Loading...
HomeMy WebLinkAboutStormwaterReport-CurveHill_22108 - Compiled STORMWATER MANAGEMENT REPORT Curve Hill Road - Yarmouth, MA September 2024 Yarmouth Stormwater Design and Implementation Project Partner: Association to Preserve Cape Cod Owner/Operator: Town of Yarmouth Curve Hill_SW Checklist • 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. Curve Hill_SW Checklist • 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 9/18/2024 Curve Hill_SW Checklist • 04/01/08 Stormwater Report Checklist • Page 3 of 8 Massachusetts Department of Environmental Protection Bureau of Resource Protection - Wetlands Program Checklist for Stormwater Report Checklist (continued) LID Measures: Stormwater Standards require LID measures to be considered. Document what environmentally sensitive design and LID Techniques were considered during the planning and design of the project: No disturbance to any Wetland Resource Areas Site Design Practices (e.g. clustered development, reduced frontage setbacks) Reduced Impervious Area (Redevelopment Only) Minimizing disturbance to existing trees and shrubs LID Site Design Credit Requested: Credit 1 Credit 2 Credit 3 Use of “country drainage” versus curb and gutter conveyance and pipe Bioretention Cells (includes Rain Gardens) Constructed Stormwater Wetlands (includes Gravel Wetlands designs) Treebox Filter Water Quality Swale Grass Channel Green Roof Other (describe): Standard 1: No New Untreated Discharges No new untreated discharges Outlets have been designed so there is no erosion or scour to wetlands and waters of the Commonwealth Supporting calculations specified in Volume 3 of the Massachusetts Stormwater Handbook included. Curve Hill_SW Checklist • 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. Curve Hill_SW Checklist • 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. Curve Hill_SW Checklist • 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. Curve Hill_SW Checklist • 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. Curve Hill_SW Checklist • 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. i STORMWATER MANAGEMENT REPORT CURVE HILL ROAD YARMOUTH STORMWATER DESIGN AND IMPLEMENTATION PROJECT YARMOUTH, MA Table of Contents STORMWATER CHECKLIST ........................................................................................................... ii 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 .............................................................................................................. 5 2.4 Soils ................................................................................................................................ 5 3.0 Proposed Conditions ...................................................................................................... 6 3.1 Drainage Areas ............................................................................................................... 6 3.2 Structural Stormwater Control Measures (SCMs) .......................................................... 6 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 Water Quality Pollutant Load Reduction Requirements ...................... 8 Table 5. Summary of Existing and Proposed Condition Peak Flow Rates and Runoff Volumes .. 9 FIGURES Under Notice of Intent (NOI) Cover Figure 1: USGS Topographic Map Figure 2: Aerial Figure 3: FEMA Figure 4: Environmental Constraints Figure 5: Soils Figure 6: Environmental Justice Communities Figure 7: Impaired Waters APPENDICES Appendix A: Drainage Areas 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 Management Report Horsley Witten Group, Inc. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 1 EXECUTIVE SUMMARY The purpose of this report is to describe existing and proposed drainage conditions of the Curve Hill Road site (UBR-4) in Yarmouth, as well as proposed green stormwater infrastructure (GSI) structures and management strategies to reduce stormwater impacts. This project is part of efforts to improve water quality in the Town of Yarmouth by reducing pollutant loads in stormwater runoff, specifically phosphorus, nitrogen, bacteria, and sediment. The Curve Hill Road 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 Great Western Road and Curve Hill Road prior to discharging to a freshwater wetland. This project involves the development of new GSI at a non-developed Town-owned property to treat the first flush of pollutants (the water quality volume (WQV), or first 1 inch of runoff) of the area draining to the site. The project includes the following structural SCMs: • Constructed wetland to provide treatment, and • Proprietary water quality unit for pretreatment. 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 recharge standard that is not applicable. The proposed constructed wetland is designed to capture and treat the full one inch of runoff of the contributing drainage area. Overall, this project will reduce on-going impacts to the natural wetland and Bass River. Table 1. Project MASMS Compliance Summary Minimum Standard Type Compliance Report Reference(s) 1 New Stormwater Conveyances Narrative Yes Section 3.2 2 Water Quantity Calculation Yes Section 4.3/Table 5 /Appendix B 3 Recharge Calculation N/A Section 4.2 /Appendix B 4 Water Quality Calculation Yes Section 4.1/Table 3/Table 4/Appendix B 5 Land Uses with Higher Potential Pollutant Loading Narrative N/A 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 F 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. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 2 1.0 INTRODUCTION This report provides a summary of the stormwater management systems proposed for Curve Hill Road in Yarmouth, MA. The Yarmouth Department of Public Works (DPW) 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 Freshwater wetland resources and 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. It’s been reported (APCC’s 2022 State of the Waters) that 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 Yarmouth 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 sites were chosen to advance to 75% designs and permitting, including this one on Curve Hill Road. Funding is available to further advance the two priority sites through 100% design and construction. 1.2 Project Goals The purpose of this project is to improve water quality in Bass River by reducing or eliminating pollutant loads from stormwater runoff from Great Western Road and Curve Hill Road using GSI SCMs. Specifically, the project aims to maximize pollutant removal (% bacteria, nitrogen and phosphorus) and water quality volume treated. Stormwater Management Report Horsley Witten Group, Inc. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 3 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 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 SCMs were selected and sized to maximize pollutant load removals. Since the waterbodies this site drain to are shellfish growing areas, have water quality impairments and are subject to TMDLs, the SCMs were chosen to maximize not only total suspended solids (TSS) removal, but total phosphorus (TP), total nitrogen (TN), and bacteria load reductions as well. MASMS was used as a reference for TSS removal estimates for constructed wetlands, 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 Curve Hill Road site (UBR-4) is located along the southern side of Curve Hill Road on Town-owned property between Curve Hill Road and Four Seasons Drive, on the western side of Yarmouth, approximately half a mile west of Bass River. The site is an undeveloped, mostly wooded, and depressed area upgradient of an existing wetland. The site is surrounded by residential properties, except for sections to the north and southwest where it directly borders the Curve Hill Road Right-of-Way. The Blue Rock Golf Course is located to the west of the site, just beyond the residential lots on the west side 1 It is important to note that these curves have a crosswalk to help users determine which specific curve to reference: for constructed wetlands, the appropriate curve is the Wet Pond Performance Curve. Stormwater Management Report Horsley Witten Group, Inc. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 4 of Curve Hill Road. 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. Part of the site is in a wellhead protection area (Zone II) (NOI Narrative Figure 4), thus, subject to MASMS Standard 6. Drainage infrastructure (e.g., catch basins, manholes, and pipes) located along Great Western Road discharges via an outlet pipe to the site. Large sediment accumulation was observed at the site; so much so that the outfall was difficult to field locate as it was buried in sediment. This sediment accumulation is likely due to the large drainage area to the Great Western Road infrastructure and the lack of existing SCMs. In addition, runoff from Curve Hill Road flows into the site via a paved flume close to the outfall from Great Western Road. 2.1 Receiving Water and Watershed Great Western Road and Curve Hill Road runoff flows through the project site and discharges into a wetland, which ultimately connects to the Bass River that flows into Nantucket Sound. Bass River 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. Bass River is located in the Bass River Watershed, for which TMDL documents have been developed for nitrogen, fecal coliform, nutrient/eutrophication biological indicators, and estuarine bioassessments. 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: • Bass River (MA96-118) “Grand Cove” portion, Yarmouth, Bass River Watershed – Impaired for total nitrogen and nutrient/eutrophication biological indicators; Category 4a (TMDL completed) of the 2022 Integrated List of Waters. • Bass River (MA96-12) Headwaters outlet, Yarmouth, Bass River Watershed – Impaired for total nitrogen, fecal coliform, and estuarine bioassessments; Category 4a (TMDL completed) of the 2022 Integrated List of Waters. 2.2 Drainage Area The Curve Hill Road project site existing contributing drainage area is approximately 13.0 acres, 4.15 acres (32%) of which is impervious. This area consists of undisturbed forest, residential properties, small lawn areas, and roads. Based on existing topography and flow paths, the total drainage area was divided into three separate drainage areas: DA1 (area draining overland on both sides of the site), DA2A (area draining to the existing paved flume on Curve Hill Road), and DA2B (area draining to the Great Western Road discharge pipe). DA2B is the largest drainage area (approximately 9.0 acres), as it includes all of the area draining to the existing drainage infrastructure along Great Western Road. All drainage areas eventually drain to the wetland, modeled as Study Point 1 (SP1). See the existing drainage area map and detailed breakdown of land cover in Appendix A, as well as the existing HydroCad model report in Appendix B. Stormwater Management Report Horsley Witten Group, Inc. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 5 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. The only wetland resource areas identified at the site are the Bordering Vegetated Wetland and the Other Areas of Flood Hazard FEMA Zone X. Invasive plant species were not observed to be significantly present at the site. This site is considered a critical area (Zone II) and it is subject to MASMS Standard 6. 