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Stormwater report for Revied plans 10.29.2025
Page 1 of 6 Pumping Station 2 Stormwater Management Report 1.0 Existing Conditions The Town of Yarmouth Department of Public Works (Yarmouth DPW) is proposing to construct a new wastewater pumping station at #280 Route 28, on the property of Bellew Tile and Marble Company. This pumping station replaces the previously proposed PS 2 at 316 Route 28. PS 2is part of a larger overall proposed wastewater collection and conveyance system being designed to collect wastewater from the Phase 1 area and convey it to the proposed Water Resource Recovery Facility at 99 Buck Island Road. This pumping station will be part of Phase 1 - Contract 6. The proposed pumping station will be located on the eastern side of the parking lot for Bellew Tile and Marble Co. The pumping station is bounded by Route 28 to the south, undeveloped land adjacent to a cranberry bog to the north and east, and Bellew Tile and Marble Company to the west. The pumping station will be constructed in an area that is a predominantly bituminous pavement and hard-packed dirt parking lot. The pumping station is partially located within the within the 100-year floodplain regulated as Land Subject to Coastal Storm Flowage, extending up to elevation 11.0 ft. The topography has grades ranging between elevation 8 to 12 feet and generally slopes from west to east. The total modeled area, which is predominantly within the limit of disturbance is 9,440 sf (0.22 ac), with an existing impervious area of 2,450 sf (0.06 ac). Figure 1 shows the existing conditions drainage area map. 2.0 Proposed Conditions Under proposed conditions, a small pumping station control building, flow meter vault, valve vault, wet well, standby generator and access driveway will be constructed on this property. The pumping station control building, wet well, and generator will be elevated to El. 14.0 to be at least 3 feet above the 100-year flood elevation. Four-inch-deep gravel stone surfacing will be placed around the control building, wet well, valve vault, and generator. The pumping station will be graded to the west to direct stormwater runoff to two catch basins that will be installed in the driveway. The catch basins will also collect stormwater runoff from the driveway. The stormwater will receive pretreatment in a proprietary separator device prior to discharge to a concrete module subsurface infiltration system. This system will provide peak attenuation, groundwater recharge and water quality treatment. The system will have an overflow pipe that will connect to an existing catch basin in Route 28. Under proposed conditions, the total impervious area is 4,440 sf (0.10 ac), an increase of 1,990 sf (0.04 ac). Because there is an increase in the impervious area, this project qualifies as a new development project under the Massachusetts Stormwater Handbook. Figure 2 shows the proposed conditions drainage area map. For this drainage analysis, the subsurface infiltration system was assumed to be a 3.5-ft high Retain-It system. The particle separator is proposed to be a Contech CDS 1515-3-C, to provide pretreatment of the stormwater from the paved areas and pumping station site. Pumping Station 2 Stormwater Management Report Page 2 of 6 3.0 Drainage Analysis CDM Smith performed drainage analyses for the PS2 pumping station site for existing and proposed conditions. The drainage analyses determined peak rates of runoff during the 2-, 10-, 25-, 50-, and 100-year, 24-hour storm events using HydroCAD, version 10.2. This computer model simulates stormwater runoff flows through drainage areas and stormwater management facilities and is based on the Natural Resources Soil Conservation Service (NRCS) Method. Following is a summary of the methodology and assumptions used to perform the drainage analyses. Precipitation data for standard storms used in the models were taken from NOAA Atlas 14, Volume 10. The estimated precipitation depths during the 2-, 10-, 25-, 50-, and 100-year 24- hour storms are 3.38, 4.92, 5.88, 6.62, and 7.37 inches, respectively (see Appendix A). The Natural Resources Conservation Service’s (NRCS) Web Soil Survey was consulted to determine the hydrologic soil groups (HSG) for the site. The NRCS has classified the site as “Carver coarse sand” and assigned HSG “A” to this soil. On September 9, 2025, CDM Smith advanced one boring at the Pumping Station 2 location. The soil in the boring was uniform, described as medium dense, fine to medium coarse sand with a trace of silt and classified as “SP” (poorly graded sand). Groundwater was encountered at approximately elevation 2.0 ft (approximately 9 feet below existing ground surface). Based on SP classification, an infiltration rate of 8.27 in/hr is assumed for the recharge calculations in the subsurface infiltration system. This value is based on Table 2.3.3 in Volume 3, Chapter 1 of Massachusetts Stormwater Handbook, where “sand” has an infiltration rate of 8.27 inches/hour and is assigned to HSG “A” soils. Appendix B provides soils information from Web Soil Survey and the geotechnical field exploration program. The project site was modeled as three drainage areas for existing conditions; this drainage area is based predominantly on the limit of disturbance for the pumping station. The drainage areas are shown on Figure 1. For existing conditions there are three design points: stormwater runoff that discharges to the existing low area near the building, stormwater runoff that discharges to the grass area to the east and stormwater runoff that discharges towards Route 28. For proposed conditions, the project site was modeled as two drainage areas: the pumping station area tributary to the subsurface infiltration system, and the pumping station site that discharges stormwater runoff to the east. The drainage areas are shown on Figure 2. For proposed conditions there are two design points: stormwater runoff that discharges to the grass area to the east and stormwater runoff that discharges towards Route 28. Curve Numbers (CNs) for the different land uses on the site were selected based on HSG “A” soils. Land uses included grass cover, dirt road, brush, gravel and paved/impervious areas. Weighted CNs were calculated in HydroCAD. Times of concentration (Tc) were based on the Velocity Method in the NRCS National Engineering Handbook (May 2010). A minimum Tc of 6 minutes was used for all drainage areas. Pumping Station 2 Stormwater Management Report Page 3 of 6 HydroCAD was used to generate peak rates of runoff for existing and proposed conditions. Table 3-1 provides a summary of modeling results for existing and proposed conditions at each design point. As this table shows, peak rates of runoff and runoff volumes for proposed conditions are less than existing conditions for all storm events. As Table 3-2 shows, for the site overall, peak rates of runoff and runoff volumes for proposed conditions are equal to or less than those for existing conditions during all modeled storm events. The HydroCAD modeling input and output can be found in Appendix C. Table 3-1 Pumping Station No. 2 – Phase 1 – Contract No. 6 Yarmouth, Massachusetts HydroCAD Modeling Results at Design Points Storm Event Existing Conditions Proposed Conditions Peak Rate of Runoff (cfs) Runoff Volume (ac-ft) Peak Rate of Runoff (cfs) Runoff Volume (ac-ft) DP: Low Area 2-Year, 24-Hour 0.11 0.008 0.00 0.000 10-Year, 24-Hour 0.18 0.013 0.00 0.000 25-Year, 24-Hour 0.22 0.017 0.00 0.000 50-Year, 24-Hour 0.26 0.019 0.00 0.000 100-Year, 24-Hour 0.29 0.022 0.00 0.000 DP: Rte. 28 2-Year, 24-Hour 0.07 0.006 0.00 0.000 10-Year, 24-Hour 0.17 0.012 0.00 0.000 25-Year, 24-Hour 0.23 0.017 0.00 0.000 50-Year, 24-Hour 0.29 0.021 0.08 0.003 100-Year, 24-Hour 0.35 0.025 0.19 0.006 DP: Grass Area 2-Year, 24-Hour 0,00 0.000 0.00 0.000 10-Year, 24-Hour 0.01 0.002 0.00 0.000 25-Year, 24-Hour 0.02 0.004 0.01 0.002 50-Year, 24-Hour 0.04 0.006 0.02 0.004 100-Year, 24-Hour 0.08 0.009 0.04 0.005 Pumping Station 2 Stormwater Management Report Page 4 of 6 Table 3-2 Pumping Station No. 2 – Phase 1 – Contract No. 6 Yarmouth, Massachusetts Summary HydroCAD Modeling Results – Entire Site Storm Event Existing Conditions Proposed Conditions Peak Rate of Runoff (cfs) Runoff Volume (ac-ft) Peak Rate of Runoff (cfs) Runoff Volume (ac-ft) 2-Year, 24-Hour 0.18 0.014 0.00 0.000 10-Year, 24-Hour 0.36 0.027 0.00 0.000 25-Year, 24-Hour 0.47 0.038 0.01 0.002 50-Year, 24-Hour 0.59 0.046 0.10 0.007 100-Year, 24-Hour 0.72 0.056 0.23 0.011 The site was also analyzed for compliance with the recharge volume (Rv) and water quality volume (WQv) requirements in the Massachusetts Stormwater Handbook. Since the pumping station site is located on HSG “A” soils, the recharge target depth factor of 0.60 inches was used. The calculation of the WQv and Rv is based on the total impervious area within the overall tributary area. The total corresponding Rv is 220 cf. Because the infiltration rate is assumed to be 8.27 in/hr based on the soil boring, the water quality volume is based on 1.0 inch times the total impervious area, with a total corresponding WQv of 370 cf. Storage for the Rv and WQv for the site is provided in the subsurface infiltration system below the outlet out of the system. The drawdown time of the water in the subsurface infiltration system was calculated using the total storage volume provided below the outlet and the total available bottom surface area of the subsurface infiltration system. The drawdown calculations indicate that stormwater will infiltrate within 2 hours, which is within the required 72 hours, based on the infiltration rate of 8.27 in/hr. Table 3-3 summarizes the impervious area, the calculated required recharge and water quality volumes, along with the total storage volume provided in the gravel stone surfacing and bioretention area. As shown in this table, the subsurface infiltration system provides sufficient storage volume to meet the total required recharge volume and water quality volume for the pumping station. Appendix D provides the recharge volume, water quality volume, and drawdown calculations. Table 3-3 Summary of Overall Impervious Area, Rv and WQv Pumping Station 2 Stormwater Management Facility Impervious Area (sf) Recharge Volume (cf) Water Quality Volume (cf) Volume Provided (cf) Subsurface Infiltration System 4,440 220 370 620 For new development projects, stormwater management systems must be designed to remove 80% of the average annual load (post-construction conditions) of Total Suspended Solids (TSS). Stormwater runoff from the entrance driveway and pumping station will receive pretreatment in deep-sump hooded catch basins and in a proprietary particle separator device prior to discharge to the subsurface Pumping Station 2 Stormwater Management Report Page 5 of 6 infiltration system. It is proposed to use a Contech CDS unit as the proprietary particle separator device. The New Jersey Department of Environmental Protection has certified that the CDS unit has a TSS removal rate of 50%. Because the infiltration rate is 8.27 in/hr, 44% TSS removal is required as pretreatment prior to discharge to the subsurface infiltration system. The combination of the deep- sump hooded catch basins with the CDS unit provides 62.5% TSS removal. With the subsurface infiltration system, the total TSS removal is 92.5%. The TSS worksheets are provided in Appendix E. 4.0 Compliance with Stormwater Standards Under the Massachusetts Stormwater Management Standards, the project is classified as a new development because the impervious area at Pumping Station 2 will increase under developed conditions. Hence, the project is required to meet the applicable Stormwater Management Standards. The following summary describes compliance with each of the stormwater standards. The Stormwater Checklist is provided at the end of this section. 4.1 Stormwater Standard No. 1 – No New Untreated Discharges The proposed project fully meets the requirement of Stormwater Standard No. 1, as there are no new untreated discharges. Stormwater runoff from the pumping station site will receive treatment in the subsurface infiltration system. 4.2 Stormwater Standard No. 2 – Peak Rate Attenuation This standard is fully met. As shown on Tables 3-1 and 3-2, peak rates of runoff and runoff volumes for proposed conditions are less than those for existing conditions for all storm events. 4.3 Stormwater Standard No. 3- Recharge Recharge to groundwater is fully met through the subsurface infiltration system. Since the soils are HSG “A” soils, the target depth factor for recharge is 0.6 inches. The Static Method was used to demonstrate that proposed subsurface infiltration system will drain within 72 hours. 4.4 Stormwater Standard No. 4 – Water Quality This standard is fully met. Water quality volume calculation is based on one inch because the infiltration rate is 8.27 in/hr. This standard is fully met; a TSS removal rate of 92.5% is provided with a treatment train of deep-sump hooded catch basins, a proprietary separator device, and a subsurface infiltration system. The TSS removal worksheets are provided in Appendix E. 4.5 Stormwater Standard No. 5 – Land Uses With Higher Potential Pollutant Loads This standard is not applicable to this project. There are no LUHPPLs in the project area. 4.6 Stormwater Standard No. 6 – Critical Areas This standard is met; the site is not located within a critical area. 4.7 Stormwater Standard No. 7 – Redevelopment This standard is not applicable to this project; it is a new development project because there is an increase in impervious area. Pumping Station 2 Stormwater Management Report Page 6 of 6 4.8 Stormwater Standard No. 8 – Construction Period Pollution Prevention and Erosion and Sedimentation Control The project is subject to a NPDES General Construction Permit, which will be obtained by the Contractor as part of the Phase 1 – Contract 6. A copy of the Stormwater Pollution Prevention Plan (SWPPP) will be submitted by the Contractor prior to construction. 4.9 Stormwater Standard No. 9 – Operation and Maintenance Plans An Operation and Maintenance Plan and Long-Term Pollution Prevention Plan are included with this submittal in Appendix F. 4.10 Stormwater Standard No. 10 – Prohibition of Illicit Discharges The proposed project fully meets the requirement of Stormwater Standard No. 10 as there are no illicit discharges. Stormwater Checklist Pumping Station 2 swcheck • 04/01/08 Stormwater Report Checklist • Page 1 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report A. Introduction Important: When filling out forms on the computer, use only the tab key to move your cursor - do not use the return key. A Stormwater Report must be submitted with the Notice of Intent permit application to document compliance with the Stormwater Management Standards. The following checklist is NOT a substitute for the Stormwater Report (which should provide more substantive and detailed information) but is offered here as a tool to help the applicant organize their Stormwater Management documentation for their Report and for the reviewer to assess this information in a consistent format. As noted in the Checklist, the Stormwater Report must contain the engineering computations and supporting information set forth in Volume 3 of the Massachusetts Stormwater Handbook. The Stormwater Report must be prepared and certified by a Registered Professional Engineer (RPE) licensed in the Commonwealth. The Stormwater Report must include: · The Stormwater Checklist completed and stamped by a Registered Professional Engineer (see page 2) that certifies that the Stormwater Report contains all required submittals.1 This Checklist is to be used as the cover for the completed Stormwater Report. · Applicant/Project Name · Project Address · Name of Firm and Registered Professional Engineer that prepared the Report · Long-Term Pollution Prevention Plan required by Standards 4-6 · Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan required by Standard 82 · Operation and Maintenance Plan required by Standard 9 In addition to all plans and supporting information, the Stormwater Report must include a brief narrative describing stormwater management practices, including environmentally sensitive site design and LID techniques, along with a diagram depicting runoff through the proposed BMP treatment train. Plans are required to show existing and proposed conditions, identify all wetland resource areas, NRCS soil types, critical areas, Land Uses with Higher Potential Pollutant Loads (LUHPPL), and any areas on the site where infiltration rate is greater than 2.4 inches per hour. The Plans shall identify the drainage areas for both existing and proposed conditions at a scale that enables verification of supporting calculations. As noted in the Checklist, the Stormwater Management Report shall document compliance with each of the Stormwater Management Standards as provided in the Massachusetts Stormwater Handbook. The soils evaluation and calculations shall be done using the methodologies set forth in Volume 3 of the Massachusetts Stormwater Handbook. To ensure that the Stormwater Report is complete, applicants are required to fill in the Stormwater Report Checklist by checking the box to indicate that the specified information has been included in the Stormwater Report. If any of the information specified in the checklist has not been submitted, the applicant must provide an explanation. The completed Stormwater Report Checklist and Certification must be submitted with the Stormwater Report. 