates ............................................................................................................ 11
3.5.1
Overview ............................................................................................................................... 11
3.5.2
Basis of Indicative Cost Estimates ........................................................................................ 11
3.5.2.1
Indicative Capital Costs ................................................................................................. 11
3.5.2.2
Indicative Annual Operating and Maintenance Costs ................................................... 12
3.5.3
3.6
4
Summary of Indicative Capital and Operating Cost Estimates ............................................. 13
Representative Options Summary ............................................................................................... 16
Risk Analysis .................................................................................................................................... 18
4.1
Introduction .................................................................................................................................. 18
4.2
Stopbanks Flooding Climate Change and Sea Level Rise .......................................................... 18
4.3
Receiving Environment ................................................................................................................ 19
4.4
Rapid Infiltration Beds ................................................................................................................. 19
4.5
Wastewater Treatment Plant Risks ............................................................................................. 20
4.6
Observational Method to Manage Risk and Stage the Project .................................................... 21
5
Recommended Strategy for Implementing Upgrades ....................................................................... 24
6
Feedback from Working Party on Preferred Option and Strategy .................................................... 25
7
Working Party Recommendation to Council ..................................................................................... 27
LIST OF TABLES
Table 1: Staging of Upgrade to Maximise Discharge to Land via RIB ...................................................... iii
Table 3-1: Concept Design Influent Flows and Loads .............................................................................. 6
Table 3-2: Treated Wastewater Quality for Different Levels of Treatment at Point of Discharge ............. 7
Table 3-3: Indicative Capital Cost of Representative Options B to E (to 2050) ...................................... 14
Table 3-4: Indicative Annual Operating and Maintenance Cost of Representative Options B to E (to
2052)
.................................................................................................................................................. 15
Table 3-5: Qualitative Assessment of Representative Options for Motueka WWTP ............................... 17
Table 4-1: Assessment of Potential Flood and Inundation Hazard ......................................................... 18
Table 4-2: Range of Height Required Under Combinations of Events .................................................... 19
Table 5-1: Staging of Upgrades to Achieve T2 Treatment and Land Discharge Via RIB ........................ 25
Table 7-1: Staging of Upgrade to Maximise Discharge to Land via RIB ................................................. 27
Status: Final
Project No.: 80501061
March 2013
Our ref: R_Motueka Treatment Options Final for RS.docx
Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
LIST OF FIGURES
Figure 2-1: Motueka WWTP Site Plan ...................................................................................................... 3
Figure 4-1: Motueka WWTP Staging Based on Effects and Initial Mix and Match Option ...................... 23
APPENDICES
Appendix A
Schematics of Treatment and Discharge Options
Appendix B
Layout of Options
Appendix C
Concept Sizing
Appendix D
Risk Assessments
LIST OF ABBREVIATIONS
Council
Tasman District Council
Motueka WWTP
Motueka Wastewater Treatment Plant
Working Party
Motueka Wastewater Working Party
WWTP
Wastewater Treatment Plant
RIB
Rapid Infiltration Basin
UV
Ultra Violet
≤
Less than or equal to
≥
Greater than or equal to
Status: Final
Project No.: 80501061
March 2013
Our ref: R_Motueka Treatment Options Final for RS.docx
Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
1
Introduction
1.1
Background
The Tasman District Council owns and operates the Motueka Wastewater Treatment Plant From the
late 1980s treated wastewater from the Motueka WWTP has been discharged to land via sand soakage
beds and, more recently, via wetlands. Solids carried over the Motueka WWTP has progressively
clogged the soil beneath the soakage beds and wetlands to the p oint that there is now little if any
soakage occurring. Since 2011 the treated wastewater has been largely discharged via overflow from
the wetland into the south channel of the Motueka River.
The current resource consent for the discharge of treated wastewater from the Motueka WWTP expires
on 2 February 2018. Under the current Consent Variation RM081130V1 the Council is required to lodge
a consent application for the proposed upgraded Motueka WWTP by 13 December 2013 and provide a
progress report by 15 July 2013.
This report presents Representative Options to upgrade the Motueka WWTP as identified by the
Motueka Wastewater Working Party (Working Party) and MWH. The Representative Options are high
level treatment and discharge options developed on the basis of the receiving environment and
necessary standards to avoid, remedy and mitigate environmental effects. The Working Party, at their
meeting on 19 February 2013, considered the Representative Options, as outlined in the working draft
version of this Report, and have recommended a preferred option. Key points of discussion and the
Working Party’s recommendations for Council are summarised in Sections 6 and 7, respectively.
The Representative Options comprise:

Option A: Decentralised Wastewater Schemes

Option B: Discharge to Land

Option C: Discharge to Surface Water

Option D: Discharge to Groundwater

Option E: Mix and Match of Options B & C, with discharge to land when conditions allow and
discharge to water at other times.

Option F: Long Term Option, off-site (ie. not on current Motueka WWTP site).
The design horizon for the WWTP for the purpose of this report is 35 years ( ie. ~ 2050), as there is
uncertainty around the longer term use of the low lying WWTP site due to the impact from se a level rise.
It is also the maximum duration of a resource consent under the Resource Management Act.
1.2
Working Party Draft Project Objectives
With regard to the guiding principles of the Resource Management Act 1991 and the Local Government
Act 2002; Council’s Strategic Vision, Long Term Plan, goals and outcomes; identified key project drivers,
and future actions identified in the Status Report from Motueka Wastewater Task Group May 2007 , the
following draft Project Objectives have been identified. These have been generally accepted by the
Working Party at its meeting on 12 June 2012.
Overall Objectives

To work in partnership with the community and tangata whenua to obtain resource consents that
encompass a high level of public health and environmental protection and the best practicable option for
Motueka wastewater management, and are in keeping with sustainable management principles. Council
will continue to improve effluent quality by upgrading its treatment plant, and in particular to reduce
overflow potential to the estuary.

In accordance with the Working Party and Iwi objectives Council will continue to progress to land based
disposal provided that it is sustainable, practicable and cost affordable.

Minimise the environmental footprint.
Tangata Whenua Cultural Objectives

To recognise and provide for the special role and relationships that Maori have as tangata whenua.

To work in partnership with tangata whenua to achieve a good understanding of the Motueka
Wastewater Scheme, so as to enable genuine and effective consultation.

Consult with and develop tangata whenua objectives and options for this project.
Status: Final
Project No.: 80501061
Page 1
March 2013
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Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Environmental Objectives

To protect the natural environment and in particular the water quality of the Motueka River and Motueka
Estuary in the area.

To comply with recreational and ecological standards and guidelines, and National and Regional Plan
requirements.

To promote where practicable the sustainable reuse of treated wastewater and residuals from the
wastewater treatment process and the minimisation of energy use.

To recognise the potential impacts from climate change.

Manage reticulation, treatment and disposal processes to avoid or mitigate odours beyond the boundary
of the site.
Social Objectives

To ensure that the Motueka Wastewater Scheme achieves the greatest practicable protection of public
health, including sea food.

To work in partnership with the community and key stakeholders to achieve a good understanding,
sustainable urban wastewater management to enable genuine and effective consultation.

To ensure that any potential adverse effects associated with the WWTP are contained within the
boundaries of Tasman District Council designated land and consistent with the Tasman District Council
being a good neighbour.
Economic Objectives

To ensure optimum economic use of the existing infrastructure.

To provide an economically sustainable Wastewater Scheme – now and in the future.

To promote outcomes that ensure sufficient flexibility to adopt new appropriate technology and more
sustainable solutions in the future, including treated wastewater reuse, where they provide more
effective solutions.

To apply appropriate technology that will protect public health and meet environmental standards and
tangata whenua and community aspirations while achieving acceptable whole of life costs.
1.3
Purpose
The purpose of this Report is to present the Representative Options for treatment and discharge of
wastewater at the Motueka WWTP. The intended audience of this Report are primarily members of the
Working Party and Council Engineering Services Committee. It is also intended this Report is used as
supporting documentation for members of the public as required.
1.4
Structure
This report is structured into seven sections:

Section 1: Introduction – provides background to this assessment

Section 2: Existing Situation – summarises the main components of the existing Motueka
WWTP and existing discharge mechanisms.

Section 3: Representative Options - summarises the Representative Options developed with the
Working Party for the Motueka WWTP upgrade. Indicative capital and operating costs are provided
for four of these options.

Section 4: Risk Analysis – summarises the key risks associated with the Motueka WWTP and
provides a framework to assist the Working Party in making a decision on the way forward for the
Motueka WWTP upgrades.

Section 5: Recommended Strategy for Implementing Upgrades – outlines how the Motueka
WWTP upgrade could be implemented in a staged approach to be more affordable for the
community while progressively working towards achieving the Working Party’s draft project
objectives.

Section 6: Feedback from Working Party on Preferred Option and Strategy – outlines key
points of discussion and decisions made at Working Party meeting, held on 19 February 2013 to
discuss Representative Options and strategy for implementing the Motueka WWTP upgrades .

