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HomeMy WebLinkAboutAPPROVED Stormwater Report 2.4.2026 STORMWATER MANAGEMENT REPORT Grove Street - Yarmouth, MA February 2026 Yarmouth Stormwater Design and Implementation Project Partner: Association to Preserve Cape Cod Owner/Operator: Town of Yarmouth i STORMWATER MANAGEMENT REPORT GROVE ST REET YARMOUTH STORMWATER DESIGN AND IMPLEMENTATION PROJECT YARMOUT H, MA Table of Contents STORMWATER CHECKLIST ........................................................................................................................... iii EXECUTIVE SUMMARY .................................................................................................................................. 1 1.0 INTRODUCTION ................................................................................................................................ 2 1.1 Background ................................................................................................................................... 2 1.2 Project Goals ................................................................................................................................. 2 1.3 Design Methodology ..................................................................................................................... 3 2.0 Existing Conditions ........................................................................................................................... 3 2.1 Receiving Water and Watershed .................................................................................................. 4 2.2 Drainage Area ............................................................................................................................... 4 2.3 Resource Areas ............................................................................................................................. 4 2.4 Soils ............................................................................................................................................... 5 3.0 Proposed Conditions ........................................................................................................................ 5 3.1 Drainage Areas ............................................................................................................................. 5 3.2 Structural Stormwater Control Measure (SCM) ........................................................................... 6 3.3 Non-structural SCMs ..................................................................................................................... 7 4.0 Stormwater Design Components ..................................................................................................... 7 4.1 Water Quality ................................................................................................................................ 7 4.2 Recharge ....................................................................................................................................... 8 4.3 Water Quantity ............................................................................................................................. 9 4.4 Erosion Control ............................................................................................................................. 9 4.5 Operation and Maintenance ....................................................................................................... 10 4.6 Illicit Discharges .......................................................................................................................... 10 5.0 REFERENCES ................................................................................................................................... 11 ii TABLES Table 1. Project MASMS Compliance Summary ........................................................................................... 1 Table 2. Test Pit (TP) Results ......................................................................................................................... 5 Table 3. Compliance with Water Quality Volume (WQV) Requirements ..................................................... 7 Table 4. Compliance with Pollutant Removal Requirements ....................................................................... 8 Table 5. Compliance with Recharge Requirements ...................................................................................... 9 Table 6. Summary of Existing and Proposed Condition Peak Flow Rates and Runoff Volumes ................... 9 FIGURES Under Notice of Intent (NOI) Cover Figure 1 – USGS Locus Figure 2 – Aerial Figure 3 – FEMA Flood Zones Figure 4 – Environmental Constraints Figure 5 – Soils Figure 6 – Environmental Justice Communities Figure 7 – Impaired Waters APPENDICES Appendix A: Drainage Area Maps Appendix B: Hydrologic/Hydraulic Model Results Appendix C: Soil Test Pit Logs Appendix D: Operation and Maintenance Guide Appendix E: Pollutant Controls During Construction Appendix F: Site Plans Stormwater Report Checklist - Grove.doc • 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. Stormwater Report Checklist - Grove.doc • 04/01/08 Stormwater Report Checklist • Page 2 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report B. Stormwater Checklist and Certification The following checklist is intended to serve as a guide for applicants as to the elements that ordinarily need to be addressed in a complete Stormwater Report. The checklist is also intended to provide conservation commissions and other reviewing authorities with a summary of the components necessary for a comprehensive Stormwater Report that addresses the ten Stormwater Standards. Note: Because stormwater requirements vary from project to project, it is possible that a complete Stormwater Report may not include information on some of the subjects specified in the Checklist. If it is determined that a specific item does not apply to the project under review, please note that the item is not applicable (N.A.) and provide the reasons for that determination. A complete checklist must include the Certification set forth below signed by the Registered Professional Engineer who prepared the Stormwater Report. Registered Professional Engineer’s Certification I have reviewed the Stormwater Report, including the soil evaluation, computations, Long-term Pollution Prevention Plan, the Construction Period Erosion and Sedimentation Control Plan (if included), the Long-term Post-Construction Operation and Maintenance Plan, the Illicit Discharge Compliance Statement (if included) and the plans showing the stormwater management system, and have determined that they have been prepared in accordance with the requirements of the Stormwater Management Standards as further elaborated by the Massachusetts Stormwater Handbook. I have also determined that the information presented in the Stormwater Checklist is accurate and that the information presented in the Stormwater Report accurately reflects conditions at the site as of the date of this permit application. Registered Professional Engineer Block and Signature Signature and Date Checklist Project Type: Is the application for new development, redevelopment, or a mix of new and redevelopment? New development Redevelopment Mix of New Development and Redevelopment 2/4/2026 Stormwater Report Checklist - Grove.doc • 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): Public Education Signage 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. Stormwater Report Checklist - Grove.doc • 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. Stormwater Report Checklist - Grove.doc • 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. Stormwater Report Checklist - Grove.doc • 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. Stormwater Report Checklist - Grove.doc • 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. Stormwater Report Checklist - Grove.doc • 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. Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 1 EXECUTIVE SUMMARY The purpose of this report is to describe existing and proposed drainage conditions of the Grove Street site (HIH-3) in Yarmouth, as well as proposed green stormwater infrastructure (GSI) structures and management strategies to reduce stormwater impacts. This project is part of the ongoing efforts to improve water quality in the Town of Yarmouth by reducing pollutant loads in stormwater runoff, specifically nitrogen, bacteria, and sediment. The Grove Street site was identified as a priority stormwater retrofit in a CZM-funded assessment focused on green infrastructure Stormwater Control Measures (SCMs) and low impact design. The main goal for this site is to capture, manage, and treat stormwater runoff from Grove Street prior to discharging onto the beach and into Hyannis Inner Harbor and Lewis Bay. This project involves the development of a new GSI system at the end of Grove Street to treat 0.93 inches of runoff from the contributing area. The project includes the following structural and non-structural stormwater control measures (SCMs): • Bioretention to filter pollutants from stormwater through plants and soil media • Pavement reduction to reduce stormwater runoff volumes • Public educational signage to inform the public Since the proposed stormwater management system is a retrofit project undertaken solely to improve water quality at the site, it falls under the redevelopment category in accordance with the Massachusetts Stormwater Management Standards (MASMS 2008), as described in Massachusetts Stormwater Handbook, Volume 1 Chapter 1. As a redevelopment project, the design is required to meet the MASMS standards to the maximum extent practicable (MEP). As shown in Table 1, the proposed project meets or exceeds each standard, except the water quality standard, which is met to the MEP. Due to site constraints, the proposed treatment SCM (bioretention) is designed to capture and treat 93% of the first one inch of runoff of its contributing drainage areas. Overall, this project will significantly improve conditions at the end of Grove Street and reduce on-going impacts to Hyannis Inner Harbor and Lewis Bay, while also providing public education and access benefits. Table 1. Project MASMS Compliance Summary Minimum Standard Type Compliance Report Reference(s) 1 New Stormwater Conveyances Narrative Yes Section 2 2 Water Quantity Calculation Yes Section 4.3/Table 6/Appendix B 3 Recharge Calculation Yes Section 4.2/Table 5/Appendix B 4 Water Quality Calculation MEP Section 4.1/Table 3/Table 4/Appendix B 5 Land Uses with Higher Potential Pollutant Loading Narrative Not Applicable Section 2.0 6 Critical Areas Narrative Yes Section 4.1 7 Redevelopment Narrative Yes Section 4.0 8 Erosion Control Narrative Yes Section 4.4/Appendix E 9 Operation and Maintenance Narrative Yes Section 4.5/Appendix D 10 Illicit Discharges Narrative Yes Section 4.6 Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 2 1.0 INTRODUCTION This report provides a summary of the stormwater management system proposed for the Grove Street site (HIH-3) in Yarmouth, MA. The Yarmouth Department of Public Works is proposing this project in collaboration with the Association to Preserve Cape Cod (APCC) as a part of a town effort (Yarmouth Stormwater Design and Implementation Project) to improve water quality in the Town of Yarmouth. The proposed project has been designed to retrofit existing impervious areas for water quality improvements and improving overall site conditions. This report describes the existing and proposed site conditions and the practices to be implemented to reduce stormwater discharges and pollutants during and after construction. As required for retrofit projects, the stormwater system for the project has been designed to conform to the requirements of the Massachusetts Stormwater Management Standards (MASMS) to the maximum extent practicable. 