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site plan 101 pages

Also attached to this agenda item: 2025-05-01 WBP Croton Point Full Set ss 250326 1CrotonPoint PlanningBoardIssue Draft eNOI Croton Point MS4 Response Letter 05012025CoHPB

STORMWATER POLLUTION PREVENTION PLAN For 1 Croton Point Croton Point Ave. April 30, 2025 Applicant Information: Note: This report in conjunction with the project plans make up the complete Stormwater Pollution Prevention Plan. PAGE 1.0 INTRODUCTION ............................................................................................................... 1 1.1 Project Description .................................................................................................... 1 1.2 Existing Site Conditions ............................................................................................ 1 1.3 Proposed Site Conditions .......................................................................................... 1 2.0 STORMWATER MANAGEMENT ................................................................................... 2p 2.1 NYSDEC Runoff Reduction Volume, RRv ................................................................. 4 2.2 NYSDEC Water Quality Volume, WQv ...................................................................... 4 2.3 NYSDEC Stream Channel Protection Volume, CPv ................................................. 5 2.4 NYSDEC Overbank Flood Control, Qp, and Extreme Flood Control, Qf ................... 6 3.0 STORMWATER CONVEYANCE SYSTEM ...................................................................... 6 4.0 EROSION AND SEDIMENT CONTROL .......................................................................... 6 4.1 Temporary Erosion and Sediment Control Facilities................................................. 7 4.2 Permanent Erosion and Sediment Control Facilities ................................................ 7 5.0 IMPLEMENTATION, MAINTENANCE & GENERAL HOUSEKEEPING ......................... 7 5.1 Construction Phase ................................................................................................... 7 5.2 Long Term Maintenance Plan ................................................................................... 9 APPENDICES Appendix A NYSDEC Water Quality Volume (WQv) Calculation Worksheets Appendix B Pre-Development Computer Data Appendix C Post-Development Computer Data Appendix D Project and Owner Information Appendix E NYSDEC SPDES General Permit for Construction Activities Construction Site Log Book Appendix F Hydrodynamic Separator Sizing and Maintenance Information Appendix G Pipe Sizing Calculations Appendix H OPRHP/SHPO Determination Letter FIGURES Figure 1: Location Map Figure 2: Pre-Development Drainage Map Figure 3: Post-Development Drainage Map 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. 1.0 INTRODUCTION 1.1 Project Description The project consists of a proposed 100-unit, for sale affordable condominium development consisting of 46 one-bedroom and 54 two-bedroom homes in a to be constructed 5-story building with requisite parking and amenities (the “Development”) to be located on lands fronting on Croton Point Avenue consisting of (i) Tax Map Parcels 79.17-1-5 & 3 owned by the Village (“Lot A”); and (ii) Tax Map Parcel 79.17-1-3 owned by Croton Point Realty Inc (the “CPR Parcel”). Lot A is currently in use as a Village commuter parking lot. The CPR Parcel is improved with an office building which is proposed to be demolished for the Development. The proposed brick and metal panel building will be served by 100 parking spaces to be located in a below grade parking level and two outdoor parking areas, including five (5) Level 2 EV charging stations. Amenities within the building will include a community room, a fitness center, a co- working lounge, a bike storage room and a roof-top deck providing expansive scenic views overlooking Croton Point Bay and the Hudson River. Sustainable building design features will likely include full electrification, solar readiness, high efficiency HVAC equipment (cold climate air source heat pumps) and appliances (Energy Star Multifamily New Construction Program) and low-flow water fixtures. In total the property consist of 1.8 ± acres and is located in the LI (Light Industrial with a Transoriented Development Overlay) zoning district, the Village of Corton-on-Hudson Water District and the Ossining Sanitary Sewer District. 1.2 Existing Site Conditions The subject project is located on Croton Point Avenue across from Veterans Plaza in the Village of Croton-On-Hudson. As previously stated, the site currently exists as a commercial development with several buildings, parking areas, walkways, and other appurtenances. The stormwater runoff from the existing property generally drains from a high point in the center of the property north and south towards the existing drain inlets and their collection system, which discharge to the west and east respectively. The northern drain inlet flows west onto MTA property and the southern drain inlet flows east onto NYSDOT property. The two drain inlets discussed above have been designed as Design Points for the purpose of stormwater quantity analysis contained herein, and are shown on Figures 2 and 3. Design Point 1 represents the existing drainage structure at the corner of Croton Point Avenue and NYS Route 9 that flows east. Design Point 2 represents the drainage structure that is part of the existing collection system that discharges west towards the Metro North Railroad property. Onsite soils belong to the Hydrologic Group B. Pursuant to the National Resource Conservation Service Web Soil Survey, the soil designations of the onsite soils consist of Urban land (Uf) and Udorthents (Ub). The soil boundaries are shown on the enclosed pre- and post-development drainage figures, Figures 2 and 3 of this report. It is proposed to construct a 21,500 sf ± (footprint area) affordable condominium with associated parking and various site appurtenances. The new five-story building will contain one hundred apartments. There will be 46 one-bedroom apartments and 54 two-bedroom apartments. Amenity spaces will also be constructed which will be used by the residents of the building only. This project is a redevelopment project with an overall decrease in impervious area. The project results in a net decrease of 0.2 acres +/-. It is proposed to maintain the overall drainage boundaries to the maximum extent practicable and tie into the existing onsite collection system in the proposed condition. New drainage structures will capture the runoff from the redeveloped site and will discharge into the hydrodynamic separators for treatment of the new impervious areas. The intent is to capture and treat the stormwater runoff from the redeveloped area of the site and treat it in accordance with the NYSDEC standards for quality and quantity prior to discharging to the existing stormwater collection systems, such there is no impact to the surrounding stormwater design. Two hydrodynamic separators are proposed in total, one tributary to each design point. As shown in the following sections of this report, the stormwater quality and quantity for the proposed development have been treated in accordance with the requirements of the General Permit, GP-0-25-001. Additionally, an erosion and sediment control plan has been prepared in accordance with the New York State Standards and Specifications for Erosion and Sediment Control (Blue Book) to protect the existing waterbodies and drainage features during construction activities. Based on discussions with the owner, a Phase 1/Phase 2 study was completed for the site. Based on the study, there is no known contamination or other restrictions on the property that would prevent the normal discharge of the footings. The 2025 GCP defines dewatering as the act of draining rainwater and/or groundwater from building foundations, vaults, or excavations / trenches. As the footing drains are defined as dewatering operations and there is no knows contamination, it is confirmed the footing drains meet the 2025 GCP definition for Uncontaminated discharges from dewatering operations. 2.0 STORMWATER MANAGEMENT The proposed stormwater management system for the project has been designed to meet the requirements of the state stormwater ordinances and guidelines, including but not limited to those of the NYSDEC. As noted in Part III.A.2 of the General Permit GP-0-25-001, consideration of future physical risks due to climate change pursuant to Community Risk and Resiliency Act (CRRA), 6 NYCRR Part 490 shall be considered. First, the CRRA primarily focuses on areas subject to flooding and areas at risk of sea level rise. The proposed project is not in an area for flood risk due to sea level rise and there are no FEMA regulated Floodways or Floodplains on the subject property or within the surrounding vicinity. Additionally, there is no immediate downstream infrastructure such as dams or major road culvert crossings that are potentially impacted by the proposed project. There are no known flood issues that have occurred in or around the project site. See below the current rainfall data obtained from the Northeast Regional Climate Center (NRCC) and the Natural Resources Conservation Service (NRCS) utilized in this report. This rainfall data which is updated annually allows designers to account for the most recent climate data recorded and allows for site specific distribution curves to be utilized. Based on the foregoing, it is believed the requirements of Part III.A.2 of General Permit GP-0-25-001 are addressed through this project SWPPP. In accordance with the GP-0-25-001, Part III.B.2.b.iii., as the subject project SWPPP was submitted for review as part of the Site Plan application to the Village of Croton-on-Hudson Planning Board prior to the issuance of the GP-0-25-001 and was developed using the 2015 NYSDEC New York State Stormwater Management Design Manual (Design Manual), the subject project may continue to design the post- construction stormwater management practices in conformance with the performance criteria in the 2015 Design Manual. Since the subject project proposes the disturbance of more than one (1) acre, coverage under the New York State Department of Environmental Conservation (NYSDEC) SPDES General Permit No. GP-0-25-001 (General Permit) is required. Chapter 4 of the NYSSMDM specifies five design criteria that are Water Quality Volume (WQv), Runoff Reduction Volume (RRv), Stream Channel Protection Volume (CPv), Overbank Flood Control (Qp), and Extreme Storm Control (Qf). The first two of these requirements relates to treating water quality, while the later pertain to stormwater quantity (peak flow) attenuation. As noted in previous sections of this report, this project is a redevelopment project with an increase in impervious area. As such the RRv requirements and CPv requirements are not required. Per Chapter 9, the proposed hydrodynamic separators 