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HomeMy WebLinkAbout2024-05-28 Stormwater Addendum STORMWATER MANAGEMENT REPORT DEFINITIVE SUBDIVISION 307 MAIN STREET 307 Main Street Hyannis, Massachusetts April 11, 2024 AMENDED: May 28, 2024 344700RP004B.docx Prepared by: Beals and Thomas, Inc. 144 Turnpike Road Southborough, MA 01772 Prepared for: WinnDevelopment 1 Washington Mall, Suite 500 Boston, MA 02108 Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts Table of Contents i TABLE OF CONTENTS 1.0 INTRODUCTION .................................................................................................................. 1 2.0 PRE-DEVELOPMENT CONDITIONS .................................................................................... 2 2.1 SITE CONDITIONS ...................................................................................................................................... 2 2.1.1 Critical Areas ................................................................................................................................. 2 2.1.2 Total Maximum Daily Loads (TMDL) ........................................................................................... 2 2.2 SOIL DESCRIPTION .................................................................................................................................... 3 2.3 HYDROLOGIC ANALYSIS (NOT INCLUDED) .................................................................................................. 3 3.0 POST-DEVELOPMENT CONDITIONS .................................................................................. 4 3.1 DESIGN STRATEGY..................................................................................................................................... 4 3.2 HYDROLOGIC ANALYSIS............................................................................................................................. 4 3.3 STORMWATER MANAGEMENT CONTROLS SIZING ....................................................................................... 5 3.4 HYDRAULIC CALCULATIONS (NOT INCLUDED) ............................................................................................ 5 3.5 COMPLIANCE WITH DEP STORMWATER MANAGEMENT STANDARDS ........................................................... 5 3.6 DEP’S CHECKLIST FOR A STORMWATER REPORT (NOT INCLUDED) .............................................................. 9 LIST OF ATTACHMENTS ATTACHMENT 1: SOIL DATA (Not Included) ATTACHMENT 2: PRE-DEVELOPMENT HYDROLOGIC ANALYSIS (Not Included) ATTACHMENT 3: POST-DEVELOPMENT HYDROLOGIC ANALYSIS ATTACHMENT 4: HYDRAULIC CALCULATIONS (Not Included) ATTACHMENT 5: TSS REMOVAL, WATER QUALITY, AND RECHARGE CALCULATIONS ATTACHMENT 6: DRAFT SITE OWNER’S MANUAL (Not Included) ATTACHMENT 7: DRAFT STORMWATER POLLUTION PREVENTION PLAN (Not Included) Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts 1 1.0 INTRODUCTION The proposed project includes a stormwater management system designed to mitigate potential impacts the proposed project could have on the existing watershed. The proposed hydrology has been updated to indicate that the overland flow from the lots prior to development (loamed and seeded areas) will be directed toward two surface infiltration basins that will not overtop during a 25-year design storm. This will be an interim condition prior to development of the lots with the multifamily buildings and parking. In response to questions raised by the Barnstable DPW Engineering Department, we have updated the stormwater analysis to include catch basin (CB-5), drain manhole (DMH-1), and leaching basin (DW-1) within Old Colony Road. The referenced structures within Old Colony Road have been included in the stormwater analysis to show that the leaching basin will retain the volume of runoff from a 25-year design storm prior to overflowing to DMH-1. Stormwater controls have been proposed to control peak runoff rates, provide water quality, promote groundwater recharge and sediment removal. The proposed system has been designed to comply with:  The 2008 Massachusetts Department of Environmental Protection (DEP) Stormwater Management Handbook,  Town of Barnstable Subdivision Rules and Regulations (the Regulations)  Town of Barnstable Zoning Ordinance as amended through November 2022 (the Ordinance), which requires projects to infiltrate the 25-year storm on site. The pre- and post-development hydrologic conditions were modeled using HydroCADTM version 10.00 to demonstrate that post-development stormwater runoff rates and volumes will be less than or equal to the pre-development rates and volumes. The following tables summarize the peak runoff rates and volumes for the pre- and post-development conditions. Table 1: Pre- & Post-development Peak Runoff Rates, units are in cubic feet per second (cfs). Storm Event Design Point 1: Main Street Design Point 2: On-Site System Pre Post Pre Post 2-Year 0.16 0.15 3.80 0.00 10-Year 0.65 0.37 6.19 0.00 25-Year 1.11 0.56 8.03 0.00 100-Year 2.17 0.97 11.70 0.00 Table 2: Pre- & Post-development Runoff Volumes, units are in acre-feet. Storm Event Design Point 1: Main Street Design Point 2: On-Site System Pre Post Pre Post 2-Year 0.02 0.01 0.26 0.00 10-Year 0.05 0.03 0.44 0.00 25-Year 0.08 0.04 0.58 0.00 100-Year 0.15 0.07 0.87 0.00 Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts 2 2.0 PRE-DEVELOPMENT CONDITIONS (NOT INCLUDED) 2.1 Site Conditions The Property is currently developed and mainly covered by either building or pavement. It contains of a two-story commercial building that is currently unoccupied, a parking lot, and limited landscaped areas. The stormwater controls on site are currently in disrepair. Several catch basins and leaching pits were found to be clogged. Based upon field investigations it appears that several on-site leaching pits previous infiltrated runoff from the parking lot, building and driveways on Old Colony Road. In the event these leaching pits reached capacity, the stormwater would sheet towards Old Colony Road and the abutting property to the south. The portions of the site along Main Street and Old Colony Road sheet flow directly into the municipal system. Catch basins on site are currently daisy chained together and do not provide for water quality treatment. Field investigations found no evidence of water quality treatment units or other methods of stormwater treatment. The design points within the hydrologic analysis represent the flow that would reach the Main Street (Design Point 1) and the internal drainage system (Design Point 2). 