Evaluation of Stormwater BMP Alternatives in the Malden River Watershed
ARCHIVES
by
MASSACHU'ET NFTITT
OF ILECHNULLG~Y
Mia Smith
JUL 02 2015
B.S. Environmental Engineering
University of Southern California, 2014
LIBRARIES
SUBMITTED TO THE DEPARTMENT OF CIVIL AND ENVIRONMENTAL
ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF
MASTER OF ENGINEERING IN CIVIL AND ENVIRONMENTAL ENGINEERING
AT THE
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
JUNE 2015
C 2015 Mia Smith. All rights reserved.
The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic
copies of this thesis document in whole or in part
in any medium now known or hereafter created.
Signature redacted
Signature of Author:
Department of Civil and Environmental Engineering
May 8, 2015
Certified by:
Signature redacted..
David Langseth
Senio,(Lecturer of Civil and Environmental Engineering
I
Thesis Advisor
Signature redacted_______
Harry Hehmond
William E. Leonhard (1940) Professor of Civil and Environmental Engineering
Thesis Advisor
Accepted by:
____Signature
redacted
f %
f
_
_
Heidi Nepf
Donald and Martha Harleman Professor of Civil and Enviromental Engineering
Chair, Graduate Program Committee
Evaluation of Stormwater BMP Alternatives in the Malden River Watershed
by
Mia Smith
Submitted to the Department of Civil and Environmental Engineering
on May 8, 2015 in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering in
Civil and Environmental Engineering
ABSTRACT
Stormwater runoff degrades urban streams through a variety of hydrologic and water quality
changes. Green infrastructure is one alternative to traditional methods of stormwater
management. This report evaluates the feasibility of four green infrastructure Best Management
Practices (BMPs) in the Malden River watershed. The WERF BMP SELECT model was used to
generate performance and cost data for bioretention systems, swales, permeable pavement, and
constructed wetlands in a portion of the Malden River watershed. Due to space constraints,
bioretention systems and swales were found to have limited applicability within the streets of the
study site. Permeable pavement was 5 to 70 times more expensive than the other BMP
alternatives. Wetlands were found to be the most cost-effective alternative. A 5.3 acre wetland
would cost $3.9 million and provide 50% Total Phosphorus reduction, 57% Total Suspended
Solids reduction, and 33% flow reduction. However, limited land availability constrains the
development of a wetland within the study site.
Thesis Supervisor: David Langseth
Title: Senior Lecturer of Civil and Environmental Engineering
Thesis Supervisor: Harry Hehmond
Title: William E. Leonhard (1940) Professor of Civil and Environmental Engineering
2
ACKNOWLEDGEMENTS
I would like to thank my advisors, Dr. David Langseth and Dr. Harold Hehmond for their
guidance. This thesis could not have been accomplished without their direction and support.
I would also like to thank the Mystic River Watershed Association, Friends of the Malden River,
the City of Malden Engineering Department, and the Everett Police Department for their
cooperation and assistance.
I am forever grateful for my parents and their love. Thank you Maggie and Sara for your
friendship.
3
TABLE OF CONTENTS
CHAPTER 1: BACKGROUND ................................................................................................................
1.1. INTRODUCTION ..............................................................................................................................
1.2. GEOGRAPHY OF THE M ALDEN RIVER .........................................................................................
8
8
8
1.3.
INDUSTRIAL LEGACY AND URBAN ENVIRONM ENT .....................................................................
10
1.4.
SEW ER SYSTEM.............................................................................................................................
REGULATORY FRAM EW ORK .........................................................................................................
COM M UNITY EFFORTS .................................................................................................................
M ITW ORK....................................................................................................................................15
THESIS STRUCTURE .......................................................................................................................
10
13
14
1.5.
1.6.
1.7.
1.8.
CHAPTER 2 : STORM WATER RUNOFF ............................................................................................
2.1. OVERVIEW OF NON-POINT SOURCE POLLUTION ......................................................................
15
16
16
2.2.
IM PACTS OF URBANIZATION: URBAN RUNOFF ........................................................................
16
2.3.
PREVIOUS STUDIES OF URBAN RUNOFF QUALITY ....................................................................
20
CHAPTER 3 : STORM W ATER M ANAGEM ENT ..................................................................................
GREY AND GREEN INFRASTRUCTURE .......................................................................................
3.1.
3.2 TYPES OF GREEN INFRASTRUCTURE .........................................................................................
GREEN INFRASTRUCTURE EVALUATION M ODELS ....................................................................
3.3.
.......
3.4. W ERF BM P SELECT M ODEL ................................................................................
22
22
23
25
25
CHAPTER 4 : M ETHODS ....................................................................................................................
4.1. OVERVIEW OF M ETHODS .............................................................................................................
4.2. STUDY SITE....................................................................................................................................
4.3. DECENTRALIZED APPROACH: BM PS IN PUBLIC STREETS ...........................................................
4.4. CENTRALIZED BM P: CONSTRUCTED W ETLAND ........................................................................
4.5. SELECT PARAM ETERS ...................................................................................................................
4.6. CALIBRATION OF FLOW ESTIM ATES .............................................................................................
30
30
30
31
39
40
41
CHAPTER 5: RESULTS.......................................................................................................................42
5.1. BM P EVALUATION BASED ON 10-YEAR RAINFALL DATA ...........................................................
5.2. RESULTS OF CALIBRATION ............................................................................................................
5.3. CONCLUSIONS ..............................................................................................................................
5.4. OTHER CONSIDERATIONS AND FUTURE RESEARCH ..................................................................
42
48
49
49
BIBLIOGRAPHY.................................................................................................................................50
APPENDIX A. DEFAULT PARAMETERS WITHIN THE WERF BMP SELECT MODEL................................53
54
A.1. DEFAULT EM CS FOR LAND USES IN THE BM P SELECT M ODEL ...................................................
54
A.2. DEFAULT EM Cs FOR VARIOUS BM PS IN THE BM P SELECT M ODEL ............................................
54
A.3. DEFAULT COST PARAM ETERS IN THE BM P SELECT M ODEL .......................................................
4
55
APPENDIX B. BIORETENTION AND SW ALE FEASIBILITY: BM P W IDTHS .............................................
B.1. M INIM UM W IDTH STANDARDS FOR ROADW AYS AND SIDEW ALKS.............................................56
B.2. DESIGN SPECIFICATIONS FOR BMPS......................................................................................... 56
B.3. M INIM UM W IDTH REQUIREMENTS FOR BMPS........................................................................ 56
57
B.4. CALCULATION OF AVAILABLE STREET W IDTHS ........................................................................
APPENDIX C. BM P PERFORMANCE AND COST RESULTS ..................................................................
C.1.
BIORETENTION POLLUTION REDUCTION...................................................................................61
C.2.
C.3.
C.4.
C.5.
C .6 .
C.7.
C.8.
C.9.
C.10.
C.11.
C.12.
C.13.
C.14.
BIORETENTION FLOW REDUCTION...............................................................................................62
BIORETENTIO N COSTS ..................................................................................................................
SW ALE POLLUTION REDUCTION................................................................................................64
SW ALE FLOW REDUCTION............................................................................................................65
SW A L E C O ST S ...............................................................................................................................
PERMEABLE PAVEMENT POLLUTION REDUCTION (PER M ILE) ................................................
PERM EABLE PAVEMENT FLOW REDUCTION (PER MILE) ...........................................................
PERM EABLE PAVEMENT COSTS (PER M ILE)...............................................................................
PERMEABLE PAVEMENT COMPARISONS TO OTHER BMPs........................................................
5.3 ACRE W ETLAND POLLUTION REDUCTION...........................................................................
5.3 ACRE W ETLAND FLOW REDUCTION .....................................................................................
5.3 ACRE W ETLAND COSTS ...........................................................................................................
W ETLAN D COM PARISONS TO OTH ER BM Ps.............................................................................
60
63
66
67
67
67
68
69
69
69
70
5
LIST OF FIGURES
Figure 1-1. Malden River Sub- Watershed.................................................................................
Figure 1-2. Geography Surrounding the Malden River ..............................................................
8
Figure 1-3. Malden River Stormwater Outfall Locations............................................................
9
7
Figure 1-4. SSO Map#15: Reported SSOs in The Malden River Watershed............................
Figure 1-5: SSO Map #16: Reported SSOs in the Malden River Watershed ............................
11
Figure2-1. Hydrographsfor Urban and Non-Urban Streams..................................................
17
Figure4-1. Study Site within the Malden Watershed ................................................................
30
33
Figure 4-2. Streets with BMP Feasibility.................................................................................
12
Figure 4-3. Typical Sidewalk Configuration within the Study Site ..........................................
Figure 4-4. FerrySt Sidewalk Configurationwith Existing GrassedArea..............................
34
35
Figure 5-1. TP Reduction for Various BMPs Across the Study Site.........................................
Figure 5-2. Cost per Kg of TP Removedfor Various BMPs .....................................................
46
47
6
LIST OF TABLES
Table 1-1. Surface Water Quality Standardsfor ClassB Warm Waters..................................
Table 1-2. Water Quality Impairment Causes on the Malden River ........................................
13
14
Table 2-1. Hydrologic Impacts From Increases in Impervious Surfaces ..................................
Table 2-2. Comparison of Median Stormwater Quality ForNURP and NSQD .......................
Table 3-1. Bioretention PollutantRemoval Efficiencies............................................................
18
21
23
Table 3-2. Swale PollutantRemoval Efficiencies ......................................................................
Table 3-3. Permeable Pavement PollutantRemoval Efficiencies ............................................
Table 3-4. Wetland PollutantRemoval Efficiencies ..................................................................
24
24
Table 3-5. Stormwater BMPs Simulated in SELECT.................................................................
Table 3-6. Water Quality ParametersSimulated in SELECT....................................................
Table 3-7. SELECT PredictionsCompared with Observed PerformanceData.
26
26
Saylor Grove Wetland, Philadelphia.........................................................................
Table 3-8. SELECT PredictionsCompared With Actual Cost Data.
Saylor Grove Wetland, Philadelphia.........................................................................
27
Table 4-1. Characteristicsof the Study Site................................................................................
Table 4-2. Breakdown of Land Uses within the Study Site .......................................................
Table 4-3. Street Segments with BMP Feasibility....................................................................
25
27
31
31
33
Table 4-4. BMP Width Designs ................................................................................................
Table 4-5. Sum m ary of BMP Sizes............................................................................................
36
38
Table 5-1. Annual Runoff Characteristicsof the Study Site .....................................................
Table 5-2. Bioretention vs. Swale Systems of Equal Surface Area...........................................
Table 5-3. Bioretention vs. Swale Systems: Results Across Entire Study Site...........................
Table 5-4. TP Reduction Equivalents OfBioretention and Swale Systems Across the Study Site
42
42
Table 5-5. Results of PermeablePavement PerMile of ParkingLane Replaced .....................
Table 5-6. Results of Wetland Sized to Treat Entire Study Site.................................................
Table 5-7. PermeablePavement Required to Attain TP Reduction
44
Equivalent of 5.3 acre W etland.................................................................................
Table 5-8. Total Reduction Potentialsfor Various BMPS across the Study Site ......................
Table 5-9. Comparisonof BMP Costs ......................................................................................
45
Table 5-10. Runoff Volumes Predictedby SELECT and SWMM Models.................
48
43
44
45
46
47
Table 5-11. Total PhosphorusReduction Percentagesfor an Individual BMP ....................... 48
Table 5-12. Total Suspended Solids Reduction Percentagesfor an IndividualBMP ............... 48
7
CHAPTER 1 : BACKGROUND
1.1.
INTRODUCTION
The Malden River, located in the Greater Boston area, has an extensive history of industrial
activity and urbanization along its banks. Centuries of abuse by these activities have reduced the
river to a degraded condition and led to concern about the River's ecological health and its
suitability for recreational use. Over the past few decades, the communities surrounding the
Malden River have been interested in improving its conditions. This thesis presents one portion
of a joint MIT effort to provide the community with further scientific information about the
Malden River. Studies include a bacterial risk assessment, a hydrological runoff model and
investigation of sediment contamination. A further description of these other studies can be
found in Section 1.6. This report focuses specifically on the evaluation of stormwater Best
Management Practice (BMP) alternatives to mitigate the effects of urban runoff into the Malden
River.
1.2.
GEOGRAPHY OF THE MALDEN RIVER
The Malden River is located within the 76-square-mile Mystic River Watershed in the Greater
Boston area of Massachusetts. Within the Mystic River Watershed, the Malden River SubWatershed covers 11 square miles in the towns of Everett, Malden, Medford, Wakefield,
Stoneham and Melrose (Figure 1-1).
Eastern
MA
Stoneham
't~
-~-
Melrose
Maiden
Medford
Legend
Study Area Outlet Location
TownBoundanes
-----
Subwatershed'
I
I
Sara Greenberg
Civil & Enviornmental MEng. 2015
Massachusetts Institute of Technology
Map by:
0
1.050
2,100
4.200
Meters
FIGURE 1-1. MALDEN RIVER SUB-WATERSHED
*Delineates the portion of the Malden River watershed that flows directly into the Outlet Location
Source: ArcMap 10.2.2 (2010)
8
Much of the Malden River flows beneath the surface and out of view. The River begins at Spot
Pond in the Middlesex Fells Reservation (Figure 1-2) and flows completely covered beneath the
cities of Melrose and Malden. The River re-surfaces from two stormwater culverts near the
center of Malden (shown circled in red in Figure 1-3). From the two culverts, the Malden River
flows aboveground for two miles, before discharging into the Mystic River. The Amelia Earhart
Dam is located a short distance downstream of where the Malden and Mystic Rivers converge.