Section 7: Working Party Recommendation to Council – provides Working Party’s
recommendations to the Council Engineering Services Committee and wider Council.
Status: Final
Project No.: 80501061
Page 2
March 2013
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Treatment and Discharge Options
2
Existing Situation
2.1
Overview
The Motueka WWTP currently serves the communities from Kaiteriteri and Riwaka through to Motueka.
The WWTP catchment is predominantly domestic in nature. The discharges from potential trade waste
contributors (excluding Talley’s Group Limited which discharges trade waste elsewhere) is assumed to
be small in volume and have a minor impact on the influent loading. Inflow and infiltration is a significant
issue, particularly throughout the older parts of the Motueka township.
The existing Motueka WWTP, shown in Figure 2-1, currently comprises:





inlet works with screening and odour control
an aeration basin
an oxidation pond
polishing ponds (former sand soakage beds)
wetlands.
For the past year the treated wastewater discharge has been predominantly via overflow to the south
channel of the Motueka River. However, with recent warmer weather, the discharge appears to be
predominantly via evapotranspiration and/or soakage through the base of the wetlands.
Motueka River
(main channel)
South Channel of
Motueka River
Treated Wastewater
Overflows
Wetland North
Beach
Drain
Polishing Pond
North
Wetland South
Rapid Infiltration
Basin Trial
Oxidation
Pond
Polishing Pond
South
Weir
Odour Control
Estuary
Aeration
Basin
Figure 2-1: Motueka WWTP Site Plan. (North facing upwards)
Status: Final
Project No.: 80501061
Page 3
March 2013
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Treatment and Discharge Options
2.2
Inlet Works
The wastewater pumped to the WWTP passes through a 3 mm mechanical step screen, from which the
screened non-biodegradable material is collected and disposed at the Eves Valley Landfill. The screen
is sized to accommodate peak flows. After the screen, approximately 2000 m³ of wastewater each day is
directed into the aeration basin. A control valve is used to direct flows greater than 2000 m³ into the
oxidation pond. The inlet structure is equipped with an emergency bypass overflow if the mechanical
screen becomes blocked or stops operating. This bypass includes a manual bar screen and wastewater
discharges directly into the aeration basin.
2.3
Odour Control
A pilot trial biological and carbon filter was installed on the inlet channel to manage peak season odour
in summer 2011. The pilot trial has been successful and Council has ordered a permanent carbon filter
unit to manage odour, to be installed in late summer 2013. This only addresses odours from the inlet
works.
2.4
Aeration Basin
The aeration basin has dimensions of approximately 40m x 60m x 2.5m deep, giving a volume of about
3
6,000m . Aeration of the basin is provided by four floating aerators; two 7.5 kW aspirator aerators and
two 7.5 kW vertical shaft aerators. With this level of aeration, the aeration basin can treat a load in the
order of 300 kg BOD per day.
2.5
Oxidation Pond
Wastewater from the aeration basin flows by gravity into the oxidation pond, which has dimen sions of
220m x 230m, giving a surface area of approximately 5 hectares. The current operating depth is
3
approximately 1.2 m which provides a volume of about 60,000 m . The existing concrete waveband
around the pond extends from approximately 0.9 m to 1.9 m from the base of the pond. The top of the
pond embankment is approximately 2.5 m from the base of the pond. The oxidation pond outlet is a
screened, rectangular weir structure located beneath the jetty in the north-eastern corner of the pond.
Based on a loading rate of 100 kg BOD/ha per day, the oxidation pond can treat a load in the order of
500 kg BOD per day. Higher loading rates can be accommodated during summer months.
3
The oxidation pond currently contains approximately 23,500 m of sludge (as at late 2012). In some
places sludge protrudes from the surface of the pond, which is causing some odour issues.
2.6
Polishing Ponds (former Sand Soakage Beds) and Wetlands
The former soakage beds currently operate as two permanently flooded polishing ponds, the depth
varying between 750mm and 950mm, with an overall area of 3.5 hectares. Wastewater from the
oxidation pond flows into the polishing ponds by gravity. The polishing ponds however provide little or no
observable soakage due to clogging although in summer they allow significant evaporation due to their
large surface area.
As a result of the soils underlying the original sand soakage area clogging, the northern end of the sand
soakage beds began to periodically overflow into the adjacent back beach area. The overflow point was
reinforced by a weir constructed in June 2005. This weir incorporated riprap protection to prevent
erosion of the soakage area embankment and potential catastrophic failure of the bund. The back beach
area has consequently developed into a wetland area and covers approximately 3.5 hectares when full,
with a maximum water depth of around two metres. Water levels in the wetland fluctuate and are
dependent on the season, groundwater level and inflow into the treatment plant.
2.7
Discharge
With typical dry weather flows the main wastewater disposal mechanism is via evaporation and soakage
through the sand beneath the wetland, into the shallow groundwater and then to Tasman Bay. There is
a low permeablity silt/mud layer beneath the wetland extending into the intertidal zone so t he
groundwater is perched on this and exits into the Bay through the fore dune . Seepage through the fore
dune into the intertidal area has been observed at low tide.
Status: Final
Project No.: 80501061
Page 4
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Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
The soil underlying the wetland has also progressively clogged over time, with soakage rates reducing.
This has resulted in the wetland overflowing at the northern end of Wetland North to the south channel
of the Motueka River for extended periods since 2011. In September 2011 the soakage area overflow
weir was moved to the southern end of the soakage area to flow into the Wetland South to maximise the
flow path through the wetland.
An Annual Monitoring Report is prepared each year that summarises the overall performance of the
existing WWTP compared to resource consent requirements, including wastewater discharge quality.
3
Representative Options
3.1
Overview
In May and June 2012 the Working Party and MWH identified six Representative Options for the Motueka
WWTP upgrade. These Representative Options, Options A to Option F, are as follows:

Option A: Decentralised Wastewater Schemes, where wastewater from one individual property
or clusters of several properties is treated and disposed of near the point of generation.

Option B: Discharge to Land, where wastewater is treated to a sufficient level prior to discharge
to rapid infiltration basins (RIBs). Treated wastewater then percolates down through the soil to
the underlying groundwater. Alternative land application mechanisms to RIBs, such as surface
irrigation, have been discounted by the Working Party due to limited available land area.

Option C: Discharge to Surface Water, where wastewater is treated to a sufficient level prior to
discharge to the south channel of the Motueka River, which drains to Tasman Bay. Discharge to
the main channel of the Motueka River was discounted by the Working Party in September 2012
due to the river’s high recreational and cultural values.

Option D: Discharge to Groundwater, where wastewater is treated to a sufficient level prior to
injection via a bore into the groundwater. The treated wastewat er then ultimately drains to
Tasman Bay and may intersect the south channel.

Option E: Mix and Match of Options B & C, where wastewater is treated to a sufficient level and
is discharged to land via RIBs when conditions allow and discharged to the south channel of the
Motueka River at other times.

Option F: Long Term Option, off-site, where wastewater is either pumped off-site (with or
without treatment) or the reticulation in the catchment is re-routed and the WWTP is located
elsewhere.
The Working Party in their June 2012 meeting discounted further progressing Option A and Option F at
this stage due to both the likely timeframe for implementation and the cost to the community of
establishing an entirely new treatment and disposal system. Options B through to E, inclusive, have
been considered further in this report.
The basis of concept design for the Representative Options is outlined in Section 3.2. This section
includes indicative treated wastewater quality for different levels of treatment (T0 – T5) at the point of
discharge from the Motueka WWTP (ie. either to land, surface water or groundwater).
Each Representative Option (ie. Options A to F) has a treatment component and a discharge
component. These are outlined in this Section as follows:



Section 3.3 outlines the treatment options that can achieve the different levels of treatments (ie. T0 to
T5). These treatment options are applicable to one or more of the Representative Options.
Section 3.4 outlines the discharge options that are applicable to each of the Representative Options
Section 3.5 outlines the total indicative capital and operating costs of each Representative Option (ie.
the treatment component and the discharge component). Where applicable, a different total cost is
provided for achieving different levels of treatment (eg. T2 and T4).
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Treatment and Discharge Options
3.2
Basis of Concept Design
This section summarises the basis of concept design used in this options assessment for purpose of
indicative costing the Options B through to E, inclusive. This options assessment includes current and
future concept design wastewater flow and loads, treated wastewater requirements and sludge
treatment and disposal requirements. A design horizon of 35 years has been used.
3.2.1
Wastewater Influent Flow and Loads
Table 3-1 summarises the concept design flow and loads used to size the WWTP upgrades. These
values are from the MWH report titled “Motueka Wastewater Treatment – Flows and Loads”, dated June
2012. The summer values have been accurately measured through influent monitoring over one year
and are representative of summer periods. The winter values have not been measured and are
indicative only and are most likely an overestimate of actual winter loads. MWH recommends the winter
design loads are confirmed by additional continuous influent monitoring for at least one month during the
winter period prior to progressing with detailed design.
Table 3-1: Concept Design Influent Flows and Loads
Summer
Year
Unit
2011
2021
Winter
2031 – 2051
2011
2021
2031 – 2051
Average Dry Weather Flow
(ADWF)
m /d
3
2,500
2,600
2,600
2,300
2,400
2,400
Average Daily Flow (ADF)
m /d
3
3,100
3,200
3,200
3,100
3,200
3,200
Peak 7-day flow
2
Peak 30-day flow
3
-
7,500
-
6,300
Average daily COD load
kg/day
1,600
1,700
1,700
1,000
1,000
1,000
Average daily BOD load
kg/day
800
800
800
500
500
500
Average daily TSS load
kg/day
1,100
1,100
1,100
700
700
700
Temperature
0
24
24
24
10
10
10
3.2.2
C
Indicative Treated Wastewater Levels
Table 3-2 summarises the indicative treated wastewater quality for six levels of treatment at the point of
discharge from the Motueka WWTP (ie. either to land, water, or groundwater). These treatment levels have
been used to develop the treatment component of each of the Representative Options. Some of the treatment
levels only apply to particular Representative Options (eg. T5 only applies to Option D). The treatment levels
(and hence treatment component) may need to be revisited when the receiving environment requirements
are confirmed after public consultation.
2
This is the peak daily flow observed over seven consecutive days. It is based on those observed in
September 2008, which were influenced by groundwater infiltration due to high ground water table.
3
This is the peak daily flow observed over 30 consecutive days. It is based on those observed in
September 2008, which were influenced by groundwater infiltration due to high ground water table
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Table 3-2: Treated Wastewater Quality for Different Levels of Treatment at Point of Discharge
Level
Level of Treatment
Median
Total
Suspended
Solids and
BOD5
(mg/L)
Median
Total
Nitrogen
(mg/L)
Median
Nitrate
Nitrogen
(mgN/L)
Median
Ammonia
Nitrogen
(mgN/L)
Median Total
Phosphorous
(mg/L)
95
Percentile
Faecal
Coliform
(cfu/100mL)
T0
Existing
≤60
≤50
≤5
≤40
≤10
≤ 100,000
T1
Existing with Solids
Reduction
≤20
≤50
≤5
≤40
≤10
≤ 100,000
T2
Solids and Pathogen
Reduction
≤20
≤50
≤5
≤40
≤10
≤ 200
T3
Solids, Pathogen and
Ammonia Reduction
≤20
≤50
≤35
≤5
≤10
≤ 200
T4
Solids, Pathogen,
Ammonia and
Nitrogen Reduction
≤20
≤15
≤10
≤5
≤10
≤ 200
T5
Solids, Pathogen,
Ammonia and
Nitrogen Reduction,
Tertiary Filtration
≤5
≤15
≤10
≤5
≤10
≤ 200
3.2.3
Solids Treatment and Disposal Requirements
3
The existing oxidation pond contains approximately 23,500 m of sludge. At an estimated dry solids
content of 4% this equates to 940 tonnes of dry solids. This sludge will need to be removed from the
oxidation pond to provide storage or capacity for treatment for Representative Options B to E, as
described under Sections 3.3.2.1 and 3.3.3.1.
As a minimum, sludge generated by the treatment processes is required to be stored on-site in pondtype structures with periodic dewatering to enable beneficial reuse off-site or disposal to landfill, whilst
minimising odours. Screenings will continue to be disposed of at the Eves Valley Landfill.
3.3
Wastewater Treatment Options (for Options B to E)
3.3.1
Overview of Treatment Options
Two broad options have been considered for the treatment component of each of the Representative
Options. These are:


utilising the existing oxidation pond (Pond Options)
converting the existing aeration basin to an activated sludge (AS) system and installing new clarifiers
(AS Options).
Additional treatment modules have then been added to the existing situation (T0), as required, to
achieve the different treatment levels (ie. T2-T5) presented in Section 3.2.2. These treatment options
are applicable to one or more of the Representative Options.
A process schematic, indicative site layout and indicative system sizing requirements for each
Representative Option (both treatment and discharge components) are provided in Appendices A to C.
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3.3.2
Oxidation Pond Based Treatment Options (Pond Options)
3.3.2.1 Pond Option – Treatment Level T2 (Base)
This Option comprises.








Reuse of existing inlet works, screen, odour control, and existing infrastructure to dispose of
collected screenings to landfill.
Reuse of existing aeration basin including existing aerators (four aerators each sized at 7.5kW,
giving a total of 30kW), oxidation pond and bypass.
Installation of new pipework to direct flow from aeration basin to south east corner of oxidation
pond.
Installation of new oxidation pond outlet on south west corner of oxidation pond to enable flow
3
balancing within the pond to 7 ML/day (7MLD, or equivalent to 7,000 m per day) and installation
of a full width baffle within the pond orientated in a north to south direction to minimise shortcircuiting.
Installation of new pumps to transfer oxidation pond effluent to the solids removal plant
Installation of a new solids removal plant (sand-ballasted coagulation-flocculation, Dissolved Air
Flotation or similar with clarifier) to treat all flows up to 7 MLD. Return of sludge to the oxidation
pond inlet. For the purpose of developing costs, it has been assumed a proprietary solids removal
plant that comprises a sand-ballasted flocculation process and a high-rate lamella plate clarifier
within one tank is installed with a control building.
Installation of a new UV disinfection unit sized to treat all flows up 7 MLD. Disinfection facility will
achieve effluent quality with 95 percentile enterococci of less than 200 cfu/100mL, which is
equivalent to a Microbiological Acceptance Criteria (MAC) Grade B beach. For the purpose of
developing costs, it has been assumed that the UV reactor will comprise two stainless channels,
each sized for 3.5 MLD, founded on a concrete pad outdoors and that two channels will only be
used approximately 20% of the year (ie. about two months).
Construction of a flood bank around the oxidation pond to 4.8m above average mean sea level
(amsl) equates 2.3m above existing stopbank, 0.8m above existing oxidation pond.
3.3.2.2 Pond Option – Treatment Level T3 (Base with Nitrification)
This Option comprises Pond Option T2 (base) components with the addition of:

Installation of new nitrifying trickling filter to reduce ammonia concentration. The filter will be
installed upstream of the solids removal plant with feed pumps and internal recycle. For the
purpose of developing costs, it has been assumed that the nitrifying filter will comprise randomly
packed plastic media installed in tankage constructed using preformed panels.
3.3.2.3 Pond Option – Treatment Level T4 (Base with Nitrification and Denitrification)
This Option comprises Pond Option T2 (base) components with the addition of:


Installation of new nitrifying/denitrifying trickling filter to reduce ammonia and total nitrogen
concentration. The filter will be installed upstream of the solids removal plant with feed pumps and
internal recycle. For the purpose of developing costs, it has been assumed that the
nitrifying/denitrifying filter will comprise randomly packed plastic media installed in tankage
constructed using preformed panels. The nitrifying/denitrifying filter is larger in diameter and has a
greater recycle rate than the nitrifying filter.
Installation of bypass of screened wastewater to the trickling filter to provide a carbon source for
denitrification. Options for a chemical carbon source were considered but disregarded due to cost
and limited availability of bulk chemical deliveries to Motueka.
3.3.2.4 Pond Option – Treatment Level T5 (T4 with Membrane Filtration)
This Option comprises Pond Option T4 components with the addition of:

Installation of a new membrane filtration plant to further reduce the suspended solids
concentration prior to bore injection disposal. The membrane plant will be installed downstream of
the UV disinfection reactor with feed and permeate pumps.
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3.3.3
Activated Sludge Based Treatment Options (AS Options)
3.3.3.1 AS Option – Treatment Level T4 (Base)
This option comprises.

Reuse of the existing inlet works, screen, odour control, and existing infrastructure to dispose of
collected screenings to the landfill.
Conversion of half of existing oxidation pond into a flow balancing pond, which will provide sidestream balancing of flows to 7 MLD prior to the activated sludge bioreactor. This will require
draining of the oxidation pond, installation of a full length earthen wall in an east to west
orientation in the pond, installation of a new inlet and outlet, extension of the existing bypass
pipework, and installation of a flow balancing pump station to transfer balanced flow back to the
inlet works. For the purpose of developing costs, it has been assumed that the flow balancing
pump will operate for approximately 20% of the year (ie. about two months).
Conversion of the existing aeration basin to an activated sludge bioreactor by incorporating a
partition to create an anoxic zone and an aerated zone, installation of surface mixers (in the
anoxic zone), slow speed surface aerators, and recycle pumps. The recycle pumps are sized to
achieve the required level of ammonia and nitrogen reduction.
Installation of new clarifiers and sludge pumps to return sludge back to the bioreactor or to sludge
storage.
Conversion of the remaining half of the existing oxidation pond for sludge storage.
Installation of new liquor return pumps to transfer supernatant from sludge storage to the inlet
works.
Installation of a pump station to deliver clarified wastewater to the UV disinfection unit.
Installation of new UV disinfection unit sized to treat all flows up to 7 MLD. Disinfection facility will
achieve effluent quality with 95 percentile enterococci of less than 200 cfu/100mL, which is
equivalent to a Microbiological Acceptance Criteria (MAC) Grade B beach. For the purpose of
developing costs, it has been assumed that the UV reactor will comprise two stainless channels,
each sized for 3.5 MLD, founded on a concrete pad outdoors and that two channels will be only be
used approximately 20% of the year (ie. about two months).
Construction of a flood bank around the oxidation pond to 4.8m above amsl.








3.3.3.2 AS Option – Treatment Level T5 (T4 with Membrane Filtration)
This option comprises AS Option T4 components with the addition of:

Installation of a new membrane filtration plant to further reduce the suspended solids
concentration prior to bore injection. The membrane plant will be installed downstream of the UV
disinfection reactor with feed and permeate pumps.
A deaeration facility to reduce the frequency of injection bores clogging.
A pump station to transfer filtered wastewater to the bore injection disposal site.


3.4
Treated Wastewater Discharge Options (for Options B to E)
3.4.1
Overview
Three broad options have been considered for the discharge component for the Representative Options.
These are:



Discharge to land via rapid infiltration basins (RIBs), which applies to Representative Options B and E
Discharge to surface water via tidal discharge, which applies to Representative Options C and E
Discharge to groundwater via bore injection, which applies to Representative Option D.
Section 3.4.2 provides an overview of the work done to done on investigating the feasibility of discharge
to land via RIBs, and storage requirements for discharge via RIB and tidal discharge. The subsequent
subsections outline the discharge component that is applicable to each of the Representative Options.
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3.4.2
Rapid Basin Infiltration or Tidal Discharge
In 2007 the Motueka Wastewater Task Group identified rapid infiltration basins (RIBs) as the desirable
disposal option for treated wastewater from the Motueka WWTP, provided it was shown to be a feasible,
4
long-term solution. Investigations to date indicate that RIB disposal of treated wastewater is difficult on
the proposed site. The Working Party September 2012 confirmed that ground disposal must be
exhausted as the preferred option. Accordingly, additional hydrogeological investigations were carried
out.
3
The Aquifer Testing and Mounding Analysis indicated for peak flows of 7,000 m per day the RIBs would
need to be spaced at least 200m apart. This is not a feasible option as there is insufficient land area at
the site.
3
The above analysis also indicated RIBs are a feasible option for 3,000m per day if.


The natural groundwater level is controlled by drainage to keep it below a critical level (yet to be
determined).
RIBs are spaced at 100m apart.
For the purpose of this options assessment it has been assumed 100% of the average flow (ie. 3,000 m
per day) will be discharged via RIBs and groundwater levels are controlled to below he critical level.
3
Typically high WWTP inflows are associated with high natural groundwater levels.
3
During periods when RIB discharge is not feasible (flows greater than 3,000m /day, high groundwater,
extreme wet weather, flooding of RIB area) treated wastewater will be discharged directly to the south
channel on an out-going tide (ie. tidal discharge).
A storage pond and discharge pumping is required for both a RIB discharge and a tidal discharge. This
is because with a RIB discharge, a RIB would be flooded intermittently and a storage facility is needed
during those times. In addition, with a tidal discharge, the wastewater would be discharged on each
outgoing tide for approximately 4 hours, and so the effluent needs storing between these hours of
discharge.
Indicative site layout and sizing requirements for storage, RIB and tidal discharge components are
provided in Appendices B and C.
3.4.3
RIB Discharge (Representative Options B and E)
This component comprises.