1.1 Background Coastal embayments across Cape Cod are significantly degraded by nutrient and bacteria impairment. Land uses, including stormwater runoff and fertilizer use, contribute on average 20% of the controllable nitrogen load within our coastal watersheds (Cape Cod Commission 208 Plan, 2015), and bacterial contamination, including cyanobacteria, regularly causes closures of beaches. In a recent report (APCC’s 2022 State of the Waters), 90% of the coastal embayments and 39% of the freshwater ponds assessed received unacceptable water quality scores. These high nutrient loads are of concern for the environment, our coastal economy, and public health as they negatively impact habitat for fish and shellfish and can result in unsafe conditions for swimming, fishing, and boating. As part of a Coastal Zone Management (CZM) Coastal Habitat and Water Quality Grant, the Town of Yarmouth Department of Public Works (DPW), APCC, and Horsley Witten Group (HW) completed a comprehensive assessment and stormwater management plan identifying and prioritizing stormwater retrofit sites on the south shore of Yarmouth. Concept designs were ranked based on various criteria including potential pollutant removal (i.e., load and drainage area), water quality status of the associated waterbody, construction cost and feasibility, and additional human use and resource benefits (restored shellfish and anadromous fish habitat, proximity to environmental justice communities, improved climate resiliency, opportunity for public education, etc.). With additional support from a second Coastal Habitat and Water Quality Grant, 25% designs were developed for five high-ranking priority sites, and two of those sites were chosen to advance through 100% design and construction, and a third site (this site) was advanced through 75% design. With additional funding from a third Coastal Habitat and Water Quality Grant, this site will be advanced through 100% design. 1.2 Project Goals The purpose of this project is to improve water quality in Hyannis Inner Harbor and Lewis Bay, and improve the Town Way to Water in conjunction with the separate Yarmouth Ways to Water project, by reducing or eliminating pollutant loads from stormwater runoff at the end of Grove Street using green stormwater infrastructure (GSI) and stormwater control measures (SCMs). Specifically, the project aims Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 3 to maximize pollutant removal (% bacteria, nitrogen, and phosphorus) and water quality volume treated, while also improving public access. 1.3 Design Methodology The design was completed by the following tasks: • Preliminary field assessment of the site and contributing drainage area to identify usage, physical and environmental constraints and opportunities, and long-term operation and maintenance concerns; • Determination of drainage areas and land coverage within the project area; • Selection of structural and non-structural SCMs best suited to site conditions, and project goals; • Structural SCM sizing and performance estimates (described further below); • Hydrologic/Hydraulic Modeling (described further below); • Grading and layout of site plan; • Erosion control plan development; and • Operation and maintenance (O&M) plan development. SCM Performance Estimates The proposed SCM was selected and sized to maximize pollutant load removals. Since the waterbodies this site drains to are shellfish growing areas with a public beach, have water quality impairments and are subject to TMDLs, the SCM was chosen to maximize not only total suspended solids (TSS) removal, but total nitrogen (TN), total phosphorus (TP) and bacteria load reductions as well. MASMS was used as a reference for TSS removal estimates for bioretentions, but the more recently developed pollutant load removal curves (USEPA 2021 & Paradigm Environmental 2019) were used for TP, TN, and bacteria.1 Hydrologic/Hydraulic Modeling Existing and proposed conditions for the project area were modeled using HydroCAD software, which combines USDA Natural Resources Conservation Service hydrology and hydraulic techniques (commonly known as SCS TR-55 and TR-20) to generate hydrographs. Conditions were evaluated for the water quality event (storm that produces 1 inch of runoff, or a roughly 1.2-inch rain event) as well as larger storm events, including the 2-, 10-, 25- and 100-year 24-hour Type III storm events. The rainfall depths used for each storm event are the NOAA+ values (NOAA Atlas 14 90% Upper Confidence value multiplied by 0.9) (NOAA NWS, 2017). Rainfall values are included in Appendix A. 2.0 Existing Conditions The Grove Street site (HIH-3) is located at the southern end of Grove Street, on the northwest side of Lewis Bay, where there is public access to Grove Street Beach. The project is proposed within the right- 1 It is important to note that these curves have a crosswalk to help users determine which specific curve to reference: for infiltrating bioretentions (no liners/underdrains), the appropriate curve is the Surface Infiltration (Soil infiltration rate = 2.41 in/hr) Performance Curve. Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 4 of-way (ROW) of Grove Street at the beach access point or Town Way to Water. The site is bordered by residential properties to the east and west. The site’s land use is not classified as a land use with higher potential pollutant loads (LUHPPL) and thus, is not subject to MASMS Standard 5. The site contains one existing SCM – a clogged leaching basin downgradient from the proposed project. Otherwise, there is no other stormwater infrastructure (e.g., catch basins, manholes, or pipes). 2.1 Receiving Water and Watershed Grove Street runoff ultimately discharges into Hyannis Inner Harbor, which flows into Lewis Bay, a bay that opens into Nantucket Sound. Hyannis Inner Harbor provides habitat for shellfish growing areas. However, it is listed as impaired for total nitrogen and fecal coliform by the most recent Massachusetts DEP 303(d) – 2022 Integrated list of Waters. Hyannis Inner Harbor is located in the Lewis Bay Watershed, for which total maximum daily load documents (TMDLs) have been developed for nitrogen. Lewis Bay itself requires a TMDL, as it falls under Category 5. The full list of impairments for this portion of the watershed is listed below, and a map showing these resources is included in NOI Narrative Figure 7: • Hyannis Inner Harbor (MA96-82) Yarmouth, Lewis Bay Watershed – Impaired for total nitrogen and fecal coliform; Category 4a (TMDL completed) of the 2022 Integrated List of Waters. • Lewis Bay (MA96-36) Yarmouth, Lewis Bay Watershed – Impaired for total nitrogen, estuarine bioassessments, fecal coliform, and nutrient/eutrophication biological indicators; Category 5 (TMDL required) of the 2022 Integrated List of Waters. 2.2 Drainage Area An existing drainage area map was created, which includes the drainage area flowing to Hyannis Inner Harbor via Grove Street Beach (SP1). The total area draining to SP1 is approximately 0.33 acres, with 0.18 acres of that being impervious area, and is only comprised of one drainage area: DA1. See the existing drainage area map and a detailed breakdown of land cover in Appendix A, as well as the existing HydroCAD model report in Appendix B. 2.3 Resource Areas HW wetland biologists delineated several resource areas at the site in November 2023. A full description of these resource areas is included in NOI Narrative, and their locations and associated buffers are shown on the plans in Appendix F. Resource areas located at or adjacent to this site include Salt Marsh, Coastal Beach, Coastal Dune, Riverfront Area, and Land Subject to Coastal Storm Flowage (LSCSF) (including AE and VE zones) (NOI Narrative Figure 3). Since the site discharges near a public beach, shellfish growing area, and within soils with a high infiltration rate, it is considered a critical area and subject to MASMS Standard 6. Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 5 2.4 Soils Soils data from the Natural Resources Conservation Service (NRCS) indicate that the soils within the drainage area are composed of Carver coarse sand, 3-8% slopes. Carver coarse sand is classified as hydrologic soil group A (HSG), as shown in NOI Narrative Figure 5. One test pit (TP) was conducted at the site on January 3, 2024 to evaluate subsurface conditions and estimated seasonal high groundwater (ESHGW) based on evidence of mottling or redox. The test pit was dug near the location of the proposed SCM, just off the west edge of pavement, and was witnessed and logged by an HW Massachusetts Title 5 Approved Soil Evaluator; results are shown in Table 2 below. Since no mottling or redox was observed, the ESHGW was based on the Mean High Water (MHW) of the nearby tidal stream. The MHW elevation was determined to be 2.31’ using LiDAR elevation data from MassGIS in combination with hydrographic survey data from a nearby NOAA tidal station located in Chatham, MA (Station ID - 8447435). See Appendix C for soil test pit log. The parent material of the native soil unit, Carver coarse sand, is sandy glaciofluvial deposits, comprising mostly outwash terraces, plains, and delta landforms. See Appendix C for soil test pit logs. Table 2. Test Pit (TP) Results Test Pit ID Surface Elevation at TP (ft) Pit Bottom Elevation (ft) Observed GW Elevation (ft) ESHGW Elevation (ft) Soil Texture(s) at SCM Max Design Infiltration Rate (in/hr) TP-1 6.7 1.0 1.0 2.3 Coarse sand 8.27 3.0 Proposed Conditions The proposed project consists of the following stormwater and related site development improvements: • GSI including an infiltrating bioretention with a sediment forebay for pretreatment; • Pavement reduction to pull the end of Grove Street back from the coastal dune; • Educational signage to inform the public about stormwater-related issues; and • A formalized pedestrian path for access to the water. The proposed GSI system is designed to meet the following major objectives: • Capture, treat, and infiltrate to the maximum extent practicable the first one inch of runoff (Water Quality Volume (WQV)); and • Engage the community with interpretive signage. 3.1 Drainage Areas The contributing drainage area from Grove Street to the study point (SP1) under proposed conditions is the same as existing, with a total of approximately 0.33 acres. However, the proposed project is Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 6 reducing impervious cover by roughly 600 square feet by replacing the portion of paved road with native vegetation, a stabilized path, and an infiltrating bioretention. The total drainage area (DA1) was subdivided into DA1A and DA1B for the proposed conditions in order to more accurately model flows to and from the proposed SCM. The proposed SCM was added as “pond” in the HydroCAD model. DA1A includes all flows from impervious areas and surrounding pervious areas to the SCM while DA1B represents just the planted area between the SCM and SP1. See the proposed drainage area map and a detailed breakdown of land cover in Appendix A, as well as the proposed HydroCAD model report in Appendix B. 3.2 Structural Stormwater Control Measure (SCM) The proposed stormwater management includes a GSI approach to capture, detain, treat, and infiltrate runoff. The stormwater management system was designed to meet Standard 1, so that no new untreated stormwater runoff will be directed to any off-site areas or resource areas. The GSI practice proposed at this site is a bioretention area. Pretreatment will be provided with a sediment forebay. Flow from large storm events will flow through the bioretention system and discharge towards the beach, as it does in existing conditions. This SCM is described in more detail below. Pretreatment A porous sediment forebay is provided for pretreatment of the runoff from the paved surfaces to allow for sediment and other debris to settle out prior to conveyance into the bioretention area. Bioretention Area A bioretention area (BIO) is a shallow depression used to treat stormwater runoff using a specific planting soil and plants to filter runoff. The method combines physical filtering and adsorption with bio- geochemical processes to remove pollutants. The system consists of an inflow component, a pretreatment element, and a shallow ponding area planted with appropriate native plant species (tolerant to both wet and dry periods as well as other site conditions such as wind, salt, shade, etc.). Some BIOs located in areas with poor drainage or high groundwater are lined and/or have underdrains, while others located greater than 2 feet above ESHGW and in sandy soils can just infiltrate the treated runoff. One BIO is proposed at the end of Grove Street within the ROW. Runoff from the road enters the BIO through a paved flume. The runoff then flows through the sediment forebay and overflows into the BIO area. Once the BIO reaches capacity, runoff will flow over the overflow spillway and continue down towards the beach. This BIO captures, treats, and infiltrates 93% of the first inch of runoff from the contributing drainage area. The BIO has greater than 2-feet separation from bottom of bed to ESHGW as required and will be planted with low-maintenance, salt-tolerant native plants that can handle periods of inundation and dry conditions. Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 7 In addition, as sea level and thus groundwater levels rise over the next 50 years, this resilient GSI practice will be able to adapt to the wetter conditions. The bioretention area will start to convert to more of a wetland as groundwater rises. The plant community will naturally change as conditions change, still providing water quality treatment for this drainage area. 3.3 Non-structural SCMs The non-structural SCMs proposed at the site include pavement reduction and public education. Pulling the road back away from the resources reduces total volume of stormwater from the site while maintaining public access to the water. The proposed signage at the site will help educate the public on watershed issues, green stormwater infrastructure, and what they can do at their own homes to reduce stormwater pollutants from their lawns and driveways. 4.0 Stormwater Design Components The proposed SCM was designed to meet a variety of goals and regulatory requirements as discussed above. As a retrofit project for managing existing impervious cover, this design must specifically comply with the redevelopment standard (MASMS Standard 7) by meeting all standards to the maximum extent practicable. The project fully meets this standard, as described in detail below. 4.1 Water Quality The main purpose of this retrofit project is to improve water quality. This section describes the treatment volumes and pollutant load reductions achieved by the proposed design and how they compare to the MASMS standards. Treatment Volume Per Standard 4 of MASMS, the stormwater management system for a new development site within soils with a rapid infiltration rate (greater than 2.4 inches per hour) must be sized to treat the first one inch of runoff and remove 80% or more of the annual post-construction load of total suspended solids (TSS). As a retrofit (falls under Standard 7 - Redevelopment), the project is only required to meet this to the maximum extent practicable. The proposed HydroCAD model results showing treatment of the water quality volume are included in Appendix B and summarized below in Table 3. Table 3. Compliance with Water Quality Volume (WQV) Requirements DA ID SCM ID IA (ac) WQv Goal (ac- ft) WQv Provided (ac-ft)* % WQv Provided Meets Reqt? Notes DA1A BIO1 0.17 0.014 0.013 93% MEP DA1B N/A 0.00 0.000 0.000 N/A N/A No impervious area TOTAL SITE: 0.17 0.014 0.014 100% MEP *From HydroCAD results – see Appendix B for volume “discarded” for WQv Event Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 8 Pollutant Load Reductions The proposed bioretention area exceeds the MASMS requirements for TSS removal and maximizes removals of the other pollutants of concern. Estimated TSS, bacteria, phosphorus (TP), and nitrogen (TN) removals for the proposed project are provided in Table 4. The proposed O&M Guide in Appendix D was developed to ensure that the stormwater system continues to function as it was designed into the future to maintain these levels of pollutant removal. Table 4. Compliance with Pollutant Removal Requirements DA ID SCM ID IA (ac) WQv Provided (ac-ft)* Runoff Depth Treated (in) TSS Removal (%)** TP Removal (%)*** TN Removal (%)*** Bacteria Removal (%)**** Meets Reqt? Notes DA1A BIO1 0.17 0.014 0.93 83% 97% 99% 99% YES DA1B N/A 0.00 0.000 0.0 0% 0% 0% 0% N/A No impervious area TOTAL SITE: 0.17 0.014 1.0 83% 97% 99% 99% YES *From HydroCAD results – see Appendix B for volume “discarded” for WQv Event **From MASMS ***From Paradigm Environmental (2019) ****From MS4 NPDES Permit Appendix F Attachment 3 (USEPA 2021) In addition, since the site is located in a critical area (near a public beach, shellfishing area, and the site has soil with a rapid infiltration rate) and must meet MASMS Standard 6, pretreatment practices before infiltration should remove 44% TSS or more. To address this, BIO1 provides 83% treatment prior to infiltrating into the underlying soils, thus fully meeting Standard 6. Long-term Pollution Prevention Plan Source control is important to ensure long-term functionality of the proposed SCMs and protect downstream resources and habitat. A long-term pollution prevention plan specific to this site is provided as a part of the O&M Guide in Appendix D. 4.2 Recharge For new development projects, the MASMS requires a specific annual “recharge” volume (Rev) based on the HSG of the soil covered by new impervious surfaces, with a higher volume required for sandy soils (HSG A) and lower for silty, clayey soils (HSG D). This project is only required by the MASMS to provide infiltration or recharge to the maximum extent practicable as a redevelopment project, as there is already pavement at the site. However, the proposed project actually exceeds the required recharge volume of Standard 3. BIO1 provides 166% of the required recharge amount for the full drainage area (DA1A). Additionally, pavement reduction has been proposed to reduce stormwater runoff. Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 9 Another requirement of Standard 3 is that infiltrating SCMs must fully drain in 72 hours. The proposed HydroCAD model results showing nearly full recharge of the first inch of runoff by the bioretention, and the drawdown time (from full basin to empty) are included in Appendix B and summarized below in Table 5. Table 5. Compliance with Recharge Requirements DA ID SCM ID IA (ac) Soil HSG Required Recharge Depth (in) Rev Goal (ac-ft) Rev Provided (ac-ft)* % Rev Provided Draw- down Time (hrs)** Meets Reqt? DA1A BIO1 0.17 A 0.6 0.008 0.013 154% 17.0 Yes DA1B N/A 0.00 A 0.6 0.000 0.000 0% N/A N/A TOTAL SITE: 0.17 0.008 0.013 154% Yes *From HydroCAD results – see Appendix B for volume “discarded” for WQv Event **From HydroCAD results – see Appendix B for hydrograph showing time from peak elevation to fully drained basins (WQv Event) 4.3 Water Quantity The main focus of this project is to improve water quality and habitat, but reducing water quantity impacts during large storm events was also considered. The proposed bioretention area will reduce peak flows and runoff volumes for the 2-, 10-, 25- and 100-year storms2. The existing and proposed HydroCAD model results for these larger storm events are included in Appendix B, and the resulting peak flows and runoff volumes are summarized below in Table 6 for both existing (EX) and proposed (PR) conditions. These results show that the proposed improvements will reduce peak flows and runoff volumes for all evaluated storms, and thus, fully meet the requirements of Standard 2 of the MASMS. Table 6. Summary of Existing and Proposed Condition Peak Flow Rates and Runoff Volumes Study Point Peak Flow, cfs Runoff Volume, acre-ft 2-yr 10-yr 25-yr 100-yr 2-yr 10-yr 25-yr 100-yr SP1 EX 0.47 0.98 1.40 2.10 0.032 0.065 0.092 0.140 PR 0.35 0.80 1.19 1.86 0.009 0.034 0.058 0.102 Reduction % 26% 18% 15% 11% 72% 48% 37% 27% *From HydroCAD results – see Appendix B 4.4 Erosion Control Controlling erosion and sedimentation from the construction site is important to meet the overall water quality goals of this retrofit project, as well as to meet MASMS Standard 8. Given this site’s size (< 1 acre of disturbance), a NPDES Construction General Permit Stormwater Pollution Plan (SWPPP) is not 2 It is important to note that while we include the results for large storm here, given the site’s location within the 100-year flood zone and an anticipated storm surge area, the area will likely be under coastal water during large storms, rendering these estimates irrelevant. Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 10 required. However, planning for effective erosion and sediment controls (ESCs) was important to this project’s design, and so an ESC Plan is included in the design plans (Appendix F), along with a detailed sequence of construction activities and ESC notes. Silt socks are proposed along the downgradient edges of the area of disturbance. Regular street sweeping will be provided along Grove Street to minimize tracking of sediment. Since there is no construction entrance/exit proposed at this site given its small size, extra care should be taken in monitoring sediment tracking and sweeping the road. Areas for other sediment traps/basins should be provided on an as-needed basis. Disturbed areas will be stabilized as soon as possible to minimize erosion and sedimentation with pavement, seeding and/or erosion control blankets, if necessary. A Pollutant Controls During Construction guide is also included in Appendix E that discusses these controls in more detail. With these layered ESCs implemented throughout the site, discharge of sediment-laden runoff during construction should be minimized to the maximum extent practicable. The contractor will be required to establish these erosion controls prior to beginning any other project- related work. The ESC Plan will also establish the limit of work, beyond which the contractor will not be allowed to perform any work. It is the contractor’s responsibility to monitor and correct erosion control practices throughout the duration of the project. Erosion control measures will not be removed until the project reaches completion as directed by the project engineer or landscape architect. 4.5 Operation and Maintenance Ongoing maintenance is vital for long-term success at the site. All SCMs were designed to be low- maintenance in nature. These SCMs will be operated and maintained appropriately during construction and post-construction as required on the construction drawings and O&M Guide per MASMS Standard 9 (Appendix D and F). 4.6 Illicit Discharges There will be no illicit discharges to the existing system by the proposed project per MASMS Standard 10. The Long-Term Pollution Prevention Plan in the O&M Guide (Appendix D) includes measures to prevent future illicit discharges. Stormwater Management Report Horsley Witten Group, Inc. Grove Street - Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA February 2026 11 5.0 REFERENCES Association to Preserve Cape Cod. 2022. State of the Waters: Cape Cod Report. Cape Cod Commission. 2015. 208 Plan – Cape Cod’s Area Wide Water Quality Management Plan Updated. Massachusetts Department of Environmental Protection (MADEP). 2008. Massachusetts Stormwater Standards Manual. MADEP. 2019. See their homepage at www.state.ma.gov/dep. MassGIS (Massachusetts Office of Geographic and Environmental Information). 2023. See their homepage at: http://www.mass.gov/mgis/. National Oceanic and Atmospheric Administration (NOAA) - National Weather Service (NWS). 2017. Point Precipitation Frequency Estimates: MA. NOAA Atlas 14, Volume 10, Version 3. https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=ma National Oceanic and Atmospheric Administration (NOAA) – Tides & Currents. 2024. Water Levels. https://tidesandcurrents.noaa.gov/waterlevels.html?id=8447435 Paradigm Environmental. 2019. USEPA Memo. Tisbury MA Impervious Cover Disconnection (ICD) Project: An Integrated Stormwater Management Approach for Promoting Urban Community Sustainability and Resilience - Task 4D. Develop Planning Level GI SCM Performance Curves for Estimating Cumulative Reductions in SW-Related Indicator Bacteria. USEPA (United States Environmental Protection Agency). 