Maid"n
Medf ni
FIGURE 1-2. GEOGRAPHY SURROUNDING THE MALDEN RIVER
Source: Google Maps (2015)
FIGURE 1-3. MALDEN RIVER STORMWATER OUTFALL LOCATIONS
Source: Nangle Associates (2014)
9
1.3.
INDUSTRIAL LEGACY AND URBAN ENVIRONMENT
The Malden River has a long legacy of abuse due to industrial activity (U.S. Army Corps of
Engineers 2008). During the Industrial Revolution, the River provided an essential means of
transportation and waste disposal for chemical, coal gasification, and other manufacturing plants.
In order to support these industries, much of the existing wetlands were dredged and filled to
straighten the river channels. Many of these historical activities have resulted in the release of oil
and hazardous materials (OHM) into the River. These contaminants include fuel by-products,
volatile organic compounds, and various metals, which can leach into the groundwater or
directly contaminate the River through natural hydrological pathways. Although many of the
industrial plants were relocated after World War 1I, industrial waste and dredged materials still
remain.
The surrounding towns of Malden, Medford and Everett have continued to develop since the
Industrial Revolution, creating an increasingly urbanized environment in the Malden River
watershed. Urban environments are characterized by large areas of impervious surfaces, such as
roadways, buildings, and parking lots, which prevent natural ground infiltration of rainfall.
Instead of percolating through the ground, rainfall runs into the storm drainage system and
eventually into the River, which increases the frequency and intensity of flooding in extreme
stormwater events. This increased volume of stormwater runoff can cause a variety of
environmental problems, including increased erosion and reduced base flows into the River.
These reduced base flows result in low water velocities and poor mixing conditions between
storm runoff events, which ultimately contribute to high bacteria concentrations in the Malden
River (Herron 2014). Other water quality concerns arise as urban pollution contaminates the
runoff before it discharges into the River.
Just downstream of where the Mystic and Malden Rivers converge, the Amelia Earhart Dam
controls the flow of the Malden River (U.S. Army Corps of Engineers 2008). The construction of
the dam has greatly changed the natural flushing of the River, leading to stratification and
depleted dissolved oxygen concentrations. These conditions have hindered the growth of a
healthy ecosystem in the Malden River.
1.4.
SEWER SYSTEM
All of the municipalities surrounding the Malden River have separate storm water and sewage
systems. Therefore there is no risk of Combined Sewer Overflows (CSOs) discharging into the
Malden River.
However, there have been incidents of the sanitary sewer systems around the Malden River
overflowing during extreme wet weather conditions. Under extreme weather conditions,
groundwater or stormwater can enter the sewer system at vulnerable points (such as blockages or
line breaks) and cause sewage to overflow downstream (US EPA 2014b). Figure 1-4 and 1-5
show the locations of reported SSO incidents that have occurred in the Malden River watershed.
Point 1+26 in Figure 1-5 shows the only known SSO that directly discharged into the Malden
River. This event occurred on March 29, 2010 and discharged over 1 million gallons of raw
sewage into the River (MADEP 2015).
10
ZO'
SSO map#: 15
FIGURE 1-4. SSO MAP#15: REPORTED SSOS IN THE MALDEN RIVER WATERSHED
Source: MWRA (2015)
11
-
oO
Location of SW
s
SSO map #. 16
FIGURE 1-5: SSO MAP #16: REPORTED SSOS IN THE MALDEN RIVER WATERSHED
Source: MWRA (2015)
12
1.5.
REGULATORY FRAMEWORK
The Massachusetts Surface Water Quality Standards (314 CMR 4.00) categorize the Malden
River as a Class B warm water. Class B waters are designated as "a habitat for fish, other aquatic
life, and wildlife", for "primary and secondary contact recreation" and for irrigation, agricultural
and industrial process uses. Class B waters should also have "consistently good aesthetic value"
(MADEP 2014). The standards that apply to the Malden River are summarized in Table 1-1.
TABLE 1-1. SURFACE WATER QUALITY STANDARDS FOR CLASS B WARM WATERS
Parameter
Class B Standard
Dissolved Oxygen
>5.0 mg/l
Where natural background conditions are lower, DO shall not be less than natural
background conditions.
Temperature
<83 0 F
The rise in temperature due to a discharge shall not exceed 5-F
pH
6.5-8.3
No more than 0.5 units outside of the natural background range.
.r
Bacteria
Bathing (non-bathing): E.coli as indicator - geometric mean of five most recent samples
taken during the same bathing season (within the most recent six months) shall not exceed
126 colonies per 100 m and no single sample shall exceed 235 colonies per 100 ml
Bathing (non-bathing): Enterococci as indicator- geometric mean of five most recent
samples taken during the same bathing season (within the most recent six months) shall not
exceed 33 colonies per 100 m and no single sample shall exceed 61 colonies per 100 ml
Solids
Shall be free from floating, suspended and settleable solids in concentrations and
combinations that would impair any use assigned to this Class, that
would cause aesthetically objectionable conditions, or that would impair the benthic biota or
degrade the chemical composition of the bottom.
Color and Turbidity
Shall be free from color and turbidity in concentrations or combinations that are aesthetically
objectionable or would impair any use assigned to this Class.
Oil and Grease
These waters shall be free from oil, grease and petrochemicals that
produce a visible film on the surface of the water, impart an oily taste to the water or an oily
or other undesirable taste to the edible portions of aquatic life, coat the banks or bottom of
the water course, or are deleterious or become toxic to aquatic life.
Taste and Odor
None in such concentrations or combinations that are aesthetically
objectionable, that would impair any use assigned to this Class, or that would cause tainting
or undesirable flavors in the edible portions of aquatic life.
12
Natural seasonal and daily variations that are necessary to protect existing and designated uses shall be maintained.
Source: MADEP (2014)
Currently, the Malden River is not in compliance with these surface water quality standards
(MADEP 2013). Section 303(d) of the Clean Water Act requires each state to publish a list of
water bodies that do not meet state water quality standards. In compliance with this mandate, the
Malden River is included on the Massachusetts' 303(d) list. The specific causes of impairment
are listed in Table 1-2 below.
13
TABLE 1-2. WATER QUALITY IMPAIRMENT CAUSES ON THE MALDEN RIVER
Malden River Impairment Causes
(Debris/Floatables/Trash*)
PCB in Fish Tissue
Chlordane
Phosphorus (Total)
DDT
Secchi disk transparency
Dissolved oxygen saturation
Secchi disk transparency
Escherichia coli
Sediment Bioassays -- Chronic Toxicity
Fecal Coliform
Freshwater
Foam/Flocs/Scum/Oil Slicks
Taste and Odor
High pH
Total Suspended Solids (TSS)
Oxygen, Dissolved
TMDL not required (Non-pollutant)
This table is in agreement with the version in the proposed 2014 IntegratedList of Waters report.
Source: MADEP (2013)
*
After identifying the impaired water bodies, each state is also required to establish priorities for
development of Total Maximum Daily Loads (TMDL) that specify "the maximum amount of a
pollutant that a water body can receive and still meet water quality standards" (MADEP 2014).
Massachusetts's current schedule for TMDL development makes no specific reference to the
Malden River. However, the Malden River is included under a broader priority to develop
watershed wide bacteria TMDLs for Boston Harbor. Final EPA approval of Boston Harbor
bacteria TMDLs is expected to occur in Fiscal Year 2015.
1.6.
COMMUNITY EFFORTS
In response to the Malden River's degraded water quality, there has been a growing community
effort to transform the River into a healthy ecosystem that can provide recreational space to the
public. Some key organizations leading this effort include the Mystic River Watershed
Association, Friends of the Malden River, and the Army Corps of Engineers.
The Mystic River Watershed Association (MyRWA) works to protect the entire Mystic River
watershed through advocacy, outreach and education, water quality monitoring, and restoration
efforts. MyRWA manages an extensive water quality monitoring program across the Mystic
River Watershed, including a sampling site on the Malden River at which samples have been
collected since July 2000.
Friends of the Malden River (FOMR) is a community group that champions environmental
conservation of the Malden River. FOMR advocates for an improved river ecosystem, focusing
directly on water quality, public access, outreach, and youth involvement (FOMR 2015).
The Army Corps of Engineers (ACE) (2008) evaluated several strategies for ecosystem
restoration along the Malden River. The ACE expressed concern about the potential for toxic
pollution in the sediments of the Malden River, which would seriously threaten the local
ecosystems and potentially inhibit recreational use of the River. The ACE published a report
which includes an environmental assessment of the Malden River, an analysis of several
14
restoration activities, and a recommended plan for ecosystem restoration. The plan recommends
the creation of a wetland habitat through the removal of invasive plant species and the deposition
of sand and gravel in various areas along the Malden River. These activities aim to reduce the
inflow of contaminated sediments, groundwater, and urban stormwater runoff, which have all
been identified as major sources of water contamination on the Malden River.
1.7.
MIT WORK
Several MIT studies were conducted to provide the communities surrounding the Malden River
with a better understanding of its current state. This report presents an evaluation of alternatives
to manage stormwater along the River. Other studies include a microbial risk assessment, a
hydrologic runoff model, and an investigation of sediment contamination. Brief summaries of
these studies are presented below.
HYDROLOGIC RUNOFF MODEL
The hydrology of a portion of the Malden River watershed was modeled using the
Environmental Protection Agency's Stormwater Management Model (SWMM) (Greenberg
2015). The model quantifies volume and flow rates of rainfall runoff as it travels across the
watershed, through the drainage system, and into the River.
MICROBIAL RISK ASSESSMENT
A microbial risk assessment was conducted to determine the risks of recreational use of the
Malden River (Jacques 2015). Rainfall and water quality data were analyzed to determine the
risk of illness assumed by recreational users of the Malden River.
INVESTIGATION OF SEDIMENT CONTAMINATION
Investigations of the sediment contamination of the Malden River were conducted (Sylman
2015; Khweis 2015; Oehmke 2015). Sediment quality data was used to calculate the potential
concentration distributions of various contaminants in the Malden River. The potential for
sediment suspension into the water column was also calculated. Further, this information was
used to conduct a preliminary risk assessment of sediment exposure during recreational
activities.
1.8.
THESIS STRUCTURE
This report evaluates alternatives to manage stormwater runoff along the Malden River. Chapters
2 and 3 provide background on the problems associated with urban stormwater runoff and the
various management options that can be used to mitigate its effects. Chapter 4 describes the
methods used to evaluate the feasibility and performance of stormwater management practices
within the Malden River watershed. Results from the evaluation are presented in Chapter 5.
15
CHAPTER 2: STORMWATER RUNOFF
2.1.
OVERVIEW OF NON-POINT SOURCE POLLUTION
The Clean Water Act (the common name for the 1972 Federal Water Pollution Control Act and
its 1977 and 1983 amendments) set the basic structure of water quality regulations in the United
States by making it illegal to discharge any pollutant from a point source into US waters without
a permit. In this context, a point source is defined as any "discernible, confined and discrete
conveyance", such as a pipe or tunnel (33 U.S.C. 1362(14)). Through this legislation, the Clean
Water Act was successful in significantly reducing point source pollution in America by the mid
1980s (EPA 1984).
Following this reduction in point source pollution, non-point source pollution came under
national attention as the next major water quality concern in America. Non-point source
pollution is generated when rainfall picks up pollutants as it moves over the ground (EPA
2015b). Unlike point source discharges, which can be easily identified and controlled, non-point
source pollution originates from many diffuse sources which can vary significantly over time in
flow and concentration (NOAA 2015b). These characteristics make non-point source pollution a
more difficult problem to address and the consequences of non-point source pollution continue to
be pervasive. The EPA highlighted this concern in a 1984 report to Congress, citing that "six out
of the ten EPA regions assert non-point source pollution as the principal remaining cause of
water quality problems" (EPA 1984).
2.2.
IMPACTS OF URBANIZATION: URBAN RUNOFF
This thesis focuses specifically on urban runoff, which is the second leading source of non-point
source pollution in the United States (EPA 1984). Distinct from other types of non-point source
pollution such as agricultural runoff, urban runoff is generated when rain flows across
impermeable surfaces of an urban landscape (e.g. roofs, lawns, streets). Impermeable surfaces
generate urban runoff by inhibiting the natural infiltration of water through soils. The decreased
infiltration and increased surface runoff initiate "synergistic interactions of many detrimental
factors" that significantly degrade stream quality (Klein 1979). The following two sections will
discuss the negative hydrologic and water quality impacts of urban runoff.
According to Klein, the impact of urban runoff on stream quality is first evidenced when
watershed imperviousness reaches 12% (1979). For the most sensitive stream ecosystems, stream
quality degradation can be seen at watershed imperviousness as low as 10%. Stream quality
continues to degrade as imperviousness increases and becomes severe once watershed
imperviousness reaches 30%.
HYDROLOGIC CONCERNS
Urban runoff generated by increased watershed imperviousness changes the natural hydrology of
an ecosystem, resulting in a variety of detrimental effects. Increased volumes of runoff travel
across surfaces with higher velocities (Strassler, Pritts, and Strellec 1999). This can be seen
clearly in Figure 2-1, which compares stormwater discharges from before and after urban
16
development. The post-development discharges arrive earlier and have much higher peak flow
volumes. This increases the frequency and volume of bankfull flows, altering natural landscapes
and habitats (CWP 2003).