Shared use of storage pond and tidal discharge pump station.
3
Installation of eight RIBs each 120m by 27m to receive peak flow of 7,000m per day and average
3
flow of 3,000m per day.
Pipework to distribute the treated wastewater to RIBs.
Control system to limit discharge to individual RIBs when groundwater mounding or natural
groundwater is elevated to prevent a discharge to surface water.
Drainage to control groundwater levels and groundwater pump station to return groundwater to
existing wetlands.
Construction of new stopbanks to protect the RIBs against flooding.
3
Installation of a new storage pond to store up to 3,000 m UV disinfected wastewater (ie.
approximately nine hours storage at 7 MLD).
Installation of a new pump station, which delivers wastewater to either RIB or tidal discharge
structure.
Construction of new stopbank to protect against flooding and coastal erosion. For costing
purposes this cost has been included within RIB discharge costs and it has been assumed that
material excavated to form RIBs is used to construct storage pond.
Wastewater discharge to RIBs must be treated to T2 level (ie. solids removal) as a minimum to minimise
risk of clogging of the RIBs. This is discussed further in Section 4.4.
4
“Motueka WWTP Upgrade - Groundwater Mounding Assessment” and “Motueka WWTP Upgrade - Rapid Infiltration Basin
Concept Design Statement”, MWH reports both dated June 2012
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Treatment and Discharge Options
3.4.4
Tidal Discharge (Representative Options C and E)
This component comprises.





Shared use of storage pond and RIB pump station.
Installation of new pipework and discharge structure within the south channel for a tidal discharge.
3
Installation of a new storage pond to store up to 3,000 m UV disinfected wastewater
(ie. approximately nine hours storage at 7 MLD).
Installation of a new pump station, which delivers wastewater to either RIB or tidal discharge
structure.
Construction of new stopbank to protect against flooding and coastal erosion. For costing
purposes this cost has been included within RIB discharge costs and it has been assumed that
material excavated to form RIBs is used to construct storage pond.
Wastewater discharge to south channel must be treated to T2 level (ie. solids removal and UV) as a
minimum to minimise risks to public health. This is discussed further in Section 4.3.
3.4.5
Bore Injection (Representative Option D)
An alternative to RIB and tidal discharge, is direct discharge to groundwater via bore injection. This
option is provided to give a perspective of costs; further work would be required to confirm the technical
feasibility of this discharge mechanism at the Motueka WWTP site, if there was a wish to pursue this
option.
This discharge option comprises.





Installation of five groundwater injection bores, each with individual pump. The number of injection
bores, location and depth needs to be confirmed.
Pipework to distribute the treated wastewater to injection bores.
Control system to limit discharge to individual bores when groundwater mounding or natural
groundwater is elevated to prevent a discharge to surface water.
Collection pipework and sump to collect purged water during backwashing of injection bores.
Backwash pump and drain to the oxidation pond inlet (Pond Options) or sludge storage pond (AS
Options).
Wastewater discharge direct to groundwater must be treated to T5 level (ie . solids removal, ammonia
removal, nitrogen reduction, UV, membrane filtration) as a minimum to reduce potential of clogging of
the groundwater injection bores.
3.5
Indicative Cost Estimates
3.5.1
Overview
This Section outlines the indicative capital and operating costs of each Representative Option (ie. the
treatment component and the discharge component). Where applicable, a different total cost is provided
for achieving different levels of treatment (eg. T2 and T4), as outlined in Section 3.2.2.
3.5.2
Basis of Indicative Cost Estimates
3.5.2.1 Indicative Capital Costs
Indicative capital cost estimates have been developed using a bottom -up approach on an individual unit
process basis for the purpose of comparing options. With the exception of bore injection, indicative
costs are based upon recent quoted or tendered prices for similar sized projects and, where required,
adjusted to current (2013) prices.
Indicative costs presented for bore injection have a greater level of uncertainty associated with them as
there is little experience with this discharge mechanism in Australasia and further work is required to
confirm the technical feasibility of this discharge mechanism at the Motueka WWTP site.
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Indicative capital cost estimates have been determined on the following basis:
Preliminary and general items
10% of capital cost
Design and construction management
15% of capital cost
Price contingency
10% of imported mechanical equipment cost
Physical contingency
30% of overall project cost
No allowance has been made for the following.