1 The Stormwater Report may also include the Illicit Discharge Compliance Statement required by Standard 10. If not included in the Stormwater Report, the Illicit Discharge Compliance Statement must be submitted prior to the discharge of stormwater runoff to the post-construction best management practices. 2 For some complex projects, it may not be possible to include the Construction Period Erosion and Sedimentation Control Plan in the Stormwater Report. In that event, the issuing authority has the discretion to issue an Order of Conditions that approves the project and includes a condition requiring the proponent to submit the Construction Period Erosion and Sedimentation Control Plan before commencing any land disturbance activity on the site. Pumping Station 2 swcheck • 04/01/08 Stormwater Report Checklist • Page 3 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) LID Measures: Stormwater Standards require LID measures to be considered. Document what environmentally sensitive design and LID Techniques were considered during the planning and design of the project: No disturbance to any Wetland Resource Areas Site Design Practices (e.g. clustered development, reduced frontage setbacks) Reduced Impervious Area (Redevelopment Only) Minimizing disturbance to existing trees and shrubs LID Site Design Credit Requested: Credit 1 Credit 2 Credit 3 Use of “country drainage” versus curb and gutter conveyance and pipe Bioretention Cells (includes Rain Gardens) Constructed Stormwater Wetlands (includes Gravel Wetlands designs) Treebox Filter Water Quality Swale Grass Channel Green Roof Other (describe): Standard 1: No New Untreated Discharges No new untreated discharges Outlets have been designed so there is no erosion or scour to wetlands and waters of the Commonwealth Supporting calculations specified in Volume 3 of the Massachusetts Stormwater Handbook included. Pumping Station 2 swcheck • 04/01/08 Stormwater Report Checklist • Page 4 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) Standard 2: Peak Rate Attenuation Standard 2 waiver requested because the project is located in land subject to coastal storm flowage and stormwater discharge is to a wetland subject to coastal flooding. Evaluation provided to determine whether off-site flooding increases during the 100-year 24-hour storm. Calculations provided to show that post-development peak discharge rates do not exceed pre- development rates for the 2-year and 10-year 24-hour storms. If evaluation shows that off-site flooding increases during the 100-year 24-hour storm, calculations are also provided to show that post-development peak discharge rates do not exceed pre-development rates for the 100-year 24- hour storm. Standard 3: Recharge Soil Analysis provided. Required Recharge Volume calculation provided. Required Recharge volume reduced through use of the LID site Design Credits. Sizing the infiltration, BMPs is based on the following method: Check the method used. Static Simple Dynamic Dynamic Field1 Runoff from all impervious areas at the site discharging to the infiltration BMP. Runoff from all impervious areas at the site is not discharging to the infiltration BMP and calculations are provided showing that the drainage area contributing runoff to the infiltration BMPs is sufficient to generate the required recharge volume. Recharge BMPs have been sized to infiltrate the Required Recharge Volume. Recharge BMPs have been sized to infiltrate the Required Recharge Volume only to the maximum extent practicable for the following reason: Site is comprised solely of C and D soils and/or bedrock at the land surface M.G.L. c. 21E sites pursuant to 310 CMR 40.0000 Solid Waste Landfill pursuant to 310 CMR 19.000 Project is otherwise subject to Stormwater Management Standards only to the maximum extent practicable. Calculations showing that the infiltration BMPs will drain in 72 hours are provided. Property includes a M.G.L. c. 21E site or a solid waste landfill and a mounding analysis is included. 1 80% TSS removal is required prior to discharge to infiltration BMP if Dynamic Field method is used. Pumping Station 2 swcheck • 04/01/08 Stormwater Report Checklist • Page 5 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) Standard 3: Recharge (continued) The infiltration BMP is used to attenuate peak flows during storms greater than or equal to the 10- year 24-hour storm and separation to seasonal high groundwater is less than 4 feet and a mounding analysis is provided. Documentation is provided showing that infiltration BMPs do not adversely impact nearby wetland resource areas. Standard 4: Water Quality The Long-Term Pollution Prevention Plan typically includes the following: · Good housekeeping practices; · Provisions for storing materials and waste products inside or under cover; · Vehicle washing controls; · Requirements for routine inspections and maintenance of stormwater BMPs; · Spill prevention and response plans; · Provisions for maintenance of lawns, gardens, and other landscaped areas; · Requirements for storage and use of fertilizers, herbicides, and pesticides; · Pet waste management provisions; · Provisions for operation and management of septic systems; · Provisions for solid waste management; · Snow disposal and plowing plans relative to Wetland Resource Areas; · Winter Road Salt and/or Sand Use and Storage restrictions; · Street sweeping schedules; · Provisions for prevention of illicit discharges to the stormwater management system; · Documentation that Stormwater BMPs are designed to provide for shutdown and containment in the event of a spill or discharges to or near critical areas or from LUHPPL; · Training for staff or personnel involved with implementing Long-Term Pollution Prevention Plan; · List of Emergency contacts for implementing Long-Term Pollution Prevention Plan. A Long-Term Pollution Prevention Plan is attached to Stormwater Report and is included as an attachment to the Wetlands Notice of Intent. Treatment BMPs subject to the 44% TSS removal pretreatment requirement and the one inch rule for calculating the water quality volume are included, and discharge: is within the Zone II or Interim Wellhead Protection Area is near or to other critical areas is within soils with a rapid infiltration rate (greater than 2.4 inches per hour) involves runoff from land uses with higher potential pollutant loads. The Required Water Quality Volume is reduced through use of the LID site Design Credits. Calculations documenting that the treatment train meets the 80% TSS removal requirement and, if applicable, the 44% TSS removal pretreatment requirement, are provided. Pumping Station 2 swcheck • 04/01/08 Stormwater Report Checklist • Page 6 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) Standard 4: Water Quality (continued) The BMP is sized (and calculations provided) based on: The ½” or 1” Water Quality Volume or The equivalent flow rate associated with the Water Quality Volume and documentation is provided showing that the BMP treats the required water quality volume. The applicant proposes to use proprietary BMPs, and documentation supporting use of proprietary BMP and proposed TSS removal rate is provided. This documentation may be in the form of the propriety BMP checklist found in Volume 2, Chapter 4 of the Massachusetts Stormwater Handbook and submitting copies of the TARP Report, STEP Report, and/or other third party studies verifying performance of the proprietary BMPs. A TMDL exists that indicates a need to reduce pollutants other than TSS and documentation showing that the BMPs selected are consistent with the TMDL is provided. Standard 5: Land Uses With Higher Potential Pollutant Loads (LUHPPLs) The NPDES Multi-Sector General Permit covers the land use and the Stormwater Pollution Prevention Plan (SWPPP) has been included with the Stormwater Report. The NPDES Multi-Sector General Permit covers the land use and the SWPPP will be submitted prior to the discharge of stormwater to the post-construction stormwater BMPs. The NPDES Multi-Sector General Permit does not cover the land use. LUHPPLs are located at the site and industry specific source control and pollution prevention measures have been proposed to reduce or eliminate the exposure of LUHPPLs to rain, snow, snow melt and runoff, and been included in the long term Pollution Prevention Plan. All exposure has been eliminated. All exposure has not been eliminated and all BMPs selected are on MassDEP LUHPPL list. The LUHPPL has the potential to generate runoff with moderate to higher concentrations of oil and grease (e.g. all parking lots with >1000 vehicle trips per day) and the treatment train includes an oil grit separator, a filtering bioretention area, a sand filter or equivalent. Standard 6: Critical Areas The discharge is near or to a critical area and the treatment train includes only BMPs that MassDEP has approved for stormwater discharges to or near that particular class of critical area. Critical areas and BMPs are identified in the Stormwater Report. Pumping Station 2 swcheck • 04/01/08 Stormwater Report Checklist • Page 7 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) Standard 7: Redevelopments and Other Projects Subject to the Standards only to the maximum extent practicable The project is subject to the Stormwater Management Standards only to the maximum Extent Practicable as a: Limited Project Small Residential Projects: 5-9 single family houses or 5-9 units in a multi-family development provided there is no discharge that may potentially affect a critical area. Small Residential Projects: 2-4 single family houses or 2-4 units in a multi-family development with a discharge to a critical area Marina and/or boatyard provided the hull painting, service and maintenance areas are protected from exposure to rain, snow, snow melt and runoff Bike Path and/or Foot Path Redevelopment Project Redevelopment portion of mix of new and redevelopment. Certain standards are not fully met (Standard No. 1, 8, 9, and 10 must always be fully met) and an explanation of why these standards are not met is contained in the Stormwater Report. The project involves redevelopment and a description of all measures that have been taken to improve existing conditions is provided in the Stormwater Report. The redevelopment checklist found in Volume 2 Chapter 3 of the Massachusetts Stormwater Handbook may be used to document that the proposed stormwater management system (a) complies with Standards 2, 3 and the pretreatment and structural BMP requirements of Standards 4-6 to the maximum extent practicable and (b) improves existing conditions. Standard 8: Construction Period Pollution Prevention and Erosion and Sedimentation Control A Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan must include the following information: · Narrative; · Construction Period Operation and Maintenance Plan; · Names of Persons or Entity Responsible for Plan Compliance; · Construction Period Pollution Prevention Measures; · Erosion and Sedimentation Control Plan Drawings; · Detail drawings and specifications for erosion control BMPs, including sizing calculations; · Vegetation Planning; · Site Development Plan; · Construction Sequencing Plan; · Sequencing of Erosion and Sedimentation Controls; · Operation and Maintenance of Erosion and Sedimentation Controls; · Inspection Schedule; · Maintenance Schedule; · Inspection and Maintenance Log Form. A Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan containing the information set forth above has been included in the Stormwater Report. Pumping Station 2 swcheck • 04/01/08 Stormwater Report Checklist • Page 8 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) Standard 8: Construction Period Pollution Prevention and Erosion and Sedimentation Control (continued) The project is highly complex and information is included in the Stormwater Report that explains why it is not possible to submit the Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan with the application. A Construction Period Pollution Prevention and Erosion and Sedimentation Control has not been included in the Stormwater Report but will be submitted before land disturbance begins. The project is not covered by a NPDES Construction General Permit. The project is covered by a NPDES Construction General Permit and a copy of the SWPPP is in the Stormwater Report. The project is covered by a NPDES Construction General Permit but no SWPPP been submitted. The SWPPP will be submitted BEFORE land disturbance begins. Standard 9: Operation and Maintenance Plan The Post Construction Operation and Maintenance Plan is included in the Stormwater Report and includes the following information: Name of the stormwater management system owners; Party responsible for operation and maintenance; Schedule for implementation of routine and non-routine maintenance tasks; Plan showing the location of all stormwater BMPs maintenance access areas; Description and delineation of public safety features; Estimated operation and maintenance budget; and Operation and Maintenance Log Form. The responsible party is not the owner of the parcel where the BMP is located and the Stormwater Report includes the following submissions: A copy of the legal instrument (deed, homeowner’s association, utility trust or other legal entity) that establishes the terms of and legal responsibility for the operation and maintenance of the project site stormwater BMPs; A plan and easement deed that allows site access for the legal entity to operate and maintain BMP functions. Standard 10: Prohibition of Illicit Discharges The Long-Term Pollution Prevention Plan includes measures to prevent illicit discharges; An Illicit Discharge Compliance Statement is attached; NO Illicit Discharge Compliance Statement is attached but will be submitted prior to the discharge of any stormwater to post-construction BMPs. Appendix A Rainfall Data NOAA Atlas 14, Volume 10, Version 3 Location name: West Yarmouth, Massachusetts, USA* Latitude: 41.6524°, Longitude: -70.2503° Elevation: 14 ft** * source: ESRI Maps ** source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES Sanja Perica, Sandra Pavlovic, Michael St. Laurent, Carl Trypaluk, Dale Unruh, Orlan Wilhite NOAA, National Weather Service, Silver Spring, Maryland PF_tabular | PF_graphical | Maps_&_aerials PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches) Duration Average recurrence interval (years) 1 2 5 10 25 50 100 200 500 1000 5-min 0.266 (0.216-0.325) 0.337 (0.273-0.412) 0.453 (0.366-0.556) 0.549 (0.441-0.679) 0.681 (0.526-0.885) 0.779 (0.589-1.04) 0.884 (0.647-1.23) 1.01 (0.687-1.42) 1.20 (0.781-1.75) 1.36 (0.863-2.03) 10-min 0.377 (0.306-0.461) 0.477 (0.387-0.584) 0.641 (0.518-0.787) 0.777 (0.623-0.960) 0.964 (0.745-1.25) 1.10 (0.833-1.47) 1.25 (0.917-1.74) 1.43 (0.974-2.02) 1.70 (1.11-2.49) 1.93 (1.22-2.88) 15-min 0.444 (0.360-0.542) 0.561 (0.455-0.687) 0.753 (0.609-0.925) 0.913 (0.733-1.13) 1.13 (0.877-1.48) 1.30 (0.980-1.73) 1.47 (1.08-2.05) 1.68 (1.15-2.38) 2.00 (1.30-2.92) 2.27 (1.44-3.39) 30-min 0.658 (0.534-0.804) 0.828 (0.672-1.01) 1.11 (0.894-1.36) 1.34 (1.07-1.65) 1.66 (1.28-2.16) 1.89 (1.43-2.52) 2.15 (1.57-2.99) 2.45 (1.67-3.46) 2.92 (1.90-4.26) 3.31 (2.10-4.94) 60-min 0.872 (0.708-1.07) 1.10 (0.888-1.34) 1.46 (1.18-1.79) 1.76 (1.41-2.18) 2.18 (1.68-2.84) 2.49 (1.88-3.32) 2.82 (2.07-3.93) 3.22 (2.19-4.54) 3.83 (2.49-5.60) 4.35 (2.76-6.48) 2-hr 1.23 (1.00-1.49) 1.52 (1.24-1.85) 2.00 (1.63-2.45) 2.41 (1.94-2.95) 2.96 (2.30-3.81) 3.36 (2.56-4.44) 3.81 (2.81-5.24) 4.34 (2.98-6.04) 5.14 (3.37-7.41) 5.82 (3.72-8.56) 3-hr 1.47 (1.20-1.78) 1.81 (1.48-2.19) 2.36 (1.93-2.87) 2.82 (2.29-3.44) 3.45 (2.70-4.42) 3.92 (3.00-5.14) 4.43 (3.28-6.05) 5.03 (3.47-6.96) 5.94 (3.92-8.50) 6.71 (4.31-9.79) 6-hr 1.92 (1.59-2.31) 2.33 (1.92-2.80) 3.00 (2.47-3.62) 3.56 (2.90-4.31) 4.32 (3.40-5.48) 4.89 (3.76-6.34) 5.50 (4.09-7.40) 6.21 (4.32-8.48) 7.26 (4.84-10.3) 8.14 (5.28-11.7) 12-hr 2.41 (2.00-2.87) 2.88 (2.39-3.44) 3.64 (3.01-4.37) 4.28 (3.52-5.15) 5.16 (4.08-6.46) 5.81 (4.50-7.44) 6.50 (4.86-8.61) 7.28 (5.12-9.83) 8.41 (5.66-11.7) 9.33 (6.12-13.3) 24-hr 2.86 (2.40-3.39) 3.38 (2.82-4.01) 4.22 (3.52-5.02) 4.92 (4.07-5.88) 5.88 (4.69-7.30) 6.62 (5.14-8.36) 7.37 (5.53-9.60) 8.19 (5.82-10.9) 9.34 (6.35-12.8) 10.3 (6.79-14.4) 2-day 3.26 (2.75-3.84) 3.81 (3.21-4.49) 4.71 (3.95-5.56) 5.45 (4.54-6.47) 6.47 (5.19-7.95) 7.25 (5.68-9.06) 8.05 (6.08-10.3) 8.90 (6.38-11.7) 10.1 (6.91-13.6) 11.0 (7.34-15.2) 3-day 3.54 (3.00-4.15) 4.10 (3.46-4.81) 5.01 (4.21-5.89) 5.76 (4.82-6.81) 6.80 (5.48-8.30) 7.59 (5.97-9.42) 8.40 (6.38-10.7) 9.26 (6.68-12.1) 10.4 (7.21-14.0) 11.4 (7.64-15.6) 4-day 3.78 (3.21-4.42) 4.34 (3.68-5.07) 5.25 (4.43-6.16) 6.01 (5.04-7.08) 7.05 (5.70-8.58) 7.84 (6.20-9.70) 8.66 (6.60-11.0) 9.53 (6.90-12.4) 10.7 (7.46-14.4) 11.7 (7.90-15.9) 7-day 4.41 (3.76-5.13) 4.98 (4.24-5.79) 5.90 (5.01-6.88) 6.67 (5.63-7.81) 7.73 (6.29-9.33) 8.53 (6.78-10.5) 9.36 (7.18-11.8) 10.2 (7.47-13.2) 11.4 (8.01-15.1) 12.4 (8.43-16.7) 10-day 5.01 (4.29-5.80) 5.60 (4.78-6.48) 6.55 (5.58-7.61) 7.35 (6.22-8.57) 8.44 (6.90-10.1) 9.28 (7.40-11.3) 10.1 (7.80-12.7) 11.0 (8.08-14.1) 12.2 (8.60-16.1) 13.2 (9.01-17.6) 20-day 6.82 (5.88-7.84) 7.50 (6.46-8.63) 8.62 (7.40-9.94) 9.55 (8.14-11.1) 10.8 (8.91-12.8) 11.8 (9.49-14.2) 12.8 (9.89-15.7) 13.8 (10.2-17.4) 15.0 (10.7-19.4) 15.9 (11.0-20.9) 30-day 8.38 (7.25-9.59) 9.16 (7.92-10.5) 10.4 (8.98-12.0) 11.5 (9.83-13.2) 12.9 (10.7-15.2) 14.1 (11.3-16.8) 15.2 (11.7-18.4) 16.2 (12.1-20.3) 17.4 (12.5-22.4) 18.3 (12.7-23.9) 45-day 10.4 (9.03-11.8) 11.3 (9.79-12.9) 12.7 (11.0-14.6) 13.9 (12.0-16.0) 15.6 (12.9-18.3) 16.9 (13.7-20.0) 18.1 (14.1-21.8) 19.2 (14.4-23.9) 20.5 (14.8-26.2) 21.4 (15.0-27.7) 60-day 12.1 (10.6-13.8) 13.1 (11.4-14.9) 14.7 (12.8-16.8) 16.0 (13.8-18.3) 17.9 (14.8-20.8) 19.3 (15.7-22.7) 20.7 (16.1-24.7) 21.8 (16.5-27.0) 23.2 (16.8-29.4) 24.1 (17.0-31.0) 1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top PF graphical Back to Top Maps & aerials Small scale terrain Large scale terrain Large scale map + – 3km 2mi + – 100km 60mi Large scale aerial Back to Top US Department of Commerce National Oceanic and Atmospheric Administration National Weather Service National Water Center 1325 East West Highway Silver Spring, MD 20910 Questions?: HDSC.Questions@noaa.gov Disclaimer + – 100km 60mi Appendix B Geotechnical Information Soil Map—Barnstable County, Massachusetts (Pumping Station No. 2) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/9/2025 Page 1 of 3 46 1 2 0 0 0 46 1 2 0 1 0 46 1 2 0 2 0 46 1 2 0 3 0 46 1 2 0 4 0 46 1 2 0 5 0 46 1 2 0 6 0 46 1 2 0 7 0 46 1 2 0 8 0 46 1 2 0 9 0 46 1 2 0 0 0 46 1 2 0 1 0 46 1 2 0 2 0 46 1 2 0 3 0 46 1 2 0 4 0 46 1 2 0 5 0 46 1 2 0 6 0 46 1 2 0 7 0 46 1 2 0 8 0 46 1 2 0 9 0 395700 395710 395720 395730 395740 395750 395760 395770 395780 395790 395800 395810 395820 395830 395840 395850 395700 395710 395720 395730 395740 395750 395760 395770 395780 395790 395800 395810 395820 395830 395840 395850 41° 39' 13'' N 70 ° 1 5 ' 9 ' ' W 41° 39' 13'' N 70 ° 1 5 ' 2 ' ' W 41° 39' 10'' N 70 ° 1 5 ' 9 ' ' W 41° 39' 10'' N 70 ° 1 5 ' 2 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 19N WGS84 0 30 60 120 180 Feet 0 10 20 40 60 Meters Map Scale: 1:714 if printed on A landscape (11" x 8.5") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:25,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Barnstable County, Massachusetts Survey Area Data: Version 24, Sep 5, 2025 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jun 10, 2022—Jun 30, 2022 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—Barnstable County, Massachusetts (Pumping Station No. 2) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/9/2025 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 55A Freetown coarse sand, 0 to 3 percent slopes, sanded surface 0.1 12.3% 252B Carver coarse sand, 3 to 8 percent slopes 0.8 87.7% Totals for Area of Interest 0.9 100.0% Soil Map—Barnstable County, Massachusetts Pumping Station No. 2 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/9/2025 Page 3 of 3 Hydrologic Soil Group—Barnstable County, Massachusetts (Pumping Station No. 2) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/9/2025 Page 1 of 4 46 1 2 0 0 0 46 1 2 0 1 0 46 1 2 0 2 0 46 1 2 0 3 0 46 1 2 0 4 0 46 1 2 0 5 0 46 1 2 0 6 0 46 1 2 0 7 0 46 1 2 0 8 0 46 1 2 0 9 0 46 1 2 0 0 0 46 1 2 0 1 0 46 1 2 0 2 0 46 1 2 0 3 0 46 1 2 0 4 0 46 1 2 0 5 0 46 1 2 0 6 0 46 1 2 0 7 0 46 1 2 0 8 0 46 1 2 0 9 0 395700 395710 395720 395730 395740 395750 395760 395770 395780 395790 395800 395810 395820 395830 395840 395850 395700 395710 395720 395730 395740 395750 395760 395770 395780 395790 395800 395810 395820 395830 395840 395850 41° 39' 13'' N 70 ° 1 5 ' 9 ' ' W 41° 39' 13'' N 70 ° 1 5 ' 2 ' ' W 41° 39' 10'' N 70 ° 1 5 ' 9 ' ' W 41° 39' 10'' N 70 ° 1 5 ' 2 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 19N WGS84 0 30 60 120 180 Feet 0 10 20 40 60 Meters Map Scale: 1:714 if printed on A landscape (11" x 8.5") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:25,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Barnstable County, Massachusetts Survey Area Data: Version 24, Sep 5, 2025 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jun 10, 2022—Jun 30, 2022 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Hydrologic Soil Group—Barnstable County, Massachusetts (Pumping Station No. 2) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/9/2025 Page 2 of 4 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 55A Freetown coarse sand, 0 to 3 percent slopes, sanded surface B/D 0.1 12.3% 252B Carver coarse sand, 3 to 8 percent slopes A 0.8 87.7% Totals for Area of Interest 0.9 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Hydrologic Soil Group—Barnstable County, Massachusetts Pumping Station No. 2 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/9/2025 Page 3 of 4 Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Barnstable County, Massachusetts Pumping Station No. 2 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/9/2025 Page 4 of 4 El e v. ( f t ) 10.0 5.0 0.0 De p t h ( f t ) 0 5 10 Sa m p l e Typ e SS SS SS SS SS SS SS Sa m p l e Nu m b e r S-1 S-2 S-3 S-4 S-5 S-6 S-7 Sa m p l e Le n g t h ( i n ) 24 24 24 24 24 24 24 Bl o w s p e r 6 i n c h e s 7 8 6 5 4 4 3 4 5 5 5 5 6 4 3 3 3 2 2 2 2 2 2 1 2 2 2 3 Sa m p l e Re c o v e r y ( i n ) 15 17 15 12 11 14 10 N-Val u e 14 7 10 7 4 4 4 Gr a p h i c L o g St r a t a SI LTY S A N D SA N D Material Description Moist, medium dense, brown, fine to coarse SAND, little silt, trace gravel (SM). Moist, loose, brown, fine to medium SAND, trace silt (SP). Moist, medium dense, tan, fine to medium SAND, trace silt (SP). Moist, loose, tan, fine to medium SAND, trace silt (SP). Wet, very loose, orange, fine to coarse SAND, trace gravel, trace silt (SP). Wet, loose, tan, fine to medium SAND, trace silt (SP). Wet, medium dense, tan, fine to medium SAND, trace silt (SP). Moist to wet, medium dense, tan, fine to medium SAND, trace silt (SP). Remarks Sheet 1 of 3 Boring Number: B-PS2 Client:Town of Yarmouth Project Name:Yarmouth Sewers Project Location:Yarmouth, MA Project Number:273132 Drilling Contractor/Driller:Northern Drill Services/Steve Perry Drilling Method/Bore Hole Diameter:Drive and Wash/4 in. Hammer Style/Weight/Drop Height/Spoon Size:Automatic/140 lb/30 in./2 in. Bore Hole Location:East Parking lot of 280 MA-28 Lat:Long: Drilling Date: Start:9/9/2025 End:9/9/2025 Surface Elevation (ft):10.0 Total Depth (ft):50.0 Depth to Initial Water Level (ft): Depth 9.0 Date 9/9/2025 Time 15:00 Abandonment Method:Completed as well. Refer to diagram. Logged By:Bryan Deely Sample Types Consistency vs Blowcount/Foot Burmister Classification AS -Auger/Grab Sample CS -California Sampler NQ -1.9" Rock Core NX -2.2" Rock Core HP -Hydro Punch SS -Split Spoon ST -Shelby Tube WS -Wash Sample GP -Geoprobe Granular (Sand): V. Loose: Loose: M. Dense: 0-4 4-10 10-30 Dense: V. Dense: 30-50 >50 Fine Grained (Clay): V. Soft: Soft: M. Stiff: <2 2-4 4-8 Stiff: V. Stiff: Hard: 8-15 15-30 >30 and some little trace 50 -35% 35 -20% 20 -10% < 10%moisture, density, color Reviewed by:Date:Boring Number:B-PS2 DRAFT El e v. ( f t ) -5.0 -10.0 -15.0 -20.0 De p t h ( f t ) 15 20 25 30 Sa m p l e Typ e SS SS SS SS SS SS SS Sa m p l e Nu m b e r S-8 S-9 S-10 S-11 S-12 S-13 S-14 Sa m p l e Le n g t h ( i n ) 24 24 24 24 24 24 24 Bl o w s p e r 6 i n c h e s 6 6 7 8 7 5 6 6 5 5 5 8 10 9 7 8 4 5 4 4 5 4 6 7 6 9 8 8 Sa m p l e Re c o v e r y ( i n ) 10 10 4 2 2 3 5 N-Val u e 13 11 10 16 9 10 17 Gr a p h i c L o g St r a t a SA N D Material Description Moist to wet, medium dense, tan, fine to medium SAND, trace silt (SP). Wet, medium dense, tan, fine to medium SAND, trace silt (SP). Wet, medium dense, tan, fine to medium SAND, trace silt (SP). Wet, medium dense, tan, fine to medium SAND, trace silt (SP). Wet, loose, tan, fine to medium SAND, trace silt (SP). Wet, medium dense, brown, fine to medium SAND, trace silt (SP). Wet, medium dense, tan, fine to medium SAND, trace silt (SP). Remarks Sheet 2 of 3 Boring Number: B-PS2 Client:Town of Yarmouth Project Name:Yarmouth Sewers Project Location:Yarmouth, MA Project Number:273132 Boring Number:B-PS2 DRAFT El e v. ( f t ) -25.0 -30.0 -35.0 -40.0 De p t h ( f t ) 35 40 45 50 Sa m p l e Typ e SS SS SS Sa m p l e Nu m b e r S-15 S-16 S-17 Sa m p l e Le n g t h ( i n ) 24 24 24 Bl o w s p e r 6 i n c h e s 7 7 8 5 4 5 6 5 7 9 8 6 Sa m p l e Re c o v e r y ( i n ) 4 7 6 N-Val u e 15 11 17 Gr a p h i c L o g St r a t a SA N D Material Description Wet, medium dense, tan, fine to medium SAND, trace silt (SP). Wet, medium dense, tan, fine to medium SAND, trace silt (SP). Wet, medium dense, tan, fine to coarse SAND, trace silt (SP). Wet, medium dense, tan, fine to medium SAND, trace silt (SP). Test boring terminated at 50.0 feet bgs. Remarks Sheet 3 of 3 Boring Number: B-PS2 Client:Town of Yarmouth Project Name:Yarmouth Sewers Project Location:Yarmouth, MA Project Number:273132 Boring Number:B-PS2 DRAFT Appendix C HydroCAD Model PS2 Proposed PS2 Existing 1S Northwest Existing 2S Southwest Existing 3S East Existing 4S Northwest Proposed 5S Southwest Proposed 6S South Proposed 7S East Proposed 1R Low Area Existing 2R Rte 28 Existing 3R Grass Area Existing 4R Existing Flow Sum 5R Rte 28 Proposed 7R Grass Area Proposed 8R Proposed Flow Sum 1P CB CB1 2P CB CB23P CB Proprietary Separator Device 4P Concrete Module Subsurface System 5P CB DMH1 Routing Diagram for 2025_10_10 Yarmouth PS2 Prepared by CDM Smith, Printed 10/27/2025 HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Subcat Reach Pond Link Type III 24-hr 2 yr 24 hr Rainfall=3.38"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 2HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1,916 sf 62.47% Impervious Runoff Depth=2.16"Subcatchment 1S: Northwest Existing Tc=6.0 min CN=88 Runoff=0.11 cfs 0.008 af Runoff Area=3,365 sf 37.09% Impervious Runoff Depth=0.88"Subcatchment 2S: Southwest Existing Tc=6.0 min CN=69 Runoff=0.07 cfs 0.006 af Runoff Area=4,163 sf 0.00% Impervious Runoff Depth=0.02"Subcatchment 3S: East Existing Tc=6.0 min CN=41 Runoff=0.00 cfs 0.000 af Runoff Area=2,095 sf 86.21% Impervious Runoff Depth=2.72"Subcatchment 4S: Northwest Proposed Tc=6.0 min CN=94 Runoff=0.15 cfs 0.011 af Runoff Area=3,103 sf 84.92% Impervious Runoff Depth=2.82"Subcatchment 5S: Southwest Proposed Tc=6.0 min CN=95 Runoff=0.22 cfs 0.017 af Runoff Area=1,279 sf 0.00% Impervious Runoff Depth=0.00"Subcatchment 6S: South Proposed Tc=6.0 min CN=39 Runoff=0.00 cfs 0.000 af Runoff Area=2,967 sf 0.00% Impervious Runoff Depth=0.00"Subcatchment 7S: East Proposed Tc=6.0 min CN=39 Runoff=0.00 cfs 0.000 af Inflow=0.11 cfs 0.008 afReach 1R: Low Area Existing Outflow=0.11 cfs 0.008 af Inflow=0.07 cfs 0.006 afReach 2R: Rte 28 Existing Outflow=0.07 cfs 0.006 af Inflow=0.00 cfs 0.000 afReach 3R: Grass Area Existing Outflow=0.00 cfs 0.000 af Inflow=0.18 cfs 0.014 afReach 4R: Existing Flow Sum Outflow=0.18 cfs 0.014 af Inflow=0.00 cfs 0.000 afReach 5R: Rte 28 Proposed Outflow=0.00 cfs 0.000 af Inflow=0.00 cfs 0.000 afReach 7R: Grass Area Proposed Outflow=0.00 cfs 0.000 af Inflow=0.00 cfs 0.000 afReach 8R: Proposed Flow Sum Outflow=0.00 cfs 0.000 af Peak Elev=7.46' Inflow=0.15 cfs 0.011 afPond 1P: CB1 12.0" Round Culvert n=0.013 L=30.5' S=0.0066 '/' Outflow=0.15 cfs 0.011 af Peak Elev=6.71' Inflow=0.22 cfs 0.017 afPond 2P: CB2 12.0" Round Culvert n=0.013 L=56.5' S=0.0050 '/' Outflow=0.22 cfs 0.017 af Type III 24-hr 2 yr 24 hr Rainfall=3.38"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 3HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Peak Elev=6.46' Inflow=0.37 cfs 0.028 afPond 3P: Proprietary Separator Device 12.0" Round Culvert n=0.013 L=7.7' S=0.0052 '/' Outflow=0.37 cfs 0.028 af Peak Elev=5.04' Storage=233 cf Inflow=0.37 cfs 0.028 afPond 4P: Concrete Module Subsurface System Discarded=0.10 cfs 0.028 af Primary=0.00 cfs 0.000 af Outflow=0.10 cfs 0.028 af Peak Elev=5.70' Inflow=0.00 cfs 0.000 afPond 5P: DMH1 12.0" Round Culvert n=0.013 L=17.0' S=0.0059 '/' Outflow=0.00 cfs 0.000 af Total Runoff Area = 0.434 ac Runoff Volume = 0.041 af Average Runoff Depth = 1.15" 63.54% Pervious = 0.276 ac 36.46% Impervious = 0.158 ac Type III 24-hr 2 yr 24 hr Rainfall=3.38"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 4HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 1S: Northwest Existing Runoff = 0.11 cfs @ 12.09 hrs, Volume= 0.008 af, Depth= 2.16" Routed to Reach 1R : Low Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 2 yr 24 hr Rainfall=3.38" Area (sf) CN Description 719 72 Dirt roads, HSG A 1,197 98 Paved parking, HSG A 1,916 88 Weighted Average 719 37.53% Pervious Area 1,197 62.47% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 2S: Southwest Existing Runoff = 0.07 cfs @ 12.10 hrs, Volume= 0.006 af, Depth= 0.88" Routed to Reach 2R : Rte 28 Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 2 yr 24 hr Rainfall=3.38" Area (sf) CN Description 1,309 39 >75% Grass cover, Good, HSG A 808 72 Dirt roads, HSG A 1,248 98 Paved parking, HSG A 3,365 69 Weighted Average 2,117 62.91% Pervious Area 1,248 37.09% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Grass Summary for Subcatchment 3S: East Existing Runoff = 0.00 cfs @ 21.16 hrs, Volume= 0.000 af, Depth= 0.02" Routed to Reach 3R : Grass Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 2 yr 24 hr Rainfall=3.38" Type III 24-hr 2 yr 24 hr Rainfall=3.38"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 5HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Area (sf) CN Description 3,031 30 Brush, Good, HSG A 1,132 72 Dirt roads, HSG A 4,163 41 Weighted Average 4,163 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement/grass Summary for Subcatchment 4S: Northwest Proposed Runoff = 0.15 cfs @ 12.08 hrs, Volume= 0.011 af, Depth= 2.72" Routed to Pond 1P : CB1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 2 yr 24 hr Rainfall=3.38" Area (sf) CN Description 63 39 >75% Grass cover, Good, HSG A 226 76 Gravel roads, HSG A 1,806 98 Paved parking, HSG A 2,095 94 Weighted Average 289 13.79% Pervious Area 1,806 86.21% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 5S: Southwest Proposed Runoff = 0.22 cfs @ 12.08 hrs, Volume= 0.017 af, Depth= 2.82" Routed to Pond 2P : CB2 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 2 yr 24 hr Rainfall=3.38" Area (sf) CN Description 468 76 Gravel roads, HSG A 2,635 98 Paved parking, HSG A 3,103 95 Weighted Average 468 15.08% Pervious Area 2,635 84.92% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Type III 24-hr 2 yr 24 hr Rainfall=3.38"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 6HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 6S: South Proposed Runoff = 0.00 cfs @ 23.64 hrs, Volume= 0.000 af, Depth= 0.00" Routed to Reach 5R : Rte 28 Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 2 yr 24 hr Rainfall=3.38" Area (sf) CN Description 1,279 39 >75% Grass cover, Good, HSG A 1,279 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Subcatchment 7S: East Proposed Runoff = 0.00 cfs @ 23.64 hrs, Volume= 0.000 af, Depth= 0.00" Routed to Reach 7R : Grass Area Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 2 yr 24 hr Rainfall=3.38" Area (sf) CN Description 2,967 39 >75% Grass cover, Good, HSG A 2,967 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Reach 1R: Low Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.044 ac, 62.47% Impervious, Inflow Depth = 2.16" for 2 yr 24 hr event Inflow = 0.11 cfs @ 12.09 hrs, Volume= 0.008 af Outflow = 0.11 cfs @ 12.09 hrs, Volume= 0.008 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 2R: Rte 28 Existing [40] Hint: Not Described (Outflow=Inflow) Type III 24-hr 2 yr 24 hr Rainfall=3.38"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 7HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Inflow Area = 0.077 ac, 37.09% Impervious, Inflow Depth = 0.88" for 2 yr 24 hr event Inflow = 0.07 cfs @ 12.10 hrs, Volume= 0.006 af Outflow = 0.07 cfs @ 12.10 hrs, Volume= 0.006 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 3R: Grass Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.096 ac, 0.00% Impervious, Inflow Depth = 0.02" for 2 yr 24 hr event Inflow = 0.00 cfs @ 21.16 hrs, Volume= 0.000 af Outflow = 0.00 cfs @ 21.16 hrs, Volume= 0.000 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 4R: Existing Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 25.89% Impervious, Inflow Depth = 0.76" for 2 yr 24 hr event Inflow = 0.18 cfs @ 12.09 hrs, Volume= 0.014 af Outflow = 0.18 cfs @ 12.09 hrs, Volume= 0.014 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 5R: Rte 28 Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.149 ac, 68.57% Impervious, Inflow Depth = 0.00" for 2 yr 24 hr event Inflow = 0.00 cfs @ 23.64 hrs, Volume= 0.000 af Outflow = 0.00 cfs @ 23.64 hrs, Volume= 0.000 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 7R: Grass Area Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.068 ac, 0.00% Impervious, Inflow Depth = 0.00" for 2 yr 24 hr event Inflow = 0.00 cfs @ 23.64 hrs, Volume= 0.000 af Outflow = 0.00 cfs @ 23.64 hrs, Volume= 0.000 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Type III 24-hr 2 yr 24 hr Rainfall=3.38"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 8HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 8R: Proposed Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 47.02% Impervious, Inflow Depth = 0.00" for 2 yr 24 hr event Inflow = 0.00 cfs @ 23.64 hrs, Volume= 0.000 af Outflow = 0.00 cfs @ 23.64 hrs, Volume= 0.000 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Pond 1P: CB1 Inflow Area = 0.048 ac, 86.21% Impervious, Inflow Depth = 2.72" for 2 yr 24 hr event Inflow = 0.15 cfs @ 12.08 hrs, Volume= 0.011 af Outflow = 0.15 cfs @ 12.08 hrs, Volume= 0.011 af, Atten= 0%, Lag= 0.0 min Primary = 0.15 cfs @ 12.08 hrs, Volume= 0.011 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 7.46' @ 12.08 hrs Flood Elev= 10.50' Device Routing Invert Outlet Devices #1 Primary 7.25'12.0" Round Culvert L= 30.