16glr and Mor-
Large
Storm
\
Rapid P,.k Discharge
Pr-devlopment
small
Post -develtoPmIt
Small
Storm
More
Runo# Volume
Lower and Less
Rapod Ptak
0
-J
TiME
-e
FIGURE 2-1. HYDROGRAPHS FOR URBAN AND NON-URBAN STREAMS
Source: CWP (2003)
Additionally, the increased volume and velocity of runoff exacerbates erosion throughout a
watershed (CWP 2003). Increased erosion further degrades natural habitats by widening channel
widths and reducing vegetative cover along stream banks. Erosion also increases sediment loads
in streams, degrading water quality in a variety of ways. The water quality impacts of sediments
are discussed later.
In addition to the problems associated with increased runoff, watershed imperviousness also
degrades ecosystems by preventing natural infiltration. Under natural conditions in many
locations, a significant portion of rainfall that infiltrates through the ground recharges
groundwater aquifers that provide base flows to nearby streams and rivers. Therefore, the
reduction in infiltration caused by urban development can reduce base flows in nearby rivers
(CWP 2003). Base flows can be reduced to as low as 10% of regional averages as watershed
imperviousness reaches 65% (Klein 1979). Rivers with such low flows are not suitable
environments for aquatic life due to impaired navigability and increased temperature
fluctuations.
17
; ,
,.
ULLm
, , ;-
-
-1
TABLE 2-1. HYDROLOGIC IMPACTS FROM INCREASES IN IMPERVIOUS SURFACES
Increased
I
topeream
Leads te:
Increased V61ome
Rulng
Fboding
Habitat Ios
Impacts
Channel
Ere.on
Stream bed
a
Wir
V
Ve
Increased Peak
e
le
of
e
of
V
V
V
Fisw
V
Increased Peak
Duratimn
Increased Stream
V
Temp.
Decreased Base
Flow__
Changes inV
sedment Lding
V
_
V
_
__
_
V
V
Source: Strassler, Pritts, and Strellec (1999)
WATER QUALITY CONCERNS
In addition to hydrologic changes, increased urban runoff also causes serious water quality
issues. Urban runoff carries contamination from a variety of pollutants deposited on urban
surfaces through direct human activities (e.g. construction) and atmospheric deposition (e.g.
automobile exhaust, coal plant emissions) (Shaver et al. 2007). The initial runoff from a rainfall
event, known as the "first flush", washes off pollutants from urban surfaces and transports them
into nearby water bodies (EPA 2000).
The major contaminants of urban runoff include sediment, nutrients, trace metals, chloride,
bacteria, hydrocarbons, and organic materials. The following discusses the sources and impacts
of the major urban runoff pollutants.
Sediment
Sediments constitute the largest portion of pollution in urban runoff (EPA 1990). The primary
source is streambank erosion, which is exacerbated by the increased volume and velocity of
runoff (CWP 2003). The second largest source of sediment is urban surfaces (such as streets,
parking lots, and lawns) which accumulate "exhaust particulates, 'blown on' soil and organic
matter, and atmospheric deposition" (CWP 2003). Street surfaces also directly generate
sediment as a result of wearing due to automobile traffic and road sanding. Construction site
erosion is the third major source of sediment.
Increased sediment loading has a variety of negative impacts on aquatic life. Sediments can
suffocate aquatic life by clogging gills or burying eggs laid on stream beds (CWP 2003).
Sediments also increase turbidity, which interferes with photosynthesis and sight-feeding. In
addition to direct effects, sediments also degrade water quality by providing a "medium for the
accumulation, transport and storage of other pollutants" (Strassler, Pritts, and Strellec 1999).
18
Nutrients
Although nutrients (primarily nitrogen and phosphorus) are naturally occurring essential
elements, they can have negative impacts when found in excessive amounts (CWP 2003).
Nutrient loadings are often attached to sediment. Common sources of nutrients in urban runoff
include chemical fertilizers, failing septic systems, pet waste, and stream bank erosion (Shaver et
al. 2007; CWP 2003). Parking lots and streets are the second largest source of phosphorus and
provide 30% of the nitrogen load in runoff (CWP 2003).
Excessive nutrient loads can result in unwanted eutrophication and depleted dissolved oxygen
levels. Other problems from nutrients include discoloration, odors, and the release of toxins
(EPA 1990).
Metals
Stormwater often contains harmful concentrations of trace metals, such as zinc, copper, lead,
cadmium, and chromium (CWP 2003). These metals, which are primarily the result of industrial
activities and vehicle maintenance, contaminate stormwater from depositions on roads and
parking lots. Metals are often transported via sediments--over half of trace metals in urban
runoff are attached to sediments.
Metals are potentially toxic to aquatic organisms (CWP 2003). Although concentrations of
metals in urban runoff do not generally cause acute toxicity, there is concern for accumulation in
animal tissues and sediments.
Chloride
Road de-icing during the winter results in significant chloride contamination of runoff (Shaver
et al. 2007). Although chloride is essential for life, excessively high concentrations are toxic to
plants and animals.
Bacteria
Sources of bacterial pollution include septic systems, CSO and SSO events, and animal waste
(Shaver et al. 2007). Bacterial contamination can be pathogenic and can result in disease
incidents or death.
Hydrocarbons
Vehicle fuels and lubricants are the source of various petroleum hydrocarbon compounds, such
as polycyclic aromatic hydrocarbons (PAH), oils, and grease (Shaver et al. 2007). Areas with
high-vehicular use (e.g. gas stations, parking lots, roads) are the main source of these
hydrocarbons, which often travel attached to sediment (CWP 2003). Like metals, hydrocarbons
can accumulate in animal tissue and sediments, presenting risk of toxicity to aquatic life.
OrganicCompounds
A variety of organic contaminants can be found in urban runoff, including MBTE and pesticides
(CWP 2003). MBTE is a potentially toxic and carcinogenic gasoline additive present in areas of
high vehicular use. Pesticides, which come from lawns, have similarly harmful effects.
19
In regions with significant snowfall, snowmelt can be a major source of many of the pollutants
listed above (Shaver et al. 2007). During the winter, litter, de-icing chemicals, vehicular
emissions, and atmospheric deposition cause significant buildup of pollution on snow (CWP
2003). Pollutants accumulated over many months can be released in high concentrations during a
few snow melt events (CWP 2003). In some cases, as much as 50% of annual sediment, nutrient,
hydrocarbon and metal loads can be attributed to snowmelt runoff (Oberts et al. 1989).
2.3.
PREVIOUS STUDIES OF URBAN RUNOFF QUALITY
The first comprehensive study of urban runoff water quality was conducted by the EPA through
its Nationwide Urban Runoff Program (NURP) (Shaver et al. 2007). Between 1978 and 1983,
NURP collected stormwater quality data from 2,300 storm events across 28 study-sites in
America. This data was compiled to establish typical water quality values of ten urban runoff
pollutants for several land use categories.
NURP reported water quality data using Event Mean Concentration (EMC) values, which are
calculated by the total mass of pollutants contained in a runoff event divided by the event's total
runoff volume (Shaver et al. 2007). EMC values are generally well represented by a lognormal
probability distribution. Thus, an EMC mean and coefficient of variation can be used to
characterize highly variable water quality data. In this way, EMC values can be used to compare
water quality at multiple sites. They can also be used to estimate the probability of pollutant
concentrations at a site with limited site specific data (Shaver et al. 2007; EPA 1990)
Several studies on stormwater quality have been conducted since NURP. In 1999, the USGS
National Water Quality Assessment (NAWQA) Program compiled data of runoff from 1,100
storm events across 10 metropolitan areas (Shaver et al. 2007). Between the 1970s and 1980s,
the Federal Highway Administration (FHWA) examined runoff from 31 highways in 11 states
and found that roadway runoff has a characteristic signature, due to its high proportion of
pollution from vehicle traffic. The FHWA also found that pollutant concentrations of roadway
runoff increase with average daily traffic (ADT) volume (Shaver et al. 2007).
In 1999, data from various stormwater databases was collected and compared to the NURP
results (Smullen, Shallcross, and Cave 1999). The study found that the results from this updated
pooled database showed lower concentrations of Total Suspended Solids and metals, possibly
resulting from increased sediment control management and the elimination of leaded gasoline
(Shaver et al. 2007). With the exception of these discrepancies, the study generally found the
updated pooled data comparable to the original NURP data (Shaver et al. 2007).
Most recently, the University of Alabama, the Center for Watershed Protection (CWP), and the
EPA have carried out a joint effort to compile the National Stormwater Quality Database
(NSQD) which encompasses NPDES monitoring data from 200 municipalities over ten years
("National Stormwater Quality Database" 2015). The database, which can be accessed online,
provides urban characterization data searchable by land use, state, and other criteria. Table 2-2
compares the original NURP data with data from the NSQD as of 2004.
20
TABLE 2-2. COMPARISON OF MEDIAN STORMWATER QUALITY FOR NURP AND NSQD
WO Paramete
ovwrad
Re__
dend
COmMral
_
_
openspe
NSOD
NUN?
_
_
_
NSOD
NURP
MS0D
NUR
COD (mg/l)
53
65
55
?3
63
5?
21
40
TSS[mg/I)
58
100
48
101
43
69
51
70
30
MW60
NURP
Pb total [ug/)
16
144
12
144
18
104
5
Cu total [ug/J
16
34
12
33
1?
29
5
11
Zn total (ug/I)
116
160
73
135
150
226
39
195
TKN [mg/l]
I.4
I.S
1.4
.9
1.60
1,18
0.60
C.97
N02 + N03 (mg/l]
0.60
0.68
0.60
0.14
0.60
0.5?
0.60
0.54
TP (mg/I]
0.2?
0.33
0.30
0.38
0.22
0.20
0.25
0.12
SRP (mg/I)
0.12
0.12
0.1?
0.14
0.11
0.08
0.08
0.03
COD = Chemical Oxygen Demand
TP = Total Phosphorus
Source: Shaver et al. (2007)
Notes:
TSS= Total Suspended solids
SRP Soluble Reactive Phosphorus
TKN = Total Kjoldahl Nitrogen
21
CHAPTER 3: STORMWATER MANAGEMENT
One method to mitigate the impacts of urban runoff is through the implementation of stormwater
Best Management Practices (BMPs). Stormwater BMPs are a category of pollution control
systems that "manage the quantity and improve the quality of stormwater runoff' (EPA 2014).
3.1.
GREY AND GREEN INFRASTRUCTURE
Stormwater BMPs can be classified into two categories: "grey" and "green" infrastructure. Grey
infrastructure refers to traditional methods of capturing and conveying runoff, such as catch
basins and stormwater drainage networks. In contrast, green infrastructure BMPs mimic natural
processes by strategically using vegetation and soils to integrate urban runoff back into natural
ecosystems (De Sousa, Montalto, and Spatari 2012). By increasing the infiltration, evaporation,
and reuse of runoff, green infrastructure BMPs reduce the volume and treat the quality of urban
runoff near the source. Examples of green infrastructure BMPs include bioretention basins, green
roofs, porous pavements, stormwater planters, and bioswales (US EPA 2014a). Some examples
of applications are presented below.
Green infrastructure has a variety of environmental and operational benefits. In addition to
providing volume reduction and quality treatment, the flexible nature of green infrastructure
design offers a "distributed approach to stormwater management that can be tailored to different
site conditions, including new development and retrofit scenarios" (Madden 2010). Additional
benefits include high returns on investment, short installation time, reduction of greenhouse
gases, as well as the social benefits of enhanced aesthetics and improved green space (Madden
2010; De Sousa, Montalto, and Spatari 2012). Due to these advantages, green infrastructure has
been gaining increased support as an effective way to manage stormwater. Green infrastructure is
officially supported by the EPA and has been successfully demonstrated in several urban
environments across America over the last decade (US EPA 2014a).
GREEN INFRASTRUCTURE CASE STUDY: PHILADELPHIA
The Philadelphia Water District (PWD)'s CSO Control Policy exemplifies the recent success of
green infrastructure systems to manage stormwater. Encouraged by the EPA's National Pollutant
Discharge Elimination System (NPDES) permit program, the PWD devised an integrated longterm plan to manage the city's stormwater. The 25-year plan, titled "Green City Clean Waters",
had a groundbreaking focus on green infrastructure (Madden 2010). The PWD designated 70%
of the plan's $2.4 billion budget specifically for green infrastructure and has been successfully
employing these tools throughout the city since 2009 (Philadelphia Water Department 2009).
GREEN INFRASTRUCTURE CASE STUDY: BOSTON
In Boston, the Charles River Watershed Association's Blue Cities Initiative champions the use of
green infrastructure throughout the Greater Boston area (CRWA 2014). "Blue Cities" uses
historic maps to understand pre-development hydrology and strategically design green
infrastructure that restores natural hydrologic function and enhances public space. Through this
initiative, the CRWA has implemented demonstration projects that effectively treat pollution,
reduce flooding, and enhance the replenishment of natural aquifers.
22
3.2
TYPES OF GREEN INFRASTRUCTURE
There are many different types of green infrastructure, each with their own advantages and
disadvantages. Ultimately, choosing between green infrastructure BMPs depends on the physical
characteristics of the given site, the desired stormwater management objectives, and the project's
budgets.
This report evaluates four different green infrastructure options for the Malden River watershed:
bioretention systems, grassed swales, permeable pavements and constructed wetlands. The first
three are decentralized management options chosen for their ease of implementation within
public streets. Constructed wetlands were chosen as a centralized management alternative to
serve as a comparison to the three decentralized options. The selection of these BMPs is
discussed further in Chapter 4. The following describes applications and benefits of the four
BMPs evaluated in this report.