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. have been designed as a flow through practice. As such, the flow through practices have been sized for the peak rate of runoff from 100% of the WQv design storm, as defined Chapter 4 to treat the WQv in accordance with the NYSSMDM. To meet the above referenced requirements, the following post construction stormwater management practices are proposed for the project: Proposed SMP ID NYSSMDM Ch. 9 Design Designation NYSDEC Uniform Stormwater Sizing Criteria Satisfied HDS 1.1 Hydrodynamic Separator (Alt. Practice) WQv HDS 2.1 Hydrodynamic Separator (Alt. Practice) WQv Sizing calculations for the hydrodynamic separators have been provided in Appendix A. Information regarding the sizing and maintenance of the proposed hydrodynamic separators can be in Appendix F. As noted above the hydrodynamic separators result in treatment of the entire site and will be sized to treat the WQv peak flow as required by Chapter 9. To address stormwater quantity requirements of the NYSDEC, the “HydroCAD” Stormwater Modeling System,” by HydroCAD Software Solutions LLC in Tamworth, New Hampshire, was used to model and assess the peak stormwater flows for the subject project. HydroCAD is a computer aided design program for modeling the hydrology and hydraulics of stormwater runoff. It is based primarily on hydrology techniques developed by the United States Department of Agriculture, Soil Conservation Service (USDA, SCS) TR-20 method combined with standard hydraulic calculations. For details on the input data for the subcatchments and design storms, please refer to Appendices B and C. The input requirements for the HydroCAD computer program are as follows: • Design storm rainfall in inches • CN (runoff curve number) values which are based on soil type and land use/ground cover • Tc (time of concentration) flow path information • Watershed Area in Acres Stormwater Basins • Surface area at appropriate elevations • Flood elevation • Outlet structure information The following is a general description of the input data used to calculate the pre- and post- development stormwater runoff values. For detailed information for each subcatchment and stormwater management practice, see Appendices B & C. The 1-year, 10-year, and 100-year 24-hour design storm were obtained from the New York State Stormwater Management Design Manual. The values provided are for 24-hour design storms. Table 2.0.1 – Precipitation Values for Corresponding Design Storms Design Storm 24-Hour Rainfall 1.1S WQv Storm 1.87” 2.1S WQv Storm 1.66” 1-Year 2.34” 10-Year 4.66” 25-Year 6.50” 8.82” The CN (runoff curve number) values utilized in this report were referenced from the USDA, SCS publication Urban Hydrology for Small Watersheds. The following is a summary of the various land uses/ground covers and their associated CN values utilized in this report. Table 2.0.2 – Project Ground Cover and Associated Curve Numbers (CN) 2.1 NYSDEC Runoff Reduction Volume, RRv The Runoff Reduction Volume (RRv) criterion is intended to replicate pre-development hydrology by maintaining preconstruction infiltration, peak flow runoff, discharge volume, as well as minimizing concentrated stormwater flow. As noted above, meeting the Runoff Reduction Volume (RRv) sizing criteria is not required for redevelopment projects with a reduction in overall impervious cover. 2.2 NYSDEC Water Quality Volume, WQv The stormwater management practice has been designed in accordance with the Water Quality Volume (WQv) Section (Chapter 4.2) of the NYSSMDM. As outlined in Chapter 4.2, the WQv is the runoff volume generated from the entire 90th percentile rain event. As previously stated, partitions of the proposed impervious surfaces will overlap existing impervious surfaces within the site area. Per Section 9.2.1.B.III of the NYSSMDM, 100% WQv is captured and treated, for a minimum of 75% of the disturbed redevelopment area. A calculation is provided below for the Total WQv required based on Section 9.2.1.B.III of the NYSSMDM and included in Appendix A: The water quality volume shall be WQv = (0.75) (P)(Rv)(A) Where, WQv = water quality volume (in acre-feet) P = 90% Rainfall Event Number Rv = 0.05 + 0.009(I), where I is percent impervious cover A = disturbed redeveloped area Total WQv Required = 5,097 cf (See Calculation in Appendix A) The proposed hydrodynamic separators (HDS 1.1 & HDS 2.1) have been designed as a flow through practice, per Chapter 9 of the NYSSMDM. As such, the flow through alternative practices have been sized for the peak rate of runoff from 100% of the WQv design storm, as defined Chapter 4 to treat the WQv in accordance with the NYSSMDM. In Appendix A of this report the calculation for the WQv to be treated. Table 2.2.1 below summarizes the WQv treatment and Required Elements for the proposed Hydrodyanmic Separators (HDS 1.1 & HDS 2.1). The hydrodynamic separators have been designed in accordance with the Chapter 9 of the Design Manual for an alternative practice. As shown on the project plans, a Hydro-Shield Advance Hydrodynamic Separator by Oldcastle are proposed. The Hydr-Shield Advance is an NJCAT verified proprietary practice. The table below summarizes the required and provided WQv treatment rates. See Appendix A and F for more sizing information. Subcatchment ID HDS ID 100% WQv* (C.F) 100%WQv Peak Flow (C.F.S) Separator Model Maximum Treatment Flow Rate (C.F.S.) Peak Flow (C.F.S.) 25-Year Peak Flow (C.F.S) 1.1S HDS 1.1 4,165 1.48 4-ft Hydro-Shield 1.49 CFS 7.4 CFS 5.06 CFS 2.1S HDS 2.1 2,586 0.88 4-ft Hydro-Shield 1.49 CFS 7.4 CFS 2.89 CFS * The total WQv required represents 75% of the WQv from onsite areas only. The 100% WQv from 1.1S & 2.1S if summed exceeds the total WQv required because it includes 100% of the volume not 75% and includes offsite areas tributary to the practice. Table 2.2.2 WQv Provided Summary Total WQv Required (C.F.) Total WQv Provided (C.F.) 5,097 6,751 It should be noted that the above tables illustrate the water quality volume requirements set forth in the NYSSWDM have been met for the Hydrodynamic Separators (HDS 1.1 & HDS 2.1). By meeting the Water Quality Volume requirements through employment of an alternative practice, the water quality objectives of the NYSDEC to treat the water quality volume will be met. 2.3 NYSDEC Stream Channel Protection Volume, CPv The Stream Channel Protection (CPv) criterion is intended to protect stream channels from erosion and is accomplished by the 24-hour extended detention of the center-of-mass of the one- year, 24-hour storm event. As per the NYSSWDM Chapter 9, if the post-construction 1-year 24 hour discharge rate and velocities are less than or equal to the pre-construction design rate, providing 24 hours detention of the 1 year storm to meet CPv criteria is not required. Table 2.3.1 below summarizes the peak flows discharging for the 1-Year 24-Hour design storm and demonstrates that the 1-Year 24-Hour post development rate is less than the predevelopment rate. Table 2.4.1– Pre and Post-Development Peak Flows at the Design Point 1-YEAR (Channel Protection Volume) Pre Post Design Point 1 3.0 2.6 Design Point 2 2.2 2.1 The data for the table above was taken from Appendix B & C of this SWPPP. As shown in the table above the peak flows discharging to the design point have beem mitigated for the 1-Year 24- Hour Storm. By providing a reduction in peak flows during the 1-Year, 24-hour storm, the NYSDEC requirements for Stream Channel Protection (Cpv) have been met. The Overbank Flood Control (Qp) requirement is intended to prevent an increase in the frequency and magnitude of out-of-bank flooding events generated by urban development. Overbank control requires storage to attenuate the post-development 10-year, 24-hour peak discharge to pre- development rates. The Extreme Flood Control (Qf) requirement is intended to prevent the increased risk of flood damage from large storm events, maintain the boundaries of the pre-development 100- year flood plain, and protect the physical integrity of stormwater management practices. Extreme flood control requires storage to attenuate the post-development 100-year, 24-hour peak discharge to pre-development rates. As shown in Table 2.4.1 attenuation for both the 10-year and 100-year 24- hour storms has been provided thus satisfying the Qp and Qf requirements. Table 2.4.1– Pre and Post-Development Peak Flows at the Design Point 24-HOUR DESIGN STORM PEAK FLOWS (c.f.s.) 10-YEAR (Overbank Flood Control) Pre Post Pre Post Design Point 1 5.2 5.0 8.6 8.4 Design Point 2 4.8 4.7 8.9 8.8 As shown in the above table the peak flows discharging to the design point in the proposed condition have been mitigated to below the existing condition levels, therefore the receiving downstream drainage systems will see a reduction in peak flows during the storm events shown above and as such satisfy the Overbank and Extreme Overbank Flood Control requirements. 3.0 STORMWATER CONVEYANCE SYSTEM The stormwater collection and conveyance systems for the project will consist of catch basins, drain inlets, yard drains, and HDPE pipe. The pipe conveyance system will be sized to collect and convey at minimum the 25-year, 1-hour design storm using the Rational Method. The Rational Method is a standard method used by engineers to develop flow rates for sizing collection systems. The Rational Method calculates flows based on a one-hour design storm. See Appendix G for Pipe Sizing Calculations 4.0 EROSION AND SEDIMENT CONTROL Erosion and sediment control should be accomplished by four basic principles: diversion of clean water, containment of sediment, treatment of dirty water, and stabilization of disturbed areas. Diversion of clean water should be accomplished with swales. This diverted water should be safely conveyed around the construction area as necessary and discharged downstream of the disturbed areas. Sediment should be contained with the use of silt fence at the toe of disturbed slopes and excavation of the temporary sediment 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. basin. Disturbed areas should be permanently stabilized within 14 days of final grading to limit the required length of time that the temporary facilities must be utilized. The owner will be responsible for the maintenance of the temporary erosion control facilities. 