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 7.25' / 7.05' S= 0.0066 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.15 cfs @ 12.08 hrs HW=7.46' TW=6.46' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.15 cfs @ 1.83 fps) Summary for Pond 2P: CB2 Inflow Area = 0.071 ac, 84.92% Impervious, Inflow Depth = 2.82" for 2 yr 24 hr event Inflow = 0.22 cfs @ 12.08 hrs, Volume= 0.017 af Outflow = 0.22 cfs @ 12.08 hrs, Volume= 0.017 af, Atten= 0%, Lag= 0.0 min Primary = 0.22 cfs @ 12.08 hrs, Volume= 0.017 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.71' @ 12.09 hrs Flood Elev= 9.67' Device Routing Invert Outlet Devices #1 Primary 6.42'12.0" Round Culvert L= 56.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.42' / 6.14' S= 0.0050 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Type III 24-hr 2 yr 24 hr Rainfall=3.38"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 9HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Primary OutFlow Max=0.22 cfs @ 12.08 hrs HW=6.71' TW=6.46' (Dynamic Tailwater) 1=Culvert (Outlet Controls 0.22 cfs @ 1.70 fps) Summary for Pond 3P: Proprietary Separator Device Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 2.78" for 2 yr 24 hr event Inflow = 0.37 cfs @ 12.08 hrs, Volume= 0.028 af Outflow = 0.37 cfs @ 12.08 hrs, Volume= 0.028 af, Atten= 0%, Lag= 0.0 min Primary = 0.37 cfs @ 12.08 hrs, Volume= 0.028 af Routed to Pond 4P : Concrete Module Subsurface System Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.46' @ 12.08 hrs Flood Elev= 11.70' Device Routing Invert Outlet Devices #1 Primary 6.09'12.0" Round Culvert L= 7.7' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.09' / 6.05' S= 0.0052 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.37 cfs @ 12.08 hrs HW=6.46' TW=4.77' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.37 cfs @ 2.09 fps) Summary for Pond 4P: Concrete Module Subsurface System Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 2.78" for 2 yr 24 hr event Inflow = 0.37 cfs @ 12.08 hrs, Volume= 0.028 af Outflow = 0.10 cfs @ 12.42 hrs, Volume= 0.028 af, Atten= 72%, Lag= 20.3 min Discarded = 0.10 cfs @ 12.42 hrs, Volume= 0.028 af Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Routed to Pond 5P : DMH1 Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 5.04' @ 12.42 hrs Surf.Area= 448 sf Storage= 233 cf Flood Elev= 8.50' Storage= 1,496 cf Plug-Flow detention time= 11.6 min calculated for 0.028 af (100% of inflow) Center-of-Mass det. time= 11.6 min ( 793.2 - 781.7 ) Volume Invert Avail.Storage Storage Description #1 4.50' 1,496 cf retain_it retain_it 3.5' x 8 Inside= 84.0"W x 42.0"H => 25.10 sf x 8.00'L = 200.8 cf Outside= 96.0"W x 50.0"H => 33.33 sf x 8.00'L = 266.7 cf 1 Rows adjusted for 110.5 cf perimeter wall Device Routing Invert Outlet Devices #1 Primary 5.95'12.0" Round Culvert L= 26.3' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.95' / 5.80' S= 0.0057 '/' Cc= 0.900 Type III 24-hr 2 yr 24 hr Rainfall=3.38"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 10HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC n= 0.013, Flow Area= 0.79 sf #2 Discarded 4.50'8.270 in/hr Exfiltration over Surface area Conductivity to Groundwater Elevation = 2.00' Phase-In= 0.01' Discarded OutFlow Max=0.10 cfs @ 12.42 hrs HW=5.04' (Free Discharge) 2=Exfiltration ( Controls 0.10 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=4.50' TW=5.70' (Dynamic Tailwater) 1=Culvert ( Controls 0.00 cfs) Summary for Pond 5P: DMH1 Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 0.00" for 2 yr 24 hr event Inflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 0%, Lag= 0.0 min Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Routed to Reach 5R : Rte 28 Proposed Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 5.70' @ 0.00 hrs Flood Elev= 11.00' Device Routing Invert Outlet Devices #1 Primary 5.70'12.0" Round Culvert L= 17.0' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.70' / 5.60' S= 0.0059 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=5.70' TW=0.00' (Dynamic Tailwater) 1=Culvert ( Controls 0.00 cfs) Type III 24-hr 10 yr 24 hr Rainfall=4.92"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 11HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1,916 sf 62.47% Impervious Runoff Depth=3.59"Subcatchment 1S: Northwest Existing Tc=6.0 min CN=88 Runoff=0.18 cfs 0.013 af Runoff Area=3,365 sf 37.09% Impervious Runoff Depth=1.90"Subcatchment 2S: Southwest Existing Tc=6.0 min CN=69 Runoff=0.17 cfs 0.012 af Runoff Area=4,163 sf 0.00% Impervious Runoff Depth=0.25"Subcatchment 3S: East Existing Tc=6.0 min CN=41 Runoff=0.01 cfs 0.002 af Runoff Area=2,095 sf 86.21% Impervious Runoff Depth=4.23"Subcatchment 4S: Northwest Proposed Tc=6.0 min CN=94 Runoff=0.22 cfs 0.017 af Runoff Area=3,103 sf 84.92% Impervious Runoff Depth=4.34"Subcatchment 5S: Southwest Proposed Tc=6.0 min CN=95 Runoff=0.33 cfs 0.026 af Runoff Area=1,279 sf 0.00% Impervious Runoff Depth=0.18"Subcatchment 6S: South Proposed Tc=6.0 min CN=39 Runoff=0.00 cfs 0.000 af Runoff Area=2,967 sf 0.00% Impervious Runoff Depth=0.18"Subcatchment 7S: East Proposed Tc=6.0 min CN=39 Runoff=0.00 cfs 0.001 af Inflow=0.18 cfs 0.013 afReach 1R: Low Area Existing Outflow=0.18 cfs 0.013 af Inflow=0.17 cfs 0.012 afReach 2R: Rte 28 Existing Outflow=0.17 cfs 0.012 af Inflow=0.01 cfs 0.002 afReach 3R: Grass Area Existing Outflow=0.01 cfs 0.002 af Inflow=0.35 cfs 0.027 afReach 4R: Existing Flow Sum Outflow=0.35 cfs 0.027 af Inflow=0.00 cfs 0.000 afReach 5R: Rte 28 Proposed Outflow=0.00 cfs 0.000 af Inflow=0.00 cfs 0.001 afReach 7R: Grass Area Proposed Outflow=0.00 cfs 0.001 af Inflow=0.00 cfs 0.001 afReach 8R: Proposed Flow Sum Outflow=0.00 cfs 0.001 af Peak Elev=7.51' Inflow=0.22 cfs 0.017 afPond 1P: CB1 12.0" Round Culvert n=0.013 L=30.5' S=0.0066 '/' Outflow=0.22 cfs 0.017 af Peak Elev=6.79' Inflow=0.33 cfs 0.026 afPond 2P: CB2 12.0" Round Culvert n=0.013 L=56.5' S=0.0050 '/' Outflow=0.33 cfs 0.026 af Type III 24-hr 10 yr 24 hr Rainfall=4.92"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 12HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Peak Elev=6.55' Inflow=0.55 cfs 0.043 afPond 3P: Proprietary Separator Device 12.0" Round Culvert n=0.013 L=7.7' S=0.0052 '/' Outflow=0.55 cfs 0.043 af Peak Elev=5.57' Storage=458 cf Inflow=0.55 cfs 0.043 afPond 4P: Concrete Module Subsurface System Discarded=0.12 cfs 0.043 af Primary=0.00 cfs 0.000 af Outflow=0.12 cfs 0.043 af Peak Elev=5.70' Inflow=0.00 cfs 0.000 afPond 5P: DMH1 12.0" Round Culvert n=0.013 L=17.0' S=0.0059 '/' Outflow=0.00 cfs 0.000 af Total Runoff Area = 0.434 ac Runoff Volume = 0.072 af Average Runoff Depth = 1.98" 63.54% Pervious = 0.276 ac 36.46% Impervious = 0.158 ac Type III 24-hr 10 yr 24 hr Rainfall=4.92"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 13HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 1S: Northwest Existing Runoff = 0.18 cfs @ 12.09 hrs, Volume= 0.013 af, Depth= 3.59" Routed to Reach 1R : Low Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 10 yr 24 hr Rainfall=4.92" Area (sf) CN Description 719 72 Dirt roads, HSG A 1,197 98 Paved parking, HSG A 1,916 88 Weighted Average 719 37.53% Pervious Area 1,197 62.47% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 2S: Southwest Existing Runoff = 0.17 cfs @ 12.09 hrs, Volume= 0.012 af, Depth= 1.90" Routed to Reach 2R : Rte 28 Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 10 yr 24 hr Rainfall=4.92" Area (sf) CN Description 1,309 39 >75% Grass cover, Good, HSG A 808 72 Dirt roads, HSG A 1,248 98 Paved parking, HSG A 3,365 69 Weighted Average 2,117 62.91% Pervious Area 1,248 37.09% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Grass Summary for Subcatchment 3S: East Existing Runoff = 0.01 cfs @ 12.42 hrs, Volume= 0.002 af, Depth= 0.25" Routed to Reach 3R : Grass Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 10 yr 24 hr Rainfall=4.92" Type III 24-hr 10 yr 24 hr Rainfall=4.92"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 14HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Area (sf) CN Description 3,031 30 Brush, Good, HSG A 1,132 72 Dirt roads, HSG A 4,163 41 Weighted Average 4,163 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement/grass Summary for Subcatchment 4S: Northwest Proposed Runoff = 0.22 cfs @ 12.08 hrs, Volume= 0.017 af, Depth= 4.23" Routed to Pond 1P : CB1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 10 yr 24 hr Rainfall=4.92" Area (sf) CN Description 63 39 >75% Grass cover, Good, HSG A 226 76 Gravel roads, HSG A 1,806 98 Paved parking, HSG A 2,095 94 Weighted Average 289 13.79% Pervious Area 1,806 86.21% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 5S: Southwest Proposed Runoff = 0.33 cfs @ 12.08 hrs, Volume= 0.026 af, Depth= 4.34" Routed to Pond 2P : CB2 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 10 yr 24 hr Rainfall=4.92" Area (sf) CN Description 468 76 Gravel roads, HSG A 2,635 98 Paved parking, HSG A 3,103 95 Weighted Average 468 15.08% Pervious Area 2,635 84.92% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Type III 24-hr 10 yr 24 hr Rainfall=4.92"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 15HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 6S: South Proposed Runoff = 0.00 cfs @ 12.49 hrs, Volume= 0.000 af, Depth= 0.18" Routed to Reach 5R : Rte 28 Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 10 yr 24 hr Rainfall=4.92" Area (sf) CN Description 1,279 39 >75% Grass cover, Good, HSG A 1,279 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Subcatchment 7S: East Proposed Runoff = 0.00 cfs @ 12.49 hrs, Volume= 0.001 af, Depth= 0.18" Routed to Reach 7R : Grass Area Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 10 yr 24 hr Rainfall=4.92" Area (sf) CN Description 2,967 39 >75% Grass cover, Good, HSG A 2,967 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Reach 1R: Low Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.044 ac, 62.47% Impervious, Inflow Depth = 3.59" for 10 yr 24 hr event Inflow = 0.18 cfs @ 12.09 hrs, Volume= 0.013 af Outflow = 0.18 cfs @ 12.09 hrs, Volume= 0.013 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 2R: Rte 28 Existing [40] Hint: Not Described (Outflow=Inflow) Type III 24-hr 10 yr 24 hr Rainfall=4.92"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 16HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Inflow Area = 0.077 ac, 37.09% Impervious, Inflow Depth = 1.90" for 10 yr 24 hr event Inflow = 0.17 cfs @ 12.09 hrs, Volume= 0.012 af Outflow = 0.17 cfs @ 12.09 hrs, Volume= 0.012 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 3R: Grass Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.096 ac, 0.00% Impervious, Inflow Depth = 0.25" for 10 yr 24 hr event Inflow = 0.01 cfs @ 12.42 hrs, Volume= 0.002 af Outflow = 0.01 cfs @ 12.42 hrs, Volume= 0.002 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 4R: Existing Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 25.89% Impervious, Inflow Depth = 1.52" for 10 yr 24 hr event Inflow = 0.35 cfs @ 12.09 hrs, Volume= 0.027 af Outflow = 0.35 cfs @ 12.09 hrs, Volume= 0.027 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 5R: Rte 28 Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.149 ac, 68.57% Impervious, Inflow Depth = 0.04" for 10 yr 24 hr event Inflow = 0.00 cfs @ 12.49 hrs, Volume= 0.000 af Outflow = 0.00 cfs @ 12.49 hrs, Volume= 0.000 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 7R: Grass Area Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.068 ac, 0.00% Impervious, Inflow Depth = 0.18" for 10 yr 24 hr event Inflow = 0.00 cfs @ 12.49 hrs, Volume= 0.001 af Outflow = 0.00 cfs @ 12.49 hrs, Volume= 0.001 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Type III 24-hr 10 yr 24 hr Rainfall=4.92"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 17HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 8R: Proposed Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 47.02% Impervious, Inflow Depth = 0.08" for 10 yr 24 hr event Inflow = 0.00 cfs @ 12.49 hrs, Volume= 0.001 af Outflow = 0.00 cfs @ 12.49 hrs, Volume= 0.001 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Pond 1P: CB1 Inflow Area = 0.048 ac, 86.21% Impervious, Inflow Depth = 4.23" for 10 yr 24 hr event Inflow = 0.22 cfs @ 12.08 hrs, Volume= 0.017 af Outflow = 0.22 cfs @ 12.08 hrs, Volume= 0.017 af, Atten= 0%, Lag= 0.0 min Primary = 0.22 cfs @ 12.08 hrs, Volume= 0.017 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 7.51' @ 12.08 hrs Flood Elev= 10.50' Device Routing Invert Outlet Devices #1 Primary 7.25'12.0" Round Culvert L= 30.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 7.25' / 7.05' S= 0.0066 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.22 cfs @ 12.08 hrs HW=7.51' TW=6.55' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.22 cfs @ 2.04 fps) Summary for Pond 2P: CB2 Inflow Area = 0.071 ac, 84.92% Impervious, Inflow Depth = 4.34" for 10 yr 24 hr event Inflow = 0.33 cfs @ 12.08 hrs, Volume= 0.026 af Outflow = 0.33 cfs @ 12.08 hrs, Volume= 0.026 af, Atten= 0%, Lag= 0.0 min Primary = 0.33 cfs @ 12.08 hrs, Volume= 0.026 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.79' @ 12.09 hrs Flood Elev= 9.67' Device Routing Invert Outlet Devices #1 Primary 6.42'12.0" Round Culvert L= 56.