BIORETENTION
Bioretention systems are shallow depressions strategically filled with soils and vegetation that
treat stormwater runoff (MADEP 2008). Pollutants are removed by filtration through the soils as
well as uptake by microbes and plants. When properly designed, these mechanisms effectively
remove TSS, nutrients, metals, organics, and bacteria. Table 3-1 provides the range of removal
efficiencies reported in the Massachusetts Stormwater Handbook.
TABLE 3-1. BIORETENTION POLLUTANT REMOVAL EFFICIENCIES
Bioretention Pollutant Removal Efficiencies
TSS
90%*
TN
30-50%
TP
30-90%
Metals
40-90%
With adequate pre-treatment such as vegetated filter strip.
Source: MADEP (2008)
*
In addition to pollutant removal, bioretention systems also provide reduction of runoff volumes
via evapotranspiration and infiltration. Bioretention systems have been shown to infiltrate an
inch or more of rainfall (MADEP 2008). They also provide social benefits, including shade,
noise absorption, and improved aesthetics (Penn DEP 2006).
Bioretention systems treat small drainage areas and are thus an attractive alternative for
retrofitting urban sites (EPA 1999). Their flexible design allows for a variety of applications,
including residential sites, parking lots, and street curbs.
23
SWALES
Swales are vegetated open channels designed to manage stormwater, similar to grassed drainage
channels (EPA 2015a). However, grassed drainage channels only provide stormwater
conveyance, while swales are designed to remove pollutants (MADEP 2008). Swales are
designed to slow down runoff, which enhances pollutant removal and flow reduction through
sedimentation and soil filtration. Table 3-2 provides a range of observed swale pollutant removal
efficiencies.
TABLE 3-2. SWALE POLLUTANT REMOVAL EFFICIENCIES
Swale Pollutant Removal Efficiencies
TSS
70%
TN
10-90%
TP
20-90%
Metals
Insufficient Data
Source: MADEP (2008)
Like bioretention systems, grass swales treat small drainage areas and are applicable as
stormwater retrofits (EPA 2015a). Because swales are linear systems, they are well suited to line
roadways and curbs, and to replace existing gutters and drainage systems. In these urban settings,
swales also enhance natural landscapes and provide aesthetic benefits.
PERMEABLE PAVEMENT
Permeable pavements are porous surfaces constructed over storage beds, which provide flow
reduction and pollution removal of stormwater through infiltration (EPA 2015a). Permeable
pavements can infiltrate up to 80% of rainfall. Table 3-3 provides a range of permeable
pavement pollutant removal efficiencies.
TABLE 3-3. PERMEABLE PAVEMENT POLLUTANT REMOVAL EFFICIENCIES
Permeable Pavement
Pollutant Removal Efficiencies
TSS
67-99%
TN
53-72%
TP
34-65%
Metals (Zn)
71-97%
Source: EPA (2015a)
Permeable pavement has a lower load-bearing capacity than traditional pavement and should
only be used to pave surfaces in low-volume areas, such as parking lots, driveways, bicycle
paths, and pedestrian walkways (MADEP 2008). When applicable, permeable pavements are
attractive options for urban watersheds because they do not take up additional land.
24
CONSTRUCTED WETLANDS
Constructed stormwater wetlands are shallow wetlands designed to treat runoff and provide flood
control (MADEP 2008). Stormwater is temporarily stored in pools that provide treatment
through settling, evapotranspiration, and infiltration. Wetland vegetation provides additional
treatment through plant uptake.
TABLE 3-4. WETLAND POLLUTANT REMOVAL EFFICIENCIES
Wetland Pollutant Removal Efficiencies
TSS
80%*
TN
20-55%
TP
40-60%
Metals
20-85%
* With adequate pre-treatment such as vegetated filter strip.
Source: MADEP (2008)
Although constructed wetlands require significant space, they also enhance communities by
providing recreational space and wildlife habitat (EPA 2004).
3.3.
GREEN INFRASTRUCTURE EVALUATION MODELS
The wide variety of stormwater management options available makes it difficult for community
leaders to assess the best options to apply locally. There are many models that can be used to
evaluate the performance and costs of green infrastructure BMPs. Planning level models provide
preliminary estimates of costs and benefits based on limited data. These can help decision
makers in understanding the relative advantages of various BMPs without the need for detailed
site assessments. Planning level tools to assess green infrastructure include the EPA National
Stormwater Calculator, the WERF BMP SELECT model, the CWP Clean Water Optimization
Tool, and the Center for Neighborhood Technology Green Values National Stormwater
Management Calculator.
There are also more complex hydrological models, such as the EPA Stormwater Management
Model (SWMM) and the Hydrological Simulation Program FORTRAN (HSPF). These models
more accurately predict how BMPs will perform within a given watershed, but require extensive
site specific data.
3.4.
WERF BMP SELECT MODEL
The main objective of this study is to help the Malden River community better understand its
stormwater management options. For these purposes, a planning level tool was found to be
appropriate. The Water Environment Research Foundation (WERF) BMP Site Effectiveness and
Life-Cycle Evaluation of Costs Tool (SELECT) provides "relative performance and cost
implications of various BMP control options" (Pomeroy and Rowney 2013). At this stage in the
Malden River's stormwater management options assessment, the relative evaluations enabled by
25
SELECT can provide insights into the feasibility and effectiveness of various alternatives.
Tables 3-5 and 3-6 show the types of BMPs and water quality parameters that can be simulated
in SELECT.
TABLE 3-5. STORMWATER BMPS SIMULATED IN SELECT
Extended Detention
Bioretention
Wetland Basin
Swale
Permeable Pavement
Filter
Generic (user-defined)
Source: Pomeroy and Rowney (2013)
TABLE 3-6. WATER QUALITY PARAMETERS SIMULATED IN SELECT
Total Suspended Solids
Total Nitrogen
Total Phosphorus
Total Zinc
Total Copper
Fecal Coliform*
*Some applications only
Source: Pomeroy and Rowney (2013)
SELECT Case Study:
SELECT was used to model the Saylor Grove Wetland in Philadelphia (Reynolds et al. 2012).
Comparing the SELECT results to actual performance and cost data provides insight into how
the tool might best be used. Table 3-7 compares SELECT performance estimates with actual
pollution removal efficiencies observed at the wetland. The similarity in the results provides
confidence in SELECT's ability to predict the performance of BMPs.
26
Table 3-8 compares SELECT cost estimates with the actual expenditures incurred. Although the
cost estimates are comparable, they are not exact. This highlights the fact that SELECT can be
used to provide a relative understanding of costs, but not to accurately estimate cost data.
TABLE 3-7. SELECT PREDICTIONS COMPARED WITH OBSERVED PERFORMANCE
DATA. SAYLOR GROVE WETLAND, PHILADELPHIA
Actual
Average
Remved -
Removed
-
%
Average
Annual %
SELECT
Observed
67.6%
12.1%
45.7%
-46.6%/
67.9%
12.2%
45.8%
-46.9%4
TSS
TN
TP
TZxi
Note: This table is reproduced as originally published by the authors. No judgements were made about
the reported significant figures.
Note: The negative percentages represent an increase in TZn. This anomaly was
observed both in the observed data and the SELECT predictions.
Source: Reynolds et al. (2012)
TABLE 3-8. SELECT PREDICTIONS COMPARED WITH ACTUAL COST DATA. SAYLOR
GROVE WETLAND, PHILADELPHIA
SELECT
Type
Actual Cost
Model
Consulting
$888,000
$927,000
O&M Present Value
$333,500
$174,000
Replacement Costs - Net
Present Value
Total without Replacement
$ -
$194,000
$1,221,500
$1,101,000
PWD Labor
Construction
Costs
Note: This table is reproduced as originally published by the authors No judgements were made about the
reported significant figures.
Source: Reynolds et al. (2012)
SELECT MODEL THEORY:
The following section summarizes the theory and underlying assumptions upon which the
SELECT model is based (Pomeroy and Rowney 2013).
RUNOFF SIMULA TION
SELECT uses hourly rainfall data to simulate watershed runoff using a modified version of the
Rational Method. First, the model computes the available depression storage value (f) for each
time step based on a user-defined maximum depression storage and hourly precipitation data
over a time period. The available depression storage capacity (f) decreases with rainfall and is
27
recovered through evaporation. Runoff occurs whenever the given depression storage is full (P-f
> 0) and is calculated as:
EQN (1)
R = (P - f) * C where (P-f) > 0;
R = runoff depth (inches over the time period);
P = instantaneous precipitation (inches over the time period)
f = available (instantaneous) depression storage (inches)
C = runoff coefficient
BMP PERFORMANCE SIMULATION:
SELECT calculates the pollutant load as the product of Event Mean Concentrations and the
volume of water (shown in Equation 2 below).
LOAD = QB * EMCws + QBMP * EMCBMP
EQN (2)
Where Load = total pollutant load discharged to receiving water
QB = runoff that bypasses the BMP (inches)
EMCws = EMC for watershed land use
QBMP = runoff treated by the BMP (inches)
EMCBMP= EMC for the BMP effluent
QB, QMP
The volumes (QB, QBMP) are calculated using two methods.
Method 1: Outflow at a specified drawdown rate
Runoff (R) from the drainage area flows into the BMP and outflow occurs at a user-defined
drawdown rate (generally 12-48 hours). A storage volume is defined by the user or calculated by
the model as a water quality capture volume (WQCV) based on the given drawdown time.
Whenever the storage volume of the BMP is exceeded, excess runoff bypasses the BMP and is
not treated. This method is used for extended detention, wetland basin, bioretention, filter, and
swale BMPs.
Method 2: Secondary initial abstractionwith regeneration (via evaporation)
This method is used for permeable pavement only. Runoff (R) generated from the surface area of
the pervious pavement is treated by the pavement, until the user-defined holding capacity is
filled. The holding capacity is then recovered through evaporation. Runoff from the watershed
not covered in permeable pavement is modeled as bypass flow.
EMCws
Default runoff EMC values (EMCws) are given for various land uses based on information from
the National Stormwater Quality Database. Appendix A. 1. provides a table of these EMC values.
EMCMP
Default BMP effluent EMC values (EMCBMP) are specific to each BMP and are based on
empirical data from the International Stormwater BMP Database. Appendix A.2 provides a table
of these EMC values.
28
COST ESTIMA TION TOOL
In addition to simulating the performance benefits, SELECT can also estimate whole life cycle
costs of each BMP. These cost calculations include capital costs, operations & maintenance
(O&M) costs, and replacement costs over each BMP's life cycle. Capital Costs are based on a
cost per acre treated. O&M costs are calculated as a percentage of the capital costs and account
for routine maintenance, corrective maintenance (e.g. periodic repair), and infrequent
maintenance (e.g. sediment removal). Replacement costs account for routine substitution of BMP
infrastructure and media. Replacement costs are also calculated as percentages of the capital
costs.
The default values for the base capital cost, O&M, and replacement percentages for each BMP
are based on WERF Whole Life Cost Models. Appendix A.3. provides a table of these default
cost parameters. In the calculation of annual costs, the model assumes a 25-year design life and
5.5% discount rate. Total costs are then calculated as the sum of the capital, O&M, and
replacement costs.
USER INPUTS
Based on this theoretical framework, users input site-specific data to evaluate BMPs as applied
within their study site. Users are required to input hourly precipitation data, the surface area of
each BMP, the drainage area that contributes to the BMP, and when applicable, the required
drawdown time. Users can also choose overwrite any default values with site-specific data when
they are available.
29
CHAPTER 4: METHODS
4.1.
OVERVIEW OF METHODS
This report evaluates the feasibility of stormwater BMPs to manage the impacts of urban runoff
on the Malden River. The BMP SELECT Model was used to compare the possibility of a
centralized wetland with the alternative of constructing many smaller, distributed BMPs
throughout the watershed. Three alternatives were evaluated for the distributed approach:
bioretention systems, swales, and permeable pavement. The following section describes the
methods used in the analysis. Results are presented in Chapter 5.
4.2.
STUDY SITE
The analysis was conducted within the study site shown in Figure 4-1 below. This area was
chosen to coincide with the SWMM model of Malden hydrology concurrently being developed
at MIT (Greenberg, 2015). Greenberg's model provided site-specific data that was used to
customize the BMP evaluation to the local context. Greenberg's data is summarized in Tables 4-
1 and 4-2 below.
Legend
Study Area
Outlet Location
Study Site
MaldenTown Line
Water Features
Map by: Sara Greenberg
Civil & Enviornmental MEng. 2015
Massachusetts Institute of Technology
0
I
0.25
0.5
1 Miles
FIGURE 4-1. STUDY SITE WITHIN THE MALDEN WATERSHED
Source: Greenberg (2015)
30
The study site is a densely urbanized environment located completely within the City of Malden.
As shown in Table 4-2, 96% of the study site is occupied with urban land uses. As a
consequence, 64.8% of the study site is impervious (Table 4-1). Upon initial assessment,
implementation opportunities for stormwater management infrastructure within this densely
urbanized environment appear limited.