4.1 Temporary Erosion and Sediment Control Facilities Temporary erosion and sediment control facilities should be installed and maintained as required to reduce the impacts to off-site properties. The owner will be required to provide maintenance for the temporary erosion and sediment control facilities. In general, the following temporary methods and materials should be used to control erosion and sedimentation from the project site: A stabilized construction entrance should be installed at the entrance to the site. The design drawings will include details to guide the contractor in the construction of this entrance. The intent of the stabilized construction entrance is to prevent the “tracking” of soil from the site. Dust control should be accomplished with water sprinkling trucks if required. During dry periods, sprinkler trucks should wet all exposed earth surfaces as required to prevent the transport of air-borne particles to adjoining areas. Siltation barriers constructed of geosynthetic filter cloth should be installed at the toe of all disturbed slopes. The intent of these barriers is to contain silt and sediment at the source and inhibit its transport by stormwater runoff. The siltation barriers will also help reduce the rate of runoff by creating filters through which the stormwater must pass. Storm drain inlet protection in the form of stone drop inlet protection will be installed around all proposed inlets. The stone drop inlet protection will serve to filter stormwater runoff before it enters the collection system. Throughout construction the concrete drainage structures, associated piping and inlet protections shall be inspected weekly and after a rainfall event. These items shall be cleaned, repaired and/or replaced when needed. 4.2 Permanent Erosion and Sediment Control Facilities Permanent erosion and sediment control will be accomplished by diverting stormwater runoff from steep slopes, controlling/reducing stormwater runoff velocities and volumes, and vegetative and structural surface stabilization. All of the permanent facilities are relatively maintenance free and only require periodic inspections. The owner will provide maintenance for all the permanent erosion and sediment control facilities. Other than the buildings and paved surfaces, disturbed surfaces will be stabilized with vegetation. The vegetation will control stormwater runoff by preventing soil erosion, reducing runoff volume and velocities, and providing a filter medium. Permanent seeding should optimally be undertaken in the spring from March 21st through May 20th and in late summer from August 15th to October 15th. 5.0 IMPLEMENTATION, MAINTENANCE & GENERAL HOUSEKEEPING 5.1 Construction Phase Details associated with the implementation and maintenance of the proposed stormwater facilities and erosion control measures during construction are shown on the project drawings. A construction sequence has been provided to guide the contractor in the installation of the erosion control measures as well as the site plan features. The erosion control plan, includes associated details and notes to aid the contractor in implementing the plan. During construction, a Site Log Book, Appendix E, is required to be kept per NYSDEC SPDES General Permit GP-0-25-001. Erosion and sediment control inspections are required to be conducted as necessary under coverage of the permit (minimum once a week, two times a week should the overall disturbance exceed five acres) and an updated logbook and a copy of the SWPPP is required to be kept on site for the duration of the construction activities. The Construction Site Log Book is an appendix taken from the New York Standards and Specifications for Erosion and Sediment Control (Blue Book). In addition to the proposed erosion and sediment control facilities, the following good housekeeping best management practices shall be implemented to mitigate potential pollution during the construction phase of the project. The general contractor overseeing the day-to-day site operation shall be responsible for the good housekeeping best management practices included in the following general categories: • Material Handling and Waste Management • Establishment of Building Material Staging Areas • Establishment of Washout Areas • Proper Equipment Fueling and Maintenance Practices • Spill Prevention and Control Plan All construction waste materials shall be collected and removed from the site regularly by the general contractor. The general contractor shall supply waste barrels for proper disposal of waste materials. All personnel working on the site shall be instructed of the proper procedures for construction waste disposal. Although it is not anticipated any hazardous waste materials will be utilized during construction, any hazardous waste materials shall be disposed of in accordance with federal, state, and local regulations. No hazardous waste shall be disposed of on-site. Hazardous waste materials shall be stored in appropriate and clearly marked containers and segregated from the other non-waste materials. All hazardous waste shall be stored in structurally sound and sealed shipping containers located in the staging areas. Material safety data sheets, material inventory, and emergency contact numbers will be maintained in the office trailer. All personnel working on the site shall be instructed of the proper procedures for hazardous waste disposal. Temporary sanitary facilities (portable toilets) shall be provided on site during the entire length of construction. The sanitary facilities shall be located in an alternate area away from the construction activities on the site. The portable toilets shall be inspected weekly for evidence of leaking holding tanks. All recyclables, including wood pallets, cardboard boxes, and all other recyclable construction scraps shall be disposed of in a designated recycling barrel provided by the contractor and removed from the site regularly. All personnel working on the site shall be instructed of the proper procedures for construction waste recycling. All construction equipment and maintenance materials shall be stored in a designated staging area. Silt fence shall be installed down gradient of the construction staging area. Shipping containers shall be utilized to store hand tools, small parts, and other construction materials, not taken off site daily. Construction waste barrels, recycling barrels and if necessary hazardous waste containers shall be located within the limits of the construction staging area. Throughout the construction of the project, several types of vehicles and equipment will be used on- site. Fueling of the equipment shall occur within the limits of the construction staging area. Fuel will be delivered to the site as needed, by the general contractor, or a party chosen by the general contractor. Only minor vehicle equipment maintenance shall occur on-site, all major maintenance shall be performed off-site. All equipment fluids generated from minor maintenance activities shall be disposed of into designated drums and stored in accordance with the hazardous waste storage as previously discussed. Vehicles and equipment shall be inspected on each day of use. Any leak discovered shall be repaired immediately. All leaking equipment unable to be repaired shall be removed from the site. Ample supplies of 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. absorbent, spill-cleanup materials, and spill kits shall be located in the construction staging area. All spills shall be cleaned up immediately upon discovery. Spent absorbent materials and rags shall be hauled off-site immediately after the spill is cleaned for disposal at a local landfill. All personnel working on the site shall be instructed of the proper procedures for spill prevention and control. During the construction phase of the project the subsurface infiltration system shall be cordoned off with construction fence to prevent undue compaction of the surrounding soils. The infiltration areas shall not be allowed to receive runoff until the contributing area to the system is completely stabilized in accordance with the erosion and sediment control notes on the project drawings. Installation of the system after the contributing area is stable will help to prevent any sediment from entering the SMP. 5.2 Long Term Maintenance Plan Each spring the paved areas should be cleaned to remove the winter’s accumulation of traction sand. After this is completed, all drain inlets sumps and the stormwater basins should be cleaned. All pipes should be checked for debris and blockages and cleaned as required. During the cleaning process, the drain inlets, catch basins, and pipes should be inspected for structural integrity and overall condition; repairs and/or replacement will be made as required. The stormwater facilities for the subject project have been designed to minimize the required maintenance. This section discusses the minimum maintenance requirements to insure long-term performance of the stormwater facilities. Initially the stormwater facilities will require an increased maintenance and inspection schedule until all portions of the site are stable. Generally, the stormwater facilities consist of either collection and conveyance components or treatment components. The stormwater collection and conveyance system is composed of HDPE, drainage pipe and precast concrete drainage structures. The owner will assume the maintenance responsibilities for the drainage system. Minimal maintenance is typically required for these facilities. All pipes should be checked for debris and blockages and cleaned as required. All drain inlet sumps shall be cleaned to removed deposited sediment. During the cleaning process, the pipes should be inspected for structural integrity and overall condition; repairs and/or replacement should be made as required. Additionally, the hydrodynamic separators shall be checked for deposited sediment. Visual inspection of the bioretention filter shall take place after major storm events. Visual inspection of the hydrodynamic separator shall take place yearly. NYSDEC Water Quality Volume WQv Calculations Worksheet WQv Flow Calculation Worksheet Project: Date: 8/1/2024 The following calculation determines the water quality flow rate for the 90% Water Quality Event using the Small Storm Hydrology Method specified in Appendix B of the New York State Stormwater Management Design Manual. Total WQv Required P = WQv 24-hour Rainfall Amount = 1.5 in. = 69696 SF Ai= Impervious Area within Subcatchment Area = I = Ai/A = 81.3 % Rv = 0.05 + 0.009 (I%) = 0.78 WQv = Water Quality Volume = 5,097 CF 1.Water Quality Volume =
 = 0.75 ∗ ∗  ∗ Y:\Insite Forms\Design\Stormwater\WQv and WQv Peak Flow and Flow Splitter\WQv Vol and Peak Flow Calc.xls WQv Flow Calculation Worksheet Project: Date: 5/1/2025 The following calculation determines the water quality flow rate for the 90% Water Quality Event using the Small Storm Hydrology Method specified in Appendix B of the New York State Stormwater Management Design Manual. HDS ID: 1.1S P = WQv 24-hour Rainfall Amount = 1.5 in. = 39204 SF Ai= Impervious Area within Subcatchment Area = I = Ai/A = 88.9 % Rv = 0.05 + 0.009 (I%) = 0.85 WQv = Water Quality Volume = 4,165 CF The WQv Peak flow is determined using HydroCAD. However, the rainfall depth (P90) Value utilized is determined from the calculation below: P90 = Calculated rainfall value (in) CNw = Weighted Curve Number = S = Maximum basin retention (in) S= (1000/CNw) - 10 = 0.64 Q = runoff generator over contributing area [Q = WQv/A] = 1.27 = 1.86 in 1.Water Quality Volume = 2.Water Quality Peak Flow