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, at 3-8% slopes, and Freetown and Swansea mucks, 0-1% slopes. Carver coarse sand is hydrologic soil group A (HSG) and hydrologic soil group B (HSG) and Freetown and Swansea mucks are hydrologic soil group B/D (HSG), as shown in NOI Narrative Figure 5 of the NOI application. One test pit (TP) was conducted at the site on January 4, 2024 in the Town right-of-way on the southern side of Curve Hill Road near 7 Curve Hill Road. The test pit was witnessed and logged by a HW Massachusetts Title 5 Approved Soil Evaluator, with the results shown in Table 2 below. See Appendix C for soil test pit logs. The test pit aimed to evaluate subsurface conditions and estimate seasonal high groundwater (ESHGW) based on evidence of mottling or redox. Since no mottling or redox was observed, the Frimpter Method (USGS, 2022; Cape Cod Commission, 2006; Cape Cod Commission, 2024)2 was used to determine what adjustments could be made to estimate ESHGW. The Frimpter Method suggested a 2-foot adjustment would be appropriate for this site. However, the bordering vegetated wetland (BVW) downgradient of the project site was delineated between elevation 6.8 and 8.0 feet closest to the outlet of the proposed GSI, a constructed wetland. Typically, groundwater is assumed within 12 inches of the surface for BVW. Furthermore, site topographical observations indicate that there are areas on the site at elevation 7 that were not delineated as a wetland. Given the test pit and site walk observations, Frimpter Method adjustments, and wetland delineation data sheets, ESHGW was assumed at 7.5 feet for this site. Table 2. Test Pit (TP) Results Test Pit ID Surface Elevation at TP (ft) Pit Bottom Elevation (ft) Observed GW (ft) ESHGW Elevation (ft)* Soil Texture(s) at SCM TP-1 11.2 5.0 6.0 7.5 Coarse sand *ESHGW determined from a combination of test pit data, site observations, wetland delineation data sheets, and Frimpter Method adjustments. 2 Index Well Mashpee 29 (MIW-29) Zone B adjustment factor in January 2024 of 2.0 feet was used. Stormwater Management Report Horsley Witten Group, Inc. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 6 3.0 Proposed Conditions The proposed project consists of the following GSI: • Constructed wetland. The proposed GSI system is designed to meet the following major objective: • Capture and treat to the maximum extent practicable the first one inch of runoff (WQv). 3.1 Drainage Areas The Curve Hill Road site contributing drainage area under proposed conditions is the same as existing conditions, with a total of approximately 13.0 acres. While DA2A and DA2B remain the same, DA1 includes the proposed constructed wetland as a pond so that it can be accurately modeled in HydroCAD. All drainage areas drain to the wetland, modeled as Study Point 1 (SP1), which is the same as existing conditions. See the proposed conditions 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 Measures (SCMs) The proposed stormwater management includes a GSI approach to capture, detain, and treat runoff. The stormwater management systems were designed to meet Standard 1, so that no new untreated stormwater runoff will be directed to any off-site areas or resource areas. There is one GSI practice proposed: a constructed wetland. Pretreatment will be provided with a water quality unit. These SCMs are described in more detail below. Pretreatment A proprietary water quality unit (WQU) is proposed for pretreatment of the runoff from the paved surfaces to collect oils, sediment, and other debris prior to discharge into the constructed wetland. Constructed Wetland (CW) Stormwater constructed wetlands mimic natural wetlands to manage and treat stormwater by allowing settling of sediments and filtering stormwater through a mix of native vegetation. The system consists of an inflow component, a series of pools of varying depths, and overflow spillway for discharge. Stormwater is designed to be directed to the stormwater constructed wetland off of Great Western Road through the existing drainage outfall pipe and off of Curve Hill Road via a drop inlet into a water quality unit. Constructed wetlands have depth zone allocations and MASMS provides target allocations (given as percentage of the stormwater wetland surface area) when designing constructed wetlands. The four depth zones include: semi-wet zone (above the normal pool elevation), high marsh zone (ranges from normal pool elevation to 6 inches below normal pool elevation), low marsh zone (ranges from 6 inches Stormwater Management Report Horsley Witten Group, Inc. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 7 to 18 inches below the normal pool elevation), and deep water zone (ranges from 1.5 to 6 feet below normal pool elevation). The purpose of the different zones is to support various types of vegetation. The proposed constructed wetland was designed to meet these target design allocations. When designing constructed wetlands, the permanent pool is set at the ESHGW elevation or at the lowest outlet elevation. For this site, an overflow weir is proposed at 7.85 feet, above the ESHGW of 7.5 feet. Thus, the permanent pool of the constructed wetland was conservatively set at 7.85 feet. 4.0 Stormwater Design Components The proposed SCMs were 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 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. However, the proposed SCM was sized to treat the full one-inch WQv for the contributing drainage areas (DA1, DA2A, and DA2B). The constructed wetland’s permanent pool (elevation 7.85 feet) can store the full WQv. 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 DA1 CW 0.28 0.346 0.346 100% Y Full WQv provided within permanent pool. No extended detention used to meet standard. DA2a 0.51 DA2b 3.36 TOTAL SITE: 4.15 0.346 0.346 100% Y *Impervious Area **From HydroCAD results – see Appendix B for storage volume during the WQ Rainfall event for Pond 7P. Stormwater Management Report Horsley Witten Group, Inc. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 8 Pollutant Load Reductions The proposed constructed wetland meet the MASMS requirements for TSS removal and maximize removals of the other pollutants of concern. Estimated TSS, TP, TN, and bacteria 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 Water Quality Pollutant Load Reduction 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? DA1 CW 0.28 0.346 1.00 88% 53% 32% 65% Y DA2a 0.51 DA2b 3.36 TOTAL SITE: 4.15 0.346 1.0 88% 53% 32% 65% Y *From HydroCAD results – see Appendix B for storage volume during the WQ Rainfall event for Pond 7P. **From MASMS ***From MS4 NPDES Permit Appendix F Attachment 3 (USEPA 2021) ****From Paradigm Environmental (2019) The project site is partially located within a wellhead protection area (Zone II) and located within the Bass River Watershed and as the project goal is to improve water quality, the proposed constructed wetland was designed to meet MASMS Standard 6. The CDS water quality unit is proposed for pretreatment prior to discharge into the constructed wetland, providing greater than 44% TSS removal. The water quality unit alone provides 87.7% TSS removal. Furthermore, constructed wetlands are recommended treatment SCMs for areas that discharge near to shellfish growing areas and to wellhead protection areas. Therefore, this project meets 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. However, no new impervious surfaces are proposed for this site as a retrofit project, and recharge is not required due to high groundwater. The proposed SCM was specifically chosen due to this groundwater constraint and therefore, the project does not take credit for recharge. Stormwater Management Report Horsley Witten Group, Inc. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 9 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 constructed wetland will reduce peak flows for the 2-, 10-, 25- and 100-year storms. The runoff volume is slightly increased under proposed conditions as there is an increase in impervious cover (e.g., water) from the constructed wetland. 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 for all evaluated storms thus, meeting the requirements of Standard 2 of the MASMS. Table 5. 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 13.98 20.58 26.28 39.41 1.170 1.859 2.485 3.681 PR 12.57 19.05 24.55 37.09 1.228 1.946 2.593 3.817 Reduction % -10% -7% -7% -6% 5% 5% 4% 4% *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 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 is to be provided along Curve Hill Road to minimize tracking of sediment. Areas for other sediment traps/basins should be provided on an as-needed basis. Dewatering will be required during construction. Dewatering will be conducted in a method to minimize downstream sedimentation and erosion, with use of a dewatering containment area. 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. Stormwater Management Report Horsley Witten Group, Inc. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 10 4.5 Operation and Maintenance Ongoing maintenance is vital for long-term success at the site. The SCM was designed to be low- maintenance in nature. The SCM 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. Curve Hill Road- Yarmouth Stormwater Design and Implementation Project- Yarmouth, MA September 2024 11 5.0 REFERENCES Association to Preserve Cape Cod. 2022. State of the Waters: Cape Cod Report. Cape Cod Commission. 2006. Technical Bulletin 92-001 “Estimation of High Groundwater Levels for Construction and Land Use Planning.” https://www.capecodcommission.org/resource- library/file/?url=/dept/commission/team/Website_Resources/regulatory/HighGroundH20TechBulletin.p df. Cape Cod Commission. 2015. 208 Plan – Cape Cod’s Area Wide Water Quality Management Plan Updated. Cape Cod Commission. 2024. Estimating High Groundwater Levels Data Viewer. Accessible at: https://cccommission.maps.arcgis.com/apps/webappviewer/index.html?id=f1d0ad5a1b5d44c7976ed6a 9749d2d4a. 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 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. Available at: https://www.epa.gov/sites/default/files/2020-01/documents/tisbury-subtask-4d-tm.pdf. 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). U.S. Geological Survey (USGS). 2022. Determining High Groundwater Levels in Massachusetts. https://www.usgs.gov/centers/new-england-water-science-center/science/updating-a-method- estimate-probable-high#web-tools. FIGURES APPENDIX A – Drainage Areas • Existing and Proposed Drainage Areas Maps • Land Coverage Summaries 20 20 25 25 30 3 0 35 35 4 0 45454040404030 10 202 5 15152025 30 35 40 35304035451025 30CURVE HILL ROADGREAT WESTERN ROAD4 SEAS O N S D R I V E VIKING ROCK ROAD NARROWS LANE PAINE ROAD Prepared For:Sheet Number:Project Number:last modified: 06/24/24 printed: 06/24/24 by gk H:\Projects\2022\22108 APCC Yarmouth\Drawings\CURVE HILL\22108A CURVE HILL RD DR.dwg Plan Set:of122108A2Town of Yarmouth DPW Phone: 74 Town Brook Road West Yarmouth, MA 02673 (508) 398-2231 ext. 1250 4/25/24 MCL GK 0SCALE IN FEET150Horsley Witten Group, Inc. Sustainable Environmental Solutions 90 Route 6A Sandwich, MA 02563 horsleywittengroup.comDA1SP1P1STUDY POINTSITE UBR-1: CURVE HILL ROAD SOTRMWATER RETROFIT DESIGN AND IMPLEMENTATION 25% DESIGN PLANS YARMOUTH, MASSACHUSETTS EXISTING DRAINAGE MAPDRAINAGE AREA0.752.00SOIL BOUNDARYTIME OF CONCENTRATION FLOW PATH5' MAJOR CONTOUR1' MINOR CONTOURCARVER COARSE SAND (HSG A)252A 0-3%252B 3-8%252C 8-15%252D 15-35%LEGENDSOIL TYPESPONDChecked By:Drawn By:Date:(ACRES)WOODSROOFTOPGRASSPAVEMENTWATERDRAINAGEAREABOUNDARYIMP. AREATOTAL AREAFREETOWN AND SWANSEAMUCKS 0-1% (HSG D)DA2BSP13.279.01EX DRAINAGE STRUCTUREEX DRAIN PIPEDA2A0.512.10252A52D52D252DA252DA252BA252CA252AA252AA252BA252CA252CADA10.281.89 20 20 25 25 30 3 0 35 35 4 0 45454040404030 10 202 5 15152025 30 35 40 35304035451025 30CURVE HILL ROADGREAT WESTERN ROAD4 SEAS O N S D R I V E VIKING ROCK ROAD NARROWS LANE PAINE ROAD Prepared For:Sheet Number:Project Number:last modified: 06/24/24 printed: 06/24/24 by gk H:\Projects\2022\22108 APCC Yarmouth\Drawings\CURVE HILL\22108A CURVE HILL RD DR.dwg Plan Set:of222108A2Town of Yarmouth DPW Phone: 74 Town Brook Road West Yarmouth, MA 02673 (508) 398-2231 ext. 1250 4/25/24 MCL GK 0SCALE IN FEET150Horsley Witten Group, Inc. Sustainable Environmental Solutions 90 Route 6A Sandwich, MA 02563 horsleywittengroup.comDA1SP1P1STUDY POINTPROPOPOSED DRAINAGE MAPDRAINAGE AREA0.752.00SOIL BOUNDARYTIME OF CONCENTRATION FLOW PATH5' MAJOR CONTOUR1' MINOR CONTOURCARVER COARSE SAND (HSG A)252A 0-3%252B 3-8%252C 8-15%252D 15-35%LEGENDSOIL TYPESPONDChecked By:Drawn By:Date:(ACRES)WOODSROOFTOPGRASSPAVEMENTWATERDRAINAGEAREABOUNDARYIMP. AREATOTAL AREAFREETOWN AND SWANSEAMUCKS 0-1% (HSG D)SP1EX DRAINAGE STRUCTUREEX DRAIN PIPEDA2a0.512.10252A52D52D252DA252DA252BA252CA252AA252AA252BA252CA252CAP1SITE UBR-1: CURVE HILL ROAD SOTRMWATER RETROFIT