Stormwater Master Plan. City of Pawtucket Pawtucket, Rhode Island. September Fuss & O Neill 317 Iron Horse Way, Suite 204 Providence, RI 02908

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1 Stormwater Master Plan City of Pawtucket Pawtucket, Rhode Island September 2017 Fuss & O Neill 317 Iron Horse Way, Suite 204 Providence, RI Project No A0

2 This project was funded by an agreement (CE00A0004) awarded by the Environmental Protection Agency to the New England Interstate Water Pollution Control Commission in partnership with the Narragansett Bay Estuary Program. Publications must also state: Although the information in this document has been funded wholly or in part by the United States Environmental Protection Agency under agreementce00a0004 to NEIWPCC, it has not undergone the Agency s publications review process and therefore, may not necessarily reflect the view of the Agency and no official endorsement should be inferred. The viewpoints expressed here do not necessarily represent those of the Narragansett Bay Estuary Program, NEIWPCC, or EPA nor does mention of trade names, commercial products, or causes constitute endorsement or recommendation for use.

3 Tables iii 1 Introduction Review of TMDL Requirements Blackstone River Ten Mile River Moshassuck River Map and Delineate Separated Catchments Characterize Separated Catchments Survey Junction Structures Delineation of Separated Catchments Catchment Prioritization Process Selection Matrix Preparation Calculations Based on GIS data Selection Matrix Scoring Final Selection of Priority Catchments BMP Selection Selected Structural BMPs Underground Infiltration Conceptual Designs Green Street Opportunity Non-structural BMPs Opinion of Probable Cost Underground Infiltration Green Street Opportunity Lifecycle Operation and Maintenance Cost Estimate City of Pawtucket Stormwater Master Plan i

4 5 Potential Pollutant Load Reduction Structural BMP Load Reductions Green Street Opportunity Catchment Focus and Prioritization Prioritized Catchments Works Cited.. 62 Figures Figure 1.1: View of the City of Pawtucket, the three major rivers that flow through it, the watershed boundaries and their impairments Figure 1.2: View of separated catchments and their proximity to priority outfalls listed in the Ten Mile River TMDL Figure 2.1: Illustration of initial digitization of possible separated infrastructure. This image is representative of areas throughout the City that were partially digitized that required further investigation to confirm whether or not they were separated Figure 2.2: Refined separated catchments (11/20/2016) Figure 2.3: Further refined separated catchments (12/20/2016) Figure 2.4: Finalized separated catchments (3/29/17) Figure 2.5: Overview of the finalized separated stormwater infrastructure throughout the City of Pawtucket Figure 2.6: Catchments for the separated stormwater systems were delineated using 2 ft contours derived from the 2011 Rhode Island Statewide LiDAR dataset Figure 3.1: Land Cover/Land Use for all separated catchments used in determining pollutant loading with the Simple Method (Steps 5 and 6) Figure 3.2: Map depicting the location of the final Top Priority catchments that were ultimately selected for structural BMP evaluation and conceptual design Figure 4.1: Typical detail of the profile of an underground infiltration chamber installation Figure 4.2: Image of an underground infiltration field during installation. Note the multiple side by side chambers Figure 4.3: Image of a typical pretreatment structure Figure 4.4: Typical detail of a bioretention basin Figure 4.5: Index sheet depicting the location of BMP conceptual designs for Priority Catchments Figure 4.6: View of a curb bump out bioretention area that could be incorporated into a green Street design for Power Road in Pawtucket, RI Figure 4.7: View of green street sidewalk bioretention installation Figure 4.8: Rendering of Power Road using Google Street View to depict the location of curb bumpouts and linear bioretention features City of Pawtucket Stormwater Master Plan ii

5 Tables Table 1.1: Waterbodies in the City of Pawtucket and their associated water quality impairments Table 1.2: Outfalls greater than 24 along the Ten Mile River listed in the TMDL Table 3.1: Scoring for parameters Percent Impervious Area, Water Quality Volume, Total Phosphorus Yield, Bacteria Yield, and Percent AB soils.. Standard deviation = σ Table 3.2: Scoring for Total Percent Tree Canopy parameter. Standard deviation = σ Table 3.3: Catchment Rating Matrix Table 3.4: Final list of catchments selected for structural BMP evaluation and conceptual designs Table 4.1: Various utility types and associated buffer widths used on either side of the pipe to minimize the potential for conflicts with BMP installation Table 4.2: Opinion of probable cost for installing underground infiltration chambers in priority catchments Table 4.3: Opinion of probable cost for bioretention areas associated with green street installation along Power Road, Pawtucket, RI Table 5.1: BMP-specific median pollutant removal efficiency (%), from Table H.3: Pollutant Removal Efficiency Rating Values for Water Quality BMPs in the 2015 Edition of the RISDISM Table 5.2: Estimated annual phosphorus and bacterial load reduction. Catchments are listed by their estimated reduction in annual bacterial load in billions of colonies Table 5.3: Estimated annual load reduction by proposed Green Street Opportunity Table 6.1: Priority Catchments ranked by their potential cost per pound of phosphorus removed City of Pawtucket Stormwater Master Plan iii

6 1 Introduction The City of Pawtucket (City) started addressing stormwater quality issues in 2003 when it developed a city-wide Stormwater Management Program Plan (SWMPP) that addressed the Rhode Island Department of Environmental Management s (RIDEM) General Permit for Small Municipal Separate Storm Sewer Systems (MS4) requirements. Since then, the City has worked to comply with that permit s requirements through the completion of outfall mapping, illicit discharge sampling, development of new stormwater regulations and training for City staff. Even with the City s ongoing work to comply with its MS4 permit, there are significant stormwater quality issues that need to be addressed. Specifically, the principal surface waters in the City are listed as impaired by RIDEM in the Integrated Water Quality Monitoring and Assessment Report and do not meet their designated uses such as safely supporting fish and wildlife (Table 1.1). These designations simply mean that the fish are not safe to eat, the water is not considered safe for swimming and that the rivers have degraded fish and wildlife habitat, all necessitating improvement in order for these uses to again be considered safe. The three major rivers in Pawtucket include the Blackstone, Ten Mile and Moshassuck Rivers. All are impaired. Figure 1.1 highlights these impaired waters and their listed impairments. RIDEM has developed Total Maximum Daily Loads (TMDLs) and action plans to reduce pollutant loadings to these impaired surface waters with the goal of restoring these rivers so that water quality can support their designated uses. Stormwater runoff draining to these waters is a major source of pollutant loadings causing these impairments. The goal of this project was to develop a city-wide plan to holistically address stormwater pollution in the areas with separate stormwater drainage systems where improvements and the addition of Best Management Practices (BMPs) could have the greatest effect. These elements include developing survey-quality mapping that can be used for future design and construction of BMPs and a public education program that builds public support. This plan will also be valuable to prioritize future capital investments for funding and implementation. Figure 1.1: View of the City of Pawtucket, the three major rivers that flow through it, the watershed boundaries and their impairments. City of Pawtucket Stormwater Master Plan 1

7 Current RIDEM regulations and the MS4 permit require that the City develop and implement strategies to reduce stormwater pollution as required by these approved TMDLs. These strategies include both non-structural measures (e.g. public education) and structural measures (i.e. best management practices) to reduce stormwater pollutants. The following report provides the critical building blocks to facilitate the City s future efforts in better managing stormwater runoff. 1.1 Review of TMDL Requirements The City of Pawtucket is subject to TMDL requirements associated with the three major rivers that flow through the City: the Blackstone River, Ten Mile River, and Moshassuck River. Table 1.1 summarizes the various impairments associated with each water body. This section presents a summary of relevant TMDL information as well as waterbody specific recommendations for TMDL implementation. This review of these requirements is a necessary step in eventually prioritizing the conceptual BMPs described later in this report. Table 1.1: Waterbodies in the City of Pawtucket and their associated water quality impairments. Water Body ID Impairment Type Cause/Impairment Blackstone River RI R-01B Fish and Wildlife Habitat Benthic Macroinvertebrate Bioassessments Cadmium Lead Oxygen, Dissolved Phosphorus (Total) Mercury in Fish Tissue PCB in Fish Tissue Enterococcus Fecal Coliform Fish Consumption Primary Contact Recreation Secondary Contact Recreation Enterococcus Moshassuck River & Tribs RI R-01B Fish and Wildlife Habitat Benthic City of Pawtucket Stormwater Master Plan 2

8 Water Body ID Impairment Type Cause/Impairment Macroinvertebrate Bioassessments Fish Consumption Primary Contact Recreation Enterococcus Secondary Contact Recreation Enterococcus Moshassuck River & Tribs RI R-01C Fish and Wildlife Habitat Benthic Macroinvertebrate Bioassessments Fish Consumption Primary Contact Recreation Enterococcus Secondary Contact Recreation Enterococcus Seekonk River (Estuary of the Blackstone) RI E-01 Fish and Wildlife Habitat Nitrogen (Total) Oxygen, Dissolved Fish Consumption -- Primary Contact Recreation Fecal Coliform Secondary Contact Recreation Fecal Coliform Ten Mile River & Tributaries RI R-01A Lead Aluminum Fish and Wildlife Habitat Iron Cadmium Phosphorus (Total) Fish Consumption City of Pawtucket Stormwater Master Plan 3

9 Water Body ID Impairment Type Cause/Impairment Source: (RIDEM, 2015) Blackstone River Primary Contact Recreation Secondary Contact Recreation Enterococcus Fecal Coliform Enterococcus Fecal Coliform The Blackstone River terminates in Pawtucket and as a result, much of the pollutant loading occurs upstream. The TMDL does not include pathogens as an impairment in the reach that passes through Pawtucket (R R-01B) because it is impossible to distinguish pathogen pollutant source due to a number of permitted Combined Sewer Overflows (CSOs) operated by the Narragansett Bay Commission (NBC). These CSOs are currently undergoing mitigation, after which the contribution of separate storm sewer systems will be assessed. The TMDL also lists lead and cadmium as pollutants of concern. It finds that sources in upstream reaches of the Blackstone River are contributing to the elevated levels of metals in the reach that passes through the City. Other direct sources of metals to this reach include CSO discharges, runoff from impervious cover that connected to the CSOs, and possible sediment resuspension. The City is coordinating with NBC and RIDOT to confirm outfall ownership and system interconnections, and to identify possible priority areas for runoff attenuation and/or treatment. The TMDL specifies that Pawtucket must evaluate the sufficiency of its six minimum measures to meet the TMDL water quality objectives and at a minimum must modify its ordinances related to post construction stormwater controls to prevent further degradation of impaired waters by promoting the use of green infrastructure as the primary method of stormwater control and achieving predevelopment groundwater recharge levels to the maximum extent practicable. The following summarizes key findings in the TMDL. Lead/Cadmium Loads for lead and cadmium from the upper segments of the Blackstone River upstream of the City of Pawtucket account for large percentages of the Dry Weather (DW) and Wet Weather (WW) loads of lead and cadmium (104% DW-lead, 207% WW-lead, 111% DWcadmium, 154% WW-cadmium) observed in the lower segment as evidenced by comparing the load at Manville Dam to Roosevelt Avenue City of Pawtucket Stormwater Master Plan 4

