&EPA
United States
Environmental Protection
Agency
2012 GREEN INFRASTRUCTURE COMMUNITY PARTNERS
Cape Cod Commission
Barnstable and Yarmouth, MA
Nitrogen-reducing Green Infrastructure in
Environmental Justice Communities
Barnstable/Yarmouth—Cape Cod, Massachusetts
April 2016
EPA832-R-15-008
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About the Green Infrastructure Technical Assistance Program
Stormwater runoff is a major cause of water pollution in urban areas. When rain falls in undeveloped
areas, soil and plants absorb and filter the water. When rain falls on our roofs, streets, and parking lots,
however, the water cannot soak into the ground. In most urban areas, stormwater is drained through
engineered collection systems and discharged into nearby water bodies. The stormwater carries trash,
bacteria, heavy metals, and other pollutants from the urban landscape, polluting the receiving waters.
Higher flows also can cause erosion and flooding in urban streams, damaging habitat, property, and
infrastructure.
Green infrastructure uses vegetation, soils, and natural processes to manage water and create healthier
urban environments. At the scale of a city or county, green infrastructure refers to the patchwork of
natural areas that provides habitat, flood protection, cleaner air, and cleaner water. At the scale of a
neighborhood or site, green infrastructure refers to stormwater management systems that mimic
nature by soaking up and storing water. These neighborhood or site-scale green infrastructure
approaches are often referred to as low impact development.
The U.S. Environmental Protection Agency (EPA) encourages using green infrastructure to help manage
stormwater runoff. In April 2011, EPA renewed its commitment to green infrastructure with the release
of the Strategic Agenda to Protect Waters and Build More Livable Communities through Green
Infrastructure. The agenda identifies technical assistance as a key activity that EPA will pursue to
accelerate the implementation of green infrastructure. In October 2013, EPA released a new Strategic
Agenda renewing the Agency's support for green infrastructure and outlining the actions the Agency
intends to take to promote its effective implementation. The agenda is the product of a cross-EPA effort
and builds upon both the 2011 Strategic Agenda and the 2008 Action Strategy.
EPA is continuing to provide technical assistance to communities working to overcome common barriers
to green infrastructure. Selected communities received assistance with a range of projects aimed at
addressing common barriers to green infrastructure, including code review, green infrastructure design,
and cost-benefit assessments.
For more information, visit http://water.epa.gov/infrastructure/greeninfrastructure/gi support.cfm.
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Acknowledgements
Principal USEPA Staff
Tamara Mittman, USEPA
Christopher Kloss, USEPA
Robert Adler, USEPA
Key Cape Cod Stakeholders
Sharon Rooney, Cape Cod Commission
Heather McElroy, Cape Cod Commission
Tabitha Harkin, Cape Cod Commission
James Sherrard, Cape Cod Commission
Dale Saad, Ph.D, Barnstable Department of Public Works
George Allaire, Yarmouth Department of Public Works
Consultant Team
Tham Saravanapavan, Tetra Tech
Russ Dudley, Tetra Tech
John Kosco, Tetra Tech
Garrett Budd, Tetra Tech
Mike Clar, Tetra Tech
This report was developed under EPA Contract No. EPA-C-11-009 as one of the 2012 EPA Green
Infrastructure Community Partner Program.
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Contents
Executive Summary 8
1. Introduction 9
2. Screening Process 11
2.1. Siting Criteria Matrix 11
2.1.1. Green Infrastructure/LID Practices 11
2.2. Green Infrastructure/LID Practice Technical Specifications 13
2.2.1. Constructed Wetlands/Stormwater Treatment Wetlands 13
2.2.2. Permeable Reactive Barriers 14
2.2.3. Phytoremediation 15
2.2.4. Biofiltration Strips (Vegetative Buffer Strips) 16
2.2.5. Bioretention 17
2.2.6. Enhanced Bioretention 19
2.2.7. Infiltration 20
2.2.8. Green Roofs 23
2.2.9. Permeable Pavement 24
2.2.10. Bioswales 26
2.2.11. Stormwater Disconnection 27
2.2.12. Gravel Wetland 27
2.3. Siting Criteria 29
2.4. Matrix Tool Application 29
2.4.1. Generic Application 29
2.4.2. Stormwater- and Wastewater-Specific Application 30
2.5. Screening Process Results 31
3. Site Assessments 32
3.1. 1 South Street - Barnstable 33
3.2. 4 Bay View Street-Barnstable 35
3.3. 0 and 47 Old Yarmouth Road - Barnstable 37
3.4. 122 Camp Street-Yarmouth 39
3.5. 669 Route 28 (Drive-ln) -Yarmouth 41
3.6. 674 Route 28 (Zooquarium) -Yarmouth 43
3.7. 165 Bearses Way-Barnstable 45
3.8. 65 Long Pond Drive-Yarmouth 47
3.9. Selection of Sites for Concept Plan Development 49
4. Model Process and Results 50
4.1. Overview of the Modeling Process 50
4.2. Evaluation of the 165 Bearses Way (School) Site 50
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4.2.1. Site Conditions 51
4.2.2. The Enhanced Bioretention for the School Site 52
4.2.3. SUSTAIN Model Setup 53
4.2.4. Model Results 55
4.2.5. Simplified Cost-Effectiveness Analysis 56
4.3. Evaluation of the 669 Route 28 (Drive-In) Site 57
4.3.1. Site Conditions 58
4.3.2. Bioretention/Phytotechnology for the Drive-In Site 59
4.3.3. SUSTAIN Model Setup 59
4.3.4. Model Results 61
4.3.5. Simplified Cost-Effectiveness Analysis 62
4.4. Groundwater Impact Analysis 63
4.5. Summary 64
5. Regulatory Pathways 65
5.1. Stormwater Discharges from Construction Activities (Construction General Permit) 65
5.2. Erosion and Sedimentation Control 65
5.3. Construction and Grading/Review/Approval 66
5.4. Special Conditions for Yarmouth Drive-In Site 66
5.4.1. Monitoring 66
5.4.2. General Regulatory Notes 66
5.4.3. Site Specific Considerations 67
5.5. Plan Development and Approval Process 67
6. Cost Estimates 68
7. Conclusions 71
8. References 72
Figures
Figure 1. Siting criteria matrix 12
Figure 2. Example of a constructed wetland system (CRWA 2008) 13
Figure 3. Typical plan view of a constructed wetland system (VADCR 2011) 14
Figure 4. Permeable reactive barrier (EPA 1999) 15
Figure 5. Typical phytoremediation process (EPA 2012) 16
Figure 6. Diagram of a typical biofiltration strip (Clar et al. 2004) 17
Figure 7. Basic bioretention models (Atchison et al. 2006) 18
Figure 8. Bioretention island (Tetra Tech) 18
Figure 9. Advanced Bioretention adapted from Lucas & Greenway (2011a) 20
Figure 10. Infiltration trench (http://ian.umces.edu/imagelibrary/) 21
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Figure 11. Landscape infiltration (VADCR 2011) 21
Figure 12. Chicago City Hall Urban Heat Island Initiative project (Source: Roofscapes, Inc.) 24
Figure 13. Permeable pavement in parking lot (Tetra Tech) 25
Figure 14. Bioswale (MDE 2009) 26
Figure 15. Stone diaphragm (VADCR 2011) 27
Figure 16. Gravel wetland (Ballestero et al. 2011) 28
Figure 17. Gravel wetland schematic (CRWA 2009) 28
Figure 18. Nitrogen removal (Ballestero et al. 2011) 29
Figure 19. Revised Screening Process Matrix 30
Figure 20. Overview of basic modeling analysis processes (Tetra Tech 2009b) 50
Figure 21. Site Plan for bioretention implementation at the School site (Cape Cod Commission/Tetra
Tech) 52
Figure 22. Cross-sectional view of the enhanced bioretention to be implemented at the School site
(Cape Cod Commission/Tetra Tech) 53
Figure 23. SUSTAIN model setup for the School site 54
Figure 24. Schematic for representing the enhanced bioretention into SUSTAIN (not to scale) 55
Figure 25. Overall water balance in the enhanced bioretention outflow at the School site 56
Figure 26. Simplified cost-effective analysis for sizing the enhanced bioretention at the School site 57
Figure 27. Site Plan for BMP implementation at the Drive-In site (Cape Cod Commission/Tetra Tech).... 58
Figure 28. Cross-sectional view of the enhanced bioretention and phytotechnology area to be
implemented at the Drive-In site (Cape Cod Commission/Tetra Tech) 59
Figure 29. SUSTAIN model setup for the Drive-In site 60
Figure 30. Schematic for representing the conventional bioretention into SUSTAIN (not to scale) 61
Figure 31. Overall water balance in the bioretention outflow at the Drive-In site 62
Figure 32. Simplified cost-effective analysis for sizing the enhanced bioretention at the Drive-In site.... 63
Tables
Table 1. Typical range of retention performance of bioretention systems expressed in terms of
concentration as opposed to mass load reduction (Lucas and Greenway 2011a) 19
Table 2. Urban Best Management Practice (BMP) Efficiencies (MDE 2011) 23
Table 3. Major land uses at the School Site 51
Table 4. List of enhanced bioretention design parameters used in the SUSTAIN representation 53
Table 5. Summary of SUSTAIN simulation results for the period of 1992/01/01 to 2002/12/31
at the School site 55
Table 6. Total cost for the enhanced bioretention at varying treatment depths 57
Table 7. Major land uses in the Drive-In site 58
Table 8. Bioretention design parameters following MassDEP design specifications 59
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Table 9. Summary of SUSTAIN simulation results for the period of 1992/01/01 to 2002/12/31 at the
Drive-In site 61
Table 10. Total cost for the conventional bioretention at varying treatment depths for the Drive-In
site 63
Table 11. Permit Requirements 65
Table 12. Preliminary Estimate of Quantities: Barnstable School Site - Enhanced Bioretention System.. 68
Table 13. Preliminary Estimate of Quantities: Yarmouth Drive-In Site-
Phytotechnology/Bioretention 68
Table 14. Preliminary Cost Estimate: Barnstable School Site - Enhanced Bioretention System 69
Table 15. Preliminary Cost Estimate: Yarmouth Drive-In Site - Phytotechnology/Bioretention 70
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Executive Summary
In many ways, Cape Cod, Massachusetts is already an example of low impact development. Very little
hardened stormwater infrastructure is present on the Cape, and stormwater runoff is often directed to
natural depression areas where it infiltrates rapidly into the sandy soils present throughout the area.
Historically, the natural infiltration capabilities of the soils also led to the installation of septic systems to
easily treat wastewater across the Cape. Unfortunately, many embayments around the Cape are now
becoming eutrophic due to the high nutrient loadings from both surface water and groundwater
sources.
Nitrogen is one of the primary pollutants impacting these embayments. Although wastewater from
septic systems represents a significant nitrogen load within impacted watersheds, the cost and logistics
of eliminating septic systems makes reducing nitrogen from wastewater difficult. As an alternative,
green infrastructure is proposed to address surface sources of nitrogen. A variety of green infrastructure
techniques are evaluated based on their efficiency in removing nitrogen and their effectiveness in the
sandy soils present on the Cape. A screening process is developed and applied to watersheds within the
communities of Yarmouth and Barnstable (two areas where environmental justice issues are also
prevalent) to identify potential sites that are most suitable for implementation of green infrastructure
techniques.
Working with a diverse group of stakeholders including consultants, staff from the Cape Cod
Commission, and local officials and community members, potential green infrastructure sites identified
through the screening process are evaluated in more depth through field visits resulting in the
development of conceptual designs on two selected sites. Conceptual green infrastructure designs at
these two sites focus on innovative practices, including enhanced bioretention and phytoremediation, to
increase nitrogen removal. Conceptual designs are also tailored to the land use and configuration of the
two sites (one site is an existing elementary school, while the other site is a proposed marina
redevelopment) to showcase additional benefits of utilizing green infrastructure for water quality
treatment.
Conceptual designs are modeled using EPA's SUSTAIN to evaluate the effectiveness of the proposed
systems in reducing stormwater runoff and total nitrogen. Modeling the proposed concepts indicates a
small reduction in runoff volume (approximately 5%) but a significant reduction in total nitrogen
(approximately 60%), based on the configuration of the techniques and the specific site conditions. An
assessment of the regulatory requirements and cost estimates of the two sites indicate few barriers to
implementation of the proposed concepts, which can serve as examples of how to effectively address
surface water sources of nitrogen. Although wastewater on the Cape represents a significant source of
pollution to local embayments, appropriate siting and use of innovative green infrastructure techniques
gives Cape Cod an alternative solution to help quickly reduce nitrogen loading within impacted
watersheds.
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I. Introduction
Cape Cod, Massachusetts is a peninsula located in the southeast portion of the Commonwealth and is
defined by water. The Cape includes 560 miles of coastline and numerous lakes, ponds, bays and inlets
that draw an estimated four million visitors to the region each year. Cape Cod is home to almost
220,000 year-round residents; the summertime population grows to an estimated 750,000 people. With
bountiful water resources and proximity to major northeast urban areas, Cape Cod has seen rapid
population growth over the last half century. Development on Cape Cod has been primarily residential
with associated commercial, industrial and tourism-based land uses.
Cape Cod geology consists primarily of sandy well-drained soils formed as a result of glacial deposits.
Cape Cod relies on a sole source aquifer (groundwater) for most of its drinking water and on its ponds,
bays, and coastal zone for much of its economy. The region also relies heavily on septic systems to
manage wastewater. Groundwater carries and ultimately discharges nitrogen from wastewater to the
coast. Of the region's 57 coastal embayments, 46 are eutrophic due to excessive nutrients and
pollutants. The watersheds of these eutrophic embayments encompass 69% of Cape Cod's land area and
2/3 of them cross town boundaries, making the restoration and management of their water quality a
regional issue.
Nitrogen is perhaps the most significant pollutant with the highest percentage resulting from the
multitude of septic systems present throughout Cape Cod. Studies from the Massachusetts Estuaries
Project (MEP) indicate that nutrients, primarily from traditional on-site septic systems and cesspools, are
seriously impairing water quality in most of the Cape Cod's estuaries studied to date. To meet the
established Total Maximum Daily Loads (TMDLs) approved by the Massachusetts Department of
Environmental Protection (MassDEP) and the United States Environmental Protection Agency (EPA), a
significant reduction of nitrogen is necessary. Although wastewater is the main source of nitrogen on
Cape Cod, eliminating excessive nutrient loading from embayments will need to address both
groundwater and stormwater through a mix of traditional and innovative wastewater management
systems, alternative nitrogen reducing options (such as aquaculture and permeable reactive barriers),
and green infrastructure. While the focus of this report is on impairments from nitrogen, it is worth
noting that many of the Cape's freshwater ponds and lakes are also impaired by phosphorous, another
nutrient, which comes from sources such as rainfall runoff, septic systems and fertilizers.
The Cape Cod Commission (CCC) is developing a Regional Wastewater Management Plan (RWMP) to
identify the best combination of watershed approaches to manage nitrogen to restore the quality of the
region's coastal waters in a ways that consider costs to homeowners to the best extent feasible. The
goal of the RWMP is to develop and implement nitrogen reducing approaches and strategies that
integrate water quality restoration with affordability, appropriate infrastructure, and growth
management. Much of the implementation will be the responsibility of the communities of Cape Cod
under their local Comprehensive Wastewater Management Plans, while the RWMP will be implemented
by the CCC with the approval of MassDEP.