2019. National Pollutant Discharge Elimination System (NPDES). See their homepage at: http://cfpub.epa.gov/NPDES/. USEPA. 2021. National Pollutant Discharge Elimination System (NPDES)-General Permits for Stormwater Discharges from Small Municipal Separate Storm Sewer Systems in Massachusetts (as modified). APPENDIX A – Drainage Areas  Existing and Proposed Drainage Areas Maps  Land Coverage Summaries 14161210864 68101214 14last modified: 02/02/26 printed: 02/02/26 by jv H:\Projects\2022\22108 APCC Yarmouth\Drawings\GROVE\22108A GROVE DA.dwg 2/2/2026 JLV CY MW 0SCALE IN FEET30DA1SP1P1252BDA1SP1607252B607Prepared For:Sheet Number:Project Number:Plan Set: Plan Title:of122108A2Town of Yarmouth DPW Phone: 74 Town Brook Road West Yarmouth, MA 02673 (508) 398-2231 ext. 1250 Horsley Witten Group, Inc. Sustainable Environmental Solutions 90 Route 6A Sandwich, MA 02563 horsleywittengroup.comDRAINAGEAREABOUNDARYDIRT/SANDROOFTOPGRASSPAVEMENTSTUDY POINTSITE HIH-3: GROVE STREET STORMWATER RETROFIT DESIGN AND IMPLEMENTATION PROJECT - 75% DESIGN YARMOUTH, MASSACHUSETTS EXISTING DRAINAGE MAPDRAINAGE AREA1,0005,000SOIL BOUNDARYTIME OF CONCENTRATION FLOW PATH2' CONTOURCARVER COARSE SAND(3 TO 8 PERCENT SLOPES) (HSG A)WATERLEGENDSOIL TYPESIMP. AREATOTAL AREA(SQUARE FEET)PONDWATERChecked By:Drawn By:Design By:Date:7,93814,530BRUSH/MEADOW 14161210864 68101214 146 5 5 6 6 5 67 776last modified: 02/02/26 printed: 02/03/26 by jv H:\Projects\2022\22108 APCC Yarmouth\Drawings\GROVE\22108A GROVE DA.dwg 2/2/2026 JLV CY MW 0SCALE IN FEET30DA1SP1P1252BDA1ASP1607252B607Prepared For:Sheet Number:Project Number:Plan Set: Plan Title:of222108A2Town of Yarmouth DPW Phone: 74 Town Brook Road West Yarmouth, MA 02673 (508) 398-2231 ext. 1250 Horsley Witten Group, Inc. Sustainable Environmental Solutions 90 Route 6A Sandwich, MA 02563 horsleywittengroup.comSTUDY POINTSITE HIH-3: GROVE STREET STORMWATER RETROFIT DESIGN AND IMPLEMENTATION PROJECT - 75% DESIGN YARMOUTH, MASSACHUSETTS PROPOSED DRAINAGE MAPDRAINAGE AREASOIL BOUNDARYTIME OF CONCENTRATION FLOW PATH2' CONTOURCARVER COARSE SAND(3 TO 8 PERCENT SLOPES) (HSG A)WATERLEGENDSOIL TYPESPONDChecked By:Drawn By:Design By:Date:7,34314,191DA1B0339BIO1DRAINAGEAREABOUNDARYDIRT/SANDROOFTOPGRASSPAVEMENT1,0005,000IMP. AREATOTAL AREA(SQUARE FEET)WATERBRUSH/MEADOW GROVE SW RETROFIT Calc'd by: YARMOUTH, MA Checked by: Date: DA1 WQv 1.21 1-yr 3.05 2-yr 3.60 5-yr 4.52 10-yr 5.29 25-yr 6.57 100-yr 8.64 DA1 Cover type Area, ft2 Area, ac Note Paved 7,938 0.182 Dirt 876 0.020 Roof 0 0.000 Water 0 0.000 Brush 1,106 0.025 Grass 4,610 0.106 Area, ft2 Area, ac Percent TOTAL 14,530 0.334 7,938 0.182 55 ALL Cover type Area, ft2 Area, ac Note Paved 7,938 0.182 Dirt 876 0.020 Roof 0 0.000 Water 0 0.000 Brush 1,106 0.025 Grass 4,610 0.106 Area, ft2 Area, ac Percent TOTAL 14,530 0.334 7,938 0.182 55 Existing Drainage Conditions DRAINAGE AREAS NOAA 14+ 24-hr Type III (inches) JLV MW 2/2/2026 END OF GROVE END OF GROVE Impervious ALL EX AREAS COMBINED Impervious GROVE SW RETROFIT Calc'd by: YARMOUTH, MA Checked by: Date: DA1A DA1B WQv 1.21 1-yr 3.05 2-yr 3.60 5-yr 4.52 10-yr 5.29 25-yr 6.57 100-yr 8.64 DA1A Cover type Area, ft2 Area, ac Note Paved 7,343 0.169 Sand 113 0.003 Dirt 615 Roof 0.000 Water 388 0.009 Brush/Meadow 1,122 0.026 Grass 4,610 0.106 Area, ft2 Area, ac Percent TOTAL 14,191 0.326 7,343 0.169 52 DA1B Cover type Area, ft2 Area, ac Note Paved 0 0.000 Sand 51 0.001 Roof 0 0.000 Water 0 0.000 Brush/Meadow 288 0.007 Grass 0 0.000 Area, ft2 Area, ac Percent TOTAL 339 0.008 0 0.000 0 ALL Cover type Area, ft2 Area, ac Note Paved 7,343 0.169 Sand 164 0.004 Dirt 615 Roof 0 0.000 Water 388 0.009 Brush/Meadow 1,410 0.032 Grass 4,610 0.106 Area, ft2 Area, ac Percent TOTAL 14,530 0.334 7,343 0.169 51 BEACH ALL PR AREAS COMBINED Impervious Impervious JLV MW Proposed Drainage Conditions 2/2/2026 DRAINAGE AREAS NOAA 14+ BIO 1 24-hr Type III (inches) BEACH BIO 1 Impervious APPENDIX B – Hydrologic/Hydraulic Model Results HydroCAD® Results  Existing  Proposed DA1 END OF GROVE SP1 STUDY POINT 1 Routing Diagram for 22108 GROVE EX Prepared by Horsley Witten Inc, Printed 2/3/2026 HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Subcat Reach Pond Link 22108 GROVE EX Printed 2/3/2026Prepared by Horsley Witten Inc Page 2HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Rainfall Events Listing Event# Event Name Storm Type Curve Mode Duration (hours) B/B Depth (inches) AMC 1 2-yr Type III 24-hr Default 24.00 1 3.60 2 2 10-yr Type III 24-hr Default 24.00 1 5.29 2 3 25-yr Type III 24-hr Default 24.00 1 6.57 2 4 100-yr Type III 24-hr Default 24.00 1 8.64 2 22108 GROVE EX Printed 2/3/2026Prepared by Horsley Witten Inc Page 3HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Area Listing (all nodes) Area (acres) CN Description (subcatchment-numbers) 0.106 39 >75% Grass cover, Good, HSG A (DA1) 0.025 30 Brush, Good, HSG A (DA1) 0.020 72 Dirt roads, HSG A (DA1) 0.182 98 Paved parking, HSG A (DA1) 0.334 73 TOTAL AREA Type III 24-hr 2-yr Rainfall=3.60"22108 GROVE EX Printed 2/3/2026Prepared by Horsley Witten Inc Page 4HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: END OF GROVE Runoff = 0.47 cfs @ 12.09 hrs, Volume= 0.032 af, Depth> 1.14" Routed to Pond SP1 : STUDY POINT 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 2-yr Rainfall=3.60" Area (sf) CN Description 7,938 98 Paved parking, HSG A 876 72 Dirt roads, HSG A 4,610 39 >75% Grass cover, Good, HSG A 1,106 30 Brush, Good, HSG A 14,530 73 Weighted Average 6,592 45.37% Pervious Area 7,938 54.63% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond SP1: STUDY POINT 1 Inflow Area = 0.334 ac, 54.63% Impervious, Inflow Depth > 1.14" for 2-yr event Inflow = 0.47 cfs @ 12.09 hrs, Volume= 0.032 af Primary = 0.47 cfs @ 12.09 hrs, Volume= 0.032 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 10-yr Rainfall=5.29"22108 GROVE EX Printed 2/3/2026Prepared by Horsley Witten Inc Page 5HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: END OF GROVE Runoff = 0.98 cfs @ 12.08 hrs, Volume= 0.065 af, Depth> 2.33" Routed to Pond SP1 : STUDY POINT 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 10-yr Rainfall=5.29" Area (sf) CN Description 7,938 98 Paved parking, HSG A 876 72 Dirt roads, HSG A 4,610 39 >75% Grass cover, Good, HSG A 1,106 30 Brush, Good, HSG A 14,530 73 Weighted Average 6,592 45.37% Pervious Area 7,938 54.63% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond SP1: STUDY POINT 1 Inflow Area = 0.334 ac, 54.63% Impervious, Inflow Depth > 2.33" for 10-yr event Inflow = 0.98 cfs @ 12.08 hrs, Volume= 0.065 af Primary = 0.98 cfs @ 12.08 hrs, Volume= 0.065 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 25-yr Rainfall=6.57"22108 GROVE EX Printed 2/3/2026Prepared by Horsley Witten Inc Page 6HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: END OF GROVE Runoff = 1.40 cfs @ 12.08 hrs, Volume= 0.092 af, Depth> 3.32" Routed to Pond SP1 : STUDY POINT 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 25-yr Rainfall=6.57" Area (sf) CN Description 7,938 98 Paved parking, HSG A 876 72 Dirt roads, HSG A 4,610 39 >75% Grass cover, Good, HSG A 1,106 30 Brush, Good, HSG A 14,530 73 Weighted Average 6,592 45.37% Pervious Area 7,938 54.63% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond SP1: STUDY POINT 1 Inflow Area = 0.334 ac, 54.63% Impervious, Inflow Depth > 3.32" for 25-yr event Inflow = 1.40 cfs @ 12.08 hrs, Volume= 0.092 af Primary = 1.40 cfs @ 12.08 hrs, Volume= 0.092 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 100-yr Rainfall=8.64"22108 GROVE EX Printed 2/3/2026Prepared by Horsley Witten Inc Page 7HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: END OF GROVE Runoff = 2.10 cfs @ 12.08 hrs, Volume= 0.140 af, Depth> 5.04" Routed to Pond SP1 : STUDY POINT 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs Type III 24-hr 100-yr Rainfall=8.64" Area (sf) CN Description 7,938 98 Paved parking, HSG A 876 72 Dirt roads, HSG A 4,610 39 >75% Grass cover, Good, HSG A 1,106 30 Brush, Good, HSG A 14,530 73 Weighted Average 6,592 45.37% Pervious Area 7,938 54.63% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond SP1: STUDY POINT 1 Inflow Area = 0.334 ac, 54.63% Impervious, Inflow Depth > 5.04" for 100-yr event Inflow = 2.10 cfs @ 12.08 hrs, Volume= 0.140 af Primary = 2.10 cfs @ 12.08 hrs, Volume= 0.140 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs DA1A BIO 1 DA1B BEACH BIO1 BIORETENTION 1 SP1 STUDY POINT 1 Routing Diagram for 22108 GROVE PR Prepared by Horsley Witten Inc, Printed 2/3/2026 HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Subcat Reach Pond Link 22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 2HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Rainfall Events Listing (selected events) Event# Event Name Storm Type Curve Mode Duration (hours) B/B Depth (inches) AMC 1 2-yr Type III 24-hr Default 24.00 1 3.60 2 2 10-yr Type III 24-hr Default 24.00 1 5.29 2 3 25-yr Type III 24-hr Default 24.00 1 6.57 2 4 100-yr Type III 24-hr Default 24.00 1 8.64 2 22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 3HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Area Listing (all nodes) Area (acres) CN Description (subcatchment-numbers) 0.106 30 >75% Grass cover, Good, HSG A (DA1A) 0.014 72 Dirt roads, HSG A (DA1A) 0.032 30 Meadow, non-grazed, HSG A (DA1A, DA1B) 0.169 98 Paved parking, HSG A (DA1A) 0.004 63 Sand, HSG A (DA1A, DA1B) 0.009 98 Water Surface, HSG A (DA1A) 0.334 68 TOTAL AREA Type III 24-hr 2-yr Rainfall=3.60"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 4HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA1A: BIO 1 Runoff = 0.36 cfs @ 12.09 hrs, Volume= 0.028 af, Depth= 1.01" Routed to Pond BIO1 : BIORETENTION 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 2-yr Rainfall=3.60" Area (sf) CN Description 7,343 98 Paved parking, HSG A 615 72 Dirt roads, HSG A * 113 63 Sand, HSG A 388 98 Water Surface, HSG A * 4,610 30 >75% Grass cover, Good, HSG A 1,122 30 Meadow, non-grazed, HSG A 14,191 69 Weighted Average 6,460 35 45.52% Pervious Area 7,731 98 54.48% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment DA1B: BEACH Runoff = 0.00 cfs @ 1.00 hrs, Volume= 0.000 af, Depth= 0.00" Routed to Pond SP1 : STUDY POINT 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 2-yr Rainfall=3.60" Area (sf) CN Description * 51 63 Sand, HSG A 288 30 Meadow, non-grazed, HSG A 339 35 Weighted Average 339 35 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond BIO1: BIORETENTION 1 Inflow Area = 0.326 ac, 54.48% Impervious, Inflow Depth = 1.01" for 2-yr event Inflow = 0.36 cfs @ 12.09 hrs, Volume= 0.028 af Outflow = 0.38 cfs @ 12.16 hrs, Volume= 0.028 af, Atten= 0%, Lag= 4.2 min Discarded = 0.02 cfs @ 12.16 hrs, Volume= 0.018 af Primary = 0.35 cfs @ 12.16 hrs, Volume= 0.009 af Routed to Pond SP1 : STUDY POINT 1 Type III 24-hr 2-yr Rainfall=3.60"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 5HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Peak Elev= 5.06' @ 12.16 hrs Surf.Area= 418 sf Storage= 192 cf Plug-Flow detention time= 58.8 min calculated for 0.028 af (100% of inflow) Center-of-Mass det. time= 58.7 min ( 928.4 - 869.7 ) Volume Invert Avail.Storage Storage Description #1 4.50' 405 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 4.50 270 0 0 5.00 400 168 168 5.50 550 238 405 Device Routing Invert Outlet Devices #1 Primary 5.00'8.5' long x 0.