 =  ∗ ∗ P90 = . (.   ).  Y:\Insite Forms\Design\Stormwater\WQv and WQv Peak Flow and Flow Splitter\WQv Vol and Peak Flow Calc.xls WQv Flow Calculation Worksheet Project: Date: 8/1/2024 The following calculation determines the water quality flow rate for the 90% Water Quality Event using the Small Storm Hydrology Method specified in Appendix B of the New York State Stormwater Management Design Manual. HDS ID: 2.1S P = WQv 24-hour Rainfall Amount = 1.5 in. = 21780 SF Ai= Impervious Area within Subcatchment Area = I = Ai/A = 100.0 % Rv = 0.05 + 0.009 (I%) = 0.95 WQv = Water Quality Volume = 2,586 CF The WQv Peak flow is determined using HydroCAD. However, the rainfall depth (P90) Value utilized is determined from the calculation below: P90 = Calculated rainfall value (in) = CNw = Weighted Curve Number = S = Maximum basin retention (in) S= (1000/CNw) - 10 = 0.2041 Q = runoff generator over contributing area [Q = WQv/A] = 1.4250 = 1.65 1.Water Quality Volume = 2.Water Quality Peak Flow
 =  ∗ ∗ P90 = .+(6.252+25).  Y:\Insite Forms\Design\Stormwater\WQv and WQv Peak Flow and Flow Splitter\WQv Vol and Peak Flow Calc.xls NY - Croton Point 24-hr S1 1-yr WQV 1.1 Rainfall=1.86" App A - WQvt - Croton Point Printed 5/1/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 1.1S: WQV Runoff = 1.48 cfs @ 12.04 hrs, Volume= 0.095 af, Depth= 1.27" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 1-yr WQV 1.1 Rainfall=1.86" CN Description * 0.800 Impervious 0.100 >75% Grass cover, Good, HSG B 0.900 Weighted Average 0.100 11.11% Pervious Area 0.800 88.89% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 6.0 Direct Entry, Subcatchment 1.1S: WQV Runoff Hydrograph Time (hours) WQV 1.1 Rainfall=1.86" Runoff Area=0.900 ac Runoff Volume=0.095 af Runoff Depth=1.27" Tc=6.0 min CN=94 1.48 cfs NY - Croton Point 24-hr S1 25-yr Rainfall=6.50" App A - WQvt - Croton Point Printed 5/1/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 1.1S: WQV Runoff = 5.06 cfs @ 12.04 hrs, Volume= 0.434 af, Depth= 5.79" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 25-yr Rainfall=6.50" CN Description * 0.800 Impervious 0.100 >75% Grass cover, Good, HSG B 0.900 Weighted Average 0.100 11.11% Pervious Area 0.800 88.89% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 6.0 Direct Entry, Subcatchment 1.1S: WQV Runoff Hydrograph Time (hours) NY - Croton Point 24-hr S1 25-yr Rainfall=6.50" Runoff Area=0.900 ac Runoff Volume=0.434 af Runoff Depth=5.79" Tc=6.0 min CN=94 5.06 cfs NY - Croton Point 24-hr S1 1-yr WQV 2.1 Rainfall=1.65" App A - WQvt - Croton Point Printed 4/30/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 2.1S: WQv Runoff = 0.88 cfs @ 12.04 hrs, Volume= 0.060 af, Depth= 1.43" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 1-yr WQV 2.1 Rainfall=1.65" CN Description * 0.500 Impervious 0.500 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 6.0 Direct Entry, Subcatchment 2.1S: WQv Runoff Hydrograph Time (hours) 0.95 0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 NY - Croton Point 24-hr S1 1-yr WQV 2.1 Rainfall=1.65" Runoff Area=0.500 ac Runoff Volume=0.060 af Runoff Depth=1.43" Tc=6.0 min CN=98 0.88 cfs NY - Croton Point 24-hr S1 25-yr Rainfall=6.50" App A - WQvt - Croton Point Printed 4/30/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 2.1S: WQv Runoff = 2.89 cfs @ 12.04 hrs, Volume= 0.261 af, Depth= 6.26" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 25-yr Rainfall=6.50" CN Description * 0.500 Impervious 0.500 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 6.0 Direct Entry, Subcatchment 2.1S: WQv Runoff Hydrograph Time (hours) NY - Croton Point 24-hr S1 25-yr Rainfall=6.50" Runoff Area=0.500 ac Runoff Volume=0.261 af Runoff Depth=6.26" Tc=6.0 min CN=98 2.89 cfs 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. PRE 1 PRE 2 Routing Diagram for App B - Pre Development - Croton Point Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C., Printed 7/31/2024 HydroCAD® 10.00-15 s/n 00891 © 2015 HydroCAD Software Solutions LLC Subcat Reach Pond Link NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" Printed 7/31/2024 Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C. Runoff = 3.0 cfs @ 12.17 hrs, Volume= 0.285 af, Depth= 2.14" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" CN Description 0.100 >75% Grass cover, Good, HSG B 1.450 Paved parking, HSG D 0.050 Woods, Good, HSG B 1.600 Weighted Average 0.150 9.38% Pervious Area 1.450 90.63% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 14.5 0.0500 0.11 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 1.6 0.0300 0.87 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 16.1 Total Subcatchment PRE 1: Runoff Hydrograph Time (hours) CN=94 3.0 cfs NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" Printed 7/31/2024 Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C. Runoff = 2.2 cfs @ 12.12 hrs, Volume= 0.178 af, Depth= 1.34" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" CN Description 0.100 >75% Grass cover, Good, HSG D 0.150 Woods, Good, HSG D 0.250 >75% Grass cover, Good, HSG B 0.200 Woods, Good, HSG B 0.900 Paved parking, HSG D 1.600 Weighted Average 0.700 43.75% Pervious Area 0.900 56.25% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 5.3 0.1000 0.13 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 3.8 0.0700 0.26 Sheet Flow, Grass: Short n= 0.150 P2= 3.37" 0.4 0.0500 1.57 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 1.5 0.0400 1.00 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 0.4 0.2100 3.21 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 0.5 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.0 0.2000 25.50 31.30 Pipe Channel, 15.0" Round Area= 1.2 sf Perim= 3.9' r= 0.31' n= 0.012 11.9 Total NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" Printed 7/31/2024 Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C. Runoff Hydrograph Time (hours) Runoff Volume=0.178 af Runoff Depth=1.34" Flow Length=385' Tc=11.9 min CN=84 2.2 cfs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" Printed 7/31/2024 Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C. Runoff = 5.2 cfs @ 12.17 hrs, Volume= 0.592 af, Depth= 4.44" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" CN Description 0.100 >75% Grass cover, Good, HSG B 1.450 Paved parking, HSG D 0.050 Woods, Good, HSG B 1.600 Weighted Average 0.150 9.38% Pervious Area 1.450 90.63% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 14.5 0.0500 0.11 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 1.6 0.0300 0.87 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 16.1 Total Subcatchment PRE 1: Runoff Hydrograph Time (hours) CN=94 5.2 cfs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" Printed 7/31/2024 Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C. Runoff = 4.8 cfs @ 12.12 hrs, Volume= 0.452 af, Depth= 3.39" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" CN Description 0.100 >75% Grass cover, Good, HSG D 0.150 Woods, Good, HSG D 0.250 >75% Grass cover, Good, HSG B 0.200 Woods, Good, HSG B 0.900 Paved parking, HSG D 1.600 Weighted Average 0.700 43.75% Pervious Area 0.900 56.25% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 5.3 0.1000 0.13 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 3.8 0.0700 0.26 Sheet Flow, Grass: Short n= 0.150 P2= 3.37" 0.4 0.0500 1.57 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 1.5 0.0400 1.00 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 0.4 0.2100 3.21 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 0.5 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.0 0.2000 25.50 31.30 Pipe Channel, 15.0" Round Area= 1.2 sf Perim= 3.9' r= 0.31' n= 0.012 11.9 Total NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" Printed 7/31/2024 Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C. Runoff Hydrograph Time (hours) Runoff Volume=0.452 af Runoff Depth=3.39" Flow Length=385' Tc=11.9 min CN=84 4.8 cfs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" Printed 7/31/2024 Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C. Runoff = 8.6 cfs @ 12.17 hrs, Volume= 1.143 af, Depth= 8.58" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" CN Description 0.100 >75% Grass cover, Good, HSG B 1.450 Paved parking, HSG D 0.050 Woods, Good, HSG B 1.600 Weighted Average 0.150 9.38% Pervious Area 1.450 90.63% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 14.5 0.0500 0.11 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 1.6 0.0300 0.87 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 16.1 Total Subcatchment PRE 1: Runoff Hydrograph Time (hours) CN=94 8.6 cfs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" Printed 7/31/2024 Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C. Runoff = 8.9 cfs @ 12.11 hrs, Volume= 0.980 af, Depth= 7.35" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" CN Description 0.100 >75% Grass cover, Good, HSG D 0.150 Woods, Good, HSG D 0.250 >75% Grass cover, Good, HSG B 0.200 Woods, Good, HSG B 0.900 Paved parking, HSG D 1.600 Weighted Average 0.700 43.75% Pervious Area 0.900 56.25% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 5.3 0.1000 0.13 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 3.8 0.0700 0.26 Sheet Flow, Grass: Short n= 0.150 P2= 3.37" 0.4 0.0500 1.57 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 1.5 0.0400 1.00 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 0.4 0.2100 3.21 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 0.5 0.0100 2.03 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.0 0.2000 25.50 31.30 Pipe Channel, 15.0" Round Area= 1.2 sf Perim= 3.9' r= 0.31' n= 0.012 11.9 Total NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" Printed 7/31/2024 Prepared by Insite Engineering, Surveying and Landscape Architecture, P.C. Runoff Hydrograph Time (hours) Runoff Volume=0.980 af Runoff Depth=7.35" Flow Length=385' Tc=11.9 min CN=84 8.9 cfs 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. 