2.1.1 Critical Areas Critical Areas as defined by Standard 6 of the 2008 MassDEP Stormwater Management Handbook are areas where high levels of stormwater treatment is required; typically the first inch of runoff is treated using specific best management practices (BMPs) and pre-treatment methods. Specific source control and pollution prevention measures are also required. The site does not contain, nor is it tributary to any Critical Areas. 2.1.2 Total Maximum Daily Loads (TMDL) A TMDL is the greatest amount of a pollutant that a waterbody can accept and still meet water quality standards for protecting public health and maintaining the designated beneficial uses of those waters for drinking, swimming, recreation, and fishing. A TMDL is implemented by specifying how much of that pollutant can come from point, nonpoint, and natural sources. MassDEP has issued a TMDL for the Cape Cod Watershed for Pathogens and further has issued a TMDL for Lewis Bay and Halls Creek for Total Nitrogen. Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts 3 2.2 Soil Description The Natural Resources Conservation Service (NRCS) lists the on-site soils as Urban land. Generally, this soil is located in areas of excavation and fill. A geotechnical study was performed by McPhail Associates. Soil textural analysis and sieve testing classified the soils on site sand. For the purposes of our analysis, we have assumed the soils to be NRCS hydrologic soil class A. 2.3 Hydrologic Analysis (Not Included) Sub-catchment areas were delineated based on existing runoff patterns and topographic information. This information is shown on the Pre-Development Conditions Hydrologic Areas Map included in Attachment 2. Summaries of each area with respect to Curve Number and Time of Concentration calculations can be found in the model results also in Attachment 2. Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts 4 3.0 POST-DEVELOPMENT CONDITIONS 3.1 Design Strategy During the design phase of the site layout, consideration was given to conserving environmentally sensitive features and minimizing impact on the existing hydrology. To achieve this, extensive grading was avoided and the site was designed to match the existing terrain where feasible. Minimizing earthwork helps to maintain the existing drainage patterns to the maximum extent practicable under post- development conditions. Through careful site planning the proposed impervious surfaces have been minimized, reducing the impact the project may have on the existing watershed. This minimization of impervious surfaces was achieved without compromising compliance to local bylaw requirements. A stormwater management system has been designed to infiltrate up to the 25-year storm in compliance with the local regulations. In addition, it will provide groundwater recharge and water quality treatment. Proprietary water quality units have been incorporated to ensure 44% total suspended solids are removed from roadway runoff prior to discharging to the infiltration systems. In addition to groundwater recharge and peak runoff mitigation, the recharge systems also provide nutrient removal. A stormwater management system has been designed to provide treatment for stormwater runoff associated with the proposed impervious surfaces on site. All stormwater BMPs were designed to treat a minimum of the first 1.0 inch of runoff generated by the on-site impervious areas. Proprietary stormwater treatment systems were designed to treat the runoff rate associated with the water quality volume in accordance with the requirements of the DEP Stormwater Handbook. Stormwater BMP sizing worksheets and water quality sizing calculations are included in Attachment 5 of this report. 3.2 Hydrologic Analysis The established design points used in the pre-development conditions analysis were used in the post-development analysis for direct comparison. The tributary areas and flow paths were modified to reflect post-development conditions. See Attachment 3 for the Post- Development Conditions Hydrologic Areas Map. Summaries of each area with respect to Curve Number and Time of Concentration calculations can be found in the model results in Attachment 3. Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts 5 3.3 Stormwater Management Controls Sizing Subsurface Infiltration Chambers The proposed stormwater infiltration system consists of StormTech MC-7200 chambers with a stone base. The whole system has been designed to handle up to the 100-year storm. The infiltration system was sized using the Static Method, as described in Chapter 3 of the Massachusetts Stormwater Handbook, using Rawl’s exfiltration rates of 2.41 inches per hour or 8.27 inches per hour based on the recommendations from the geotechnical engineer. The system has been designed to meet the required recharge volume, and will fully dewater within 72 hours. Interim Infiltration Basins The proposed interim infiltration basins have been designed to retain the 100-year storm from the contributing loamed and seeded lots prior to development of the lots. The system will fully dewater within 72 hours. Dry Well The proposed dry well has been designed to retain the 25-year storm from the tributary area within Old Colony Road prior to overflowing into the Old Colony drainage system. The dry well will fully dewater within 72 hours. 3.4 Hydraulic Calculations (Not Included) In compliance with Barnstable requirements, the proposed storm drain system was analyzed based on the 50-year storm event using the Rational Formula. A watershed map and detailed hydraulic analysis are provided in Attachment 4. 3.5 Compliance with DEP Stormwater Management Standards The proposed stormwater management system was designed in compliance with the ten (10) DEP Stormwater Management Standards. The following summary provides key information related to the proposed stormwater management system, its design elements, and mitigation measures for potential impacts. Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts 6 STANDARD 1: No new stormwater conveyance (e.g. outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. There are no wetlands or waters on or near the site; therefore, this standard does not apply. STANDARD 2: Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. The stormwater management design will control post-development peak discharge rates for the 2-, 10-, and 100-year, 24-hour storms so as to maintain pre-development peak discharge rates. Refer to Section 1.0 Introduction for a summary of the peak runoff rates. STANDARD 3: Loss of annual recharge to groundwater shall be eliminated or minimized through the use of environmentally sensitive site design, low impact development techniques, stormwater management practices and good operation and maintenance. At a minimum, the annual recharge from the post-development site shall approximate the annual recharge from pre- development conditions based on soil types. This Standard is met when the stormwater management system is designed to infiltrate the required recharge volume as determined in accordance with the Massachusetts Stormwater Handbook. The stormwater management system includes subsurface infiltration systems and open infiltration basins that will effectively recharge groundwater on-site. Infiltration BMPs were sized using the static method based on the required recharge volume for the post- development site. As a result, annual recharge from the post-development site will approximate the annual recharge from the site under pre-development conditions. See Attachment 5 for stormwater BMP design worksheets and Groundwater Recharge Calculation. STANDARD 4: Stormwater management systems shall be designed to remove 80% of the average annual post-construction load of Total Suspended Solids (TSS). The proposed project will meet the water quality requirements of Standard 4 using several on-site treatment trains that achieve 80% TSS removal. Refer to Attachment 5 for the TSS removal worksheets. Structural BMPs designed for water quality treatment, including the deep sump hooded catch basins, and proprietary water quality treatment systems, were sized to capture and treat the flow rate associated with the first 1.0-inch of runoff from proposed impervious surfaces. All proposed stormwater management BMPs will be operated and maintained to ensure continued water quality treatment of runoff. Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts 7 The Site Owner’s Manual complies with the Long-Term Pollution Prevention Plan (Standard 4) and the Long-Term Operation and Maintenance Plan (Standard 9) requirements of the 2008 Massachusetts Department of Environmental Protection (MassDEP) Stormwater Management Standards. The Manual outlines source control and pollution prevention measures and maintenance requirements of stormwater best management practices (BMPs) associated with the proposed development. STANDARD 5: For land uses with higher potential pollutant loads (LUHPPLs), source control and pollution prevention shall be implemented in accordance with the Massachusetts Stormwater Handbook to eliminate or reduce the discharge of stormwater runoff from such land uses to the maximum extent practicable. The Project is not associated with stormwater discharges from land uses with higher potential pollutant loads. STANDARD 6: Stormwater discharges to critical areas must utilize certain stormwater management BMPs approved for critical areas. Critical areas are Outstanding Resource Waters, shellfish beds, swimming beaches, coldwater fisheries and recharge areas for public water supplies. There are no stormwater discharges to critical areas associated with this project. STANDARD 7: Redevelopment of previously developed sites must meet the Stormwater Management Standards to the maximum extent practicable. However, if it is not practicable to meet all the Standards, new (retrofitted or expanded) stormwater management systems must be designed to improve existing conditions. The proposed project qualifies as a redevelopment project. However, it fully complies with all standards of the Stormwater Management Handbook. STANDARD 8: A plan to control construction-related impacts during erosion, sedimentation and other pollutant sources during construction and land disturbance activities (construction period erosion, sedimentation, and pollution prevention plan) shall be developed and implemented. A Stormwater Pollution Prevention Plan (SWPPP) has been developed to comply with Section 3 of the NPDES Construction General Permit for Stormwater Discharges; therefore, the requirements of Standard 8 are fulfilled. Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts 8 STANDARD 9: A Long-Term Operation and Maintenance (O&M) Plan shall be developed and implemented to ensure that stormwater management systems function as designed. The Site Owner’s Manual complies with the Long-Term Pollution Prevention Plan (Standard 4) and the Long-Term Operation and Maintenance Plan (Standard 9) requirements of the 2008 Massachusetts Department of Environmental Protection (MassDEP) Stormwater Management Standards. The Manual outlines source control and pollution prevention measures and maintenance requirements of the stormwater best management practices (BMPs) associated with the proposed development. STANDARD 10: All illicit discharges to the stormwater management system are prohibited. There will be no illicit discharges to the proposed stormwater management system associated with the proposed project. An Illicit Discharge Compliance Statement will be provided prior to the discharge of any stormwater to any post-construction BMPs. Definitive Subdivision - 307 Main Street Stormwater Management Report Hyannis, Massachusetts 9 3.6 DEP’s Checklist for a Stormwater Report (Not Included) Attachment 3 Post-Development Hydrologic Analysis Calculation Summary Definitive Subdivision - 307 Main Street Hyannis, Massachusetts Proposed Hydrology Calculation Summary Objective 1. To demonstrate that the post-development stormwater runoff rates and runoff volumes will be less than or equal to the existing runoff rates and runoff volumes. 2. To demonstrate that the project will retain the 25-year storm on site. Conclusions Table 1: Pre- & Post-development Peak Runoff Rate Comparison, units are in cubic feet per second (cfs). Storm Event Design Point 1: Main Street Design Point 2: On-Site System Pre Post Pre Post 2-Year 0.16 0.15 3.80 0.00 10-Year 0.65 0.37 6.19 0.00 25-Year 1.11 0.56 8.03 0.00 100-Year 2.17 0.97 11.70 0.00 Table 2: Pre- & Post-development Runoff Volume Comparison, units are in acre-feet. Storm Event Design Point 1: Main Street Design Point 2: On-Site System Pre Post Pre Post 2-Year 0.02 0.01 0.26 0.00 10-Year 0.05 0.03 0.44 0.00 25-Year 0.08 0.04 0.58 0.00 100-Year 0.15 0.07 0.87 0.00 Interim Infiltration Basins The proposed interim infiltration basins will retain the 100-year storm from the contributing loamed and seeded lots prior to development of the lots. Dry Well The proposed dry well will retain the 25-year storm from the tributary area within Old Colony Road prior to overflowing into the Old Colony drainage system. Calculation Methods 1. Runoff curve numbers (CN), time-of concentration (Tc), and runoff rates were calculated based on TR-55 methodology. 2. AutoCAD 2019 computer program was utilized for digitizing ground cover areas. 