DESIGN AND IMPLEMENTATION 25% DESIGN PLANS YARMOUTH, MASSACHUSETTSDA10.281.89DA2b3.279.01 CURVE HILL, YARMOUTH STORMWATER Calc'd by: YARMOUTH, MA Checked by: Date: DA1 DA2a WQv 1.21 DA2b 1-yr 3.05 2-yr 3.60 5-yr 4.51 10-yr 5.27 25-yr 6.53 100-yr 8.59 500-yr 11.43 DA1 Cover type Area, ft 2 Area, ac Note Paved 3,469 0.080 Permeable 0.000 Roof 8,516 0.196 Water 0 0.000 Woods 46,010 1.056 Grass 24,504 0.563 Area, ft 2 Area, ac Percent TOTAL 82,499 1.894 11,985 0.275 15 DA2a Cover type Area, ft 2 Area, ac Note Paved 14,426 0.331 Permeable 0 0.000 Roof 7,938 0.182 Water 0.000 Woods 25,978 0.596 Grass 43,234 0.993 Area, ft 2 Area, ac Percent TOTAL 91,576 2.102 22,364 0.513 24 Impervious Curve Hill Road GSG GK 7/15/2024 Wetland Wetland Great Western Road Curve Hill Road Impervious Existing Drainage Conditions DRAINAGE AREAS NOAA 14+ 24-hr Type III (inches) DA2b Cover type Area, ft 2 Area, ac Note Paved 110,080 2.527 Permeable 0 0.000 Roof 35,831 0.823 Water 394 0.009 Woods 81,217 1.864 Grass 165,043 3.789 Area, ft 2 Area, ac Percent TOTAL 392,565 9.012 146,305 3.359 37 ALL Cover type Area, ft 2 Area, ac Note Paved 127,975 2.938 Permeable 0 0.000 Roof 52,285 0.378 Water 394 0.000 Woods 153,205 1.653 Grass 232,781 1.555 Area, ft 2 Area, ac Percent TOTAL 566,640 13.008 180,654 4.147 32 ALL EX AREAS COMBINED Impervious Great Western Road Impervious CURVE HILL, YARMOUTH STORMWATER Calc'd by: YARMOUTH, MA Checked by: Date: DA1 DA2a WQv 1.21 DA2b 1-yr 3.05 2-yr 3.60 5-yr 4.51 10-yr 5.27 25-yr 6.53 100-yr 8.59 500-yr 11.43 DA1 Cover type Area, ft 2 Area, ac Note Paved 3,469 0.080 Permeable 0.000 Roof 8,516 0.196 Water 9,145 0.210 Woods 36,865 0.846 Grass 24,504 0.563 Area, ft 2 Area, ac Percent TOTAL 82,499 1.894 11,985 0.275 15 DA2a Cover type Area, ft 2 Area, ac Note Paved 14,426 0.331 Permeable 0 0.000 Roof 7,938 0.182 Water 0.000 Woods 25,978 0.596 Grass 43,234 0.993 Area, ft 2 Area, ac Percent TOTAL 91,576 2.102 22,364 0.513 24 Wetland Impervious Curve Hill Road Impervious GK Proposed Drainage Conditions DRAINAGE AREAS NOAA 14+ Wetland 24-hr Type III (inches) Curve Hill Road Great Western Road DA2b Cover type Area, ft 2 Area, ac Note Paved 110,080 2.527 Permeable 0 0.000 Roof 35,831 0.823 Water 394 0.009 Woods 81,217 1.864 Grass 165,043 3.789 Area, ft 2 Area, ac Percent TOTAL 392,565 9.012 146,305 3.359 37 ALL Cover type Area, ft 2 Area, ac Note Paved 127,975 2.938 Permeable 0 0.000 Roof 52,285 1.200 Water 9,539 0.219 Woods 144,060 3.307 Grass 232,781 5.344 Area, ft 2 Area, ac Percent TOTAL 566,640 13.008 180,260 4.138 32 ALL PR AREAS COMBINED Impervious Impervious Great Western Road APPENDIX B – Hydrologic/Hydraulic Model Results HydroCAD® Results • Existing • Proposed Contech Water Quality Unit Removal Calculations DA1 0.28/1.89 DA2A 0.51/2.10 DA2B 3.36/9.01 1P Curve Hill Wetland Routing Diagram for 22108 CURVE EX_reportPrepared by Horsley Witten Inc, Printed 9/17/2024 HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcat Reach Pond Link 22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 2HydroCAD® 10.20-4b s/n 01445 © 2023 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 5.27 2 3 25 YR Type III 24-hr Default 24.00 1 6.53 2 4 100 YR Type III 24-hr Default 24.00 1 8.59 2 5 WQ Type III 24-hr Default 24.00 1 1.21 2 22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 3HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Area Listing (all nodes) Area (acres) CN Description (subcatchment-numbers) 5.344 39 >75% Grass cover, Good, HSG A (DA1, DA2A, DA2B) 0.080 98 Paved parking, HSG A (DA1) 1.200 98 Roofs, HSG A (DA1, DA2A, DA2B) 2.858 98 Unconnected pavement, HSG A (DA2A, DA2B) 0.009 98 Water Surface, HSG A (DA2B) 3.517 30 Woods, Good, HSG A (DA1, DA2A, DA2B) 13.008 55 TOTAL AREA 22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 4HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Soil Listing (all nodes) Area (acres) Soil Group Subcatchment Numbers 13.008 HSG A DA1, DA2A, DA2B 0.000 HSG B 0.000 HSG C 0.000 HSG D 0.000 Other 13.008 TOTAL AREA 22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 5HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Ground Covers (all nodes) HSG-A (acres) HSG-B (acres) HSG-C (acres) HSG-D (acres) Other (acres) Total (acres) Ground Cover Subcatchment Numbers 5.344 0.000 0.000 0.000 0.000 5.344 >75% Grass cover, Good DA1, DA2A, DA2B 0.080 0.000 0.000 0.000 0.000 0.080 Paved parking DA1 1.200 0.000 0.000 0.000 0.000 1.200 Roofs DA1, DA2A, DA2B 2.858 0.000 0.000 0.000 0.000 2.858 Unconnected pavement DA2A, DA2B 0.009 0.000 0.000 0.000 0.000 0.009 Water Surface DA2B 3.517 0.000 0.000 0.000 0.000 3.517 Woods, Good DA1, DA2A, DA2B 13.008 0.000 0.000 0.000 0.000 13.008 TOTAL AREA 22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 6HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Pipe Listing (all nodes) Line# Node Number In-Invert (feet) Out-Invert (feet) Length (feet) Slope (ft/ft) n Width (inches) Diam/Height (inches) Inside-Fill (inches) Node Name 1 DA2B 0.00 0.00 1,259.0 0.0300 0.013 0.0 12.0 0.0 Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 7HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=0.49"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=0.93 cfs 0.078 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=0.83"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=1.73 cfs 0.145 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=1.26"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=11.32 cfs 0.947 af Inflow=13.98 cfs 1.170 afPond 1P: Curve Hill Wetland Primary=13.98 cfs 1.170 af Total Runoff Area = 13.008 ac Runoff Volume = 1.170 af Average Runoff Depth = 1.08" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 8HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 0.93 cfs @ 12.10 hrs, Volume= 0.078 af, Depth= 0.49" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 2 YR Rainfall=3.60" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 46,010 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)1 0 Type III 24-hr 2 YR Rainfall=3.60" Runoff Area=82,499 sf Runoff Volume=0.078 af Runoff Depth=0.49" Tc=7.1 min CN=WQ 0.93 cfs Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 9HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 1.73 cfs @ 12.10 hrs, Volume= 0.145 af, Depth= 0.83" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 2 YR Rainfall=3.60" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)1 0 Type III 24-hr 2 YR Rainfall=3.60" Runoff Area=91,576 sf Runoff Volume=0.145 af Runoff Depth=0.83" Tc=7.1 min UI Adjusted CN=WQ 1.73 cfs Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 10HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 [47] Hint: Peak is 183% of capacity of segment #3 Runoff = 11.32 cfs @ 12.10 hrs, Volume= 0.947 af, Depth= 1.26" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 2 YR Rainfall=3.60" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 11HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)12 11 10 9 8 7 6 5 4 3 2 1 0 Type III 24-hr 2 YR Rainfall=3.60" Runoff Area=392,565 sf Runoff Volume=0.947 af Runoff Depth=1.26" Flow Length=1,733' Tc=7.1 min CN=WQ 11.32 cfs Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 12HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 1P: Curve Hill Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 1.08" for 2 YR event Inflow = 13.98 cfs @ 12.10 hrs, Volume= 1.170 af Primary = 13.98 cfs @ 12.10 hrs, Volume= 1.170 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 1P: Curve Hill Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=13.008 ac 13.98 cfs13.98 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 13HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=0.82"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=1.37 cfs 0.129 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=1.36"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=2.55 cfs 0.237 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=1.99"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=16.67 cfs 1.492 af Inflow=20.58 cfs 1.859 afPond 1P: Curve Hill Wetland Primary=20.58 cfs 1.859 af Total Runoff Area = 13.008 ac Runoff Volume = 1.859 af Average Runoff Depth = 1.71" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 14HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 1.37 cfs @ 12.10 hrs, Volume= 0.129 af, Depth= 0.82" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 10 YR Rainfall=5.27" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 46,010 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)1 0 Type III 24-hr 10 YR Rainfall=5.27" Runoff Area=82,499 sf Runoff Volume=0.129 af Runoff Depth=0.82" Tc=7.1 min CN=WQ 1.37 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 15HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 2.55 cfs @ 12.10 hrs, Volume= 0.237 af, Depth= 1.36" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 10 YR Rainfall=5.27" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)2 1 0 Type III 24-hr 10 YR Rainfall=5.27" Runoff Area=91,576 sf Runoff Volume=0.237 af Runoff Depth=1.36" Tc=7.1 min UI Adjusted CN=WQ 2.55 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 16HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 [47] Hint: Peak is 270% of capacity of segment #3 Runoff = 16.67 cfs @ 12.10 hrs, Volume= 1.492 af, Depth= 1.99" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 10 YR Rainfall=5.27" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 17HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Type III 24-hr 10 YR Rainfall=5.27" Runoff Area=392,565 sf Runoff Volume=1.492 af Runoff Depth=1.99" Flow Length=1,733' Tc=7.1 min CN=WQ 16.67 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 18HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 1P: Curve Hill Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 1.71" for 10 YR event Inflow = 20.58 cfs @ 12.10 hrs, Volume= 1.859 af Primary = 20.58 cfs @ 12.10 hrs, Volume= 1.859 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 1P: Curve Hill Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=13.008 ac 20.58 cfs20.58 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 19HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=1.17"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=1.77 cfs 0.185 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=1.86"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=3.30 cfs 0.326 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=2.63"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=21.21 cfs 1.974 af Inflow=26.28 cfs 2.485 afPond 1P: Curve Hill Wetland Primary=26.28 cfs 2.485 af Total Runoff Area = 13.008 ac Runoff Volume = 2.485 af Average Runoff Depth = 2.29" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 20HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 1.77 cfs @ 12.10 hrs, Volume= 0.185 af, Depth= 1.17" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 25 YR Rainfall=6.53" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 46,010 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)1 0 Type III 24-hr 25 YR Rainfall=6.53" Runoff Area=82,499 sf Runoff Volume=0.185 af Runoff Depth=1.17" Tc=7.1 min CN=WQ 1.77 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 21HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 3.30 cfs @ 12.10 hrs, Volume= 0.326 af, Depth= 1.86" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 25 YR Rainfall=6.53" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)3 2 1 0 Type III 24-hr 25 YR Rainfall=6.53" Runoff Area=91,576 sf Runoff Volume=0.326 af Runoff Depth=1.86" Tc=7.1 min UI Adjusted CN=WQ 3.30 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 22HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 [47] Hint: Peak is 344% of capacity of segment #3 Runoff = 21.21 cfs @ 12.10 hrs, Volume= 1.974 af, Depth= 2.63" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 25 YR Rainfall=6.53" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 23HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Type III 24-hr 25 YR Rainfall=6.53" Runoff Area=392,565 sf Runoff Volume=1.974 af Runoff Depth=2.63" Flow Length=1,733' Tc=7.1 min CN=WQ 21.21 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 24HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 1P: Curve Hill Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 2.29" for 25 YR event Inflow = 26.28 cfs @ 12.10 hrs, Volume= 2.485 af Primary = 26.28 cfs @ 12.10 hrs, Volume= 2.485 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 1P: Curve Hill Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Inflow Area=13.008 ac 26.28 cfs26.28 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 25HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=1.95"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=2.85 cfs 0.307 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=2.87"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=5.24 cfs 0.502 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=3.82"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=31.32 cfs 2.871 af Inflow=39.41 cfs 3.681 afPond 1P: Curve Hill Wetland Primary=39.41 cfs 3.681 af Total Runoff Area = 13.008 ac Runoff Volume = 3.681 af Average Runoff Depth = 3.40" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 26HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 2.85 cfs @ 12.11 hrs, Volume= 0.307 af, Depth= 1.95" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 100 YR Rainfall=8.59" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 46,010 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)3 2 1 0 Type III 24-hr 100 YR Rainfall=8.59" Runoff Area=82,499 sf Runoff Volume=0.307 af Runoff Depth=1.95" Tc=7.1 min CN=WQ 2.85 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 27HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 5.24 cfs @ 12.11 hrs, Volume= 0.502 af, Depth= 2.87" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 100 YR Rainfall=8.59" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)5 4 3 2 1 0 Type III 24-hr 100 YR Rainfall=8.59" Runoff Area=91,576 sf Runoff Volume=0.502 af Runoff Depth=2.87" Tc=7.1 min UI Adjusted CN=WQ 5.24 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 28HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 [47] Hint: Peak is 508% of capacity of segment #3 Runoff = 31.32 cfs @ 12.10 hrs, Volume= 2.871 af, Depth= 3.82" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 100 YR Rainfall=8.59" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 29HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Type III 24-hr 100 YR Rainfall=8.59" Runoff Area=392,565 sf Runoff Volume=2.871 af Runoff Depth=3.82" Flow Length=1,733' Tc=7.1 min CN=WQ 31.32 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 30HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 1P: Curve Hill Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 3.40" for 100 YR event Inflow = 39.41 cfs @ 12.10 hrs, Volume= 3.681 af Primary = 39.41 cfs @ 12.10 hrs, Volume= 3.681 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 1P: Curve Hill Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Inflow Area=13.008 ac 39.41 cfs39.41 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 31HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=0.14"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=0.29 cfs 0.023 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=0.24"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=0.55 cfs 0.043 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=0.37"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=3.57 cfs 0.279 af Inflow=4.41 cfs 0.344 afPond 1P: Curve Hill Wetland Primary=4.41 cfs 0.344 af Total Runoff Area = 13.008 ac Runoff Volume = 0.344 af Average Runoff Depth = 0.32" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr WQ Rainfall=1.21"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 32HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 0.29 cfs @ 12.10 hrs, Volume= 0.023 af, Depth= 0.14" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr WQ Rainfall=1.21" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 46,010 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)0.32 0.3 0.28 0.26 0.24 0.22 0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 Type III 24-hr WQ Rainfall=1.21" Runoff Area=82,499 sf Runoff Volume=0.023 af Runoff Depth=0.14" Tc=7.1 min CN=WQ 0.29 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 33HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 0.55 cfs @ 12.10 hrs, Volume= 0.043 af, Depth= 0.24" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr WQ Rainfall=1.21" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 Type III 24-hr WQ Rainfall=1.21" Runoff Area=91,576 sf Runoff Volume=0.043 af Runoff Depth=0.24" Tc=7.1 min UI Adjusted CN=WQ 0.55 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 34HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 Runoff = 3.57 cfs @ 12.10 hrs, Volume= 0.279 af, Depth= 0.37" Routed to Pond 1P : Curve Hill Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr WQ Rainfall=1.21" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr WQ Rainfall=1.21"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 35HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)3 2 1 0 Type III 24-hr WQ Rainfall=1.21" Runoff Area=392,565 sf Runoff Volume=0.279 af Runoff Depth=0.37" Flow Length=1,733' Tc=7.1 min CN=WQ 3.57 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE EX_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 36HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 1P: Curve Hill Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 0.32" for WQ event Inflow = 4.41 cfs @ 12.10 hrs, Volume= 0.344 af Primary = 4.41 cfs @ 12.10 hrs, Volume= 0.344 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 1P: Curve Hill Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)4 3 2 1 0 Inflow Area=13.008 ac 4.41 cfs4.41 cfs DA1 0.28/1.89 DA2A 0.51/2.10 DA2B 3.36/9.01 3PCB CDS Unit 4P Existing Wetland 7P Constructed Wetland Routing Diagram for 22108 CURVE PR_reportPrepared by Horsley Witten Inc, Printed 9/17/2024 HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcat Reach Pond Link 22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 2HydroCAD® 10.20-4b s/n 01445 © 2023 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 5.27 2 3 25 YR Type III 24-hr Default 24.00 1 6.53 2 4 100 YR Type III 24-hr Default 24.00 1 8.59 2 5 WQ Type III 24-hr Default 24.00 1 1.21 2 22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 3HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Area Listing (all nodes) Area (acres) CN Description (subcatchment-numbers) 5.344 39 >75% Grass cover, Good, HSG A (DA1, DA2A, DA2B) 0.080 98 Paved parking, HSG A (DA1) 1.200 98 Roofs, HSG A (DA1, DA2A, DA2B) 2.858 98 Unconnected pavement, HSG A (DA2A, DA2B) 0.210 98 Water Surface, 0% imp, HSG A (DA1) 0.009 98 Water Surface, HSG A (DA2B) 3.307 30 Woods, Good, HSG A (DA1, DA2A, DA2B) 13.008 56 TOTAL AREA 22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 4HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Soil Listing (all nodes) Area (acres) Soil Group Subcatchment Numbers 13.008 HSG A DA1, DA2A, DA2B 0.000 HSG B 0.000 HSG C 0.000 HSG D 0.000 Other 13.008 TOTAL AREA 22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 5HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Ground Covers (all nodes) HSG-A (acres) HSG-B (acres) HSG-C (acres) HSG-D (acres) Other (acres) Total (acres) Ground Cover Subcatchment Numbers 5.344 0.000 0.000 0.000 0.000 5.344 >75% Grass cover, Good DA1, DA2A, DA2B 0.080 0.000 0.000 0.000 0.000 0.080 Paved parking DA1 1.200 0.000 0.000 0.000 0.000 1.200 Roofs DA1, DA2A, DA2B 2.858 0.000 0.000 0.000 0.000 2.858 Unconnected pavement DA2A, DA2B 0.009 0.000 0.000 0.000 0.000 0.009 Water Surface DA2B 0.210 0.000 0.000 0.000 0.000 0.210 Water Surface, 0% imp DA1 3.307 0.000 0.000 0.000 0.000 3.307 Woods, Good DA1, DA2A, DA2B 13.008 0.000 0.000 0.000 0.000 13.008 TOTAL AREA 22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 6HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Pipe Listing (all nodes) Line# Node Number In-Invert (feet) Out-Invert (feet) Length (feet) Slope (ft/ft) n Width (inches) Diam/Height (inches) Inside-Fill (inches) Node Name 1 DA2B 0.00 0.00 1,259.0 0.0300 0.013 0.0 12.0 0.0 2 3P 7.50 7.00 36.0 0.0139 0.013 0.0 24.0 0.0 Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 7HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=0.87"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=1.63 cfs 0.137 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=0.83"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=1.73 cfs 0.145 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=1.26"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=11.32 cfs 0.947 af Peak Elev=9.69' Inflow=13.05 cfs 1.092 afPond 3P: CDS Unit 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' Outflow=13.05 cfs 1.092 af Inflow=12.57 cfs 1.228 afPond 4P: Existing Wetland Primary=12.57 cfs 1.228 af Peak Elev=8.33' Storage=19,781 cf Inflow=14.69 cfs 1.228 afPond 7P: Constructed Wetland Outflow=12.57 cfs 1.228 af Total Runoff Area = 13.008 ac Runoff Volume = 1.228 af Average Runoff Depth = 1.13" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 8HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 1.63 cfs @ 12.10 hrs, Volume= 0.137 af, Depth= 0.87" Routed to Pond 7P : Constructed Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 2 YR Rainfall=3.60" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 36,865 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 9,145 98 Water Surface, 0% imp, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)1 0 Type III 24-hr 2 YR Rainfall=3.60" Runoff Area=82,499 sf Runoff Volume=0.137 af Runoff Depth=0.87" Tc=7.1 min CN=WQ 1.63 cfs Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 9HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 1.73 cfs @ 12.10 hrs, Volume= 0.145 af, Depth= 0.83" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 2 YR Rainfall=3.60" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)1 0 Type III 24-hr 2 YR Rainfall=3.60" Runoff Area=91,576 sf Runoff Volume=0.145 af Runoff Depth=0.83" Tc=7.1 min UI Adjusted CN=WQ 1.73 cfs Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 10HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 [47] Hint: Peak is 183% of capacity of segment #3 Runoff = 11.32 cfs @ 12.10 hrs, Volume= 0.947 af, Depth= 1.26" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 2 YR Rainfall=3.60" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 11HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)12 11 10 9 8 7 6 5 4 3 2 1 0 Type III 24-hr 2 YR Rainfall=3.60" Runoff Area=392,565 sf Runoff Volume=0.947 af Runoff Depth=1.26" Flow Length=1,733' Tc=7.1 min CN=WQ 11.32 cfs Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 12HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 3P: CDS Unit [57] Hint: Peaked at 9.69' (Flood elevation advised) Inflow Area = 11.114 ac, 34.84% Impervious, Inflow Depth = 1.18" for 2 YR event Inflow = 13.05 cfs @ 12.10 hrs, Volume= 1.092 af Outflow = 13.05 cfs @ 12.10 hrs, Volume= 1.092 af, Atten= 0%, Lag= 0.0 min Primary = 13.05 cfs @ 12.10 hrs, Volume= 1.092 af Routed to Pond 7P : Constructed Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Peak Elev= 9.69' @ 12.10 hrs Device Routing Invert Outlet Devices #1 Primary 7.50'24.0" Round Culvert L= 36.0' CMP, projecting, no headwall, Ke= 0.900 Inlet / Outlet Invert= 7.50' / 7.00' S= 0.0139 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf Primary OutFlow Max=13.02 cfs @ 12.10 hrs HW=9.69' TW=7.50' (Fixed TW Elev= 7.50') 1=Culvert (Inlet Controls 13.02 cfs @ 4.14 fps) Pond 3P: CDS Unit Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=11.114 ac Peak Elev=9.69' 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' 13.05 cfs13.05 cfs Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 13HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 4P: Existing Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 1.13" for 2 YR event Inflow = 12.57 cfs @ 12.15 hrs, Volume= 1.228 af Primary = 12.57 cfs @ 12.15 hrs, Volume= 1.228 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 4P: Existing Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=13.008 ac 12.57 cfs12.57 cfs Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 14HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 7P: Constructed Wetland [81] Warning: Exceeded Pond 3P by 0.36' @ 24.40 hrs Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 1.13" for 2 YR event Inflow = 14.69 cfs @ 12.10 hrs, Volume= 1.228 af Outflow = 12.57 cfs @ 12.15 hrs, Volume= 1.228 af, Atten= 14%, Lag= 3.1 min Primary = 12.57 cfs @ 12.15 hrs, Volume= 1.228 af Routed to Pond 4P : Existing Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Starting Elev= 7.85' Surf.Area= 9,158 sf Storage= 15,149 cf Peak Elev= 8.33' @ 12.15 hrs Surf.Area= 10,013 sf Storage= 19,781 cf (4,632 cf above start) Plug-Flow detention time= 183.9 min calculated for 0.881 af (72% of inflow) Center-of-Mass det. time= 13.0 min ( 770.4 - 757.3 ) Volume Invert Avail.Storage Storage Description #1 3.00' 38,706 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 3.00 304 0 0 4.00 822 563 563 5.00 1,688 1,255 1,818 6.00 3,104 2,396 4,214 7.00 6,142 4,623 8,837 7.35 6,936 2,289 11,126 7.85 9,158 4,024 15,149 8.00 9,416 1,393 16,542 9.00 11,206 10,311 26,853 10.00 12,500 11,853 38,706 Device Routing Invert Outlet Devices #1 Primary 7.85'13.0' long + 3.0 '/' SideZ x 11.2' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.54 2.59 2.70 2.68 2.67 2.68 2.66 2.64 Primary OutFlow Max=12.49 cfs @ 12.15 hrs HW=8.33' TW=7.85' (Fixed TW Elev= 7.85') 1=Broad-Crested Rectangular Weir (Weir Controls 12.49 cfs @ 1.79 fps) Type III 24-hr 2 YR Rainfall=3.60"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 15HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Pond 7P: Constructed Wetland Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=13.008 ac Peak Elev=8.33' Storage=19,781 cf 14.69 cfs 12.57 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 16HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=1.37"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=2.41 cfs 0.217 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=1.36"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=2.55 cfs 0.237 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=1.99"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=16.67 cfs 1.492 af Peak Elev=11.09' Inflow=19.21 cfs 1.730 afPond 3P: CDS Unit 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' Outflow=19.21 cfs 1.730 af Inflow=19.05 cfs 1.946 afPond 4P: Existing Wetland Primary=19.05 cfs 1.946 af Peak Elev=8.47' Storage=21,156 cf Inflow=21.62 cfs 1.946 afPond 7P: Constructed Wetland Outflow=19.05 cfs 1.946 af Total Runoff Area = 13.008 ac Runoff Volume = 1.946 af Average Runoff Depth = 1.80" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 17HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 2.41 cfs @ 12.10 hrs, Volume= 0.217 af, Depth= 1.37" Routed to Pond 7P : Constructed Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 10 YR Rainfall=5.27" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 36,865 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 9,145 98 Water Surface, 0% imp, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)2 1 0 Type III 24-hr 10 YR Rainfall=5.27" Runoff Area=82,499 sf Runoff Volume=0.217 af Runoff Depth=1.37" Tc=7.1 min CN=WQ 2.41 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 18HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 2.55 cfs @ 12.10 hrs, Volume= 0.237 af, Depth= 1.36" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 10 YR Rainfall=5.27" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)2 1 0 Type III 24-hr 10 YR Rainfall=5.27" Runoff Area=91,576 sf Runoff Volume=0.237 af Runoff Depth=1.36" Tc=7.1 min UI Adjusted CN=WQ 2.55 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 19HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 [47] Hint: Peak is 270% of capacity of segment #3 Runoff = 16.67 cfs @ 12.10 hrs, Volume= 1.492 af, Depth= 1.99" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 10 YR Rainfall=5.27" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 20HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Type III 24-hr 10 YR Rainfall=5.27" Runoff Area=392,565 sf Runoff Volume=1.492 af Runoff Depth=1.99" Flow Length=1,733' Tc=7.1 min CN=WQ 16.67 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 21HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 3P: CDS Unit [57] Hint: Peaked at 11.09' (Flood elevation advised) Inflow Area = 11.114 ac, 34.84% Impervious, Inflow Depth = 1.87" for 10 YR event Inflow = 19.21 cfs @ 12.10 hrs, Volume= 1.730 af Outflow = 19.21 cfs @ 12.10 hrs, Volume= 1.730 af, Atten= 0%, Lag= 0.0 min Primary = 19.21 cfs @ 12.10 hrs, Volume= 1.730 af Routed to Pond 7P : Constructed Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Peak Elev= 11.09' @ 12.10 hrs Device Routing Invert Outlet Devices #1 Primary 7.50'24.0" Round Culvert L= 36.0' CMP, projecting, no headwall, Ke= 0.900 Inlet / Outlet Invert= 7.50' / 7.00' S= 0.0139 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf Primary OutFlow Max=19.16 cfs @ 12.10 hrs HW=11.07' TW=7.50' (Fixed TW Elev= 7.50') 1=Culvert (Inlet Controls 19.16 cfs @ 6.10 fps) Pond 3P: CDS Unit Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=11.114 ac Peak Elev=11.09' 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' 19.21 cfs19.21 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 22HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 4P: Existing Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 1.80" for 10 YR event Inflow = 19.05 cfs @ 12.14 hrs, Volume= 1.946 af Primary = 19.05 cfs @ 12.14 hrs, Volume= 1.946 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 4P: Existing Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=13.008 ac 19.05 cfs19.05 cfs Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 23HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 7P: Constructed Wetland [81] Warning: Exceeded Pond 3P by 0.37' @ 24.40 hrs Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 1.80" for 10 YR event Inflow = 21.62 cfs @ 12.10 hrs, Volume= 1.946 af Outflow = 19.05 cfs @ 12.14 hrs, Volume= 1.946 af, Atten= 12%, Lag= 2.8 min Primary = 19.05 cfs @ 12.14 hrs, Volume= 1.946 af Routed to Pond 4P : Existing Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Starting Elev= 7.85' Surf.Area= 9,158 sf Storage= 15,149 cf Peak Elev= 8.47' @ 12.14 hrs Surf.Area= 10,256 sf Storage= 21,156 cf (6,007 cf above start) Plug-Flow detention time= 151.3 min calculated for 1.599 af (82% of inflow) Center-of-Mass det. time= 11.9 min ( 775.6 - 763.8 ) Volume Invert Avail.Storage Storage Description #1 3.00' 38,706 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 3.00 304 0 0 4.00 822 563 563 5.00 1,688 1,255 1,818 6.00 3,104 2,396 4,214 7.00 6,142 4,623 8,837 7.35 6,936 2,289 11,126 7.85 9,158 4,024 15,149 8.00 9,416 1,393 16,542 9.00 11,206 10,311 26,853 10.00 12,500 11,853 38,706 Device Routing Invert Outlet Devices #1 Primary 7.85'13.0' long + 3.0 '/' SideZ x 11.2' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.54 2.59 2.70 2.68 2.67 2.68 2.66 2.64 Primary OutFlow Max=18.98 cfs @ 12.14 hrs HW=8.47' TW=7.85' (Fixed TW Elev= 7.85') 1=Broad-Crested Rectangular Weir (Weir Controls 18.98 cfs @ 2.07 fps) Type III 24-hr 10 YR Rainfall=5.27"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 24HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Pond 7P: Constructed Wetland Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=13.008 ac Peak Elev=8.47' Storage=21,156 cf 21.62 cfs 19.05 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 25HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=1.85"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=3.07 cfs 0.293 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=1.86"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=3.30 cfs 0.326 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=2.63"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=21.21 cfs 1.974 af Peak Elev=12.71' Inflow=24.51 cfs 2.300 afPond 3P: CDS Unit 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' Outflow=24.51 cfs 2.300 af Inflow=24.55 cfs 2.593 afPond 4P: Existing Wetland Primary=24.55 cfs 2.593 af Peak Elev=8.58' Storage=22,265 cf Inflow=27.57 cfs 2.593 afPond 7P: Constructed Wetland Outflow=24.55 cfs 2.593 af Total Runoff Area = 13.008 ac Runoff Volume = 2.593 af Average Runoff Depth = 2.39" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 26HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 3.07 cfs @ 12.10 hrs, Volume= 0.293 af, Depth= 1.85" Routed to Pond 7P : Constructed Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 25 YR Rainfall=6.53" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 36,865 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 9,145 98 Water Surface, 0% imp, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)3 2 1 0 Type III 24-hr 25 YR Rainfall=6.53" Runoff Area=82,499 sf Runoff Volume=0.293 af Runoff Depth=1.85" Tc=7.1 min CN=WQ 3.07 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 27HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 3.30 cfs @ 12.10 hrs, Volume= 0.326 af, Depth= 1.86" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 25 YR Rainfall=6.53" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)3 2 1 0 Type III 24-hr 25 YR Rainfall=6.53" Runoff Area=91,576 sf Runoff Volume=0.326 af Runoff Depth=1.86" Tc=7.1 min UI Adjusted CN=WQ 3.30 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 28HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 [47] Hint: Peak is 344% of capacity of segment #3 Runoff = 21.21 cfs @ 12.10 hrs, Volume= 1.974 af, Depth= 2.63" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 25 YR Rainfall=6.53" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 29HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Type III 24-hr 25 YR Rainfall=6.53" Runoff Area=392,565 sf Runoff Volume=1.974 af Runoff Depth=2.63" Flow Length=1,733' Tc=7.1 min CN=WQ 21.21 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 30HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 3P: CDS Unit [57] Hint: Peaked at 12.71' (Flood elevation advised) Inflow Area = 11.114 ac, 34.84% Impervious, Inflow Depth = 2.48" for 25 YR event Inflow = 24.51 cfs @ 12.10 hrs, Volume= 2.300 af Outflow = 24.51 cfs @ 12.10 hrs, Volume= 2.300 af, Atten= 0%, Lag= 0.0 min Primary = 24.51 cfs @ 12.10 hrs, Volume= 2.300 af Routed to Pond 7P : Constructed Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Peak Elev= 12.71' @ 12.10 hrs Device Routing Invert Outlet Devices #1 Primary 7.50'24.0" Round Culvert L= 36.0' CMP, projecting, no headwall, Ke= 0.900 Inlet / Outlet Invert= 7.50' / 7.00' S= 0.0139 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf Primary OutFlow Max=24.47 cfs @ 12.10 hrs HW=12.70' TW=7.50' (Fixed TW Elev= 7.50') 1=Culvert (Inlet Controls 24.47 cfs @ 7.79 fps) Pond 3P: CDS Unit Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)26 24 22 20 18 16 14 12 10 8 6 4 2 0 Inflow Area=11.114 ac Peak Elev=12.71' 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' 24.51 cfs24.51 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 31HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 4P: Existing Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 2.39" for 25 YR event Inflow = 24.55 cfs @ 12.15 hrs, Volume= 2.593 af Primary = 24.55 cfs @ 12.15 hrs, Volume= 2.593 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 4P: Existing Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)26 24 22 20 18 16 14 12 10 8 6 4 2 0 Inflow Area=13.008 ac 24.55 cfs24.55 cfs Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 32HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 7P: Constructed Wetland [81] Warning: Exceeded Pond 3P by 0.37' @ 24.40 hrs Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 2.39" for 25 YR event Inflow = 27.57 cfs @ 12.10 hrs, Volume= 2.593 af Outflow = 24.55 cfs @ 12.15 hrs, Volume= 2.593 af, Atten= 11%, Lag= 2.7 min Primary = 24.55 cfs @ 12.15 hrs, Volume= 2.593 af Routed to Pond 4P : Existing Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Starting Elev= 7.85' Surf.Area= 9,158 sf Storage= 15,149 cf Peak Elev= 8.58' @ 12.15 hrs Surf.Area= 10,447 sf Storage= 22,265 cf (7,116 cf above start) Plug-Flow detention time= 128.9 min