1.0S & 1.1S 2.0S & 2.1S DP 1 DESIGN POINT 1 DP 2 DESIGN POINT 2 Routing Diagram for App C - Post Development - Croton Point Prepared by {enter your company name here}, Printed 3/26/2025 HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Subcat Reach Pond Link NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 1.0S & 1.1S: Runoff = 2.6 cfs @ 12.17 hrs, Volume= 0.249 af, Depth= 1.87" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" CN Description 0.250 >75% Grass cover, Good, HSG B 0.050 Woods, Good, HSG B 1.300 Paved parking, HSG D 1.600 Weighted Average 0.300 18.75% Pervious Area 1.300 81.25% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 14.5 0.0500 0.11 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 1.6 0.0300 0.87 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 16.1 Total Subcatchment 1.0S & 1.1S: Runoff Hydrograph Time (hours) Runoff Volume=0.249 af Runoff Depth=1.87" CN=91 2.6 cfs NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 2.0S & 2.1S: Runoff = 2.1 cfs @ 12.12 hrs, Volume= 0.170 af, Depth= 1.27" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" CN Description 0.150 >75% Grass cover, Good, HSG D 0.100 Woods, Good, HSG D 0.300 >75% Grass cover, Good, HSG B 0.200 Woods, Good, HSG B 0.850 Paved parking, HSG D 1.600 Weighted Average 0.750 46.88% Pervious Area 0.850 53.13% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 5.3 0.1000 0.13 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 3.8 0.0700 0.26 Sheet Flow, Grass: Short n= 0.150 P2= 3.37" 0.4 0.0500 1.57 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 1.5 0.0400 1.00 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 0.4 0.2100 3.21 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 0.2 0.1000 2.21 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 0.2 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.1 0.0010 1.80 2.21 Pipe Channel, 15.0" Round Area= 1.2 sf Perim= 3.9' r= 0.31' n= 0.012 11.9 Total NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Subcatchment 2.0S & 2.1S: Runoff Hydrograph Time (hours) Runoff Volume=0.170 af Runoff Depth=1.27" Flow Length=374' Tc=11.9 min CN=83 2.1 cfs NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Reach DP 1: DESIGN POINT 1 Inflow Area = 1.600 ac, 81.25% Impervious, Inflow Depth = 1.87" for 1-yr event Inflow = 2.6 cfs @ 12.17 hrs, Volume= 0.249 af Outflow = 2.6 cfs @ 12.17 hrs, Volume= 0.249 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs Reach DP 1: DESIGN POINT 1 Inflow Outflow Hydrograph Time (hours) 2.6 cfs 2.6 cfs NY - Croton Point 24-hr S1 1-yr Rainfall=2.78" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Reach DP 2: DESIGN POINT 2 Inflow Area = 1.600 ac, 53.13% Impervious, Inflow Depth = 1.27" for 1-yr event Inflow = 2.1 cfs @ 12.12 hrs, Volume= 0.170 af Outflow = 2.1 cfs @ 12.12 hrs, Volume= 0.170 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs Reach DP 2: DESIGN POINT 2 Inflow Outflow Hydrograph Time (hours) 2.1 cfs 2.1 cfs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 1.0S & 1.1S: Runoff = 5.0 cfs @ 12.17 hrs, Volume= 0.548 af, Depth= 4.11" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" CN Description 0.250 >75% Grass cover, Good, HSG B 0.050 Woods, Good, HSG B 1.300 Paved parking, HSG D 1.600 Weighted Average 0.300 18.75% Pervious Area 1.300 81.25% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 14.5 0.0500 0.11 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 1.6 0.0300 0.87 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 16.1 Total Subcatchment 1.0S & 1.1S: Runoff Hydrograph Time (hours) Runoff Volume=0.548 af Runoff Depth=4.11" CN=91 5.0 cfs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 2.0S & 2.1S: Runoff = 4.7 cfs @ 12.12 hrs, Volume= 0.439 af, Depth= 3.29" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" CN Description 0.150 >75% Grass cover, Good, HSG D 0.100 Woods, Good, HSG D 0.300 >75% Grass cover, Good, HSG B 0.200 Woods, Good, HSG B 0.850 Paved parking, HSG D 1.600 Weighted Average 0.750 46.88% Pervious Area 0.850 53.13% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 5.3 0.1000 0.13 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 3.8 0.0700 0.26 Sheet Flow, Grass: Short n= 0.150 P2= 3.37" 0.4 0.0500 1.57 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 1.5 0.0400 1.00 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 0.4 0.2100 3.21 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 0.2 0.1000 2.21 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 0.2 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.1 0.0010 1.80 2.21 Pipe Channel, 15.0" Round Area= 1.2 sf Perim= 3.9' r= 0.31' n= 0.012 11.9 Total NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Subcatchment 2.0S & 2.1S: Runoff Hydrograph Time (hours) Runoff Volume=0.439 af Runoff Depth=3.29" Flow Length=374' Tc=11.9 min CN=83 4.7 cfs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Reach DP 1: DESIGN POINT 1 Inflow Area = 1.600 ac, 81.25% Impervious, Inflow Depth = 4.11" for 10-yr event Inflow = 5.0 cfs @ 12.17 hrs, Volume= 0.548 af Outflow = 5.0 cfs @ 12.17 hrs, Volume= 0.548 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs Reach DP 1: DESIGN POINT 1 Inflow Outflow Hydrograph Time (hours) 5.0 cfs 5.0 cfs NY - Croton Point 24-hr S1 10-yr Rainfall=5.13" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Reach DP 2: DESIGN POINT 2 Inflow Area = 1.600 ac, 53.13% Impervious, Inflow Depth = 3.29" for 10-yr event Inflow = 4.7 cfs @ 12.12 hrs, Volume= 0.439 af Outflow = 4.7 cfs @ 12.12 hrs, Volume= 0.439 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs Reach DP 2: DESIGN POINT 2 Inflow Outflow Hydrograph Time (hours) 4.7 cfs 4.7 cfs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 1.0S & 1.1S: Runoff = 8.4 cfs @ 12.17 hrs, Volume= 1.095 af, Depth= 8.21" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" CN Description 0.250 >75% Grass cover, Good, HSG B 0.050 Woods, Good, HSG B 1.300 Paved parking, HSG D 1.600 Weighted Average 0.300 18.75% Pervious Area 1.300 81.25% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 14.5 0.0500 0.11 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 1.6 0.0300 0.87 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 16.1 Total Subcatchment 1.0S & 1.1S: Runoff Hydrograph Time (hours) Runoff Volume=1.095 af Runoff Depth=8.21" CN=91 8.4 cfs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Subcatchment 2.0S & 2.1S: Runoff = 8.8 cfs @ 12.11 hrs, Volume= 0.963 af, Depth= 7.23" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" CN Description 0.150 >75% Grass cover, Good, HSG D 0.100 Woods, Good, HSG D 0.300 >75% Grass cover, Good, HSG B 0.200 Woods, Good, HSG B 0.850 Paved parking, HSG D 1.600 Weighted Average 0.750 46.88% Pervious Area 0.850 53.13% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (cfs) 5.3 0.1000 0.13 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.37" 3.8 0.0700 0.26 Sheet Flow, Grass: Short n= 0.150 P2= 3.37" 0.4 0.0500 1.57 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 1.5 0.0400 1.00 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 0.4 0.2100 3.21 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 0.2 0.1000 2.21 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 0.2 0.0150 2.49 Shallow Concentrated Flow, Paved Kv= 20.3 fps 0.1 0.0010 1.80 2.21 Pipe Channel, 15.0" Round Area= 1.2 sf Perim= 3.9' r= 0.31' n= 0.012 11.9 Total NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Subcatchment 2.0S & 2.1S: Runoff Hydrograph Time (hours) Runoff Volume=0.963 af Runoff Depth=7.23" Flow Length=374' Tc=11.9 min CN=83 8.8 cfs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Reach DP 1: DESIGN POINT 1 Inflow Area = 1.600 ac, 81.25% Impervious, Inflow Depth = 8.21" for 100-yr event Inflow = 8.4 cfs @ 12.17 hrs, Volume= 1.095 af Outflow = 8.4 cfs @ 12.17 hrs, Volume= 1.095 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs Reach DP 1: DESIGN POINT 1 Inflow Outflow Hydrograph Time (hours) 8.4 cfs 8.4 cfs NY - Croton Point 24-hr S1 100-yr Rainfall=9.30" Printed 3/26/2025 Prepared by {enter your company name here} HydroCAD® 10.00-15 s/n 02171 © 2015 HydroCAD Software Solutions LLC Summary for Reach DP 2: DESIGN POINT 2 Inflow Area = 1.600 ac, 53.13% Impervious, Inflow Depth = 7.23" for 100-yr event Inflow = 8.8 cfs @ 12.11 hrs, Volume= 0.963 af Outflow = 8.8 cfs @ 12.11 hrs, Volume= 0.963 af, Atten= 0%, Lag= 0.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs Reach DP 2: DESIGN POINT 2 Inflow Outflow Hydrograph Time (hours) 8.8 cfs 8.8 cfs 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. Party Responsible for Implementation of the Stormwater Pollution Prevention Plan: Qualified Professional Responsible for Inspection of the Stormwater Pollution Prevention Plan: Inspector to be determined at time of construction 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. NYSDEC SPDES General Permit for Construction Activities Construction Site Log Book November 2016 Page F.1 New York State Standards and Specifications For Erosion and Sediment Control STATE POLLUTANT DISCHARGE ELIMINATION SYSTEM FOR CONSTRUCTION ACTIVITIES SAMPLE CONSTRUCTION SITE LOG BOOK Table of Contents I. Pre-Construction Meeting Documents a. Preamble to Site Assessment and Inspections b. Pre-Construction Site Assessment Checklist II. Construction Duration Inspections a. Directions b. Modification to the SWPPP APPENDIX F CONSTRUCTION SITE INSPECTION AND MAINTENANCE LOG BOOK November 2016 Page F.2 New York State Standards and Specifications For Erosion and Sediment Control I. The Following Information To Be Read By All Person’s Involved in The Construction of Stormwater Re- lated Activities: The Operator agrees to have a qualified inspector1 conduct an assessment of the site prior to the commence- ment of construction2 and certify in this inspection report that the appropriate erosion and sediment controls described in the SWPPP have been adequately installed or implemented to ensure overall preparedness of the site for the commencement of construction. Prior to the commencement of construction, the Operator shall certify in this site logbook that the SWPPP has been prepared in accordance with the State’s standards and meets all Federal, State and local erosion and sediment control requirements. A preconstruction meeting should be held to review all of the SWPPP requirements with construction personnel. When construction starts, site inspections shall be conducted by the qualified inspector at least every 7 cal- endar days. The Operator shall maintain a record of all inspection reports in this site logbook. The site log- book shall be maintained on site and be made available to the permitting authorities upon request. Prior to filing the Notice of Termination or the end of permit term, the Operator shall have a qualified in- spector perform a final site inspection. The qualified inspector shall certify that the site has undergone final stabilization3 using either vegetative or structural stabilization methods and that all temporary erosion and sediment controls (such as silt fencing) not needed for long-term erosion control have been removed. In addition, the Operator must identify and certify that all permanent structures described in the SWPPP have been constructed and provide the owner(s) with an operation and maintenance plan that ensures the struc- ture(s) continuously functions as designed. 1 Refer to “Qualified Inspector” inspection requirements in the current SPDES General Permit for Stormwater Discharges from Construction Activity for complete list of inspection requirements. 2 “Commencement of construction” means the initial removal of vegetation and disturbance of soils associated with clearing, grading or excavating activities or other construction activities. 3 “Final stabilization” means that all soil-disturbing activities at the site have been completed and a uniform, perennial vegetative cover with a density of eighty (80) percent has been established or equivalent stabilization measures (such as the use of mulches or geotextiles) have been employed on all unpaved areas and areas not covered by permanent struc- tures. 