10 according to the approved TMDL. There are thirteen CSOs that discharge combined wastewater and stormwater into the Blackstone along this lower segment of the river. CSO discharges include a mix of domestic, commercial, and industrial wastewater and stormwater runoff, and contain a mix of human, commercial, and industrial wastes as well as pollutants washed from streets, parking lots, and other surfaces from the impervious areas of Pawtucket and Central Falls. Additional sources of lead and cadmium in this segment described in the TMDL include runoff discharged directly from impervious surfaces in this very urbanized watershed. Stormwater The lower section of the Blackstone River will benefit from reductions in dissolved metals achieved in the upper reaches of the river. There is no meaningful method to determine specific dissolved metals loading from any nonpoint sources of pollution, the thirteen combined sewer outfalls and multiple stormwater outfalls discharging to this section of the Blackstone River. Other possible sources include illicit discharges to storm drains, illegal sources, groundwater and sediment contamination, and dry weather CSO discharges. Pawtucket-specific recommendations: Per the TMDL, Pawtucket is required to evaluate the sufficiency of its six minimum measures to meet the TMDL water quality objectives and at a minimum modify its ordinances related to post construction stormwater controls to prevent further degradation of these impaired waters. The City has already begun to address these recommendations by taking the recommended first step of coordinating with NBC and RIDOT to confirm outfall ownership (whether CSO or separate stormwater outfall) and system interconnections, and to identify possible priority areas for runoff attenuation and/or treatment. City of Pawtucket Stormwater Master Plan 5

11 1.1.2 Ten Mile River The Ten Mile River watershed falls largely within Massachusetts and is largely effluent driven, which means that it derives much of its baseflow during dry weather from treated wastewater discharged by publicly owned treatment facilities in Massachusetts. The majority of the TMDL requirements must therefore be achieved before the Massachusetts/Rhode Island state line for meaningful progress to be made in the RI portion of the river. The approved TMDL lists pathogens, cadmium, lead, aluminum, iron, and phosphorus as pollutants of concern in the watershed, though cadmium and lead do not apply to the reach that passes through Pawtucket. According to the TMDL the Pawtucket portion of the river has both point and non-point sources of pathogens (stormwater outfalls and waterfowl). These sources require reductions of pathogen concentrations greater than 50% in dry and wet weather. Waterfowl management strategies at Slater Pond Park have been implemented in accordance with the TMDL to discourage nuisance waterfowl. Figure 1.2: View of separated catchments and their proximity to priority outfalls listed in the Ten Mile River TMDL. The TMDL finds that stormwater from urbanized land uses is the largest and most controllable source of phosphorus, pathogens, and metals in the Rhode Island portion of the Ten Mile River. An 80% reduction in growing season total phosphorus load is required for the upper Ten Mile River and is applied at the state boundary for sources of phosphorus originating in Massachusetts as well as source City of Pawtucket Stormwater Master Plan 6

12 categories in the RI portion of the watershed. Controllable sources of phosphorus include urban stormwater and the Pawtucket Country Club. According to the TMDL the City must make modifications to its Minimum Control Measures under their Rhode Island Pollution Discharge Elimination System (RIPDES) permit to be consistent with requirements of the TMDL. It must also assess and prioritize drainage systems for the design and construction of BMPs that reduce both the pollutants of concern and stormwater volumes to the maximum extent feasible. Priority should be given to those outfalls greater than 24-inches in diameter and identified in Table 1.2. Figure 1.2 shows the priority catchments identified in the Ten Mile River segment in Pawtucket, RI, and their proximity to the outfalls specifically called out within the TMDL. The following summarizes key findings from the TMDL. Table 1.2: Outfalls greater than 24 along the Ten Mile River listed in the TMDL. TMDL Outfall Direct Pipe Diameter Latitude Longitude Receiving Waterbody ID Discharge to 028 River Ten Mile River 039 Stream 36 and Ten Mile River near Daggett Avenue 041 River Ten Mile River 042 Pond Slater Park Pond Ten Mile River Pathogens The required fecal coliform concentration reduction for the upper Ten Mile River segment is 65% and the required enterococci concentration reduction is 93%. For this segment of the river, the most significant source of pathogens, aside from sources originating upstream in Massachusetts and quantified at the state line, is stormwater runoff from contributing watershed areas in the City of Pawtucket, RI and along Route I-95 in the Town of Seekonk, MA. The City of Pawtucket, Town of Seekonk and RIDOT all own outfalls contributing to stormwater inputs along this stretch of river. Other possible sources present during both wet and dry weather may include (and have historically included) illicit discharges to stormdrains and leaking sanitary sewer lines. According to the TMDL it is not likely that waterfowl are a significant contributor to pathogen impairments from the state line to Slater Park Pond. Downstream of the pond, however, geese are listed as a likely source of pathogen impairment. This lower section of the river, City of Pawtucket Stormwater Master Plan 7

13 from the outflow of Slater Park Pond to the inflow of Central Pond, has ideal habitat for waterfowl including a golf course and Slater Park itself. Historically, there has been visual evidence of fecal material deposited by geese visible along shorelines and even shallow substrates within Slater Park Pond itself. At present, the golf course has been incorporating geese management practices and the visual evidence of fecal material has been decreasing according to the TMDL. The second, specific source detailed in the TMDL is the pond within Slater Memorial Park in Pawtucket, RI. The area is known to harbor significant populations of several species of waterfowl including ducks, swans as well as resident geese populations. The TMDL recommends measures that can be taken by the park staff to discourage or remove resident geese and other waterfowl from this location. The City is currently implementing landscaping features to discourage geese from accessing the pond. Metals Under dry weather conditions, only reductions in aluminum are necessary, and in wet weather, both aluminum and iron reductions are necessary. No dry weather point sources of aluminum have been identified in this segment. Wet weather sources of aluminum and iron likely include discharges from MS4s in both MA and RI however a lack of data makes it impossible to determine the contribution from either MS4 or the percentage of aluminum and iron that can be attributed to MS4 discharges. Outfalls owned by the City of Pawtucket as well as RIDOT discharge to this segment. These outfalls will receive 100% of the Waste Load Allocation (WLA). Other possible sources include illicit discharges to storm drains or other illegal sources. MS4 Operator Specific Stormwater Measures for City of Pawtucket According to the TMDL, the City must revise its Stormwater Management Program Plan (SWMPP) to describe the additional controls that have or will be implemented to address the TMDL s provisions. Included in the enhanced practices called for by the TMDL are Public Education and Outreach efforts focused on both water quality and quantity concerns within the Ten Mile River Watershed. Also required are modifications to construction and post-construction ordinances to prevent any net increase in nutrients, metals, and bacteria from new construction and to reduce, to the maximum extent feasible, these pollutants from redevelopment projects. According to the TMDL the City must also assess and prioritize drainage systems for the design and construction of BMPs that reduce both the pollutants of concern and stormwater volumes to the maximum extent feasible. Priority should be given to those outfalls greater than 24-inches in diameter (Figure 1.2) Moshassuck River A TMDL for enterococcus was approved in According to the TMDL, this pollutant stems from stormwater runoff, sewer leaks, and animal waste for the reach of the river flowing through Pawtucket, ending at the first CSO outfall near the Weeden St bridge. This northern section extends about one-third (1/3) of a mile into Pawtucket, and includes some stormwater outfalls. A TMDL for City of Pawtucket Stormwater Master Plan 8

14 enterococcus is scheduled for 2025 for the reach extending south from Weeden St, but RIDEM expects that NBC s CSO abatement will negate the need for a TMDL. In order to meet TMDL requirements, the City needs to review and revise, as necessary, their MS4 Stormwater Management Program Plan to incorporate additional BMPs in their six minimum control measures that help to reduce bacteria pollution in the Moshassuck River. The City is also required to revise its post construction stormwater control ordinance so that it requires applicable development and redevelopment projects use Low Impact Development techniques as the primary stormwater control to the maximum extent practicable and maintain groundwater recharge to pre-development levels. There are no requirements that the City install structural BMPs in order to meet TMDL requirements. 2 Map and Delineate Separated Catchments The City of Pawtucket has both separated stormwater infrastructure and combined sewer systems that convey both stormwater and sanitary sewage to the wastewater treatment plant owned and operated by the Narraganset Bay Commision (NBC). Since the majority of combined flows reach the wastewater treatment plant, this management plan aimed to focus on those catchments that are separated from all sanitary inputs that, at present, receive no level of treatment at all. In order to evaluate the various separated stormwater areas across the City it was important to verify the accuracy of current data sets. In order to identify and verify the extent of the various separated stormwater catchments a process was initiated to review and evaluate the following: Characterize the extent of separated systems Survey junction structures to ground-truth data sets further Delineate separated catchments The following sections describe the process by which the catchments that were presumed to be separated were evaluated and eventually corroborated as separate stromwater infrastructure. Figure 2.1: Illustration of initial digitization of possible separated infrastructure. This image is representative of areas throughout the City that were partially digitized that required further investigation to confirm whether or not they were separated. City of Pawtucket Stormwater Master Plan 9

15 2.1 Characterize Separated Catchments The initial step taken for this project was to digitally map all of the separated catchments located within the City using the most up to date information available. Existing stormwater drainage data was provided by the City and Narragansett Bay Commission (NBC). This data included scanned images of paper mapping in PDF format for catchment areas presumed to be separated as well as PDF images of the combined sanitary sewer system. Much of the information in the presumed separated areas had been digitized previously for the City by Mainstreet GIS. That digital information was reviewed by Fuss & O Neill and City staff and additional areas were digitized that were presumed to be separated from the combined sanitary sewer system. Figures 2.1 through 2.4 show a section of the City with areas presumed to be separated from the initial digitized mapping and the iterative process by which the separated areas were narrowed down. Each individual alignment was reviewed and compared to the available paper mapping to verify the extent of the separated system. Figure 2.4 shows the finalized separated alignments. These areas were reviewed and altered during the mapping review phase and later refined based on field survey of infrastructure components. 2.2 Survey Junction Structures Once the digital information was as complete as it could be based on the available mapping, a field survey was targeted on manholes and key infrastructure presumed to be within the separated catchment areas that were acting as junction structures in order to field check the digitized information, provide more accurate data and better delineate the extent of the separated system. Field survey data was collected in January, 2017 by a licensed land surveyor. Data collected during inspection included rim elevations of structures as well as the invert elevations of connected pipes. This information was used to refine the extent of separated areas, remove areas that were found to be combined, and act as the basis for delineations of the various separated catchments across the City. City of Pawtucket Stormwater Master Plan 10

16 Figure 2.2: Refined separated catchments (11/20/2016). Figure 2.3: Further refined separated catchments (12/20/2016) Figures 2.2 through 2.4 show the iterative process of adding and subtracting areas presumed to be separated based on available information. Figure 2.2 shows areas in the central part of the city. Based on the reviewed maps portions of the area circled in the middle were altered to reflect available paper maps. Figure 2.3 continues the process illustrating the elimination of some areas entirely (circled area to the west) when the available mapping showed they were not part of the separated system. Finally, Figure 2.4 shows the finalized separated alignments. These areas were reviewed and altered during the mapping review phase and later refined based on field survey of infrastructure components. Figure 2.4: Finalized separated catchments (3/29/17). City of Pawtucket Stormwater Master Plan 11

17 Figure 2.5: Overview of the finalized separated stormwater infrastructure throughout the City of Pawtucket. City of Pawtucket Stormwater Master Plan 12