The dispersed pattern of development, relatively low incomes and aging population on Cape Cod, and its
fragile natural environment, make the cost of constructing sewer systems throughout the entire region
both impractical and unsustainable, particularly for the most vulnerable populations. To achieve TMDLs
at affordable rates, the communities and the CCC will consider installing sewers in more densely
populated areas while also capitalizing on advanced decentralized wastewater systems, natural
attenuation, and green infrastructure methods to remove nitrogen and other pollutants from the Cape's
watersheds.
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As part of the RWMP, CCC staff has examined opportunities including dredging, inlet widening, and
aquaculture. However, additional data are needed to establish the percent nitrogen removal that can be
attained using green infrastructure solutions. This EPA technical assistance focused on the use of
constructed wetlands and green infrastructure stormwater management practices to reduce nitrogen
within Environmental Justice (EJ) communities.
The overall intention of this project is to identify areas within EJ communities where pollutants from
stormwater may be addressed closer to the source at a reasonable scale and cost. It also offers greater
opportunities for creating access to green open space, providing air quality benefits, recreational
opportunities, and re-establishing the human-environment connection. Many of the green
infrastructure options discussed in this report are transferable among similar communities and can
provide EJ community youth with construction and landscaping skills and improved job opportunities for
building and maintaining these practices. Such projects are needed throughout the region and could
help provide sustainable solutions for community resiliency.
Technical assistance was provided through EPA's 2012 Green Infrastructure Technical Assistance
Program to develop conceptual designs for green infrastructure projects in the Lewis Bay/Parkers River
watersheds. These concepts are specifically targeted and designed to remove nitrogen from
groundwater and stormwater sources.
As part of the project, a screening process was refined to utilize a siting criteria matrix to identify areas
of opportunity for green infrastructure practices. The green infrastructure practices identified and
assessed as part of the screening process were specifically selected for nitrogen reduction capabilities
and included constructed wetlands, phytoremediation, enhanced bioretention and many others.
Application of the screening process resulted in the selection of eight high opportunity sites for green
infrastructure placement. These sites were investigated in more detail through a field site assessment
that evaluated physical, public outreach, economic, water quality, and constructability considerations.
The project team presented the screening process and the site opportunities to a group of local
stakeholders from the towns of Barnstable and Yarmouth. This group of stakeholders, Commission staff,
and consultants collectively selected two sites to advance to conceptual designs. An advanced
bioretention system was designed for an elementary school in Barnstable and a
bioretention/phytoremediation area was designed for a proposed marina site in Yarmouth. In addition,
conceptual plans and details, an analysis of the regulatory pathway, and cost estimates for the two sites
were also developed.
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2. Screening Process
The project team collaborated to develop a screening process to identify site opportunities for green
infrastructure and LID practices throughout the Lewis Bay and Parkers River watersheds. The screening
process began with a desktop investigation of potential sites by utilizing a siting criteria matrix
developed by CCC. This matrix tool was applied to parcels within the Lewis Bay and Parkers River
watersheds. Field assessments of the highest scoring parcels were performed by CCC resulting in eight
potential sites for the development of conceptual green infrastructure designs; four sites were identified
in Barnstable and four in Yarmouth.
2.1.1. Green Infrastructure/LID Practices
The siting criteria matrix consists of multiple GIS-based data layers (termed "siting criteria") along the
vertical axis and a collection of potential green infrastructure and LID practices on the horizontal axis
(See Figure 1 below). The practices identified have been selected based on their high nitrogen removal
efficiencies and represent a range of practices that are applicable in a wide variety of conditions.
Since the proposed green infrastructure and LID practices are applicable in a variety of settings, one can
expect a range of performance from any given practice, depending on how appropriate it is for the
selected location. "A variety of site criteria should be evaluated to determine if a specific practice is
suitable for a given site; an V in the matrix below indicates siting criteria that are used to help identify
appropriate sites for different practices. Alternatively, some practices may not be appropriate for a
location when evaluated with some siting criteria; these are designated in the matrix with a 'c' (for
constrained). Blanks in the matrix indicate that the specific practice is not impacted either positively or
negatively by the siting criteria -the siting criteria has no real influence on whether the site is
appropriate for implementation of the green infrastructure or LID practice. As an example of how this
matrix is used, sites with well drained soils are appropriate for most of the techniques evaluated,
including infiltration and phytoremediation. But if a high groundwater table is also present, this
constraint can make the site infeasible for infiltration practices while phytoremediation is not
significantly limited by this condition. Utilization of the siting criteria matrix is necessary to identify
appropriate, technique-specific sites for potential implementation.
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Siting Criteria
Floodplain: V zone
Floodplain: A zone
SLOSH
350 ft buffer to vernal pool
100 ft buffer to wetland
USGS zone of contribution
Zone ll's
Soils: disturbed
Soils: well drained
Within open space: agricultural
Within open space: protected
Within open space: recreation
Within open space: government
Adjacent to open space: agricultural
Adjacent to open space: protected
Adjacent to open space: recreation
Adjacent to open space: government
Wellhead Protection Areas (i.e. Zone I)
DEP wetlands
Endangered species habitat
Depth to groundwater > 4'
Depth to groundwater < 4'
Proximity to golf courses, athletic fields
Impervious areas
Proximity to schools, etc.
Constructed
Wetlands
c
c
c
c
X
c
X
X
c
X
X
X
X
c
c
c
c
X
X
X
X
Permeable Reactive
Barriers
X
X
X
X
X
X
c
X
c
X
Stormwater
Treatment
Wetlands
X
X
X
c
c
X
X
X
X
c
X
X
X
c
X
X
c
c
c
c
X
X
X
X
Phytoremediation
c
c
c
c
X
X
c
X
X
Biofiltration Strips
X
X
X
c
c
X
X
X
X
c
X
X
X
c
X
X
X
X
Bioretention/Advan
ced Bioretention
c
c
X
X
c
X
c
X
X
Infiltration
c
X
c
X
c
X
X
c
01
£
o
Permeable
Pavement
c
c
c
c
X
c
X
c
X
X
Bioswales2
c
X
X
Stormwater
Disconnection
X
X
X
X
Gravel Wetland
c
c
c
c
X
c
X
1 Green roofs have a significantly different set of siting criteria from other stormwater LID techniques
2 Although bioswales can be designed to function as infiltration BMPs, those mentioned here are designed as water quality BMPs
3 An "x" indicates that a practice is appropriate for a site, based on the evaluation criterion, while a "c" indicates that a practice may have
significant constraints at a site.
Figure I. Siting criteria matrix
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Larger practices such as permeable reactive barriers have a large number of siting criteria and site
constraints that are necessary to evaluate to determine appropriate locations because these practices
are highly dependent on specific site conditions. This limits the areas where placement of these
techniques is feasible and beneficial. Alternatively, practices such as bioretention or pervious pavement
can be applied to a wide variety of sites and conditions and have fewer siting criteria or constraints.
A detailed understanding of the characteristics of each practice is important to determine optimal sites.
Several of the potential techniques to be evaluated for this project are described in Section 2 below.
Siting criteria and constraints used in the screening process to identify appropriate sites are discussed;
variations of these techniques could be proposed as part of the concept plan development.
2.2. Green Infrastructure/LID Practice Technical Specifications
2.2.1. Constructed Wetlands/Stormwater Treatment Wetlands
Description: Constructed wetlands are intended to simulate the functions of natural wetlands by
utilizing vegetation, soils, and microbial activity (MassDEP 2003). Constructed wetlands are typically
separated into surface flow wetlands and subsurface flow wetlands (which will be discussed in a
following section).
Surface flow wetlands (often called stormwater treatment wetlands) treat surface water runoff from
storm events. Constructed wetlands are generally implemented in upland areas, as placement in or near
natural wetlands and streams require a Section 404 permit, and care should be taken in regards to the
constructed wetland discharge, which can impact the water temperature of fisheries or the hydroperiod
of downstream wetlands (VADCR 2011).
Constructed wetlands can be built in areas of high groundwater, which can be used to maintain the
hydrology. Designs should create a long flowpath and a footprint equal to approximately 3% of the
contributing drainage area (VADCR 2011). An example of a constructed wetland is shown in Figure 2
below and a typical plan view is shown in Figure 3.
Figure 2. Example of a constructed wetland system (CRWA 2008)
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Figure 3. Typical plan view of a constructed wetland system (VADCR 201 I)
Nitrogen Removal Process and Efficiency: Nitrogen (N) removal occurs through physicochemical and
biological processes, with the main nitrogen removal process being nitrification followed by
denitrification (Lee et al. 2009). Connection to the groundwater table can result in treatment of nitrogen
from septic system discharges but can also reduce the pollutant removal efficiency of the system, since
constructed wetlands require a long residence time for pollutant removal. Total nitrogen (TN) removal
for constructed wetlands can reach a maximum of 55% (CRWA 2008). If properly designed and
constructed, constructed wetlands can achieve high pollutant removal for a period of 10 years with
minimal maintenance.
Effectiveness in the sandy soils such as on Cape Cod: Constructed wetlands require proper hydrology to
maintain necessary plant communities and provide aerobic and anaerobic zones for nutrient processing.
This may not be possible in highly permeable upland areas unless groundwater interaction is available.
Implementation in these areas could require an impermeable liner which would increase the cost and
eliminate the ability to treat septic system discharges.
2.2.2. Permeable Reactive Barriers
Description: A Permeable Reactive Barrier (PRB) is a stratified multi-media biofilter containing sand,
expanded clay and lignocellulosics (plant dry matter), and/or elemental sulfur (Figure 4). PRBs are
trenches, or trench-like features, filled with organic materials such as sawdust and/or wood chips that
serve as energy sources - food - for microbes/bacteria for removal by denitrification (Ecosite 2011). To
be effective, PRBs must be able to intercept the flow of groundwater containing nitrogen without
getting bypassed either below or around the barrier (ITRC 2011). This requirement results in placement
of PRBs where the groundwater is typically shallow. Since PRBs are a passive in-situ technique, they are
reliant on the natural groundwater gradient for treatment and require a higher permeability than the
surrounding soil to ensure transport through the PRB. The lignocellulosics used in nitrogen-removal
PRBs have a high porosity, improving the groundwater transport through the systems.
PRBs are highly effective in treating groundwater nitrogen, particularly due to the low nitrogen
concentrations (often 1.0 mg/L-5.0 mg/L) found in contaminated groundwater. PRB's should be placed
only into freshwater groundwater -because coastal salt water can rot saw dust or wood chips. PRBs
placed in tidal zones can also be affected by density driven circulation which can result in the nitrate
plume undercutting the PRB (Vallino et al. 2008).
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ground surface
permeable
reactive
barrier
contaminated
ground water
direction of ground water flow |
I permeable
I reactive
i barrier
clean
ground water
Figure 4. Permeable reactive barrier (EPA 1999)
Nitrogen removal process and efficiency: This technology can provide effective removal at runoff
concentrations, and remains effective after 15 years. TN reductions of greater than 95% can be achieved
at retention times less than 10 hours (Ecosite 2011). NITREX™ PRBs are proprietary practices that have
been installed in locations on Cape Cod that have a specific media mix to remove nitrogen. Studies have
shown that these systems can remove 99% of groundwater nitrate concentrations. Other non-
proprietary practices are currently being developed and tested for efficiency in groundwater nitrate
removal.
Effectiveness in the sandy soils such as on Cape Cod: PRBs require a higher permeability than the
surrounding soil to prevent bypass flows around the system. Implementation in sandy soils could limit
the effectiveness or require a much larger PRB.
2.2.3. Phytoremediation
Description: Phytoremediation utilizes specific plant communities (Figure 5) to uptake and either store
or process pollutants, or to change pollutants to less harmful forms by microbes located near plant roots
(EPA 2001). Phytoremediation is a low-cost, aesthetically-pleasing alternative for pollutant removal. Past
nitrogen-removal phytoremediation projects have focused on hazardous metals and chemicals but
recent projects have studied the nitrogen uptake capability of aquatic plants such as water hyacinth.
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tree roots take
in water and
pollution from
the ground
polluted soil
water enters tree
where pollution is
cleaned up
clean soil
clean
groundwater
water table -
polluted
groundwater
Figure 5. Typical phytoremediation process (EPA 2012)
Nitrogen removal process and efficiency: Phytoremediation is a promising technique for nitrogen
reduction but limited information is available on removal efficiency, especially in cold weather climates
such as Cape Cod.
Effectiveness in the sandy soils such as on Cape Cod: To be effective, trees in upland areas should have
root systems that can penetrate the groundwater table. Phytoremediation can be used in sandy
conditions as long as the soils can support the types of trees used and the root systems can reach the
groundwater table. Property owners, developers, landscape architects, and site engineers should
consult with soils maps, town/USGS hydrogeologic GIS data layers, or conduct at least a minimal
hydrogeologic assessment to determine groundwater depths suitable to the region's vegetation used in
this technique.
2.2.4. Biofiltration Strips (Vegetative Buffer Strips)
Description: Biofiltration strips, or vegetated buffer strips, are densely vegetated areas of land that
accept runoff as sheet flow and facilitate sediment attenuation and pollutant removal (Clar et al. 2004)
(Figure 6). Biofiltration strips are often used to treat runoff from roads, parking lots, rooftops, and other
impervious surfaces or are used as pretreatment.
Biofiltration strips require sheet flow to be effective; if runoff concentrates before reaching the
biofiltration then a level spreader can be used to distribute the flow. Large runoff flows should be
avoided to prevent concentrated flow, limiting the size and treatment area of the biofiltration strip. The
contributing drainage area should be kept to a maximum of 5 acres to prevent concentrated flows (Clar
et al. 2004).
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Impervious surface
Wooded cover
Receiving \
water )
Figure 6. Diagram of a typical biofiltration strip (Clar et al. 2004)
Nitrogen removal process and efficiency: If flow rates are kept low, biofiltration strips are effective at
removing sediment and phosphorus (P). Nitrogen removal rates are significantly lower with only 10%
removal of nitrate/nitrite. The best performance for this type of nitrogen removal are in areas of high
infiltration.
Effectiveness in the sandy soils such as on Cape Cod: The best pollutant reduction for biofiltration strips
are attained in highly permeable soils making this technique widely useable in many areas of Cape Cod,
especially as a pretreatment technique for other green infrastructure features.
2.2.5. Bioretention
Description: Bioretention is a method of treating stormwater by ponding water in shallow depressions
underlain by a sandy engineered soil media (Figure 7 and Figure 8), through which most of the runoff
passes and includes common practices like rain gardens (Clar 1993). Bioretention can easily be
incorporated into the landscape to address and maintain any or all of the essential hydrologic functions
including: canopy interception, evapotranspiration, groundwater recharge, water quality control, runoff
volume and peak discharge control. Pollutants in runoff are then settled, filtered, adsorbed, taken up,
immobilized, and/or transformed. This extensive array of pollutant retention mechanisms makes
bioretention one of the most effective practices in the designer's toolbox.
17
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ta
Limiting Layer
Undent rain
"Basic" Facility
Figure 7. Basic bioretention models (Atchison et al. 2006)
Limiting Layer
"Enhanced" Facility
Figure 8. Bioretention island (Tetra Tech)
Nitrogen removal process and efficiency: Table 1 presents a generalized summary of bioretention
performance for a variety of stressors. Numerous studies (as cited in Davis et al. 2009) document that
bioretention performs well for total suspended solids (TSS) and associated particulate stressors, as well
as metals and hydrocarbons. This is due to the effectiveness of bioretention at filtering solids while the
negatively charged organic amendments have a very high affinity for positively charged metals.