3. Peak runoff rates were computed using HydroCAD version 10.20. Calculation Summary Definitive Subdivision - 307 Main Street Hyannis, Massachusetts Assumptions 1. Ground cover types were determined using on-site visual observations and aerial imagery. 2. Hydrologic soil groups were based on United States Department of Agriculture, NRCS Soil Survey map information. Soils are classified as Hydrologic Soil Group A. 3. Stormwater runoff from off-site tributary areas was included in the calculation. 4. Due to the nature of the site, a minimum Tc of 6 minutes was chosen for all subcatchments. 5. The exfiltration rate is 8.27 in/hour or 2.41 in/hr based on recommendations from the geotechnical engineer. 6. Stone voids are 40% of the total volume. Sources of Data/ Equations 1. “Existing Conditions Hydrology Calculation Summary” prepared by Beals and Thomas, dated July 22, 2023 (344700CS001A.pdf). 2. NRCS Web Soil Survey Hydrologic Soil Group – Barnstable County, Massachusetts, downloaded from Web Soil Survey on 6/15/2023. 3. NRCC Rainfall data for Barnstable County. 4. TR-55 Urban Hydrology for Small Watersheds, SCS, 1986. 5. Massachusetts DEP Stormwater Management Handbook, February 2008. 6. “Foundation Engineering Report- 307 Main Street” prepared by McPhail Associates, LLC and dated August 22, 2023. The report includes infiltration rates. List of Attachments 1. Proposed Conditions Hydrology Map and HydroCAD Model Reports 2. Infiltration of the 25-Year Storm REV CALC. BY DATE CHECKED BY DATE APPROVED BY DATE 0 K. Pritchard 04/04/2024 P. Thompson 04/05/2024 P. Thompson 04/11/2024 1 K. Pritchard 05/24/2024 P. Thompson 05/24/2024 P. Thompson 05/28/2024 344700CS004B.docx Calculation Summary Definitive Subdivision - 307 Main Street Hyannis, Massachusetts Attachment 1 Proposed Conditions Hydrology Watershed Map(NO HATCH)MAIN STREETO L D C O L O N Y R O A D Definitive Subdivision - 307 Main StreetHyannis, MassachusettsB+T Drawing No. 344700P018B-001Date: 05/27/2024 Scale: 1" = 60'Proposed Conditions Hydrology Off-Site Interim Conditions PDA-1A PDA-1A PDA-2A PDA-2A PDA-2B PDA-2B PDA-2C1 PDA-2C1 PDA-2C2 PDA-2C2 PDA-3A PDA-3A (OFF-SITE) 1R Main Street 2R Old Colony Road 4R On-site Stormwater Management System 1P Subsurface Infiltration System-1 2P Subsurface Infiltration System-2 3P Inf Basin 1 4P Inf Basin 2 5P Dry Well-1 Routing Diagram for 344700HC003B-definitive Prepared by Beals & Thomas Inc, Printed 5/27/2024 HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Subcat Reach Pond Link Post-DevelopmentG:\Projdata\3447\Eng\ 344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 2HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Area Listing (all nodes) Area (acres) CN Description (subcatchment-numbers) 1.384 39 >75% Grass cover, Good, HSG A (PDA-1A, PDA-2A, PDA-2B, PDA-2C1, PDA-2C2, PDA-3A) 0.028 30 Brush, Good, HSG A (PDA-2C2, PDA-3A) 0.075 30 Meadow, non-grazed, HSG A (PDA-1A) 0.540 98 Paved parking, HSG A (PDA-1A, PDA-2A, PDA-2B, PDA-2C1, PDA-2C2, PDA-3A) 2.027 54 TOTAL AREA Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 2-Year Rainfall=3.32"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 3HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=7,363 sf 55.54% Impervious Runoff Depth>0.80"Subcatchment PDA-1A: PDA-1A Tc=6.0 min CN=68 Runoff=0.15 cfs 0.011 af Runoff Area=7,600 sf 72.51% Impervious Runoff Depth>1.63"Subcatchment PDA-2A: PDA-2A Tc=6.0 min CN=82 Runoff=0.35 cfs 0.024 af Runoff Area=6,490 sf 90.60% Impervious Runoff Depth>2.46"Subcatchment PDA-2B: PDA-2B Tc=6.0 min CN=92 Runoff=0.43 cfs 0.031 af Runoff Area=0.630 ac 8.33% Impervious Runoff Depth>0.04"Subcatchment PDA-2C1: PDA-2C1 Tc=6.0 min CN=44 Runoff=0.00 cfs 0.002 af Runoff Area=0.811 ac 6.73% Impervious Runoff Depth>0.03"Subcatchment PDA-2C2: PDA-2C2 Tc=6.0 min CN=43 Runoff=0.00 cfs 0.002 af Runoff Area=0.093 ac 82.77% Impervious Runoff Depth>2.10"Subcatchment PDA-3A: PDA-3A (OFF-SITE) Tc=6.0 min CN=88 Runoff=0.24 cfs 0.016 af Inflow=0.15 cfs 0.011 afReach 1R: Main Street Outflow=0.15 cfs 0.011 af Inflow=0.00 cfs 0.000 afReach 2R: Old Colony Road Outflow=0.00 cfs 0.000 af Inflow=0.00 cfs 0.000 afReach 4R: On-site Stormwater Management System Outflow=0.00 cfs 0.000 af Peak Elev=19.88' Storage=0.007 af Inflow=0.35 cfs 0.024 afPond 1P: Subsurface Infiltration System-1 Discarded=0.04 cfs 0.024 af Primary=0.00 cfs 0.000 af Outflow=0.04 cfs 0.024 af Peak Elev=24.54' Storage=0.007 af Inflow=0.43 cfs 0.031 afPond 2P: Subsurface Infiltration System-2 Discarded=0.08 cfs 0.031 af Primary=0.00 cfs 0.000 af Outflow=0.08 cfs 0.031 af Peak Elev=26.00' Storage=1 cf Inflow=0.00 cfs 0.002 afPond 3P: Inf Basin 1 Outflow=0.00 cfs 0.002 af Peak Elev=25.00' Storage=1 cf Inflow=0.00 cfs 0.002 afPond 4P: Inf Basin 2 Outflow=0.00 cfs 0.002 af Peak Elev=16.11' Storage=0.006 af Inflow=0.24 cfs 0.016 afPond 5P: Dry Well-1 Discarded=0.02 cfs 0.016 af Primary=0.00 cfs 0.000 af Outflow=0.02 cfs 0.016 af Total Runoff Area = 2.027 ac Runoff Volume = 0.086 af Average Runoff Depth = 0.51" 73.37% Pervious = 1.487 ac 26.63% Impervious = 0.540 ac Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 10-Year Rainfall=4.89"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 11HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=7,363 sf 55.54% Impervious Runoff Depth>1.80"Subcatchment PDA-1A: PDA-1A Tc=6.0 min CN=68 Runoff=0.37 cfs 0.025 af Runoff Area=7,600 sf 72.51% Impervious Runoff Depth>2.98"Subcatchment PDA-2A: PDA-2A Tc=6.0 min CN=82 Runoff=0.63 cfs 0.043 af Runoff Area=6,490 sf 90.60% Impervious Runoff Depth>3.98"Subcatchment PDA-2B: PDA-2B Tc=6.0 min CN=92 Runoff=0.67 cfs 0.049 af Runoff Area=0.630 ac 8.33% Impervious Runoff Depth>0.36"Subcatchment PDA-2C1: PDA-2C1 Tc=6.0 min CN=44 Runoff=0.08 cfs 0.019 af Runoff Area=0.811 ac 6.73% Impervious Runoff Depth>0.32"Subcatchment PDA-2C2: PDA-2C2 Tc=6.0 min CN=43 Runoff=0.07 cfs 0.022 af Runoff Area=0.093 ac 82.77% Impervious Runoff Depth>3.56"Subcatchment PDA-3A: PDA-3A (OFF-SITE) Tc=6.0 min CN=88 Runoff=0.39 cfs 0.028 af Inflow=0.37 cfs 0.025 afReach 1R: Main Street Outflow=0.37 cfs 0.025 af Inflow=0.00 cfs 0.000 afReach 2R: Old Colony Road Outflow=0.00 cfs 0.000 af Inflow=0.00 cfs 0.000 afReach 4R: On-site Stormwater Management System Outflow=0.00 cfs 0.000 af Peak Elev=20.60' Storage=0.018 af Inflow=0.63 cfs 0.043 afPond 1P: Subsurface Infiltration System-1 Discarded=0.04 cfs 0.043 af Primary=0.00 cfs 0.000 af Outflow=0.04 cfs 0.043 af Peak Elev=25.57' Storage=0.015 af Inflow=0.67 cfs 0.049 afPond 2P: Subsurface Infiltration System-2 Discarded=0.08 cfs 0.049 af Primary=0.00 cfs 0.000 af Outflow=0.08 cfs 0.049 af Peak Elev=26.01' Storage=18 cf Inflow=0.08 cfs 0.019 afPond 3P: Inf Basin 1 Outflow=0.07 cfs 0.019 af Peak Elev=25.01' Storage=27 cf Inflow=0.07 cfs 0.022 afPond 4P: Inf Basin 2 Outflow=0.06 cfs 0.022 af Peak