1. Notice of Intent, SWPPP, and Contractors Certification: [ ] [ ] [ ] Has a Notice of Intent been filed with the NYS Department of Conservation? [ ] [ ] [ ] Is the Plan current? What is the latest revision date?______________ [ ] [ ] [ ] Is a copy of the NOI (with brief description) onsite? Where?______________ [ ] [ ] [ ] Have all contractors involved with stormwater related activities signed a contractor’s certification? [ ] [ ] [ ] Are construction limits clearly flagged or fenced? [ ] [ ] [ ] Important trees and associated rooting zones, on-site septic system absorption fields, existing vegetated areas suitable for filter strips, especially in perimeter areas, have been flagged for protection. [ ] [ ] [ ] Creek crossings installed prior to land-disturbing activity, including clearing and blasting. [ ] [ ] [ ] Clean stormwater runoff has been diverted from areas to be disturbed. [ ] [ ] [ ] Bodies of water located either on site or in the vicinity of the site have been identified and protected. [ ] [ ] [ ] Appropriate practices to protect on-site or downstream surface water are installed. [ ] [ ] [ ] Are clearing and grading operations divided into areas <5 acres? [ ] [ ] [ ] A temporary construction entrance to capture mud and debris from construction vehicles before they enter the public highway has been installed. [ ] [ ] [ ] Other access areas (entrances, construction routes, equipment parking areas) are stabilized immediately as work takes place with gravel or other cover. [ ] [ ] [ ] Sediment tracked onto public streets is removed or cleaned on a regular basis. [ ] [ ] [ ] Silt fence material and installation comply with the standard drawing and specifications. [ ] [ ] [ ] Silt fences are installed at appropriate spacing intervals [ ] [ ] [ ] Sediment/detention basin was installed as first land disturbing activity. [ ] [ ] [ ] Sediment traps and barriers are installed. 6. Pollution Prevention for Waste and Hazardous Materials Yes No NA [ ] [ ] [ ] The Operator or designated representative has been assigned to implement the spill prevention avoidance and response plan. [ ] [ ] [ ] The plan is contained in the SWPPP on page ______ [ ] [ ] [ ] Appropriate materials to control spills are onsite. Where? __________________ November 2016 Page F.4 New York State Standards and Specifications For Erosion and Sediment Control II. CONSTRUCTION DURATION INSPECTIONS a. Directions: Inspection Forms will be filled out during the entire construction phase of the project. 1) On a site map, indicate the extent of all disturbed site areas and drainage pathways. Indicate site areas that are expected to undergo initial disturbance or significant site work within the next 14-day period; 2) Indicate on a site map all areas of the site that have undergone temporary or permanent stabilization; 3) Indicate all disturbed site areas that have not undergone active site work during the previous 14-day period; 4) Inspect all sediment control practices and record the approximate degree of sediment accumulation as a percentage of sediment storage volume (for example, 10 percent, 20 percent, 50 percent); 5) Inspect all erosion and sediment control practices and record all maintenance requirements such as verifying the integrity of barrier or diversion systems (earthen berms or silt fencing) and containment systems (sediment basins and sediment traps). Identify any evidence of rill or gully erosion occurring on slopes and any loss of stabilizing vegetation or seeding/mulching. Document any excessive deposition of sediment or ponding water along barrier or diversion systems. Record the depth of sediment within containment structures, any erosion near outlet and overflow structures, and verify the ability of rock filters around perforated riser pipes to pass water; and 6) Immediately report to the Operator any deficiencies that are identified with the implementation of the SWPPP. The above signed acknowledges that, to the best of his/her knowledge, all information provided on the forms is accurate and complete. [ ] [ ] [ ] Is there an increase in turbidity causing a substantial visible contrast to natural conditions at the outfalls? [ ] [ ] [ ] Is there residue from oil and floating substances, visible oil film, or globules or grease at the outfalls? [ ] [ ] [ ] All disturbance is within the limits of the approved plans. [ ] [ ] [ ] Have receiving lake/bay, stream, and/or wetland been impacted by silt from project? [ ] [ ] [ ] Is construction site litter, debris and spoils appropriately managed? [ ] [ ] [ ] Are facilities and equipment necessary for implementation of erosion and sediment control in working order and/or properly maintained? [ ] [ ] [ ] Is construction impacting the adjacent property? [ ] [ ] [ ] Is dust adequately controlled? [ ] [ ] [ ] Maximum diameter pipes necessary to span creek without dredging are installed. [ ] [ ] [ ] Installed non-woven geotextile fabric beneath approaches. [ ] [ ] [ ] Is fill composed of aggregate (no earth or soil)? [ ] [ ] [ ] Rock on approaches is clean enough to remove mud from vehicles & prevent sediment from entering stream during high flow. [ ] [ ] [ ] Stone is clean enough to effectively remove mud from vehicles. [ ] [ ] [ ] Installed per standards and specifications? [ ] [ ] [ ] Does all traffic use the stabilized entrance to enter and leave site? [ ] [ ] [ ] Is adequate drainage provided to prevent ponding at entrance? [ ] [ ] [ ] Upstream and downstream berms (sandbags, inflatable dams, etc.) are installed per plan. [ ] [ ] [ ] Clean water from upstream pool is being pumped to the downstream pool. [ ] [ ] [ ] Sediment laden water from work area is being discharged to a silt-trapping device. [ ] [ ] [ ] Constructed upstream berm with one-foot minimum freeboard. [ ] [ ] [ ] Installed per plan. [ ] [ ] [ ] Constructed on undisturbed soil, not on fill, receiving only clear, non-sediment laden flow. [ ] [ ] [ ] Flow sheets out of level spreader without erosion on downstream edge. [ ] [ ] [ ] Installed per plan with minimum side slopes 2H:1V or flatter. [ ] [ ] [ ] Stabilized by geotextile fabric, seed, or mulch with no erosion occurring. [ ] [ ] [ ] Sediment-laden runoff directed to sediment trapping structure 4. Stone Check Dam Yes No NA [ ] [ ] [ ] Is channel stable? (flow is not eroding soil underneath or around the structure). [ ] [ ] [ ] Check is in good condition (rocks in place and no permanent pools behind the structure). [ ] [ ] [ ] Has accumulated sediment been removed?. [ ] [ ] [ ] Installed per plan. [ ] [ ] [ ] Installed concurrently with pipe installation. [ ] [ ] [ ] Stockpiles are stabilized with vegetation and/or mulch. [ ] [ ] [ ] Sediment control is installed at the toe of the slope. [ ] [ ] [ ] Temporary seedings and mulch have been applied to idle areas. [ ] [ ] [ ] 4 inches minimum of topsoil has been applied under permanent seedings Sediment Control Practices 1. Silt Fence and Linear Barriers Yes No NA [ ] [ ] [ ] Installed on Contour, 10 feet from toe of slope (not across conveyance channels). [ ] [ ] [ ] Joints constructed by wrapping the two ends together for continuous support. [ ] [ ] [ ] Fabric buried 6 inches minimum. [ ] [ ] [ ] Posts are stable, fabric is tight and without rips or frayed areas. 2. Storm Drain Inlet Protection (Use for Stone & Block; Filter Fabric; Curb; or, Excavated; Filter Sock or Manufactured practices) [ ] [ ] [ ] Installed concrete blocks lengthwise so open ends face outward, not upward. [ ] [ ] [ ] Placed wire screen between No. 3 crushed stone and concrete blocks. [ ] [ ] [ ] Drainage area is 1acre or less. [ ] [ ] [ ] Excavated area is 900 cubic feet. [ ] [ ] [ ] Excavated side slopes should be 2:1. [ ] [ ] [ ] 2” x 4” frame is constructed and structurally sound. [ ] [ ] [ ] Posts 3-foot maximum spacing between posts. [ ] [ ] [ ] Fabric is embedded 1 to 1.5 feet below ground and secured to frame/posts with staples at max 8- inch spacing. [ ] [ ] [ ] Posts are stable, fabric is tight and without rips or frayed areas. [ ] [ ] [ ] Manufactured insert fabric is free of tears and punctures. [ ] [ ] [ ] Filter Sock is not torn or flattened and fill material is contained within the mesh sock. [ ] [ ] [ ] Outlet structure is constructed per the approved plan or drawing. [ ] [ ] [ ] Geotextile fabric has been placed beneath rock fill. [ ] [ ] [ ] Sediment trap slopes and disturbed areas are stabilized. [ ] [ ] [ ] Basin and outlet structure constructed per the approved plan. [ ] [ ] [ ] Basin side slopes are stabilized with seed/mulch. [ ] [ ] [ ] Drainage structure flushed and basin surface restored upon removal of sediment basin facility. [ ] [ ] [ ] Sediment basin dewatering pool is dewatering at appropriate rate. Note: Not all erosion and sediment control practices are included in this listing. Add additional pages to this list as required by site specific design. All practices shall be maintained in accordance with their respective standards. Construction inspection checklists for post-development stormwater management practices can be found in Appendix F of the New York Stormwater Management Design Manual. b. Modifications to the SWPPP (To be completed as described below) 1. There is a significant change in design, construction, operation, or maintenance which may have a significant effect on the potential for the discharge of pollutants to the waters of the United States and which has not otherwise been addressed in the SWPPP; or 2. The SWPPP proves to be ineffective in: a. Eliminating or significantly minimizing pollutants from sources identified in the SWPPP and as required by this permit; or b. Achieving the general objectives of controlling pollutants in stormwater discharges from permitted construction activity; and 3. Additionally, the SWPPP shall be amended to identify any new contractor or subcontractor that will implement any measure of the SWPPP. b. "I certify under penalty of law that this document and all attachments were prepared under my direction or supervision in accordance with a system designed to assure that qualified personnel properly gathered and evaluated the information submitted. Based on my inquiry of the person or persons who manage the system, or those persons directly responsible for gathering the information, the information submitted is, to the best of my knowledge and belief, true, accurate, and complete. Further, I hereby certify that the SWPPP meets all Federal, State, and local erosion and sediment control requirements. I am aware that false statements made herein are punishable as a class A misdemeanor pursuant to Section 210.45 of the Penal Law. " Title Date: Phone: Email: “ I hereby certify that I meet the criteria set forth in the General Permit to conduct site inspections for this project and that the appropriate erosion and sediment controls described in the SWPPP and as described in the following Pre-construction Site Assessment Checklist have been adequately installed or implemented, ensuring the overall preparedness of this site for the commencement of construction.” Title Date: Phone: Email: “I hereby certify that I