Biological activity also effectively removes biochemical oxygen demand (BOD) and hydrocarbons.
However, many properties of typical bioretention systems also impede effective nutrient retention.
Negatively charged dissolved P and N are actively repelled by the negative binding sites that dominate
typical bioretention media. Furthermore, particulate nitrogen has many components that break down
18
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and are eventually transformed into negatively charged dissolved forms. As a result, retention of these
forms of N and P is much less effective.
Table I. Typical range of retention performance of bioretention systems expressed in terms of
concentration as opposed to mass load reduction (Lucas and Greenway 201 la).
Runoff Stressor
Total Suspended Solids (TSS)
Biological Oxygen Demand (BOD)
Total Copper
Total Zinc
Oil and Grease
Particulate Phosphorus
Dissolved Phosphorus
Dissolved Nitrogen
Particulate Nitrogen
Typical
Inflow (mg/l)
15-350
1.50-22.0
0.01-0.28
0.03-0.35
0.40-20.0
0.10-2.20
0.05-1.50
0.10-3.70
0.50-3.50
Range of Reduction
90-99%
80-90%
60-90%
85-95%
95-99%
95-99%
10-30%
-40-40%
25-50%
As P is often the 'limiting' nutrient (the principal controlling factor) for freshwater impoundments, such
as lakes and reservoirs, excess P increases eutrophication by stimulating the growth of plankton and
larger aquatic plants. On the other hand, as N is often the 'limiting' nutrient for salty-mixed estuarine
waters, excess nitrogen causes eutrophication - excessive plant growth and low dissolved oxygen - in
these ecosystems, although P at times can also be implicated (Correll 1999). N is the second most
common element in living cells and P is a fundamental component of cellular metabolism. N is the
fundamental element in all amino acids that make up proteins, and is also a basic component of DNA. N
and P are typically found at an N:P ratio of approximately 16:1 in plankton.
Effectiveness in the sandy soils such as on Cape Cod: Bioretention tends to work best in sandy soils
such as those present in many areas of Cape Cod. Sandy soils allow bioretention systems to be designed
as infiltration systems, which provide better performance than filter designs. In addition, sandy soils are
well suited for the use of in-situ design and construction techniques for bioretention systems (Clar 2010)
that can reduce construction costs to 25% of traditional systems.
2.2.6. Enhanced Bioretention
Description: Specialty media can be combined with outlet controls to improve nutrient retention
performance of bioretention systems. Media can be amended with materials with a high P sorption
capacity to improve P retention. The enhanced (or advanced) bioretention system (ABS) contains high
amounts of alum from water treatment residuals (WTRs). Adding WTR amendments to media greatly
improves P retention (Lucas and Greenway 2011).
Increasing hydraulic retention time also increases N retention. The outlet used in the ABS provides a
novel approach to resolve the conflicting goals of restricting flows to extend retention time for N
retention, while minimizing bypass flows (Figure 9). This is accomplished by a dual stage outlet (Lucas
and Greenway 2011a). The lower outlet is elevated above the stone layer so as to provide a saturated
zone and regulated to provide a flow rate of approximately 8 cm-h"1 when the media begins to pond.
19
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Surface Ponding
at high flows
Inflow from
source area
Bypass overflows only
during extreme events
High flows through^ *•
Upper Outlet
Low flows through
Lower Outlet
Low and high flows
through Media
Low and high flows
through Underdrain
Saturated
Zone
Liner installed if
native infiltration
rate>10cm-rr1
Figure 9. Advanced Bioretention adapted from Lucas & Greenway (20! la)
It is supplemented by an upper outlet that flows when ponding occurs, with its flow rate determined by
media saturated hydraulic conductivity (Ksat) and relative head. Due to high Ksat in the media, this
arrangement allows for substantial flows to pass through the media. With such an outlet, the plug flow
retention through rapidly infiltrating media time increases to 150 minutes compared to the free
discharge retention time less than 20 minutes (Lucas and Greenway 2011b). This results in greatly
improved N retention compared to free discharge bioretention systems typically used (Lucas and
Greenway 2011c).
Nitrogen removal process and efficiency: The initial N and P retention performance of the ABS
presented in Lucas and Greenway (2011a) showed that Total Dissolved Phosphorus (TOP) retention from
stormwater after over 30 years of urban runoff was 93%, with 99% retention of PO4-P.
Lucas and Greenway (2011a) present results from large events (approximately 6 month recurrence
interval for Brisbane, Australia) that show TN retention of 66%, with NOX retention of 62%. The
corresponding retention in typical bioretention systems was 27% and 19% respectively, documenting
the benefits of the dual outlet of the ABS in increasing N retention. When subjected to a smaller dose
representative of a more typical event, TN retention increased to as high as 78%, while NOx retention
was as high as 94%. The ABS was able to provide a significant increase in N retention compared to the
corresponding free discharge treatment.
Effectiveness in the sandy soils such as on Cape Cod: The advanced bioretention system is more
effective than typical retention techniques in sandy soils. It does not require liners and can work in any
soil.
2.2.7. Infiltration
Description: Infiltration is used to both describe a process whereby stormwater is infiltrated into the
soil, and also a series of storm water practices whose primary function is to infiltrate storm water runoff.
These stormwater practices include infiltration trenches (Figure 10), infiltration basins, landscape
infiltration (Figure 11), and dry wells. In addition, a number of practices also use infiltration as part of
20
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the design when suitable soils are present. These practices include bioretention, bioswales, and filter
strips.
Figure 10. Infiltration trench (http:llian.umces.edulimagelibraryf)
DISCI-IAflQE TO RAIN
GAflCCN OR OTHER TREATMENT PRACTICE
(SCE SPECIFICATIONS FOfi tKTA^S
DOWNSPOUT
DISCONNECTION MINIVUM LENGTH AS
REQUIRED
-SIV«>LE raSCONNECTlON;
-SCXL COMPOST AWtNOfcD HL1E.H PATH
-PRETREATMENT VulTH CONCENTRATED
INFLOW TO RAN GARDEN
Figure I I. Landscape infiltration (VADCR20I I)
21
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Nitrogen removal process and efficiency: EPA's Chesapeake Bay Program (CBP) and the Maryland
Department of the Environment (2009) report total nitrogen (TN) removal rates as high as 80% for
stormwater infiltration practices as shown in Table 2 below. However in the same table, they report that
landscape infiltration practices have a nitrogen removal rate of 50%. Removal efficiencies for total
phosphorous (TP) and total suspended solids (TSS) are shown a well. Both of the rates appear rather
high compared to the reported removal rates for bioretention practices shown in Table 1. The
bioretention removal rates from Table 1 represent a conservative assessment of infiltration removal
rates.
Effectiveness in the sandy soils such as on Cape Cod: Infiltration practices require well-drained sandy
soils, which are present in many areas of Cape Cod. The presence of high water tables will limit the use
of this practice.
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Table 2. Urban Best Management Practice (BMP) Efficiencies (MDE 201 I)
BMP Practice
CBP Structural BMPs
Drv Detention Ponds
Hydiodvnamic Structures
Drv Extended Detention Ponds
Wet Ponds and Wetlands
Infiltration Practices
Filtering Practices
Vegetated Open Channels
Erosion and .Sediment Control
Stormwater Management by Era
Development Between 1985 - 2002
Urban BMP Retrofit
Development Between 2002 and 2010
Development After 2010
ESD to the MEP from the Manual
Green Roofs
Permeable Pavements
Reinforced Turf
Disconnection of Rooftop Runoff
Disconnection of Non-Rooftop Runoff
Sheetflow to Conservation Areas
Rainwater Harvestina
Submersed Gravel Wetlands
Landscape Infiltration
Infiltration Beniis
Drv Wells
Micro-Bioretention
Rain Gardens
Grass. Wet. or Bio-Swale
Enhanced Filters
Additional Structural BMP Guidance
Redevelopment (MDE)
Existing Roadway Disconnect (MDE)
Step Pool Storm Conveyance (MDE)
TN
5%
5%
20%
20%
80° o
40%
45%
25%
17%
25%
30%
50%
50° o
50%
50° o
50%
50%
50%
50%
50%
50%
50%
50%
50%
50%
50%
50%
50%
50%
50%
TP
10%
10%
20%
45%
85%
60%
45%
40%
30%
35%
40%
60%
60%
60%
60%
60%
60%
60%
60%
60%
60%
60%
60%
60%
60%
60" o
60%
60%
60%
60%
TSS
10%
10%
60%
60%
95%
80%
70%
40%
40%
65%
80%
90%
90%
909 b
90%
90%
90%
90%
90%
90%
90%
90%
90%
90%
90%
90° o
90%
90%
90%
90%
(Adapted from CBP Urban BMP Efficiencies, and Stonnwater Management by Era. MDE 2009)
2.2.8. Green Roofs
Description: Green roofs are alternative roofing systems that replace conventional construction
materials or retrofit existing roofs and include a protective covering of planting media and vegetation.
Also known as vegetated roofs or eco-roofs, these may be used in place of traditional flat or pitched
roofs to reduce impervious cover and more closely mimic natural hydrology to help mitigate stormwater
impacts. The vegetative cover of green roofs can also lower ambient air temperatures in the summer
and provide insulation in the winter, therefore reducing cooling and heating demands for buildings.
23
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There are two basic green roof designs that are distinguished by media thickness and the plant varieties
that are used. The more common or "extensive" green roof (Figure 12) is a lightweight system where
the media layer is between two and six inches thick. This limits plants to low-growing, hardy herbaceous
varieties. An extensive green roof may be constructed off-site as a modular system with drainage layers,
growing media, and plants installed in interlocking grids. Conventional construction methods may also
be used to install each component separately.
"Intensive" green roofs have thicker soil layers (eight inches or greater) and are capable of supporting
more diverse plant communities including trees and shrubs. A more robust structural loading capacity is
needed to support the additional weight of the media and plants. Intensive green roofs are more
complex and expensive to design, construct, maintain, and therefore are less commonly used.
linn
nun
i mi"
i n »"
n id"11
Figure 12. Chicago City Hall Urban Heat Island Initiative project (Source: Roofscapes, Inc.)
Nitrogen removal process and efficiency: EPA's Chesapeake Bay Program and the Maryland
Department of the Environment (Table 2) report that green roofs have a nitrogen removal rate of 50%
(MDE2011).
Effectiveness in the sandy soils such as on Cape Cod: The soil type is not a factor in green roof selection
or design.
2.2.9. Permeable Pavement
Description: Permeable pavements are alternatives to traditional pavements or concrete that may be
used to reduce imperviousness (Figure 13). While there are many different materials commercially
available, permeable pavements may be divided into three basic types: porous bituminous asphalt,
porous concrete, and interlocking concrete paving blocks or grid pavers. Permeable pavements typically
24
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consist of a porous surface overlaying a course and uniformly graded stone or sand drainage system.
Stormwater drains through the surface course, is captured in the drainage system, and infiltrates into
the surrounding soils. Permeable pavements significantly reduce the amount of impervious cover,
provide water quality and groundwater recharge benefits, and may help mitigate temperature
increases.
Figure I 3. Permeable pavement in parking lot (Tetra Tech)
Nitrogen removal process and efficiency: In a review of stormwater control measures used to manage
nitrogen, Collins et. al (2010) indicated that, "several studies have suggested that aerobic conditions,
which typically occur as runoff drains through permeable pavements, can result in nitrification of NH4+
to NO3~." Substantially lower NH4-N and total Kjeldhal nitrogen (TKN) concentrations and higher NO3-N
concentrations have been measured in permeable pavement drainage as compared to asphalt runoff in
multiple experiments. A few studies have shown a decrease in concentrations of all measured nitrogen
species (NH4-N, TKN, and NO3-N) (EWRI 2012).
EPA's Chesapeake Bay Program and the Maryland Department of the Environment recommend using a
50% nitrogen removal rate for permeable pavements (Table 2) (MDE 2011).
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Effectiveness in the sandy soils such as on Cape Cod: Permeable pavement stormwater practices are
essentially infiltration techniques and, as such, work best with well drained sandy soils such as are
present in many areas of Cape Cod. The presence of high water tables will limit the use of this practice.
2.2.10. Bioswales
Description: Bioswales are channels that provide conveyance, water quality treatment, and flow
attenuation of stormwater runoff (Figure 14). Bioswales provide pollutant removal through vegetative
filtering, sedimentation, biological uptake, and infiltration into the underlying soil media. Both wet and
dry bioswales can be implemented, the appropriate type being dependent upon site soils, topography,
and drainage characteristics.
•APPROVED PLAN CHANNEL WIOTH-
PEA GRAVEL
D1APHRAM
(No. 67 STONE,
WIN 6*< 12-s)
STONE RESERVOIR
(No 67 STONE
JM'PIAWTWG MEDIA
'(WIN. 2 fl. THICKh
4" BRIDGING LAYER
'd/a* - 3,'a- STONEJ
PERFORMED UNCERDRAIN
•
Section
CHANNEL BOTTOM
WIDTH?, an
Plan View
Figure 14. Bioswale (MDE 2009)
Nitrogen removal process and efficiency: EPA's Chesapeake Bay Program and the Maryland
Department of the Environmental recommend using a 50% removal rate for bioswales (Table 2) (MDE
2011).
Effectiveness in the sandy soils such as on Cape Cod: Bioswale stormwater practices work best with
well-drained soils that encourage infiltration as part of the water quality treatment approach; well-
drained soils are present in many areas of Cape Cod. The presence of high water tables may require the
use of a wet swale.
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2.2.1 I. Stormwater Disconnection
Description: Stormwater disconnection is used to describe a process whereby stormwaterfrom
impervious surfaces is directed to pervious areas such as lawns, where the runoff has an opportunity to
be filtered and infiltrated into the soil. Stormwater disconnection can also refer to a series of
Stormwater practices conceived to achieve this objective. Commonly used practices include rooftop
downspout disconnection, impervious non-rooftop area disconnection, and discharge to conservation
areas (MDE 2009). A number of practices can be used to achieve the disconnection including rain
gardens, dry wells, and stone diaphragms, such as the one shown in Figure 15.
GRAVEL DIAPHRAGM SHEET FLOW PRETREATMENT
fc=J ? t31 fcj1 ta 113 Itr"
NTS
Figure 15. Stone diaphragm (VADCR 20! I)
Nitrogen removal process and efficiency: EPA's Chesapeake Bay Program and the Maryland
Department of the Environment recommend using a 50% removal rate for Stormwater disconnection
(Table 2) (MDE 2011).
Effectiveness in the sandy soils such as on Cape Cod: Stormwater disconnection practices work best
with well drained sandy soils, which are present in many areas of Cape Cod.
2.2.12. Gravel Wetland
Description: The gravel wetland is designed as a series of flow-through treatment cells, preceded by a
sedimentation basin (Figure 16 and Figure 17). It is designed to attenuate peak flows and provide
subsurface anaerobic treatment. The subdrains distribute the incoming flow, which then passes through
the gravel substrate, and then to the opposite subdrains, into the adjacent cell, and then exits the
treatment system by gravity. In the event of a high intensity event, the water quality volume is stored
above the wetlands, and drains into the perforated riser on one end of the wetland, and into the
substrate. Biological treatment occurs through plant uptake and soil microorganism activities. This is
followed by physical-chemical treatment within the soil including filtering and absorption with organic
matter and mineral complexes.