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 Coef. (English) 2.80 2.92 3.08 3.30 3.32 #2 Discarded 4.50'2.410 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.02 cfs @ 12.16 hrs HW=5.06' (Free Discharge) 2=Exfiltration (Exfiltration Controls 0.02 cfs) Primary OutFlow Max=0.32 cfs @ 12.16 hrs HW=5.06' (Free Discharge) 1=Broad-Crested Rectangular Weir (Weir Controls 0.32 cfs @ 0.66 fps) Summary for Pond SP1: STUDY POINT 1 Inflow Area = 0.334 ac, 53.21% Impervious, Inflow Depth = 0.33" for 2-yr event Inflow = 0.35 cfs @ 12.16 hrs, Volume= 0.009 af Primary = 0.35 cfs @ 12.16 hrs, Volume= 0.009 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 10-yr Rainfall=5.29"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 6HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA1A: BIO 1 Runoff = 0.82 cfs @ 12.08 hrs, Volume= 0.059 af, Depth= 2.17" Routed to Pond BIO1 : BIORETENTION 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 10-yr Rainfall=5.29" Area (sf) CN Description 7,343 98 Paved parking, HSG A 615 72 Dirt roads, HSG A * 113 63 Sand, HSG A 388 98 Water Surface, HSG A * 4,610 30 >75% Grass cover, Good, HSG A 1,122 30 Meadow, non-grazed, HSG A 14,191 69 Weighted Average 6,460 35 45.52% Pervious Area 7,731 98 54.48% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment DA1B: BEACH Runoff = 0.00 cfs @ 14.75 hrs, Volume= 0.000 af, Depth= 0.12" Routed to Pond SP1 : STUDY POINT 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 10-yr Rainfall=5.29" Area (sf) CN Description * 51 63 Sand, HSG A 288 30 Meadow, non-grazed, HSG A 339 35 Weighted Average 339 35 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond BIO1: BIORETENTION 1 Inflow Area = 0.326 ac, 54.48% Impervious, Inflow Depth = 2.17" for 10-yr event Inflow = 0.82 cfs @ 12.08 hrs, Volume= 0.059 af Outflow = 0.82 cfs @ 12.10 hrs, Volume= 0.059 af, Atten= 0%, Lag= 0.8 min Discarded = 0.02 cfs @ 12.10 hrs, Volume= 0.025 af Primary = 0.80 cfs @ 12.10 hrs, Volume= 0.034 af Routed to Pond SP1 : STUDY POINT 1 Type III 24-hr 10-yr Rainfall=5.29"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 7HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Peak Elev= 5.10' @ 12.10 hrs Surf.Area= 431 sf Storage= 211 cf Plug-Flow detention time= 43.2 min calculated for 0.059 af (100% of inflow) Center-of-Mass det. time= 43.2 min ( 889.4 - 846.2 ) Volume Invert Avail.Storage Storage Description #1 4.50' 405 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 4.50 270 0 0 5.00 400 168 168 5.50 550 238 405 Device Routing Invert Outlet Devices #1 Primary 5.00'8.5' long x 0.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 Coef. (English) 2.80 2.92 3.08 3.30 3.32 #2 Discarded 4.50'2.410 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.02 cfs @ 12.10 hrs HW=5.10' (Free Discharge) 2=Exfiltration (Exfiltration Controls 0.02 cfs) Primary OutFlow Max=0.78 cfs @ 12.10 hrs HW=5.10' (Free Discharge) 1=Broad-Crested Rectangular Weir (Weir Controls 0.78 cfs @ 0.90 fps) Summary for Pond SP1: STUDY POINT 1 Inflow Area = 0.334 ac, 53.21% Impervious, Inflow Depth = 1.23" for 10-yr event Inflow = 0.80 cfs @ 12.10 hrs, Volume= 0.034 af Primary = 0.80 cfs @ 12.10 hrs, Volume= 0.034 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 25-yr Rainfall=6.57"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 8HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA1A: BIO 1 Runoff = 1.21 cfs @ 12.08 hrs, Volume= 0.086 af, Depth= 3.16" Routed to Pond BIO1 : BIORETENTION 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 25-yr Rainfall=6.57" Area (sf) CN Description 7,343 98 Paved parking, HSG A 615 72 Dirt roads, HSG A * 113 63 Sand, HSG A 388 98 Water Surface, HSG A * 4,610 30 >75% Grass cover, Good, HSG A 1,122 30 Meadow, non-grazed, HSG A 14,191 69 Weighted Average 6,460 35 45.52% Pervious Area 7,731 98 54.48% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment DA1B: BEACH Runoff = 0.00 cfs @ 12.38 hrs, Volume= 0.000 af, Depth= 0.38" Routed to Pond SP1 : STUDY POINT 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 25-yr Rainfall=6.57" Area (sf) CN Description * 51 63 Sand, HSG A 288 30 Meadow, non-grazed, HSG A 339 35 Weighted Average 339 35 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond BIO1: BIORETENTION 1 Inflow Area = 0.326 ac, 54.48% Impervious, Inflow Depth = 3.16" for 25-yr event Inflow = 1.21 cfs @ 12.08 hrs, Volume= 0.086 af Outflow = 1.21 cfs @ 12.09 hrs, Volume= 0.086 af, Atten= 0%, Lag= 0.8 min Discarded = 0.02 cfs @ 12.09 hrs, Volume= 0.029 af Primary = 1.19 cfs @ 12.09 hrs, Volume= 0.057 af Routed to Pond SP1 : STUDY POINT 1 Type III 24-hr 25-yr Rainfall=6.57"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 9HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Peak Elev= 5.14' @ 12.09 hrs Surf.Area= 441 sf Storage= 224 cf Plug-Flow detention time= 36.1 min calculated for 0.086 af (100% of inflow) Center-of-Mass det. time= 36.0 min ( 871.2 - 835.2 ) Volume Invert Avail.Storage Storage Description #1 4.50' 405 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 4.50 270 0 0 5.00 400 168 168 5.50 550 238 405 Device Routing Invert Outlet Devices #1 Primary 5.00'8.5' long x 0.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 Coef. (English) 2.80 2.92 3.08 3.30 3.32 #2 Discarded 4.50'2.410 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.02 cfs @ 12.09 hrs HW=5.13' (Free Discharge) 2=Exfiltration (Exfiltration Controls 0.02 cfs) Primary OutFlow Max=1.16 cfs @ 12.09 hrs HW=5.13' (Free Discharge) 1=Broad-Crested Rectangular Weir (Weir Controls 1.16 cfs @ 1.02 fps) Summary for Pond SP1: STUDY POINT 1 Inflow Area = 0.334 ac, 53.21% Impervious, Inflow Depth = 2.07" for 25-yr event Inflow = 1.19 cfs @ 12.09 hrs, Volume= 0.058 af Primary = 1.19 cfs @ 12.09 hrs, Volume= 0.058 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 100-yr Rainfall=8.64"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 10HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA1A: BIO 1 Runoff = 1.87 cfs @ 12.08 hrs, Volume= 0.133 af, Depth= 4.90" Routed to Pond BIO1 : BIORETENTION 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 100-yr Rainfall=8.64" Area (sf) CN Description 7,343 98 Paved parking, HSG A 615 72 Dirt roads, HSG A * 113 63 Sand, HSG A 388 98 Water Surface, HSG A * 4,610 30 >75% Grass cover, Good, HSG A 1,122 30 Meadow, non-grazed, HSG A 14,191 69 Weighted Average 6,460 35 45.52% Pervious Area 7,731 98 54.48% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment DA1B: BEACH Runoff = 0.01 cfs @ 12.12 hrs, Volume= 0.001 af, Depth= 1.03" Routed to Pond SP1 : STUDY POINT 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr 100-yr Rainfall=8.64" Area (sf) CN Description * 51 63 Sand, HSG A 288 30 Meadow, non-grazed, HSG A 339 35 Weighted Average 339 35 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond BIO1: BIORETENTION 1 Inflow Area = 0.326 ac, 54.48% Impervious, Inflow Depth = 4.90" for 100-yr event Inflow = 1.87 cfs @ 12.08 hrs, Volume= 0.133 af Outflow = 1.88 cfs @ 12.09 hrs, Volume= 0.133 af, Atten= 0%, Lag= 0.7 min Discarded = 0.03 cfs @ 12.09 hrs, Volume= 0.032 af Primary = 1.85 cfs @ 12.09 hrs, Volume= 0.101 af Routed to Pond SP1 : STUDY POINT 1 Type III 24-hr 100-yr Rainfall=8.64"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 11HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Peak Elev= 5.18' @ 12.09 hrs Surf.Area= 455 sf Storage= 245 cf Plug-Flow detention time= 26.6 min calculated for 0.133 af (100% of inflow) Center-of-Mass det. time= 26.6 min ( 849.2 - 822.6 ) Volume Invert Avail.Storage Storage Description #1 4.50' 405 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 4.50 270 0 0 5.00 400 168 168 5.50 550 238 405 Device Routing Invert Outlet Devices #1 Primary 5.00'8.5' long x 0.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 Coef. (English) 2.80 2.92 3.08 3.30 3.32 #2 Discarded 4.50'2.410 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.03 cfs @ 12.09 hrs HW=5.18' (Free Discharge) 2=Exfiltration (Exfiltration Controls 0.03 cfs) Primary OutFlow Max=1.81 cfs @ 12.09 hrs HW=5.18' (Free Discharge) 1=Broad-Crested Rectangular Weir (Weir Controls 1.81 cfs @ 1.19 fps) Summary for Pond SP1: STUDY POINT 1 Inflow Area = 0.334 ac, 53.21% Impervious, Inflow Depth = 3.67" for 100-yr event Inflow = 1.86 cfs @ 12.09 hrs, Volume= 0.102 af Primary = 1.86 cfs @ 12.09 hrs, Volume= 0.102 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs 22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 1HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Rainfall Events Listing (selected events) Event# Event Name Storm Type Curve Mode Duration (hours) B/B Depth (inches) AMC 1 WQv Type III 24-hr Default 24.00 1 1.19 2 Type III 24-hr WQv Rainfall=1.19"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 2HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA1A: BIO 1 Runoff = 0.19 cfs @ 12.07 hrs, Volume= 0.014 af, Depth= 0.53" Routed to Pond BIO1 : BIORETENTION 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr WQv Rainfall=1.19" Area (sf) CN Description 7,343 98 Paved parking, HSG A 615 72 Dirt roads, HSG A * 113 63 Sand, HSG A 388 98 Water Surface, HSG A * 4,610 30 >75% Grass cover, Good, HSG A 1,122 30 Meadow, non-grazed, HSG A 14,191 Weighted Average 6,460 35 45.52% Pervious Area 7,731 98 54.48% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Subcatchment DA1B: BEACH Runoff = 0.00 cfs @ 23.98 hrs, Volume= 0.000 af, Depth= 0.00" Routed to Pond SP1 : STUDY POINT 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Type III 24-hr WQv Rainfall=1.19" Area (sf) CN Description * 51 63 Sand, HSG A 288 30 Meadow, non-grazed, HSG A 339 Weighted Average 339 35 100.00% Pervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Summary for Pond BIO1: BIORETENTION 1 Inflow Area = 0.326 ac, 54.48% Impervious, Inflow Depth = 0.53" for WQv event Inflow = 0.19 cfs @ 12.07 hrs, Volume= 0.014 af Outflow = 0.09 cfs @ 12.27 hrs, Volume= 0.014 af, Atten= 53%, Lag= 11.8 min Discarded = 0.02 cfs @ 12.27 hrs, Volume= 0.013 af Primary = 0.07 cfs @ 12.27 hrs, Volume= 0.001 af Routed to Pond SP1 : STUDY POINT 1 Type III 24-hr WQv Rainfall=1.19"22108 GROVE PR Printed 2/3/2026Prepared by Horsley Witten Inc Page 3HydroCAD® 10.20-6a s/n 01445 © 2024 HydroCAD Software Solutions LLC Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs Peak Elev= 5.02' @ 12.27 hrs Surf.Area= 406 sf Storage= 176 cf Plug-Flow detention time= 52.4 min calculated for 0.014 af (100% of inflow) Center-of-Mass det. time= 52.3 min ( 834.5 - 782.1 ) Volume Invert Avail.Storage Storage Description #1 4.50' 405 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 4.50 270 0 0 5.00 400 168 168 5.50 550 238 405 Device Routing Invert Outlet Devices #1 Primary 5.00'8.5' long x 0.5' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 Coef. (English) 2.80 2.92 3.08 3.30 3.32 #2 Discarded 4.50'2.410 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.02 cfs @ 12.27 hrs HW=5.02' (Free Discharge) 2=Exfiltration (Exfiltration Controls 0.02 cfs) Primary OutFlow Max=0.06 cfs @ 12.27 hrs HW=5.02' (Free Discharge) 1=Broad-Crested Rectangular Weir (Weir Controls 0.06 cfs @ 0.38 fps) Summary for Pond SP1: STUDY POINT 1 Inflow Area = 0.334 ac, 53.21% Impervious, Inflow Depth = 0.04" for WQv event Inflow = 0.07 cfs @ 12.27 hrs, Volume= 0.001 af Primary = 0.07 cfs @ 12.27 hrs, Volume= 0.001 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.05 hrs APPENDIX C – Soil Test Pit Logs Surface elevation 850A 30F Sun WeatherTimeDateHole # 3. Distances From: 4. Unsuitable Materials Present: 5. Groundwater Observed: Open Water Body Property Line 75 10 Sandy glaciofluvial deposits Moraines, outwash plains Landform Position on Landscape (SU, SH, BS, FS, TS) ROW Surface Stones (e.g. cobbles, stones, boulders, etc.) Grass, brambles Additional Notes: Drinking Water Well Drainage Way 1. Land Use: Description of Location: 2. Soil Parent Material: (e.g. woodland, agricultural field, vacant lot, etc.) M Fi Soil Log 36-69 C CS 10YR 5/6 M Fi 24-36 B MS 10YR 4/6 - - M Fi - - Depth (in) Soil Horizon/ Layer Soil Texture (USDA) Soil Matrix: Color- Moist (Munsell) 9-24 FILL SL MIX - - - - M Fi0-9 A SL 10YR 2/2 If Yes: If Yes:69"Depth standing water in holeDepth weeping from pit Soil Consistence (Moist) Soil StructureRedoximorphic Features Coarse Fragments % by Volume Cobbles/StonesColorPercentGravel Other Depth Other Wetlands 50 feet feet feet feet feet feet North side of edge of pavement, end of Grove St 6.7 Form 11 - Soil Suitability Assessment for On-Site Sewage Disposal C. On-Site Review Commonwealth of Massachusetts YarmouthCity/Town of Vegetation Slope (%) Latitude Longitude 41º38'46.80"N 70º16'12.07"WDeep Observation Hole Number:1 1/4/24 3-8No Yes No Disturbed Soil Fill Material Weathered/Fractured Rock Bedrock Yes No APPENDIX D – Operation and Maintenance Guide Stormwater O&M Guide 1 February 2026 Grove Street Stormwater Retrofit Project – Yarmouth, MA Stormwater Operations & Maintenance Guide Grove Street Stormwater Retrofit Project Table of Contents 1. INTRODUCTION ......................................................................................................................... 