understand and agree to comply with the terms and conditions of the SWPPP and agree to implement any corrective actions identified by the qualified inspector during a site inspection. I also understand that the owner or operator must comply with the terms and conditions of the most current version of the New York State Pollutant Discharge Elimination System (“SPDES”) general permit for stormwater discharges from construction activities and that it is unlawful for any person to cause or contribute to a violation of water quality standards. Furthermore, I understand that certifying false, incorrect or inaccurate information is a violation of the referenced permit and the laws of the State of New York and could subject me to criminal, civil and/or administrative proceedings.” Date Print Name Title Signature of Trained Contractor Date Print Name of Trained Contractor Title Name of Contracting Firm Street Address City, State, Zip Telephone No. A copy of this statement shall be retained as part of the Stormwater Pollution Prevention Plan (SWPPP) for a period off at least five (5) years after the subject property is stabilized. TAHESHA L. WAY Lt. Governor SHAWN M. LATOURETTE Commissioner DEPARTMENT OF ENVIRONMENTAL PROTECTION DIVISION OF WATERSHED PROTECTION AND RESTORATION BUREAU OF NJPDES STORMWATER PERMITTING & WATER QUALITY MANAGEMENT P.O. Box 420 Mail Code 501-02A Trenton, New Jersey 08625-0420 609-633-7021 / Fax: 609-777-0432 https://dep.nj.gov/stormwater/ October 3, 2024 Jeremy Fink, P.E. Associate Director of Product Development Hydro International 94 Hutchins Drive Portland, ME 04102 Re: Hydro-Shield Advance Plus Hydrodynamic Separator Online Installation TSS Removal Rate 50% Dear Mr. Fink: The Stormwater Management rules under N.J.A.C. 7:8-5.2(f) and 5.2(j) allow the use of manufactured treatment devices (MTDs) for compliance with the design and performance standards at N.J.A.C. 7:8-5 if the pollutant removal rates have been verified by the New Jersey Corporation for Advanced Technology (NJCAT) and have been certified by the New Jersey Department of Environmental Protection (NJDEP). Hydro International has requested a Laboratory Certification for the Hydro-Shield Advance Plus Hydrodynamic Separator (Hydro-Shield Advance Plus). The project falls under the “Procedure for Obtaining Verification of a Stormwater Manufactured Treatment Device from New Jersey Corporation for Advance Technology” dated August 4, 2021. The applicable protocol is the “New Jersey Laboratory Testing Protocol to Assess Total Suspended Solids Removal by a Hydrodynamic Sedimentation Manufactured Treatment Device” dated January 1, 2021, and last updated April 25, 2023. NJCAT verification documents submitted to the NJDEP indicate that the requirements of the aforementioned protocol have been met or exceeded. The NJCAT letter also included a recommended certification TSS removal rate and the required maintenance plan. The NJCAT Verification Report with the Verification Appendix (dated September 2024) for this device is published online at http://www.njcat.org/verification-process/technology-verification-database.html. The NJDEP certifies the use of the Hydro-Shield Advance Plus by Hydro International at a TSS removal rate of 50% when designed, operated and maintained in accordance with the information provided in the Verification Appendix and the following conditions: New Jersey is an Equal Opportunity Employer l Printed on Recycled Paper and Recyclable 1. The maximum treatment flow rate (MTFR) for the manufactured treatment device (MTD) is calculated using the New Jersey Water Quality Design Storm (1.25 inches in 2 hrs) in N.J.A.C. 7:8- 5.5. 2. The Hydro-Shield Advance Plus stormwater treatment device shall be installed using the same configuration reviewed by NJCAT and shall be sized in accordance with the criteria specified in item 6 below. 3. This Hydro-Shield Advance Plus stormwater treatment device cannot be used in series with another MTD or a media filter (such as a sand filter) to achieve an enhanced removal rate for total suspended solids (TSS) removal under N.J.A.C. 7:8-5.5. 4. Additional design criteria for MTDs can be found in Chapter 11.3 of the New Jersey Stormwater Best Management Practices (NJ Stormwater BMP) Manual which can be found on-line at https://dep.nj.gov/stormwater/. 5. The maintenance plan for a site using this device shall incorporate, at a minimum, the maintenance requirements for the Hydro-Shield Advance Plus. A copy of the maintenance plan is attached to this certification. However, it is recommended to review the maintenance website at https://hydro- int.com/sites/default/files/2024-09/HSA_OandM_.pdf for any changes to the maintenance requirements. The example below demonstrates the sizing procedure for the Hydro-Shield Advance Plus: A 0.25-acre impervious site with a slope of 5% is to be treated to 50% TSS removal using a Hydro-Shield Advance Plus. The hydraulically most distant point to the inlet of the Hydro-Shield Advance Plus is 110 feet. The site is located in an area for which the projected 2-year storm rainfall depth was calculated to be 3.84 inches. The site runoff (Q) was based on the following: CN = 98 (Curve Number for impervious) Dimensionless Unit Hydrograph (DUH) = SCS Standard DUH (peak rate factor of 484) Time of concentration = 0.8 minutes Q = 0.77 cfs Given the site runoff is 0.77 cfs and based on Table 1 below, the Hydro-Shield Advance Plus 4-ft Model with an MTFR of 1.49 cfs would be the smallest model approved that could be used for this site that could remove 50% of the TSS from the impervious area without exceeding the MTFR. The sizing table corresponding to the available system models is noted below. Additional specifications regarding each model can be found in the Verification Appendix. Table 1: Hydro-Shield Advance Plus Models and Associated MTFRs Hydro-Shield Advance Plus Model Diameter (ft) Maximum Treatment Flow Rate (cfs) Effective Treatment Area (sq. ft.) Hydraulic Loading Rate (gpm/sq. ft.) 4-ft 1.49 12.6 53.1 6-ft 3.35 28.3 53.1 8-ft 5.95 50.3 53.1 Be advised a detailed maintenance plan is mandatory for any project with a Stormwater BMP subject to the Stormwater Management Rules, N.J.A.C. 7:8. The plan must include all the items identified in the Stormwater Management Rules, N.J.A.C. 7:8-5.8. Such items include, but are not limited to, the list of inspection and maintenance equipment and tools, specific corrective and preventative maintenance tasks, indication of problems in the system, and training of maintenance personnel. Additional information can be found in Chapter 8: Maintenance and Retrofit of Stormwater Management Measures. If you have any questions regarding the above information, please contact Lisa Schaefer of my office at lisa.schaefer@dep.nj.gov. Bureau of NJPDES Stormwater Permitting & Water Quality Management Division of Watershed Protection and Restoration New Jersey Department of Environmental Protection Attachment: Maintenance Plan c: Hydro-Shield™ Advance Hydrodynamic Separator for Stormwater Treatment Table of Contents Hydro-ShieldTM Advance by Hydro International - Introduction - Operation - Pollutant Capture and Retention Model Sizes and Configuration - Hydro-ShieldTM Advance Components Maintenance - Overview - Maintenance Equipment Considerations - Determining Your Maintenance Schedule Maintenance Procedures - Inspection - Floatables and Sediment Clean Out Hydro-ShieldTM Advance Installation Log Hydro-ShieldTM Advance Inspection and Maintenance Log COPYRIGHT STATEMENT: The contents of this manual, including the graphics contained herein, are intended for the use of the recipient to whom the document and all associated information are directed. Hydro International plc owns the copyright of this document, which is supplied in confidence. It must not be used for any purpose other than that for which it is supplied and must not be reproduced, in whole or in part stored in a retrieval system or transmitted in any form or by any means without prior permission in writing from Hydro International plc. Hydro-Shield™ Advance is a trademarked hydrodynamic vortex separation device of Hydro International plc. A patent covering the Hydro-Shield™ Advance has been granted. DISCLAIMER: Information and data contained in this manual is exclusively for the purpose of assisting in the operation and maintenance of Hydro International plc’s First Defense®. No warranty is given nor can liability be accepted for use of this information for any other purpose. Hydro International plc has a policy of continuous product development and reserves the right to amend specifications without notice. I. Hydro-Shield™ Advance by Hydro International Introduction The Hydro-Shield™ Advance leads a new generation of hydrodynamic separator for stormwater treatment that utilize lamella technology for optimal settling performance. It efficiently removes total suspended solids (TSS), trash and hydrocarbons from stormwater runoff without washing out previously captured pollutants while providing an internal peak flow bypass. The Hydro-Shield™ Advance is available in multiple model configurations to accommodate a wide range of pipe sizes, peak flows and depth constraints. The Hydro-Shield™ Advance operates on simple fluid hydraulics combined with a lamella treatment module for increased efficiency. It is self- activating, has no moving parts, no external power requirement and is fabricated with durable non-corrosive components. No manual procedures are required to operate the unit and maintenance is limited to monitoring accumulations of stored pollutants and periodic clean-outs. The Hydro- Shield™ Advance has been designed to allow for easy and safe access for inspection, monitoring and clean-out procedures. Neither entry into the unit nor removal of the internal components is necessary for maintenance, thus safety concerns related to confined-space-entry are avoided. The internal components of the Hydro-Shield™ Advance have been designed to optimize pollutant capture. Sediment is captured and retained in the base of the unit (Fig.1). The pollutant storage volumes are isolated from the built-in bypass chamber to prevent washout during high-flow storm events. The sump of the Hydro-Shield™ Advance retains a standing water level between storm events. This ensures a quiescent flow regime at the onset of a storm, preventing resuspension and washout of pollutants captured during previous events. • Stormwater treatment at the point of entry into the drainage line • Sites constrained by space, topography or drainage profiles with limited slope and depth of cover • Retrofit installations where stormwater treatment is placed on or tied into an existing storm drain line • Pretreatment for filters, infiltration and storage Advantages • Integral bypass conveys large peak flows without the need for “offline” arrangements using separate junction manholes • Advanced Treatment module for effective sediment capture • Easy installation and maintenance • Accommodates large