27
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Figure 16. Gravel wetland (Ballestero et al. 201 I)
INLET FROM SEDIMENTATION FOREBAY
(12" PIPE)
RISER
(6-PERFORATED PIPE)
DENSE WETLAND
VEGETATION
24'SUBSURFACE
GRAVEL
(314.' CRUSH ED
STONE)
SUBSURFACE DRAIN
|6'PERFORATED PIPE)
OUTLET PIPE
(ELEVATED PIPE
8- BELOW WETLAND SURFACE
TO ENSURE THAT SOU. IS
CONTINUOUSLY SATURATED)
Figure 17. Gravel wetland schematic (CRWA 2009)
Nitrogen removal process and efficiency: UNH Stormwater Center provides the following guidance and
nitrogen removal efficiencies (Figure 18) (Ballestero et al. 2011):
• Systems must be vegetated, sedimentation plays a minor role;
• Biologically-mediated conversion processes, whether aerobic or anaerobic;
• Microbial decomposition of organic matter produces reduced NH3 which is treated commonly
through biological oxidation (nitrified) to NO2/NO3 and then treated by biological reduction
anaerobically to N2.
Organic N=TKN
TN = Organic N+NH3+NH4+NO2+NO3
28
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100%
90%
o 8°%
&70%
I 60%
| 50%
1 40%
E 30%
B
20%
10%
0%
Gravel Wetland Performance
46 mg/L 769 ug/L 0.27 mg/L 0.046 mg/L 0.09 mg/L
UAnnual
MedRE
TSS
TPH-D
DIN
Zn
TP
Figure 18. Nitrogen removal (Ballestero et al. 201 I)
Effectiveness in the sandy soils such as on Cape Cod: The gravel wetland must be lined at the bottom to
maintain anaerobic conditions and is not dependent on soil type.
2.3. Siting Criteria
Siting criteria can consist of both positive criteria and constraints. To identify locations for potential
green infrastructure practices, siting criteria have been selected that focus on significant sources of
nitrogen, high public exposure, favorable site conditions, and ease of implementation. Siting criteria that
focus on public exposure and ease of implementation can be applied universally and tend to identify
publicly owned land or community amenities in high-density areas. Other criteria are highly dependent
on the practice evaluated. Impervious area represents a significant source of nitrogen and serves as a
siting criteria for green infrastructure. These same sites would not necessarily favor groundwater-
intercepting techniques, as wastewater in high-density areas is often collected and treated for nitrogen
removal at a central location. In other cases, siting criteria that indicate an appropriate location for one
practice could be a constraint for another. For example, infiltration-based practices require well-draining
soils while constructed wetlands are not feasible in well-draining soils unless a high groundwater table is
present. The screening process utilizes the siting criteria matrix to differentiate parcels based on these
green infrastructure and LID practices.
2.4. Matrix Tool Application
2.4.1. Generic Application
Once the practices were identified and the siting criteria matrix developed, the CCC (GIS program)
applied the siting criteria to each parcel within the two target watersheds in Yarmouth and Barnstable.
The siting criteria matrix was initially applied generically. The green infrastructure practices were not
evaluated separately; instead, parcels were assessed using a combination of all siting parameters for
both wastewater and stormwater applications. A total of 14 siting parameters were assessed for each
site and weighted equally, giving potential sites a maximum score of 14. CCC decided not to apply the
constraints identified within the matrix to the parcels so that the number of potential sites would not be
significantly reduced. Applying constraints during the screening process could eliminate high
opportunity parcels if only a small piece contained a defined constraint. Instead, CCC evaluated site
constraints during the field assessments of the selected parcels.
29
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The initial generic application of the matrix as part of the screening process resulted in 14 parcels that
received a score of eight or more. A few of these initial 14 were eliminated based on review of aerial
photos indicating that they were highly developed sites and/or privately owned. The remaining eight
parcels were selected for further investigation through field assessments. Characteristics such as
topography, development condition, neighboring uses, etc. were evaluated on the site, and
presence/absence of wetlands, known location of Zone II and floodplains, and other constraints were
discussed in the field and noted on site assessment forms.
Following analysis of these initial field results, CCC revised the criteria over the course of two more
iterations to include the following resources, addressing both stormwater and wastewater siting
interests: Environmental Justice communities, well drained soils, within recreation and/or government
open space, adjacent to protected and/or government open space, proximity to golf courses, and
impervious surfaces. In total, there were eight potential siting criteria (see Figure 19 below); when the
GIS had run these criteria within the impaired watersheds within Barnstable and Yarmouth, the highest
possible score was five. CCC filtered the results to show all parcels with a score of four or above that
were coded as publicly owned. This exercise confirmed the sites previously visited and added 14 more
parcels that CCC staff thought should be evaluated. Additional field visits were made, noting constraints
in the field on site assessment forms.
Siting Criteria
Soils: disturbed
Soils: well drained
Within open space: recreation
Within open space: gowrnment
Adjacent to open space: recreation
Adjacent to open space: gowrnment
Proximity to golf courses, athletic fields
Impervious areas
1 Green roofs have a significantly different set of siting criteria from other stormwater LID techniques
Figure 19. Revised Screening Process Matrix
During the course of the field visits and the intervening time, CCC staff had opportunities to speak with a
few abutters and potential project partners, which assisted in the decision to move forward or drop sites
from consideration. Sites such as 122 Camp Street, a privately owned condominium/affordable housing
project, initially seemed an unlikely candidate until a conversation with a resident indicated the
potential for innovative solutions on the site.
2.4.2. Stormwater- and Wastewater-Specific Application
The initial, generic application of the siting criteria matrix resulted in 14 parcels that ranked highly for all
siting criteria. These parcels contain a mix of parameters that favor techniques to address groundwater
sources, stormwater sources, or both. In the end, the CCC settled on a refined set of siting criteria to
identify potential sites, as discussed above. However, during the course of examining appropriate
criteria to identify viable sites, the CCC ran separate screening processes to address green infrastructure
practices that favor groundwater sources and LID practices that favor stormwater sources,
30
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independently. This iteration, separating the screening approaches, resulted in fewer siting criteria to
evaluate but more technique-specific sites. CCC applied the siting criteria matrix to parcels utilizing this
specific approach, which confirmed sites previously selected, and identified additional high opportunity
areas for green infrastructure and LID practices.
2.5. Screening Process Results
A desktop-based application of the different iterations of the siting criteria matrix identified more than
15 total high opportunity areas for the placement of green infrastructure and LID practices. Subsequent
field assessments identified six potential sites from the original generic matrix application and an
additional two (2) sites from the specific matrix application. These sites were equally distributed
between the communities of Barnstable and Yarmouth. Maps of these sites, along with a further
suitability analysis examining possible constraints based on the field assessments, is included in the
assessment of potential sites. These eight sites will be evaluated in more detail with input from other
community stakeholders to identify two sites for green infrastructure conceptual designs.
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3. Site Assessments
The CCC utilized the previously developed siting criteria matrix tool to identify potential sites for
application of green infrastructure or LID. A total of 17 parameters were used as siting criteria within the
tool and several sites were identified that contained eight or more of these parameters. After careful
analysis of the tool results, 14 sites were selected for further feasibility assessment within the field.
These 14 sites were located in environmental justice communities in both Barnstable and Yarmouth.
Potential siting constraints were evaluated during the field assessment rather than in the tool.
Following the field assessment, the project team collectively reviewed the 14 tool-identified sites to
select six potential green infrastructure or LID sites. These sites were split evenly between Barnstable
and Yarmouth. Two additional sites were identified by CCC staff in the field and added to the list of
potential sites. Based on GIS data of the sites and information provided by CCC from field assessments, a
constructability assessment of the eight total potential sites was performed to evaluate a variety of
physical, social, and economic factors. The constructability assessment of each of the eight potential
sites is presented below in Sections 3.1 - 3.8. Pictures from the field assessments are presented along
with aerial imagery for each of the sites (All images courtesy of Tetra Tech). Discussions of the physical,
social, economic, and water quality considerations are included based on an evaluation of factors by the
project team. Water Quality Volumes were calculated by siting a potential practice, delineating the total
drainage area treated by the technique, assessing the amount of impervious surface within the
treatment area, then applying a 1-inch storm event over the impervious area. This follows the process
established in the Massachusetts Stormwater Handbook found here:
http://www.mass.aov/eea/aaencies/massdep/water/reaulations/massachusetts-stormwater-
handbook.html. This evaluation leads to a constructability assessment to determine the feasibility of
implementing green infrastructure practices on each site.
This assessment offers limited guidance on potential techniques to be implemented, focusing primarily
on the potential for implementation and any possible barriers to be resolved. A 'map' of suggested
practices and their estimated treatment area is shown as part of the constructability assessment. These
practices and their associated treatment areas have not been completely field-verified for feasibility.
They serve primarily as an indication of a practice that might be feasible on the site.
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3.1. I South Street - Barnstable
Both the Anchor-In Hotel (at 1 South Street)
and an adjacent public boat ramp appear to
be suitable for small scale LID techniques.
Physical Considerations
ubhc Outreach and Education
Considerations
conomic Considerations
Water Quality Considerations
Jby
ter
This site is located within a highly urban area and is bounded
the Hyannis Harbor. Although this results in potentially greater
treatment it limits the size of the practice. The Anchor-In Hotel
has a high percentage of impervious area and a minimal amount
of available open space, limiting the options to small scale
practices. There is an open, unused parcel as part of the public
boat ramp but it has a small footprint, considerable land slope,
and is contained by a bulkhead. The drainage area for this site is
currently unknown but the field visit identified a ~24"
stormwater outfall within the bulkhead.
The location of the boat ramp on the Hyannis Harbor, near both
the Hyannis-Nantucket Ferry and the Hyannis Marina, results in
high visibility and an opportunity to provide public exposure to
green infrastructure practices.
Anchor Inn is privately owned; any proposed techniques would
require support from the landowner which could be difficult at
this site. The boat ramp is publicly owned and although
property is highly valued in this area, the site identified is small
and would not impact other uses.
Drainage flows south along the roadway towards the open area.
If drainage is redirected away from the existing stormwater
inlets and channels, nearly 0.75 acres could be collected, nearly
all of which would be impervious area. This would result in an
estimated Water Quality Volume of nearly 2,300 cubic feet.
33
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Constructability Assessment
This site has a high potential for small scale LID techniques to
treat stormwater runoff from the surrounding parcels. A
bioretention area could be placed in the small open area of the
public boat ramp to collect impervious area runoff from the
roadway and adjacent hotel, as shown below.
34
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3.2. 4 Bay View Street - Barnstable
The Cape Cod Hospital employee parking
area contains an extensive impervious area
along with a large, mounded, unused
median.
hysical Considerations
Public Outreach and Education
Considerations
Economic Considerations
Water Quality Considerations
At approximately 6,500 SF, the grassy median area is large
enough to support green infrastructure practices to address
stormwater runoff from the parking area. A further examination
of the site topography and stormwater infrastructure is needed
to determine the potential treatment area available. As shown in
the aerial photography, the southern parking area appears to be
in need of repair; future rehabilitation of the parking area could
help direct more runoff to the median. The Zone II boundary and
cranberry bogs in the SE corner of the site would need to be
delineated to ensure that any potential practices proposed in the
open area south of the parking area would avoid these areas.
The Cape Cod Hospital is a single entity with a large amount of
impervious area. Treating this impervious area with green
infrastructure would serve as a model of community
responsibility.
By utilizing unused areas of a parking lot, it is assumed that land
costs would be negligible. Tying into an already existing
stormwater network or re-grading/re-paving areas to expand the
treatment area could lead to increased retrofit costs. These
potential costs can be minimized by using in-situ design methods.
Drainage flows south over the parking lot, collected in
stormwater inlets, and discharged to an infiltration basin near
the cranberry bogs. If drainage is redirected away from the
existing stormwater inlets and a curb cut is added to the median,
nearly 1.9 acres of stormwater could be collected, mostly from
impervious areas. This would result in an estimated Water
Quality Volume of nearly 6,000 cubic feet.
35
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Constructability Assessment
This site has a high potential for a small scale practice to treat
stormwater runoff from the employee parking area, assuming
runoff could be directed to the median area. A bioretention area
would be ideal within the median, otherwise the existing
infiltration basin could be possibly converted to a bioretention
area to increase pollutant removal. Although there is significant
impervious area treated, infiltration is already proposed so
additional treatment would require an advanced practice.
Constructed wetlands are also a possibility to provide additional
treatment, although there is limited available space between the
existing paved parking lot and the cranberry bogs. A concept plan
has been previously proposed to reintroduce treated wastewater
into this area to replenish the public water supply. It is suggested
that any large scale projects outside of the parking lot boundaries
should consider this proposed plan.
36
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3.3. 0 and 47 Old Yarmouth Road - Barnstable
Both 0 and 47 Old Yarmouth Road are
fairly open parcels located near a major
arterial roadway and large impervious
areas.
hysical Considerations
Public Outreach and Education
Considerations
Economic Considerations
Water Quality Considerations
hese sites are located within a drinking water supply area,
limiting the suitability for infiltration. Significant open area is
available surrounding the drinking water tower and a major
arterial roadway and quasi-industrial area is located nearby,
providing a potentially high source load. Further investigation of
topography and any stormwater infrastructure is needed to
determine if runoff could be directed to these sites. An
investigation into groundwater flow would also help determine if
green infrastructure could be implemented to intercept and treat
groundwater before it reaches the drinking water wells.
These sites have very minimal public exposure.
There should be enough open area surrounding the drinking
water tower to place a small practice without impacting land costs
and to avoid major retrofit costs. Any larger facility would
potential impact usable land. Significant costs could also be
incurred to direct water to the practice.
Information by town officials indicated there is a flooding issue
near the intersection of Yarmouth Road and Old Yarmouth Road.
Originally, a bioretention area located near the buildings was
anticipated to collect nearly 0.8 acres (resulting in 1,000 cubic
feet of Water Quality Volume) but the site visit confirmed that
collection in this area would be difficult.
37
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Constructability Assessment
Although these sites have a large amount of open space and a
potentially large treatment area, directing flows to the site could
be difficult. Also, the location within a drinking water supply area
significantly limits the type of suitable techniques. A better
alternative than the bioretention area might be a
bioswale/biofiltration located at the area that is prone to
flooding. This would improve the safety and provide additional
water quality treatment before the runoff enters the water supply
area. Plans to redevelop the corridor could significantly reduce
the flooding and water quality problems.
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3.4. 122 Camp Street - Yarmouth
This site consists of condo units as part
of an affordable housing project. The
site is about 50% developed and
includes a RUCK wastewater system
with high operation and maintenance
costs.
Public Outreach and Education
Considerations
conomic Considerations
Water Quality Considerations
Since the majority of the site is not yet developed, there is significant
opportunity to integrate green infrastructure and LID into the future
development plans. An investigation of any stormwater
infrastructure would be necessary to properly locate any treatment
practices. This site is also adjacent to the 47 Old Yarmouth Road site,
which contains several drinking water wells.
With more than 100 total housing units planned, this site represents
a high exposure area within an environmental justice community.
unity.
Since this site is privately owned and yet to be fully developed, any
potential practice will have to be sited with input from the
developer. Although it is outside of the scope of this project, working
with the developer to help address the high operation and
maintenance costs associated with the existing RUCK system might
provide a financial incentive to implement alternative treatment
practices.