TABLE 4-1. CHARACTERISTICS OF THE STUDY SITE
Area
527 acres
% Impervious Area
64.8%
Slope
2.2%
Depression Storage
0.1028 inches
Source: Greenberg (2015)
TABLE 4-2. BREAKDOWN OF LAND USES WITHIN THE STUDY SITE
1,270,608
60
Commercial
402,936
19
Industrial
203,564
10
Urban
Public/Institutional
155,363
Transportation
4,902
Other
0
2
Subtotal
2,037,373 m
96%
Recreation
63,210
3
Cemetery
17,419
<1
Forest
13,496
<1
Water
102
Subtotal
Total
7
'
Urban
Residential
94,227 m
<1
2
2,131,600
4%
100%
Source: Greenberg (2015)
4.3.
DECENTRALIZED APPROACH: BMPS IN PUBLIC STREETS
One approach to stormwater management is to implement many small BMPs throughout the
watershed. This decentralized approach is particularly appealing in the densely urbanized study
site, where the lack of open-space limits the development of a larger, centralized system.
Public streets are an attractive location for decentralized stormwater management. First of all,
potential applicability is large because streets are pervasive throughout the area. Secondly, streets
have an advantage from a planning perspective because they are public land and do not have the
31
additional ownership obstacles that come with private property. Thirdly, street BMPs directly
treat roadway runoff and thus provide greater water quality benefits than other BMPs that
intercept rainfall before it comes into contact with contaminated urban roads. For these reasons,
public streets were chosen as the focus for the decentralized BMP approach within this analysis.
However, it is important to keep in mind that there are other locations for decentralized BMPs
within the study site. These include private parking lots, residential homes, and other public
spaces such as schools, parks, and cemeteries. These applications were not considered in this
report either because they are not public land or because they do not directly treat roadway
runoff.
Based on the literature review, bioretention systems, grass swales, and permeable pavements
were chosen as BMP options applicable within public streets.
BIORETENTION AND SWALES
Bioretention systems and grass swales can be applied in many different ways within an urban
street. In some situations, they can be implemented to replace street parking. However, this
option was not considered within the study site where existing parking spaces serve a critical
function. Instead, the possibility of bioretention systems and swales along pedestrian sidewalks
was considered.
SITE FEASIBILITY: IDENTIFYING STREETS WITH SUFFICIENT WIDTH
The main constraint for implementing BMPs along a sidewalk is space. The study site has many
narrow streets which have limited extra width to accommodate BMPs. Thus, the first step in
assessing the feasibility of bioretention and swale BMPs was to identify streets that have
sufficient width for BMP implementation. The following section summarizes the width
calculations that can be found in Appendix B.
First, each street within the study site was measured using satellite imagery and the distance
measurement tool provided by Google (Google Maps 2015). For each street, the sidewalk width
and the roadway width were measured. Then, these measured widths were compared to street
and sidewalk width standards prescribed by the Boston Complete Streets Design Guidelines
(Boston Transportation Department 2013). Available sidewalk and roadway widths were
calculated for each street by subtracting the standards from the measured widths.
Next, minimum widths necessary for each BMP were calculated. Bioretention systems and
swales require at least 2 feet and 3 feet respectively (SFPUC 2009). For each BMP, 8 inches of
spacing is required on either side (Boston Transportation Department 2013). Thus, minimum
widths necessary for implementation were calculated by adding 16 inches to the required BMP
width. Based on this calculation, bioretention systems and swales require 3.3 and 4.3 feet
respectively. Streets with BMP feasibility were identified by comparing these minimum widths
to the available widths calculated for each street.
Based on the width feasibility calculations, the majority of streets in the study site were found to
be too narrow for bioretention systems or grass swales. Only five street segments within the
32
study site were identified to have BMP feasibility. The five feasible streets are summarized in
Table 4-3 and highlighted in yellow on Figure 4-2.
TABLE 4-3. STREET SEGMENTS WITH BMP FEASIBILITY
Cross St
0.3 miles
Eastern Ave
0.1 miles
Ferry St
0.4 miles
Main St
0.5 miles
Walnut St
0.1 miles
Total
1.4 miles
Legend
Study Area Outlet Location
Study Site
MaldenTown Line
Water Features
Map by: Sara Greenberg
Civil & Enviornmental MEng. 2015
Massachusetts Institute of Technology
0
I
0.25
0.5
1 Miles
FIGURE 4-2. STREETS WITH BMP FEASIBILITY
Note: Streets with BMP feasibility are highlighted in yellow
Source: Greenberg (2015)
33
As shown in Figure 4-2, the northern section of the study site has no streets wide enough to
accommodate BMPs. All five street segments with BMP feasibility are located within the
southern section of the study site. This demonstrates that BMP feasibility is variable even within
a small area. Therefore, the results discussed in this report are specific to this study site only and
are not representative of the Malden watershed at large.
It is worth noting that all of the feasible streets are larger streets with two driving lanes and two
parking lanes. No smaller residential streets (e.g. one lane streets) had any BMP feasibility.
The majority of the streets identified have paved sidewalks directly adjacent to the roadway, with
limited plantings within the sidewalks. This configuration is shown in Figure 4-3. One exception
was a short segment on the west side of Ferry Street, which has an existing grassed area between
the sidewalk and the roadway (shown in Figure 4-4). For this segment of Ferry Street, BMPs
were specifically modeled to replace the existing grassed area.
FIGURE 4-3. TYPICAL SIDEWALK CONFIGURATION WITHIN THE STUDY SITE
Source: Google Maps (2015)
34
FIGURE 4-4. FERRY ST SIDEWALK CONFIGURATION WITH EXISTING GRASSED AREA
Source: Google Maps (2015)
PRELIMINARY DESIGN
After identifying streets feasible for bioretention and swale deployment, BMP surface areas were
calculated. Since bioretention and swale designs are heavily determined by site-specific
characteristics, each street segment was considered individually.
BMP WIDTHS
For each street, BMP widths were designed based on the available width measurements and
various site-specific constraints. These design considerations are discussed below and the final
BMP widths are presented in Table 4-4.
Cross St, Main St
Both Cross Street and Main Street have 3 feet of available width in the roadway and 3
feet of available width in each of the sidewalks along either side of the road. By splitting
the available roadway width in half, 4.5 foot wide BMPs were designed along either side
of the road.
Eastern Ave
Eastern Ave has 3 feet of available width in the roadway. The sidewalk along the north
side of the road has no available width, while the sidewalk along the south side has 3 feet
of available width. By consolidating all of the available roadway width to the south side,
6 foot wide BMPs were designed to run along the south side of the road only.
35
Ferry St
Ferry Street has 3 feet of available width in the roadway and an additional 2 feet of
available width in the sidewalks along either side of the road. By splitting the available
roadway width in half, 3.5 foot wide BMPs were designed along either side of the road.
A section of Ferry Street (the west side of the road between Clayton St and Cross St) has
8 feet of existing grassed area within the sidewalk. For this section (shown in Figure 4-4),
8 foot wide BMPs were modeled to replace the existing grassed area.
Walnut St
The segment of Walnut St between Judson Street and Cross Street has 2 feet of available
roadway width, 3 feet of available sidewalk width on the west side, and 13 feet of
available sidewalk width on the east side. By consolidating the entire available roadway
width to the west side, 5 foot wide and 13 foot wide BMPs were modeled on the west and
east side of the road respectively.
TABLE 4-4. BMP WIDTH DESIGNS
Cross St
0.3 miles
Eastern
Ave
0.1 miles
Ferry St
Main St
Walnut St
0.4 miles
0.5 miles
Between Main St and Walnut St
Both sides of road.
4.5
x
x
Between Main St and Ferry St
South side of road only.
6
Between Eastern Ave and Cross St.
Both sides of road.
4
Between Clayton St and Cross St
West side of road.
(Replace existing grassed area)
8
x
x
4.5
x
x
x
x
Between Eastern Ave and Appleton St.
Both sides of road.
Between Judson St and Cross St.
West side of road.
5x
Between Judson St and Cross St.
East side of road.
13
x
0.1 miles
BMP LENGTHS
BMP lengths were designed for each street by measuring the lengths of sidewalks between rights
of ways (e.g. roadways, driveways, crosswalks) (Google Maps 2015). These length
measurements can be found in Appendix B.
36
The measured lengths were modified to include the following considerations:
* 3 feet of spacing between a BMP and the right of way (PWD 2014)
* 5 feet of spacing between a BMP and a fire hydrant
(Boston Transportation Department 2013)
* Maximum length of 48 feet (two car lengths). (City of Danbury 2015)
Regular breaks in the BMPs allow pedestrians to safely exit parked cars and enter the
sidewalk.
o Note: Existing street signs, utility lights and mailboxes were ignored. It is assumed that
the breaks for pedestrian safety would be strategically located to accommodate these
street fixtures.
o Note: Existing street trees were also ignored in this analysis. Although outside the scope
of this study, preserving street trees should be a priority whenever possible in actual BMP
implementation (Boston Transportation Department 2013).
BMP SURFACE AREAS
BMP surface areas were calculated by multiplying the BMP widths and lengths. These surface
areas were rounded to the nearest ten to simplify the number of inputs into the SELECT Model.
Table 4-5 summarizes the resulting 23 BMP surface areas. Table 4-5 also shows the number of
bioretention and swale systems possible for each size. There are slightly fewer swale systems
possible due to their larger width requirement.
Finally, the BMP surface areas were modeled in SELECT to generate performance and cost data
for bioretention and swale systems.
Summary of Modeling Scenarios:
1) Bioretention Potential across study site (# and sizes of BMPs as shown in Table 4-5)
2) Swale Potential across study site (# and sizes of BMPs as shown in Table 4-5)
37
TABLE 4-5. SUMMARY OF BMP SIZES
30
2
1
40
2
2
50
2
2
60
5
3
70
16
15
80
26
24
90
34
16
100
20
14
110
33
26
120
33
24
130
8
8
140
22
22
150
9
9
190
2
2
200
1
1
500
1
1
760
1
1
860
1
1
1030
1
1
1600
1
1
1640
1
1
1830
3270
1
1
1
1
PERMEABLE PAVEMENT
Permeable pavement was considered as a third option for decentralized stormwater management
within public streets. Unlike bioretention systems or swales, the design of permeable pavement
does not depend on site-specific characteristics. Permeable pavement is applicable in any
roadway with low traffic volumes. Therefore, SELECT was used to model the replacement of
one mile of parking lane with permeable pavement.
Surface Area of Permeable Pavement = Length x Width of Parking Lane
5280 ft
x 8 ft' = 42,240 ft 2
1 mile
Surface Area of Permeable Pavement per mile = 1 mile x 1 ml
City of Danbury, 2015
38
The surface area of permeable pavement per mile was input in SELECT to generate performance
and cost data. Once the performance and cost results were computed per mile, permeable
pavement can be easily compared with other BMPs. For example, the length and cost of
permeable pavement (PP) required to match the Total Phosphorus (TP) reduction achieved by
bioretention (BR) systems can be calculated by:
Length of PP equivalent of BR TP removal [miles]
Cost of PP equivalent of BR TP removal
=
Total BR TP removal [kg]
[kg1
PP TP removal per mile [mile]
Length of PP equivalent of BR TP removal [miles]
Cost of PP per mile
Similar calculations were performed to compare permeable pavement with the other types of
performance data (TSS removal, flow reduction) and other BMP alternatives (swales, wetland).
Summary of Modeling Scenarios:
1)
2)
3)
4)
4.4.
One mile of Permeable Pavement (PP)
Length of PP required to match bioretention performance (TP, TSS, Flow)
Length of PP required to match swale performance (TP, TSS, Flow)
Length of PP required to match wetland performance (TP, TSS, Flow)
CENTRALIZED BMP: CONSTRUCTED WETLAND
In contrast to decentralized BMPs, stormwater can also be managed through a centralized BMP,
such as a constructed wetland.
SELECT was used to model a constructed wetland that treats runoff from the entire study-site.
Open space to construct this wetland is limited within the study site. Nonetheless, the wetland
was modeled to give a comparison of the relative performance and costs of the decentralized
options.
The wetland was sized based on technical specification standards within the Massachusetts
Stormwater Handbook:
Surface Area of Wetland = 1% of contributing drainage area*
Surface Area of Wetland to treat entire study site = 0.01 x 527 acres = 5.3 acres
Permanent Pool Volume (PPV) of Wetland = 45% of BMP Surface Area* x 18 inches*
1 ft
43,560 ft 2
) x (18 in x 12 in) = 155,000 ft3
acre
PPV of Wetland to treat entire study site = 0.45 x (5.3 acre x
2008
* MADEP,
The surface area and permanent pool volume were input in SELECT to generate performance
and cost data.
39
For comparison, wetlands were also sized to match the performance from bioretention and swale
systems. This was done through an iterative process of adjusting and modeling various wetland
sizes.
Summary of Modeling Scenarios:
1) Wetland sized to treat entire study-site
2) Wetland sized to match bioretention performance (TP, TSS, Flow)
3) Wetland sized to match swale performance (TP, TSS, Flow)
4.5.
SELECT PARAMETERS
All nine scenarios described above (1 bioretention scenario, 1 swale scenario, 4 permeable
pavement scenarios and 3 wetland scenarios) were modeled in SELECT to generate performance
and cost data. The following section summarizes the parameters used in the BMP SELECT
model. Results from the analysis are presented and discussed in Chapter 5.
PrecipitationData
Hourly precipitation data recorded at Boston Logan International Airport between 01/01/2004
and 12/31/2013 (NOAA 2015a).
Evaporation Data
Monthly mean evaporation data from the Boston Weather Service Forecast Office (NOAA
1982).