Elev=16.77' Storage=0.012 af Inflow=0.39 cfs 0.028 afPond 5P: Dry Well-1 Discarded=0.02 cfs 0.028 af Primary=0.00 cfs 0.000 af Outflow=0.02 cfs 0.028 af Total Runoff Area = 2.027 ac Runoff Volume = 0.187 af Average Runoff Depth = 1.11" 73.37% Pervious = 1.487 ac 26.63% Impervious = 0.540 ac Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 25-Year Rainfall=6.10"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 19HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=7,363 sf 55.54% Impervious Runoff Depth>2.69"Subcatchment PDA-1A: PDA-1A Tc=6.0 min CN=68 Runoff=0.56 cfs 0.038 af Runoff Area=7,600 sf 72.51% Impervious Runoff Depth>4.07"Subcatchment PDA-2A: PDA-2A Tc=6.0 min CN=82 Runoff=0.85 cfs 0.059 af Runoff Area=6,490 sf 90.60% Impervious Runoff Depth>5.16"Subcatchment PDA-2B: PDA-2B Tc=6.0 min CN=92 Runoff=0.86 cfs 0.064 af Runoff Area=0.630 ac 8.33% Impervious Runoff Depth>0.77"Subcatchment PDA-2C1: PDA-2C1 Tc=6.0 min CN=44 Runoff=0.40 cfs 0.041 af Runoff Area=0.811 ac 6.73% Impervious Runoff Depth>0.71"Subcatchment PDA-2C2: PDA-2C2 Tc=6.0 min CN=43 Runoff=0.43 cfs 0.048 af Runoff Area=0.093 ac 82.77% Impervious Runoff Depth>4.72"Subcatchment PDA-3A: PDA-3A (OFF-SITE) Tc=6.0 min CN=88 Runoff=0.51 cfs 0.037 af Inflow=0.56 cfs 0.038 afReach 1R: Main Street Outflow=0.56 cfs 0.038 af Inflow=0.00 cfs 0.000 afReach 2R: Old Colony Road Outflow=0.00 cfs 0.000 af Inflow=0.00 cfs 0.000 afReach 4R: On-site Stormwater Management System Outflow=0.00 cfs 0.000 af Peak Elev=21.28' Storage=0.027 af Inflow=0.85 cfs 0.059 afPond 1P: Subsurface Infiltration System-1 Discarded=0.04 cfs 0.052 af Primary=0.00 cfs 0.000 af Outflow=0.04 cfs 0.052 af Peak Elev=26.55' Storage=0.021 af Inflow=0.86 cfs 0.064 afPond 2P: Subsurface Infiltration System-2 Discarded=0.08 cfs 0.064 af Primary=0.00 cfs 0.000 af Outflow=0.08 cfs 0.064 af Peak Elev=26.09' Storage=193 cf Inflow=0.40 cfs 0.041 afPond 3P: Inf Basin 1 Outflow=0.12 cfs 0.041 af Peak Elev=25.07' Storage=191 cf Inflow=0.43 cfs 0.048 afPond 4P: Inf Basin 2 Outflow=0.16 cfs 0.048 af Peak Elev=17.35' Storage=0.017 af Inflow=0.51 cfs 0.037 afPond 5P: Dry Well-1 Discarded=0.02 cfs 0.031 af Primary=0.00 cfs 0.000 af Outflow=0.02 cfs 0.031 af Total Runoff Area = 2.027 ac Runoff Volume = 0.287 af Average Runoff Depth = 1.70" 73.37% Pervious = 1.487 ac 26.63% Impervious = 0.540 ac Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 27HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=7,363 sf 55.54% Impervious Runoff Depth>4.70"Subcatchment PDA-1A: PDA-1A Tc=6.0 min CN=68 Runoff=0.97 cfs 0.066 af Runoff Area=7,600 sf 72.51% Impervious Runoff Depth>6.38"Subcatchment PDA-2A: PDA-2A Tc=6.0 min CN=82 Runoff=1.30 cfs 0.093 af Runoff Area=6,490 sf 90.60% Impervious Runoff Depth>7.58"Subcatchment PDA-2B: PDA-2B Tc=6.0 min CN=92 Runoff=1.24 cfs 0.094 af Runoff Area=0.630 ac 8.33% Impervious Runoff Depth>1.92"Subcatchment PDA-2C1: PDA-2C1 Tc=6.0 min CN=44 Runoff=1.35 cfs 0.101 af Runoff Area=0.811 ac 6.73% Impervious Runoff Depth>1.81"Subcatchment PDA-2C2: PDA-2C2 Tc=6.0 min CN=43 Runoff=1.60 cfs 0.122 af Runoff Area=0.093 ac 82.77% Impervious Runoff Depth>7.10"Subcatchment PDA-3A: PDA-3A (OFF-SITE) Tc=6.0 min CN=88 Runoff=0.75 cfs 0.055 af Inflow=0.97 cfs 0.066 afReach 1R: Main Street Outflow=0.97 cfs 0.066 af Inflow=0.00 cfs 0.000 afReach 2R: Old Colony Road Outflow=0.00 cfs 0.000 af Inflow=0.00 cfs 0.000 afReach 4R: On-site Stormwater Management System Outflow=0.00 cfs 0.000 af Peak Elev=22.97' Storage=0.050 af Inflow=1.30 cfs 0.093 afPond 1P: Subsurface Infiltration System-1 Discarded=0.04 cfs 0.057 af Primary=0.00 cfs 0.000 af Outflow=0.04 cfs 0.057 af Peak Elev=29.49' Storage=0.037 af Inflow=1.24 cfs 0.094 afPond 2P: Subsurface Infiltration System-2 Discarded=0.08 cfs 0.094 af Primary=0.00 cfs 0.000 af Outflow=0.08 cfs 0.094 af Peak Elev=26.55' Storage=1,350 cf Inflow=1.35 cfs 0.101 afPond 3P: Inf Basin 1 Outflow=0.15 cfs 0.101 af Peak Elev=25.52' Storage=1,598 cf Inflow=1.60 cfs 0.122 afPond 4P: Inf Basin 2 Outflow=0.19 cfs 0.122 af Peak Elev=18.67' Storage=0.030 af Inflow=0.75 cfs 0.055 afPond 5P: Dry Well-1 Discarded=0.02 cfs 0.034 af Primary=0.00 cfs 0.000 af Outflow=0.02 cfs 0.034 af Total Runoff Area = 2.027 ac Runoff Volume = 0.532 af Average Runoff Depth = 3.15" 73.37% Pervious = 1.487 ac 26.63% Impervious = 0.540 ac Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 28HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment PDA-1A: PDA-1A Runoff =0.97 cfs @ 12.13 hrs, Volume=0.066 af, Depth>4.70" Routed to Reach 1R : Main Street Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=8.55" Area (sf)CN Description 1 39 >75% Grass cover, Good, HSG A 3,273 30 Meadow, non-grazed, HSG A 4,089 98 Paved parking, HSG A 7,363 68 Weighted Average 3,274 44.46% Pervious Area 4,089 55.54% Impervious Area Tc Length Slope Velocity Capacity Description (min)(feet)(ft/ft)(ft/sec)(cfs) 6.0 Direct Entry, Summary for Subcatchment PDA-2A: PDA-2A Runoff =1.30 cfs @ 12.13 hrs, Volume=0.093 af, Depth>6.38" Routed to Pond 1P : Subsurface Infiltration System-1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=8.55" Area (sf)CN Description 2,089 39 >75% Grass cover, Good, HSG A 5,511 98 Paved parking, HSG A 7,600 82 Weighted Average 2,089 27.49% Pervious Area 5,511 72.51% Impervious Area Tc Length Slope Velocity Capacity Description (min)(feet)(ft/ft)(ft/sec)(cfs) 6.0 Direct Entry, Summary for Subcatchment PDA-2B: PDA-2B Runoff =1.24 cfs @ 12.13 hrs, Volume=0.094 af, Depth>7.58" Routed to Pond 2P : Subsurface Infiltration System-2 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=8.55" Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 29HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Area (sf)CN Description 610 39 >75% Grass cover, Good, HSG A 5,880 98 Paved parking, HSG A 6,490 92 Weighted Average 610 9.40% Pervious Area 5,880 90.60% Impervious Area Tc Length Slope Velocity Capacity Description (min)(feet)(ft/ft)(ft/sec)(cfs) 6.0 Direct Entry, Summary for Subcatchment PDA-2C1: PDA-2C1 Runoff =1.35 cfs @ 12.14 hrs, Volume=0.101 af, Depth>1.92" Routed to Pond 3P : Inf Basin 1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=8.55" Area (ac)CN Description 0.578 39 >75% Grass cover, Good, HSG A 0.053 98 Paved parking, HSG A 0.630 44 Weighted Average 0.578 91.67% Pervious Area 0.053 8.33% Impervious Area Tc Length Slope Velocity Capacity Description (min)(feet)(ft/ft)(ft/sec)(cfs) 6.0 Direct Entry, Summary for Subcatchment PDA-2C2: PDA-2C2 Runoff =1.60 cfs @ 12.14 hrs, Volume=0.122 af, Depth>1.81" Routed to Pond 4P : Inf Basin 2 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=8.55" Area (ac)CN Description 0.728 39 >75% Grass cover, Good, HSG A 0.028 30 