Goods and services taxes (GST) or import duties.
Obtaining resource consents or building consents.
Any geotechnical work that may be required for each of the alternatives .
Work associated with de-establishment of existing plant no longer required under each alternative or
rehabilitation of the site (eg. wetlands, polishing ponds). This work will depend on the total solution
for the Motueka WWTP upgrade, phasing of construction as well as the Council’s long-term plan for
the site.
Upgrading power supply to the site.
Further investigation work required to confirm technical feasibility of each option .
Purchasing imported fill material if material excavated from the RIB area is not suitable for
construction of the storage pond.
Purchasing imported fill material if the quantity of material excavated from the RIB area is not
sufficient for construction of the storage pond due to staging of RIB construction.
Purchasing additional land or land lease costs.
Any upgrading of the access road to the site.
Permanent sludge handling facilities.
3.5.2.2 Indicative Annual Operating and Maintenance Costs
The indicative operating costs of the alternatives are based on 2021 flows and loads and have been
determined on the following basis.
Electricity
$0.14 per kWh (to be confirmed)
Coagulant, dry (for solids removal)
$14 per kg
Flocculant, dry (for solids removal)
$18 per kg
Sand (for solids removal)
$1000 per tonne
Labour
$70,000 per year per operator
Aside from the initial oxidation pond desludging included in the capital cost of each option, no allowance
has been made for on-going sludge handling and disposal.
The indicative maintenance costs associated with the new or modified infrastructure have been based
on the following assumptions:
Civil works
0.5 percent of capital cost
Mechanical and electrical plant
4.0 percent of capital cost
Membranes
1.0 percent of capital cost
In addition to those items described above, Council is also required to fund depreciation of capital works
items to provide funds for replacement of physical works. Depreciation has been assessed for new or
modified infrastructure using a straight-line depreciation method based on the following broad asset
lives:
Civil works and pipework
75 years
Mechanical, electrical and control plant
15 years
The values are consistent with the recommendations contained in the International Infrastructure
Management Manual prepared by the New Zealand National Asset Management Steering Group and
the Institute of Public Works Engineering Australia.
No allowance has been made for operating, maintenance costs or depreciation associated with existing
infrastructure common to all options (ie. screening and odour control at inlet works).
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3.5.3
Summary of Indicative Capital and Operating Cost Estimates
A summary of the indicative estimated capital and operating costs associated with Representative
Options B to E for upgrading Motueka WWTP are presented in Table 3-3 and Table 3-4, respectively.
These indicative costs are for upgrading the WWTP to accommodate flows and loads up to 2050.
Indicative costs presented for direct groundwater bore injection have a greater level of uncertainty
associated with them as there is little experience with this discharge mechanism in Australasia and
further work is required to confirm the technical feasibility of this discharge mechanism at the Motueka
WWTP site.
Indicative costs have been grouped into wastewater treatment and discharge units to provide a
perspective of how costs could be staged. Total costs have been grouped into level of treatment (T2, T4
and T5) and stopbank and groundwater drainage costs.
The need for ammonia and nitrogen reduction prior to discharge to the receiving environment is yet to
be confirmed. It is possible that, given a tidal discharge, these treatment s teps will not be required. The
capital and operating costs of these treatment modules are included in the total project cost given in
Table 3-3 and Table 3-4 but are shaded in green.
Groundwater drainage and stop bank protection works could be deferred if the Council accepts the risk
of flooding. This approach needs to be confirmed by the Working Party. The capital and operating costs
of these treatment modules are included in the total project cost given in Table 3-3 and Table 3-4 but
are shaded in orange.
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Table 3-3: Indicative Capital Cost of Representative Options B to E (to 2050)
Option B
RIB
Component
Option C
Tidal
Option D
Bore Injection
Option E
RIB+Tidal
Pond
AS
Pond
AS
Pond
AS
Pond
AS
2,600,000
2,600,000
2,600,000
2,600,000
2,600,000
2,600,000
2,600,000
2,600,000
below
650,000
below
650,000
below
650,000
below
650,000
270,000
5,760,000
270,000
5,760,000
270,000
5,760,000
270,000
5,760,000
Solids Removal
2,720,000
above
2,720,000
above
2,720,000
above
2,720,000
above
Ammonia
Reduction
2,890,000
above
2,890,000
above
2,890,000
above
2,890,000
above
220,000
above
220,000
above
220,000
above
220,000
above
1,050,000
1,400,000
1,050,000
1,400,000
1,050,000
1,400,000
1,050,000
1,400,000
610,000
610,000
610,000
610,000
-
-
610,000
610,000
-
-
720,000
720,000
-
-
720,000
720,000
4,940,000
4,940,000
-
-
-
-
4,940,000
4,940,000
-
-
-
-
10,060,000
10,060,000
-
-
RIBs drainage &
stopbank
3,540,000
3,540,000
-
-
-
-
3,540,000
3,540,000
Oxidation Pond
Stopbank
1,050,000
1,050,000
1,050,000
1,050,000
1,050,000
1,050,000
1,050,000
1,050,000
-
-
12.9M
Treatment
Desludging
Flow Balancing
Biological
Treatment
Nitrogen
Reduction
(additional to
above)
UV Disinfection
Discharge
Storage and
Discharge Pumps
Tidal Discharge
RIBs (eight)
Membranes and
Bores
Stopbanks
Total Costs
Total Cost-T2
12.2M
Total Cost-T4
15.3M
16.0M
11.1M
11.7M
-
-
16.0M
16.7M
Total Cost-T5
-
-
-
-
19.8M
20.5M
-
-
4.6M
4.6M
1.1M
1.1M
1.1M
1.1M
4.6M
4.6M
Total CostDrainage &
Stopbanks
Notes:
1.
2.
3.
4.
5.
6.
7.8M
Treatment Levels T2, T4 and T5 as described in Section 3.2.2.
Ammonia and nitrogen reduction (shaded green) may not be required.
No land costs or leases included.
UV disinfection has a higher capital cost with AS based options than oxidation pond based options as a feed pump
station is required. With the oxidation pond based options, wastewater will gravitate from the proprietary solids removal
module outlet through UV disinfection channel(s) to the storage pond.
RIB drainage and stop banks (shaded orange) could be deferred if accept risks.
Costs are indicative, prepared for consenting purposes. If costs are within 10-15% then assume they are the same.
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Treatment and Discharge Options
Table 3-4: Indicative Annual Operating and Maintenance Cost of Representative Options B to E
(to 2052)
Option B
RIB
Component
Pond
Option C
Tidal
AS
Pond
Option D
Bore Injection
AS
Pond
AS
Option E
RIB+Tidal
Pond
AS
Treatment
Desludging
Common
Common
Common
Common
Common
Common
Common
Common
Flow Balancing
below
20,000
below
20,000
below
20,000
below
20,000
Biological
Treatment
46,000
332,000
46,000
332,000
46,000
332,000
46,000
332,000
Solids Removal
262,000
above
262,000
above
262,000
above
262,000
above
Ammonia
Reduction
77,000
above
77,000
above
77,000
above
77,000
above
Nitrogen
Reduction
(additional to
above)
7,000
above
7,000
above
7,000
above
7,000
above
122,000
144,000
122,000
144,000
122,000
144,000
122,000
144,000
42,000
42,000
42,000
42,000
-
-
42,000
42,000
-
-
11,000
11,000
-
-
11,000
11,000
58,000
58,000
-
-
-
-
58,000
58,000
-
-
-
-
467,000
467,000
-
-
RIBs drainage &
stopbank
70,000
70,000
-
-
-
-
70,000
70,000
Oxidation Pond
Stopbank
12,000
12,000
12,000
12,000
12,000
12,000
12,000
12,000
-
-
540k
UV Disinfection
Discharge
Storage and
Discharge Pumps
Tidal Discharge
RIBs (eight)
Membranes and
Bores
Stopbanks
Total Costs
Total Cost-T2
530k
Total Cost-T4
610k
600k
560k
550k
-
-
620k
610k
Total Cost-T5
-
-
-
-
970k
960k
-
-
80k
80k
10k
10k
10k
10k
80k
80k
Total CostDrainage &
Stopbanks
Notes:
1.
2.
3.
4.
5.
6.
480k
Treatment Levels T2, T4 and T5 as described in Section 3.2.2.
Ammonia and nitrogen reduction (shaded green) may not be required.
UV disinfection has a higher operating cost with AS based options than oxidation pond based options as a feed pump
station is required. With the oxidation pond based options, wastewater will gravitate from the proprietary solids removal
module outlet through UV disinfection channel(s) to the storage pond.
RIB drainage and stop banks (shaded orange) could be deferred if accept risks.
Costs of sludge handling of a similar order in each option. Costs of sludge handling are typically in the order of 30% to
50% of wastewater treatment plant operating costs.
Costs are indicative, prepared for consenting purposes. If costs are within 10-15% then assume they are the same.
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Treatment and Discharge Options
3.6
Representative Options Summary
A qualitative assessment of each of the Representative Options with respect to receiving environment,
public health, social, cultural, economic consideration and key advantages an d disadvantages is
presented in Table 3-5. Indicative capital and operating costs have not been determined for
Representative Options A and F have been included in this assessment.
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Treatment and Discharge Options
Table 3-5: Qualitative Assessment of Representative Options for Motueka WWTP
Representative
Treatment and
Discharge
Option
Option A
Decentralised
Wastewater
Schemes
Description
Receiving Environment
Treat and disposal of Motueka, Riwaka and Kaiteriteri individually with
standalone treatment and disposal systems. One or more individual site
for each community.
Site specific; discharge to land,
groundwater or surface water.
Social and
Public Health
Community preference for
centralised treatment and
to reuse investment in the
existing infrastructure at
Motueka.
Maori/
Cultural
(Site and
Spiritual)
Iwi to advise.
Economics
Capital
Cost
T2-T4: High
Operating &
Maintenance
Cost
T2-T4: High
Site specific
considerations.
Option B
Discharge to
Land
Oxidation pond-based treatment with solids reduction to reduce soil
clogging in RIBs and additional unit processes as required (eg. UV
disinfection, nitrification, denitrification); OR
Activated sludge-based treatment with UV disinfection if required.
Discharge to Rapid Infiltration Basins (RIBs); treated wastewater
percolates down through soil to underlying groundwater.
Groundwater will meet surface
water where the south river
channel has cut through upper
confining layer. Difficult to
estimate the flow to surface
waters and dilutions. Limited
dilution within groundwater.
Ammonia and nitrogen
reduction may not be required.
Option C
Discharge to
Surface Water
Oxidation pond-based treatment with solids reduction to improve clarity
and additional unit processes as required (eg. UV disinfection,
nitrification, denitrification); OR
South channel of Motueka
River, which drains to Tasman
Bay.
Activated sludge-based treatment with UV disinfection if required.
TDC Water Plan quality required
after reasonable mixing.
Assumed mixing zone and
dilutions.
Tidal discharge via south channel of Motueka River.
Option D
Discharge to
Groundwater
Oxidation pond-based treatment with solids reduction to reduce bore
clogging, UV disinfection for pathogens (if required), nitrification and
denitrication to reduce bore clogging, and membrane filtration to reduce
bore clogging; OR
Activated sludge-based treatment with UV disinfection (if required) and
membrane filtration to reduce bore clogging.
Direct injection into underlying groundwater via bore.
Option E
Mix and Match
of Options B
and C
Oxidation pond-based treatment with solids reduction and additional
unit processes as required (eg. UV disinfection, nitrification,
denitrification); OR
Activated sludge-based treatment with UV disinfection if required.
With reduced infiltration area
from pumping into groundwater,
need greater removal of solids
and organic material than RIBs
(Option B) to prevent bacterial
growth and soil clogging.
Otherwise similar to Option B
above.
The available area of land and
groundwater properties will
determine the portions of mix
and match.
Long Term
Option, Off-site
Option for this includes reverse direct of wastewater reticulation
pumping, establish new wastewater treatment plant on non-flood prone
land away from the coast, storage dams and reuse treated wastewater
for the water short areas of the Moutere Hills.
Iwi and
Wakatu
support this
option.
T2: $12M
(+$5M)
T2: $530k
(+$80k)
T4: $16M
(+$5M)
T4: $600k
(+$80k)
UV disinfection likely to be
required to minimise public
health risk or perception of
risk.
Iwi have
advised this is
culturally
offensive.
T2: $8M
(+$1M)
T2: $480k
(+$10k)
T4: $12M
(+$1M)
T4: $550k
(+$10k)
Public Health Risk
Assessment required.
Main channel
of Motueka
River has high
recreational
and cultural
values
associated.
UV disinfection may be
required to minimise public
health risk or perception of
risk.
Need advice
from Iwi.
Not feasible in the short to medium
term.
Greater resilience in terms of
natural disasters (flooding,
earthquakes) as more than one
treatment plant.
Greater number of schemes to
manage and likely to be greater
total capital and operating costs.
Proven, robust treatment
technology with low operator
input.
Risk of groundwater mounding.
Discharge route favoured by
Working Party and iwi.
Proven, robust treatment
technology with low operator
input.
Risk if unable to discharge to land
100% time, particularly when peak
inflows coincide with high
groundwater table.
Discharge route is offensive to iwi.
Discharge on out-going tide during
period of greatest flow (and
available dilution) so may mitigate
ammonia toxicity.
T5: $21
(+$1M)
T5: $960k
(+$10k)
Reduced land required compared
to RIBs. Ability to spread the
bores to reduced groundwater
mounding.
Risk of groundwater mounding
less than Option B.
Iwi have
advised this is
culturally
offensive.
Risk of soil clogging if solids not
removed.
Tidal discharge able to be used
100% of the time.
Public Health Risk
Assessment required.
UV disinfection likely to be
required to minimise public
health risk or perception of
risk.
Key Disadvantages
Smaller individual areas of land
required for each scheme.
Public Health Risk
Assessment required.
T2: $13M
(+$5M)
T2: $540k
(+$80k)
T4: $17M
(+$5M)
T4: $610k
(+$80k)
Public Health Risk
Assessment required.
Discharge to land via RIBs (Option B) when conditions allow and
discharge to south channel of the Motueka River (Option C) at other
times (ie. when groundwater levels are too high, flooding).
Option F
UV disinfection may be
required to minimise public
health risk from shellfish
ingestion or perception of
risk.
Key Advantages
Proven, robust treatment
technology with low operator
input.
Maximise discharge to land when
groundwater conditions allow and
meets Working Party Objectives.
High technology treatment required
with membrane filtration to removal
all solids to prevent bore clogging.
High level of operator expertise
required.
Risk of soil clogging even with high
level of treatment; need for greater
number of bores to provide
redundancy.
Investment both in land, WWTP
and tidal outfall.
Typically in wet weather both the
river flows and groundwater will be
higher.
Low risk with multiple discharge
routes (ie. RIB and tidal).
Site specific; discharge to land,
groundwater or surface water.
Site specific
considerations.
The life of the existing site will be determined by sea level rise and
flooding. However it may be feasible to retain treatment on this site and
pump the treated wastewater to an alternative site for land disposal.
Iwi have
advised this is
their
preference in
the long term.
T2-T4: High
T2-T4: High
Maximise existing infrastructure
until not feasible to continue past
2052 due to flooding risk.
Not feasible in the short to medium
term. Required to upgrade the
current WWTP and discharge
system.
Notes:
1. Capital and operating costs are given for pond-based option for T2, activated sludge based option for T4 and T5. Capital and operating costs for stop banks and RIB drainage are not included in the total but are provided in brackets.
2. Costs of sludge handling of a similar order in each option. Costs of sludge handling are typically in the order of 30% to 50% of wastewater treatment plant operating costs.
3. Costs are indicative, prepared for consenting purposes. If costs are within 10-15% then assume they are the same
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Treatment and Discharge Options
4
Risk Analysis
4.1
Introduction
The following section overviews the key risks identified as part of this project for the Motueka WWTP
upgrade and associated discharge arrangements.
These key risks are associated with the following.




Stop banks, flooding, climate change and associated predicted sea level rise risk.
Receiving environment and public health.
Discharge to land via rapid infiltration beds.
General wastewater treatment plant risks.Geotechnical work for new structures.
For each of the associated key risks, which are described in the following subsections, there is a need to
identify.