18 2.3 Delineation of Separated Catchments Once the infrastructure associated with the individual separated systems was finalized, the individual catchment areas were delineated in GIS for each of the outfalls serving separated systems. Catchments were delineated using data previously described and 2-foot contour data derived from the 2011 Statewide LiDAR dataset available through RIGIS (Rhode Island Geographic Information system, www. rigis.org/data). These subwatershed delineations were created in a single shapefile (Catchments.shp) and served as the basis for the analysis in the steps outlined in Section 3.1 used in populating the selection matrix. An area field was added to the shapefile s attribute table and the catchment area was calculated using the Calculate Geometry tool within the attribute table to determine the total areas area draining to each outfall in acres. This analysis yielded 29 discrete, separated, catchment areas draining to the three major rivers flowing through the City. THIS ANALYSIS YIELDED 29 DISCRETE, SEPARATED CATCHMENT AREAS DRAINING TO THE THREE MAJOR RIVERS FLOWING THROUGH THE CITY. Figure 2.6: Catchments for the separated stormwater systems were delineated using 2 ft contours derived from the 2011 Rhode Island Statewide LiDAR dataset. City of Pawtucket Stormwater Master Plan 13

19 3 Catchment Prioritization Process 3.1 Selection Matrix Preparation Once the 29 catchments were delineated a selection matrix was created to prioritize them. The intent was to extract a smaller subset of catchments for closer evaluation and propose conceptual designs for structural BMP retrofits within this subset of catchments. The prioritization process aimed to select for catchments that: Are subject to a TMDL Exhibit higher pollutant loads Have larger percentages of impervious area Have smaller amounts of green space/tree canopy, and Have at least a portion of the catchment within an Environmental Justice Community The following describes the development of the rating matrix to screen and prioritize the separated stormwater catchment areas described in Sections 2.1 and 2.2. The matrix is based on both data generated from existing GIS datasets and from models developed for this project. The following is a list of selection criteria used to prioritize the separated catchment areas: Priority Water Quality Segment o Utilizing the 2012 Integrated Water Quality and Assessment report data available from RIGIS, Priority Water Quality Segments are those water body segments that are placed under either of the following assessment categories: Category 4a (impaired or threatened for one or more designated uses but does not require development of a TMDL.; however, a TMDL has been completed) or Category 5 (impaired or threatened for one or more designated uses by a pollutant(s), and requires a TMDL) o Scored as a value of 1 or 2. All catchments drained to either a category 4a or category 5 water quality segment. Catchments that drain to a category 4a water quality segment were given a higher ranking due to the need to comply with TMDL recommendations in these segments. Environmental Justice Community o A community in which there is a recognized need for an improvement in environmental justice, which is defined by the U.S. Environmental protection Agency as the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income, with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies. City of Pawtucket Stormwater Master Plan 14

20 o Scored as a binary value (0 or 1). Catchments which contain a portion of an environmental justice community were scored a 1, because construction of a stormwater treatment practice in these areas can help advance environmental justice goals, while those located outside of an environmental justice community received a 0. Percent Impervious o The percentage of the total area in each catchment that is covered by a paved or otherwise impermeable surface. These surfaces prevent the infiltration of storm runoff. Increased runoff carries with it an increased amount of pollutants and thus a greater negative impact on stormwater quality. o Scored on a scale of 1-4. The percent impervious varied across catchments with a minimum value of over 53% impervious and a maximum value of 100% impervious. The standard deviation was calculated across all catchments and applied to the scoring described above and in Table 3.3. Higher scores were assigned to catchments with higher imperviousness. Water Quality Volume o The amount of stormwater runoff from any given storm that must be captured and treated in order to remove a significant fraction of stormwater pollutants on an average annual basis. This represents the entire runoff volume for 90% of the average annual storm events and is equivalent to the first 1.2 inches of rainfall over the impervious surface. o Scored on a scale of 1-4. Higher scores were assigned to catchments that produce a higher water quality volume. Percent A and B soils o The percentage of the total area in each subwatershed that is underlain by soils categorized by Hydrologic Soil Group as either Type A and/or Type B based on RIGIS data. These soils are well-drained, which is advantageous in the construction of stormwater best management practices, especially if constructing a best management practice that utilizes infiltration. o Scored on a scale of 1-4. Higher scores were assigned to catchments with higher percent A and/or B soils due to the increased potential for treatment and ease of design and construction associated with these soils. Estimated Total Phosphorus Yield o The estimated amount of phosphorus (in pounds) that is expected to be generated within the subwatershed and conveyed via stormwater runoff to the outfall. The estimated phosphorus yield is dependent on activities carried out on the site as well as the amount of impervious surface area generating runoff. This parameter was calculated by computing the annual load of Total Phosphorus, described in Section 3.2, and then dividing that by the actual number of acres within that particular catchment in order to produce a yield (lbs TP/year/acre). o Scored on a scale of 1-4, with higher scores assigned to catchments that generate higher estimated phosphorus yields. City of Pawtucket Stormwater Master Plan 15

21 Estimated Bacteria Yield o The estimated amount of bacteria (in billions of colonies) that is expected to be generated within the subwatershed and conveyed via stormwater runoff to the outfall. The estimated bacterial yield is dependent on activities carried out on the site as well as the amount of impervious surface area generating runoff. This parameter was calculated by computing the annual load of Bacteria, described in Section 3.2, and then dividing that by the actual number of acres within that particular catchment in order to produce a yield (billion colonies /year/acre). o Scored on a scale of 1-4, with higher scores assigned to catchments that generate higher estimated bacteria yields. Total Percent Canopy o The percent of the subwatershed area covered by tree canopy. Green infrastructure BMPs such as tree filters could improve tree canopy in neighborhoods which would serve to improve water quality, reduce heat impacts, improve resiliency to future climate change impacts and improve neighborhood aesthetics. o Scored on a scale of 1-4. Higher scores were assigned to catchments that have a lower total percent canopy, as implementing green infrastructure in these areas would have greater benefits for that community. GIS Processing and Analysis The following describes the step-by-step process by which data was analyzed in a GIS to calculate parameters used in the Selection Matrix: Steps 1 and 2: The initial characterization of separated stormwater infrastructure and delineation of the separated catchments is described in Sections 2.1 and 2.2 respectively. Step 3: Each of the 29 subwatershed boundaries was extracted from the shapefile created in Step 2 using the Select tool, with the following input in the SQL Query Builder: Ctchmnt_ID = Subwatershed Name This resulted in the creation of 29 individual shapefiles (Armistice.shp, Bowles.shp, etc.), each containing a single polygon representing a subwatershed boundary. Step 4: The RIGIS 2011 Impervious Surfaces dataset was converted from raster format to polygon format using the Raster to Polygon tool. The impervious cover data within each subwatershed boundary was extracted using the Clip tool (Clipped), where the impervious cover shapefile served as the Input Features and the subwatershed boundaries served as the Clip Features. This resulted in 29 individual shapefiles (e.g. Armistice Imp.shp, Bowles Imp.shp, etc.) containing impervious and non-impervious areas within each subwatershed. Field calculations within the attribute table were used to determine the total impervious surface area in acres within each subwatershed. City of Pawtucket Stormwater Master Plan 16

22 Step 5: The RIGIS 2011 Land Cover and Land Use dataset consists of a vector dataset containing polygons representing areas of classified land use types. This dataset was clipped to each subwatershed boundary, resulting in a land use shapefile for each of the 29 catchments (e.g. Armistice LU.shp, Bowles.LU.shp, etc). Field calculations were used to determine the area within each polygon associated with each of the land use types contained within each subwatershed. Step 6: To facilitate further analysis of pollutant loadings, the land use shapefile and the impervious area shapefile for each subwatershed was overlaid using the Intersect tool to produce a shapefile for each of a 29 catchments (e.g. Armistice IMP_LU.shp, Bowles IMP_LU.shp, etc.), in which the watershed was broken down by both land use and impervious cover. Field calculations were performed to determine the total area in acres for each polygon in the resulting shapefile, allowing the determination of the total area and total impervious area of each land use type for each subwatershed. Figure 3.1: Land Cover/Land Use for all separated catchments used in determining pollutant loading with the Simple Method (Steps 5 and 6). Step 7: The RIGIS 2011 Soils Data dataset was Clipped to each subwatershed boundary to create 29 shapefiles containing soils data for each subwatershed (e.g. ArmisticeSoils.shp, BowlesSoils.shp, etc.). Field calculations were completed to determine the total area of each subwatershed underlain by either Type A or B soils, which was in turn used to determine the percent of each subwatershed area underlain by Type A or B soils. City of Pawtucket Stormwater Master Plan 17

23 Step 8: The National Land Cover Database 2011 (NLCD, 2011) USFS Tree Canopy Cartographic dataset was used to determine the approximate percentage of tree canopy cover in each subwatershed. The dataset, which consists of a continuous dataset comprised of 30m x 30m pixels with an associated percent tree canopy cover determined for each pixel, was overlaid on the subwatershed boundaries, which were used to extract the overlying ixels from the raster dataset using the Extract by Mask Tool. This resulted in 29 individual file system raster datasets (e.g. ArmisticeTC, BowlesTC, etc., Appendix A).Fields were then added to the attribute table for each of the 29 raster layers in order to calculate the tree canopy area for each subwatershed. The first field added was Pixel Area which was populated as follows for each record in the attribute table: Pixel Area = acres A field for canopy area was then added to each layer and was calculated as follows: Canopy Area (acres) = Pixel Area x Value x Count/100 where Value represents the percent tree canopy cover within each pixel and Count is the number of pixels with a given Value within each subwatershed. The percent tree canopy cover was then calculated using values from the statistics tool within the attribute table using the following formula: Percent tree canopy area = Sum(Canopy Area Field) Sum(Count Field) where both Canopy Area and Count were summed for every record in the attribute table for each subwatershed. Step 9: A dataset containing environmental justice boundaries (EPA, 2007) was obtained and was Clipped to the Rhode Island State Boundary (State Boundary, RIGIS, 1997). Visual inspection was used to determine whether a subwatershed was partially contained within a designated Environmental Justice community. City of Pawtucket Stormwater Master Plan 18

24 3.2 Calculations Based on GIS data The impervious area values derived in Step 4 were used to determine the percent impervious area for each subwatershed. This value was then used to calculate Water Quality Volume (WQv) according to the following formula: where Impervious Area is measured in acres. WQv (acre feet) = 1 inch Impervious Area 12 Watershed information derived from GIS data was also used to develop a Simple Method model of each of the catchments in order to assess relative loadings of total phosphorus and bacteria, the pollutants of concern in this study. The shapefiles produced in Step 6 were used to determine the area of each land use type within each subwatershed, and the percentage of each land cover type that was impervious. This allowed the determination of the pollutant loading for each land use type within each watershed. The annual phosphorus load was calculated using the following formula: where L = Annual Phosphorus Load (pounds) R = Annual Runoff (inches) C = Pollutant Concentration (mg/l) A = Area (acres) L = x R x C x A Pollutant Concentration values were based upon recommended values for Initial Event Mean Concentration (EMC) Values reported in Quality Assurance Project Plan. Development of a Watershed Based Plan for Massachusetts (BETA Group, Inc., 2006) and are summarized in Appendix B. The RISDISM has EMC values that are more general than those described by BETA. The EMCs selected for this project more closely aligned with the more specific Land Use designations than those published in the RISDISM. As some land use areas in the land use dataset were not represented in this document, these land use types were modeled as similar land use types described in the report, as summarized in Appendix B. The decisions regarding which EMC values to use for a given land use type were based on similarities in vegetative cover and human activities occurring on the site between the land use types in question and those addressed in the report. After calculating the Annual Phosphorus load anticipated from each individual land use type within each subwatershed, the resulting loads were summed to determine a total phosphorus load for each subwatershed. City of Pawtucket Stormwater Master Plan 19