Watershed Parameters
% Imperviousness: 64.8% (Greenberg 2015)
Runoff Coefficient: 0.447 (Calculated by SELECT based on % imperviousness)
Depression Storage: 0.1028 inches (Greenberg 2015)
Quality Parameters: SELECT Default EMC Values for Residential Land Use (Appendix A. 1)
BMP Parameters
Quality and Quantity Values: SELECT Default EMC Values for BMPs (Appendix A.2)
Cost Values: SELECT Default Cost Parameters (Appendix A.3)
BMP Area: Surface Areas as calculated in Section 4.3.1
Bioretention & Swale Specific BMP Parameters
Drawdown Time: 12 hours (MADEP 2008)
Water Quality Control Volume: 0.3 inches (Calculated by SELECT based on 12 hr Drawdown)
BioretentionSpecific BMP Parameters
Permanent Pool Volume (normalized by area): 0 inches
PermeablePavement Specific BMP Parameters
Holding Capacity: 1 inch (MADEP 2008)
Wetland Specific BMP Parameters
Permanent Pool Volume: 0.45 x BMP area x 18" (Section 4.4)
40
4.6.
CALIBRATION OF FLOW ESTIMATES
The runoff volumes predicted by SELECT were calibrated to the volumes predicted by
Greenberg's SWMM model, which is more heavily based on site-specific data and should
provide more accurate estimates. The performance of BMP alternatives were remodeled in
SELECT using the newly calibrated flow volumes.
The two models were calibrated over an extreme storm event in April 2004 during which 5.5
inches fell over three days.
PrecipitationData
Hourly precipitation data recorded at Boston Logan International Airport between 19:00 pm on
03/31/2004 and 06:00 am on 04/02/2004 (NOAA 2015a).
Results from this calibration can be found in Chapter 5.
41
CHAPTER 5: RESULTS
This chapter presents the key results from the evaluation of BMPs. Section 5.1 describes results
generated from ten years of rainfall data. Section 5.2 discusses the results after calibration of the
SELECT and SWMM models. Detailed calculations can be found in Appendix C.
5.1.
BMP EVALUATION BASED ON 10-YEAR RAINFALL DATA
Table 2-1 summarizes annual runoff characteristics calculated by SELECT based on ten years
(2004-2013) of hourly rainfall data. These runoff characteristics provide the basis for the BMP
performance estimates discussed in the rest of this section.
TABLE 5-1. ANNUAL RUNOFF CHARACTERISTICS OF THE STUDY SITE
TP Load
240 kg
TSS Load
38,900 kg
Total Flow
304,000,000 ft 3
BIORETENTION VS. SWALE
BIORETENTION VS. SWALE: INDIVIDUAL UNIT
Table 5-2 compares bioretention systems and swales of equal surface area. A bioretention unit
costs 5.7 times more than a swale, but achieves better performance. Bioretention systems remove
1.9 times more TP and 1.1 times more TSS than swales. The two types of BMPs are expected to
achieve the same flow reduction.
TP Reduction
51%
27%
1.9
TSS Reduction
68%
60%
1.1
Flow Reduction
19%
19%
1
Cost
1
5.7
*Detailed calculations can be found in Appendix C. 1.
42
BIORETENTION VS. SWALE: RESULTS ACROSS STUDY SITE
Table 5-3 compares bioretention and swale systems across the entire study site. Bioretention to
swale performance ratios are higher across the study site than when comparing individual units.
This is because a larger number of bioretention systems can be implemented due to their lower
width requirement.
Note that the reduction percentages across the study site (Table 5-3) are much lower than the
percentages across each individual BMP unit (Table 5-2). This discrepancy highlights the low
applicability of bioretention and swale systems in streets within the study site. Although the
individual BMPs are relatively effective, there are very few streets in which their implementation
is feasible.
TABLE 5-3. BIORETENTION VS. SWALE SYSTEMS: RESULTS ACROSS ENTIRE STUDY SITE
Bioretention
SwaleBortnto
Swale
# of units
223
177
Annual TP Reduction across
study site
3.7 kg
2%
1.7 kg
<1%
2.2
Annual TSS Reduction
across study site
780 kg
2%
600 kg
2%
1.3
Annual Flow Reduction
across study site
1,730,000 ft3
<1%
1,500,000 ft3
<1%
1.2
Total Cost (NPV)
$1,590,000
$216,000
5 to 8*
*Cost ratio is variable. For BMP sizes between 30 ft and 140 ft the bioretention:swale cost ratio is 5.7.
For BMP sizes between 150 ft2 and 3270 ft 2 the cost ratio is 7.5.
BIORETENTION AND SWALE VS. PERMEABLE PAVEMENT AND WETLAND
For comparison, permeable pavement and wetlands were sized to achieve the performance
provided by bioretention and swale systems across the study site (Table 5-4). The TP reduced by
bioretention systems across the study site could alternatively be achieved by 15 miles of
permeable pavement. 15 miles of permeable pavement would cost $8,400,000 (more than 5 times
the cost of bioretention). Alternatively, the same results could be achieved by a 0.2 acre wetland,
which would only cost $121,000 (less than a tenth the cost of bioretention).
The TP reduced by swales across the study site could be achieved by 7 miles of permeable
pavement, which would cost $3,900,000 (18 times as much as swales). The same results could
also be achieved by a 0.1 acre wetland, which would only cost $55,000 (a fourth of the cost of
swale).
Table 5-4 only shows the TP reduction equivalents. Designs for TSS and flow reduction
equivalents can be found in Appendix C. In general, wetlands can provide equivalent benefits at
much lower costs, while permeable pavements require significantly higher costs.
43
TABLE 5-4. TP REDUCTION EQUIVALENTS OF BIORETENTION AND
SWALE SYSTEMS ACROSS THE STUDY SITE
Equivalent Permeable
Pavement
15 miles
7 miles
Equivalent Wetland
0.2 acres
0.1 acres
PERMEABLE PAVEMENT
Table 5-5 summarizes the results of permeable pavement replacing one mile of parking lane.
54% of the TP, TSS and flow passing through the permeable pavement are reduced. This is less
than one percent reduction across the entire study site.
TABLE 5-5. RESULTS OF PERMEABLE PAVEMENT PER MILE OF PARKING LANE REPLACED
0.2 kg
Annual TSS
39 kg
Removal
Annual Flow
304,000 ft3
Reduction V)_$551,_
Total Cost (NPV)
$551,000
54%
<1%
54%
<1%
54%
_
-
__-_-
<1%
-
Annual H'
Removal
Of course, the actual reduction percentages across the study site will increase with the length of
parking lane replaced. This study did not measure the total length of parking lanes within the
study site, under the assumption that this will not be the limiting constraint. It is likely that the
implementation of permeable pavement would be limited by budget, due to the high costs of
permeable pavement in comparison with the other BMPs.
44
WETLAND RESULTS
Table 5-6 summarizes the results of a wetland sized to treat the entire study site. The 5.3 acre
wetland is expected to reduce 50% of TP, 57% of TSS and 33% of flow from the annual runoff.
These percentages represent results through the wetland and across the entire study site. The
values are equivalent because the wetland was specifically designed to treat runoff from the
entire study site. The total cost of the wetland (exclusive of land acquisition) is $3,900,000.
TABLE 5-6. RESULTS OF WETLAND SIZED TO TREAT ENTIRE STUDY SITE
Area
5.3 acres
Annual TP Removal
1520 kg
Annual TSS Removal
22,000 kg
Annual Flow Reduction
90'33%,000 fP
Total Cost
$3,920,000
57%
The reduction achieved by the 5.3 acre wetland is not possible through bioretention or swale
systems across the study site due to the limited feasibility of these BMPs. However, the total TP
reduction provided by the wetland could be achieved by 600 miles of permeable pavement
(Table 5-7). This would cost $273,000,000 (70 times the cost of the wetland).
TABLE 5-7. PERMEABLE PAVEMENT REQUIRED TO ATTAIN TP REDUCTION EQUIVALENT OF
5.3 ACRE WETLAND
5.3 acre Wetland
Equivalent Permeable
Pavement
500 miles
Note: TSS and flow reduction equivalents can be found in Appendix C.
45
COMPARISON OF ALTERNATIVES:
COMPARISON OF PERFORMANCE
Table 5-8 and Figure 5-1 compare the performance of the 5.3 acre wetland with the performance
of swales and bioretention across the study site. The wetland provides much higher reductions of
TP, TSS and flow.
TABLE 5-8. TOTAL REDUCTION POTENTIALS FOR VARIOUS BMPS ACROSS THE STUDY SITE
Swales
across study site
Bioretenton
acrss study site
Wetland
(5.3 acre)
Annual TP Reduction
<1%
2%
50%
Annual TSS Reduction
2%
2%
57%
Annual Flow Reduction
<1%
<1%
33%
Total Phosphorus Reduction
Across the Study Site
60%
50%
40%
30%
20%
10%
0%
Swales
Bioretention
Wetland
FIGURE 5-1. TP REDUCTION FOR VARIOUS BMPS ACROSS THE STUDY SITE
COMPARISON OF COST
Table 5-9 and Figure 5-2 compare the cost of the four BMP alternatives. The wetland is the most
cost-effective management option. Permeable pavement costs many times more than any of the
other BMPs.
It is important to keep in mind that none of the costs include the cost of land. From a publicplanning perspective, the cost of land is negligible in swale, bioretention, and permeable
pavement BMPs, all of which were designed to be built on public land. However, the land on
46
which a wetland is built would likely need to be purchased. Thus, the wetland costs presented in
this report represent a practical minimum.
TABLE 5-9. COMPARISON OF BMP COSTS
Cost/kg
TP Reduction
TSS
edction
Flow Redution
$33,000
$130,000
$430,000
$2,300,000
$60
$400
$2,000
$14,000
< $1
< $1
$1
$2
Note: Costs do not include the cost of land.
Note: Each water quality parameter was separately evaluated against the total cost.
Cost/kg of TP Removed
$2,500,000
$2,000,000
$1,500,000
$1,000,000
$500,000
$0
Wetland
Swale
Bioretention
Permeable
Pavement
FIGURE 5-2. COST PER KG OF TP REMOVED FOR VARIOUS BMPS
Note: Costs do not include the cost of land.
47
5.2.
RESULTS OF CALIBRATION
Table 5-10 compares runoff volumes from the April 2004 storm event predicted by the SELECT
and SWMM models. The two SWMM estimates are based on competing infiltration theories.
The SELECT model predicted lower runoff volumes than either SWMM estimate.
TABLE 5-10. RUNOFF VOLUMES PREDICTED BY SELECT AND SWMM MODELS
Runoff Volume
(ft)
70,000,000
60,000,000
37,000,000
Depression storage and runoff coefficient values within the SELECT model were adjusted to
calibrate the runoff volumes to the SWMM estimates. Tables 5-11 and 5-12 compare BMP
performance before and after calibration. In general, the SELECT reduction percentages are
relatively insensitive to the calibration. This could be because SELECT calculates removal
efficiencies based on the maximum capacity of each BMP. Once the BMP capacity is reached,
any additional runoff volume will contribute to bypass flow. Thus, by increasing the runoff
volumes, the calibration exercise only increased bypass flow without having a major effect on
flow through the actual BMP.
However, the calibration did marginally decrease the expected performance of the various
BMPs. This could indicate that the performance results presented in Section 5.1 run slightly
high.
TABLE 5-11. TOTAL PHOSPHORUS REDUCTION PERCENTAGES FOR AN INDIVIDUAL BMP
Original SELECT Results
65%
37%
73%
SWMM Calibrated Results
(Green Ampt Theory)
63%
33%
73%
SWMM Calibrated Results
(Curve Number Theory)
64%
I
34%
I
73%
1
_1
TABLE 5-12. TOTAL SUSPENDED SOLIDS REDUCTION PERCENTAGES FOR AN INDIVIDUAL BMP
Original SELECT Results
85%
75%
84%
SWMM Calibrated Results
(Green Ampt Theory)
84%
73%
84%
SWMM Calibrated Results
(Curve Number Theory)
84%
74%
84%
48
5.3.
CONCLUSIONS
This report provides a comparison of the benefits and costs of four stormwater management
alternatives: bioretention systems, swales, permeable pavement and wetlands. Any application of
this information will be greatly influenced by the given budget and the availability of land for a
wetland, neither of which was considered in this analysis. Nonetheless, the results provide a
preliminary understanding of the relative advantages of the BMP alternatives. Key conclusions
from the evaluation are summarized here.
Bioretention and swale systems have limited feasibility in streets within the study site. Only five
streets were found to be wide enough for the implementation of either BMP. If applied in these
five streets, bioretention systems are expected to perform better than swales. This is both because
bioretention units are more effective than swales and because bioretention units have more
applicability due to their lower width requirement. However, the higher performance of
bioretention systems across the study site (2.2 times as much TP removal, 1.3 times as much TSS
removal, and 1.2 times as much flow reduction) is attained at 5 to 8 times the cost. Although
bioretention systems do perform better, swales provide relatively similar results at a much lower
cost. Therefore, swales may be a more attractive option, depending on budget constraints and
performance objectives.
Overall, the wetland is the most cost-effective alternative for stormwater management within the
watershed. Wetlands can perform as well as bioretention and swale systems at much lower costs.
Further, a wetland can be sized to treat the entire study site and reduce more pollution than
possible by either bioretention or swales. The caveat is the limited land available for wetlands
within the study site. However, if the community were to designate land for stormwater
management, wetlands would provide the most reduction (of TP, TSS and flow) for the lowest
cost.
In contrast, permeable pavement is the most expensive management option. Permeable pavement
costs at least five to seventy times as much as the other BMPs.