calculated for 2.245 af (87% of inflow) Center-of-Mass det. time= 11.0 min ( 781.4 - 770.4 ) Volume Invert Avail.Storage Storage Description #1 3.00' 38,706 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 3.00 304 0 0 4.00 822 563 563 5.00 1,688 1,255 1,818 6.00 3,104 2,396 4,214 7.00 6,142 4,623 8,837 7.35 6,936 2,289 11,126 7.85 9,158 4,024 15,149 8.00 9,416 1,393 16,542 9.00 11,206 10,311 26,853 10.00 12,500 11,853 38,706 Device Routing Invert Outlet Devices #1 Primary 7.85'13.0' long + 3.0 '/' SideZ x 11.2' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.54 2.59 2.70 2.68 2.67 2.68 2.66 2.64 Primary OutFlow Max=24.42 cfs @ 12.15 hrs HW=8.57' TW=7.85' (Fixed TW Elev= 7.85') 1=Broad-Crested Rectangular Weir (Weir Controls 24.42 cfs @ 2.22 fps) Type III 24-hr 25 YR Rainfall=6.53"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 33HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Pond 7P: Constructed Wetland Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Inflow Area=13.008 ac Peak Elev=8.58' Storage=22,265 cf 27.57 cfs 24.55 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 34HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=2.81"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=4.55 cfs 0.444 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=2.87"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=5.24 cfs 0.502 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=3.82"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=31.32 cfs 2.871 af Peak Elev=17.87' Inflow=36.56 cfs 3.373 afPond 3P: CDS Unit 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' Outflow=36.56 cfs 3.373 af Inflow=37.09 cfs 3.817 afPond 4P: Existing Wetland Primary=37.09 cfs 3.817 af Peak Elev=8.79' Storage=24,523 cf Inflow=41.11 cfs 3.817 afPond 7P: Constructed Wetland Outflow=37.09 cfs 3.817 af Total Runoff Area = 13.008 ac Runoff Volume = 3.817 af Average Runoff Depth = 3.52" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 35HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 4.55 cfs @ 12.10 hrs, Volume= 0.444 af, Depth= 2.81" Routed to Pond 7P : Constructed Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 100 YR Rainfall=8.59" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 36,865 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 9,145 98 Water Surface, 0% imp, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)5 4 3 2 1 0 Type III 24-hr 100 YR Rainfall=8.59" Runoff Area=82,499 sf Runoff Volume=0.444 af Runoff Depth=2.81" Tc=7.1 min CN=WQ 4.55 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 36HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 5.24 cfs @ 12.11 hrs, Volume= 0.502 af, Depth= 2.87" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 100 YR Rainfall=8.59" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)5 4 3 2 1 0 Type III 24-hr 100 YR Rainfall=8.59" Runoff Area=91,576 sf Runoff Volume=0.502 af Runoff Depth=2.87" Tc=7.1 min UI Adjusted CN=WQ 5.24 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 37HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 [47] Hint: Peak is 508% of capacity of segment #3 Runoff = 31.32 cfs @ 12.10 hrs, Volume= 2.871 af, Depth= 3.82" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr 100 YR Rainfall=8.59" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 38HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Type III 24-hr 100 YR Rainfall=8.59" Runoff Area=392,565 sf Runoff Volume=2.871 af Runoff Depth=3.82" Flow Length=1,733' Tc=7.1 min CN=WQ 31.32 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 39HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 3P: CDS Unit [57] Hint: Peaked at 17.87' (Flood elevation advised) Inflow Area = 11.114 ac, 34.84% Impervious, Inflow Depth = 3.64" for 100 YR event Inflow = 36.56 cfs @ 12.10 hrs, Volume= 3.373 af Outflow = 36.56 cfs @ 12.10 hrs, Volume= 3.373 af, Atten= 0%, Lag= 0.0 min Primary = 36.56 cfs @ 12.10 hrs, Volume= 3.373 af Routed to Pond 7P : Constructed Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Peak Elev= 17.87' @ 12.10 hrs Device Routing Invert Outlet Devices #1 Primary 7.50'24.0" Round Culvert L= 36.0' CMP, projecting, no headwall, Ke= 0.900 Inlet / Outlet Invert= 7.50' / 7.00' S= 0.0139 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf Primary OutFlow Max=36.44 cfs @ 12.10 hrs HW=17.81' TW=7.50' (Fixed TW Elev= 7.50') 1=Culvert (Inlet Controls 36.44 cfs @ 11.60 fps) Pond 3P: CDS Unit Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Inflow Area=11.114 ac Peak Elev=17.87' 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' 36.56 cfs36.56 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 40HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 4P: Existing Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 3.52" for 100 YR event Inflow = 37.09 cfs @ 12.15 hrs, Volume= 3.817 af Primary = 37.09 cfs @ 12.15 hrs, Volume= 3.817 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 4P: Existing Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Inflow Area=13.008 ac 37.09 cfs37.09 cfs Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 41HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 7P: Constructed Wetland [81] Warning: Exceeded Pond 3P by 0.38' @ 24.38 hrs Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 3.52" for 100 YR event Inflow = 41.11 cfs @ 12.10 hrs, Volume= 3.817 af Outflow = 37.09 cfs @ 12.15 hrs, Volume= 3.817 af, Atten= 10%, Lag= 2.6 min Primary = 37.09 cfs @ 12.15 hrs, Volume= 3.817 af Routed to Pond 4P : Existing Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Starting Elev= 7.85' Surf.Area= 9,158 sf Storage= 15,149 cf Peak Elev= 8.79' @ 12.15 hrs Surf.Area= 10,827 sf Storage= 24,523 cf (9,374 cf above start) Plug-Flow detention time= 99.5 min calculated for 3.468 af (91% of inflow) Center-of-Mass det. time= 9.7 min ( 787.3 - 777.6 ) Volume Invert Avail.Storage Storage Description #1 3.00' 38,706 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 3.00 304 0 0 4.00 822 563 563 5.00 1,688 1,255 1,818 6.00 3,104 2,396 4,214 7.00 6,142 4,623 8,837 7.35 6,936 2,289 11,126 7.85 9,158 4,024 15,149 8.00 9,416 1,393 16,542 9.00 11,206 10,311 26,853 10.00 12,500 11,853 38,706 Device Routing Invert Outlet Devices #1 Primary 7.85'13.0' long + 3.0 '/' SideZ x 11.2' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.54 2.59 2.70 2.68 2.67 2.68 2.66 2.64 Primary OutFlow Max=36.92 cfs @ 12.15 hrs HW=8.79' TW=7.85' (Fixed TW Elev= 7.85') 1=Broad-Crested Rectangular Weir (Weir Controls 36.92 cfs @ 2.49 fps) Type III 24-hr 100 YR Rainfall=8.59"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 42HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Pond 7P: Constructed Wetland Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Inflow Area=13.008 ac Peak Elev=8.79' Storage=24,523 cf 41.11 cfs 37.09 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 43HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Time span=0.00-48.00 hrs, dt=0.02 hrs, 2401 points Runoff by SCS TR-20 method, UH=SCS, Weighted-Q Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=82,499 sf 14.53% Impervious Runoff Depth=0.25"Subcatchment DA1: 0.28/1.89 Tc=7.1 min CN=WQ Runoff=0.52 cfs 0.040 af Runoff Area=91,576 sf 24.42% Impervious Runoff Depth=0.24"Subcatchment DA2A: 0.51/2.10 Tc=7.1 min UI Adjusted CN=WQ Runoff=0.55 cfs 0.043 af Runoff Area=392,565 sf 37.27% Impervious Runoff Depth=0.37"Subcatchment DA2B: 3.36/9.01 Flow Length=1,733' Tc=7.1 min CN=WQ Runoff=3.57 cfs 0.279 af Peak Elev=8.49' Inflow=4.12 cfs 0.321 afPond 3P: CDS Unit 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' Outflow=4.12 cfs 0.321 af Inflow=3.52 cfs 0.361 afPond 4P: Existing Wetland Primary=3.52 cfs 0.361 af Peak Elev=8.07' Storage=17,179 cf Inflow=4.63 cfs 0.361 afPond 7P: Constructed Wetland Outflow=3.52 cfs 0.361 af Total Runoff Area = 13.008 ac Runoff Volume = 0.361 af Average Runoff Depth = 0.33" 68.12% Pervious = 8.861 ac 31.88% Impervious = 4.147 ac Type III 24-hr WQ Rainfall=1.21"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 44HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA1: 0.28/1.89 Runoff = 0.52 cfs @ 12.10 hrs, Volume= 0.040 af, Depth= 0.25" Routed to Pond 7P : Constructed Wetland Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr WQ Rainfall=1.21" Area (sf) CN Description 3,469 98 Paved parking, HSG A 8,516 98 Roofs, HSG A 36,865 30 Woods, Good, HSG A 24,504 39 >75% Grass cover, Good, HSG A 9,145 98 Water Surface, 0% imp, HSG A 82,499 Weighted Average 70,514 85.47% Pervious Area 11,985 14.53% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA1: 0.28/1.89 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 Type III 24-hr WQ Rainfall=1.21" Runoff Area=82,499 sf Runoff Volume=0.040 af Runoff Depth=0.25" Tc=7.1 min CN=WQ 0.52 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 45HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2A: 0.51/2.10 Runoff = 0.55 cfs @ 12.10 hrs, Volume= 0.043 af, Depth= 0.24" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr WQ Rainfall=1.21" Area (sf) CN Adj Description 14,426 98 98 Unconnected pavement, HSG A 7,938 98 98 Roofs, HSG A 25,978 30 30 Woods, Good, HSG A 43,234 39 39 >75% Grass cover, Good, HSG A 91,576 Weighted Average 69,212 75.58% Pervious Area 22,364 24.42% Impervious Area 14,426 64.51% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 7.1 Direct Entry, From DA 2B Subcatchment DA2A: 0.51/2.10 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 Type III 24-hr WQ Rainfall=1.21" Runoff Area=91,576 sf Runoff Volume=0.043 af Runoff Depth=0.24" Tc=7.1 min UI Adjusted CN=WQ 0.55 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 46HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment DA2B: 3.36/9.01 Runoff = 3.57 cfs @ 12.10 hrs, Volume= 0.279 af, Depth= 0.37" Routed to Pond 3P : CDS Unit Runoff by SCS TR-20 method, UH=SCS, Weighted-Q, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Type III 24-hr WQ Rainfall=1.21" Area (sf) CN Description 110,080 98 Unconnected pavement, HSG A 35,831 98 Roofs, HSG A 394 98 Water Surface, HSG A 81,217 30 Woods, Good, HSG A 165,043 39 >75% Grass cover, Good, HSG A 392,565 Weighted Average 246,260 62.73% Pervious Area 146,305 37.27% Impervious Area 110,080 75.24% Unconnected Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.9 50 0.0100 0.96 Sheet Flow, Smooth surfaces n= 0.011 P2= 3.60" 3.5 424 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 2.7 1,259 0.0300 7.86 6.17 Pipe Channel, CMP_Round 12" 12.0" Round Area= 0.8 sf Perim= 3.1' r= 0.25' n= 0.013 Corrugated PE, smooth interior 7.1 1,733 Total Type III 24-hr WQ Rainfall=1.21"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 47HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Subcatchment DA2B: 3.36/9.01 Runoff Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)3 2 1 0 Type III 24-hr WQ Rainfall=1.21" Runoff Area=392,565 sf Runoff Volume=0.279 af Runoff Depth=0.37" Flow Length=1,733' Tc=7.1 min CN=WQ 3.57 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 48HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 3P: CDS Unit [57] Hint: Peaked at 8.49' (Flood elevation advised) Inflow Area = 11.114 ac, 34.84% Impervious, Inflow Depth = 0.35" for WQ event Inflow = 4.12 cfs @ 12.10 hrs, Volume= 0.321 af Outflow = 4.12 cfs @ 12.10 hrs, Volume= 0.321 af, Atten= 0%, Lag= 0.0 min Primary = 4.12 cfs @ 12.10 hrs, Volume= 0.321 af Routed to Pond 7P : Constructed Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Peak Elev= 8.49' @ 12.10 hrs Device Routing Invert Outlet Devices #1 Primary 7.50'24.0" Round Culvert L= 36.0' CMP, projecting, no headwall, Ke= 0.900 Inlet / Outlet Invert= 7.50' / 7.00' S= 0.0139 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf Primary OutFlow Max=4.11 cfs @ 12.10 hrs HW=8.48' TW=7.50' (Fixed TW Elev= 7.50') 1=Culvert (Inlet Controls 4.11 cfs @ 2.67 fps) Pond 3P: CDS Unit Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)4 3 2 1 0 Inflow Area=11.114 ac Peak Elev=8.49' 24.0" Round Culvert n=0.013 L=36.0' S=0.0139 '/' 4.12 cfs4.12 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 49HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 4P: Existing Wetland [40] Hint: Not Described (Outflow=Inflow) Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 0.33" for WQ event Inflow = 3.52 cfs @ 12.17 hrs, Volume= 0.361 af Primary = 3.52 cfs @ 12.17 hrs, Volume= 0.361 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Pond 4P: Existing Wetland InflowPrimary Hydrograph Time (hours) 484644424038363432302826242220181614121086420Flow (cfs)3 2 1 0 Inflow Area=13.008 ac 3.52 cfs3.52 cfs Type III 24-hr WQ Rainfall=1.21"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 50HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Summary for Pond 7P: Constructed Wetland [81] Warning: Exceeded Pond 3P by 0.35' @ 24.40 hrs Inflow Area = 13.008 ac, 31.88% Impervious, Inflow Depth = 0.33" for WQ event Inflow = 4.63 cfs @ 12.10 hrs, Volume= 0.361 af Outflow = 3.52 cfs @ 12.17 hrs, Volume= 0.361 af, Atten= 24%, Lag= 4.4 min Primary = 3.52 cfs @ 12.17 hrs, Volume= 0.361 af Routed to Pond 4P : Existing Wetland Routing by Stor-Ind method, Time Span= 0.00-48.00 hrs, dt= 0.02 hrs Starting Elev= 7.85' Surf.Area= 9,158 sf Storage= 15,149 cf Peak Elev= 8.07' @ 12.17 hrs Surf.Area= 9,536 sf Storage= 17,179 cf (2,029 cf above start) Plug-Flow detention time= 952.0 min calculated for 0.014 af (4% of inflow) Center-of-Mass det. time= 16.3 min ( 799.1 - 782.8 ) Volume Invert Avail.Storage Storage Description #1 3.00' 38,706 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 3.00 304 0 0 4.00 822 563 563 5.00 1,688 1,255 1,818 6.00 3,104 2,396 4,214 7.00 6,142 4,623 8,837 7.35 6,936 2,289 11,126 7.85 9,158 4,024 15,149 8.00 9,416 1,393 16,542 9.00 11,206 10,311 26,853 10.00 12,500 11,853 38,706 Device Routing Invert Outlet Devices #1 Primary 7.85'13.0' long + 3.0 '/' SideZ x 11.2' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.54 2.59 2.70 2.68 2.67 2.68 2.66 2.64 Primary OutFlow Max=3.47 cfs @ 12.17 hrs HW=8.07' TW=7.85' (Fixed TW Elev= 7.85') 1=Broad-Crested Rectangular Weir (Weir Controls 3.47 cfs @ 1.17 fps) Type III 24-hr WQ Rainfall=1.21"22108 CURVE PR_report Printed 9/17/2024Prepared by Horsley Witten Inc Page 51HydroCAD® 10.20-4b s/n 01445 © 2023 HydroCAD Software Solutions LLC Pond 7P: Constructed Wetland Inflow Primary Hydrograph Time (hours)484644424038363432302826242220181614121086420Flow (cfs)5 4 3 2 1 0 Inflow Area=13.008 ac Peak Elev=8.07' Storage=17,179 cf 4.63 cfs 3.52 cfs AREA 11.11 acres CS-6 WEIGHTED C 0.51 110 microns TC 5.00 minutes RAINFALL STATION 66 Rainfall Intensity1 (in/hr) Hydraulic Loading Rate (gpm/ft2) Removal Efficiency (%) Incremental Removal (%) 0.08 7.20 100.0 35.3 0.16 14.39 98.4 23.4 0.24 21.59 91.6 11.8 0.32 28.78 84.8 6.6 0.40 35.98 78.1 3.8 0.48 43.17 71.3 2.5 0.56 50.37 64.6 1.1 0.64 57.56 57.8 1.1 0.72 64.76 51.0 1.0 0.80 71.96 44.3 0.4 1.00 89.94 27.4 0.6 2.00 115.09 2.4 0.1 3.00 115.09 1.6 0.0 87.7 0.0% 98.8% 87.7% 1 - Based on 14 years of 15 minute precipitation data from NCDC station 3821, Hyannis, in Barnstable County, MA 2 - Reduction due to use of 60-minute data for a site that has a time of concentration less than 30-minutes. Removal Efficiency Adjustment2 = Predicted % Annual Rainfall Treated = Predicted Net Annual Load Removal Efficiency = 1.7% 1.8% 1.9% 0.9% 2.3% 2.9% 0.2% 3.5% CASCADE MODEL PARTICLE SIZE Percent Rainfall Volume1 35.3% 23.8% 12.9% 7.8% 4.9% HDS Estimated Net Annual Solids Load Reduction Based on the Rational Rainfall Method CURVE HILL YARMOUTH, MA APPENDIX C – Soil Test Pit Logs Surface elevation Additional Notes: --M Fi42-75 C CS 10YR 8/1 --M Fi18-42 B MS 10YR 3/6 --M Fr4-18 E MS 10YR 2/1 --M Fr0-4 A MS 10YR 3/2 4. Unsuitable Materials Present:If Yes: 5. Groundwater Observed:63"If Yes:Depth weeping from pit Other Depth Color Percent Gravel Cobbles/Stones Depth standing water in hole Soil Log Depth (in) Soil Horizon/ Layer Soil Texture (USDA) Soil Matrix: Color- Moist (Munsell)Redoximorphic Features Coarse Fragments % by Volume Soil Structure Soil Consistence (Moist) Property Line 10 Drinking Water Well Otherfeetfeet feet 3. Distances From:Open Water Body >200 Drainage Way Wetlands 2. Soil Parent Material:Sandy glaciofluvial deposits Moraines, outwash plains Landform Position on Landscape (SU, SH, BS, FS, TS) >200feetfeet feet (e.g. woodland, agricultural field, vacant lot, etc.)Vegetation Surface Stones (e.g. cobbles, stones, boulders, etc.)Slope (%) Description of Location:South side of Curve Hill Rd in front of #7 11.2 Longitude 1. Land Use:Conservation land Scrub oak and pine No 3-8 70º10'07034"W Commonwealth of Massachusetts City/Town of Yarmouth Form 11 - Soil Suitability Assessment for On-Site Sewage Disposal C. On-Site Review Deep Observation Hole Number:Hole #Date Time Weather Latitude 1 1/4/24 1200P 40F Sun 41º41'08.88"N Yes No Disturbed Soil Fill Material Weathered/Fractured Rock Bedrock Yes No APPENDIX D – Operation and Maintenance Guide Stormwater O&M Guide 1 September 2024 Curve Hill Road Stormwater Retrofit Project – Yarmouth, MA Stormwater Operations & Maintenance Guide Curve Hill Road 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: CONSTRUCTED WETLAND ........................................ 6 5. PLANTINGS ............................................................................................................................ 8 5.1. Plantings ........................................................................................................................................ 8 6. GENERAL SITE MAINTENANCE ..................................................................................... 17 7. LONG-TERM POLLUTION PREVENTION MEASURES ................................................ 19 APPENDICES A. Maintenance Checklists B. Overall Stormwater Control Measures Locations Plan C. Planting Plan Stormwater O&M Guide 2 September 2024 Curve Hill Road Stormwater Retrofit Project – Yarmouth, MA 1. INTRODUCTION This document provides a general description along with the operation and maintenance requirements for the Curve Hill Road Stormwater Retrofit project, located at Curve Hill Road in Yarmouth, Massachusetts. 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 • Trash & Debris • Pet Waste • Pavement Sweeping • Contributing Drainage Areas • Snow Removal • De-icing 3. Long-Term Pollution Prevention Measures Stormwater O&M Guide 3 September 2024 Curve Hill Road Stormwater Retrofit Project – Yarmouth, MA 2. RESPONSIBLE PARTIES AND BUDGET The Curve Hill Road site is Town-owned property. The drainage from Great Western Road and Curve Hill Road is Town-owned roads. The Town will provide staff, volunteers as possible, and funding for the long- term O&M at the site. The estimated average annual O&M budget for the proposed system is shown below: • Constructed Wetland: $1,000 ($1,000/Wetland) • Drainage Structures (WQU 100) $500 ($500/structure) 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: Division of Natural Resources Bill Bonnetti 424 Route 28 West Yarmouth, MA 02673 508-760-4800 Owner - Signature: Date: Owner - Signature: Date: Stormwater O&M Guide 4 September 2024 Curve Hill Road 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 (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 September 2024 Curve Hill Road Stormwater Retrofit Project – Yarmouth, MA The Town will be able to access the constructed wetland and overflow spillway by a eight-foot wide maintenance access path located along eastern side of the constructed wetland. The Town will use a skid-steer to drive maintenance tools and supplies to the overflow spillway. This maintenance access will need to be maintained regularly (e.g., mowed). 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 (Appendix A) along with a plan showing the location of the items to be inspected and maintained (Appendix B). 3.3. What practices are used at this site? The following practices are present at this site: a. Constructed Wetland: a constructed wetland provides temporary storage in shallow and deep pools that support wetland habitat. Similar to natural wetlands, constructed wetlands use natural processes to treat the stormwater: uptake through vegetation, sedimentation, and biological processes. b. Water Quality Unit: this structure provides the pretreatment prior to the stormwater discharging into the constructed wetland. 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 September 2024 Curve Hill Road Stormwater Retrofit Project – Yarmouth, MA 4. STRUCTURAL COMPONENTS: CONSTRUCTED WETLAND Structural Components 1. Collect: Stormwater runoff is directed through a pipe routing to the initial stabilized outfall and wetland cell where stormwater enters the system. 2. Capture Sediment: Sand and debris settle out within the Water Quality Unit and the first wetland cell. 3. Move Water: Stormwater moves from low marsh areas to micropools which provide additional treatment through sedimentation as well as plant uptake. 4. Treat and Manage: Plants in the constructed wetland help to slow the water down and water is treated when it filters through the soil and plant roots. Planted vegetation remove phosphorous and bacteria and allow stormwater to infiltrate into the soil. 5. Overflow: Treated stormwater will discharge over a stabilized stone spillway. 2 4 5 1 3 Stormwater O&M Guide 7 September 2024 Curve Hill Road Stormwater Retrofit Project Yarmouth, MA MAINTENANCE SCHEDULE: CONSTRUCTED WETLAND A site inspection of the constructed wetland components, including the water quality unit used for pretreatment, 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 Appendix A for more information. Constructed Wetland and Water Quality Unit 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 See Plantings section for information on plantings maintenance of the constructed wetland. Use the plantings maintenance calendar to combine maintenance efforts. Stormwater O&M Guide 8 September 2024 Curve Hill Road Stormwater Retrofit Project Yarmouth, MA 5. PLANTINGS 5.1. Plantings By design, plants in constructed stormwater wetland practices filter stormwater to remove pollutants through uptake, retention, and settling, while providing visual interest and wildlife habitat year-round. These plantings do not require fertilizers, watering, or mowing. The planting design for the site consists of a “no mow” maintenance strategy including wetland edge plantings and wetland plantings. The plantings maintenance checklist is included in Appendix A, and the full planting plan is available in Appendix D. Wetland Edge Wetland Stormwater O&M Guide 9 September 2024 Curve Hill Road Stormwater Retrofit Project Yarmouth, MA PLANTINGS: WETLAND AND WETLAND EDGE AREA MAINTENANCE By design, plants in constructed wetlands 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). The project area is designated as “no mow” with both Wetland Edge and Wetland Plantings. 