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.42' / 6.14' S= 0.0050 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Type III 24-hr 10 yr 24 hr Rainfall=4.92"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 18HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Primary OutFlow Max=0.33 cfs @ 12.08 hrs HW=6.79' TW=6.55' (Dynamic Tailwater) 1=Culvert (Outlet Controls 0.33 cfs @ 1.83 fps) Summary for Pond 3P: Proprietary Separator Device Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 4.30" for 10 yr 24 hr event Inflow = 0.55 cfs @ 12.08 hrs, Volume= 0.043 af Outflow = 0.55 cfs @ 12.08 hrs, Volume= 0.043 af, Atten= 0%, Lag= 0.0 min Primary = 0.55 cfs @ 12.08 hrs, Volume= 0.043 af Routed to Pond 4P : Concrete Module Subsurface System Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.55' @ 12.08 hrs Flood Elev= 11.70' Device Routing Invert Outlet Devices #1 Primary 6.09'12.0" Round Culvert L= 7.7' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.09' / 6.05' S= 0.0052 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.55 cfs @ 12.08 hrs HW=6.55' TW=5.05' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.55 cfs @ 2.32 fps) Summary for Pond 4P: Concrete Module Subsurface System Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 4.30" for 10 yr 24 hr event Inflow = 0.55 cfs @ 12.08 hrs, Volume= 0.043 af Outflow = 0.12 cfs @ 12.49 hrs, Volume= 0.043 af, Atten= 78%, Lag= 24.2 min Discarded = 0.12 cfs @ 12.49 hrs, Volume= 0.043 af Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Routed to Pond 5P : DMH1 Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 5.57' @ 12.49 hrs Surf.Area= 448 sf Storage= 458 cf Flood Elev= 8.50' Storage= 1,496 cf Plug-Flow detention time= 22.0 min calculated for 0.043 af (100% of inflow) Center-of-Mass det. time= 22.0 min ( 792.8 - 770.8 ) Volume Invert Avail.Storage Storage Description #1 4.50' 1,496 cf retain_it retain_it 3.5' x 8 Inside= 84.0"W x 42.0"H => 25.10 sf x 8.00'L = 200.8 cf Outside= 96.0"W x 50.0"H => 33.33 sf x 8.00'L = 266.7 cf 1 Rows adjusted for 110.5 cf perimeter wall Device Routing Invert Outlet Devices #1 Primary 5.95'12.0" Round Culvert L= 26.3' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.95' / 5.80' S= 0.0057 '/' Cc= 0.900 Type III 24-hr 10 yr 24 hr Rainfall=4.92"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 19HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC n= 0.013, Flow Area= 0.79 sf #2 Discarded 4.50'8.270 in/hr Exfiltration over Surface area Conductivity to Groundwater Elevation = 2.00' Phase-In= 0.01' Discarded OutFlow Max=0.12 cfs @ 12.49 hrs HW=5.57' (Free Discharge) 2=Exfiltration ( Controls 0.12 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=4.50' TW=5.70' (Dynamic Tailwater) 1=Culvert ( Controls 0.00 cfs) Summary for Pond 5P: DMH1 Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 0.00" for 10 yr 24 hr event Inflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 0%, Lag= 0.0 min Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Routed to Reach 5R : Rte 28 Proposed Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 5.70' @ 0.00 hrs Flood Elev= 11.00' Device Routing Invert Outlet Devices #1 Primary 5.70'12.0" Round Culvert L= 17.0' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.70' / 5.60' S= 0.0059 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=5.70' TW=0.00' (Dynamic Tailwater) 1=Culvert ( Controls 0.00 cfs) Type III 24-hr 25 yr 24 hr Rainfall=5.88"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 20HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1,916 sf 62.47% Impervious Runoff Depth=4.51"Subcatchment 1S: Northwest Existing Tc=6.0 min CN=88 Runoff=0.22 cfs 0.017 af Runoff Area=3,365 sf 37.09% Impervious Runoff Depth=2.62"Subcatchment 2S: Southwest Existing Tc=6.0 min CN=69 Runoff=0.23 cfs 0.017 af Runoff Area=4,163 sf 0.00% Impervious Runoff Depth=0.52"Subcatchment 3S: East Existing Tc=6.0 min CN=41 Runoff=0.02 cfs 0.004 af Runoff Area=2,095 sf 86.21% Impervious Runoff Depth=5.18"Subcatchment 4S: Northwest Proposed Tc=6.0 min CN=94 Runoff=0.27 cfs 0.021 af Runoff Area=3,103 sf 84.92% Impervious Runoff Depth=5.29"Subcatchment 5S: Southwest Proposed Tc=6.0 min CN=95 Runoff=0.40 cfs 0.031 af Runoff Area=1,279 sf 0.00% Impervious Runoff Depth=0.41"Subcatchment 6S: South Proposed Tc=6.0 min CN=39 Runoff=0.00 cfs 0.001 af Runoff Area=2,967 sf 0.00% Impervious Runoff Depth=0.41"Subcatchment 7S: East Proposed Tc=6.0 min CN=39 Runoff=0.01 cfs 0.002 af Inflow=0.22 cfs 0.017 afReach 1R: Low Area Existing Outflow=0.22 cfs 0.017 af Inflow=0.23 cfs 0.017 afReach 2R: Rte 28 Existing Outflow=0.23 cfs 0.017 af Inflow=0.02 cfs 0.004 afReach 3R: Grass Area Existing Outflow=0.02 cfs 0.004 af Inflow=0.47 cfs 0.038 afReach 4R: Existing Flow Sum Outflow=0.47 cfs 0.038 af Inflow=0.00 cfs 0.001 afReach 5R: Rte 28 Proposed Outflow=0.00 cfs 0.001 af Inflow=0.01 cfs 0.002 afReach 7R: Grass Area Proposed Outflow=0.01 cfs 0.002 af Inflow=0.02 cfs 0.003 afReach 8R: Proposed Flow Sum Outflow=0.02 cfs 0.003 af Peak Elev=7.54' Inflow=0.27 cfs 0.021 afPond 1P: CB1 12.0" Round Culvert n=0.013 L=30.5' S=0.0066 '/' Outflow=0.27 cfs 0.021 af Peak Elev=6.84' Inflow=0.40 cfs 0.031 afPond 2P: CB2 12.0" Round Culvert n=0.013 L=56.5' S=0.0050 '/' Outflow=0.40 cfs 0.031 af Type III 24-hr 25 yr 24 hr Rainfall=5.88"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 21HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Peak Elev=6.60' Inflow=0.67 cfs 0.052 afPond 3P: Proprietary Separator Device 12.0" Round Culvert n=0.013 L=7.7' S=0.0052 '/' Outflow=0.67 cfs 0.052 af Peak Elev=5.91' Storage=604 cf Inflow=0.67 cfs 0.052 afPond 4P: Concrete Module Subsurface System Discarded=0.13 cfs 0.052 af Primary=0.00 cfs 0.000 af Outflow=0.13 cfs 0.052 af Peak Elev=5.70' Inflow=0.00 cfs 0.000 afPond 5P: DMH1 12.0" Round Culvert n=0.013 L=17.0' S=0.0059 '/' Outflow=0.00 cfs 0.000 af Total Runoff Area = 0.434 ac Runoff Volume = 0.093 af Average Runoff Depth = 2.57" 63.54% Pervious = 0.276 ac 36.46% Impervious = 0.158 ac Type III 24-hr 25 yr 24 hr Rainfall=5.88"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 22HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 1S: Northwest Existing Runoff = 0.22 cfs @ 12.09 hrs, Volume= 0.017 af, Depth= 4.51" Routed to Reach 1R : Low Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 25 yr 24 hr Rainfall=5.88" Area (sf) CN Description 719 72 Dirt roads, HSG A 1,197 98 Paved parking, HSG A 1,916 88 Weighted Average 719 37.53% Pervious Area 1,197 62.47% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 2S: Southwest Existing Runoff = 0.23 cfs @ 12.09 hrs, Volume= 0.017 af, Depth= 2.62" Routed to Reach 2R : Rte 28 Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 25 yr 24 hr Rainfall=5.88" Area (sf) CN Description 1,309 39 >75% Grass cover, Good, HSG A 808 72 Dirt roads, HSG A 1,248 98 Paved parking, HSG A 3,365 69 Weighted Average 2,117 62.91% Pervious Area 1,248 37.09% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Grass Summary for Subcatchment 3S: East Existing Runoff = 0.02 cfs @ 12.31 hrs, Volume= 0.004 af, Depth= 0.52" Routed to Reach 3R : Grass Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 25 yr 24 hr Rainfall=5.88" Type III 24-hr 25 yr 24 hr Rainfall=5.88"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 23HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Area (sf) CN Description 3,031 30 Brush, Good, HSG A 1,132 72 Dirt roads, HSG A 4,163 41 Weighted Average 4,163 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement/grass Summary for Subcatchment 4S: Northwest Proposed Runoff = 0.27 cfs @ 12.08 hrs, Volume= 0.021 af, Depth= 5.18" Routed to Pond 1P : CB1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 25 yr 24 hr Rainfall=5.88" Area (sf) CN Description 63 39 >75% Grass cover, Good, HSG A 226 76 Gravel roads, HSG A 1,806 98 Paved parking, HSG A 2,095 94 Weighted Average 289 13.79% Pervious Area 1,806 86.21% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 5S: Southwest Proposed Runoff = 0.40 cfs @ 12.08 hrs, Volume= 0.031 af, Depth= 5.29" Routed to Pond 2P : CB2 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 25 yr 24 hr Rainfall=5.88" Area (sf) CN Description 468 76 Gravel roads, HSG A 2,635 98 Paved parking, HSG A 3,103 95 Weighted Average 468 15.08% Pervious Area 2,635 84.92% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Type III 24-hr 25 yr 24 hr Rainfall=5.88"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 24HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 6S: South Proposed Runoff = 0.00 cfs @ 12.36 hrs, Volume= 0.001 af, Depth= 0.41" Routed to Reach 5R : Rte 28 Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 25 yr 24 hr Rainfall=5.88" Area (sf) CN Description 1,279 39 >75% Grass cover, Good, HSG A 1,279 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Subcatchment 7S: East Proposed Runoff = 0.01 cfs @ 12.36 hrs, Volume= 0.002 af, Depth= 0.41" Routed to Reach 7R : Grass Area Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 25 yr 24 hr Rainfall=5.88" Area (sf) CN Description 2,967 39 >75% Grass cover, Good, HSG A 2,967 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Reach 1R: Low Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.044 ac, 62.47% Impervious, Inflow Depth = 4.51" for 25 yr 24 hr event Inflow = 0.22 cfs @ 12.09 hrs, Volume= 0.017 af Outflow = 0.22 cfs @ 12.09 hrs, Volume= 0.017 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 2R: Rte 28 Existing [40] Hint: Not Described (Outflow=Inflow) Type III 24-hr 25 yr 24 hr Rainfall=5.88"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 25HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Inflow Area = 0.077 ac, 37.09% Impervious, Inflow Depth = 2.62" for 25 yr 24 hr event Inflow = 0.23 cfs @ 12.09 hrs, Volume= 0.017 af Outflow = 0.23 cfs @ 12.09 hrs, Volume= 0.017 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 3R: Grass Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.096 ac, 0.00% Impervious, Inflow Depth = 0.52" for 25 yr 24 hr event Inflow = 0.02 cfs @ 12.31 hrs, Volume= 0.004 af Outflow = 0.02 cfs @ 12.31 hrs, Volume= 0.004 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 4R: Existing Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 25.89% Impervious, Inflow Depth = 2.08" for 25 yr 24 hr event Inflow = 0.47 cfs @ 12.09 hrs, Volume= 0.038 af Outflow = 0.47 cfs @ 12.09 hrs, Volume= 0.038 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 5R: Rte 28 Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.149 ac, 68.57% Impervious, Inflow Depth = 0.08" for 25 yr 24 hr event Inflow = 0.00 cfs @ 12.36 hrs, Volume= 0.001 af Outflow = 0.00 cfs @ 12.36 hrs, Volume= 0.001 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 7R: Grass Area Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.068 ac, 0.00% Impervious, Inflow Depth = 0.41" for 25 yr 24 hr event Inflow = 0.01 cfs @ 12.36 hrs, Volume= 0.002 af Outflow = 0.01 cfs @ 12.36 hrs, Volume= 0.002 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Type III 24-hr 25 yr 24 hr Rainfall=5.88"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 26HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 8R: Proposed Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 47.02% Impervious, Inflow Depth = 0.19" for 25 yr 24 hr event Inflow = 0.02 cfs @ 12.36 hrs, Volume= 0.003 af Outflow = 0.02 cfs @ 12.36 hrs, Volume= 0.003 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Pond 1P: CB1 Inflow Area = 0.048 ac, 86.21% Impervious, Inflow Depth = 5.18" for 25 yr 24 hr event Inflow = 0.27 cfs @ 12.08 hrs, Volume= 0.021 af Outflow = 0.27 cfs @ 12.08 hrs, Volume= 0.021 af, Atten= 0%, Lag= 0.0 min Primary = 0.27 cfs @ 12.08 hrs, Volume= 0.021 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 7.54' @ 12.08 hrs Flood Elev= 10.50' Device Routing Invert Outlet Devices #1 Primary 7.25'12.0" Round Culvert L= 30.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 7.25' / 7.05' S= 0.0066 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.27 cfs @ 12.08 hrs HW=7.54' TW=6.60' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.27 cfs @ 2.14 fps) Summary for Pond 2P: CB2 Inflow Area = 0.071 ac, 84.92% Impervious, Inflow Depth = 5.29" for 25 yr 24 hr event Inflow = 0.40 cfs @ 12.08 hrs, Volume= 0.031 af Outflow = 0.40 cfs @ 12.08 hrs, Volume= 0.031 af, Atten= 0%, Lag= 0.0 min Primary = 0.40 cfs @ 12.08 hrs, Volume= 0.031 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.84' @ 12.09 hrs Flood Elev= 9.67' Device Routing Invert Outlet Devices #1 Primary 6.42'12.0" Round Culvert L= 56.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.42' / 6.14' S= 0.0050 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Type III 24-hr 25 yr 24 hr Rainfall=5.88"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 27HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Primary OutFlow Max=0.39 cfs @ 12.08 hrs HW=6.83' TW=6.60' (Dynamic Tailwater) 1=Culvert (Outlet Controls 0.39 cfs @ 1.88 fps) Summary for Pond 3P: Proprietary Separator Device Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 5.25" for 25 yr 24 hr event Inflow = 0.67 cfs @ 12.08 hrs, Volume= 0.052 af Outflow = 0.67 cfs @ 12.08 hrs, Volume= 0.052 af, Atten= 0%, Lag= 0.0 min Primary = 0.67 cfs @ 12.08 hrs, Volume= 0.052 af Routed to Pond 4P : Concrete Module Subsurface System Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.60' @ 12.08 hrs Flood Elev= 11.70' Device Routing Invert Outlet Devices #1 Primary 6.09'12.0" Round Culvert L= 7.7' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.09' / 6.05' S= 0.0052 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.67 cfs @ 12.08 hrs HW=6.60' TW=5.24' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.67 cfs @ 2.43 fps) Summary for Pond 4P: Concrete Module Subsurface System Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 5.25" for 25 yr 24 hr event Inflow = 0.67 cfs @ 12.08 hrs, Volume= 0.052 af Outflow = 0.13 cfs @ 12.51 hrs, Volume= 0.052 af, Atten= 80%, Lag= 25.5 min Discarded = 0.13 cfs @ 12.51 hrs, Volume= 0.052 af Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Routed to Pond 5P : DMH1 Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 5.91' @ 12.51 hrs Surf.Area= 448 sf Storage= 604 cf Flood Elev= 8.50' Storage= 1,496 cf Plug-Flow detention time= 28.2 min calculated for 0.052 af (100% of inflow) Center-of-Mass det. time= 28.2 min ( 794.2 - 766.1 ) Volume Invert Avail.Storage Storage Description #1 4.50' 1,496 cf retain_it retain_it 3.5' x 8 Inside= 84.0"W x 42.0"H => 25.10 sf x 8.00'L = 200.8 cf Outside= 96.0"W x 50.0"H => 33.33 sf x 8.00'L = 266.7 cf 1 Rows adjusted for 110.5 cf perimeter wall Device Routing Invert Outlet Devices #1 Primary 5.95'12.0" Round Culvert L= 26.3' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.95' / 5.80' S= 0.0057 '/' Cc= 0.900 Type III 24-hr 25 yr 24 hr Rainfall=5.88"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 28HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC n= 0.013, Flow Area= 0.79 sf #2 Discarded 4.50'8.270 in/hr Exfiltration over Surface area Conductivity to Groundwater Elevation = 2.00' Phase-In= 0.01' Discarded OutFlow Max=0.13 cfs @ 12.51 hrs HW=5.91' (Free Discharge) 2=Exfiltration ( Controls 0.13 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=4.50' TW=5.70' (Dynamic Tailwater) 1=Culvert ( Controls 0.00 cfs) Summary for Pond 5P: DMH1 Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 0.00" for 25 yr 24 hr event Inflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Outflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 0%, Lag= 0.0 min Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af Routed to Reach 5R : Rte 28 Proposed Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 5.70' @ 0.00 hrs Flood Elev= 11.00' Device Routing Invert Outlet Devices #1 Primary 5.70'12.0" Round Culvert L= 17.0' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.70' / 5.60' S= 0.0059 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=5.70' TW=0.00' (Dynamic Tailwater) 1=Culvert ( Controls 0.00 cfs) Type III 24-hr 50 yr 24 hr Rainfall=6.62"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 29HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1,916 sf 62.47% Impervious Runoff Depth=5.22"Subcatchment 1S: Northwest Existing Tc=6.0 min CN=88 Runoff=0.26 cfs 0.019 af Runoff Area=3,365 sf 37.09% Impervious Runoff Depth=3.20"Subcatchment 2S: Southwest Existing Tc=6.0 min CN=69 Runoff=0.29 cfs 0.021 af Runoff Area=4,163 sf 0.00% Impervious Runoff Depth=0.77"Subcatchment 3S: East Existing Tc=6.0 min CN=41 Runoff=0.04 cfs 0.006 af Runoff Area=2,095 sf 86.21% Impervious Runoff Depth=5.91"Subcatchment 4S: Northwest Proposed Tc=6.0 min CN=94 Runoff=0.30 cfs 0.024 af Runoff Area=3,103 sf 84.92% Impervious Runoff Depth=6.03"Subcatchment 5S: Southwest Proposed Tc=6.0 min CN=95 Runoff=0.45 cfs 0.036 af Runoff Area=1,279 sf 0.00% Impervious Runoff Depth=0.64"Subcatchment 6S: South Proposed Tc=6.0 min CN=39 Runoff=0.01 cfs 0.002 af Runoff Area=2,967 sf 0.00% Impervious Runoff Depth=0.64"Subcatchment 7S: East Proposed Tc=6.0 min CN=39 Runoff=0.02 cfs 0.004 af Inflow=0.26 cfs 0.019 afReach 1R: Low Area Existing Outflow=0.26 cfs 0.019 af Inflow=0.29 cfs 0.021 afReach 2R: Rte 28 Existing Outflow=0.29 cfs 0.021 af Inflow=0.04 cfs 0.006 afReach 3R: Grass Area Existing Outflow=0.04 cfs 0.006 af Inflow=0.58 cfs 0.046 afReach 4R: Existing Flow Sum Outflow=0.58 cfs 0.046 af Inflow=0.07 cfs 0.003 afReach 5R: Rte 28 Proposed Outflow=0.07 cfs 0.003 af Inflow=0.02 cfs 0.004 afReach 7R: Grass Area Proposed Outflow=0.02 cfs 0.004 af Inflow=0.09 cfs 0.007 afReach 8R: Proposed Flow Sum Outflow=0.09 cfs 0.007 af Peak Elev=7.56' Inflow=0.30 cfs 0.024 afPond 1P: CB1 12.0" Round Culvert n=0.013 L=30.5' S=0.0066 '/' Outflow=0.30 cfs 0.024 af Peak Elev=6.87' Inflow=0.45 cfs 0.036 afPond 2P: CB2 12.0" Round Culvert n=0.013 L=56.5' S=0.0050 '/' Outflow=0.45 cfs 0.036 af Type III 24-hr 50 yr 24 hr Rainfall=6.62"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 30HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Peak Elev=6.63' Inflow=0.76 cfs 0.059 afPond 3P: Proprietary Separator Device 12.0" Round Culvert n=0.013 L=7.7' S=0.0052 '/' Outflow=0.76 cfs 0.059 af Peak Elev=6.10' Storage=683 cf Inflow=0.76 cfs 0.059 afPond 4P: Concrete Module Subsurface System Discarded=0.14 cfs 0.058 af Primary=0.07 cfs 0.001 af Outflow=0.21 cfs 0.059 af Peak Elev=5.85' Inflow=0.07 cfs 0.001 afPond 5P: DMH1 12.0" Round Culvert n=0.013 L=17.0' S=0.0059 '/' Outflow=0.07 cfs 0.001 af Total Runoff Area = 0.434 ac Runoff Volume = 0.111 af Average Runoff Depth = 3.06" 63.54% Pervious = 0.276 ac 36.46% Impervious = 0.158 ac Type III 24-hr 50 yr 24 hr Rainfall=6.62"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 31HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 1S: Northwest Existing Runoff = 0.26 cfs @ 12.08 hrs, Volume= 0.019 af, Depth= 5.22" Routed to Reach 1R : Low Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 50 yr 24 hr Rainfall=6.62" Area (sf) CN Description 719 72 Dirt roads, HSG A 1,197 98 Paved parking, HSG A 1,916 88 Weighted Average 