25 Similarly, the bacterial load for each land use type was calculated as where L = Annual Bacterial Load (billions of colonies) R = Annual Runoff (inches) C = Pollutant Concentration (mg/l) A = Area (acres) L = R C A The loads for each land use type present in a given subwatershed were summed to determine the total bacterial load for the watershed. Annual runoff was determined using the following formula which is a simplified calculation used for these purposes: where R = P Pj Rv R = Annual Runoff (inches) P = annual Rainfall (inches), determined from Figure H-8 of the Rhode Island Stormwater Design and Installation Standards Manual, 2015 Edition (RIDEM, 2015) and set to 48 inches. Pj = Fraction of rainfall events producing runoff (set to 0.9) Rv = Runoff Coefficient. The Runoff Coefficient is calculated as: Rv = Percent Impervious Area (RISDISM, 2010) The loading from each land use type within the watershed was then summed to determine the overall pollutant loading for each pollutant in each watershed. City of Pawtucket Stormwater Master Plan 20

26 3.3 Selection Matrix Scoring Each of the parameters was scored for each watershed, with higher scores indicating a greater potential for water quality improvements. Priority Water Quality Segment and Environmental Justice Community parameters were scored on scales of 1 or 2 and 0 or 1 respectively. The Percent Impervious Area, Water Quality Volume, Total Phosphorus Yield, Bacteria Yield, and Percent AB soils were scored on a range of 1-4 where higher values meant higher scores. Due to the proximity of the catchments and their similar development pattern, many of the watersheds exhibited similar values for the parameters assessed. Using the results from all 29 catchments, the mean and standard deviation were determined for the following parameters in the matrix: Percent Impervious Area, Water Quality Volume, Total Phosphorus Yield, Bacteria Yield, Tree Canopy, and Percent AB soils. These values were used to distribute the scores for each parameter across a normal distribution. Table 3.1 shows the scoring values for the matrix parameters Percent Impervious Area, Water Quality Volume, Total Phosphorus Yield, Bacteria Yield, and Percent AB soils where σ is equal to one standard deviation. Scores were attributed by evaluating there relation to the mean. Values less than one standard deviation from the mean were given a score of 1, values between the mean and one standard deviation less than the mean were given a score of two, values above the mean and within one standard deviation were given a score of 3, and values greater than one standard deviation from the mean were given a score of four.. The greater the value the greater the overall score. Table 3.1: Scoring for parameters Percent Impervious Area, Water Quality Volume, Total Phosphorus Yield, Bacteria Yield, and Percent AB soils.. Standard deviation = σ. Relation to the Mean Score <-1σ 1-1σ 2 +1σ 3 >+1σ 4 Scoring for the Total Percent Tree Canopy parameter similarly used the variation around the mean value however higher scores were given to catchments with less tree canopy (Table 3.2). The greater the Percent Tree Canopy value the lower the score. City of Pawtucket Stormwater Master Plan 21

27 Table 3.2: Scoring for Total Percent Tree Canopy parameter. Standard deviation = σ. Relation to the Mean Score <-1σ 4-1σ 3 +1σ 2 >+1σ 1 The presence of an Environmental Justice Community or Priority Water Quality Segment 4a or 5 were each scored as a binary parameter, with 1 representing the presence of one of these areas of interest and 0 representing the absence. The final score for each matrix was then determined by summing the scores for each watershed parameter, the watersheds were sorted by the resulting final score (Table 3.3). City of Pawtucket Stormwater Master Plan 22

28 Table 3.3: Catchment Rating Matrix. Rank Subwatershed ID Waterbody Priority Water Quality Segment Environmental Justice Community % Impervious Score WQv (acre ft) Score % A and B Soils Score Total P Yield (lbs/yr/acre) Score Total Bacteria Yield (Billion Colonies/yr/acre) Score Total % Canopy Score Total Score 1 Weeden Moshassuck River % % % Fairview Moshassuck River % % % Bowles Seekonk River % % % Mineral Spring Moshassuck River % % % Waterman Ten Mile River % % % Armistice Ten Mile River % % % Daggett 1 Ten Mile River % % % School 1 Seekonk River % % % Manton Ten Mile River % % % Pinecrest Ten Mile River % % % Central Ten Mile River % % % Taft 2 Seekonk River % % % Division 1 Seekonk River % % % School 2 Seekonk River % % % Morris Moshassuck River % % % Smithfield Moshassuck River % % % Power Moshassuck River % % % Division 2 Seekonk River % % % Taft 1 Seekonk River % % % Exchange Blackstone River % % % Roosevelt Blackstone River % % % Main Blackstone River % % % George Seekonk River % % % Roosevelt Ext Seekonk River % % % Broadway Seekonk River % % % Leonard Jenard Moshassuck River % % % Crest Ten Mile River % % % Charlton Seekonk River % % % Taft 3 Seekonk River % % % 3 14 City of Pawtucket Stormwater Master Plan 23

29 3.4 Final Selection of Priority Catchments The selection matrix developed for this project was used as an initial step in identifying the final list of the top ten priority catchments that would be evaluated for conceptual stormwater BMPs. The prioritized list of catchments created by the matrix was reviewed and evaluated by Fuss & O Neill and City staff during a workshop. Evaluation and selection of priority catchments included the review of the selection matrix ranking, a review of recommendations and requirements specified by pertinent TMDLs, and additional firsthand knowledge of constructability based on recent and short term capital improvement projects throughout the City. Preference was given to those catchments that scored high on the selection matrix, met specific TMDL requirements and did not have barriers to construction such as recently repaved road surfaces or sidewalks that would prevent, or make less desirable, installation of the proposed BMPs. Figure 3.2: Map depicting the location of the final Top Priority catchments that were ultimately selected for structural BMP evaluation and conceptual design. City of Pawtucket Stormwater Master Plan 24

30 As described in Section 1.1, the Ten Mile River is the only river in the City subject to a TMDL that specifically requires the assessment and prioritization of drainage systems owned by the City for the design and construction of BMPs that reduce both the pollutants of concern (phosphorus, bacteria) to the maximum extent feasible. Based on these more stringent requirements it was determined that all catchments associated with the Ten Mile River TMDL should receive a priority listing regardless of their matrix rated position. Of the seven separated catchments located within the Ten Mile River watershed only Central and Crest were outside of the initial Top 10 ranking of the selection matrix. The Central catchment was ranked 11 th while Crest was near the bottom of the selection matrix ranking based on its low percentage of impervious surface and high percentage of tree canopy. Despite the low matrix ranking, the Crest catchment was added to the priority list due to its inclusion in the Ten Mile River watershed. It was also determined that the catchments associated with the Seekonk River should also be excluded. These catchments discharge to the Seekonk River (estuarine portion of the Blackstone River) which does not currently have a TMDL and that WWTP upgrades to facilities in Massachusetts along with CSO abatement in Pawtucket and Providence would eliminate the need for a TMDL. Once these catchments were excludedthe Morris catchment was the next catchment on the selection matrix. Table 3.4: Final list of catchments selected for structural BMP evaluation and conceptual designs. Catchment ID Receiving Waterbody WQv (ft 3 ) % Impervious Armistice Ten Mile River 152, % Central Ten Mile River 56, % Crest Ten Mile River 39, % Daggett 1 Ten Mile River 69, % Fairview Moshassuck River 421, % Manton Ten Mile River 36, % Mineral Spring Moshassuck River 91, % Morris Moshassuck River 21, % Pinecrest Ten Mile River 159, % Waterman Ten Mile River 87, % Weeden Moshassuck River 89, % City of Pawtucket Stormwater Master Plan 25

31 4 BMP Selection While there are many different types of structural BMPs available, not all BMPs are desirable in all locations for a variety of reasons including the type of soils, cost, maintenance requirements, and pollutant removal efficiency for various pollutants of concern. A variety of structural BMPs were identified as possibilities for this project and presented to the City so that a subset of these practices could be selected for the conceptual designs within the selected catchment areas. Various practices that were proposed for this project include bioretention (in various forms), porous pavement and sidewalks, underground infiltration, and Wet Vegetated Treatment Systems (WVTS). 4.1 Selected Structural BMPs On March 29 th, 2017, Fuss & O Neill and City of Pawtucket staff evaluated the comprehensive list of potential structural BMPs that could be incorporated into conceptual designs used to treat stromwater in the priority catchments identified in Section 3.5. Acceptance criteria for structural practices included maintenance requirements (including the possible need for specialized maintenance equipment), ease of installation, winter performance, pollutant removal efficiency, and overall cost to construct. Figure 4.1: Typical detail of the profile of an underground infiltration chamber installation. Source: After deliberation it was decided that underground infiltration practices, although typically more expensive than most similarly sized structural BMPs, met or exceeded the other evaluation criteria and therefore would be the best choice for conceptual designs in the priority catchments previously selected. Figure 4.2: Image of an underground infiltration field during installation. Note the multiple side by side chambers. Source: Underground infiltration chambers, similar to the typical detail in Figure 4.2, can be ideal BMP candidates in highly urbanized areas where available space is limited to the road Right of Way (ROW). In the City of Pawtucket, it was determined that for the conceptual design phase of this project these infiltration practices would be best proposed as single-wide and double-wide linear installations in order for them to fit within available footprints City of Pawtucket Stormwater Master Plan 26

32 within the road ROW. In areas where more space was available, the underground infiltration systems were proposed as fields of varying width based on the available width and potential conflicts with utilities. In order for these underground infiltration chambers to function properly and reach or exceed their design life there needs to be adequate pretreatment of stromwater in order to prevent clogging. Pretreatment practices could vary on a site-by-site basis when appropriately sized during a more final design phase. For purposes of this project a surrogate pretreatment structure was selected for both its concept as well as its price, to be included in the overall opinion of probable cost described later in Section 4.5. The pretreatment structure selected was a common oil and grit separator (Figure 4.3). Finally, it was determined that a surface BMP concept would be beneficial as both a demonstration project to further educate citizens on the importance of stormwater management. This would help build support for similar programs within the City for both the proposed structural BMP installations and non-structural programs such as the Street Tree and Rain Barrel programs discussed later in Section 4.4 as well as increase overall treatment within the selected catchment. For pollutant removal calculations and pricing purposes, the structural BMP proposed for the Green Street opportunity was bioretention. These bioretention areas would be designed specifically to meet site-specific needs and constraints. Designs would include curb bump outs and linear features intertwined with pedestrian right-of-ways and possibly a bike lane as well. A further description of the Green Street Opportunity can be found in Section 4.3. Figure 4.3: Image of a typical pretreatment structure Source: Figure 4.4: Typical detail of a bioretention basin. City of Pawtucket Stormwater Master Plan 27