A method to avoid, remedy, mitigate or accept that risk.
Determine the effectiveness of those measures for that risk.
Provide a project pathway through those combined risks in a logical sequence to avoid prejudging
options while avoiding excessive costs.
Individual risks are detailed further in Appendix D.
4.2
Stopbanks Flooding Climate Change and Sea Level Rise
The information provided in Assessment of Potential Flood and Inundation Hazard June 2012 is
summarised in Table 4-1. In this table, storm surge is the seawater that is pushed ahead of a storm
event.
Table 4-1: Assessment of Potential Flood and Inundation Hazard
Tidal Component
Level Above Mean Sea Level (m)
Mean High Water Springs
2.0
Storm Surge
0.5
Wave Run up
0.3
Safety Margin
0.0
Total
2.8
This compares to 2.5m mean sea level of the existing stop-bank around the proposed RIB area and
4.0m height of the oxidation pond embankment. Thus the proposed RIB area is at risk from high tides
and storm events prior to consideration of flooding and climate change.
The Table 4-2 indicates the range of expected combinations of.




Sea level.
Sea and flood level.
Including climate change from 2012 to 2052 the proposed life of this project .
Out to 2090 when the site becomes untenable based on the best information provided by Mi nistry of
nd
the Environment “Coastal Hazards and Climate Change” 2 edition July 2008.
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Treatment and Discharge Options
Table 4-2: Range of Height Required Under Combinations of Events
Extra height
Required height
Extra height
required to
incl 0.9m
required to
Existing Stopbank
Freeboard
Oxidation Pond
around RIB land
(m)
embankment (m)
(m)
Sea level only
(m)
Sea + 100yr
River Flood
(m)
2012
2.8
3.7
4.6
2.1
0.6
2052
3.05
3.95
4.85
2.35
0.85
2090
3.7
4.6
5.5
3
1.5
Year
The conclusions from this are.



That there is considerable additional height required on the existing stopbank and new stopbank
required to protect the proposed RIBs and WWTP upgrade.
That the site may not have a long term future past 2052.
While it may be desirable long term to move to a new site, this does not deal with the current risks to
the environment and public health nor community desire for land discharge.
4.3
Receiving Environment
The current discharge from the overflow from the wetlands is to the south channel of the Motueka River.
The risks from this discharge relate to.


Public health with elevated indicator bacteria pathogen levels in the discharge .
Ammonia toxicity to aquatic life especially at low tide (oxidation ponds are not effective at reducing
ammonia).
To mitigate the public health risk, UV disinfection of the oxidation pond effluent is required. But this first
requires removal of the solids to provide sufficient clarity for the UV disinfection to be effective,
particularly during summer months when algae concentrations are high.
The existing wetlands are located below the high spring tide level and sea water floods in during peak
tides and could scour out the wetlands and possibly the polishing ponds (“soakage beds”). When this
occurs there is the possibility of the loss of the wetlands at short notice.
Therefore to mitigate existing risks to public health and the receiving environment.


First priority- removal of solids and UV disinfection to mitigate public health risk.
Second priority- treat for ammonia. The level of ammonia reduction required is dependent on the
discharge route and actual effects on the environment. A tidal discharge, with discharge on an outgoing tide during the period of greatest flow (and available dilutio n), may mitigate the risk of
ammonia toxicity.
It is noted that solids removal is also required for the RIBs as discussed below.
4.4
Rapid Infiltration Beds
The MWH report titled “Motueka Wastewater Treatment Plant Upgrade Aquifer Testing and Mounding
Analysis” (December 2012) found that there is a range of aquifer parameters (eg. transmissivity from
2,000 to 5,000 m/day) that have a significant impact on the groundwater mounding.
If the lower aquifer transmissivity value is used then RIBs will need to be spaced a considerable
distance apart and groundwater controls will be required. If the higher aquifer transmissivity value is
used the RIBs can be spaced closer.
It is possible to refine the analysis with more investigations or to numerically model the expected
groundwater mounding to provide better estimates. However the geology of the site is variable locally ,
both vertically and horizontally, and further modelling is likely to still leave doubts about the functionality
of the RIBs.
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Treatment and Discharge Options
The best information available to date is that RIBs.


3
Should function adequately in average inflows of 3,000 m /day subject to control of peak
groundwater levels.
3
But are unlikely to function for more than short periods with peak discharges of 7,000 m /day.
The best way to refine the functionality of the RIBs is to progressively construct the RIBs over a number
of years and, if groundwater mounding is significant, to mitigate that mounding through.



Up-gradient groundwater cutoff drains.
Lateral under drains between RIBs.
Grounding water pumping bores to lower the groundwater.
None of these groundwater mitigation measures can be guaranteed as effective at this point in the
project.
At present we have allowed for the RIBs to be spaced at 100m centres. This sp acing could be
decreased or increased as information is obtained.
As a prerequisite to the RIB prototype the wastewater will need to be treated to a higher standard that
avoids clogging of the aquifer by removing the bulk of the solids and organic (BOD) l oading.
In summary:





RIBs are at risk from elevated natural groundwater levels which coincides with peak wastewater
inflows.
There is limited ability to store or attenuate the flows through the WWTP due to the long periods of
elevated inflows.
Reticulation improvements have not decreased significantly the groundwater inflows from 2000 2012.
3
Subject to prototype testing, RIBs maybe effective at average design flows of 3,000 m per day.
3
RIBs are unlikely to be effective for sustained period of flows in the order of 7,000 m per day.
Based on the Working Party’s objective for discharge to land, it is recommended that the RIBs are
constructed over a number of years. The first RIB will be a full scale prototype in order to refine the
mounding estimates, and optimise RIB spacing and groundwater controls based on actual performance.
4.5
Wastewater Treatment Plant Risks
There are a range of risks associated with all wastewater treatment plants.
Most of the risks associated with the treatment processes have established risk management techniques
(such as duplication of critical elements) that are not unique to Motueka WWTP; these are not discussed
further here.
The Motueka WWTP is located on sediments that could be expected to settle in an extreme earthquake
due to liquefaction. This risk has not been quantified.
The raising of the stopbanks around the oxidation pond area could reduce stability of the embankments
over lower strength sediments this will need to be considered.
A greater power supply is required with increasing level of treatment and pumping requirements. An
assessment of available power supply to the site will need to be considered.
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Treatment and Discharge Options
Other risks include.


Investing in treatment upgrades that are not required to minimise current environmental effects (eg.
committing to capital and operating costs associated with ammonia reduction if ammonia toxicity is not
an issue). This can be mitigated by adopting a staged approach to the upgrades, with upgrades
implemented as needed on an effects-based approach.
Investing in treatment upgrades that are not able to be relocated if the site is abandoned. Traditional
activated sludge systems utilise concrete tankage would need to be abandoned; whereas additional
treatment modules can be added to the existing aeration and oxidation pond system that could be
relocated/reused if a new site is obtained. Examples of such modules include proprietary “off-the-shelf”
solids removal units, skid mounted pumps, UV units in stainless steel channels, random plastic trickling
filter media and preformed panels for trickling filter tankage. Such an approach minimises
overcapitalising at the Motueka site in the short to medium term.
4.6
Observational Method to Manage Risk and Stage the Project
In considering the pathway forward it is important to recognise the following.














The investment at Motueka WWTP is medium term out to 2050.
There is no proven ability to reduce groundwater infiltration and WWTP inflows within the Motueka
WWTP catchment at present.
There is no effective soakage within the existing polishing ponds (former sand soakage beds) and
wetlands, all treated wastewater currently discharges to the south channel of the Motueka River in
wet weather.
The existing discharge is unsatisfactory from the perspective of environmental, public health, iwi and
community objectives.
A transition to land discharge will be required.
There will be a probable loss of dunes and wetland in a storm.
The environmental value of the current wetlands is being degraded by the existing solids and
ammonia loads.
3
The best geology and hydrogeology information is that RIBs will function adequately at 3,000 m /day
provided groundwater levels are controlled but will not function at sustained peak flows of
3
7,000 m /day.
The level at which the groundwater needs controlling to has yet to be determined.
Due to uncertainty with geology and hydrogeology variables, the design process for RIBs and
ground disposal cannot be predefined. There are a range of parameters that could apply and
groundwater controls that could be applied.
[1]
RIBs are best proven through the Observation Method by constructing the first RIB as a full scale
prototype and subsequent RIBs over time with a comprehensive and robust monitoring system and a
contingency and improvement plan.
RIB land requirements are subject to land availability.
Selection of treatment modules that are able to be staged to minimise actual environmental effects
is an objective, with upgrades implemented as needed in based on effects. Such an approach is
more affordable for the connected communities whilst progressively working towards achieving the
Working Party’s draft project objectives.
Selection of treatment modules and equipment that is relocatable/reusable if a new site is obtained
is preferred due to long term flooding risk.
Based on workshops with the Working Party, it is considered the priorities for Motueka WWTP are as
follows.






Priority 1: Sludge Removal from the ponds to reduce odour and improve treatment
Priority 2: Treatment to reduce solids to allow initial construction of first RIB.
Priority 2: UV disinfection.
Priority 3: Initial construction of first RIB.
Priority 4: Monitoring of first RIB to refine the design for further RIBs.
Priority 5: Construct of additional RIBs.
[1]
Peck, R.B (1969). Advantages and limitations of the observational method in applied soil mechanics, Geotechnique, 19, No. 1, pp.
171–187
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Treatment and Discharge Options
The following works were not prioritised by the Working Party at this stage.