This site is fairly flat and there is no stormwater collection system. All
impervious areas are already disconnected and infiltrate directly.
Collecting stormwater doesn't seem necessary or possible, limiting
the water quality analysis. Any additional water quality benefits
would come from interaction with groundwater sources.
39
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Constructability Assessment
Implementation in this area is dependent on buy-in from the
developer. Currently, collection of stormwater doesn't seem feasible
or necessary. But a discussion with residents during a site visit
indicated that the existing RUCK system is both highly functioning
and expensive. It might be possible to add a permeable reactive
barrier (PRB) to help reduce the monitoring requirements of the
RUCK system (and the operational costs).
40
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3.5. 669 Route 28 (Drive-In) - Yarmouth
This site is a former drive-in movie theater
where historic wetlands were filled with
poor-quality soil. The site is currently
unused but redevelopment plans have
been discussed.
Public Outreach and Education
Considerations
Economic Considerations
The former parking area represents ample open space to
implement a green infrastructure or LID although this area is
partially located within a hazardous floodplain. A potentially high
groundwater table would limit the implementation of infiltration-
based stormwater practices but is highly suitable for practices
that intercept groundwater, such as constructed wetlands or
permeable reactive barriers. The fact that historic wetlands were
once present on the site makes this type of technique more
desirable. The location along a channel running from Swan Pond
to the coast makes this area a high priority for treatment.
The existing drive-in is a high exposure site that is currently being
underutilized. Including innovative green infrastructure or LID
into any potential redevelopment of the site would greatly
expand the public perception of these types of practices.
f r'ltn
Construction on this site could involve excavation and off-site
removal due to the existing fill material but construction costs
should remain fairly low due to the easy access and already
cleared site. There are plans to convert this site into a future
marina and other public uses, limiting the ability to place a large
scale practice such as a constructed wetland. Implementing a LID
facility (like a permeable reactive barrier with a small footprint)
that would not impact future development plans would be
important to reduce opportunity costs.
-------
Water Quality Considerations
Although the site is fairly flat, initial estimates of the drainage
area indicate nearly 14 acres of treatment is available (depending
on the presence of a storm drain network). Even though only 5
acres of this is impervious area, it still results in a potential Water
Quality Volume of 18,000 cu. ft. The opportunity is high to treat a
considerable amount of runoff.
Constructability Assessment
This site has high potential to install for a practice that both
treats stormwater runoff, as well as intercepting and treating
groundwater flows. If the necessary space is not available as part
of the redevelopment, a smaller LID facility to treat stormwater
only could be implemented. A possible opportunity might be a
phytoremediation/bioretention facility with an adjacent
permeable reactive barrier to increase nitrogen removal.
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3.6. 674 Route 28 (Zooquarium) - Yarmouth
This privately owned site has been a popular
marine tourist attraction for over 40 years.
Water quality research is currently being
performed at an on-site greenhouse.
ublic Outreach and Education
Considerations
Economic Considerations
:ant
is
The buildings, driveway, and parking area represent a significant
amount of impervious area that can be treated. Open space is
available but potential placement is limited by impervious and
wetland areas on site. There is evidence of a high groundwater
table on the site, limiting the use of infiltration practices. In-situ
design techniques for LID can help address high groundwater
concerns and the large amount of open space available might be
more suitable for vegetative buffers. No stormwater
infrastructure appears to be present although a further
investigation into the topography and groundwater table will be
necessary to determine possible locations.
Green Infrastructure and LID associated with popular tourist
attractions have high visibility within the community to both
residents and visitors.
This site is privately owned so any proposed technique would
need approval from the property owner. Since a research
greenhouse is located on site, the property owner seems
committed to environmental causes and could be a strong
partner. Access to the site and possible facility locations are
fairly open, reducing the cost to retrofit the site. Long term
maintenance responsibility should be addressed; green
infrastructure practices with low maintenance costs might
provide additional motivation to the property owner.
43
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Water Quality Considerations
This site is also fairly flat and is partially located with the buffer
area of wetlands associated with the river. There is minimal
space to install on-ground techniques and minimal drainage area
that can be easily collected and treated. There is approximately
0.25 acres of roof area which can be easily collected and
treated, resulting in a Water Quality Volume of nearly 1,000 cu.
ft.
Constructability Assessment
Assuming the property owner buys into the project, this site
represents a good opportunity for green infrastructure or LID.
The high groundwater table and the presence of wetlands
significantly limits both the type and location of practices but
does not exclude the implementation of a treatment practices
on this site. One potential opportunity that would not affect any
additional space would be the design of a green roof on top of
the existing zooquarium building.
44
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3.7. 165 Bearses Way - Barnstable
This elementary school has
significant open space and
impervious area, along with high
public exposure.
Public Outreach and Education
Considerations
conomic Considerations
MI
This is the only school located within the two targeted watersheds in these
communities. Considerable impervious cover is present on the school site and
the area is surrounded by medium density residential land, resulting in
significant nitrogen sources within the treatment area. Open areas are
present on the site but large green infrastructure practices could potentially
impact the usability of the site. Undisturbed forested area in the NW portion
of the site and potential wetlands in the southern portion should be avoided.
Several practices could be implemented throughout the site without greatly
impacting the existing use. A recently redeveloped community center
of the school has already implemented bioretention and permeable
pavement, and additional practices on the school site would be a natural
extension.
greatly
• south
ural
Schools have very high visibility and represent excellent opportunities to
promote green infrastructure throughout the community. In addition, on-site
practices can be integrated into environmental education curriculum for the
students.
The school is publicly-owned, reducing any land costs associated with the site.
Economic considerations should include any potential redevelopment or
expansion planned for the site. Larger scale practices such as constructed
wetlands could incur significant construction costs due to excavation and <
site removal.
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Water Quality Considerations
The total treatment area available is dependent upon the location of the
green infrastructure practice on the site. A bioretention facility located where
runoff enters the recreational fields would collect much of the school and
surrounding paved areas, resulting in a treatment area of more than 1.5
acres, resulting in a Water Quality Volume of 3,700 cu. ft. A constructed
wetland in the southern portion of the site near the pond could collect a
treatment area of nearly 10 acres, resulting in a Water Quality Volume of
13,400 cu. ft.
Constructability Assessment
This site is an excellent opportunity for bioretention or permeable pavement.
As determined during a site visit, runoff from the school and surrounding
paved areas is concentrated into a single asphalt-lined drainage swale and
directed into the recreational fields, which act like a large infiltration basin.
This area would be a great opportunity for a green infrastructure practice to
provide additional water quality treatment. Larger practices such as
constructed wetlands will require a greater amount of open space and will
incur significant construction costs.
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3.8. 65 Long Pond Drive - Yarmouth
This site consists of high-density residential
bordered by open water, commercial area,
and a driving range.
'hysical Considerations
High density residential area is separated from Swan Pond by a
forested buffer. Impervious areas such as roads and sidewalks
within the residential area seem to discharge to grassy median
areas, but drainage of the large commercial area to the SE is
unknown. The high quality of the forested buffer and the limited
amount of open space limits the suitability for large scale
practices such as constructed wetlands. Smaller scale practices
can help reduce nitrogen entering Swan Pond but a further
investigation into stormwater infrastructure and drainage is
needed. A large open area is located SW of the residential area
but any green infrastructure or LID in this area could affect the
existing use of the driving range. Still, if stormwater could be
directed to this open area from the surrounding impervious
areas, a significant amount of treatment is possible. A publicly
owned parcel is located north of the residential area but this
parcel is a well-established natural area and retrofits should be
avoided.
Public Outreach and Education
Considerations
Potential green infrastructure practices would be located away
from community centers and major roadways and have limited
visibility, reducing the public exposure.
The residential area and the driving range are both privately
owned and any implemented green infrastructure practices could
greatly impact opportunity costs, driving up the total cost of the
project.
47
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Water Quality Considerations
The high density residential, paved parking areas, and open
medians make this site ideal for retrofits. A site visit, though,
revealed that there is no storm drain network and that runoff
is currently entering infiltration areas. Although nearly 2.5
acres of treatment area is available, resulting in a Water
Quality Volume of more than 4,000 cu. ft., collecting this runoff
and providing additional treatment would be difficult.
Constructability Assessment
The limited amount of open space prevents the implementation
of large scale practices and encourages small-scale practices such
as bioretention. Space constraints and private ownership make
siting potential techniques difficult and potentially costly. In
addition, runoff is already distributed and entering infiltration
areas, preventing significant gains from additional water quality
treatment.
48
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3.9. Selection of Sites for Concept Plan Development
On November 15-16, 2012, the project team presented the results of the screening process and site
assessments to a collection of local stakeholders from Yarmouth and Barnstable. The group assessed the
sites collectively and selected two sites for advancement to conceptual designs - the 165 Bearses Way
(School) site in Barnstable and the 669 Route 28 (Drive-In) site in Yarmouth. These two sites were
selected after discussing the assessment metrics, site visits to the two locations, a discussion of the
benefits and constraints present at each site, and the perceived likelihood of the projects to be
implemented on the two sites. At these two sites, an enhanced bioretention facility is proposed at the
School site while a bioretention/phytotechnology area is proposed at the Drive-In site. The concept
plans developed for these two sites are included in the Appendix.
49
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4. Model Process and Results
As part of this study, hydrologic modeling was performed to quantify the environmental benefits of the
proposed concept designs. Hydrologic and water quality (i.e. TN) benefits were evaluated for the green
infrastructure opportunities at each of the two sites using EPA's System for Urban Stormwater Analysis
and Integration (SUSTAIN) model. In addition, a simplified cost-effective analysis was conducted at both
sites to provide a more comprehensive basis for stormwater management decision-making. The
SUSTAIN hydrologic simulation provided results for stormwater flows only but a discussion of additional
water quality benefits from groundwater interaction is also included.
4.1. Overview of the Modeling Process
SUSTAIN incorporates water hydrologic and optimization algorithms to evaluate the impacts of BMPs on
water quality and quantity (Tetra Tech 2009b). An overview of the modeling setup is shown in Figure 20.
The SUSTAIN model is used to simulate the cumulative hydrologic and water quality benefits from the
BMPs implemented at the two project sites by performing a water balance at each BMP site.
Rainfall;
Deposition
Evapotranspiration;
Plant uptake
Stormwater runoff
Overflow
Infiltration (if applicable)
Figure 20. Overview of basic modeling analysis processes (Tetra Tech 2009b)
Long-term hydrologic and water quality time series are needed in the SUSTAIN model for evaluating
cumulative BMP performances. The development of hydrologic/water quality performance curves is an
intensive process and significant effort was saved on this project by using performance curves
developed for a separate project for the Boston area. Continuous runoff time series based on the rainfall
data from Boston Logan International Airport were obtained to run the simulations (Tetra Tech 2009a).
The hourly time series cover the period of 1992/01/01 to 2002/12/31. Although these curves were not
developed using precipitation data from Cape Cod, the general hydrologic regime is assumed to be
consistent between the two sites over the performance period.
4.2. Evaluation of the 165 Bearses Way (School) Site
An innovative practice that has the combined features of both gravel wetland and bioretention is
proposed at the School site. The innovative practice, referred to as enhanced bioretention, has been
researched by the University of New Hampshire Stormwater Center (UNHSC). BMP monitoring data
show that it has relatively high efficiencies for removing TN. CCC, in developing the 20% concept plans
for the School site, proposed a facility that includes two enhanced bioretention cells and one
conventional bioretention cell. The two enhanced bioretention cells are designed to capture all runoff
50
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from the site and overflow into the conventional bioretention cell. Since the exact configuration of the
site is not yet finalized, the SUSTAIN model will evaluate the pollutant reduction potential of the
enhanced bioretention cells as a conservative approach. The additional bioretention cell should provide
additional water quality treatment beyond what is included in this modeling memo.
4.2.1. Site Conditions
The School site is located at a local school, with most of the stormwater runoff from the school site
being routed to the BMP. Major land uses at the School site include buildings, transportation (road,
parking lot, driveway, etc.), playground, and open space. A summary of the land uses is shown in Table
3. The School site has a total drainage area of 3.87 acres and the imperviousness percentage is 53%. The
enhanced bioretention was originally sized to treat one inch of runoff from the impervious surfaces but
the size of the facility was decreased by CCC during the iterative design process. The proposed 20%
concept design includes two enhanced bioretention cells and one conventional bioretention cell, all with
approximately equal footprints. The enhanced bioretention cells were reduced to focus on costs; with
the current sizing these two cells treat approximately 0.55 inches of runoff from the treatment area.
More discussion on the water quality treatment is included in Section 4.2.4 Model Results.
Table 3. Major land uses at the School Site
Land use type
Building
Playground
Transport
Open space
Total
Area (acre)
0.49
0.01
1.57
1.80
3.87
The site plan for implementing the enhanced bioretention at the School site is shown in Figure 21. The
bioretention cell receives stormwater runoff from the nearby school buildings and parking lots and the
outflow is routed through a conventional bioretention cell and onto an open recreational field where it
is infiltrated.
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Figure 21. Site Plan for bioretention implementation at the School site
(Cape Cod Commission/Tetra Tech)
4.2.2. The Enhanced Bioretention for the School Site
A cross-section view of the enhanced bioretention proposed for the School site is shown in Figure 22. As
shown in the figure, the profile of the enhanced bioretention includes an average of four inches of
ponding depth, two feet of bioretention soil mix, six inches of gravel, and two and half feet of crushed
stone layer. The design enhancement concept was introduced by UNHSC and this design was built at a
Municipal Lot along Pettee Brook Lane in the City of Durham, NH. Monitoring data from the enhanced
bioretention indicate that pollutant removal, TN in particular, is relatively high (i.e. 86% removal of TN
when treating one inch of runoff from commercial land use) (Tetra Tech 2012). Stormwater runoff
enters the enhanced bioretention through surface flow and filters through the bioretention soil mix,
flows above the geomembrane when present, and enters into a permanent pool of water held within
the crushed stone layer. The anaerobic environment (similar to a gravel wetland) is the key element for
effective TN removal. The enhanced bioretention is lined in highly porous soils to maintain anaerobic
conditions within the substrate.
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Native Grass
Native Sedge
Surface Slope @ 1.3%
Native Shrubs
Ponding Depth
5- Bioretention Soil Mix
£• Pea Gravel
-HOPE Geomembrane at 1% Slope
' I" Crushed Stone
Figure 22. Cross-sectional view of the enhanced bioretention to be implemented at the School site
(Cape Cod Commission/Tetra Tech)
A list of design parameters for the enhanced bioretention is summarized in Table 4 below.
Table 4. List of enhanced bioretention design parameters used in the SUSTAIN representation
Components
Ponding area
Planting soil mix
Stone reservoir
Orifice
Overflow weir
Parameters
Depth (ft)
Depth (ft)
Porosity
Hydraulic conductivity (in/hr)
Depth (ft)
Porosity
Hydraulic conductivity (in/hr)
Diameter (in)
Inlet offset from soil surface (ft)
Length (ft)
Value
0.33
2
0.24
2.5
2.5
0.42
5000
12
2.5
3.14
The enhanced bioretention has been previously calibrated using observed data from the UNHSC (Tetra
Tech 2012). The calibrated SUSTAIN model is used for carrying out the long-term simulations of
hydrologic and water quality benefits at the site.