719 37.53% Pervious Area 1,197 62.47% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 2S: Southwest Existing Runoff = 0.29 cfs @ 12.09 hrs, Volume= 0.021 af, Depth= 3.20" Routed to Reach 2R : Rte 28 Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 50 yr 24 hr Rainfall=6.62" Area (sf) CN Description 1,309 39 >75% Grass cover, Good, HSG A 808 72 Dirt roads, HSG A 1,248 98 Paved parking, HSG A 3,365 69 Weighted Average 2,117 62.91% Pervious Area 1,248 37.09% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Grass Summary for Subcatchment 3S: East Existing Runoff = 0.04 cfs @ 12.14 hrs, Volume= 0.006 af, Depth= 0.77" Routed to Reach 3R : Grass Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 50 yr 24 hr Rainfall=6.62" Type III 24-hr 50 yr 24 hr Rainfall=6.62"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 32HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Area (sf) CN Description 3,031 30 Brush, Good, HSG A 1,132 72 Dirt roads, HSG A 4,163 41 Weighted Average 4,163 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement/grass Summary for Subcatchment 4S: Northwest Proposed Runoff = 0.30 cfs @ 12.08 hrs, Volume= 0.024 af, Depth= 5.91" Routed to Pond 1P : CB1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 50 yr 24 hr Rainfall=6.62" Area (sf) CN Description 63 39 >75% Grass cover, Good, HSG A 226 76 Gravel roads, HSG A 1,806 98 Paved parking, HSG A 2,095 94 Weighted Average 289 13.79% Pervious Area 1,806 86.21% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 5S: Southwest Proposed Runoff = 0.45 cfs @ 12.08 hrs, Volume= 0.036 af, Depth= 6.03" Routed to Pond 2P : CB2 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 50 yr 24 hr Rainfall=6.62" Area (sf) CN Description 468 76 Gravel roads, HSG A 2,635 98 Paved parking, HSG A 3,103 95 Weighted Average 468 15.08% Pervious Area 2,635 84.92% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Type III 24-hr 50 yr 24 hr Rainfall=6.62"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 33HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 6S: South Proposed Runoff = 0.01 cfs @ 12.28 hrs, Volume= 0.002 af, Depth= 0.64" Routed to Reach 5R : Rte 28 Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 50 yr 24 hr Rainfall=6.62" Area (sf) CN Description 1,279 39 >75% Grass cover, Good, HSG A 1,279 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Subcatchment 7S: East Proposed Runoff = 0.02 cfs @ 12.28 hrs, Volume= 0.004 af, Depth= 0.64" Routed to Reach 7R : Grass Area Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 50 yr 24 hr Rainfall=6.62" Area (sf) CN Description 2,967 39 >75% Grass cover, Good, HSG A 2,967 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Reach 1R: Low Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.044 ac, 62.47% Impervious, Inflow Depth = 5.22" for 50 yr 24 hr event Inflow = 0.26 cfs @ 12.08 hrs, Volume= 0.019 af Outflow = 0.26 cfs @ 12.08 hrs, Volume= 0.019 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 2R: Rte 28 Existing [40] Hint: Not Described (Outflow=Inflow) Type III 24-hr 50 yr 24 hr Rainfall=6.62"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 34HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Inflow Area = 0.077 ac, 37.09% Impervious, Inflow Depth = 3.20" for 50 yr 24 hr event Inflow = 0.29 cfs @ 12.09 hrs, Volume= 0.021 af Outflow = 0.29 cfs @ 12.09 hrs, Volume= 0.021 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 3R: Grass Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.096 ac, 0.00% Impervious, Inflow Depth = 0.77" for 50 yr 24 hr event Inflow = 0.04 cfs @ 12.14 hrs, Volume= 0.006 af Outflow = 0.04 cfs @ 12.14 hrs, Volume= 0.006 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 4R: Existing Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 25.89% Impervious, Inflow Depth = 2.54" for 50 yr 24 hr event Inflow = 0.58 cfs @ 12.09 hrs, Volume= 0.046 af Outflow = 0.58 cfs @ 12.09 hrs, Volume= 0.046 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 5R: Rte 28 Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.149 ac, 68.57% Impervious, Inflow Depth = 0.24" for 50 yr 24 hr event Inflow = 0.07 cfs @ 12.43 hrs, Volume= 0.003 af Outflow = 0.07 cfs @ 12.43 hrs, Volume= 0.003 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 7R: Grass Area Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.068 ac, 0.00% Impervious, Inflow Depth = 0.64" for 50 yr 24 hr event Inflow = 0.02 cfs @ 12.28 hrs, Volume= 0.004 af Outflow = 0.02 cfs @ 12.28 hrs, Volume= 0.004 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Type III 24-hr 50 yr 24 hr Rainfall=6.62"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 35HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 8R: Proposed Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 47.02% Impervious, Inflow Depth = 0.36" for 50 yr 24 hr event Inflow = 0.09 cfs @ 12.42 hrs, Volume= 0.007 af Outflow = 0.09 cfs @ 12.42 hrs, Volume= 0.007 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Pond 1P: CB1 Inflow Area = 0.048 ac, 86.21% Impervious, Inflow Depth = 5.91" for 50 yr 24 hr event Inflow = 0.30 cfs @ 12.08 hrs, Volume= 0.024 af Outflow = 0.30 cfs @ 12.08 hrs, Volume= 0.024 af, Atten= 0%, Lag= 0.0 min Primary = 0.30 cfs @ 12.08 hrs, Volume= 0.024 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 7.56' @ 12.08 hrs Flood Elev= 10.50' Device Routing Invert Outlet Devices #1 Primary 7.25'12.0" Round Culvert L= 30.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 7.25' / 7.05' S= 0.0066 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.30 cfs @ 12.08 hrs HW=7.56' TW=6.63' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.30 cfs @ 2.21 fps) Summary for Pond 2P: CB2 Inflow Area = 0.071 ac, 84.92% Impervious, Inflow Depth = 6.03" for 50 yr 24 hr event Inflow = 0.45 cfs @ 12.08 hrs, Volume= 0.036 af Outflow = 0.45 cfs @ 12.08 hrs, Volume= 0.036 af, Atten= 0%, Lag= 0.0 min Primary = 0.45 cfs @ 12.08 hrs, Volume= 0.036 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.87' @ 12.09 hrs Flood Elev= 9.67' Device Routing Invert Outlet Devices #1 Primary 6.42'12.0" Round Culvert L= 56.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.42' / 6.14' S= 0.0050 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Type III 24-hr 50 yr 24 hr Rainfall=6.62"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 36HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Primary OutFlow Max=0.44 cfs @ 12.08 hrs HW=6.87' TW=6.63' (Dynamic Tailwater) 1=Culvert (Outlet Controls 0.44 cfs @ 1.92 fps) Summary for Pond 3P: Proprietary Separator Device Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 5.98" for 50 yr 24 hr event Inflow = 0.76 cfs @ 12.08 hrs, Volume= 0.059 af Outflow = 0.76 cfs @ 12.08 hrs, Volume= 0.059 af, Atten= 0%, Lag= 0.0 min Primary = 0.76 cfs @ 12.08 hrs, Volume= 0.059 af Routed to Pond 4P : Concrete Module Subsurface System Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.63' @ 12.08 hrs Flood Elev= 11.70' Device Routing Invert Outlet Devices #1 Primary 6.09'12.0" Round Culvert L= 7.7' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.09' / 6.05' S= 0.0052 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.75 cfs @ 12.08 hrs HW=6.63' TW=5.38' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.75 cfs @ 2.51 fps) Summary for Pond 4P: Concrete Module Subsurface System Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 5.98" for 50 yr 24 hr event Inflow = 0.76 cfs @ 12.08 hrs, Volume= 0.059 af Outflow = 0.21 cfs @ 12.43 hrs, Volume= 0.059 af, Atten= 73%, Lag= 20.7 min Discarded = 0.14 cfs @ 12.43 hrs, Volume= 0.058 af Primary = 0.07 cfs @ 12.43 hrs, Volume= 0.001 af Routed to Pond 5P : DMH1 Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.10' @ 12.43 hrs Surf.Area= 448 sf Storage= 683 cf Flood Elev= 8.50' Storage= 1,496 cf Plug-Flow detention time= 29.8 min calculated for 0.059 af (100% of inflow) Center-of-Mass det. time= 29.8 min ( 793.0 - 763.2 ) Volume Invert Avail.Storage Storage Description #1 4.50' 1,496 cf retain_it retain_it 3.5' x 8 Inside= 84.0"W x 42.0"H => 25.10 sf x 8.00'L = 200.8 cf Outside= 96.0"W x 50.0"H => 33.33 sf x 8.00'L = 266.7 cf 1 Rows adjusted for 110.5 cf perimeter wall Device Routing Invert Outlet Devices #1 Primary 5.95'12.0" Round Culvert L= 26.3' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.95' / 5.80' S= 0.0057 '/' Cc= 0.900 Type III 24-hr 50 yr 24 hr Rainfall=6.62"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 37HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC n= 0.013, Flow Area= 0.79 sf #2 Discarded 4.50'8.270 in/hr Exfiltration over Surface area Conductivity to Groundwater Elevation = 2.00' Phase-In= 0.01' Discarded OutFlow Max=0.14 cfs @ 12.43 hrs HW=6.10' (Free Discharge) 2=Exfiltration ( Controls 0.14 cfs) Primary OutFlow Max=0.07 cfs @ 12.43 hrs HW=6.10' TW=5.85' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.07 cfs @ 1.41 fps) Summary for Pond 5P: DMH1 Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 0.14" for 50 yr 24 hr event Inflow = 0.07 cfs @ 12.43 hrs, Volume= 0.001 af Outflow = 0.07 cfs @ 12.43 hrs, Volume= 0.001 af, Atten= 0%, Lag= 0.0 min Primary = 0.07 cfs @ 12.43 hrs, Volume= 0.001 af Routed to Reach 5R : Rte 28 Proposed Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 5.85' @ 12.43 hrs Flood Elev= 11.00' Device Routing Invert Outlet Devices #1 Primary 5.70'12.0" Round Culvert L= 17.0' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.70' / 5.60' S= 0.0059 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.07 cfs @ 12.43 hrs HW=5.85' TW=0.00' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.07 cfs @ 1.41 fps) Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 38HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1,916 sf 62.47% Impervious Runoff Depth=5.95"Subcatchment 1S: Northwest Existing Tc=6.0 min CN=88 Runoff=0.29 cfs 0.022 af Runoff Area=3,365 sf 37.09% Impervious Runoff Depth=3.82"Subcatchment 2S: Southwest Existing Tc=6.0 min CN=69 Runoff=0.35 cfs 0.025 af Runoff Area=4,163 sf 0.00% Impervious Runoff Depth=1.07"Subcatchment 3S: East Existing Tc=6.0 min CN=41 Runoff=0.08 cfs 0.009 af Runoff Area=2,095 sf 86.21% Impervious Runoff Depth=6.66"Subcatchment 4S: Northwest Proposed Tc=6.0 min CN=94 Runoff=0.34 cfs 0.027 af Runoff Area=3,103 sf 84.92% Impervious Runoff Depth=6.77"Subcatchment 5S: Southwest Proposed Tc=6.0 min CN=95 Runoff=0.51 cfs 0.040 af Runoff Area=1,279 sf 0.00% Impervious Runoff Depth=0.90"Subcatchment 6S: South Proposed Tc=6.0 min CN=39 Runoff=0.02 cfs 0.002 af Runoff Area=2,967 sf 0.00% Impervious Runoff Depth=0.90"Subcatchment 7S: East Proposed Tc=6.0 min CN=39 Runoff=0.04 cfs 0.005 af Inflow=0.29 cfs 0.022 afReach 1R: Low Area Existing Outflow=0.29 cfs 0.022 af Inflow=0.35 cfs 0.025 afReach 2R: Rte 28 Existing Outflow=0.35 cfs 0.025 af Inflow=0.08 cfs 0.009 afReach 3R: Grass Area Existing Outflow=0.08 cfs 0.009 af Inflow=0.71 cfs 0.055 afReach 4R: Existing Flow Sum Outflow=0.71 cfs 0.055 af Inflow=0.18 cfs 0.006 afReach 5R: Rte 28 Proposed Outflow=0.18 cfs 0.006 af Inflow=0.04 cfs 0.005 afReach 7R: Grass Area Proposed Outflow=0.04 cfs 0.005 af Inflow=0.21 cfs 0.012 afReach 8R: Proposed Flow Sum Outflow=0.21 cfs 0.012 af Peak Elev=7.58' Inflow=0.34 cfs 0.027 afPond 1P: CB1 12.0" Round Culvert n=0.013 L=30.5' S=0.0066 '/' Outflow=0.34 cfs 0.027 af Peak Elev=6.90' Inflow=0.51 cfs 0.040 afPond 2P: CB2 12.0" Round Culvert n=0.013 L=56.5' S=0.0050 '/' Outflow=0.51 cfs 0.040 af Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 39HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Peak Elev=6.67' Inflow=0.85 cfs 0.067 afPond 3P: Proprietary Separator Device 12.0" Round Culvert n=0.013 L=7.7' S=0.0052 '/' Outflow=0.85 cfs 0.067 af Peak Elev=6.18' Storage=719 cf Inflow=0.85 cfs 0.067 afPond 4P: Concrete Module Subsurface System Discarded=0.14 cfs 0.063 af Primary=0.17 cfs 0.004 af Outflow=0.31 cfs 0.067 af Peak Elev=5.93' Inflow=0.17 cfs 0.004 afPond 5P: DMH1 12.0" Round Culvert n=0.013 L=17.0' S=0.0059 '/' Outflow=0.17 cfs 0.004 af Total Runoff Area = 0.434 ac Runoff Volume = 0.129 af Average Runoff Depth = 3.57" 63.54% Pervious = 0.276 ac 36.46% Impervious = 0.158 ac Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 40HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 1S: Northwest Existing Runoff = 0.29 cfs @ 12.08 hrs, Volume= 0.022 af, Depth= 5.95" Routed to Reach 1R : Low Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 100 yr 24 hr Rainfall=7.37" Area (sf) CN Description 719 72 Dirt roads, HSG A 1,197 98 Paved parking, HSG A 1,916 88 Weighted Average 719 37.53% Pervious Area 1,197 62.47% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 2S: Southwest Existing Runoff = 0.35 cfs @ 12.09 hrs, Volume= 0.025 af, Depth= 3.82" Routed to Reach 2R : Rte 28 Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 100 yr 24 hr Rainfall=7.37" Area (sf) CN Description 1,309 39 >75% Grass cover, Good, HSG A 808 72 Dirt roads, HSG A 1,248 98 Paved parking, HSG A 3,365 69 Weighted Average 2,117 62.91% Pervious Area 1,248 37.09% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Grass Summary for Subcatchment 3S: East Existing Runoff = 0.08 cfs @ 12.12 hrs, Volume= 0.009 af, Depth= 1.07" Routed to Reach 3R : Grass Area Existing Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 100 yr 24 hr Rainfall=7.37" Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 41HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Area (sf) CN Description 3,031 30 Brush, Good, HSG A 1,132 72 Dirt roads, HSG A 4,163 41 Weighted Average 4,163 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement/grass Summary for Subcatchment 4S: Northwest Proposed Runoff = 0.34 cfs @ 12.08 hrs, Volume= 0.027 af, Depth= 6.66" Routed to Pond 1P : CB1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 100 yr 24 hr Rainfall=7.37" Area (sf) CN Description 63 39 >75% Grass cover, Good, HSG A 226 76 Gravel roads, HSG A 1,806 98 Paved parking, HSG A 2,095 94 Weighted Average 289 13.79% Pervious Area 1,806 86.21% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Pavement Summary for Subcatchment 5S: Southwest Proposed Runoff = 0.51 cfs @ 12.08 hrs, Volume= 0.040 af, Depth= 6.77" Routed to Pond 2P : CB2 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 100 yr 24 hr Rainfall=7.37" Area (sf) CN Description 468 76 Gravel roads, HSG A 2,635 98 Paved parking, HSG A 3,103 95 Weighted Average 468 15.08% Pervious Area 2,635 84.92% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 42HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment 6S: South Proposed Runoff = 0.02 cfs @ 12.13 hrs, Volume= 0.002 af, Depth= 0.90" Routed to Reach 5R : Rte 28 Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 100 yr 24 hr Rainfall=7.37" Area (sf) CN Description 1,279 39 >75% Grass cover, Good, HSG A 1,279 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Subcatchment 7S: East Proposed Runoff = 0.04 cfs @ 12.13 hrs, Volume= 0.005 af, Depth= 0.90" Routed to Reach 7R : Grass Area Proposed Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 100 yr 24 hr Rainfall=7.37" Area (sf) CN Description 2,967 39 >75% Grass cover, Good, HSG A 2,967 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 Direct Entry, Gravel/grass Summary for Reach 1R: Low Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.044 ac, 62.47% Impervious, Inflow Depth = 5.95" for 100 yr 24 hr event Inflow = 0.29 cfs @ 12.08 hrs, Volume= 0.022 af Outflow = 0.29 cfs @ 12.08 hrs, Volume= 0.022 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 2R: Rte 28 Existing [40] Hint: Not Described (Outflow=Inflow) Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 43HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Inflow Area = 0.077 ac, 37.09% Impervious, Inflow Depth = 3.82" for 100 yr 24 hr event Inflow = 0.35 cfs @ 12.09 hrs, Volume= 0.025 af Outflow = 0.35 cfs @ 12.09 hrs, Volume= 0.025 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 3R: Grass Area Existing [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.096 ac, 0.00% Impervious, Inflow Depth = 1.07" for 100 yr 24 hr event Inflow = 0.08 cfs @ 12.12 hrs, Volume= 0.009 af Outflow = 0.08 cfs @ 12.12 hrs, Volume= 0.009 af, Atten= 0%, Lag= 0.0 min Routed to Reach 4R : Existing Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 4R: Existing Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 25.89% Impervious, Inflow Depth = 3.04" for 100 yr 24 hr event Inflow = 0.71 cfs @ 12.09 hrs, Volume= 0.055 af Outflow = 0.71 cfs @ 12.09 hrs, Volume= 0.055 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 5R: Rte 28 Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.149 ac, 68.57% Impervious, Inflow Depth = 0.52" for 100 yr 24 hr event Inflow = 0.18 cfs @ 12.33 hrs, Volume= 0.006 af Outflow = 0.18 cfs @ 12.33 hrs, Volume= 0.006 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 7R: Grass Area Proposed [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.068 ac, 0.00% Impervious, Inflow Depth = 0.90" for 100 yr 24 hr event Inflow = 0.04 cfs @ 12.13 hrs, Volume= 0.005 af Outflow = 0.04 cfs @ 12.13 hrs, Volume= 0.005 af, Atten= 0%, Lag= 0.0 min Routed to Reach 8R : Proposed Flow Sum Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 44HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Reach 8R: Proposed Flow Sum [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 0.217 ac, 47.02% Impervious, Inflow Depth = 0.64" for 100 yr 24 hr event Inflow = 0.21 cfs @ 12.33 hrs, Volume= 0.012 af Outflow = 0.21 cfs @ 12.33 hrs, Volume= 0.012 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Summary for Pond 1P: CB1 Inflow Area = 0.048 ac, 86.21% Impervious, Inflow Depth = 6.66" for 100 yr 24 hr event Inflow = 0.34 cfs @ 12.08 hrs, Volume= 0.027 af Outflow = 0.34 cfs @ 12.08 hrs, Volume= 0.027 af, Atten= 0%, Lag= 0.0 min Primary = 0.34 cfs @ 12.08 hrs, Volume= 0.027 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 7.58' @ 12.08 hrs Flood Elev= 10.50' Device Routing Invert Outlet Devices #1 Primary 7.25'12.0" Round Culvert L= 30.