Brush, Good, HSG A 0.055 98 Paved parking, HSG A 0.811 43 Weighted Average 0.756 93.27% Pervious Area 0.055 6.73% Impervious Area Tc Length Slope Velocity Capacity Description (min)(feet)(ft/ft)(ft/sec)(cfs) 6.0 Direct Entry, Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 30HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Summary for Subcatchment PDA-3A: PDA-3A (OFF-SITE) Runoff =0.75 cfs @ 12.13 hrs, Volume=0.055 af, Depth>7.10" Routed to Pond 5P : Dry Well-1 Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=8.55" Area (ac)CN Description 0.016 39 >75% Grass cover, Good, HSG A 0.000 30 Brush, Good, HSG A 0.077 98 Paved parking, HSG A 0.093 88 Weighted Average 0.016 17.23% Pervious Area 0.077 82.77% Impervious Area Tc Length Slope Velocity Capacity Description (min)(feet)(ft/ft)(ft/sec)(cfs) 6.0 Direct Entry, Summary for Reach 1R: Main Street [40] Hint: Not Described (Outflow=Inflow) Inflow Area =0.169 ac,55.54% Impervious, Inflow Depth > 4.70" for 100-Year event Inflow =0.97 cfs @ 12.13 hrs, Volume=0.066 af Outflow =0.97 cfs @ 12.13 hrs, Volume=0.066 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Summary for Reach 2R: Old Colony Road [40] Hint: Not Described (Outflow=Inflow) Inflow Area =0.093 ac,82.77% Impervious, Inflow Depth = 0.00" for 100-Year event Inflow =0.00 cfs @ 0.00 hrs, Volume=0.000 af Outflow =0.00 cfs @ 0.00 hrs, Volume=0.000 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Summary for Reach 4R: On-site Stormwater Management System [40] Hint: Not Described (Outflow=Inflow) Inflow Area =1.764 ac,20.89% Impervious, Inflow Depth = 0.00" for 100-Year event Inflow =0.00 cfs @ 0.00 hrs, Volume=0.000 af Outflow =0.00 cfs @ 0.00 hrs, Volume=0.000 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 31HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Summary for Pond 1P: Subsurface Infiltration System-1 Inflow Area =0.174 ac,72.51% Impervious, Inflow Depth > 6.38" for 100-Year event Inflow =1.30 cfs @ 12.13 hrs, Volume=0.093 af Outflow =0.04 cfs @ 10.35 hrs, Volume=0.057 af, Atten= 97%, Lag= 0.0 min Discarded =0.04 cfs @ 10.35 hrs, Volume=0.057 af Primary =0.00 cfs @ 0.00 hrs, Volume=0.000 af Routed to Reach 4R : On-site Stormwater Management System Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Peak Elev= 22.97' @ 15.12 hrs Surf.Area= 0.018 ac Storage= 0.050 af Plug-Flow detention time= 277.2 min calculated for 0.056 af (61% of inflow) Center-of-Mass det. time= 166.2 min ( 967.5 - 801.3 ) Volume Invert Avail.Storage Storage Description #1A 19.00'0.031 af 19.42'W x 40.42'L x 6.75'H Field A 0.122 af Overall - 0.044 af Embedded = 0.078 af x 40.0% Voids #2A 19.75'0.044 af ADS_StormTech MC-7200 +Cap x 10 Inside #1 Effective Size= 91.2"W x 60.0"H => 26.68 sf x 6.59'L = 175.9 cf Overall Size= 100.0"W x 60.0"H x 6.95'L with 0.36' Overlap 10 Chambers in 2 Rows Cap Storage= 39.5 cf x 2 x 2 rows = 158.0 cf 0.075 af Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Discarded 19.00'2.410 in/hr Exfiltration over Surface area #2 Primary 25.25'24.0" x 24.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads Discarded OutFlow Max=0.04 cfs @ 10.35 hrs HW=19.07' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.04 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=19.00' (Free Discharge) 2=Orifice/Grate ( Controls 0.00 cfs) Summary for Pond 2P: Subsurface Infiltration System-2 Inflow Area =0.149 ac,90.60% Impervious, Inflow Depth > 7.58" for 100-Year event Inflow =1.24 cfs @ 12.13 hrs, Volume=0.094 af Outflow =0.08 cfs @ 10.90 hrs, Volume=0.094 af, Atten= 94%, Lag= 0.0 min Discarded =0.08 cfs @ 10.90 hrs, Volume=0.094 af Primary =0.00 cfs @ 0.00 hrs, Volume=0.000 af Routed to Reach 4R : On-site Stormwater Management System Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Peak Elev= 29.49' @ 13.47 hrs Surf.Area= 0.010 ac Storage= 0.037 af Plug-Flow detention time= 154.3 min calculated for 0.094 af (100% of inflow) Center-of-Mass det. time= 153.9 min ( 923.8 - 769.8 ) Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 32HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Volume Invert Avail.Storage Storage Description #1A 23.25'0.017 af 10.33'W x 40.42'L x 6.75'H Field A 0.065 af Overall - 0.022 af Embedded = 0.043 af x 40.0% Voids #2A 24.00'0.022 af ADS_StormTech MC-7200 +Cap x 5 Inside #1 Effective Size= 91.2"W x 60.0"H => 26.68 sf x 6.59'L = 175.9 cf Overall Size= 100.0"W x 60.0"H x 6.95'L with 0.36' Overlap Cap Storage= 39.5 cf x 2 x 1 rows = 79.0 cf 0.039 af Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Discarded 23.25'8.270 in/hr Exfiltration over Surface area #2 Primary 29.75'24.0" x 24.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads Discarded OutFlow Max=0.08 cfs @ 10.90 hrs HW=23.32' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.08 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=23.25' (Free Discharge) 2=Orifice/Grate ( Controls 0.00 cfs) Summary for Pond 3P: Inf Basin 1 Inflow Area =0.630 ac,8.33% Impervious, Inflow Depth > 1.92" for 100-Year event Inflow =1.35 cfs @ 12.14 hrs, Volume=0.101 af Outflow =0.15 cfs @ 13.40 hrs, Volume=0.101 af, Atten= 89%, Lag= 75.5 min Discarded =0.15 cfs @ 13.40 hrs, Volume=0.101 af Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs / 2 Peak Elev= 26.55' @ 13.40 hrs Surf.Area= 2,745 sf Storage= 1,350 cf Plug-Flow detention time= 81.3 min calculated for 0.100 af (100% of inflow) Center-of-Mass det. time= 80.1 min ( 978.2 - 898.2 ) Volume Invert Avail.Storage Storage Description #1 26.00'4,455 cf Basin 1 (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet)(sq-ft)(cubic-feet)(cubic-feet) 26.00 2,132 0 0 27.00 3,239 2,686 2,686 27.50 3,840 1,770 4,455 Device Routing Invert Outlet Devices #1 Discarded 26.00'2.410 in/hr Exfiltration over Horizontal area Discarded OutFlow Max=0.15 cfs @ 13.40 hrs HW=26.55' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.15 cfs) Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/28/2024Prepared by Beals & Thomas Inc Page 33HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Summary for Pond 4P: Inf Basin 2 Inflow Area =0.811 ac,6.73% Impervious, Inflow Depth > 1.81" for 100-Year event Inflow =1.60 cfs @ 12.14 hrs, Volume=0.122 af Outflow =0.19 cfs @ 13.39 hrs, Volume=0.122 af, Atten= 88%, Lag= 74.9 min Discarded =0.19 cfs @ 13.39 hrs, Volume=0.122 af Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs / 2 Peak Elev= 25.52' @ 13.39 hrs Surf.Area= 3,397 sf Storage= 1,598 cf Plug-Flow detention time= 77.5 min calculated for 0.122 af (99% of inflow) Center-of-Mass det. time= 75.6 min ( 977.6 - 902.0 ) Volume Invert Avail.Storage Storage Description #1 25.00'11,419 cf Basin 2 (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet)(sq-ft)(cubic-feet)(cubic-feet) 