4.2.3. SUSTAIN Model Setup
The School Site is represented in the SUSTAIN model in the ArcGIS environment. The model setup is
shown in Figure 23. Runoff from the watershed is routed to the enhanced bioretention and the
assessment point is located downstream of the enhanced bioretention.
53
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Legend
Drainage area delineation
Flow routing
—»— BMP outflow
• Surface runoff
BMPs
\£ Enhanced bioretention
& Outlet (assessment point)
N
A
45 BO
180
• Feet
Figure 23. SUSTAIN model setup for the School site
A schematic drawing of the proposed representation scheme in SUSTAIN is shown in Figure 24 below. As
shown, the representation consists of a ponding area on the top, a soil mix layer, a crush stone layer, an
overflow weir (Weir #1) at the maximum depth of ponding area, and an overflow orifice (Orifice #1) for
discharging water exceeding the maximum permanent pool depth. When stormwater enters into the
BMP, the water will first infiltrate into the soil water mix, and the percolated water enters the crush
stone layer to form a permanent subsurface pool of water. After the permanent pool of water exceeds a
certain depth, overflow is discharged through Orifice #1. During this process, whenever the ponding
depth is exceeded, overflow occurs through Weir #1. Flows from Weir #1 and Orifice #1 are combined to
form the overflow routed to downstream. The proposed representation scheme captures major
hydrological processes occurring in the enhanced bioretention.
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New BMP
Weir#1
Orifice #1
Figure 24. Schematic for representing the enhanced bioretention into SUSTAIN (not to scale)
SUSTAIN model parameters representing hydrological and water quality processes were calibrated
based on monitoring data collected by UNHSC (Tetra Tech 2012) and the same model parameters were
used in the analysis assuming that the proposed enhanced bioretention will have similar treatment
capability to the one installed by UNHSC. The SUSTAIN model setup for the School site is evaluated
through continuous simulation for the period of 1992/01/01 to 2002/12/31. The cumulative total runoff
volume reduction, TN removal, and the water balance in the enhanced bioretention are summarized at
the end of the simulation process.
4.2.4. Model Results
The SUSTAIN analysis for the School site is summarized in Table 5 below. As shown in the table, the
overall runoff volume reduction from the enhanced bioretention is 4.1%, and the overall TN load
removal from the site is 65%. Since the configuration of the enhanced bioretention requires a liner to
create anaerobic conditions, no infiltration is possible and the only reduction in stormwater volume
occurs through evapotranspiration. Although the enhanced bioretention system can treat the equivalent
of the 0.55 inch runoff event within the two enhanced bioretention cells, most of this water flows
through the system resulting in a small reduction in total runoff volume. Although the reduction in
runoff volume is small, the enhanced bioretention system will adjust the hydrograph of storm events
and impact the downstream hydrology and, as Table 5 shows, significantly reduce the total nitrogen
load that is exported over the 10 year simulation period. These results are conservative, as it is expected
that the additional bioretention cell will provide additional water quality treatment.
Table 5. Summary of SUSTAIN simulation results for the period of 1992/01/01 to 2002/12/31
at the School site
Total inflow
Total outflow
Percentage of reduction
Runoff volume (ft3)
5,953,767
5,709,634
4.1%
Total Nitrogen (Ibs)
416.6
144.52
65%
The overall water balance of outflow at the enhanced bioretention throughout the simulation period is
presented in Figure 25. As shown, the only loss from the system is through the evapotranspiration (ET)
process. No percolation occurs due to the lined bottom of the BMP.
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Figure 25. Overall water balance in the enhanced bioretention outflow at the School site
4.2.5. Simplified Cost-Effectiveness Analysis
While continuous simulations of the enhanced bioretention provides a solid assessment of cumulative
hydrologic and water quality performances for the BMP, it is always in the best interest of the decision-
makers to have a full understanding of the cost-effectiveness of a particular technique. To provide a
comprehensive picture about the hydrologic and water quality performances of the enhanced
bioretention, the SUSTAIN model is commissioned to simulate the BMP for sizes that treat impervious
runoff depths for a range of runoff depths rather than just the one inch. This analysis results in
simplified performance curves for the BMP.
The analysis results are presented in Figure 26 below. As the BMP size increases, the total runoff volume
reduction percentage increases almost linearly (albeit at a relatively small rate). The TN removal
percentages, meanwhile, increase dramatically when the BMP is sized to treat 0.1 to 0.6 inches of
impervious runoff, and then tends to level off. This simplified analysis can greatly improve the decision-
making for appropriately sizing BMPs, especially when either the site conditions or the budget become
limiting factors and assuming there are no regulatory sizing requirements.
The trend of diminishing return in TN removal as the BMP sizes increase is more obvious when the BMP
costs are also considered. In the absence of locally available BMP cost, it was assumed that the unit
construction cost of enhanced bioretention volume is $5.00 per cubic feet. This information does not
have any relation to actual construction costs associated with BMPs in the Cape Cod region, and should
be limited to use for evaluating the relative differences of BMP cost for planning purposes only. The
corresponding costs and the rates of TN removal percentage increase as the BMP volume increases are
summarized in Table 6.
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Total runoffvolume reduction
Total Nitrogen removal
0.2
0.4 0.6 0.8 1
Treated depth of runoff (in)
1.2
1.4
Figure 26. Simplified cost-effective analysis for sizing the enhanced bioretention at the School site
Table 6. Total cost for the enhanced bioretention at varying treatment depths
Treated depth of
runoff
0.1 in
0.2 in
0.4 in
0.6 in
0.8 in
1.0 in
1.2 in
1.5 in
Total BMP
volume (ft3)
751
1,502
3,005
4,508
6,011
7,514
9,017
11,271
Total cost ($)
3,755
7,510
15,025
22,540
30,055
37,570
45,085
56,355
TN removal
34%
46%
59%
67%
72%
76%
79%
82%
Increase in
total cost ($)
-
3,755
7,515
7,515
7,515
7,515
7,515
11,270
Increase in TN
removal
-
12%
13%
8%
5%
4%
3%
3%
As shown in Table 6, the greatest gains in TN removal per unit cost occur at lower runoff depths due to
the effectiveness of treating the first flush of contaminants. This information will allow decision-makers
to efficiently allocate the budget when faced with competing projects and ensure that the money spent
will yield the most cost-effective results. In the case of the school site, doubling the size of the enhanced
bioretention would only provide an additional 13% of TN removal at approximately double the cost. This
validates the reduced-size design at the School site.
4.3. Evaluation of the 669 Route 28 (Drive-In) Site
A unique pilot project is proposed for the Drive-In site that combines traditional LID approaches to
collect and treat stormwater runoff with innovative green infrastructure practices designed to provide
additional treatment to the shallow groundwater located on site. The 20% concept design developed by
CCC integrates the green infrastructure project into the town's proposed marina redevelopment plan.
The design includes a bioretention area and phytotechnology plantings down-gradient of a proposed
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leach field associated with the new marina. The bioretention area is expected to provide TN removal
benefits to stormwater inflows, with the bioretention TN removal efficiencies based on previous studies
conducted at Anacostia River, Maryland (Tetra Tech 2008). The additional phytotechnology component
will treat wastewater effluent from the leaching area reducing nitrogen within the shallow groundwater
before it enters Parkers River. The phytotechnology component cannot be modeled as part of this
analysis, as SUSTAIN only has the capability to model stormwater flows, so this analysis will only address
the bioretention. Similar to the School site, the modeling results for the Drive-In site will be conservative
with additional pollutant removal available from the complete green infrastructure project.
4.3.1. Site Conditions
The Drive-In site receives runoff from nearby residential and commercial areas. Major land uses in the
site include commercial, residential, transport, and open space. A summary of the land use areas in the
Drive-In site is shown in Table 7 below. As shown, the total drainage area is about 2.96 acres, and the
aggregated imperviousness percentage is about 30%. The conventional BMP is sized to treat one inch of
runoff from the impervious surfaces. The site plan for the Drive-In site is shown in Figure 27 below, with
runoff from nearby residential, commercial, and transportation areas directed to the bioretention area.
Table 7. Major land uses in the Drive-In site
Land use type
Commercial
Residential
Transport
Open space
Total
Area (acre)
0.17
0.09
0.64
2.06
2.96
Figure 27. Site Plan for BMP implementation at the Drive-In site (Cape Cod Commission/Tetra Tech)
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4.3.2. Bioretention/Phytotechnology for the Drive-In Site
An innovative bioretention area/phytotechnology treatment area is proposed at the Drive-In site. To the
maximum extent practicable with a new and innovative approach, the bioretention area design will
follow that specified in the Massachusetts Stormwater Handbook (MassDEP 2008). However, as this
approach contains an integrated phytotechnology intercepting groundwater, a characteristic strictly
avoided with stormwater controls, the project design will not be limited by current stormwater
standards. A cross-sectional view for the phyto/bioretention area is shown in Figure 28 below.
Native Shrubs
Q.5-1' Topsoil amendment
Typical LeachfieW sand
Native Settoe ,
/~
Porting Depth
Deep Rooting Tree
Proposed
Driveway
Mi,
%}A\ 1'\ ^Hru----r^-,
£
1" Crushed Stone
High Grourxtoater
Figure 28. Cross-sectional view of the enhanced bioretention and phytotechnology area to be
implemented at the Drive-In site (Cape Cod Commission/Tetra Tech)
Following the MassDEP design specifications, the design parameters for the bioretention are
summarized in Table 8 below. As shown in the table, the bioretention has an effective depth of about
1.3 feet. Considering the fact that the Drive-In site has a relatively high groundwater table, the gravel
layer is likely to be submerged in water when groundwater rises to seasonal high levels. Thus, the
effective depth for the bioretention area is conservatively estimated as 1 foot.
Table 8. Bioretention design parameters following MassDEP design specifications
Components
Ponding area
Planting soil mix
Gravel layer
Parameters
Depth (in)
Depth (in)
Porosity
Hydraulic conductivity (in/hr)
Depth (in)
Porosity
Hydraulic conductivity (in/hr)
Value
6
21
0.3
2.5
8
0.4
14
4.3.3. SUSTAIN Model Setup
The Drive-In Site is represented in the SUSTAIN model in the ArcGIS environment. The model setup is
shown in Figure 29. Runoff from contributing areas is routed to the bioretention unit and the
assessment point is located downstream of the bioretention.
59
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Legend
i I
Drainage area delineation
Flow routing
—»— BMP outflow
• Surface runoff
BMPs
41 BioRetention
^2 Outlet (assessment point)
N
A
100 200
400
• Feet
Figure 29. SUSTAIN model setup for the Drive-In site
A schematic drawing of the conventional bioretention representation scheme is illustrated in Figure 30
below. As shown in the figure, surface runoff entering the bioretention area first fills the ponding area,
the water filters through the planting soil mix, and then enters the gravel layer. During this process,
overflow is routed through the overflow weir to downstream when the inflow rate exceeds the
infiltration rate into the planting soil mix.
The SUSTAIN model hydrologic and water quality parameters were previously calibrated in a study
carried out at Anacostia River watershed, Prince George's County, Maryland (Tetra Tech 2008). Similar
to the analysis carried out for the School site, the SUSTAIN model setup for the Drive-In site is also
evaluated through continuous simulation for the period of 1992/01/01 to 2002/12/31. The cumulative
total runoff volume reduction, TN removal, and the water balance in the conventional bioretention are
summarized at the end of the simulation process.
60
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So// mix
Overflow
Figure 30. Schematic for representing the conventional bioretention into SUSTAIN (not to scale)
4.3.4. Model Results
The SUSTAIN analysis for the Drive-In site, representing the total runoff volume and nitrogen removed
over the ten year simulation period, is summarized in Table 9 below. As shown in the table, the overall
runoff volume reduction from the bioretention is 2.8%, and the overall TN load removal from the site is
60% assuming that the bioretention is sized to treat 1 inch of runoff from impervious surface.
Table 9. Summary of SUSTAIN simulation results for the period of 1992/01/01 to 2002/12/31
at the Drive-In site
Total inflow
Total outflow
Percentage of reduction
Runoff volume (ft3)
4,587,781
4,458,432
2.8%
Total Nitrogen (Ibs)
321.2
127.6
60%
The overall water balance of outflow at the conventional bioretention unit throughout the simulation
period is presented in Figure 31. Similar to the School site, the only loss from the system is through the
ET process. Although instead of an impermeable liner preventing infiltration, no deep percolation occurs
at the Drive-In site since it is assumed that the gravel layer is already submerged by a high groundwater
table. The bioretention/phytoremediation system functions primarily as flow through treatment for
storm events.
61
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Figure 31. Overall water balance in the bioretention outflow at the Drive-In site
4.3.5. Simplified Cost-Effectiveness Analysis
A simplified cost-effectiveness analysis similar to the one conducted for the enhanced bioretention at
the School site was also carried out for the conventional bioretention at the Drive-In site. The SUSTAIN
model was set up to evaluate corresponding total runoff volume and TN removal percentages when the
conventional bioretention is sized to treat impervious runoff depths other than one inch. A simplified
performance curve was also generated for the conventional bioretention.
The simplified cost-effectiveness analysis results for the conventional bioretention are illustrated in
Figure 32. As shown in the figure, overall the results demonstrate a pattern similar to that is previously
observed for the enhanced bioretention. As the BMP sizes increase, the total runoff volume reduction
percentages also increase almost linearly. The TN removal percentages increase more dramatically when
the BMP is sized to treat 0.1 to 0.6 inches of impervious runoff, and the curve then tends to level off for
treatment depths higher than 0.6 inches.
The pattern of diminishing return in TN removal as the BMP sizes increase is also analyzed for the
conventional bioretention at the Drive-In site. For simplification purposes, the unit construction cost of
the conventional bioretention is also assumed to be $5.00 per cubic feet1. Again this information does
not have any relation to actual construction costs associated with BMPs in the Cape Cod region, and
should be limited to use for evaluating the relative differences of BMP cost for planning purposes only.
The corresponding costs and the rates of TN removal percentage increase as the BMP volume increases
are summarized in Table 10.
1 This does not represent the actual construction cost, simply an arbitrary number used to illustrate the cost optimization.
62
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Total runoff volume reduction
Total Nitrogen removal
0%
0.2
0.4
0.6 0.8 1
Treated depth of runoff (in)
1.2
1.4
Figure 32. Simplified cost-effective analysis for sizing the enhanced bioretention at the Drive-In site
Table 10. Total cost for the conventional bioretention at varying treatment depths for the Drive-In site
Treated depth of
runoff
0.1 in
0.2 in
0.4 in
0.6 in
0.8 in
1.0 in
1.2 in
1.5 in
Total BMP
volume (ft3)
327
653
1,307
1,960
2,614
3,267
3,920
4,901
Total cost ($)
1,634
3,267
6,534
9,801
13,068
16,335
19,602
24,503
TN removal
30%
36%
45%
52%
57%
60%
63%
67%
Increase in
total cost ($)
-
1,634
3,267
3,267
3,267
3,267
3,267
4,901
Increase in TN
removal
-
7%
9%
6%
5%
4%
3%
4%
As shown in Table 10, the general pattern is similar to what was observed for the enhanced
bioretention. That is, the rate of increase in TN percentage removal diminishes as the BMP sizes
increase. This information is expected to help make cost-effective and defensible stormwater
management decisions.