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 7.25' / 7.05' S= 0.0066 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.34 cfs @ 12.08 hrs HW=7.58' TW=6.67' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.34 cfs @ 2.28 fps) Summary for Pond 2P: CB2 Inflow Area = 0.071 ac, 84.92% Impervious, Inflow Depth = 6.77" for 100 yr 24 hr event Inflow = 0.51 cfs @ 12.08 hrs, Volume= 0.040 af Outflow = 0.51 cfs @ 12.08 hrs, Volume= 0.040 af, Atten= 0%, Lag= 0.0 min Primary = 0.51 cfs @ 12.08 hrs, Volume= 0.040 af Routed to Pond 3P : Proprietary Separator Device Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.90' @ 12.09 hrs Flood Elev= 9.67' Device Routing Invert Outlet Devices #1 Primary 6.42'12.0" Round Culvert L= 56.5' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.42' / 6.14' S= 0.0050 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 45HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Primary OutFlow Max=0.49 cfs @ 12.08 hrs HW=6.90' TW=6.67' (Dynamic Tailwater) 1=Culvert (Outlet Controls 0.49 cfs @ 1.95 fps) Summary for Pond 3P: Proprietary Separator Device Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 6.73" for 100 yr 24 hr event Inflow = 0.85 cfs @ 12.08 hrs, Volume= 0.067 af Outflow = 0.85 cfs @ 12.08 hrs, Volume= 0.067 af, Atten= 0%, Lag= 0.0 min Primary = 0.85 cfs @ 12.08 hrs, Volume= 0.067 af Routed to Pond 4P : Concrete Module Subsurface System Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.67' @ 12.08 hrs Flood Elev= 11.70' Device Routing Invert Outlet Devices #1 Primary 6.09'12.0" Round Culvert L= 7.7' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 6.09' / 6.05' S= 0.0052 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.84 cfs @ 12.08 hrs HW=6.67' TW=5.53' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.84 cfs @ 2.59 fps) Summary for Pond 4P: Concrete Module Subsurface System Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 6.73" for 100 yr 24 hr event Inflow = 0.85 cfs @ 12.08 hrs, Volume= 0.067 af Outflow = 0.31 cfs @ 12.33 hrs, Volume= 0.067 af, Atten= 63%, Lag= 14.8 min Discarded = 0.14 cfs @ 12.33 hrs, Volume= 0.063 af Primary = 0.17 cfs @ 12.33 hrs, Volume= 0.004 af Routed to Pond 5P : DMH1 Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 6.18' @ 12.33 hrs Surf.Area= 448 sf Storage= 719 cf Flood Elev= 8.50' Storage= 1,496 cf Plug-Flow detention time= 29.0 min calculated for 0.067 af (100% of inflow) Center-of-Mass det. time= 29.0 min ( 789.6 - 760.6 ) Volume Invert Avail.Storage Storage Description #1 4.50' 1,496 cf retain_it retain_it 3.5' x 8 Inside= 84.0"W x 42.0"H => 25.10 sf x 8.00'L = 200.8 cf Outside= 96.0"W x 50.0"H => 33.33 sf x 8.00'L = 266.7 cf 1 Rows adjusted for 110.5 cf perimeter wall Device Routing Invert Outlet Devices #1 Primary 5.95'12.0" Round Culvert L= 26.3' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.95' / 5.80' S= 0.0057 '/' Cc= 0.900 Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/27/2025Prepared by CDM Smith Page 46HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC n= 0.013, Flow Area= 0.79 sf #2 Discarded 4.50'8.270 in/hr Exfiltration over Surface area Conductivity to Groundwater Elevation = 2.00' Phase-In= 0.01' Discarded OutFlow Max=0.14 cfs @ 12.33 hrs HW=6.18' (Free Discharge) 2=Exfiltration ( Controls 0.14 cfs) Primary OutFlow Max=0.17 cfs @ 12.33 hrs HW=6.18' TW=5.93' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.17 cfs @ 1.81 fps) Summary for Pond 5P: DMH1 Inflow Area = 0.119 ac, 85.44% Impervious, Inflow Depth = 0.42" for 100 yr 24 hr event Inflow = 0.17 cfs @ 12.33 hrs, Volume= 0.004 af Outflow = 0.17 cfs @ 12.33 hrs, Volume= 0.004 af, Atten= 0%, Lag= 0.0 min Primary = 0.17 cfs @ 12.33 hrs, Volume= 0.004 af Routed to Reach 5R : Rte 28 Proposed Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 5.93' @ 12.33 hrs Flood Elev= 11.00' Device Routing Invert Outlet Devices #1 Primary 5.70'12.0" Round Culvert L= 17.0' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 5.70' / 5.60' S= 0.0059 '/' Cc= 0.900 n= 0.013, Flow Area= 0.79 sf Primary OutFlow Max=0.17 cfs @ 12.33 hrs HW=5.93' TW=0.00' (Dynamic Tailwater) 1=Culvert (Barrel Controls 0.17 cfs @ 1.80 fps) Appendix D Recharge Volume and Water Quality Volume Calculations Pumping Station 2 WQv and Rv Calculations Water Quality Volume - Overall Recharge Volume - Overall Impervious Area: 4,441 sf Impervious Area: 4,441 sf WQV Target: 1.0 in Rv Target: 0.60 in WQv Required:370 cf Rv Required:222 cf WQv Required:0.008 af Rv Required:0.005 af Water Quality Volume -Subsurface Infiltration System Recharge Volume - Subsurface Infiltration System Impervious Area: 4,441 sf Impervious Area: 4,441 sf WQV Target: 1.0 in Rv Target: 0.60 in WQv Required:370 cf Rv Required:222 cf WQv Required:0.008 af Rv Required:0.005 af Total Volume Provided:620 cf Total Volume Provided:620 cf Drawdown Time - Bioretention Area 8.27 in/hr infiltration rate 448 sf, bottom area 620 cf, total volume provided 2 hours <72 hours, ok Type III 24-hr 100 yr 24 hr Rainfall=7.37"2025_10_10 Yarmouth PS2 Printed 10/15/2025Prepared by CDM Smith HydroCAD® 10.20-5c s/n 01469 © 2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond 4P: Concrete Module Subsurface System Elevation (feet) Surface (sq-ft) Storage (cubic-feet) 4.50 448 0 4.55 448 21 4.60 448 43 4.65 448 64 4.70 448 85 4.75 448 107 4.80 448 128 4.85 448 150 4.90 448 171 4.95 448 192 5.00 448 214 5.05 448 235 5.10 448 256 5.15 448 278 5.20 448 299 5.25 448 321 5.30 448 342 5.35 448 363 5.40 448 385 5.45 448 406 5.50 448 427 5.55 448 449 5.60 448 470 5.65 448 491 5.70 448 513 5.75 448 534 5.80 448 556 5.85 448 577 5.90 448 598 5.95 448 620 6.00 448 641 6.05 448 662 6.10 448 684 6.15 448 705 6.20 448 726 6.25 448 748 6.30 448 769 6.35 448 791 6.40 448 812 6.45 448 833 6.50 448 855 6.55 448 876 6.60 448 897 6.65 448 919 6.70 448 940 6.75 448 962 6.80 448 983 6.85 448 1,004 6.90 448 1,026 6.95 448 1,047 7.00 448 1,068 7.05 448 1,090 Elevation (feet) Surface (sq-ft) Storage (cubic-feet) 7.10 448 1,111 7.15 448 1,132 7.20 448 1,154 7.25 448 1,175 7.30 448 1,197 7.35 448 1,218 7.40 448 1,239 7.45 448 1,261 7.50 448 1,282 7.55 448 1,303 7.60 448 1,325 7.65 448 1,346 7.70 448 1,368 7.75 448 1,389 7.80 448 1,410 7.85 448 1,432 7.90 448 1,453 7.95 448 1,474 8.00 0 1,496 8.05 0 1,496 8.10 0 1,496 8.15 0 1,496 8.20 0 1,496 8.25 0 1,496 8.30 0 1,496 8.35 0 1,496 8.40 0 1,496 8.45 0 1,496 8.50 0 1,496 8.55 0 1,496 8.60 0 1,496 8.65 0 1,496 Appendix E TSS Removal Spreadsheet INSTRUCTIONS:Non-automated: Mar. 4, 2008 1. Sheet is nonautomated. Print sheet and complete using hand calculations. Column A and B: See MassDEP Structural BMP Table 2. The calculations must be completed using the Column Headings specified in Chart and Not the Excel Column Headings 3. To complete Chart Column D, multiple Column B value within Row x Column C value within Row 4. To complete Chart Column E value, subtract Column D value within Row from Column C within Row 5. Total TSS Removal = Sum All Values in Column D Location: A B C D E TSS Removal Starting TSS Amount Remaining BMP1 Rate1 Load* Removed (B*C) Load (C-D) 1.00 Total TSS Removal = Separate Form Needs to be Completed for Each Outlet or BMP Train Project: Prepared By:*Equals remaining load from previous BMP (E) Date:which enters the BMP TS S R e m o v a l Ca l c u l a t i o n W o r k s h e e t Non-automated TSS Calculation Sheet must be used if Proprietary BMP Proposed 1. From MassDEP Stormwater Handbook Vol. 1 Mass. Dept. of Environmental Protection INSTRUCTIONS:Non-automated: Mar. 4, 2008 1. Sheet is nonautomated. Print sheet and complete using hand calculations. Column A and B: See MassDEP Structural BMP Table 2. The calculations must be completed using the Column Headings specified in Chart and Not the Excel Column Headings 3. To complete Chart Column D, multiple Column B value within Row x Column C value within Row 4. To complete Chart Column E value, subtract Column D value within Row from Column C within Row 5. Total TSS Removal = Sum All Values in Column D Location: A B C D E TSS Removal Starting TSS Amount Remaining BMP1 Rate1 Load* Removed (B*C) Load (C-D) 1.00 Total TSS Removal = Separate Form Needs to be Completed for Each Outlet or BMP Train Project: Prepared By:*Equals remaining load from previous BMP (E) Date:which enters the BMP TS S R e m o v a l Ca l c u l a t i o n W o r k s h e e t Non-automated TSS Calculation Sheet must be used if Proprietary BMP Proposed 1. From MassDEP Stormwater Handbook Vol. 1 Mass. Dept. of Environmental Protection Appendix F Operation and Maintenance Plan/ Long-Term Pollution Prevention Plan Page | 1 Appendix F - PS2 O_And_M_Ltp Post-Construction Operation and Maintenance Plan Project: Phase 1 – Contract No. 6 - Pumping Station 2 Location: 280 Main Street, West Yarmouth, MA Owner/Responsible Party: Town of Yarmouth Department of Public Works This document describes the operation and maintenance activities for the proposed stormwater management facilities associated with Pumping Station 2. Deep-Sump Hooded Catch Basin Deep-sump hooded catch basins are located in the parking areas and driveway. Maintenance activities include the following: · Inspect the catch basins four times per year for depth of sediment and physical condition of the catch basin. · Clean out the catch basins two times per year, particularly at the end of the foliage and snow removal seasons, or more frequently, if needed. · Repair or replace damaged catch basin hoods. · Dispose of catch basin cleanings at a landfill or other facility permitted by MassDEP to accept solid waste, without any prior approval by MassDEP, unless the sediments are contaminated. Contech CDS Unit · The CDS unit is a proprietary particle separator device located adjacent to the subsurface infiltration system. Routine maintenance should follow manufacturer’s instructions, which are attached. Subsurface Infiltration System The subsurface infiltration system is located within the driveway. Maintenance activities include the following: · During the first year of operation, inspect the chamber after major rainfall events, but at least twice per year to gain an understanding of the sediment buildup in this chamber. The actual frequency of maintenance can be determined after the first year of operation. · Remove accumulated sediment using a vacuum. · Dispose of the sediment at a landfill or other facility permitted by MassDEP to accept solid waste, without any prior approval by MassDEP, unless the sediments are contaminated. · Routine maintenance should follow manufacturer’s instructions, which are attached. Page | 2 Appendix F - PS2 O_And_M_Ltp Stormwater Management Facility Inspection Form Location: Pumping Station 2 280 Main Street, West Yarmouth, MA Inspected By: Inspection Date: BMP Measure Status/Inspection Action Taken Deep Sump Catch Basin CDS Unit Subsurface Infiltration System Page | 3 Appendix F - PS2 O_And_M_Ltp Long-Term Pollution Prevention Plan The following practices will be employed at Pumping Station 2 to provide source control and pollution prevention: 1. The driveway will be periodically swept to remove trash and debris. 2. The subsurface infiltration system area will be periodically inspected to remove trash and debris. 3. No hazardous materials shall be stored outside at the site. 4. Salt and de-icing chemicals shall be used sparingly at the site. 5. Any spills that occur at the site shall be contained and cleaned up in a timely manner to prevent the spilled product from entering the catch basins and the subsurface infiltration system. All personnel who provide regular maintenance at Pumping Station 2 shall be trained annually on the pollution prevention measures described above. CDS® Inspection and Maintenance Guide ENGINEERED SOLUTIONS Maintenance The CDS system should be inspected at regular intervals and maintained when necessary to ensure optimum performance. The rate at which the system collects pollutants will depend more heavily on site activities than the size of the unit. For example, unstable soils or heavy winter sanding will cause the grit chamber to fill more quickly but regular sweeping of paved surfaces will slow accumulation. Inspection Inspection is the key to effective maintenance and is easily performed. Pollutant transport and deposition may vary from year to year and regular inspections will help ensure that the system is cleaned out at the appropriate time. At a minimum, inspections should be performed twice per year (e.g. spring and fall) however more frequent inspections may be necessary in climates where winter sanding operations may lead to rapid accumulations, or in equipment washdown areas. Installations should also be inspected more frequently where excessive amounts of trash are expected. The visual inspection should ascertain that the system components are in working order and that there are no blockages or obstructions in the inlet and separation screen. The inspection should also quantify the accumulation of hydrocarbons, trash, and sediment in the system. Measuring pollutant accumulation can be done with a calibrated dipstick, tape measure or other measuring instrument. If absorbent material is used for enhanced removal of hydrocarbons, the level of discoloration of the sorbent material should also be identified during inspection. It is useful and often required as part of an operating permit to keep a record of each inspection. A simple form for doing so is provided. Access to the CDS unit is typically achieved through two manhole access covers. One opening allows for inspection and cleanout of the separation chamber (cylinder and screen) and isolated sump. The other allows for inspection and cleanout of sediment captured and retained outside the screen. For deep units, a single manhole access point would allows both sump cleanout and access outside the screen. The CDS system should be cleaned when the level of sediment has reached 75% of capacity in the isolated sump or when an appreciable level of hydrocarbons and trash has accumulated. If absorbent material is used, it should be replaced when significant discoloration has occurred. Performance will not be impacted until 100% of the sump capacity is exceeded however it is recommended that the system be cleaned prior to that for easier removal of sediment. The level of sediment is easily determined by measuring from finished grade down to the top of the sediment pile. To avoid underestimating the level of sediment in the chamber, the measuring device must be lowered to the top of the sediment pile carefully. Particles at the top of the pile typically offer less resistance to the end of the rod than consolidated particles toward the bottom of the pile. Once this measurement is recorded, it should be compared to the as-built drawing for the unit to determine weather the height of the sediment pile off the bottom of the sump floor exceeds 75% of the total height of isolated sump. Cleaning Cleaning of a CDS systems should be done during dry weather conditions when no flow is entering the system. The use of a vacuum truck is generally the most effective and convenient method of removing pollutants from the system. Simply remove the manhole covers and insert the vacuum hose into the sump. The system should be completely drained down and the sump fully evacuated of sediment. The area outside the screen should also be cleaned out if pollutant build-up exists in this area. In installations where the risk of petroleum spills is small, liquid contaminants may not accumulate as quickly as sediment. However, the system should be cleaned out immediately in the event of an oil or gasoline spill should be cleaned out immediately. Motor oil and other hydrocarbons that accumulate on a more routine basis should be removed when an appreciable layer has been captured. To remove these pollutants, it may be preferable to use absorbent pads since they are usually less expensive to dispose than the oil/water emulsion that may be created by vacuuming the oily layer. Trash and debris can be netted out to