33 4.2 Underground Infiltration Conceptual Designs In order to determine appropriate locations to recommend underground infiltration chambers it was first necessary to review available utility data associated with the chosen priority catchments. Data was obtained for sewers and water mains in digital, shapefile format. The gas main data was obtained in paper form and was digitized by City staff. It should be noted that the accuracy of this data is approximate and all proposed BMP designs would require further utility confirmation and evaluation of potential conflicts during the final design phase prior to implementation. Once all of the utility data was in a digital format it was incorporated into the GIS database. Each utility was buffered by an appropriate distance to minimize the potential for conflicts. Table 4.1 shows the buffer width used for each utility type. Once the utility data was buffered, underground infiltration chamber systems were located in areas free of known conflicts. Each catchment was evaluated for BMP suitability from the outfall upstream to its headwaters in an attempt to concentrate proposed practices as low in the catchment as possible in order to maximize treatment of the WQv for each catchment. Suitability criteria included available space and lack of utility buffer conflicts. Table 4.1 outlines the buffer widths applied to various utilities located within the catchment used in site suitability evaluations. Table 4.1: Various utility types and associated buffer widths used on either side of the pipe to minimize the potential for conflicts with BMP installation. Utility Type Buffer Width (ft) Gas 5.5 Water 3 Sewer 3 Proposed BMP locations were further reviewed using aerial imagery and Google Street View to evaluate potential conflicts with overhead electric utilities as well as evaluate road and sidewalk conditions. BMPs were conceptually placed to avoid areas where it was believed recent road or sidewalk improvements have taken place thus taking into consideration the time, effort and cost that has already been expended in these locations. A specific infiltration chamber (StormTech SC-740) was used for purposes of sizing and cost estimation. By choosing one specific chamber size the evaluation of catchments was streamlined and made as uniform as possible. This allowed for better comparison between catchments by overall cost. In the future, site specific constraints may require alternate chambers be used, either by size or manufacturer, depending on a number of factors including depth to ground water, capacity, actual space available in order to avoid utility conflicts, and cost. The following pages show the individual catchment areas and the location of proposed underground infiltration in relation to existing utility infrastructure. Each sheet describes the proposed BMP concept for the catchment and also provides information such as the WQv, the potential percentage of the WQv that could be treated if all proposed practices were installed, the annual pollutant load for both phosphorus and bacteria, the City of Pawtucket Stormwater Master Plan 28

34 estimated pollutant load removal based on treatment of the WQv, and the opinion of probable cost for installation of all proposed BMPs. It should be noted that the opinion of probable cost is a conservative estimate and takes into account the installation of all proposed BMPs in the catchment. For catchments where it is possible to treat over 100% of the WQv, the actual cost would likely be lower than what is described here. The opinions of probable cost for both the underground infiltration practices as well as the Green Street opportunity are described further in Section 4.5. Pollutant load reductions were estimated and are explained in detail in Section 5. The overall pollutant load reduction for each catchment was included with the conceptual design and calculated based on the percent of the WQv that could be treated. Where proposed BMPs allowed for treatment of more than 100% of the WQv, calculations on pollutant load reductions were based on treating only 100% of the WQv. City of Pawtucket Stormwater Master Plan 29

35 Figure 4.5: Index sheet depicting the location of BMP conceptual designs for Priority Catchments. City of Pawtucket Stormwater Master Plan 30

36 Water Quality Volume WQv for 1 of Runoff 36,568 ft 3 % WQv Treated 127% Single Width Infiltration Chambers: 56% WQv treated Underground Infiltration Field: 71% WQv treated Annual Pollutant Load Total Phosphorus 61 lbs/year Bacteria (FC) 7,400 billion colonies/year Proposed Concept: Three infiltration fields ranging from 3 to 5 rows wide are recommended for installation midway through the catchment to treat the bulk of the impervious area, within a parking lot and along Parkview Drive. In addition, installation of single width linear infiltration units is recommended along Manton Street to treat the remainder of the water quality volume. Estimated Pollutant Removal Based on Treatment of the 1 WQv Total Phosphorus 34 lbs/year Bacteria (FC) 6,700 billion colonies/year Opinion of Probable Cost Pretreatment: $30,000 Single Width Infiltration Chambers: $350,000 Underground Infiltration Fields: $490,000 Total: $870,000 City of Pawtucket Stormwater Master Plan 31

37 Water Quality Volume WQv for 1 of Runoff 21,746 ft 3 % WQv Treated 306% Single Width Infiltration Chambers: 151% WQv treated Underground Infiltration Field: 145% WQv treated Annual Pollutant Load Total phosphorus 30 lbs/year Bacteria (FC) 3,700 billion colonies/year Estimated Pollutant Removal Based on Treatment of the WQv Total Phosphorus 16 lbs/year Bacteria (FC) 3,300 billion colonies/year Opinion of Probable Cost Pretreatment: $30,000 Single Width Infiltration Chambers: $570,000 Underground Infiltration Fields: $670,000 Total: $1,270,000 Proposed Concept Three larger infiltration fields are recommended for this watershed. One larger infiltration field is recommended for the tennis and basketball courts at the intersection of Morris Avenue and Smithfield Avenue, near the center of the watershed. While this installation is currently sized to be 12 rows wide, the footprint and cost may be reduced in final design. The other two infiltration fields are recommended for installation within the cul-de-sac at the southeast end of Morris Avenue. Each of these installations consists of three rows of infiltration chambers; length varies between rows in each installation in order to fit within the cul-desac footprint. Additionally, installation of single width linear infiltration units is recommended along Morris Avenue. The total cost of installation includes both the single-width infiltration chambers and the larger infiltration fields. Each of these recommended BMPs has the ability to treat more than the WQv making it likely only one of the options, or a hybrid approach, would be selected in this catchment. City of Pawtucket Stormwater Master Plan 32

38 Water Quality Volume WQv for 1 of Runoff 91,382 ft 3 % WQv Treated 240% Single Width Infiltration Chambers: 20% WQv treated Double Width Infiltration Chambers: 106% WQv treated Underground Infiltration Field: 114% WQv treated Annual Pollutant Load Total phosphorus 97 lbs/year Bacteria (FC) 13,000 billion colonies/year Estimated Pollutant Removal Based on Treatment of the 1 WQv Total Phosphorus 53 lbs/year Bacteria (FC) 11,700 billion colonies/year Opinion of Probable Cost Pretreatment: $70,000 Single Width Infiltration Chambers: $310,000 Double Width Infiltration Chambers: $1,860,000 Underground Infiltration Fields: $2,120,000 Total: $4,360,000 Proposed Concept Three infiltration fields are recommended for installation at the parking lot, basketball court, and Slater School Playground located adjacent to the M. Virginia Cunningham Elementary School and Samuel Slater Middle School. While these installations are currently sized to be 20 10, and 16 rows wide, respectively, the footprint and cost may be reduced in final design. Installation at a public school would provide additional educational opportunities. Double width infiltration units are recommended along the north side of Mineral Spring Avenue. These units would mainly be installed beneath the road, except near the watershed outlet, where a portion of one installation would likely need to be located beneath the sidewalk. Single width infiltration units are proposed for installation beneath sidewalks along Abbott Street and Baldwin Street, and beneath the road and sidewalks along Lorraine Street. City of Pawtucket Stormwater Master Plan 33

39 Water Quality Volume WQv for 1 of Runoff 68,819 ft 3 % WQv Treated 139% Single Width Infiltration Chambers: 35% WQv treated Double Width Infiltration Chambers: 104% WQv treated Annual Pollutant Load Total phosphorus 94 lbs/year Bacteria (FC) 11,000 billion colonies/year Proposed Concept A combination of double and single width infiltration installations is recommended for the catchment. These include single width installations under London, Orient, Hutchinson, and Bristol Avenues, and double width installations along Orient and Daggett Avenues. These installations would likely be located under the roadway, with one exception on Orient Avenue where a single row of infiltration units could need to be installed beneath the sidewalk depending on utility locations. Estimated Pollutant Removal Based on Treatment of the WQv Total Phosphorus 52 lbs/year Bacteria (FC) 9,900 billion colonies/year Opinion of Probable Cost Pretreatment: $45,000 Single Width Infiltration Chambers: $420,000 Double Width Infiltration Chambers: $1,397,000 Total: $1,862,000 City of Pawtucket Stormwater Master Plan 34

40 Proposed Concept: A combination of single and double width infiltration chambers are recommended for the catchment. These include single-width installations under Eddington Street, Stafford Street, Parkside Avenue, and Brookdale Boulevard, and doublewidth installations along Armistice Boulevard and Daggett Avenue. All of these installations are located under the roadway or right-of-way. Additionally, two underground infiltration fields are recommended on Armistice Boulevard near the outfall. One installation consists of three rows of infiltration chambers, while the other consists of 5 rows of chambers. These infiltration fields would be installed beneath the roadway island that is currently in place along Armistice Boulevard. Water Quality Volume WQv for 1 of Runoff 152,732 ft 3 % WQv Treated 129% Single Width Infiltration Chambers: 59% WQv treated Double Width Infiltration Chambers: 44% WQv treated Underground Infiltration Field: 27% WQv treated Annual Pollutant Load Total phosphorus 241 lbs/year Bacteria (FC) 28,600 billion colonies/year Estimated Pollutant Removal Based on Treatment of the WQv Total Phosphorus 134 lbs/year Bacteria (FC) 25,700 billion colonies/year Opinion of Probable Cost Pretreatment: $75,000 Single Width Infiltration Chambers: $1,554,000 Double Width Infiltration Chambers: $1,288,000 Underground Infiltration Fields: $798,000 Total: $3,715,000 City of Pawtucket Stormwater Master Plan 35

41 Proposed Concept Three infiltration fields are recommended for this installation including two installations consisting of three rows of chambers installed beneath the road surface on Derby Street and Cooper Street. In addition, a larger underground infiltration field, 18 rows wide, is proposed at a church parking lot on Weeden Street. Although this is not public property, its location in the watershed would allow treatment of a significant portion of the water quality volume while minimizing pretreatment and traffic and utility conflicts. Additionally, single width infiltration units are proposed within the roadway along Weeden Street, Lorraine Street and Larch Street. Water Quality Volume WQv for 1 of Runoff 89,294 ft 3 % WQv Treated 129% Single Width Infiltration Chambers: 45% WQv treated Underground Infiltration Field: 84% WQv treated Annual Pollutant Load Total phosphorus 125 lbs/year Bacteria (FC) 15,000 billion colonies/year Estimated Pollutant Removal Based on Treatment of the WQv Total Phosphorus 69 lbs/year Bacteria (FC) 13,500 billion colonies/year Opinion of Probable Cost Pretreatment: $50,000 Single Width Infiltration Chambers: $694,000 Underground Infiltration Fields: $1,524,000 Total: $2,268,000 City of Pawtucket Stormwater Master Plan 36

42 Proposed Concept Proposed installations consist entirely of double width infiltration chambers installed under the roadway along Central Avenue and Daggett Avenue. Water Quality Volume WQv for 1 of Runoff 56,667ft 3 % WQv Treated 125% Double Width Infiltration Chambers: 125% WQv treated Annual Pollutant Load Total phosphorus 60 lbs/year Bacteria (FC) 7,600 billion colonies/year Estimated Pollutant Removal Based on Treatment of the WQv Total Phosphorus 33 lbs/year Bacteria (FC) 6,800 billion colonies/year Opinion of Probable Cost Pretreatment: $30,000 Double Width Infiltration Chambers: $1,361,000 Total: $1,391,000 City of Pawtucket Stormwater Master Plan 37