25.00 2,715 0 0 26.00 4,019 3,367 3,367 27.00 5,611 4,815 8,182 27.50 7,337 3,237 11,419 Device Routing Invert Outlet Devices #1 Discarded 25.00'2.410 in/hr Exfiltration over Horizontal area Discarded OutFlow Max=0.19 cfs @ 13.39 hrs HW=25.52' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.19 cfs) Summary for Pond 5P: Dry Well-1 Inflow Area =0.093 ac,82.77% Impervious, Inflow Depth > 7.10" for 100-Year event Inflow =0.75 cfs @ 12.13 hrs, Volume=0.055 af Outflow =0.02 cfs @ 10.05 hrs, Volume=0.034 af, Atten= 97%, Lag= 0.0 min Discarded =0.02 cfs @ 10.05 hrs, Volume=0.034 af Primary =0.00 cfs @ 0.00 hrs, Volume=0.000 af Routed to Reach 2R : Old Colony Road Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Peak Elev= 18.67' @ 15.05 hrs Surf.Area= 0.010 ac Storage= 0.030 af Plug-Flow detention time= 270.2 min calculated for 0.034 af (61% of inflow) Center-of-Mass det. time= 158.2 min ( 942.0 - 783.9 ) Volume Invert Avail.Storage Storage Description #1A 15.50'0.000 af 32.00'W x 14.00'L x 5.67'H Field A 0.058 af Overall - 0.058 af Embedded = 0.000 af x 40.0% Voids #2A 15.50'0.047 af Concrete Galley 8x14x5.7 x 4 Inside #1 Inside= 84.0"W x 60.0"H => 39.20 sf x 13.00'L = 509.6 cf Outside= 96.0"W x 68.0"H => 45.36 sf x 14.00'L = 635.0 cf 4 Chambers in 4 Rows 0.047 af Total Available Storage Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/28/2024Prepared by Beals & Thomas Inc Page 34HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Discarded 15.50'2.410 in/hr Exfiltration over Surface area #2 Primary 20.00'12.0" Round Culvert L= 10.0' RCP, rounded edge headwall, Ke= 0.100 Inlet / Outlet Invert= 19.50' / 20.00' S= -0.0500 '/' Cc= 0.900 n= 0.011 Concrete pipe, straight & clean, Flow Area= 0.79 sf Discarded OutFlow Max=0.02 cfs @ 10.05 hrs HW=15.56' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.02 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=15.50' (Free Discharge) 2=Culvert ( Controls 0.00 cfs) Proposed Hydrology Calculation Summary Attachment 2 25-Year Storm Retention Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 25-Year Rainfall=6.10"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 19HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=7,363 sf 55.54% Impervious Runoff Depth>2.69"Subcatchment PDA-1A: PDA-1A Tc=6.0 min CN=68 Runoff=0.56 cfs 0.038 af Runoff Area=7,600 sf 72.51% Impervious Runoff Depth>4.07"Subcatchment PDA-2A: PDA-2A Tc=6.0 min CN=82 Runoff=0.85 cfs 0.059 af Runoff Area=6,490 sf 90.60% Impervious Runoff Depth>5.16"Subcatchment PDA-2B: PDA-2B Tc=6.0 min CN=92 Runoff=0.86 cfs 0.064 af Runoff Area=0.630 ac 8.33% Impervious Runoff Depth>0.77"Subcatchment PDA-2C1: PDA-2C1 Tc=6.0 min CN=44 Runoff=0.40 cfs 0.041 af Runoff Area=0.811 ac 6.73% Impervious Runoff Depth>0.71"Subcatchment PDA-2C2: PDA-2C2 Tc=6.0 min CN=43 Runoff=0.43 cfs 0.048 af Runoff Area=0.093 ac 82.77% Impervious Runoff Depth>4.72"Subcatchment PDA-3A: PDA-3A (OFF-SITE) Tc=6.0 min CN=88 Runoff=0.51 cfs 0.037 af Inflow=0.56 cfs 0.038 afReach 1R: Main Street Outflow=0.56 cfs 0.038 af Inflow=0.00 cfs 0.000 afReach 2R: Old Colony Road Outflow=0.00 cfs 0.000 af Inflow=0.00 cfs 0.000 afReach 4R: On-site Stormwater Management System Outflow=0.00 cfs 0.000 af Peak Elev=21.28' Storage=0.027 af Inflow=0.85 cfs 0.059 afPond 1P: Subsurface Infiltration System-1 Discarded=0.04 cfs 0.052 af Primary=0.00 cfs 0.000 af Outflow=0.04 cfs 0.052 af Peak Elev=26.55' Storage=0.021 af Inflow=0.86 cfs 0.064 afPond 2P: Subsurface Infiltration System-2 Discarded=0.08 cfs 0.064 af Primary=0.00 cfs 0.000 af Outflow=0.08 cfs 0.064 af Peak Elev=26.09' Storage=193 cf Inflow=0.40 cfs 0.041 afPond 3P: Inf Basin 1 Outflow=0.12 cfs 0.041 af Peak Elev=25.07' Storage=191 cf Inflow=0.43 cfs 0.048 afPond 4P: Inf Basin 2 Outflow=0.16 cfs 0.048 af Peak Elev=17.35' Storage=0.017 af Inflow=0.51 cfs 0.037 afPond 5P: Dry Well-1 Discarded=0.02 cfs 0.031 af Primary=0.00 cfs 0.000 af Outflow=0.02 cfs 0.031 af Total Runoff Area = 2.027 ac Runoff Volume = 0.287 af Average Runoff Depth = 1.70" 73.37% Pervious = 1.487 ac 26.63% Impervious = 0.540 ac Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 31HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Summary for Pond 1P: Subsurface Infiltration System-1 Inflow Area =0.174 ac,72.51% Impervious, Inflow Depth > 6.38" for 100-Year event Inflow =1.30 cfs @ 12.13 hrs, Volume=0.093 af Outflow =0.04 cfs @ 10.35 hrs, Volume=0.057 af, Atten= 97%, Lag= 0.0 min Discarded =0.04 cfs @ 10.35 hrs, Volume=0.057 af Primary =0.00 cfs @ 0.00 hrs, Volume=0.000 af Routed to Reach 4R : On-site Stormwater Management System Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Peak Elev= 22.97' @ 15.12 hrs Surf.Area= 0.018 ac Storage= 0.050 af Plug-Flow detention time= 277.2 min calculated for 0.056 af (61% of inflow) Center-of-Mass det. time= 166.2 min ( 967.5 - 801.3 ) Volume Invert Avail.Storage Storage Description #1A 19.00'0.031 af 19.42'W x 40.42'L x 6.75'H Field A 0.122 af Overall - 0.044 af Embedded = 0.078 af x 40.0% Voids #2A 19.75'0.044 af ADS_StormTech MC-7200 +Cap x 10 Inside #1 Effective Size= 91.2"W x 60.0"H => 26.68 sf x 6.59'L = 175.9 cf Overall Size= 100.0"W x 60.0"H x 6.95'L with 0.36' Overlap 10 Chambers in 2 Rows Cap Storage= 39.5 cf x 2 x 2 rows = 158.0 cf 0.075 af Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Discarded 19.00'2.410 in/hr Exfiltration over Surface area #2 Primary 25.25'24.0" x 24.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads Discarded OutFlow Max=0.04 cfs @ 10.35 hrs HW=19.07' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.04 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=19.00' (Free Discharge) 2=Orifice/Grate ( Controls 0.00 cfs) Summary for Pond 2P: Subsurface Infiltration System-2 Inflow Area =0.149 ac,90.60% Impervious, Inflow Depth > 7.58" for 100-Year event Inflow =1.24 cfs @ 12.13 hrs, Volume=0.094 af Outflow =0.08 cfs @ 10.90 hrs, Volume=0.094 af, Atten= 94%, Lag= 0.0 min Discarded =0.08 cfs @ 10.90 hrs, Volume=0.094 af Primary =0.00 cfs @ 0.00 hrs, Volume=0.000 af Routed to Reach 4R : On-site Stormwater Management System Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Peak Elev= 29.49' @ 13.47 hrs Surf.Area= 0.010 ac Storage= 0.037 af Plug-Flow detention time= 154.3 min calculated for 0.094 af (100% of inflow) Center-of-Mass det. time= 153.9 min ( 923.8 - 769.8 ) Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 32HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Volume Invert Avail.Storage Storage Description #1A 23.25'0.017 af 10.33'W x 40.42'L x 6.75'H Field A 0.065 af Overall - 0.022 af Embedded = 0.043 af x 40.0% Voids #2A 24.00'0.022 af ADS_StormTech MC-7200 +Cap x 5 Inside #1 Effective Size= 91.2"W