4.4. Groundwater Impact Analysis
The proposed green infrastructure plan for the Drive-In site represents a unique opportunity to
integrate the treatment of wastewater in groundwater into a stormwater LID system. Typically, high
groundwater is undesirable for bioretention facilities but at this site, the plan takes advantage of the
high groundwater table to provide additional treatment through phytotechnology. Research by CCC has
found that phytotechnology is capable of treating nitrogen in groundwater by using plants which draw in
63
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nutrients, creating an environment near the root zone that encourages nitrogen processing, and utilizing
nitrogen to build plant material. The actual amount of removal is not well established and can be
difficult to quantify, but a study of sewage treatment potential of water hyacinth resulted in upwards of
90% removal of TN from wastewater samples (USEPA 1988).
SUSTAIN is not capable of modeling nitrogen removal in groundwater as a result of phytotechnology.
The modeled results from the conventional bioretention system represent a conservative reduction of
nitrogen at this site. A thoughtful and detailed monitoring program, if added to this green infrastructure
plan, could quantify the water volumes and nitrogen quantities at various points. This could lead to the
future modification of BMP designs, the widespread implementation of phytotechnology for the
treatment of wastewater, and the expansion of the SUSTAIN model. The close working relationship CCC
has developed with the town increases the potential for this to be a successful and innovative green
infrastructure project.
The SUSTAIN model is used to evaluate the hydrologic and water quality benefits from two proposed
stormwater BMPs at the communities of Barnstable and Yarmouth. The two BMPs, one an innovative
enhanced bioretention and the other a conventional bioretention, are first evaluated for treating one-
inch of runoff from impervious surfaces. A simplified cost-effectiveness analysis is then carried out for
each BMP, in which the BMPs are sized to treat impervious runoff depths varying from 0.1 inches to 1.5
inches. The analysis results demonstrate the general pattern of diminishing rate of increase in TN
removal percentages as the BMP sizes increase due to the high concentration of pollutants included in
the first flush of stormwater entering the BMP from the drainage area. While the analyses are
conducted using assumed BMP construction cost values, the overall cost-effectiveness information of
the two BMPs can greatly help stormwater decision-makers in making informed and defendable
management decisions.
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5. Regulatory Pathways
The project team conducted a review and evaluation of the regulatory requirements associated with the
implementation of the proposed green infrastructure concept plans. The review includes local,
Commonwealth, and federal requirements to implement the proposed projects in Barnstable and
Yarmouth. A summary of required permits for these green infrastructure projects is included in Table 11
and a further discussion of the results of the review and recommendations is provided below. In general,
very few permits are required to implement these two green infrastructure projects.
Table I I. Permit Requirements
Permit Level
Local
Commonwealth
Federal
Barnstable (School site)
No requirements1
No requirements
No requirements
Yarmouth (Drive-In site)
No requirements2
Approval of Installation of an Alternate System for
Piloting (BRP WP 64b) - monitoring required
No requirements
1 Personal communication with Dale Saad, Ph.D., Senior Project Manager, Water, Sewer and Green Energy Barnstable DPW,
Tel: 508-790-6300
2 Personal communication with George Allaire, Director of Public Works, Town of Yarmouth, Tel: 508-398-2231
5.1. Stormwater Discharges from Construction Activities (Construction General
Permit)
Construction sites that disturb one or more acres and that discharge stormwater to a surface water of
the United States, or to a municipal separate storm sewer system (MS4) that discharges to a surface
water of the United States, are required to obtain coverage under the National Pollutant Discharge
Elimination System (NPDES) General Permit for Storm Water Discharges from Construction Activities
(also known as the "Construction General Permit" or "CGP") issued by the EPA. Although the
Commonwealth has not joined with EPA in issuing the CGP, Massachusetts has issued a 401 Water
Quality Certification for the permit. The Water Quality Certification requires compliance with certain
Commonwealth regulations and policies, including the Massachusetts Clean Waters Act, Massachusetts
Water Quality Standards, Surface Water Discharge Permit Program Regulations, Wetlands Protection
Act, Wetlands Regulations, Final Orders of Conditions issued pursuant to the Wetlands Protection Act,
Massachusetts Stormwater Management Policy, and the Massachusetts Endangered Species Act. If the
requirements of the water quality certification are violated, MassDEP has the authority to require that
the violations be corrected and to take any action authorized by the General Laws of the
Commonwealth, the Massachusetts Clean Waters Act, and the regulations promulgated there under.
Since the scope of work at both proposed sites is less than one acre this CGP requirement will not apply.
5.2. Erosion and Sedimentation Control
The Wetlands Regulations also recognize that stormwater discharges may adversely impact wetland
resource areas during construction. To prevent this impact, the Wetlands Regulations, 310 CMR
10.05(6)(b)(l), provide that the Order of Conditions shall impose conditions to control erosion and
sedimentation within resource areas and the Buffer Zone. Erosion and sedimentation control is
required, even if the project is a single-family house that is exempt from the requirement to comply with
the Stormwater Management Standards. For projects subject to the Stormwater Management
Standards, Standard 8, set forth in the Wetlands Regulations at 310 CMR 10.06(6)(k)(8), requires the
development and implementation of a construction-period erosion, sedimentation and pollution
prevention plan.
65
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Erosion and sediment control plans will be developed as part of the construction plan set and included
with the final construction plans. They will be prepared by a licensed professional engineer and
submitted for review at the 70% plan stage.
5.3. Construction and Grading/Review/Approval
Construction and grading plans for each of the two green infrastructure projects will be prepared and
submitted to the town's public works department for review and approval. These plans will also include
the erosion and sediment control plans.
There are no review fees or other charge for these plans based on personal communication with Dale
Saad, Ph.D., Senior Project Manager, Water, Sewer and Green Energy Barnstable DPW, Tel: 508-790-
6300, and Mr. George Allaire, Director of Public Works, Town of Yarmouth, Tel: 508-398-2231.
5.4. Special Conditions for Yarmouth Drive-In Site
Because the Yarmouth Drive-In site is proposed to provide treatment downfield of a Title V leaching
field it is subject to certain special provisions. These requirements were identified, below, by Brian
Dudley from MassDEP at a meeting with CCC staff to review 20% design plans for the Yarmouth drive-in
site and discuss regulatory approaches incorporating a phytotechnology/bioretention system down
gradient of a proposed Title V leaching field associated with the Town's marina project. The
requirements are summarized below:
5.4.1. Monitoring
An extensive monitoring plan will be required for a piloting program. This plan is suggested to
incorporate preconstruction information including groundwater flow paths and determinations of
existing contaminants and plumes in the immediate area. A monitoring plan should include specifics
such as the monitoring approach (i.e. mass balance or ground water concentration measurements),
monitoring locations, sampling standards, sampling frequency and time frame. The time frame may be
dictated by MassDEP staff.
MassDEP staff suggests monitoring wells up gradient of the leach field, down gradient of the leach field
and up gradient of the phytotechnology/bioretention system and either monitoring wells or a
monitoring fence down gradient of the phytotechnology/bioretention system. Mr. Dudley suggested
that County Health Department lab may be able to assist with monitoring to reduce costs (contact
George Heufelder, Director, Barnstable County Department of Health and Environment).
5.4.2. General Regulatory Notes
When installing a pilot program a site must also prove they have the ability to install a conventional
system capable of meeting the loading requirements in the event the pilot does not perform as
expected.
In addition to the BRP WP 64b form (attached), a Standard Transmittal Form will need to be filled out
with the state when seeking piloting approval.
Consideration of the Wetland Protection Act and associated buffers will need to be taken into account
when constructing any septic treatment system, Review of the project site indicates that the proposed
phyto-bio system facility is outside the 100' wetland buffer.
66
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5.4.3. Site Specific Considerations
An alternate leach field, such as a drip dispersal system that is approved by MassDEP for general use,
may be utilized to lower the mounding requirements of the leaching area. A drip dispersal system
requires a 3-foot high mound and then 6 to 9 inches of fill on top. This may facilitate ease of
construction near the adjacent property boundary.
A design that captures leach field effluent and forces it horizontally towards the phytotechnology/
bioretention system above the high ground water level should not pose a problem for MassDEP as long
as a 5-foot depth prior to any ponding above the liner is achieved. This will meet MassDEP standards for
pathogen removal. If integrated into a pilot study no 50' setback from leach field to infiltration area is
required. Although the site is located within a flood zone "A", "A" flood zones will not be an issue from a
MassDEP standpoint.
Compliance with 310 CMR 15.214 (nitrogen sensitive areas) needs to be confirmed. Initial review and
conversation with MassDEP staff indicates that the drive-in location is not located within a nitrogen
sensitive area under MassDEP regulations, defined by location in Zone II, IWPA or specific nitrogen-
sensitive designated area. However, site will be required to meet Developments of Regional Impact (DRI)
Minimum Performance Standards as location is within a watershed with an interim TMDL established.
Since this location is not a nitrogen sensitive area CCC will not be held to the more stringent design flow
of 440 gallons/acre/day. However, due to the overall acreage of the site it may still fall in compliance
with this requirement.
5.5. Plan Development and Approval Process
The project team recommends the following procedures for plan development and seeking approval of
the plans:
• 30% Stage - Submit the 30% concept plans to the respective towns and MassDEP (Yarmouth site
only) to get the town representatives and MassDEP familiar with the concepts and to obtain
comments and input to the plans.
• 70% Stage - Incorporate the town's input into a 70% stage construction plan set and resubmit
these plans to the respective towns and MassDEP for a second review and comment period.
These plans will consist of full scale construction plans showing the following elements:
1. proposed limits of disturbance
2. existing and propose grading
3. erosion and sediment control plan
4. all construction details
5. additional requirements for Yarmouth drive-in site
a. proposed monitoring plan
b. preparation and submittal of BRP WP 64b form, and a Standard Transmittal Form to
state
c. show location of alternate leach field
6. updated cost estimate for both sites
These plans will prepared and sealed by a licensed professional engineer
• 100% (Final) Stage - Incorporate the 70% stage plan review comments into a 100% or final stage
of plans and resubmit to the respective towns and MassDEP to obtain final approval for the
plans. These plans will include:
1. all the elements described in 70% submittal plans
2. a complete set of bid document plans and specifications
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6. Cost Estimates
A preliminary cost estimate has been developed for the proposed practices described in the 30%
concept plans for both the School site and the Drive-In site in Barnstable and Yarmouth, respectively.
This cost estimate is based on designs for an enhanced bioretention design concept (i.e., pioneered at
the University of New Hampshire Stormwater Research Center) proposed at the Barnstable School site
and a phytotechnology/bioretention concept proposed for the former Drive-In site and proposed marina
facility in Yarmouth.
The cost breakdown for these two facilities is provided below. The costs were developed using the
following approach:
• An estimate of quantities was developed for each facility based on the 30% concept plans. This
estimate is summarized in Table 12 and Table 13, respectively.
• Unit cost estimates were applied to the estimated quantities to arrive at a preliminary cost.
These unit costs are based on actual projects designed and built within the last 3 years in the
northeastern U.S.
• A contingency factor of 20% was added to the cost estimate to reflect the degree of uncertainty
and level of detail associated with a 30% concept plan.
The total estimated cost for each proposed facility is summarized in Table 14 and Table 15.
Table 12. Preliminary Estimate of Quantities: Barnstable School Site - Enhanced Bioretention System
ITEM
Excavation -1*
Excavation -2*
Gravel/stone-1
Gravel/stone-2
Media - 1
Media -2
Geotextile-HDPE
LENGTH
ft
200
75
200
75
200
75
200
WIDTH
ft
25
25
25
25
25
25
25
DEPTH
ft
5.5
4.8
3
3
2
1.7
1
TOTAL
cf
27,500
9,000
5,625
13,000
10,000
3,188
5,000
cy
1,019
333
208
481
370
188
556
NOTES: Excavation-1 * = excavation for enhanced bioretention area
Excavation -2* = excavation for traditional bioretention area
Gravel/stone -1 = enhanced bioretention area
Gravel/stone -2 = traditional bioretention area Media -1 = enhanced bioretention area
Media -2 = traditional bioretention area
Table 13. Preliminary Estimate of Quantities: Yarmouth Drive-In Site - Phytotechnology/Bioretention
ITEM
Excavation-1*
Excavation-2*
Media
Gravel/stone
Topsoil Amend
LENGTH
ft
200
100
200
200
700
WIDTH
ft
25
25
25
25
30
DEPTH
ft
4.8
2
2
3
1
TOTAL
cf
24,000
5,000
9,000
12,500
21,000
cy
889
185
333
463
778
68
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Table 14. Preliminary Cost Estimate: Barnstable School Site - Enhanced Bioretention System
ITEM
A. Design
Surveys
Geotech
Design
B. Construction
Stakeout
E&S
Excavation*
Media Mix
Gravel/stone
Geotex-HDPE
6" Underdrain
Access Pavers
Trees
Shrubs
Grass
Sedges
Signage
As-builts
Unit
EA
EA
LS
LS
LS
CY
CY
CY
SY
LF
SF
EA
EA
EA
EA
EA
LS
Unit Cost
5,000
3,000
15,000
Subtotal 1
1
1
25
35
25
20
15
6
2
40
25
50
1,000
1,000
Subtotal 2
PROJECT
TOTAL
Qty
1
1
1
1,000
2,000
1352
488
690
556
60
320
100
30
30
20
1
1
Total 1
5,000
3,000
15,000
23,000
1,000
2,000
33,800
17,080
17,250
11,120
900
1920
200
1,200
750
1,000
1,000
1,000
90,220
Conting
(20%)
4,600
18,044
TOTAL
27,600
108,264
135,864
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Table 15. Preliminary Cost Estimate: Yarmouth Drive-In Site - Phytotechnology/Bioretention
ITEM
A. Design
Surveys
Geotech
Design
Permits
B. Construction
Stakeout
E&S
Excavation*
Media Mix
Gravel/stone
Topsoil Amend
Trees
Shrubs
Grass
Sedges
Signage
As-builts
Unit
EA
EA
LS
LS
LS
LS
CY
CY
CY
CY
EA
EA
EA
EA
EA
LS
Unit Cost
5,000
3,000
15,000
2,000
Subtotal 1
1
1
25
35
25
25
27
109
57
200
1,000
1,000
SUBTOTAL 2
PROJECT
TOTAL
Qty
1
1
1
1
1,000
2,000
1074
333
463
778
100
30
30
20
1
1
Total 1
5,000
3,000
15,000
2,000
25,000
1,000
2,000
26,850
11,655
11,575
19,450
2,700
3,270
1,710
4,000
1,000
1,000
86,210
Conting
(20%)
5,000
17,242
TOTAL
30,000
103,452
133,452
'Includes 6 in. ponding depth & disposal of soil onsite
(Note: If soil if taken offsite increase excavation cost by $ 95,000)
Cost / IA = $ 133,452 / 0.90 = $ 148,280
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7. Conclusions
In a more traditional sense, Cape Cod is already implementing many LID/green infrastructure principles.
The sandy, well-drained soils found on the Cape already promote high rates of stormwater infiltration,
eliminating the need for considerable stormwater infrastructure in many areas. Permeable soils have
reduced the need to treat stormwater quantity but have also removed the incentive to treat stormwater
quality. Nitrogen can easily enter the groundwater table through surface runoff and septic systems and
proceed untreated to local embayments, leading to eutrophication and subsequent loss of aquatic
habitat.