2 2. RESPONSIBLE PARTIES AND BUDGET ........................................................................................ 3 3. GREEN STORMWATER INFRASTRUCTURE ................................................................................ 4 3.1. How Does Green Infrastructure Work? ........................................................................................ 4 3.2. What is required for Maintenance? .............................................................................................. 4 3.3. What practices are used at this site? ............................................................................................ 5 4. STRUCTURAL COMPONENTS: BIORETENTION AREA ................................................................ 6 5. PLANTINGS ................................................................................................................................ 8 5.1. Plantings ........................................................................................................................................ 8 6. GENERAL SITE MAINTENANCE ............................................................................................... 18 7. LONG-TERM POLLUTION PREVENTION MEASURES ............................................................... 19 ATTACHMENTS A. Maintenance Checklists B. Overall Stormwater Control Measures Locations Plan C. Planting Plan Stormwater O&M Guide 2 February 2026 Grove Street Stormwater Retrofit Project – Yarmouth, MA 1. INTRODUCTION This document provides a general description along with the operation and maintenance requirements for the Grove Street Stormwater Retrofit project within the right-of-way of Grove Street at the beach access point. The responsible parties are required to inspect and maintain all measures as outlined in this maintenance guide throughout the year. Site maintenance is divided into three categories as outlined below. 1. Green Stormwater Infrastructure • Structural Components • Structural Maintenance Schedule • Planting • Landscape Maintenance Schedule • Weed Guide 2. General Site Maintenance • Access Path • Trash & Debris • Pet Waste • Pavement Sweeping • Contributing Drainage Areas • Snow Removal • De-icing 3. Long-Term Pollution Prevention Measures Stormwater O&M Guide 3 February 2026 Grove Street Stormwater Retrofit Project – Yarmouth, MA 2. RESPONSIBLE PARTIES AND BUDGET Grove Street is a Town-owned and operated road. The Town will provide staff, volunteers as possible, and funding for the long-term O&M at the site. Estimated average annual O&M budget for the proposed system: • Bioretentions (1): $2,500 ($2,500/Bio) Replacement costs include all design components, plantings, and assumed escalation rate. Owner contact information is provided below: Owner: Town of Yarmouth Contact: Department of Public Works Amanda Lima, Town Engineer 74 Town Brook Road West Yarmouth, MA 02673 508-398-2231 Contact: Town of Yarmouth Department of Public Works Nathan Whetten, Senior Project Manager 74 Town Brook Road West Yarmouth, MA 02673 508-398-2231 Owner - Signature: Date: Owner - Signature: Date: Stormwater O&M Guide 4 February 2026 Grove Street Stormwater Retrofit Project – Yarmouth, MA 3. GREEN STORMWATER INFRASTRUCTURE 3.1. How Does Green Infrastructure Work? Green Stormwater Infrastructure (GSI) is a nature-based approach to stormwater treatment and management. These stormwater practices or “treatment areas” are designed to mimic nature and use the natural filtration properties of soil and plants to remove pollutants from stormwater runoff prior to discharging to the municipal drainage system or waterbodies. GSI relies on the following basic steps to function properly. Structural components of the practices facilitate the functioning of the steps. If one of these steps, or components, does not work properly, the entire system can be compromised and the GSI practice itself could be contributing to maintenance problems. This can lead to landscape nuisances, more frequent maintenance, and costly repairs/improvement. The steps are: 1. Collect (Inlets) 2. Move Water (Conveyance) if needed, can come after capturing sediment 3. Capture Sediment (Pretreatment) 4. Treat and Manage (Filter, Infiltrate or Store) 5. Overflow (Structures and Spillways) 3.2. What is required for Maintenance? As these are nature-based systems that rely on plant upkeep, the maintenance for GSI typically falls under landscape and general site maintenance services. Proper operation and maintenance (O&M) are vital to its long-term viability. Regularly scheduled maintenance can prevent system failures due to sediment build-up, damage, or deterioration. The maintenance requirements outlined in this guide are critical to ensure proper treatment, maintain storage capacity and preserve the visual integrity. General maintenance includes the following: 1. Removing sediment from the pretreatment practices used to capture sediment. 2. Maintaining the proper drainage function and pollutant removal capacity of the systems. 3. Maintaining healthy native trees, plants, and vegetative cover as well as the removal of unwanted weeds and invasive species. It is recommended that all practices be maintained regularly as part of the routine landscape maintenance or at a minimum four times per year and after major rain events: • Early Spring: during spring cleanup • Summer: during lawn mowing and other routine site maintenance • Early Fall: when leaves begin to fall • Late Fall/Early Winter: after all the leaves have fallen during leaf removal • After major storm events: 2” of rain or greater. Stormwater O&M Guide 5 February 2026 Grove Street Stormwater Retrofit Project – Yarmouth, MA The following sections describe the general function and landscape maintenance of each practice on the site. Included in the appendices is a specific Inspection Report for the site (Attachment A) along with a plan showing the location of the items to be inspected and maintained (Attachment B). 3.3. What practices are used at this site? The following practices are present at this site: a. Bioretention Area: A bioretention area is a stormwater management practice to manage and treat stormwater runoff using a conditioned planting soil bed or “filter” media and plants to filter runoff captured in a shallow depression. The method combines physical filtering and adsorption with bio-geochemical processes to remove pollutants. The maintenance for the green infrastructure is divided into two categories: a. The Structural Components that make up the basic steps of a functioning system. b. The Plantings that are the landscape and filtration element. Each category is further described in the sections below. Stormwater O&M Guide 6 February 2026 Grove Street Stormwater Retrofit Project – Yarmouth, MA 4. STRUCTURAL COMPONENTS: BIORETENTION AREA Structural Components 1. Collect: Stormwater runoff is directed to paved flume inlet where stormwater enters the sediment forebay. 2. Capture Sediment: Sand and debris settle out within sediment forebays. 3. Move Water: The stormwater discharges directly to the bioretention area via a boulder spillway. 4. Treat and Manage: Stormwater overtops the forebay spillway and flows through the planted bioretention area. Plants slow the water down, and the soil media and plant roots filter the runoff, removing nutrients and bacteria. The treated water then infiltrates into the soil below or overflows as described below. 5. Overflow: During larger rain events, the water level will rise and once the bioretention area reaches capacity, runoff will flow over the overflow spillway and continue down to the salt marsh and tidal river. 4 3 2 1 5 Stormwater O&M Guide 7 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA MAINTENANCE SCHEDULE: BIORETENTION AREA A site inspection of the bioretention components shall be conducted at least twice a year in the Spring and Fall, and after major storm events (2” of rain or greater). Debris and trash should be removed monthly (between April and November) and sediment removal should occur during the two site inspections and during the monthly debris and trash inspections as needed. See the calendar below and the Inspection Report in Attachment A for more information. Bioretention General Maintenance Schedule Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec Task Frequency & Time of the Year Site Inspection X X Debris & Trash Removal X X X X X X X X Sediment Removal X x x x x x x X should also be completed after major storm events X required inspection x as needed • When removing trash and debris during monthly inspections look for: o If sediment is > 3” in paver lined sediment forebays. Ensure sediment does not cause blockage of inlet or spillway. If it is, remove sediment. o If standing water does not drain after 48 hours. See Inspection Report for action items. • After rain event look for: o If standing water does not drain after 48 hours. See Inspection Report for action items. See Plantings section for information on plantings maintenance of the bioretention area. Use the plantings maintenance calendar to combine maintenance efforts. Stormwater O&M Guide 8 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA 5. PLANTINGS 5.1. Plantings The planting design for the site consists of three landscape maintenance areas- the “mow as needed” areas, “Seasonal mowing only” and the “Invasive removal by hand only” along the dune as indicated. In addition to the three maintenance areas the vegetation should be cut back, as needed, to keep the path clear. The plantings maintenance checklist is included in Attachment A, and the full planting plan is available in Attachment C. Stormwater O&M Guide 9 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA PLANTINGS: “MOW AS NEEDED” AREA MAINTENANCE There is an area of the site that is allowed to be maintained to low height “lawn” as necessary. Landscape maintenance of “mowed” lawn areas includes the following: Seeding Reseed bare spots with a seed mix that matches existing species. Mowing/Weed Whacking Cut only 1/3 of vegetation height at one time. Do not mow/cut during drought periods or when excessively wet. Depending on height of grasses and the time of year, grass cuttings/stalks may need to be raked and removed from site. Watering Allowing the area to “brown” is desired. Water only during drought conditions or during reseeding establishment period. Fertilizing No fertilizer shall be used. Weeding Weeding should be limited to invasive and weedy species (see section 3.6 Weed Identification below and the Weed Guide at https://web.uri.edu/riss/files/In-the-Weeds.pdf). Non-chemical methods (hand pulling and hoeing) are required; chemical herbicides should be avoided. Properly remove and dispose of all invasive species off site as to prevent colonization elsewhere, this includes disposal on land beyond the project area. Monitoring During the establishment period, walk the mow areas monthly during the first year to look for invasive species, bare spots and identify potential pest or disease problems. Properly remove and dispose of all invasive species as to prevent colonization elsewhere, this includes disposal on land beyond the project area. Debris & Trash Remove and properly dispose litter from all areas prior to mowing/cutting. Stormwater O&M Guide 10 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA PLANTINGS: “SEASONAL MOWING ONLY” AREA MAINTENANCE (UPLAND AND BIORETENTION AREAS) By design, plants in the bioretention and upland planting areas are meant to flourish throughout the growing season leaving dry standing stalks during the dormant months. Plants do not require fertilizers or watering (except during drought or establishment period). This area, as well as the area surrounding the forebay, is designated as “seasonal mowing only.” Frequent mowing would eliminate selected meadow species, may promote the growth of undesirable plants, and require additional maintenance and watering. It is recommended this area be cut back no more than one time per year and only as necessary. Remove and replace vegetation as