5.4.
OTHER CONSIDERATIONS AND FUTURE RESEARCH
This report evaluated a small portion of the Malden River watershed. However, BMP feasibility
is extremely sensitive to site-specific conditions. Therefore, the information in this report should
not be directly applied to other areas of the watershed. Instead, these other areas should be
evaluated independently.
Further, this report analyzed three aspects of stormwater (TP, TSS, and flow) for four stormwater
BMPs (bioretention systems, swales, permeable pavement, and wetlands). There are many other
stormwater management objectives (e.g. bacteria, heavy metals) and BMPs (e.g. parking lot
retrofits) that could be evaluated in the future.
49
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Khweis, Majdolene. 2015. "Organic Sediment Analysis and Distribution on the Malden River."
Senior Capstone Project, Massachusetts Institute of Technology.
Madden, Sarah. 2010. "Choosing Green Over Gray: Philadelphia's Innovative Stormwater
Infrastructure Plan." Cambridge, MA: Massachusetts Institute of Technology.
50
MADEP. 2008. "Massachusetts Stormwater Handbook."
http://www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-stormwaterhandbook.html.
. 2013. Massachusetts Year 2012 IntegratedList of Waters. Commonwealth of
Massachusetts: MADEP.
http://www.mass.gov/eea/docs/dep/water/resources/07v5/12list2.pdf.
. 2014. MassachusettsSurface Water Quality Standards. 314 CMR 4.00.
http://www.mass.gov/eea/docs/dep/service/regulations/314cmrO4.pdf,
http://water.epa.gov/scitech/swguidance/standards/wqslibrary/upload/mawqs-figures tab
les.pdf.
. 2014. Massachusetts Year 2014 IntegratedList of Waters. Commonwealth of
Massachusetts: MADEP.
http://www.mass.gov/eea/docs/dep/water/resources/07v5/14iwlistp.pdf.
. 2015. "Malden SSO Database."
MWRA. 2015. "Malden Watershed SSO Locations."
Nangle Associates. 2014. "Malden River Outfalls."
"National Stormwater Quality Database." 2015. InternationalStormwater Quality Database.
Accessed May 4. http://www.bmpdatabase.org/nsqd.html.
NOAA. 1982. Mean Monthly, Seasonal, and Annual Pan Evaporationfor the United States.
NOAA Technical Report NWS 34. Washington D.C.: U.S. Department of Commerce
National Oceanic and Atomspheric Administration National Weather Service.
http://www.nws.noaa.gov/oh/hdsc/PMPrelatedstudies/TR34.pdf.
. 2015a. "National Climatic Data Center." NCDC Time-Related Maps. Accessed May 3.
http://gis.ncdc.noaa.gov/map/viewer/#app=cdo.
. 2015b. "Nonpoint Source Pollution." NOAA Ocean Service Education. Accessed April
16. http://oceanservice.noaa.gov/education/kits/pollution/04nonpointsource.html.
Oehmke, Theresa. 2015. "Potential for Sediment Re-Suspension and Transport in the Malden
River." Senior Capstone Project, Massachusetts Institute of Technology.
Penn DEP. 2006. "Pennsylvania Stormwater Best Management Practices Manual BMP 6.4.5:
Rain Garden/Bioretention." http://www.elibrary.dep.state.pa.us/dsweb/Get/Document67993/6.4.5%20BMP%2ORain%20Garden%20Bioretention.pdf.
Philadelphia Water Department. 2009. Green City Clean Waters. The City of Philadelphia's
ProgramforCombined Sewer Overflow Control. A Long Term Control Plan Update.
Philadelphia, PA: Philadelphia Water Department.
Pomeroy, C.A., and A.Charles Rowney. 2013. "User's Guide to the BMP SELECT Model
Version 2.0." Water Environment Research Foundation.
PWD. 2014. "City of Philadelphia Green Streets Design Manual." Philadelphia Water
Department.
http://www.phillywatersheds.org/img/GSDM/GSDMFINAL_20140211 .pdf.
Reynolds, Shannon K., Christine A. Pomeroy, A. Charles Rowney, and Chris M. Rowney. 2012.
Linking Stormwater BMP Systems Water Quality and Quantity Performanceto Whole
Life Cycle Cost to Improve BMP Selection andDesign. World Environmental and Water
Resources Congress. American Society of Civil Engineers.
https://soundcloud.com/muramasamusic/sets/someday-somewhere-ep.
51
SFPUC. 2009. "San Francisco Stormwater Design Guidelines." San Francisco Public Utilites
Commission. http://www.sfwater.org/Modules/ShowDocument.aspx?documentID=2779.
Shaver, Earl, Richard Homer, Joseph Skupien, Chris May, and Graeme Ridley. 2007.
"Fundamentals of Urban Runoff Management: Technical and Institutional Issues." North
American Lake Management Society. http://www.ilmalakes.org/PDF/Fundamentalsfullmanuallowres.pdf.
Smullen, James T., Amy L. Shallcross, and Kelly A. Cave. 1999. "Updating the US Nationwide
Urban Runoff Quality Data Base." Water Science and Technology 39 (12): 9-16.
Strassler, Eric, Jesse Pritts, and Kristen Strellec. 1999. PreliminaryData Summary of Urban
Storm Water Best Management Practices. EPA-821-R-99-012. Washington DC: US
Environmental Protection Agency.
http://water.epa.gov/scitech/wastetech/guide/stormwater/upload/20061 0_3 1_guide stor
mwaterusw b.pdf.
Sylman, Shanasia. 2015. "Inorganic Contaminants in the Sediments of the Malden River:
Distributions and Associated Risks." Senior Capstone Project, Massachusetts Institute of
Technology.
U.S. Army Corps of Engineers. 2008. Malden River Ecosystem Restoration:DetailedProject
Report & EnvironmentalAssessment.
US EPA. 2014a. EnhancingSustainable Communities with Green Infrastructure. 100-R-14-006.
US EPA.
US EPA, OW. 2014b. "Sanitary Sewer Overflows and Peak Flows." Overviews & Factsheets.
September 9. http://water.epa.gov/polwaste/npdes/sso/.
52
APPENDIX A. DEFAULT PARAMETERS WITHIN THE WERF BMP SELECT MODEL
53
DEFAULT EMCs FOR LAND USES IN THE BMP SELECT MODEL
A. 1.
SU
SaM.s
dSingiWeTotal
T
Fbngmebru
Narqum
a
otal
COMTotalm
Total0
VebtqTt
(aptls
TOW
Tsta1amc
cap
MEAN
STD
MEAN
STD
MEAN
STD
MEAN
STD
MEAN
STU
MEAN
STD
Resideadal
48.06
3.29
0.30
2.22
2.18
1.87
5620
11.98
75.62
2.48
12.75
2.55
Conmercial
49.44
3.29
2.28
2.21
1.99
3728
9.92
154.08
2.31
17.92
2.46
Undeveloped
53.96
5.58
0.21
0.24
3.08
1.47
2.18
7729
4.19
36.78
3.31
8.32
332
MEAN - Geometric Mean. STD - Standard Deviation
Note: This table is reproduced as originally published by the authors. No judgements were made
about the reported significant figures.
Source: Pomeroy and Rowney (2013)
DEFAULT EMCs FOR VARIOUS BMPS IN THE BMP SELECT MODEL
A.2.
sTotal
ar
C.KMUW
(m0040
TOia
Illad
Eeqk"ON
1ft"fiko
b
T"
W
CpW
MEAN
STD
MEAN
STD
MEAN
STD
MEAN
STD
MEAN
STD
MEAN
STD
Extended
22.40
2.95
0.23
2.28
2.00
1.93
836
16.70
24.40
4.20
5 50
3.33
Weiland
Basins
9.06
3.95
.0
2.7
1.20
2.43
2260
17.90
21.30
2.77
3.52
2.11
Bieretendon
7.69
12.70
9.05
14.50
3.71
3.77
3.83
2.95
0.11
0.20
0.09
4.15
2.14
2.53
2.69
2.41
N.A.
4610
7.02
7.03
5.94
2.27
2.37
2.89
2.51
13.20
25.40
15.60
15.50
3.89
2.35
4.08
0.09
0.99
0.74
0.95
1.27
3.44
7.77
2.30
Swale
Media Filters
Perimeable
Pavement
2.60
524
N.A.
9.25
15.20
2.44
N.A.
N.A.
Not available.
MEAN - Geometric Mean. STD - Standard Deviation
N.A.
Note: This table is reproduced as originally published by the authors. No judgements were made
about the reported significant figures.
Source: Pomeroy and Rowney (2013)
DEFAULT COST PARAMETERS IN THE BMP SELECT MODEL
A.3.
&WP
Extended
Detention'-'
Wetland
($fhcm tey*1"- arm (%-/* 2 ()
3.750
%) -M(M)
2.7
5.5
80
25
3.750
1.42
1.4
5.5
80
25
BioretentionT
53,000
1
3.5
5.5
80
25
Swale S
Media Filters
3750
22
5-4
5.5
0
N.A.
N.A.
N.A.
N.A.
N.A.
Basins I
80
5.5
2.3
1
374,000
Permeable
Pavement 1.4
N.A. Not available.
Source: 'Lampe et al. 2005. 'Pomeroy and Houdeshel. 2009.
Base cost includes engineering & planning. Medium maintenance.
4
Assumes new solid concrete (not paver blocks), includes engineering and planning, contingency. Medium
maintenance.
25
N.A.
25
Note: This table is reproduced as originally published by the authors. No judgements were made
about the reported significant figures.
Source: Pomeroy and Rowney (2013)
54
APPENDIX B. BIORETENTION AND SWALE FEASIBILITY: BMP WIDTHS
55
B.1.
MINIMUM WIDTH STANDARDS FOR ROADWAYS AND SIDEWALKS
Type
MNfimum Width (ft)
Travel Lane
10
Parking Lane
7
Travel + Parking
19
Sidewalk
7
Source: Boston Transportation Department (2013)
B.2.
DESIGN SPECIFICATIONS FOR BMPS
Bioretention'
2 feet
Swale'
3 feet
Spacing 2
8 inches
Sources: 'San Francisco Public Utilities Commission (2009),
2Boston Transportation Department (2013).
B.3.
MINIMUM WIDTH REQUIREMENTS FOR BMPS
Minimum width requirements were calculatedusing the specifications in Table B.2.
8 inches of spacing were added to either side of the minimum widthfor BMPs.
Bioretention
3.3 feet
Swale
4.3 feet
56
B.4.
CALCULATION OF TOTAL AVAILABLE STREET WIDTHS
North Section of Studv Site
Alboin St
8
22
2
1
29
1
0
2
Auburn St
7
24
1
2
28
0
0
0
Bowers Ave
7
25
2
1
29
0
0
0
1
19
0
3
3
2
38
0
0
0
0
0
0
Bryant St
7
22
1
Baker St
7
25
2
Clark St
6
18
1
1
19
Cross St
7
22
1
1
19
0
3
3
0
0
Concord St
Fairview
7
24
2
1
29
0
Ave
8
25
2
1
29
1
0
2
Faulkner St
8
25
1
2
28
1
0
2
Franklin St
Granville
Ave
7
23
2
2
38
0
0
0
6
21
1
1
19
0
2
2
1
19
0
0
0
2
38
1
0
2
0
0
0
Harding Ave
0
16
1
Holden St
8
34
2
Lynde St
Mountain
7
24
2
2
38
Ave
10
28
2
1
29
3
0
6*
St
10
29
2
1
29
3
0
6*
Norwood St
0
18
1
1
19
0
0
0
Page St
7
25
2
1
29
0
0
0
19
0
1
1
Mt Vernon
Park St
7
20
1
1
Pierce St
Plymouth
7
23
2
0
20
0
3
3
Rd
7
24
2
2
38
0
0
0
0
0
Porter St
Richardson
7
24
2
2
38
0
St
7
19
1
1
19
0
0
0
Rutland St
7
25
2
1
29
0
0
0
Salem St
9
40
2
2
38
2
2
6*
19
1
3
5*
19
0
0
0
0
0
Sprague St
8
22
1
1
Spring St
6
18
1
1
Starbird St
7
24
2
2
38
0
Tremont St
7
24
1
2
28
0
0
0
4*
3
Webster St
Wolcott St
9
28
2
1
29
2
0
7
22
1
1
19
0
3
57
B.4.
CONTINUED
South Section of Study Site
Streets where the Total Available Street Width exceeds the Minimum Width Requiredfor BMPs (Table B.3) are
highlighted in blue (Cross St, EasternAve, Ferry St, Main St, Walnut St).
Acorn St
7
24
2
I
29
0
0
0
Appleton St
7
24
2
1
29
0
0
0
Ashland St
7
24
2
1
29
0
0
0
BarrettSt
6
23
2
1
29
0
0
0
St
7
23
2
1
29
0
0
0
Clarendon St
7
24
2
2
38
0
0
0
Clayton St
7
26
2
2
28
0
0
0
10
41
2
2
38
3
3
Brackenbury
High
1
Eastern Ave
(West of
Ferry St,
North Side)
0
7
10
41
2
2
38
3
3
35
2
2
38
0
0
10
40
2
2
38
2
3
Franklin St
7
24
2
2
38
0
0
0
Garland Ave
8
23
2
2
38
0
1
2
Gould Ave
7
20
1
1
19
1
0
1
Green St
10
28
2
1
29
0
3
62
Hancock St
10
30
2
2
38
0
3
6
2
High St
10
29
2
2
38
0
3
6
2
7
25
2
1
29
0
0
Eastern
(East of
Ferry St) 17
N
Hillside Ave
1Eastern Ave is analyzed in three parts because of varying widths along the road. West of Ferry St, the sidewalks on the north
side of Eastern Ave are narrower than those on the south side. The calculations above only consider available street width for the
South Side of the road to avoid double counting. Eastern Ave narrows to the east of Ferry St.