Construct tidal discharge.
Construct RIB stopbanks.
Monitoring of ammonia and nitrogen levels in the receiving environment.
Treatment to reduce ammonia if the discharge is to RIBs and monitoring of the south channel of the
Motueka River to indicated elevated ammonia beyond a mixing zone at low tide.
Treatment to reduce nitrogen if required. However, the need for this has not been established at
present.
The initial outcome of the investigations to date and priorities of the Working Party is logically a Mix and
Match Option initially as a step toward the Working Party’s goal of land disposal.
Under a Mix and Match Option, the RIBs could be installed without stop bank protection and
groundwater drainage initially. The infrequent risk of flooding may be acceptable if the RIBs are
designed to anticipate flooding and allow for quick restoration.
Figure 4-1 below indicates the staging of the elements and their interrelationships.
If the RIB prototype and groundwater controls are not feasible or practicable from a cost perspective a
Decision Point is reached for:
1. a partial discharge to land, Option E Mix and Match
2. or Option C discharge to surface waters.
Otherwise the objective of land disposal would continue as the objective.
Given the risks at the Motueka WWTP site, an “adaptive management” or “monitor and review”
approach could be used. Such an approach could comprise staged improvements, monitoring, and
implementing pre-identified actions (eg. construction of additional RIBs, further treatment modules)
based on observed effects on the receiving environment.
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Treatment and Discharge Options
Motueka Wastewater Treatment & Disposal Investigation
Project Priorities & Staging based on Effects & RIBs
Colour Key
Start
Priorities and Decision Tree
Investigate
Solids Reduction
Existing after
oxidation pond
treatment
Priority 1
Priority 2
Priority 3
ou
Gr
To
To
S
nd
urf
ac
Construct 1st RIB
as Prototype
eW
ate
rs
UV Disinfection
Monitoring
Initially
Refine RIB
design-spacing
underdrains etc
groundwater
mounding?
Control
groundwaterPassive
Drainage or
Pump
Pump to Polishing Ponds
& Wetland
South Channel Motueka River
Decision Time
Decision Time
Decide if Option B
100% Land ?
or
Option E Mix and Match
Flow Split dependent on
groundwater level
Longer Term
Alternative
land disharge
site?
Option B
Option E
Construct
RIBs(7)
Ammonia reduction & or
UV (if required) see
notes 1& 2 below
Mix & Match
Construct
RIBs
Storage & Tidal Discharge
Note 1
Ammonia reduction;
 Probably required if long term
discharge to south channel
without tidal discharge
 RIBs- Monitor south channel if
high ammonia from lack of
groundwater dilution then treat
Note 2
Subject to public health
risk assessment;
 UV disinfection not
required for RIBs
 Required for surface
water discharge
 Stopbanks to be
considered if life
greater than say 20
years
Ammonia Reduction (if
required) see notes 1
below
Figure 4-1: Motueka WWTP Staging Based on Effects and Option E: Mix and Match
Status: Final
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Treatment and Discharge Options
5
Recommended Strategy for Implementing
Upgrades
Both iwi and the Working Party preference in the short term and long term is for land disposal (ie. Option
B). However, as discussed in Section 4, there are significant risks around this option that are best
quantified by a progressive construction programme for the RIBs.
The benefits of implementing Motueka WWTP upgrades in a staged adaptive management approach, as
described in Section 4.6, based on the Working Party’s priorities and overall objective of land disposal
include.



Minimises public health risks associated with the current surface water discharge in the short term.
Gains an understanding of the ability of RIBs to accommodate average and sustained peak
wastewater flows prior to commitment to 100% discharge to land.
Provides time for on-going monitoring of the effluent quality and targeted environmental monitoring,
which will provide greater certainty around whether or not treatment modules to reduce ammonia or
nitrogen are required.
This adaptive management based approach will ensure that capital investment (and annual operating
cost of treatment) is targeted on areas of need, making it more affordable for the community whilst
progressively working towards achieving the Working Party’s Draft Project Objectives. Such an
approach lends itself to an oxidation pond-based treatment option with additional treatment modules (ie.
T2, T3 and T4) added as required, rather than an activated sludge based treatment option. These
modules can then be selected to be able to be relocated/reused if a new site is obtained; which also
minimises over-capitalising at the Motueka site in the short to medium term.
Based on the priorities presented in Section 4.6, it is recommended that the Motueka WWTP upgrades
could be implemented in six stages using an oxidation pond-based treatment option and combination of
land and surface water discharge as outlined in Table 5-1.
As there are unknowns around the long-term feasibility of the site and level of treatment required to
minimise environmental effects with respect to ammonia toxicity (and nitrogen), staged works are based
on achieving a treatment level of T2 only and do not include RIB groundwater drainage or flood
protection works.
Table 5-1 compares each stage of work with relative level of achievement of the Working Party’s
cultural, public health and environmental objectives with an indicative capital cost. It also provides an
indicative timeframe for each stage of work.
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Treatment and Discharge Options
Table 5-1: Staging of Upgrades to Achieve T2 Treatment and Land Discharge Via RIB
Stage
1
2
3
4
5
6
Scope
Treatment
Discharge
Working
Party
Priority
Cultural
Values
Public
Health
Values1
Enviro.
Values
Capital
Cost
Timing

$2.6M
20132014


$4.1M
2014



~$0.6M
2015



TBC
20152016
Additional
RIB +
Existing
discharge


$4.3M
(~$0.6M
per RIB)
20172018
RIB + tidal


>$1.3M
20172018
Desludge
oxidation pond
T1
Existing
discharge
1
Modify oxidation
pond, install
solids removal
and UV
Install prototype
RIB
T2
Existing
discharge
2
T2
3
Observe
prototype RIB
performance and
environmental
effects
Decision Point
T2
RIB +
Existing
discharge
RIB +
Existing
discharge
4
Install additional
RIBs. Observe
RIB performance
and
environmental.
effects
Install storage
pond and tidal
discharge
T2
T2
The level of ammonia reduction required is dependent on the discharge route and actual effects on the
environment. A tidal discharge, with discharge on an out-going tide during the period of greatest flow
(and available dilution), may mitigate the risk of ammonia toxicity.
In summary, due to the outlined risks and uncertainties associated with RIBs and groundwater
mounding, it is recommended that a staged adaptive management approach to Motueka Wastewater
Treatment and Disposal is adopted by the Working Party as set out in Table 5-1.
6
Feedback from Working Party on Preferred Option
and Strategy
At the Motueka Wastewater Project Working Party meeting on 19 February 2013, the Working Party
considered each of the Representative Options. Key points of discussion, key decisions and the
Working Party’s recommendations from the meeting are included below.
A key objective of the Working Party is for land disposal which is Option B: Discharge to Land.
The hydrogeological information including Peer Review by Aqualinc Research indicates that Option B:
3
Discharge to Land has a low feasibility of working during wet periods with 7,000 m /day inflow but will be
3
feasible under average conditions of 3,000m /day. During wet periods with peak wastewater inflow and
discharge there is also high groundwater at the disposal site. This significantly limits land disposal
during those times. An alternative discharge is required during these wet periods. During the wet 2008
year high inflows and groundwater last up to 66 days.
In normal conditions, around 3,000m³/day, land application via RIB appears viable (using conservative
data). The proposed first RIB will determine the RIB spacing requirement and monitoring and testing will
better define the hydraulic loading rate. It is not possible to computer model this due to vertical and
horizontal variation in the aquifer and neighbouring south channel. The hydrogeological work to dates
indicates RIB spacing and hydraulic loading can only be better defined through operation of a full scale
RIB.
Status: Final
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Treatment and Discharge Options
In summary 100% land disposal is difficult at the current Motueka WWTP site.
The Working Party agreed on the need to go ahead with the first RIB to determine the final RIB spacing
and whether there is a 100% land disposal solution as a commitment to iwi and the working party
objectives.
Key questions and points raised were;


Why not treat to a higher standard and discharge to surface waters?
A mix of land disposal and match of surface water discharge when conditions are unsuitable is
used elsewhere on similar difficult sites such as Blenheim treated wastewater disposal.
Further consultation with iwi is required to examine Option E: Mix and Match including ways to address
and mitigate the cultural affront for direct discharge to surface waters such as additional treatment or
land passage.
There is an overarching need to improve the treatment and current discharge for public health reasons
and make progress toward the goal of land disposal.
Furthermore the cost of sludge removal, dewatering and disposal to land is expensive and alternatives
need to be investigated to reduce this cost.
The Working Party agreed in principle with Stages 1 to 4 prior to committing to other stages. Land
disposal as a solution should be exhausted. The recommendation to the Council should include the cost
estimates.
Status: Final
Project No.: 80501061
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Treatment and Discharge Options
7
Working Party Recommendation to Council
The Working Party recommends the following actions to the Tasman District Council;
1) That the Council accepts in principle Option E “Mix and Match of Options B and C” treatment and
discharge initially, with staged construction of land disposal.
2) That the Council budgets for staging of the upgrades as outlined in Table 7-1 below.
Table 7-1: Staging of Upgrade to Maximise Discharge to Land via RIB
Stage
Scope
Discharge
Indicative Capital
5
Cost
Timing
1
Desludge oxidation pond
Existing
$2.6M
2013-2014
2
Modify oxidation pond, install solids removal and UV
Existing
$4.1M
2014
3
Install prototype RIB
RIB + Existing
~$0.6M
2015
4
Observe prototype RIB performance and
environmental effects
RIB + Existing
TBC
2015-2016
Decision point
5
Install additional RIBs. Observe RIB performance and
environmental. effects
RIB + Existing
$4.3M
(~$0.6M per RIB)
2017-2018
6
Install storage pond and tidal discharge
RIB + tidal
>$1.3M
2016
3) That the Council considers the necessity for further upgrades to the treatment and discharge of
treated wastewater, once Stages 1 to 4 above have been implemented.
4) That the Council implement a consultation strategy as detailed below:








5
Preferred option and strategy recommended by Working Party 19 February 2013
Council Engineering Services Committee issue the Council Summary document for public
feedback 28 March 2013
Site inspection by public early May 2013
Open/Information day in Memorial Hall (or other) early May 2013
Three weeks for feedback and follow up 1 June 2013
Report back to Working Party on feedback 11 June 2013
Working Party to recommend preferred option for upgrade to the Council to start formal consent
process
Present Working Party’s recommendation to Council Engineering Service Committee 1 August
2013 for approval to proceed with consenting.
Costs are indicative, prepared for consenting purposes. See basis of indicative costs in Section 3.5.2.
Status: Final
Project No.: 80501061
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Treatment and Discharge Options
Appendix A Schematics of Treatment and
Discharge Options
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Treatment and Discharge Options
Schematic of Motueka WWTP Treatment Options with Discharge to via RIB (Option B), via Tidal Discharge (Option C ), via Bore Injection
(Option D), and ), via Mix and Match of RIB and Tidal Discharge (Option E, ie. Option B + Option C)
Status: Final
Project No.: 80501061
March 2013
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Treatment and Discharge Options
Appendix B
Status: Final
Project No.: 80501061
Layout of Options
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Treatment and Discharge Options
Appendix C
Status: Final
Project No.: 80501061
Concept Sizing
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Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Table C-2: Potential System Sizing Requirements for Motueka WWTP Treatment and Discharge Options
Pond Option T2
Aeration, Ox. Pond, Solids Removal
Treatment
NO3N<5mg/L, NH4N<40mg/L
Inlet Works (existing)
Existing; screening & odour control
Pond Option T3
Aeration, Ox. Pond, Solids
Removal, NTF
Pond Option T4
Aeration, Ox. Pond, Solids Removal,
denit/nitTF
AS Option T4
AS Bioreactor, Flow Balancing
NO3N<30mg/L, NH4N<5mg/L
Inlet Works (existing)
Existing; screening & odour control
NO3N<10mg/L, NH4N<5mg/L
Inlet Works (existing)
Existing; screening & odour control
New bypass to filter for 0.6 MLD
Aeration Basin (existing)
3
Existing: 6,000 m , 2.5m deep (approx.)
Existing; 4x7.5kW surface aerators
Aeration Basin (existing)
3
Existing: 6,000 m , 2.5m deep
(approx.)
Existing; 4x7.5kW surface aerators
Oxidation Pond (existing)
2
Existing: 50,000 m (approx.)
3
60,000 m (operating depth 1.2m)
3
100,000 m (total depth 2m, excl 0.5m
free board)
New inlet and outlet
Modify inlet/outlet to enable flow
balancing to attenuate peak daily flows to
7MLD
Install full width baffle north-south
orientation to improve flow path
Oxidation Pond (existing)
2
Existing: 50,000 m (approx.)
3
60,000 m (operating depth 1.2m)
3
100,000 m (total depth 2m, excl
0.5m free board)
New inlet and outlet
Modify inlet/outlet to enable flow
balancing to attenuate peak daily
flows to 7MLD
Install full width baffle north-south
orientation to improve flow path
Oxidation Pond (existing)
2
Existing: 50,000 m (approx.)
3
60,000 m (operating depth 1.2m)
3
100,000 m (total depth 2m, excl 0.5m free
board)
New inlet and outlet
Modify inlet/outlet to enable flow balancing
to attenuate peak daily flows to 7MLD
Flow Balancing (Existing Ox. Pond)
2
Half existing: 25,000 m (approx.)
3
50,000 m (operating depth 2m, excl
0.5m free board). New full width earthen
wall east-west orientation
Install full width baffle north-south
orientation to improve flow path
1+1 No. Flow balancing pumps, each
7 MLD
Nitrifying Trickling Filter
1+1 No. NTF feed/recycle pumps,
each 5.2 MLD (200% ADF)
1 No. 16m diameter, 4m media
depth
3
Media Volume 805 m
Media Specific Surface Area
2
3
100m /m
0
0
30 day SRT; 7 -24
3
Fan capacity 40 m /min (1.5 PF)
NTF flush to inlet works
Nitrifying/Denitrifying Trickling Filter
1+1 No. NTF feed/recycle pumps, each 8
MLD (300% ADF)
1 No. 20m diameter, 5m media depth
Bioreactor (Existing Aeration Basin)
Aeration Basin (existing)
3
Existing: 6,000 m , 2.5m deep (approx.)
Status: Final
Project No.: 80501061
NO3N<10mg/L, NH4N<5mg/L
Inlet Works (existing)
Existing; screening & odour control
New bypass >3MLD to flow balancing
Existing; 4x7.5kW surface aerators
3
Media Volume 1,570 m
2
3
Media Specific Surface Area 100m /m
0
0
30 day SRT; 7 -24
3
Fan capacity 80 m /min (1.5 PF)
NTF flush to inlet works
Modify existing oxidation pond to enable
side-stream flow balancing in half the
pond to attenuate peak daily flows to
7MLD
Partition existing aeration basin to
create anoxic and aerobic zones
1 No. full-width baffle
0
0
25 day SRT (2021); 10 -24
2,500 mg/L MLSS (2021)
3
1,800 m anoxic, 2.5m deep
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Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Pond Option T2
Aeration, Ox. Pond, Solids Removal
Pond Option T3
Aeration, Ox. Pond, Solids
Removal, NTF
Pond Option T4
Aeration, Ox. Pond, Solids Removal,
denit/nitTF
AS Option T4
AS Bioreactor, Flow Balancing
3
4,200 m aerobic, 2.5m deep
2 No. 5.5kW mixers
3+1 No. 30 kW slow speed surface
aerators
‘A’-Recycle Pumps
300% ADF, 1+1, each 8MLD
Solids Removal Unit (new)
2+1 No. feed pumps, each 3.5 MLD
1 No. proprietary unit
Capacity 7MLD at overflow of 60m/hour
Solids Removal Unit (new)
2+1 No. feed pumps, each 3.5 MLD
1 No. proprietary unit
Capacity 7MLD at overflow of 60m/hour
Clarifier (new)
1 No. 17m diameter
4m sidewater depth
incl. sand-ballasted flocculation and high
rate settler
Solids Removal Unit (new)
2+1 No. feed pumps, each 3.5 MLD
1 No. proprietary unit
Capacity 7MLD at overflow of
60m/hour
incl. sand-ballasted flocculation and
high rate settler
incl. sand-ballasted flocculation and high
rate settler
RAS Pumps
90% ADF, 1+1, each 2.6 MLD
Cationic polymer batching and dosing
unit (13 kg/day)
Sludge returned to oxidation pond
Cationic polymer batching and
dosing unit (13 kg/day)
Sludge returned to oxidation pond
Cationic polymer batching and dosing unit
(13 kg/day)
Sludge returned to oxidation pond
UV Disinfection (new)
(gravity flow from sand ballasted
flocculation unit)
Process capacity: 7MLD; 3.5 MLD per
channel
2 channel, 2 banks (duty/assist)
96 No. LPHO 3” spacing UV lamps
UV Disinfection (new)
(gravity flow from sand ballasted
flocculation unit)
Process capacity: 7MLD; 3.5 MLD
per channel
2 channel, 2 banks (duty/assist)
96 No. LPHO 3” spacing UV lamps
UV Disinfection (new)
(gravity flow from sand ballasted
flocculation unit)
Process capacity: 7MLD; 3.5 MLD per
channel
2 channel, 2 banks (duty/assist)
96 No. LPHO 3” spacing UV lamps
UV Disinfection (new)
2+1 No. UV feed pumps, each 3.5 MLD
Discharge (Representative Option E)
Storage & Discharge Pumps (new)
Storage & Discharge Pumps (new)
Storage & Discharge Pumps (new)
Storage & Discharge Pumps (new)
Status: Final
Project No.: 80501061
Sludge discharged to sludge storage
pond
Sludge Storage Pond (existing)
2
Half existing oxidation pond: 25,000 m
(approx.)
3
50,000 m (operating depth 2m, excl
0.5m free board, incl 0.5m surface
water layer to limit odour)
Supernatant pumped back to inlet works
Process capacity: 7MLD; 3.5 MLD per
channel
2 channel, 2 banks (duty/assist)
96 No. LPHO 3” spacing UV lamps
March 2013
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Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Pond Option T2
Aeration, Ox. Pond, Solids Removal
3
Pond Option T3
Aeration, Ox. Pond, Solids
Removal, NTF
3
Pond Option T4
Aeration, Ox. Pond, Solids Removal,
denit/nitTF
3
AS Option T4
AS Bioreactor, Flow Balancing
3
1 No 2,700 m (9h @ 7MLD)
1 No. 40m x 45m
1.5m sidewall depth
0.5m freeboard
Discharge Pumps (RIB+Outfall)
2+1 No., each 10 MLD
1 No 2,700 m (9h @ 7MLD)
1 No. 40m x 45m
1.5m sidewall depth
0.5m freeboard
Discharge Pumps (RIB+Outfall)
2+1 No., each 10 MLD
1 No 2,700 m (9h @ 7MLD)
1 No. 40m x 45m
1.5m sidewall depth
0.5m freeboard
Discharge Pumps (RIB+Outfall)
2+1 No., each 10 MLD
1 No 1,900 m (9h @ 5MLD)
1 No. 40m x 35m
1.5m sidewall depth
0.5m freeboard
Discharge Pumps (RIB+Outfall)
2+1 No., each 10 MLD
RIBs (new)
8 No. 120 x 27m
1m sidewall depth below ground
1.5m sidewall depth above ground
RIB (new)
8 No. 120 x 27m
1m sidewall depth below ground
1.5m sidewall depth above ground
RIB (new)
8 No. 120 x 27m
1m sidewall depth below ground
1.5m sidewall depth above ground
RIB (new)
8 No. 120 x 27m
1m sidewall depth below ground
1.5m sidewall depth above ground
River Outfall (new)
Outlet structure
Manual high level overflow (emergency)
River Outfall (new)
Outlet structure
Manual high level overflow
(emergency)
River Outfall (new)
Outlet structure
Manual high level overflow (emergency)
River Outfall (new)
Outlet structure
Manual high level overflow (emergency)
2021 Sludge
Pond Sludge: 250 kg DS/day (~10%
settled)
TF Sludge: <30 kg DS/day (~4%
settled)
Sand ballasted flocculation Sludge:
250 kg DS/day (~4% settled)
1+1, each 7 MLD
2021 Sludge
Pond Sludge: 200 kg DS/day (~10%
settled)
TF Sludge: 300 kg DS/day (~4% settled)
2021 Sludge
Pond Sludge: nil
Sludge Handling
2021 Sludge
Pond Sludge: 250 kg DS/day (~10%
settled)
Sand ballasted flocculation Sludge: 250
kg DS/day (~4% settled)
1+1, each 7 MLD
Status: Final
Project No.: 80501061
Sand ballasted flocculation Sludge: ~200
kg DS/day (~4% settled)
1+1, each 7 MLD
Bioreactor: 600 kg DS/day (~3%
settled)
1+1, each 7 MLD
March 2013
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Motueka Wastewater Treatment Plant Upgrade
Treatment and Discharge Options
Appendix D
Status: Final
Project No.: 80501061
Risk Assessments
March 2013
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