separate it from the other pollutants. The screen should be power washed to ensure it is free of trash and debris. Manhole covers should be securely seated following cleaning activities to prevent leakage of runoff into the system from above and also to ensure that proper safety precautions have been followed. Confined space entry procedures need to be followed if physical access is required. Disposal of all material removed from the CDS system should be done in accordance with local regulations. In many jurisdictions, disposal of the sediments may be handled in the same manner as the disposal of sediments removed from catch basins or deep sump manholes. Table 1: CDS Maintenance Indicators and Sediment Storage Capacities 800.925.5240 www.ContechES.com Support • Drawings and specifications are available at www.contechstormwater.com. • Site-specific design support is available from our engineers. ©2017 Contech Engineered Solutions LLC, a QUIKRETE Company Contech Engineered Solutions LLC provides site solutions for the civil engineering industry. Contech’s portfolio includes bridges, drainage, sanitary sewer, stormwater, earth stabilization and wastewater treament products. For information, visit www.ContechES.com or call 800.338.1122 NOTHING IN THIS CATALOG SHOULD BE CONSTRUED AS AN EXPRESSED WARRANTY OR AN IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. SEE THE CONTECH STANDARD CONDITION OF SALES (VIEWABLE AT WWW.CONTECHES.COM/COS) FOR MORE INFORMATION. The product(s) described may be protected by one or more of the following US patents: 5,322,629; 5,624,576; 5,707,527; 5,759,415; 5,788,848; 5,985,157; 6,027,639; 6,350,374; 6,406,218; 6,641,720; 6,511,595; 6,649,048; 6,991,114; 6,998,038; 7,186,058; 7,296,692; 7,297,266; 7,517,450 related foreign patents or other patents pending. ENGINEERED SOLUTIONS CDS Model Diameter Distance from Water Surface to Top of Sediment Pile Sediment Storage Capacity ft m ft m y3 m3 CDS1515 3 0.9 3.0 0.9 0.5 0.4 CDS2015 4 1.2 3.0 0.9 0.9 0.7 CDS2015 5 1.3 3.0 0.9 1.3 1.0 CDS2020 5 1.3 3.5 1.1 1.3 1.0 CDS2025 5 1.3 4.0 1.2 1.3 1.0 CDS3020 6 1.8 4.0 1.2 2.1 1.6 CDS3025 6 1.8 4.0 1.2 2.1 1.6 CDS3030 6 1.8 4.6 1.4 2.1 1.6 CDS3035 6 1.8 5.0 1.5 2.1 1.6 CDS4030 8 2.4 4.6 1.4 5.6 4.3 CDS4040 8 2.4 5.7 1.7 5.6 4.3 CDS4045 8 2.4 6.2 1.9 5.6 4.3 CDS5640 10 3.0 6.3 1.9 8.7 6.7 CDS5653 10 3.0 7.7 2.3 8.7 6.7 CDS5668 10 3.0 9.3 2.8 8.7 6.7 CDS5678 10 3.0 10.3 3.1 8.7 6.7 CDS Inspection & Maintenance Log CDS Model: Location: Water Floatable Describe Maintenance Date depth to Layer Maintenance Personnel Comments sediment1 Thickness2 Performed —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— 1. The water depth to sediment is determined by taking two measurements with a stadia rod: one measurement from the manhole opening to the top of the sediment pile and the other from the manhole opening to the water surface. If the difference between these measurements is less than the values listed in table 1 the system should be cleaned out. Note: to avoid underestimating the volume of sediment in the chamber, the measuring device must be carefully lowered to the top of the sediment pile. 2. For optimum performance, the system should be cleaned out when the floating hydrocarbon layer accumulates to an appreciable thickness. In the event of an oil spill, the system should be cleaned immediately.CDS Maintenance Guide - 7/18 (PDF) OWNERS MAINTENANCE MANUAL retain-it, LLC 560 Salmon Brook Street Granby, CT 06035 (860) 413-3050 1 retain-it ® Owners Maintenance Manual Table of Contents Description Engineering Design Specifications Daily Operation and Long Term Maintenance System Operation Periodic Inspection Visual Inspection Guide Internal Flow Evaluation Low, Medium and High Flow Pollution Storage Capacities Oil and Grease Sediments Trash and Debris Standard Maintenance Emergency Spill Conditions Sample Maintenance Log 2 Description retain-it ® is a subsurface Storm Water Management system constructed of precast concrete structures. They are installed in a side by side configuration creating a continuous internal flow channel integrated throughout the system. Systems are constructed with designated inlet and outlet modules, some with multiple inlets and outlets depending on the site storm water system layout. Infiltration systems typically have an inlet and sidewalls/ base constructed on a stone infiltration blanket with geofabric installed at the native soil interface. Other systems incorporate outlet flow control devices. Detention systems are typically lined with a watertight membrane and have inlet and outlet control devices. The retain-it ® system can consist of multiple varying layouts, with no two the same. Given this, it should be noted that the operation and maintenance requirements are very similar regardless of the intended layout. It is important that the end user know the specific elements of each system so as to understand how best to optimize it’s operation. Installation per Design: Operation is simple to follow where the installation was performed in accordance with the design specifications, drawings and calculations. Specifics shall be identified in the design drawings. As-built drawings will benefit the locating of specific design modules where the system has been buried below a parking lot area. Optional access manholes or removable grates may be installed above every inlet/outlet pipe and at critical design elements designated by the design. Daily Operation and Long Term Maintenance: In general, daily usage of the system is self sufficient and will operate without requiring any outside assistance, except for periodic inspection to verify optimal performance and maintenance for removal of collected pollutants. A longer term maintenance program should incorporate a more thorough inspection of the all elements of the system to verify proper operating condition. This is more important with the infiltration type of systems where the soil infiltration surface may become restricted due to fine particle build up. Long term maintenance should include provisions for cleaning and removal of collected solids, oils and debris from the system. System Operation: The system operational function is initiated according to rainfall runoff flows entering the structure. Internally, the runoff flows in a set pattern or sequence throughout the module layout in accordance with the hydraulic design conditions. The flows primarily operate on system head derived from the changes in 3 elevation from the internal water surface and the outlet invert elevation. Some designs incorporate internal flow controls to satisfy hydraulic conditions that enhance water quality treatment or other intended purposes. Modified systems may incorporate a pump, but in general there are no mechanical apparatus required. End user operations primarily consist of inspection and maintenance of the system over time. Periodic Inspection: Important note - All storm water management systems react differently depending on the conditions that are characteristic to the contributing water shed. Variables such as storm intensity, runoff flow rates, site geology, surface stabilization and pollution load will affect the system operation. As does the inspection and maintenance frequency to ensure optimum effectiveness. Inspections should be done periodically, with a greater number scheduled during the system start up and less frequently as the operator becomes familiar with the system performance characteristics. It is recommended that the end user keep records of the performance using the inspection log record sheet found in the back of this manual. These records shall identify the cycle of maintenance “system calibration” required for the specific applications based on the contributing water shed variables operating under “normal” conditions. Please note that immediate maintenance may be required during “non-normal” events such as during adverse weather conditions or emergency fuel spills. See information on emergency spills in this manual. Visual inspection of all assessable components shall be performed throughout the lifetime of the system. Access has been supplied at critical points to monitor hydraulic performance and removed pollutants buildup. Standard Maintenance: After construction has been completed and all disturbed surfaces have been stabilized by means of vegetation, asphalt or concrete surfaces, and all drainage system components have been constructed and are free of construction debris and sediments; then the storm water management system can be considered in an operational status. Periodic visual inspections will help to identify issues of concern.The usual indicators are signs of slow flows, backed up water, visible oil, trash and debris or an excessive amount of sediment in the storage area. Normal operational flows can be observed to flow freely at the predicted design elevations, from the inlet to the outlet module, following a serpintine path thru the storage and attenuation modules. Note that some modules are designed to permanently 4 retain water where others may hold water and slowly release it over a typical 24 hour period. During a storm water event, the flows and water surface elevations will fluctuate from a low flow to a high flow/ storage status. The storage modules should fill during the event and drain down within a 24 hour period after the event has stopped. All pipes, orifices, weirs and standpipes should pass flows freely and at optimum capacity. Standard maintenance is performed using a vacuum truck to suction the accumulated sediments, oils and greases and trash and debris from the system. Whereas an on-site maintenance staff can remove these items by hand, it is preferred that the vacuum truck be used as dictated by specific system conditions. When a specialized module designed to have a permanent water level is used, the vacuum truck should pump the liquid level down to inspect the below water elevation structures and sump storage areas. Oils and greases can be handled by on-site staff by utilizing absorbent products that soak up the oils (and not) converting the oils from a liquid into a manageable solid form. These oil soaked absorbent materials should be disposed of in an approved manner. Sediments, trash and debris shall be removed and disposed of in an approved manner. Any indications of hazardous material, determined by visual inspection, testing, smell or abnormality, should be reported and handled per appropriate regulations. Flow Conditions System operators should familiarize themselves with proper hydraulic flow condition indicators, acceptable depths of sedimentation, debris and trash build up, and concentrations of oils and greases. Hydraulic flow conditions are those that are established by the design as either a flow/storage or as a water quality treatment function. Both have performance characteristics that can be visually identified so as to determine the effective and efficient operation of the system. The engineering design drawings should note the various expected water surface level elevations that are achieved during different design storms within the various modules. Since it is difficult for a visual inspection to coincide with the exact time given water elevations are predicted, the following guidelines are given for evaluation. Visual Inspection Guide: Internal Flow Evaluation Low flow: water should flow freely from the inlet to the outlet, travelling the intended attenuation path thru the system with the water surface elevation below the structure 5 beam height (12” deep), the system should drain completely 24 hours after a storm event, Medium flow: the system should hold and maintain a water level during the 24 hour storm event and yet continually fill as the storm increases or drain downward as the event recedes. Flow within the system should occur freely from inlet to outlet only being restricted when a flow control structure has been integrally designed in place. Flow control devices may result in a water level backing up either temporarily or permanently; noting devices such as water quality modules may require a permanent water level to operate properly (see water quality treatment). Other system applications should drain completely 24 hours after a storm event. High flow: the system should fill to the maximum design storm water level elevation (hydraulic grade line) per design. In most cases, that is the highest storage elevation available in the system, at the underside of the module top slab, or the invert of the overflow pipe. As the storm event recedes, the water level should begin to drain down via flow thru the system and discharge. The system should drain completely within 24 hours after a storm event. Pollutant Storage Capacities Oil and Grease Oil and Grease Collection (with optional Oil water separator module specified) - Oil and grease accumulation is generally a function related to vehicle parking lot and drive areas, oil generating land uses or emergency spill conditions. It is important to maintain the system from accumulating excessive volumes of oils in that they may wash over into other sections of the system potentially clogging and reducing the infiltration capacity, blocking control devices and contaminating the overall system. The following standards apply. Oil should not accumulate more than a visible sheen on the water surface in the oil water separation module only. A sheen is described as a fine, thin oil layer on the water surface identified by the glossy rainbow colors. A dipstick (dry wooden stick) can be used as a probe to determine the thickness of oil on the surface. Accumulated oils could be associated with insufficient maintenance or a potential large volume oil resource. Any accumulation of oil should be promptly maintained by an experienced waste handler. Emergency spills such as those generated by an accidental spill shall be contained and removed immediately before the next storm event. Spills shall be handled in accordance with local environmental regulations. See spill and accumulated oil maintenance procedures. 6 Sediments Sediments (with optional primary grit module or sedimentation modules specified) - Sediments shall be periodically removed from the system as they accumulate within the designated storage modules. The inlet modules are generally equipped with a sediment storage sump located in the base of the inlet structure. Inspection should be performed after major storm events or a minimum of annually, unless a different inspection cycle has been determined to be sufficient. Inspection shall consist of using a probe to determine the presence of and depth of the accumulated solids. Access is via the 24” manhole. Note that excessive volumes of sediments will reduce the performance and efficiency of the system. Regional accumulations of solids such as those associated with ice and snow, may result in large springtime volumes of sand and gravels used for traction and ice control. Trash and Debris Trash and Debris (with optional trash and debris module specified) - Trash and debris accumulates in the inlet module in three forms; floating debris, neutrally buoyant, and heavy material. The floating debris is visible from the access manhole floating on the water surface in the form of but not limited to wood, paper, plastic, foam, bottles and cans. The neutrally buoyant material resides below the surface and combines with the natural flow regime of the system. It is hard to detect and can only be recognized when at a high concentration appears as a thickening of the water viscosity. Heavier material will simply settle to the sump base and combine with the sediments. Note that trash and debris typically cause the most problems when they become lodged in a flow control device such as an outlet elbow, riser pipe, and orifice or weir structure. This can be detected visibly when the system is pumped down during maintenance. It can also be evaluated as a condition when flow is impeded and the water level backs up higher than the design elevations. Emergency Spill Conditions (with optional emergency spill control module specified): Emergency spill conditions are defined as an excessive accumulation of hydrocarbons such as oil, gasoline, diesel fuel, transmission oil or antifreeze usually resulting from an accidental discharge. Excessive accumulation is described as any amount larger than a thin “sheen” visible on the water surface. 7 Care should be given in handling these types of fluids. The incident should be reported to the appropriate authorities and should be mitigated by a hazardous waste consultant approved for such matters. 8 retain-it ® Maintenance Log Storm Water Management System Location: ID #: Date Inspection Notes Inspector Note the following conditions: Inlet Module Outlet Module Water Quality Module Oil Elbow Oil Accumulation Sedimentation Accumulation Trash and Debris Quantity Flow Conditions Flow Control Outlet Structure Overflow Pipe