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 include: Seeding and Planting Loam, reseed and plant bare spots with the specified species and seed mix as shown on the Planting Plan. Cutting Back It is not recommended to cut back plantings within the wetland. If cutting is necessary along the wetland edge, cut by hand with shears a maximum of once a year in mid spring. Otherwise, allow areas to grow to their natural heights to maintain a natural wetland appearance. Do NOT cut any wetland edge 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 constructed wetland. Use a leaf blower as needed to assist in clean-up. Mowing/Weed Whacking Do not mow or weed whack this area. Pruning Prune trees and shrubs to remove deadwood and low hanging branches. Watering Water only during drought conditions or during seeding/plant 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 wetland edge monthly to look for invasive and weedy species, bare spots, and to identify potential pest or disease problems. Carefully remove and dispose of all Stormwater O&M Guide 10 September 2024 Curve Hill Road Stormwater Retrofit Project Yarmouth, MA invasive and weedy species to prevent colonization elsewhere. This includes disposal on land beyond the project area. Observe and map the following on a bi-annual basis, for the first three years, minimum: • The types and distribution of the dominant wetland plants in the constructed wetland • The presence and distribution of planted wetland species • The presence and distribution of invasive wetland species (invasives must be removed) • Indications that other species are replacing the planted wetland species • Percentage of standing water that is unvegetated (excluding the deep water cells which are not suitable for emergent plant growth) • The maximum elevation and the vegetative condition in this zone, • Stability of the original depth zones and the micro-topographic features • Accumulation of sediment in the forebay and micropool; and survival rate of plants (cells with dead plants must be replanted) Debris & Trash Remove and properly dispose of litter from all areas. Stormwater O&M Guide 11 September 2024 Curve Hill Road Stormwater Retrofit Project Yarmouth, MA PLANTINGS: REPLACEMENTS Plants in constructed wetlands require varying levels of inundation and filter out pollutants. The plants along the wetland edge need to withstand periods of drought during dry months and water inundation during the wet season and large rain storms. If replacements are needed, use the planting plan as a guide (see Appendix D). However, if a certain species of plants has not done well in the constructed wetland, do not replace with that same species. Rather, replant with one or more of the other species that has thrived under the site conditions at similar depths, or have a wetland bilogist choose a different species based on current photos of the site. Replacement plants selected should be native to the local area to provide additional habitat and pollinator value. The following should be considered when selecting plants for a constructed wetland: • Use native and pollinator-friendly plants. • Adaptable to both drought conditions for short periods of time and water inundation based on the location and water depths within the wetland. • Be salt and wind tolerant • Use a mix of different plant species that will create a resilient plant community including cold & warm season grasses, perennials, emergent aquatic vegetation, and groundcovers in all areas. Stormwater O&M Guide 12 September 2024 Curve Hill Road Stormwater Retrofit Project Yarmouth, MA PLANTINGS: MAINTENANCE SCHEDULE By design, plants in the constructed wetland are meant to filter the stormwater as it temporarily stores stormwater to remove pollutants by means of uptake, retention, or settling (Massachusetts Stormwater Handbook). The plantings also 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 section above. Weeding and monitoring for invasive species should occur quarterly during the growing season. An annual spring “clean up” includes pruning as needed. See the calendar below, the Plantings Maintenance Checklist in Appendix A, the Weed Identification section, and the Weed Identification Guide at https://web.uri.edu/riss/files/In-the-Weeds.pdf for more information. https://www.mass.gov/doc/massachusetts-stormwater-handbook-vol-2-ch-2-stormwater-best- management-practices/download Constructed Wetland Annual 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 Seeding x x x x Plant Replacement x x x x X required x as needed Stormwater O&M Guide 13 September 2024 Curve Hill Road 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 14 September 2024 Curve Hill Road 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 15 September 2024 Curve Hill Road 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 16 September 2024 Curve Hill Road 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 17 September 2024 Curve Hill Road 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 constructed wetland 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. Mosquito Management Mosquitoes are common in natural wetlands and can be expected in constructed wetlands. Immediately after construction has completed, prior to emergence and maturation of vegetative communities, it is difficult to forecast the degree to which nuisance insects will be an issue. The best approach to avoiding mosquito problems in constructed wetlands is to eliminate areas of open, stagnant water. Flowing water, shaded water, and vegetated areas discourage mosquito larval growth. Removing sticks, branches, or fallen vegetation that inhibits free hydrological movement between deep pools or that block the outlet snout will help keep water freely flowing throughout the system. Other insect larvae that naturally occur in wetlands, such as those of dragonflies, prey on mosquito larvae. Tree swallows and bats can eat thousands of adult mosquitoes every day. Adding bird or bat habitats can reduce the numbers of adult mosquitoes significantly. The Pumpkinseed (Lepomis gibbosus) is a small sunfish, native to Massachusetts, that feeds primarily on insects, also feeding on crustaceans, very small fish, and aquatic vegetation. If these strategies fail to adequately curb the nuisance of mosquito populations breeding in the constructed wetland, insecticides, oils, or bacterial agents can be used, although the effects on the wetland and downstream ecosystems are not well understood, and these methods should be used only Stormwater O&M Guide 18 September 2024 Curve Hill Road Stormwater Retrofit Project Yarmouth, MA as a last resort. Bacillus thuringiensis isroelensis (Bti) is a group of bacteria that can be used as a biological control agent, killing the larvae of various species of mosquito, gnat, and black fly. Stormwater O&M Guide 19 September 2024 Curve Hill Road 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. APPENDIX A – Maintenance Checklists • Constructed Wetland Operation and Maintenance Checklist Curve Hill Road Stormwater Retrofit Project 1 Date: Time: Inspector: *Sediment shall be disposed of offsite in a pre-approved location. Maintenance Item Description Maintenance (Y/N) 1. COLLECT Includes: Pipe Inlet Area, Drop Inlet Frequency: Inspect four times per years during regular park maintenance and after major storm events (2” of rain or greater) When: March, June, September, November Surface Debris Cleaning Remove all trash, leaf litter and inlet clogging. Inlets Check for clogging and sediment accumulation that impacts inflow. If sediment/debris accumulation is observed, remove and dispose. Actions to be taken: 2. CAPTURE Includes: Water Quality Unit Frequency: Inspect four times per year and after major storm events the first year; then annually and after major storm events (2” of rain or greater) When: March, June, September, November Debris Cleanout Remove all trash and debris. Side Slopes Signs of erosion gullies, animal burrowing, overtopping, or slumping 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 or you cannot see stones.* Actions to be taken: 3 & 4. MOVE & FILTER Includes: Low Marsh with Permanent pools and Micropools Frequency: Inspect four times per year during regular park maintenance and after major storm events (2” of rain or greater) When: March, June, September, November Operation and Maintenance Checklist Curve Hill Road Stormwater Retrofit Project 2 Maintenance Item Description Maintenance (Y/N) Debris Cleanout Remove trash and debris from the wetland. Remove any fallen branches that prevent free hydraulic movement between the micropools. Sediment/Organic Debris Removal Remove and properly dispose of when build-up is greater than or equal to 3 inches.* Erosion Check for areas of erosion/ gullies, particularly along the steep slopes. Repair/reseed as necessary Vegetation Maintenance Replacement See Landscape Maintenance Actions to be taken: 5. OVERFLOW Includes: Overflow Spillway Frequency: Inspect bi-annually and after major storm events (2” of rain or greater) When: March and September Overflow Spillways Water level should be at the concrete curb of the spillway. Check for sediment accumulation that impacts outflow. Check for leaf litter, debris, and inlet clogging. If sediment, litter or debris has accumulated, schedule cleaning. Actions to be taken: Other Routine Grounds Maintenance Includes: Surrounding landscape beyond the practice. Frequency: Inspect four times per year during regular park maintenance and after major storm events When: March, June, September, November Debris Removal Remove trash from perimeter areas. Contributing drainage area Look for sediment sources from erosion in the surrounding area. Drainage Network Ensure proper operation. Path Repairs Check path for ponding and other obstructions. Repair paths as needed to ensure positive drainage. Remove obstructions as needed. Pavement Sweeping Sweep the access road and parking lot once a year after spring thaw. Actions to be taken: Operation and Maintenance Checklist Curve Hill Road Stormwater Retrofit Project 3 Maintenance Item Description Maintenance (Y/N) Plantings Maintenance Checklist Curve Hill Road Stormwater Retrofit Project 1 Location: Date: Inspector: Task Description Complete (Y/N) Cutting • Cut with shears as desired once a year in the early spring. • Do not cut lower than 6”. • Blow out leaves and cuttings for easy removal. • Remove cuttings. 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. Seeding • Loam and re-seed bare spots with the specified seed mix as shown on the Planting Plan. Plant Replacement • Replace/replant diseases, unhealthy or dead plans to maintain a healthy plant community Fertilizing NONE Mulch NONE Debris Removal • Remove trash from perimeter areas. Actions to be taken: *Invasive species shall be disposed of offsite in a pre-approved location. Wetland Wetland Edge All areas (Wetland and Wetland Edge) APPENDIX B – Overall SCM Locations APPENDIX C – Planting Plan APPENDIX E – Pollutant Controls During Construction Pollutant Controls During Construction 1 August 2024 Curve Hilld Road 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. • Silt Sacks (or approved equivalent) will be installed at catch basins and following construction of the proposed overflow structures to prevent sedimentation during construction. The silt sack will be emptied/replaced and disposed of off-site if damage is observed. • Sediment Traps/Basins. The water quality unit, catch basin, and inlet pipe into the constructed wetland will be installed first, so that sediment from the roadways is captured by the water quality unit before discharging onto the site. The constructed wetland will be dewatered during construction activities from . Heavy equipment will not be allowed to operate on the surface location where the system is planned because soil compaction can adversely impact the long- term performance. Light earth-moving equipment will be used for excavation and construction of the system. All excavated materials from the area will be removed and disposed of in an approved location. • Construction Entrance will be installed. All construction vehicles must use this access point to ensure sediment is not tracked off site. • Slope Stabilization will occur immediately upon obtaining final grades as shown on the project site plans. 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 pipes, structures, and constructed wetland, 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. Pollutant Controls During Construction 2 August 2024 Curve Hilld Road Stormwater Retrofit Project – Yarmouth, MA 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. 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. • 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. Pollutant Controls During Construction 3 August 2024 Curve Hilld Road Stormwater Retrofit Project – Yarmouth, MA • 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. • Snow Removal Plan – Plowed snow collected from the roadway and parking areas 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. Pollutant Controls During Construction 4 August 2024 Curve Hilld Road Stormwater Retrofit Project – Yarmouth, MA o The site superintendent will conduct daily inspections to ensure proper use and disposal of materials. 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: Pollutant Controls During Construction 5 August 2024 Curve Hilld Road Stormwater Retrofit Project – Yarmouth, MA • 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. • 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