43 Water Quality Volume WQv for 1 of Runoff 421,819 ft 3 % WQv Treated 105% Single Width Infiltration Chambers: 35% WQv treated Double Width Infiltration Chambers: 70% WQv treated Annual Pollutant Load Total phosphorus 632 lbs/year Bacteria (FC) 78,700 billion colonies/year Estimated Pollutant Removal Based on Treatment of the WQv Total Phosphorus 348 lbs/year Bacteria (FC) 70,800 billion colonies/year Opinion of Probable Cost Pretreatment: $275,000 Single Width Infiltration Chambers: $2,571,000 Double Width Infiltration Chambers: $5,683,000 Total: $8,529,000 Green Street Opportunity Opinion of Probable Cost: $408,000 Proposed Concept A combination of double and single width infiltration installations are recommended throughout the catchment. Due to a lack of space and potential utility conflicts, many proposed installations are located under sidewalks or the right-of-way, as well as under roadways. Due to the dispersed nature of the installations, a large number of pretreatment units are required. The number of pretreatment structures may be able to be reduced during the final design phase. A Green Street (Section 4.3) is also proposed for Power Road, which would treat an additional 3% of the water quality volume. City of Pawtucket Stormwater Master Plan 38

44 City of Pawtucket Stormwater Master Plan 39

45 City of Pawtucket Stormwater Master Plan 40

46 Proposed Concept A combination of double and single width infiltration installations are recommended within the catchment, where allowed by utilities. These include single-width installations under Waterman Street, Annie Street, Greenslitt Avenue, and Gates Street, and double width installations along Rowe Avenue and Benjamin Street. In order to avoid potential utility conflicts within the roadway, both double width and three of the single width installations proposed are located within the right of way or under the sidewalk. Water Quality Volume WQv for 1 of Runoff 87,082 ft 3 % WQv Treated 92% Single Width Infiltration Chambers: 49% WQv treated Double Width Infiltration Chambers: 44% WQv treated Annual Pollutant Load Total phosphorus 143 lbs/year Bacteria (FC) 17,400 billion colonies/year Estimated Pollutant Removal Based on Treatment of the WQv Total Phosphorus 73 lbs/year Bacteria (FC) 14,500 billion colonies/year Opinion of Probable Cost Pretreatment: $55,000 Single Width Infiltration Chambers: $732,000 Double Width Infiltration Chambers: $734,000 Total: $1,521,000 City of Pawtucket Stormwater Master Plan 41

47 Proposed Concept Two infiltration fields are proposed at the northeast corner of Crest Drive, one within the cul-de-sac and the other at the turn across the road from the cul-de-sac. The installation within the cul-de-sac consists of six rows of infiltration chambers. The length of the installation varies between rows, to fit within the cul-de-sac. The installation at the corner across from the culde-sac consists of four rows of infiltration chambers, with the length of rows varying to fit within the paved area at the corner. In addition, singlewidth infiltration chambers are proposed within the roadway along Crest Drive and Pinecrest Drive, and a double-width installation is proposed within the roadway on Pinecrest Drive. Water Quality Volume WQv for 1 of Runoff 39,977 ft 3 % WQv Treated 72% Single Width Infiltration Chambers: 35% WQv treated Double Width Infiltration Chambers: 10% WQv treated Underground Infiltration Field: 26% WQv treated Annual Pollutant Load Total phosphorus 68 lbs/year Bacteria (FC) 8,200 billion colonies/year Estimated Pollutant Removal Based on 72% Treatment of the 1 WQv Total Phosphorus 27 lbs/year Bacteria (FC) 5,300 billion colonies/year Opinion of Probable Cost Pretreatment: $35,000 Single Width Infiltration Chambers: $242,000 Double Width Infiltration Chambers: $70,000 Underground Infiltration Fields: $204,000 City of Pawtucket Stormwater Master Plan 42

48 Water Quality Volume WQv for 1 of Runoff 159,248 ft 3 % WQv Treated 62% Single Width Infiltration Chambers: 42% WQv treated Double Width Infiltration Chambers: 20% WQv treated Annual Pollutant Load Total phosphorus 265 lbs/year Bacteria (FC) 31,900 billion colonies/year Estimated Pollutant Removal Based on 62% Treatment of the WQv Total Phosphorus 91 lbs/year Bacteria (FC) 17,900 billion colonies/year Opinion of Probable Cost Pretreatment: $50,000 Single Width Infiltration Chambers: $1,175,000 Double Width Infiltration Chambers: $607,000 Total: $1,882,000 Proposed Concept A combination of double and single width infiltration chambers are recommended within the catchment. Single-width infiltration installations are proposed along Gould Street, Maplecrest Drive, Wheeler Street, Archer Street, Karen Drive, Rice Street, and Arland Drive. Double-width infiltration chambers are proposed along Arland Drive and Pinecrest Drive. In order to avoid potential utility conflicts within the roadway, proposed single-width installations are located within the right of way or under the sidewalk. City of Pawtucket Stormwater Master Plan 43

49 4.3 Green Street Opportunity In addition to the underground infiltration BMPs recommended for the priority Catchments it was also desirable to locate an area within the City, preferably within one of the priority catchments, where surface Green Infrastructure practices could be incorporated into the design. The Green Street opportunity was envisioned as a demonstration project to highlight the need for improved stormwater management while including a more aesthetically pleasing and functional design. Several areas were evaluated for Green Street potential including streets within the Central, Fairview, Armistice, Daggett 1, and Waterman priority catchments. Fuss & O Neill and City staff reviewed possible locations and evaluated their potential based on criteria such as overall road width, sidewalk width, perceived need for onstreet parking, and potential utility conflicts. It was decided that Power Road, within the Fairview catchment would be selected for the Green Street conceptual design. Currently, the road has wide sidewalks on either side of the street and under-utilized on-street parking that could be used for surface stormwater treatment features. Figure 4.6: View of a curb bump out bioretention area that could be incorporated into a green Street design for Power Road in Pawtucket, RI. Source: City of Pawtucket Stormwater Master Plan 44

50 The conceptual designs depict the location of linear bioretention features and curb bumpouts where bioretention could also be implemented. These features, once installed, would have additional benefits beyond their stormwater treatment function. The curb bumpouts can help to slow down motorists in an area adding a traffic calming benefit. Also, the inclusion of plantings, including street trees, should improve the overall aesthetic of the neighborhood which currently lacks green, vegetated surfaces and has a limited number of street trees at present. Figures 4.7 and 4.8 help to illustrate the green street concept and how it may appear once installed. The rendering in Figure 4.8 shows the on-street location of the curb bump-out and the linear bioretention that could be installed along Power Road in Pawtucket, RI. The second image (Figure 4.7) shows a typical linear bioretention area installed along a street where sidewalk width is reduced to make room for the bioretention feature. These installations can include various plantings depending on desired maintenance requirements and often can be designed to work in concert with additional treatment structures as well as outlet to existing infrastructure if needed. Figure 4.7: View of green street sidewalk bioretention installation. Source: Figure 4.8: Rendering of Power Road using Google Street View to depict the location of curb bumpouts and linear bioretention features. Source: Google Street View, Image capture November City of Pawtucket Stormwater Master Plan 45

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57 4.4 Non-structural BMPs Non-structural stormwater best management practices are those which do not involve stormwater infrastructure, but instead rely on maintenance and good housekeeping activities or programs and practices focused on altering behaviors. Non-structural BMPs are important parts of an overall stormwater management plan and should support the selection of structural practices. Non-structural BMPs that are currently part of the City of Pawtucket s SWMPP include the following: Catch Basin Cleaning On an annual basis the City cleans between 15% and 50% of catch basins city wide. The City believes these measures have significantly reduced flood frequency which previously affected the City. Because the City maintains detailed records of catch basin cleaning, it may be feasible to prioritize catch basins cleaning in separated areas and increase the frequency of cleanings in areas with increased sediment loadings. Street Sweeping The City of Pawtucket already sweeps all streets within its regulated area regardless of whether or not they are within a separated catchment area. Recently, the City moved to monthly street-sweeping on the same day as trash collection in order to minimize disruption to on-street parking. The City expects this will improve sweeping efficiency by reducing the number of vehicles obstructing sweepers thus increasing the road miles swept. Current sweeping efforts remove over 350 tons of sand and debris annually. The City has also transitioned away from using only sand to a sand/salt mixture for winter deicing to reduce the sand load entering catch basins. In order to respond to the three TMDLs, the City will evaluate the effectiveness of the street sweeping program and look at alternative approaches to improve sediment recapture. Approaches that could be incorporated into the street sweeping program include increasing the frequency of road sweeping at the beginning of the street sweeping season in order to increase the efficiency of collection by sweeping streets prior to large Spring precipitation events. The City could also ensure that municipal and institutional parking lots are swept and encourage the sweeping of privately-owned parking lots at least once per year. Sweeping frequency could also be more focused, and increased in those areas known to service separated catchments. While the sweeping of all City streets is ideal, sweeping those areas known to service separated catchments can help focus effort in those areas that have a direct impact on receiving waters. Waste Management in Parks The City has a number of public parks and open spaces that have waste management programs in place. These programs are integral to stormwater management plans, especially for bacteria impaired waters. The regular removal and proper disposal of wastes generated at public open space and recreational areas add benefits not only to improved water quality but also enhanced aesthetics. City of Pawtucket Stormwater Master Plan 52

58 Goose Abatement Residential goose populations have been shown to have negative impacts on aquatic environments. The City has documented issues with resident goose populations at Slater Pond Park. The City has recently installed a vegetated waterfowl buffer along the western shore of Slater Pond. In addition to the installation of the vegetated buffer, additional waterfowl management measures are being considered. Egg oiling/addling and educational signage instructing park visitors on the importance of not feeding waterfowl are just two examples of goose abatement program enhancements being considered. Dog Waste Similar to goose waste, dog waste can be a major contributor of bacterial pollution related to stormwater. The City should consider a comprehensive dog-waste program which would include possible evaluation and modification of City ordinances, educational signage at appropriate public parks and recreational areas, and collection stations in high traffic areas. Outreach materials The City already disseminates stormwater informational materials in fulfillment of their MS4 permit. In recent years the City has included signage at Slater Park educating visitors on the negative impacts that waterfowl, especially resident geese populations, can have on stormwater quality. In 2015 there was also a Goose Abatement workshop held at the park to further educate visitors and residents on the negative impacts geese can have on water quality. Both the installation of signage and the goose abatement workshop directly respond to recommendations in the Blackstone River TMDL. In the future, the City plans to increase the general stormwater outreach portion of its SWMPP to include materials created as part of this project. Two separate sets of outreach materials were created during this project and they will be used for years to come. The first new outreach tool is a door hanger that has been created that describes, in both English and Spanish, how residents can help reduce the negative impacts of stormwater by reducing fertilizer usage, cleaning up after pets responsibly, and using phosphate-free detergents for car washing activities. This door hanger is expected to be placed throughout the City, especially targeting those neighborhoods within the separated catchments identified during this project. The final version of the door hanger can be found in Appendix C. The second outreach tool developed for this project is a Pawtucket-centric stormwater educational video that will be made available online and promoted through the City s social media accounts at various times throughout the year. The video can be viewed at The video helps to educate residents on the negative impacts of stormwater and at the same time highlight two specific programs in the City that residents can participate in that can help reduce stormwater impacts. Both of these new outreach tools will increase stormwater awareness throughout the City and also directly respond to recommendations in all three TMDLs that call for increased targeted outreach. City of Pawtucket Stormwater Master Plan 53