necessary, using the appropriate species as shown on the Planting Plan. The best time to plant is in early to mid-fall or early to mid-spring. Specific maintenance activities of the “seasonal mowing only” area include: Seeding Reseed bare spots with the specified seed mix as shown on the Planting Plan. Cutting Back Recommend cutting with shears a maximum of once a year in early spring. Otherwise, allow areas to grow to their natural heights (12” to 36”) to maintain a meadow appearance. Do NOT cut area lower than 6” – maintain sporadic wooden stakes on site at 6” height to provide visual cues during cutting. Depending on height of grasses and the time of year, grass cuttings/stalks may need to be raked and removed from site so as not to clog the bioretention. Use a leaf blower as needed to assist in clean-up. Pruning Prune trees and shrubs to remove deadwood and low hanging or obstructing branches. Watering Water only during drought conditions or during reseeding establishment period. Fertilizing No fertilizer shall be used. Weeding Weeding should be limited to invasive and weedy species (see section on Weed Identification below and the Weed Guide at https://web.uri.edu/riss/files/In-the-Weeds.pdf). Non-chemical methods (hand pulling and hoeing) are required; chemical herbicides should be avoided. Properly remove and dispose off site all invasive species as to prevent colonization elsewhere; this includes disposal on land beyond the project area. Monitoring During the establishment period, walk the “seasonal mowing only” areas monthly without the intent to cut, but to look for invasive species, bare spots and identify potential pest or disease problems. Debris & Trash Remove and properly dispose of litter from all areas. Stormwater O&M Guide 11 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA PLANTINGS: “INVASIVE REMOVAL BY HAND” AREA MAINTENANCE (DUNE) This area is a delineated dune and is not to be disturbed unless to remove invasive species by hand. Maintenance of dune areas includes the following: Monitoring Walk the area to look for potential invasive species and identify potential disease. Weeding Weeding should be limited to invasive and weedy species (see section 3.6 Weed Identification below and the Weed Guide at https://web.uri.edu/riss/files/In-the-Weeds.pdf). Non-chemical methods (hand pulling and hoeing) are required; chemical herbicides should be avoided. Properly remove and dispose of all invasive species as to prevent colonization elsewhere; this includes disposal on land beyond the project area. Watering Water only during drought conditions or during the plant establishment period. Debris & Trash Remove and properly dispose litter from all natural areas. Stormwater O&M Guide 12 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA PLANTINGS: REPLACEMENTS The plants that thrive in bioretention areas are typically quite drought tolerant due to the filter profile having a top layer of planting soil and sandy soil media below. They need to be able to withstand periods of inundation after storm events; however, when it doesn’t rain, there will be less water held naturally in the sand than in other soil types for the plants to use, so they need to tolerate dry periods as well. Specifying plants native to the area increases the ecosystem benefits by helping to support native wildlife like pollinators. If replacements are needed, use the planting plan as a guide (see Attachment C). However, if all the plants of a certain species have not done well in the bioretention area or other locations on the site, do not replace with that same species. Rather, replant with one or more of the other species that has thrived under the conditions or have a plant professional choose a different species based on current photos of the site. Site specific considerations for plants in bioretention areas should be: • Preferably native and pollinator-friendly • Drought tolerant • Tolerant of inundation for 24 hours • Size constraints: - taller perennials at the bottom of the bioretention - shorter perennials on the side slopes • Salt and wind tolerant • A mix of different types of plants that will create a resilient plant community: cold & warm season grasses, perennials, groundcovers in all areas. Stormwater O&M Guide 13 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA PLANTINGS: MAINTENANCE SCHEDULE By design, plants in the bioretention area are meant to help filter the stormwater as it passes through and flourish throughout the growing season. The plants do not require fertilizers or mulch, and, after establishment, only need water during periods of drought. Remove and replace vegetation as necessary, using the appropriate species as discussed in the no-mow section above. Weeding and monitoring for invasive species should occur quarterly during the growing season. An annual spring “clean up” includes cutting last season’s growth of the perennials and pruning as needed. See the calendar below, the Plantings Maintenance Checklist in Attachment A, the Weed Identification section, and the Weed Identification Guide at https://web.uri.edu/riss/files/In-the-Weeds.pdf for more information. Bioretention Landscape Maintenance Schedule Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Task Frequency & Time of the Year Cutting X Weeding X X X X Monitoring X X X X Watering x x x x Plant Replacement x x x x No “Mow” Areas All areas X required x as needed • Trash and debris are removed during monthly structural component inspections but can also be completed during landscape maintenance visits for weeding and monitoring. Stormwater O&M Guide 14 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA PLANTINGS: WEED IDENTIFICATION Yellow Toadflax (Linaris vulgaris) Redroot Pigweed- (Amaranthus retroflexus) Smartweed (Polygonum lapathifolium) Dandelion (Taraxacum officinale) Stormwater O&M Guide 15 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA PLANTINGS: WEED IDENTIFICATION Fireweed (Erechtites hieracifolia) Spotted Spurge (Euphorbia maculata) Crabgrass (Digitaria ischaemum) Crabgrass with seedheads Ragweed (Ambrosia artemisiifolia) Japanese Knotweed (Polygonum cuspidatum) Stormwater O&M Guide 16 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA PLANTINGS: WEED IDENTIFICATION Ragweed (Ambrosia artemisiifolia) Oriental Bittersweet (Celastrus orbiculatus) Green Foxtail (Setaria viridis) Norway Maple Tree Seedling (Acer platanoides) Stormwater O&M Guide 17 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA PLANTINGS: WEED IDENTIFICATION Catalpa Tree Seedling (Catalpa speciosa) Purple Loosestrife (Lythrum salicaria) Field Bindweed (Convolvulus arvensis) Black Swallow-wort (Cynanchum louisea) Stormwater O&M Guide 18 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA 6. GENERAL SITE MAINTENANCE General site maintenance includes the following requirements: Trash & Debris Remove and properly dispose of all trash and debris. Pet Waste Visitors to the site are encouraged to pick up after their pets. Remove and properly dispose of all pet waste left behind. Pet waste should be picked up and disposed of properly to reduce bacteria and nutrient levels in stormwater. Pavement Sweeping Paved roadways should be mechanically swept, at a minimum of once per year in early spring, to remove accumulated sand and sediment debris. Snow Removal Due to the potential for plant damage, snow piling and or removal is NOT recommended in the bioretention area. De-Icing When de-icing compounds are necessary for areas draining to the green stormwater infrastructure, the least harmful chemicals should be used. Excessive salting should be avoided. Use of large amounts of sand should also be avoided, since it may obstruct the conveyance system. Stormwater O&M Guide 19 February 2026 Grove Street Stormwater Retrofit Project Yarmouth, MA 7. LONG-TERM POLLUTION PREVENTION MEASURES Long-term pollution prevention measures implemented at the site reduce pollutants in stormwater discharges. The following precautions will be employed on an on-going basis. Spill Prevention & Control Measures To minimize the risk of spills or other accidental exposure of materials and substances to stormwater runoff, the following material management is to be used when working on site. • Any materials stored on-site will be stored in a neat, orderly manner in their appropriate containers. • Products will be kept in their original containers with the original manufacturer’s label. • Substances will not be mixed with one another unless recommended by the manufacturer. • Manufacturers’ recommendations for proper use and disposal will be followed. • The contractor’s supervisor will be issued this Guide to ensure proper use and disposal of materials. Materials or substances listed below may be present on-site for maintenance and care should be taken to avoid spills: o Petroleum Based Products The following product-specific measures will be followed on-site: • Petroleum Products - All on-site vehicles will be monitored for leaks and receive preventative maintenance to reduce the chance of leakage. • Grass Clipping, Leaf Litter and Plant Debris – are to be removed from the property and not disposed on site. ATTACHMENT A – Maintenance Checklists • Bioretention Area Operation and Maintenance Checklist Grove Street Stormwater Retrofit Project 1 Date: Time: Inspector: Maintenance Item Description Maintenance (Y/N) 1, 2 & 3. Inlet Flume, Sediment Forebay, and Forebay Spillway Debris Cleanout Remove all trash, leaf litter and debris from the inlet and water quality unit. Sediment/Organic Debris Removal Check for clogging and sediment accumulation that impacts inflow and outflow. Remove and properly dispose of when sediment is >3” in forebays. Remove/cut any vegetation that sprouts through voids in stone, pavement, or pavers. Erosion Check for areas of erosion (gullies, animal burrowing, or overtopping), particularly near forebay spillway boulders, perimeter, and guard rail posts. Repair as necessary and return to design grades. Actions to be taken: 4 & 5. Bioretention Area and Overflow Spillway Debris Cleanout Remove trash and debris from the surface. Erosion Signs of erosion gullies, animal burrowing, or overtopping are observed. Repair as necessary. Sediment/Organic Debris Removal Remove sediment accumulation and properly dispose when accumulation is greater than or equal to 3 inches.* Water Draining properly If standing water is observed in bioretention area for more than 48 hours after a storm event, rototill or aerate the bottom 6 inches to break up any hard-packed sediment, and re-plant as needed. Look for areas of erosion in the overflow spillway between the boulders, vegetated area, and beach. Repair as necessary. Actions to be taken: Operation and Maintenance Checklist Grove Street Stormwater Retrofit Project 2 Maintenance Item Description Maintenance (Y/N) General Site Maintenance Debris Removal Remove trash from perimeter areas. Pet Waste Removal Remove any pet waste from perimeter areas. Pavement Sweeping Sweep road minimum once a year after spring thaw. Contributing drainage area Confirm that contributing drainage area stabilized – stabilize as necessary. Snow Removal Ensure snow piles do no block inlet flume and are not placed in the bioretention area. De-Icing Do not remove ice in the bioretention areas. If needed on road, use de-icing compounds with the least harmful chemicals. Avoid excessive salting or large amounts of sand. Actions to be taken: *Sediment shall be disposed of offsite in a pre-approved location. Plantings Maintenance Checklist Grove Street Stormwater Retrofit Project 1 Location: Date: Inspector: Task Description Complete (Y/N) Cutting • Cut with shears once a year in the early spring. • Do not cut lower than 12”. • Do not cut planted shrubs or trees • Blow out leaves and cuttings for easy removal. • Remove cuttings so the bioretention area does not clog. Weeding • Weeding should be limited to invasive and exotic species, which can overwhelm the desired plant community.* • Non-chemical methods including hand pulling and hoeing are recommended. • Chemical herbicides are not allowed. Monitoring • Look for potential invasive species and identify potential disease. Remove and dispose of all invasive species.