2 There is only enough width to accommodate BMPs if available widths from the sidewalks on either side of the street are
consolidated. Since this would require considerable reconstruction of the existing roadways, these scenarios are not considered
feasible for the purposes of this report.
0
01
B.4.
CONTINUED
South Section of Study Site
Holyoke St
7
22
1
1
19
3
0
3
Howard St
7
24
2
2
38
0
0
0
James St
8
24
1
2
29
0
1
2
Judson St
8
28
2
2
38
0
1
2
Linwood St
6
20
2
1
29
0
0
0
Lowell St
7
24
2
2
38
0
0
0
Madison St
9
30
2
2
38
0
2
42
0
3
3
0
9
62
Magnolia St
7
24
1
2
28
Main St
10
41
2
2
38
Medford St
10
29
2
1
29
0
3
0
Meridian St
Newhall St
(West of High
St)
Newhall St
(East of High
St)
8
25
2
2
38
0
1
2
6
17
1
1
19
0
0
0
7
24
2
2
38
0
0
0
Oxford St
7
22
2
1
29
0
0
0
Pratt St
7
24
2
2
38
0
0
0
Stevens St
0
16
1
1
19
0
0
0
Tufts St
6
24
2
2
38
0
0
0
Upham St
7
22
1
1
19
3
0
3
10
30
1
2
28
2
3
5
13
13
62
Walnut St
(Judson St to
Cross St)
(West Side)
3
Walnut St
(Judson St to
Cross St)
(East Side) 3
20
Walnut St
(Cross St to
Oxford St) 3
10
28
1
2
28
0
3
Warren Ave
8
24
2
2
38
0
0
Wilson Ave
10
30
2
2
38
0
3
7
23
2
1
29
0
0
Wyeth St
3 Walnut St is analyzed in three parts because of varying widths along the road. The road is wider between Judson St and Cross
St than it is elsewhere. Within the section between Judson St and Cross St, the east side of the road has a much larger sidewalk.
The calculations above only consider available street width for the West Side of the road to avoid double counting.
0
6
2
0
APPENDIX C. BMP PERFORMANCE AND COST RESULTS
60
C. 1.
BIORETENTION POLLUTION REDUCTION
0.006
0.003
0.003
52
1.1
0.3
0.8
69
0.007
1.4
40
2
0.008
0.004
0.004
51
1.3
0.4
0.9
68
0.008
1.8
50
2
0.011
0.005
0.006
52
1.7
0.5
1.2
68
0.011
2.3
60
5
0.013
0.006
0.007
51
2.1
0.6
1.5
68
0.033
7.03
70
16
0.015
0.007
0.008
52
2.4
0.8
1.6
68
0.122
25.7
80
26
0.017
0.008
0.009
51
2.7
0.9
1.8
68
0.228
48.2
90
34
0.019
0.009
0.01
51
3.0
1.0
2.0
68
0.330
70.2
51
3.4
1.1
2.3
68
0.216
46.2
30
100
20
0.021
0.01
0.01
110
33
0.023
0.011
0.012
51
3.8
1.2
2.6
68
0.399
84.8
120
33
0.025
0.012
0.013
51
4.1
1.3
2.8
68
0.429
90.8
130
8
0.028
0.014
0.014
51
4.4
1.4
3.0
68
0.114
24.1
140
22
0.03
0.014
0.015
51
4.7
1.5
3.2
68
0.334
70.8
150
9
0.032
0.016
0.016
51
5.1
1.6
3.5
68
0.147
31.2
190
2
0.04
0.02
0.02
51
6.4
2.1
4.3
68
0.041
8.7
200
1
0.042
0.021
0.021
51
6.8
2.2
4.6
68
0.022
4.6
500
1
0.11
0.05
0.06
51
17.0
5.4
11.6
68
0.054
11.6
760
1
0.16
0.08
0.08
51
25.8
8.2
17.6
68
0.083
17.6
860
1
0.18
0.09
0.09
51
29.2
9.3
19.9
68
0.093
19.9
1030
1
0.22
0.11
0.11
51
34.9
11.2
23.7
68
0.112
23.7
1600
1
0.34
0.17
0.17
51
54.3
17.4
36.9
68
0.174
36.9
1640
1
0.35
0.17
0.18
51
55.6
17.8
37.8
68
0.178
37.8
1830
1
0.39
0.19
0.2
51
62.0
19.8
42.2
68
0.199
42.2
3270
1
0.69
0.34
0.35
51
111.0
35.4
75.6
68
0.355
75.6
Average
51%
Average
68%
TOWa68%
Removal
3.7 kg
I
780 kg
61
C.2.
BIORETENTION FLOW REDUCTION
A
I
30
40
50
60
70
80
90
100
110
120
130
140
150
190
200
500
760
860
1030
1600
1640
1830
3270
RI
2
2
2
5
16
26
34
20
33
33
8
22
9
2
1
1
1
1
1
1
1
1
1
r
8,089
10,400
13,289
16,178
18,489
21,378
23,689
26,578
29,467
31,779
34,668
36,979
39,868
50,268
53,157
132,892
201,649
228,228
273,296
424,677
435,077
485,345
866,688
1
6,500
8,400
10,700
13,100
14,900
17,300
19,100
21,500
23,800
25,700
28,000
29,900
32,200
40,600
42,900
107,300
162,900
184,300
220,700
343,000
351,400
392,000
700,000
1,589
2,000
2,589
3,078
3,589
4,078
4,589
5,078
5,667
6,079
6,668
7,079
7,668
9,668
10,257
25,592
38,749
43,928
52,596
81,677
83,677
93,345
166699
20
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
3,178
4,001
5,178
15,391
57,429
106,036
156,042
101,568
187,024
200,592
53,340
155,731
69,009
19,336
10,257
25,592
38,749
43,928
52,596
81,677
83,677
93,345
166,688
1,730,000
ft
62
C.3.
BIORETENTION COSTS
Cost Per Uj
756
355
972
1,242
1,512
1,728
1,998
2,214
2,484
2,754
2,970
3,240
3,456
3,726
4,698
4,968
12,420
18,846
21,330
456
583
710
811
938
1,039
1,166
1,293
1,394
1,521
1,623
3,726
4,698
4,968
12,420
18,846
21,330
159
204
261
317
363
419
464
521
578
623
680
725
782
987
1,043
2,608
3,958
4,479
1,270
1,632
2,086
2,539
2,902
3,355
3,717
4,171
4,625
4,987
5,441
5,804
8,234
10,382
10,979
27,448
41,649
47,138
2,540
3,264
4,172
12,695
46,431
87,229
126,377
83,419
152,623
164,569
43,528
127,687
74,109
20,765
10,979
27,448
41,649
47,138
25,542
25,542
5,364
56,447
56,447
39,689
40,661
45,359
80,999
39,689
40,661
45,359
80,999
8,335
8,539
9,525
17,010
87,713
89,861
100,244
179,007
TOTAL COST
87,713
89,861
100,244
179,007
$1,590,000
63
C.4.
SWALE POLLUTION REDUCTION
30
I
0.006
0.005
40
2
0.008
50
2
0.011
60
3
70
80
90
0.002
28
1.03
0.41
0.62
60
0.002
0.006
0.002
27
1.33
0.54
0.79
60
0.004
1.58
0.008
0.003
28
1.70
0.68
1.02
60
0.006
2.04
0.013
0.009
0.003
27
2.07
0.84
1.23
59
0.010
3.69
15
0.015
0.011
0.004
27
2.36
0.95
1.41
60
0.062
21.14
24
0.017
0.013
0.005
27
2.73
1.11
1.62
59
0.110
38.88
16
0.019
0.014
0.005
27
3.03
1.22
1.81
60
0.082
28.96
100
14
0.021
0.016
0.006
27
3.40
1.38
2.02
59
0.080
28.28
110
26
0.024
0.017
0.006
27
3.77
1.52
2.25
60
0.166
58.50
120
24
0.025
0.019
0.007
27
4.06
1.65
2.41
59
0.166
57.84
130
8
0.028
0.020
0.008
27
4.43
1.79
2.64
60
0.060
21.12
140
22
0.030
0.022
0.008
27
4.73
1.90
2.83
60
0.176
62.26
150
9
0.032
0.023
0.009
27
5.10
2.06
3.04
60
0.077
27.36
190
2
0.040
0.029
0.011
27
6.43
2.60
3.83
60
0.022
7.66
200
1
0.042
0.031
0.012
27
6.80
2.74
4.06
60
0.012
4.06
500
1
0.106
0.077
0.029
27
17.00
6.86
10.14
60
0.029
10.14
760
1
0.161
0.117
0.044
27
25.80
10.41
15.39
60
0.044
15.39
860
1
0.161
0.117
0.044
27
25.80
10.41
15.39
60
0.044
15.39
1030
1
0.218
0.159
0.059
27
34.90
14.12
20.78
60
0.059
20.78
1600
1
0.339
0.247
0.092
27
54.30
21.94
32.36
60
0.092
32.36
1640
1
0.347
0.253
0.094
27
55.60
22.47
33.13
60
0.094
33.13
1830
1
0.387
0.282
0.105
27
62.00
25.07
36.93
60
0.105
36.93
3270
1
0.692
0.504
0.188
27
111.00
44.77
66.23
60
0.188
66.23
Avg.
1
27%
Avg.
0.62
60%
Total
Rpemoval
1.7 kg I 600 kg
64
C.5.
SWALE FLOW REDUCTION
30
40
50
60
70
80
90
100
110
120
130
140
150
190
200
500
760
860
1030
1600
1640
1830
3270
1
2
2
3
15
24
16
14
26
24
8
22
9
2
1
1
1
1
1
1
1
1
1
8,089
10,400
13,289
16,178
18,489
21,378
23,689
26,578
29,467
31,779
34,668
36,979
39,868
50,268
53,157
132,892
201,649
228,228
273,296
424,677
435,077
485,345
866,688
6,500
8,400
10,700
13,100
14,900
17,300
19,100
21,500
23,800
25,700
28,000
29,900
32,200
40,600
42,900
107,300
162,900
184,300
220,700
343,000
351,400
392,000
700,000
1,589
2,000
2,589
3,078
3,589
4,078
4,589
5,078
5,667
6,079
6,668
7,079
7,668
9,668
10,257
25,592
38,749
43,928
52,596
81,677
83,677
93,345
166,688
A9
20
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19
19%
1,589
4,001
5,178
9,235
53,840
97,879
73,431
71,098
147,352
145,885
53,340
155,731
69,009
19,336
10,257
25,592
38,749
43,928
52,596
81,677
83,677
93,345
166,688
Tol flow 1,500,000
3
Re d-kt'= ft
65
SWALE COSTS
116
149
190
231
264
306
338
380
421
454
84
108
137
167
191
221
245
275
305
329
24
31
40
48
55
64
71
80
88
95
495
359
104
958
7,664
528
569
718
759
1,898
2,879
382
412
519
549
1,372
2,082
2,356
2,821
4,384
4,491
5,010
8,947
111
119
151
159
398
605
684
819
1,273
1,305
1,455
2,599
1,021
1,100
1,387
1,467
3,668
5,566
6,299
7,543
11,721
12,008
13,396
23,921
TOTAL COST
22,462
9,900
2,775
1,467
3,668
5,566
6,299
7,543
11,721
12,008
13,396
23,921
$216,000
3,259
3,902
6,064
6,212
6,930
12,375
224
288
367
446
510
591
654
735
814
878
224
576
734
1,338
7,650
14,184
10,464
10,290
21,164
21,072
,
C.6.
66
C.7.
PERMEABLE PAVEMENT POLLUTION REDUCTION (PER MILE)
0.4
C.8.
0.2
54%
72
33
39
54%
PERMEABLE PAVEMENT FLOW REDUCTION (PER MILE)
560,000
C.9.
0.2
260,000
54%
304,000
PERMEABLE PAVEMENT COSTS (PER MILE)
Capital Costs
O&M Costs
Rplcmn
$363,000
$112,000
$76,000
$551,000
67
C.10.
PERMEABLE PAVEMENT COMPARISONS TO OTHER BMPs
I
I
,
,.
I
**For example, 15 miles of permeable pavement would attain the same TP Reduction
achieved by bioretention systems applied across the study site. This would cost $8,415,000.
68
C. 11. 5.3 ACRE WETLAND POLLUTION REDUCTION
(SIZED TO TREAT ENTIRE STUDY SITE)
(kg)
243
123
120
50%
38,000
16,000
22,000
57%
C.12. 5.3 ACRE WETLAND FLOW REDUCTION
(SIZED TO TREAT ENTIRE STUDY SITE)
304,000,000
205,000,000
99,000,000
33%
C.13. 5.3 ACRE WETLAND COSTS
(SIZED TO TREAT ENTIRE STUDY SITE)
$2,800,000
$530,000
$590,000
$3,920,000
69
C.14. WETLAND COMPARISONS TO OTHER BMPs
ACROSS THE STUDY SITE
**For example, a 0.16 acre wetland would be attain the same TP Reduction achieved by
bioretention systems applied across the study site. This would cost $121,000.
70