59 Tree Planting Program The City has a long standing tree planting program where residents can apply for street trees to be installed in their neighborhood. This program leads to the installation of over 100 street trees annually, many more than that in some high demand years. This program improves water quality, reduces heat impacts, improves resiliency to future climate change impacts and improves neighborhood aesthetics. It is recommended that this program continue and, where appropriate, consider incorporating additional green infrastructure practices such as bioretention or tree filters. Rain Barrel Program The City recently launched a rain barrel program similar to the tree planting program where residents can apply to have rain barrels installed at their property. This program is also free to residents and will improve overall stormwater awareness while decreasing volumes of stormwater during precipitation events. While attenuation of peak flows due to rain barrel installation is likely to be modest in the short term, widespread adoption could result in meaningful reductions in peak flows that would benefit both the combined sewer areas (by reducing the number of CSO events) and the separated areas by reducing total runoff. 4.5 Opinion of Probable Cost In order to better evaluate and prioritize the conceptual BMPs proposed in Section 4.2 and 4.3 opinions of probable cost were developed for both underground infiltration chambers and green street retrofits. The sections below detail those estimates and describe the prioritization of Top Priority catchments based on the potential percentage of the WQv that could be treated in these catchments Underground Infiltration For underground infiltration BMPs the opinion of probable cost was calculated on a per linear foot basis. The cost was calculated by assuming the installation of one standard length of infiltration chamber. Costs for individual line items were obtained from the RIDOT Weighted Average Unit Bid Prices (2017) and professional judgement. Double-width infiltration systems and Infiltration Field costs were calculated by multiplying the length of the proposed system by the number of chamber rows. For example, 200 linear feet of double-width infiltration would be calculated by multiplying the cost per linear foot ($400) by the length (200 ) by the number of rows (2). The full cost estimate can be viewed in Appendix D. Once the per unit cost was established, it was applied to the length of infiltration chamber needed in each Priority Catchment. Lengths of proposed infiltration chamber were calculated using GIS. Pretreatment structures were visually located in each catchment and estimated at $5,000 per structure. Table 4.2 lists Top Priority separated catchments along with associated costs for installation of underground infiltration systems within specific catchments. Underground Infiltration Cost per Linear Foot = $ City of Pawtucket Stormwater Master Plan 54

60 Table 4.2: Opinion of probable cost for installing underground infiltration chambers in priority catchments. Priority Catchment Single- Width Infiltration System Double- Width Infiltration System Infiltration Field Pretreatment Total (for all recommended practices) Potential Percentage of WQv Treated Cost to Treat 50% of WQv Cost to Treat 100% of the WQv 1 Total Phosphorus Removed (lbs) Cost per Pound TP Removed Catchment Manton $350,000 $0 $490,000 $30,000 $870, % $343,000 $685, $20,147 Ten Mile Armistice $1,554,000 $1,288,000 $798,000 $75,000 $3,720, % $1,442,000 $2,884, $21,848 Ten Mile Waterman $732,000 $734,000 $0 $55,000 $1,520,000 92% $826,000 $1,520, $22,630 Ten Mile Fairview $2,571,000 $5,683,000 $0 $275,000 $8,530, % $4,062,000 $8,124, $23,345 Moshassuck Weeden $694,000 $0 $1,524,000 $50,000 $2,270, % $880,000 $1,760, $25,507 Moshassuck Daggett 1 $420,000 $1,397,000 $0 $45,000 $1,860, % $669,000 $1,338, $25,731 Ten Mile Morris $569,000 $0 $672,000 $30,000 $1,270, % $208,000 $415, $25,938 Moshassuck Crest $242,000 $0 $274,000 $35,000 $550,000 72% $382,000 $550, $28,296 Ten Mile Pinecrest $1,175,000 $607,000 $0 $100,000 $1,880,000 62% $1,516,000 $1,880, $33,319 Ten Mile Central $0 $1,361,000 $0 $30,000 $1,390, % $556,000 $1,112, $33,697 Ten Mile Mineral Spring $309,000 $1,860,000 $2,120,000 $70,000 $4,360, % $909,000 $1,817, $34,283 Moshassuck TOTAL $11,793,000 $22,085,000 1 In some instances it was not possible to recommend enough practices capable of treating 100% of the WQv. In these instances the highest percentage of treatment possible was used for removal calculations and cost estimation. BMP recommendations for individual catchments frequently exceeded the ability to treat 100% of the WQv. This was done intentionally in order to create flexibility in later design phases where additional barriers to implementation may be encountered. The total cost to install all recommended practices was determined by following steps described previously. A cost per percent WQv treated was then established and extrapolated to determine the cost to treat 100% and 50% of the WQv respectively. These costs were further normalized by calculating the cost per pound of phosphorus removed per catchment assuming treatment of the highest percentage of the WQv possible up to 100% of the WQv. It should be noted that these costs are preliminary and based off of conceptual designs and include a 30% contingency. A more refined cost analysis should be included in any pilot study of areas being targeted for installation. City of Pawtucket Stormwater Master Plan 55

61 4.5.2 Green Street Opportunity A similar estimated opinion of probable cost was prepared for the Green Street opportunity area along Power Road in the Fairview catchment using a surrogate bioretention area (20 x 10 ) in order to estimate a cost per square foot for planning purposes. Costs for individual line items were obtained from the RIDOT Weighted Average Unit Bid Prices (2017) and professional judgement. The full cost estimate can be viewed in Appendix D. Once the per unit cost was developed it was applied to the proposed square footage of green street installations proposed along Power Road as calculated using GIS. These installations included both linear bioretention areas, primarily on the western side of the road, and curb bump out bioretention area, primarily located on the eastern side of the road. Bioretention Cost per Square Foot = $25.00 Table 4.3: Opinion of probable cost for bioretention areas associated with green street installation along Power Road, Pawtucket, RI. Assumed Unit Cost (per ft 2 ) $25.00 Total Area Installed (ft 2 ) 16,327 Total Estimated Cost (nearest $1,000) $408, Lifecycle Operation and Maintenance Cost Estimate The operation and maintenance of stormwater BMPs, especially infiltration and bioretention practices, is critical to effective stormwater treatment. The underground infiltration chambers proposed for this project would work in conjunction with pretreatment structures such as swirl or oil and grit separators. Typical maintenance procedures for these pretreatment structures involve annual inspection and cleaning out of accumulated sediment and debris using a vactor truck or similar industrial vacuum. The life cycle cost for these requirements is available in Appendix D and includes the hourly cost of the necessary equipment and staff projected out over the life of the anticipated service life of the equipment, waste disposal, and eventual structure replacement. According to these assumptions the annual maintenance cost per pretreatment structure would be approximately $600. Similarly, the typical annual maintenance requirements for typical bioretention areas were identified. The costs to maintain bioretention areas can vary based on the degree of landscaping that is incorporated into the design. Bioretention with more complicated landscaping and more demanding tree and plant species will typically cost more to maintain over the lifecycle of the practice than similarly sized areas that are merely grassed or have limited vegetation or mulching requirements. For this plan it was determined that a base level of maintenance, including inspection, weeding, pruning, adding additional mulch and plant replacement would account for a more intensive maintenance regimen since one of the criteria of the bioretention areas was an enhanced aesthetic appearance. The life cycle cost for these requirements is available in Appendix D and includes costs for mulching, watering, City of Pawtucket Stormwater Master Plan 56

62 weeding, pruning, plant replacement. According to these assumptions the annual maintenance cost of bioretention areas is estimated to be $5.00 per square foot. 5 Potential Pollutant Load Reduction The goal of this conceptual design was to address stormwater pollution practices within the catchments such that they would treat 100% of the WQv and therefore provide a reduction in the pollutant loads affecting water quality. In many catchments the conceptual designs were designed to accommodate volumes exceeding 100% of the WQv. The additional WQv treatment was proposed for redundancy in siting BMPs allowing for changes and alterations based on additional site specific information that would be gathered at a later design phase. The potential pollutant load reduction for each catchment was calculated according to the following formula: Potential Pollutant Load Reduction = Estimated Pollutant Load Pollutant Removal Efficiency Rating %WQv treated where Estimated Pollutant Load = the estimated phosphorus or bacteria load calculated as described in in Section 3.2 Pollutant Removal Efficiency Rating = BMP-specific median pollutant removal efficiency (%), from Table H.3: Pollutant Removal Efficiency Rating Values for Water Quality BMPs in the RISDISM. These efficiency ratings are listed in Table 5.1. % WQv Treated = The percentage of the WQv treated by conceptually placed practices for the catchment (calculated as described in Section 3.2), up to 100% of the WQv BMPs were conceptually placed in each catchment in as many locations as possible that met installation criteria. This led to a situation where many catchments were able to treat larger volumes of stormwater than the typically accepted 1 of runoff from paved surfaces for WQv. For purposes of calculating the potential pollutant load reduction, the %WQv Treated was restricted to 100% of the WQv despite the fact that it was possible treat more since BMPs typically become less efficient when designed for larger volumes. Table 5.1: BMP-specific median pollutant removal efficiency (%), from Table H.3: Pollutant Removal Efficiency Rating Values for Water Quality BMPs in the 2015 Edition of the RISDISM. Water Quality BMP Median Pollutant Removal Efficiency (%) Total Phosphorus Bacteria (FC) Underground Infiltration Chambers 55% 90% Bioretention 30% 70% City of Pawtucket Stormwater Master Plan 57

63 5.1 Structural BMP Load Reductions Potential pollutant load reduction for the structural BMPs was calculated using pollutant removal efficiency for underground infiltration chambers listed in Table 5.1. Table 5.2 lists the catchments in order of pollutant reduction, ranked by bacterial removal. Table 5.2: Estimated annual phosphorus and bacterial load reduction. Catchments are listed by their estimated reduction in annual bacterial load in billions of colonies. Catchment Total Phosphorus Load Estimated Annual Phosphorus Load Reduction (lbs) Percent Reduction Total Bacteria Load (billions of colonies) Estimated Annual Bacteria Load Reduction (billions of colonies removed) Percent Reduction Fairview % 78,651 70,800 90% Armistice % 28,614 25,700 90% Pinecrest % 31,874 17,900 56% Waterman % 17,381 14,500 83% Weeden % 14,962 13,500 90% Mineral Spring % 12,989 11,700 90% Daggett % 11,033 9,900 90% Central % 7,553 6,800 90% Manton % 7,370 6,700 90% Crest % 8,233 5,300 64% Morris % 3,660 3,300 90% In general, larger watersheds and watersheds dominated by a high- and medium-density residential land use type (e.g. Fairview, Armistice, Pinecrest, and Waterman) are ranked highest in Table 5.2 because these watersheds produce the largest annual pollutant loads. Treating even a moderate percentage of these watersheds results in a higher pollutant removal than treatment of the full WQv in smaller watersheds (e.g. Morris, Crest, and Manton), which have less potential to produce pollutants due mainly to their small size, as well as the relative proportions of different land use types within the watershed. City of Pawtucket Stormwater Master Plan 58