Many coastal communities in the U.S. are facing similar nutrient pollution issues. Although groundwater
sources of nitrogen from inefficient septic systems represent a significant pollutant load to local
embayments, it is possible to reduce nitrogen loading through green infrastructure techniques that treat
stormwater runoff. Use of innovative designs, thoughtful siting, and optimization of these techniques
can make treating stormwater sources of nitrogen cost effective. In addition, green infrastructure can be
easily placed throughout the watershed, resulting in multiple benefits for environmental justice
communities on the Cape, while providing centralized wastewater treatment to take individual septic
systems offline requires significant capital costs and a long timeframe.
The concepts presented in this study provide additional nitrogen removal options for both surface and
groundwater sources; future monitoring efforts at the sites will establish the hydrologic and water
quality effectiveness to guide future water quality projects on Cape Cod. The concepts have been
located on public, highly visible land to promote the need for water quality treatment to protect the
Cape's embayments and to reduce barriers to implementation such as land ownership. Tetra Tech and
CCC have presented these concepts to the Towns of Barnstable and Yarmouth to begin to obtain public
approval for the projects. CCC is currently pursuing funding opportunities to advance these projects to
the final design and construction phase, using the modeling, costs, and design plans included in this
report to prepare grant applications. Once implemented and established, the two projects will serve as
educational and visual examples of future opportunities throughout Cape Cod. The lessons learned from
this project will help Cape Cod and communities across the country better address coastal water quality
issues.
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Lucas, W. and M. Greenway. 2011a. Nutrient Retention Performance of Advanced Bioretention Systems:
Results from Three Years of Mesocosm Studies. Paper presented at the 2011 Low Impact
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Lucas W. C. and M. Greenway. 2011b. Phosphorus Retention by Bioretention Mesocosms Using Media
Formulated for Phosphorus Sorption: Response to Accelerated Loads. J. Irrigation Drainage Eng.
137, 144.
Lucas, W.C. and M. Greenway. 2011c. Hydraulic Response and Nitrogen Retention in Bioretention
Mesocosms with Regulated Outlets: Part Il-Nitrogen Retention. Water Env. Res. 83(8) 703-713.
Maryland Department of the Environment (MDE). 2009. Chapter 5, Environmental Site Design, Maryland
Design Manual for Stormwater Management.
Maryland Department of the Environment (MDE). 2011. Accounting for Stormwater Wasteload
Allocations and Impervious Acres Treated: Guidance for National Pollutant Discharge Elimination
System Stormwater Permits, Baltimore, MD.
Massachusetts Department of Environmental Protection (MassDEP). 2003. The Massachusetts Estuaries
Project Embayment Restoration and Guidance for Implementation Strategies.
Massachusetts Department of Environmental Protection (MassDEP). 2008. Structural BMP Specifications
for the Massachusetts Stormwater Handbook. Volume 2, Chapter 2. Massachusetts Department of
Environmental Protection, Worcester, MA.
Tetra Tech. 2008. Identifying Appropriate Types, Sizes, and Locations of LID BMPs at Memorial Peace
Cross Site near the Anacostia River. Prepared for Prince George's County, Maryland: Department of
Environmental Resources. Prepared by Tetra Tech, Inc, Fairfax, VA.
Tetra Tech. 2009a. Stormwater Best Management Practices (BMP) Performance Analysis. Prepared for
the U.S. Environmental Protection Agency Region 1, Boston, MA: EPA Region 1. Prepared by Tetra
Tech, Inc., Fairfax, VA. Available at:
http://www.epa.gov/regionl/npdes/stormwater/assets/pdfs/BMP-Performance-Analysis-Report.pdf
Tetra Tech. 2009b. SUSTAIN -A Framework for Placement of Best Management Practices in Urban
Watersheds to Protect Water Quality. Prepared for the U.S. Environmental Protection Agency
National Risk Management Research Laboratory: EPA Office of Research and Development.
Prepared by Tetra Tech, Inc., Fairfax, VA.
Tetra Tech. 2012. Technical Memo: Development of Cumulative Performance Curves for an Enhanced
Bioretention BMP. Prepared for the U.S. Environmental Protection Agency Region 1, Boston, MA:
EPA Region 1. Prepared by Tetra Tech, Inc., Fairfax, VA.
United States Environmental Protection Agency (EPA). 1988. Design Manual: Constructed Wetlands and
Aquatic Plant Systems for Municipal Wastewater Treatment. Office of Research and Development,
Center for Environmental Research Information, Cincinnati, OH. EPA/625/1-88/022.
United States Environmental Protection Agency (EPA). 1999. Field Applications of In Situ Remediation
Technologies: Permeable Reactive Barriers. Office of Solid Waste and Emergency Response.
Technology Innovation Office Washington, DC. EPA542-R-99-002.
United States Environmental Protection Agency (EPA). 2012. A Citizen's Guide to Phytoremediation.
Office of Solid Waste and Emergency Response, U.S. EPA, 5102G. EPA 542-F-12-016.
73
-------
University of New Hampshire Stormwater Center (UNHSC). 2012. Subsurface Gravel Wetlands for the
Treatment of Stormwater, Presented at the NJASLA 2012 Annual Meeting and Expo in Atlantic City,
NJ, January 29-31, 2012.
Vallino, J. and K. Foreman. 2008. Effectiveness of Reactive Barriers for Reducing N-Loading to the Coastal
Zone. A final report submitted to the NOAA/UNH Cooperative Institute for Coastal and Estuarine
Environmental Technology (CICEET). Ecosystems Center Marine Biological Laboratory Woods Hole,
MA.
Virginia Department of Conservation Resources (VADCR). 2011. Virginia OCR Stormwater Design
Specification No. 13 Constructed Wetlands.
74
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Appendix
75
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.EGEND
Parcel
Boudary
Treeline
Building
Paved
Road
Property
Object
Parking
Area
NOTES:
1. CIS Data provided by Cape Cod Commission and
the towns of Barnstable and Yarmouth
2. Buildings, road boundaries, and parking lots are
estimated from USGS 2009 orthoimagery
3. Additional site infrastructure in addition to what is
shown, such as underground utilities, may be
present on site. A more detailed site investigation
should be completed as part of a complete
design.
A
-------
B
A
Watershed Characteristics
Watershed Area, acres 3.87
Retrofit Characteristics
Town
Street Address
Total Impervious, %
Design Storm Event, in
Barnstable
165 Bearses Way
53.5
1"
Proposed Retrofit
Water Quality Volume, ft3
BMP footprint, ft2
Typ Ponding Depth, ft
Typ Media Depth, ft
Bioretention (Enhanced
and Traditional)
7,507
3650
0.33 (Enhanced)
0.50 (Traditional)
2.0 (Enhanced)
1.7 (Traditional)
Proposed Retrofit Description: The proposed retrofit would utilize a portion of the school's recreational
area. Flows from the impervious driving area would enter the enhanced bioretention cells through two
curb cuts on either end and through a sediment forebay/seating area in the center. The seating area
provides a focal point for the bioretention area that can be used for classroom exercises, while also
providing a sediment forebay to reduce the amount of sediment that would impact treatment and
maintenance. Flows would enter the enhanced bioretention through the gaps in the large structure rocks
used for seating. After the enhanced bioretention cells are filled, water would spill over a grassed weir
into the traditional bioretention cell where it would infiltrate into the existing soils.
NOTES:
1. The Enhanced Bioretention is to be completely lined
with an HOPE liner.
2. Trees and deep rooting shrubs should not be planted in
the Enhanced Bioretention to avoid puncturing the liner.
3. The outlet from the Enhanced Bioretention should be
discharged into a perforated pipe that is sized to
discharge outflows via infiltration to the in-situ soil.
4. Larger flow events are anticipated to overflow to the
surrounding recreational area through the traditional
bioretention area.
5. Curb cuts should be constructed of rock sized to resist
the erosive entrance velocities.
6. The existing playground area is anticipated to be
removed.
7. Pedestrian access to the recreational area is proposed
through two mounded crushed rock access paths. A
small fence should be placed around the cells to
prevent pedestrian access.
8. This is a conceptual plan and is not to be used for
construction.
Plant Symbology
Tree
SEDIMENT
CESS AREA
MOUNDED
PERMEABLE PAVER
ACCESS, PAThl)
RTO
IONAL
BIORETENTION
HANCE
RETEN
PERFORATED
PIPE
-------
B
A
~~>
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\ P P
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\ CO CO
\
\
\ "\
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\- ^ n
- — |
PAVER STONES ^^.
HOPE LINER (1% SLOPE) -^ N.
aNirpn FV/ST/NG G
RAD§ — — -T
iETENTION __ ^- - 1
" ~~ M ppnpnSED SLOPED
NDING
'""^ - 2x2x4' STRUCTURE DEPTH
ROCK SEATING
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30' 60'
III 1
VERTICAL
3' 6'
III 1
O
ENTION
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0')
RAVEL (0.51)
'EL (2.5')
100 200
CROSS SECTION B-B1 CROSS SECTION C-C1
PM|_| A MPFn
/ BIORETENTION
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i ROCK // PERMEABLE PAVER
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/ /
| / / / WEIR TO //
/ 7 / TRADITIONAL /
/ / BIORETENTION / /
rr A\~ EXISTING GRADE //\
\FOREBAY / i
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yWlfy^frr^iVI
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1
29
28
27
- 05' PONDING
DEPTH 26
WEIR 25
BIORETENTION
MEDIA (1.7')
j
(PEA GRAVEL (0.51)
| 22
3/4"GRAVEL(2.1')
21
20
19
00 C
EXISTING RP^nc
\
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\
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/;
/
/
s
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K
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1
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BIORETENTION
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i
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4" GRAVEL (2.2')
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Date: 03/11/2013
Designed By: CCC
Drawn By: RDD
Checked By:
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Copyright: Tetra Tech
-------
Parcel
Boudary
Treeline
Building
Paved
Road
Unpaved
Road
Storm
Sewer
NOTES:
1. GIS Data provided by Cape Cod Commission and
the towns of Barnstable and Yarmouth
2. Buildings, road boundaries, and parking lots are
estimated from USGS 2009 orthoimagery
3. Additional site infrastructure in addition to what is
shown, such as underground utilities, may be
present on site. A more detailed site investigation
should be completed as part of a complete
design.
-------
A
Watershed Characteristics
Watershed Area, acres 2.96
Town Yarmouth
Street Address Route 28
Total Impervious, % 30.4
Design Storm Event, in 1"
Retrofit Characteristics
Proposed Retrofit
Bioretention/
Phytoremediation with
Permeable Reactive Barrier
Water Quality Volume, ft3 3,270
BMP footprint, ft2 3,360
Typ Ponding Depth, ft 0.5
Typ Media Depth, ft 1.8
Proposed Retrofit Description: The proposed retrofit would be coordinated with the redevelopment of
the site for use as a marina. A raised leach field is proposed near the entrance to the site to accept
wastewater flows from the future marina facilities. A combined bioretention/phytoremediation/
permeable reactive barrier is designed between the proposed leach field and the new marina entrance
road. This BMP facility will collect storm water from the neighboring residences, the surrounding
impervious area, the future entrance road, and any other storm water that might be routed to the BMP
from the redeveloped site. This BMP will be allowed to drain freely, although the groundwater table in
this area is relatively shallow. To take advantage of the shallow groundwater table and provide additional
treatment of nitrogen, the bioretention area will include deep rooting trees with high nitrogen removal
capabilities as well as a permeable reactive barrier that contains organic material.
Plant Symbology
Tf66
O Shrub
O Grass
0 Perennial
I---X-] Bioinfiltration/Phytoremediation
ORNAMENTAL
LANDSCAPI
BIORETENTION/
PHYTOTECHNOLOGY
RAISED
FIELD
-------
A
NOTES:
1. The dry swale should be sized to convey the
storm events into the bioretention without
erosive velocities.
2. Sampling wells are to be included in the final
design. The locations are dependent on the
final configuration of the bioretention area and
the raised leach field.
3. An outlet is needed for the bioretention area for
larger flows; this outlet should be included in
the final design and coordinated with the
proposed marina design.
4. Salix Discolor and/or Salix Nigra (both male
species) should be used for the
phytotechnology component due to the invasive
tendencies of willows.
4. Long willow cuttings should be used for the
phytotechnology component. These cuttings
should be placed in the in-situ soil; the
bioretention media layers should be carefully
placed around the cuttings. These cuttings
should be densely spaced (suggest 5 foot on
center). More detailed planting plans will be
included in the final design.
5. This is a conceptual plan and is not to be used
for construction.
Plant Symbology
Tf66
O Shrub
O Grass
0 Perennial
I---X-] Bioinfiltration/Phytoremediation
URB CUT L
RAISED
FIELD
felORETENTIOlW
RHYTOTECHNOLOGY
CURB CUT
ORNAMENTAL
LANDSCAPING
-------
1 | Z 0 | +
f^
\
PLANT LIST
Key
G1
G2
G3
P1
P2
P3
P4
S1
S2
S3
S4
S5
S6
S7
T1
T2
T3
T4
Plant Type
herbaceous
herbaceous
herbaceous
herbaceous
herbaceous
herbaceous
herbaceous
shrub
shrub
shrub
shrub
shrub
shrub
shrub
tree
tree
tree
tree
Scientific
Name
Andropogon
gerardii
Calamagrostis
canadensis
Carex sp.
Baptisia
australis
Eupatorium
purpureum
subsp.
maculatum
'Gateway'
Iris versicolor
Liatris sp.
Amelanchier
canadensis,
Amelanchier
arborea
Aronia
arbutifolia
Clethra alnifolia
Cornus
amomum
Ilex verticillata
Vaccinium
corymbosum
Viburnum
lentago
Acer rubrum
Carpinus
caroliniana
Nyssa
sylvatica
Quercus alba
Common
Name
Big Bluestem
Blue Joint Grass,
Reed Grass
Various Sedge
Species (check
individual species
and habitat types)
Blue False Indigo
Joe-Pye Weed
Blue flag iris
Blazing Star
Shadblow/
Serviceberry
Red Chokeberry
Sweet Pepperbush
Silky Dogwood
Winterberry Holly
Highbush
Blueberry
Nannyberry
Red Maple
American
Hornbeam
Black Gum/Tupelo
White Oak
Zone
3 to 9
3
3t9
4 to 8
3 to 9
5 to 9
4 to 9
4 to 9
3 to 9
4
3 to 9
3 to 8
2t8
3 to 9
3 to 9
3 to 9
3 to 9
Mature
Height
to 6'
2-4'
2-4'
3-4'
4-5'
2-2.5'
to 5'
18'+
6-10'
3-8'
5-8'
6-10'
6-12'
14-16'
60-75'
20-30'
30-50'
50-80'
a
I D
HORIZONTAL
0 3ff 60'
VERTICAL
0 3' 6'
CROSS SECTION A-A
> •
12
10
9
8
7
6
5
4
3
2
1
0
4J.ii.iF
LLT..V.&I.L
PROPOSED LEACH
FIELD (BY OTHERS)
% w
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\
\ \
\ EXISTING GRADE \
\
SEASONAL HIGH
GROUNDWATER TABLE
GROUNDWATER FLOW — »-
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DEPTh
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BIORET
MEDI/c
j PEA GF
3/4" GRA\
DEEP ROOTING
WILLOW (5' SPACING
RECOMMENDED)
NDING
OPOSED MARINA
TRANCE ROAD
ENTION
'(1.8')
5AVEL (0.5')
'EL (2.0')
100
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www.tetratech.com
10306 EATON PLACE SUITE 340
FAIRFAX VA 22030
703.385.6000V
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------- |