* (see weeding) Watering • During establishment or drought conditions, plants should be watered a minimum of once every seven to ten days. Plant Replacement • Replace/replant diseases, unhealthy or dead plans to maintain a healthy plant community Fertilizing NONE Mulch NONE Mowing • Mow or line-trim as needed to provide and maintain access and visual clearance along guardrails and bicycle parking. • Do not cut lower than 4” • Blow out leaves and cuttings for easy removal. • Remove cuttings so the bioretention area does not clog. Actions to be taken: *Invasive species shall be disposed of offsite in a pre-approved location. Species observed on or nearby site include Asian bittersweet and multiflora rose. Mow as needed areas Seasonal mowing only and Invasive removal by hand only areas All areas ATTACHMENT B – Overall SCM Locations ATTACHMENT C – Planting Plan APPENDIX E – Pollutant Controls During Construction Pollutant Controls During Construction 1 October 2025 Grove Street Stormwater Retrofit Project – Yarmouth, MA POLLUTANT CONTROLS DURING CONSTRUCTION 1.1 Structural Practices The following are the structural practices that will be implemented as part of the construction activity. • Sediment Silt Sock Barrier will be installed prior to commencement of construction. The silt sock will be used on the downgradient portions of the limit of work to allow water to flow through it while keeping sediment on site. The Town will be informed upon their installation so that they may inspect these barriers prior to construction. Portions of these barriers will be replaced and/or repaired as necessary. Barriers will be installed parallel to land slope at the perimeter of the work site, as shown on the Plans. Details are provided in the Plans. • Temporary Sediment Traps/Basins should be installed as needed during construction. All sediment traps/basins will be inspected at least once every seven calendar days and immediately after storm events by the Construction Manager. • Slope Stabilization will occur immediately upon obtaining final grades as shown on the project site plans. Runoff should be blocked from entering the paved flume/bioretention area until final stabilization has been achieved. Areas that fail to stabilize will be re-graded to final grade and stabilized as necessary. The amount of land disturbed will be minimized to reduce potential for erosion and sedimentation. Stabilization measures shall be initiated within 14 days following the end of construction at each portion of the site and as soon as practicable. The entire stormwater management system including bioretention area, will be inspected upon completion of construction. Sediment will be removed from all elements of the stormwater management system. All control measures must be installed and maintained in accordance with manufacturer’s specifications, good engineering practices, and in accordance with this report (every seven calendar days and after storm events). If inspections show that a control has failed or been installed incorrectly, the Operator must replace or modify it within 24 hours. 1.2 Stabilization Practices The amount of land disturbed during construction will be minimized to reduce the potential for erosion and sedimentation. Prompt surface stabilization will be provided to control erosion in areas where disturbances cannot be avoided during construction. Stabilization measures shall be initiated within 14 days following the end of construction at each portion of the site. Exceptions to this requirement are allowable when snow cover prevents the initiation of stabilization within 14 days, in which case such measures shall be undertaken as soon as possible. Pollutant Controls During Construction 2 October 2025 Grove Street Stormwater Retrofit Project – Yarmouth, MA Stabilization measures that will be, or may be, used during construction are described below: • Temporary Seeding – Temporary seeding of disturbed surfaces with fast-growing grasses (annual rye) to provide greater resistance to stormwater runoff and/or wind erosion for areas where construction has temporarily ceased. • Permanent Seeding – Permanent seeding of surfaces with vegetation, including but not limited to grass, trees, bushes, and shrubs, to stabilize the soil. Establishing a permanent and sustainable ground cover at a site stabilizes the soil while reducing the sediment content in runoff. • Permanent Planting –establish all planting as required at the completion of the project. Bioretention area is to remain offline, blocked from road runoff at inflow, until permanent planting is established. • Erosion Control Blankets - install erosion control blankets along all slopes greater than 3:1. • Mulching – materials, including but not limited to hay, grass, woodchips, straw, and gravel will be placed on the soil surface to cover and hold in place disturbed soils. Temporary seeding or other soil stabilization measures will be provided where construction activities have ceased at the site. Topsoil stockpiles will be temporarily seeded or covered to prevent erosion and will be surrounded with silt fence or silt sock. When the site’s final grade has been established, permanent vegetation will be planted on the disturbed areas. The vegetation will consist of grass, shrubs, bushes, and trees in the locations indicated on the plans. 1.3 Other Types of Controls Additional controls/practices will be undertaken to reduce pollution in stormwater runoff flows which include, but are not limited to, control of off-site mud tracking from construction site, dust suppression, proper sanitary waste disposal, earthwork procedures timed and conducted in manners aimed to minimize erosion and sedimentation, snow removal plans, proper management of waste materials, proper management of hazardous waste, proper material stockpiling, and spill prevention and control measures. • Dust Suppression – Water sprays shall be used to control dust during extended dry periods during construction. • Earthwork – The exposure of disturbed surfaces to stormwater and potential stormwater erosion will be minimized by well-organized earthwork procedures. Stabilization procedures shall be undertaken in accordance with this report. Grubbing during wet seasons will be avoided if feasible. Pollutant Controls During Construction 3 October 2025 Grove Street Stormwater Retrofit Project – Yarmouth, MA • Snow Removal Plan – Plowed snow collected from the roadway will be deposited onto free draining, pervious surfaces, away from the sites drainage conveyance structures to maximize infiltration. • Waste Materials – Dumpsters rented from a licensed solid waste management company will be used to store solid waste and debris that cannot be recycled, reused or salvaged. The dumpsters will meet all local and state solid waste management regulations. Dumpsters will be covered when refuse is not being directly deposited or withdrawn from them. Potentially hazardous wastes will be separated from normal wastes, including segregation of storage areas and proper labeling of containers. Removal of all waste from the site will be performed by licensed contractors in accordance with applicable regulatory requirements and disposed of at either local or regional approved facilities. Waste materials will not be buried on-site. All site personnel will be instructed regarding the correct procedures for waste disposal. Notices stating these procedures will be posted at the site. Solvents and flushing materials used during construction and pre-operational cleaning will be provided, handled, managed, and removed by the contractor for appropriate off-site disposal. • Hazardous Waste Materials – Any disposal of hazardous materials will be completed using the required paperwork. Copies will be provided to the Engineer and to the city. • Spill Prevention and Control Measures – To minimize the risk of spills or other accidental exposure of materials and substances to stormwater runoff, the following material management practices will be used throughout the project: o An effort will be made to store only enough products required to do the job. o All materials stored on-site will be stored in a neat, orderly manner in their appropriate containers and, if possible, under a roof or other enclosure. o Products will be kept in their original containers with the original manufacturer’s label. o Substances will not be mixed with one another unless recommended by the manufacturer. o Whenever possible, the maximum amount of a product will be used before disposing of the container. o Manufacturers’ recommendations for proper use and disposal will be followed. o The site superintendent will conduct daily inspections to ensure proper use and disposal of materials. Pollutant Controls During Construction 4 October 2025 Grove Street Stormwater Retrofit Project – Yarmouth, MA To reduce the risk associated with hazardous materials used on the site, the following practices will be used: - Products will be kept in original containers unless they are not resealable. - Original labels and material safety data sheets will be retained and kept on-site; they contain important product information. - If surplus product must be disposed of, manufacturers’ or local and state recommended methods for proper disposal will be followed. • Materials List - Materials or substances listed below are expected to be present on-site during construction: - Concrete - Fertilizers - Asphalt - Petroleum Based Products - Paints (enamel and latex) - Cleaning Solvents - Metal Studs - Wood - Concrete - Tar - Sealants - Adhesives The following product-specific practices will be followed on-site: Petroleum Products - All on-site vehicles will be monitored for leaks and receive preventative maintenance to reduce the chance of leakage. Petroleum products will be stored in tightly sealed containers which area clearly labeled. Any asphalt substances used on-site will be applied according to the manufacturers’ recommendations. Paints – All containers will be tightly sealed and stored indoors when not required for use. Excess paint will not be discharged to the storm sewer system but will be properly disposed of according to the manufacturers’ instructions or state and local regulations. Concrete Trucks – Concrete trucks will not be allowed to wash out or discharge surplus concrete or drum wash water on the site. In addition to the good housekeeping and material management practices discussed in the previous sections of this plan, the following practices will be followed for spill prevention and cleanup: • Manufacturers’ recommended methods for spill cleanup will be clearly posted, and site personnel will be made aware of the procedures and location of the information and cleanup supplies. Pollutant Controls During Construction 5 October 2025 Grove Street Stormwater Retrofit Project – Yarmouth, MA • Materials and equipment necessary for spill cleanup will be kept in the material storage area on-site. Equipment and materials will include, but not be limited to, brooms, dust pans, mops, rags, gloves, goggles, speedi-dry, sand, sawdust, and plastic and metal trash containers specifically for this purpose. • All spills will be cleaned up immediately after discovery. Spills large enough to reach the storm water system will be reported to the National Response Center at 1-800-424-8802. • The spill area will be kept well ventilated and personnel will wear appropriate protective clothing to prevent injury from contact with a hazardous substance. • Spills of toxic or hazardous material will be reported to the appropriate state or local government agency, regardless of the size. • The site superintendent responsible for the day-to-day site operations will be the spill prevention and clean-up coordinator. He will designate at least three other site personnel who will receive spill prevention and cleanup training. These individuals will each become responsible for a particular phase of prevention and cleanup. The names of responsible spill personnel will be posted in the material storage area and in the on-site office trailer. APPENDIX F – Site Plans