64 5.2 Green Street Opportunity The annual pollutant loads for phosphorus and bacteria were calculated using the equations described in Section 3.3, using a subcatchment of the Fairview catchment. Potential pollutant load reduction for the green street was calculated using pollutant removal efficiency for bioretention BMPs described in Table 5.1. The pollutant load removal, as with the pollutant loading calculation, is based on the separate delineation of the subwatershed draining to the proposed green street, rather than the full Fairvew subwatershed. The potential pollutant load reduction was estimated and is listed in Table 5.3. Table 5.3: Estimated annual load reduction by proposed Green Street Opportunity. Subwatershed ID Estimated Annual Phosphorus Load Reduction (lbs) Estimated Annual Bacteria Load Reduction (billions of colonies removed) Green Street Opportunity - Fairview 6.6 1,874 These reductions are much smaller than the annual reductions associated with the proposed structural BMPs (see Table 5.2, above) due to the limited space available and the lower potential reduction ratings associated with bioretention. However, the construction of a green street along Power Road would act as a demonstration project and would provide other benefits in addition to any pollutant reduction achieved. These benefits are discussed in Section 4.3. City of Pawtucket Stormwater Master Plan 59

65 6 Catchment Focus and Prioritization 6.1 Prioritized Catchments Catchments were prioritized by their ability to treat and remove pollutants of concern, specifically phosphorus. The total cost to install all recommended practices was used to determine the cost for each catchment to treat 100% of the WQv. This cost was then divided by the amount of phosphorus each catchment was able to eliminate calculated as described in Section 5. The ratio was calculated for each subwatershed as follows: Cost per Pound of Phosphorus Removed = Catchments were ranked by this prorated cost, as shown in Table 6.1. Table 6.1: Priority Catchments ranked by their potential cost per pound of phosphorus removed. Cost to Treat 100% WQv Pounds of Phosphorus Removed Rank Catchment Cost per Pound TP Removed 1 Manton $20,147 2 Armistice $21,848 3 Waterman $22,630 4 Fairview $23,345 5 Weeden $25,507 6 Daggett 1 $25,731 7 Morris $25,938 8 Crest $28,296 9 Pinecrest $33, Central $33, Mineral Spring $34,283 City of Pawtucket Stormwater Master Plan 60

66 It is recommended that implementation follow the prioritization listed in Table 6.1. This prioritization does not take into external factors such as the flexibility of design offered to some catchments by the recommendation of additional BMPs able to treat more than 100% of the WQv or the availability of funding sources. City of Pawtucket Stormwater Master Plan 61

67 7 Works Cited BETA Group, Inc. (2006). Quality Assurance Project Plan. Development of a Watershed Based Plan for Massachusetts. RIDEM. (2015). Rhode Island Stormwater Design and Installation Standards Manual. RIDEM. (2015). State of Rhode Island 303(d) list:list of Impaired Waters. Rhode Island Department of Environmental Management. City of Pawtucket Stormwater Master Plan 62

68 Appendix A GIS Files (On Separate Drive) City of Pawtucket Stormwater Master Plan

69 Appendix B EMC Values and Pollutant Loading Calculations City of Pawtucket Stormwater Master Plan

70 Simple Method Annual Runoff Runoff Coefficient Nutrients/TSS Bacteria L= 0.226*R*C*A L= 1.03*10 3 *R*C*A R = P*Pj*Rv Rv = (Ia) L = Annual Load (pounds) L = Annual Load (Billion Colonies) R = Annual Runoff (inches) Rv = Runoff Coefficient R = Annual Runoff (inches) R = Annual Runoff (inches) P = Annual Rainfall (inches) Ia = Impervious fraction C = Pollutant Concentration (mg/l) C = Pollutant Concentration (mg/l) Pj = Fraction of rainfall events producing runoff (usually 0.9) A = Area (acres) A = Area (acres) Rv = Runoff Coefficient 1.03*10 3 = Unit conversion factor Table 3 Initial Even Mean Concentration (EMC) Values Assigned EMC Values used to calculate pollutant loads Land Use % Impervious 1 TN (mg/l) TP (mg/l) TSS (mg/l) FC Agriculture/Pasture ,000 Commercial ,306 Cranberry Bog ,000 Forest/Rural Open High Density Residential ,901 Highways Industrial ,467 Low Density Residential ,950 Medium Density Residential ,360 Mining Urban Open ,000 Waste Disposal ,500 Water Based Rec ,000 Water/Wetland BETA Group, Inc. (2006). Quality Assurance Project Plan. Development of a Watershed Based Plan for Massachusetts. Land Use High Density Residential (<1/8 acre lots) Deciduous Forest (>80% hardwood) Institutional (schools, hospitals, churches, etc.) Commercial (sale of products and services) Vacant Land Medium High Density Residential (1/4 to 1/8 acre lots) Developed Recreation (all recreation) Cemeteries Mixed Forest Transitional Areas (urban open) Roads (divided highways >200' plus related facilities) Industrial (manufacturing, design, assembly, etc.) Power Lines (>100' or more width) Commercial/Industrial Mixed Railroads (and associated facilities) Other Transportation (terminals, docks, etc.) Orchards, Groves, Nurseries Modeled As High Density Residential Forest/Rural Open Industrial Commercial Urban Open Medium Density Residential Forest/Rural Open Forest/Rural Open Forest/Rural Open Urban Open Highways Industrial Urban Open Commercial Highways Highways Urban Open Rainfall Assumed Values Variable (unit) Value Annual rainfall, P (in.), from RISDISM 48 Fraction of rainfall events producing runoff, Pj 0.9

71 Pollutant Loading Calculations for all Catchments Waterman Land use Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient, Rv Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Deciduous Forest (>80% hardwood) Commercial (sale of products and services) Pinecrest Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Institutional (schools, hospitals, churches, etc.) Taft 1 Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Commercial (sale of products and services) Vacant Land Deciduous Forest (>80% hardwood) Armistice Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Industrial (manufacturing, design, assembly, etc.) Medium High Density Residential (1/4 to 1/8 acre lots) Cemeteries Deciduous Forest (>80% hardwood) Mixed Forest Charlton Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Medium High Density Residential (1/4 to 1/8 acre lots) Commercial (sale of products and services) Industrial (manufacturing, design, assembly, etc.) Cemeteries Deciduous Forest (>80% hardwood) Transitional Areas (urban open) Daggett 1 Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Industrial (manufacturing, design, assembly, etc.) Developed Recreation (all recreation) Cemeteries Central Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Medium High Density Residential (1/4 to 1/8 acre lots) Commercial (sale of products and services) Decidiou Forest are * Division 1 Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Commercial (sale of products and services) Roads (divided highways >200' plus related facilities) Vacant Land Deciduous Forest (>80% hardwood)

72 School 1 School 2 Exchange Transitional Areas (urban open) Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Commercial (sale of products and services) Institutional (schools, hospitals, churches, etc.) Deciduous Forest (>80% hardwood) Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Medium High Density Residential (1/4 to 1/8 acre lots) Commercial (sale of products and services) Industrial (manufacturing, design, assembly, etc.) Power Lines (100' or more width) Developed Recreation (all recreation) Deciduous Forest (>80% hardwood) Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) Commercial (sale of products and services) Industrial (manufacturing, design, assembly, etc.) Institutional (schools, hospitals, churches, etc.)

73 Roosevelt Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) Commercial (sale of products and services) Institutional (schools, hospitals, churches, etc.) Main Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) Commercial (sale of products and services) Institutional (schools, hospitals, churches, etc.) Morris Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Commercial (sale of products and services) Developed Recreation (all recreation) Institutional (schools, hospitals, churches, etc.) Deciduous Forest (>80% hardwood) Fairview Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Medium High Density Residential (1/4 to 1/8 acre lots) Commercial (sale of products and services) Industrial (manufacturing, design, assembly, etc.) Developed Recreation (all recreation) Institutional (schools, hospitals, churches, etc.) Deciduous Forest (>80% hardwood) Smithfield Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Medium High Density Residential (1/4 to 1/8 acre lots) Commercial (sale of products and services) Developed Recreation (all recreation) Cemeteries Institutional (schools, hospitals, churches, etc.) Power Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Medium High Density Residential (1/4 to 1/8 acre lots) Commercial (sale of products and services) Commercial/Industrial Mixed Cemeteries Bowles Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Institutional (schools, hospitals, churches, etc.) Taft 2 Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Vacant Land Deciduous Forest (>80% hardwood) George Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Commercial (sale of products and services) Cemeteries Institutional (schools, hospitals, churches, etc.)

74 Deciduous Forest (>80% hardwood) Roads (divided highways >200' plus related facilities) Division 2 Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) Vacant Land Deciduous Forest (>80% hardwood) Taft 3 Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Vacant Land Deciduous Forest (>80% hardwood) Roads (divided highways >200' plus related facilities) Roosevelt Ext Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) Commercial (sale of products and services) Roads (divided highways >200' plus related facilities) Manton Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Power Lines (100' or more width) Institutional (schools, hospitals, churches, etc.) Broadway Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Commercial (sale of products and services) Roads (divided highways >200' plus related facilities) Vacant Land Institutional (schools, hospitals, churches, etc.) Deciduous Forest (>80% hardwood)

75 Mineral Spring Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Commercial (sale of products and services) Railroads (and associated facilities) Institutional (schools, hospitals, churches, etc.) Deciduous Forest (>80% hardwood) Weeden Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Commercial (sale of products and services) Industrial (manufacturing, design, assembly, etc.) Railroads (and associated facilities) Institutional (schools, hospitals, churches, etc.) Deciduous Forest (>80% hardwood) Leonard Jenard Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Railroads (and associated facilities) Other Transportation (terminals, docks, etc.) Developed Recreation (all recreation) Institutional (schools, hospitals, churches, etc.) Orchards, Groves, Nurseries Deciduous Forest (>80% hardwood) Crest Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Green Street Power Road (Fairview) Area, A (ac) Impervious Area (ac) I (%) Runoff Coefficient Annual Runoff, R (in.) P (lb) Bacteria (billion colonies) High Density Residential (<1/8 acre lots) Commercial (sale of products and services) Medium High Density Residential (1/4 to 1/8 acre lots)

76 Appendix C Outreach Materials: Door Hanger City of Pawtucket Stormwater Master Plan

77 One City One Direction One Chance Pawtucket rising up to make a difference All city runoff drains to Narragansett Bay To protect water quality for our children and future Rescue our Rivers! Did you know that environmental health officials have advised: NO SWIMMING in any of the City s rivers due to pollution? We need YOUR HELP! Your property drains to the river. Actions YOU can take to help clean up our rivers: Pick up pet waste - it washes into the rivers Reduce the use of fertilizer on your lawn - check the label, you may need to use less than you think If you wash your car at home, use phosphate-free soap Apply for a FREE street tree or rain barrel from the City DPW (see website link below) Visit this link to find what else you can do to Rescue our Rivers

78 Una Ciudad Una Dirección Una Oportunidad Pawtucket se alza para marcar la diferencia Todos los desagües de la Ciudad desembocan en Narrangansett Bay Para proteger la calidad del agua para nuestros hijos y ara el futuro Salva nuestros ríos! Sabías que las autoridades sanitarias aconsejan NO NADAR en ningún río de la Ciudad debido a la contaminación?! Necesitamos tu ayuda! El desagüe de tu propiedad desemboca en el río Acciones que puedes llevar a cabo para colaborar en la limpieza de nuestros ríos: Recoge los excrementos de las mascotas - acaban en el río Reduce el uso de fertilizantes en tu césped. Revisa las etiquetas, quizás necesites utilizar menos cantidad de lo que crees. Si lavas tu coche en casa, utiliza jabones sin fosfato Solicita un barril gratutio para lluvia o árbol al DPW (Departamento de Obras Públicas) de la Ciudad (consulta el enlace a la página web bajo estas líneas) Visita este enlace para saber qué más puedes hacer para salvar nuestros ríos