x 60.0"H => 26.68 sf x 6.59'L = 175.9 cf Overall Size= 100.0"W x 60.0"H x 6.95'L with 0.36' Overlap Cap Storage= 39.5 cf x 2 x 1 rows = 79.0 cf 0.039 af Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Discarded 23.25'8.270 in/hr Exfiltration over Surface area #2 Primary 29.75'24.0" x 24.0" Horiz. Orifice/Grate C= 0.600 Limited to weir flow at low heads Discarded OutFlow Max=0.08 cfs @ 10.90 hrs HW=23.32' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.08 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=23.25' (Free Discharge) 2=Orifice/Grate ( Controls 0.00 cfs) Summary for Pond 3P: Inf Basin 1 Inflow Area =0.630 ac,8.33% Impervious, Inflow Depth > 1.92" for 100-Year event Inflow =1.35 cfs @ 12.14 hrs, Volume=0.101 af Outflow =0.15 cfs @ 13.40 hrs, Volume=0.101 af, Atten= 89%, Lag= 75.5 min Discarded =0.15 cfs @ 13.40 hrs, Volume=0.101 af Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs / 2 Peak Elev= 26.55' @ 13.40 hrs Surf.Area= 2,745 sf Storage= 1,350 cf Plug-Flow detention time= 81.3 min calculated for 0.100 af (100% of inflow) Center-of-Mass det. time= 80.1 min ( 978.2 - 898.2 ) Volume Invert Avail.Storage Storage Description #1 26.00'4,455 cf Basin 1 (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet)(sq-ft)(cubic-feet)(cubic-feet) 26.00 2,132 0 0 27.00 3,239 2,686 2,686 27.50 3,840 1,770 4,455 Device Routing Invert Outlet Devices #1 Discarded 26.00'2.410 in/hr Exfiltration over Horizontal area Discarded OutFlow Max=0.15 cfs @ 13.40 hrs HW=26.55' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.15 cfs) Post-DevelopmentG:\Projdata\3447\Eng\ NRCC 24-hr C 100-Year Rainfall=8.55"344700HC003B-definitive Printed 5/27/2024Prepared by Beals & Thomas Inc Page 33HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Summary for Pond 4P: Inf Basin 2 Inflow Area =0.811 ac,6.73% Impervious, Inflow Depth > 1.81" for 100-Year event Inflow =1.60 cfs @ 12.14 hrs, Volume=0.122 af Outflow =0.19 cfs @ 13.39 hrs, Volume=0.122 af, Atten= 88%, Lag= 74.9 min Discarded =0.19 cfs @ 13.39 hrs, Volume=0.122 af Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs / 2 Peak Elev= 25.52' @ 13.39 hrs Surf.Area= 3,397 sf Storage= 1,598 cf Plug-Flow detention time= 77.5 min calculated for 0.122 af (99% of inflow) Center-of-Mass det. time= 75.6 min ( 977.6 - 902.0 ) Volume Invert Avail.Storage Storage Description #1 25.00'11,419 cf Basin 2 (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet)(sq-ft)(cubic-feet)(cubic-feet) 25.00 2,715 0 0 26.00 4,019 3,367 3,367 27.00 5,611 4,815 8,182 27.50 7,337 3,237 11,419 Device Routing Invert Outlet Devices #1 Discarded 25.00'2.410 in/hr Exfiltration over Horizontal area Discarded OutFlow Max=0.19 cfs @ 13.39 hrs HW=25.52' (Free Discharge) 1=Exfiltration (Exfiltration Controls 0.19 cfs) Summary for Pond 5P: Dry Well-1 Inflow Area =0.093 ac,82.77% Impervious, Inflow Depth > 7.10" for 100-Year event Inflow =0.75 cfs @ 12.13 hrs, Volume=0.055 af Outflow =0.02 cfs @ 10.05 hrs, Volume=0.034 af, Atten= 97%, Lag= 0.0 min Discarded =0.02 cfs @ 10.05 hrs, Volume=0.034 af Primary =0.00 cfs @ 0.00 hrs, Volume=0.000 af Routed to Reach 2R : Old Colony Road Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Peak Elev= 18.67' @ 15.05 hrs Surf.Area= 0.010 ac Storage= 0.030 af Plug-Flow detention time= 270.2 min calculated for 0.034 af (61% of inflow) Center-of-Mass det. time= 158.2 min ( 942.0 - 783.9 ) Volume Invert Avail.Storage Storage Description #1A 15.50'0.000 af 32.00'W x 14.00'L x 5.67'H Field A 0.058 af Overall - 0.058 af Embedded = 0.000 af x 40.0% Voids #2A 15.50'0.047 af Concrete Galley 8x14x5.7 x 4 Inside #1 Inside= 84.0"W x 60.0"H => 39.20 sf x 13.00'L = 509.6 cf Outside= 96.0"W x 68.0"H => 45.36 sf x 14.00'L = 635.0 cf 4 Chambers in 4 Rows 0.047 af Total Available Storage G:\Projdata\3447\Eng\ NRCC 24-hr C 25-Year Rainfall=6.10"344700HC003B-definitive Printed 5/23/2024Prepared by Beals & Thomas Inc HydroCAD® 10.20-4b s/n 04493 © 2023 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond 6P: Dry Well-1 Elevation (feet) Surface (acres) Storage (acre-feet) 15.50 0.010 0.000 15.60 0.010 0.001 15.70 0.010 0.002 15.80 0.010 0.003 15.90 0.010 0.004 16.00 0.010 0.005 16.10 0.010 0.006 16.20 0.010 0.007 16.30 0.010 0.007 16.40 0.010 0.008 16.50 0.010 0.009 16.60 0.010 0.010 16.70 0.010 0.011 16.80 0.010 0.012 16.90 0.010 0.013 17.00 0.010 0.014 17.10 0.010 0.015 17.20 0.010 0.016 17.30 0.010 0.017 17.40 0.010 0.018 17.50 0.010 0.019 17.60 0.010 0.020 17.70 0.010 0.021 17.80 0.010 0.022 17.90 0.010 0.022 18.00 0.010 0.023 18.10 0.010 0.024 18.20 0.010 0.025 18.30 0.010 0.026 18.40 0.010 0.027 18.50 0.010 0.028 18.60 0.010 0.029 18.70 0.010 0.030 18.80 0.010 0.031 18.90 0.010 0.032 19.00 0.010 0.033 19.10 0.010 0.034 19.20 0.010 0.035 19.30 0.010 0.036 19.40 0.010 0.037 19.50 0.010 0.037 19.60 0.010 0.038 19.70 0.010 0.039 19.80 0.010 0.040 19.90 0.010 0.041 20.00 0.010 0.042 20.10 0.010 0.043 20.20 0.010 0.044 20.30 0.010 0.045 20.40 0.010 0.046 20.50 0.010 0.047 20.60 0.010 0.047 20.70 0.010 0.047 20.80 0.010 0.047 20.90 0.010 0.047 Elevation (feet) Surface (acres) Storage (acre-feet) 21.00 0.010 0.047 21.10 0.010 0.047 Attachment 5 TSS Removal, Water Quality Volume, and Recharge Calculations (Updated Drawdown Calculations Only) Rv = Storage Volume Below Outlet [Ac-ft] Subsurface Infiltration System-1 0.075 Ac-ft 2.410 in/hr 0.018 Acres 20.724 Hours Subsurface Infiltration System-2 0.039 Ac-ft 8.270 in/hr 0.010 Acres 5.904 Hours Infiltration Basin 1 0.102 Ac-ft (4,455 cf) 2.410 in/hr 0.049 Acres (2,132 sf) 10.405 Hours Infiltration Basin 2 0.262 Ac-ft (11,419 cf) 2.410 in/hr 0.062 Acres (2,715 sf) 20.942 Hours Dry Well 1 0.040 Ac-ft 2.410 in/hr 0.010 Acres 19.917 Hours Note: JOB NO. COMPUTED BY: CHECKED BY: JOB: DATE: DATE: K = Standard 3: Drawdown 3447.00 307 Main St - Hyannis KJP 05/27/24 Rv = Drawdown Time =where: Bottom Area= Bottom Area of Recharge System [Ac] K= Infiltration Rate [in/hr] Rv (K) (Bottom Area) Bottom Area = Drawdown Time =< 72 Hours, Design is in compliance with the standard. < 72 Hours, Design is in compliance with the standard. 1. The infiltration BMPs have been designed to fully drain within 72 hours, therefore the proposed stormwater management design is in compliance with Standard 3 . 2. Infiltration Rates based on geotechnical report prepared by McPhail Associates dated 08/22/2023. Rv = K = Bottom Area = Drawdown Time = Rv = K = Bottom Area = Drawdown Time =< 72 Hours, Design is in compliance with the standard. Rv = K = Bottom Area = Drawdown Time =< 72 Hours, Design is in compliance with the standard. Rv = K = Bottom Area = Drawdown Time =< 72 Hours, Design is in compliance with the standard. 344700SWM002B.xlsx PAT 05/28/2024