pipe diameters Figure 1: Pollutant storage volume in the Hydro-Shield™ Advance Sediment Storage II. Model Sizes & Configurations The Hydro-Shield™ Advance inlet and internal bypass arrangements are available in several model sizes and configurations. All Hydro-Shield™ Advance models include the internal components that are designed to remove and retain total suspended solids (TSS), (Fig.2). Hydro-Shield™ Advance model sizes (diameter) are shown in Table 1. Hydro-Shield™ Advance Components 1. Inlet Pipe 2. Treatment Module 3. Outlet Module 4. Outlet Pipe 5. Internal Bypass 6. Sediment Storage 7. Cover(s) Hydro-Shield Advance Model Sizes (MH Dia.) HSA-4ft HSA-6ft HSA-8ft Overview The Hydro-Shield™ Advance protects the environment by removing a wide range of pollutants from stormwater runoff. Periodic removal of these captured pollutants is essential to the continuous, long-term functioning of the Hydro-Shield™ Advance. The unit will efficiently capture and retain sediment until the stated sediment storage capacity has been reached. The Hydro-Shield™ Advance will continue to operate afterwards but prolonged operation will reduce removal efficiency and may cause damage to the equipment. The Hydro-Shield™ Advance allows for easy and safe inspection, monitoring and clean-out procedures. A commercially or municipally owned sump-vac is used to remove the captured sediment. Access ports are located in the top of the manhole. Maintenance events may include inspection, floatables removal, or sediment removal. Maintenance events do not require entry into the manhole, nor do they require the internal components of the Hydro-Shield™ Advance to be removed. In the case of inspection and floatables removal, a vactor truck is not required. However, a vactor truck is required if the maintenance event is to include sediment removal. The internal components of the Hydro-Shield™ Advance have a dedicated area on the perimeter through which the sediment storage sump can be accessed with a sump vac hose. Access to the Outlet Module is also provided. (Fig.3). On 4ft units, access is via a shared manhole cover. Larger units are provided with 2 separate covers. The frequency of clean-out is determined in the field after installation. During the first year of operation, the unit should be inspected every six months to determine the rate of sediment and floatables accumulation. A simple probe such as a Sludge-Judge® can be used to determine the level of accumulated solids stored in the sump. This information can be recorded in the maintenance log (see page 9) to establish a routine maintenance schedule. The vactor procedure, including both sediment and floatables removal, for Hydro-Shield™ Advance typically takes less than 30 minutes Fig.3 Hydro-Shield™ Advance maintenance access. Sediment Cleanout Access Outlet Module Access Inspection Procedures 1. Set up any necessary safety equipment around the access port or grate of the Hydro-Shield™ Advance as stipulated by local ordinances. Safety equipment should notify passing pedestrian and road traffic that work is being done. 2. Remove the manhole lid(s). 3. Without entering the vessel, look down into the chamber to inspect the inside. Make note of any irregularities. Fig.4 shows the standing water level that should be observed. 4. Without entering the vessel, use the pole with the skimmer net to remove floatables and loose debris from the components and water surface. 5. Using a sediment probe such as a Sludge Judge®, measure the depth of sediment that has collected in the sump of the vessel. 6. On the Maintenance Log (see page 9), record the date, unit location, estimated volume of floatables and gross debris removed, and the depth of sediment measured. Also note any apparent irregularities such as damaged components or blockages. 7. Securely replace the grate or lid. 8. Take down safety equipment. 9. Notify Hydro International of any irregularities noted during inspection Floatables and Sediment Clean Out Floatables clean out is typically done in conjunction with sediment removal. A commercially or municipally owned sump-vac is used to remove captured sediment and floatables (Fig.4). Floatables and loose debris can also be netted with a skimmer and pole. The access port located at the top of the manhole provides unobstructed access for a vactor hose to be lowered to the base of the sump. • Floatables and sump clean out are typically conducted once a year during any season. • Floatables and sump clean out should occur as soon as possible following a spill in the contributing drainage area. • Safety Equipment (traffic cones, etc) • Crow bar or other tool to remove grate or lid • Pole with skimmer or net (if only floatables are being removed) • Sediment probe (such as a Sludge Judge®) • Vactor truck (flexible hose recommended) - Spray hose or wand and clean water • Hydro-Shield™ Advance Maintenance Log Fig.4 Floatables are removed with a vactor hose Hydro International, 94 Hutchins Drive, Portland ME04102 Tel: +1 (207) 756 6200 Fax: +1 (207) 756 6212 Web: hydro-int.com Procedures Floatables and Sediment Clean Out Procedures 1. Set up any necessary safety equipment around the access port or grate of the Hydro-Shield™ Advance as stipulated by local ordinances. Safety equipment should notify passing pedestrian and road traffic that work is being done. 2. Remove the lid(s) to the manhole. 3. Without entering the vessel, look down into the chamber to inspect the inside. Make note of any irregularities. 4. Remove floatables on the surface of the water with the vactor hose or with the skimmer or net 5. Using a sediment probe such as a Sludge Judge®, measure the depth of sediment that has collected in the sump of the vessel and record it in the Maintenance Log (page 9). 6. Once all floatables have been removed, drop the vactor hose to the base of the sump. Vactor out the sediment and gross debris off the sump floor 7. Once the water level is below the Treatment Module, visually inspect the Outlet Module and inside of the Treatment Module 8. If necessary, use a spray hose or wand to dislodge any debris or silt and flush them into the sump. 9. Retract the vactor hose from the vessel. 10. On the Maintenance Log provided by Hydro International, record the date, unit location, estimated volume of floatables and gross debris removed, and the depth of sediment measured. Also note any apparent irregularities such as damaged components, blockages, or irregularly high or low water levels. 11. Securely replace the lid(s). - Every 6 months after the first year of installation - Once per year, with sediment removal - Following a spill in the drainage area - Once per year or as needed - Following a spill in the drainage area Inspection Floatables Removal Sediment Removal Activity Frequency NOTE: For most clean outs the entire volume of liquid does not need to be removed from the manhole. Only remove the first few inches of oils and floatables from the water surface to reduce the total volume of liquid removed during a clean out Hydro-Shield™ Advance Installation Log HYDRO INTERNATIONAL REFERENCE NUMBER: OWNER: FAX: FAX: INSTALLATION DATE: / / MODEL SIZE (CIRCLE ONE): INLET : Hydro-Shield™ Advance Inspection and Maintenance Log Date Initials Depth of Floatables and Oils Sediment Depth Measured Volume of Sediment Removed Site Activity and Comments Hydro-Shield TM Advance The Hydro-Shield™ Advance is a next generation hydrodynamic separator designed for optimal stormwater treatment, utilizing lamella technology to remove pollutants. With flexible design options it effectively prevents pollutant washout during high-flow storm events, ensuring reliable performance under varying conditions. Highest Flow Rates on the Market Flexible Configurations Ease of Maintenance Advanced Hydrodynamic Separation Advanced Hydrodynamic Separation Leveraging over 40 years of engineering excellence, the Hydro-ShieldTM Advance was designed by the leading water experts from Hydro International, developers of Downstream Defender® and First Defense®. With NJCAT2021 protocol approval, utilize the advanced hydrodynamic separator with the highest treatment flow rate available on the market. • Removal of total suspended solids (TSS) and floatable trash from stormwater runoff • New construction or redevelopment of commercial and residential sites • Pollutant hotspots such as maintenance yards, parking lots, gas stations, streets, highways, airports and transportation hubs • Site constrained LID or green infrastructure-based developments • LEED® development projects 1. Governed by peak hydraulic flow of max pipe size. 2. If exceeded, system will enter bypass at lower flow rates than the stated MTF. 3. Current NJ approval for a single inlet pipe, co-linear with outlet pipe (no inlet pipe angle). 4. Recommended maintenance intervals, based on 50% full sump: Shallow 154 months Standard 70 months Plus 45 months Technical Specifications Hydro-ShieldTM Advance - Sizing Table Unit Size Configuration Model Number Max WQ Flow [cfs] Peak Flow1 [cfs] Max Pipe Size [in] 4 FT Shallow HSA-4S 0.44 7.4 Standard HSA-4 0.96 7.4 Plus HSA-4P 1.48 7.4 6 FT Shallow HSA-6S 0.98 Standard HSA-6 2.16 Plus HSA-6P 3.33 Power Flow, High Removal Efficiency. Revision 12/2024 4-A-111 Trusted partnerships. Full scale solutions. www.oldcastleinfrastructure.com | (888) 965-3227 Feature Benefit Highest treatment flow rate available on the market. Smaller Footprint for lower costs. Bypass flow only limited by pipe size. Easy retrofit design and online use to reduce number of structures and manage cost. Configurable cone stacks by manhole size and depth. More flexible depth and footprint configurations when working in space con- strained sites, especially rock or high ground water. Model size overlap. Pipe size, peak flows, and treatment flows are not locked to one size chamber, allowing for optimized design and cost control. Treatment flow overlap. Engineers don't have to specify the exact model, allowing contractors to work with us based on site conditions and other factors to get the best value option. APPENDIX G Pipe Sizing Calculations Design Storm: 25-Year FROM TO A (ac.) C CA A (ac.) C CA INLET PIPE TOTAL DESIGN CAP. V(ft/s) n s (%) L (ft) DIA (in) FROM TO CB 3C CB 3B 0.15 0.9 0.14 0.00 0.3 0.00 0.14 - 7.2 1.0 4.2 4.4 0.012 1.2 CB 3C CB 3B CB 3B CB 3A 0.05 0.9 0.05 0.00 0.3 0.00 0.19 - 7.2 1.4 5.2 5.6 0.012 1.8 CB 3B CB 3A CB 3A CB 3 0.09 0.9 0.08 0.02 0.3 0.01 0.28 - 7.2 2.0 6.0 6.9 0.012 2.4 CB 3A CB 3 CB 3 CB 2 0.05 0.9 0.05 0.02 0.3 0.01 0.34 - 7.2 2.4 6.6 7.8 0.012 2.9 CB 3 CB 2 CB 2 HDS 1.1 0.47 0.9 0.42 0.06 0.3 0.02 0.78 - 7.2 5.6 11.9 9.6 0.012 2.9 CB 2 HDS 1.1 HDS 1.1 EX DI 0.00 0.9 0.00 0.00 0.3 0.00 0.78 - 7.2 5.6 24.1 11.2 0.012 4.5 HDS 1.1 EX DI CB 8 CB 7 0.10 0.9 0.09 0.00 0.3 0.00 0.09 - 7.2 0.6 5.5 4.7 0.012 2.0 CB 8 CB 7 CB 7 DMH 6 0.10 0.9 0.09 0.00 0.3 0.00 0.18 - 7.2 1.3 3.0 3.7 0.012 0.6 CB 7 DMH 6 DMH 6 HDS 2.1 0.00 0.9 0.00 0.00 0.3 0.00 0.33 - 7.2 2.4 4.9 4.0 0.012 0.5 DMH 6 HDS 2.1 HDS 2.1 DI 5 0.00 0.9 0.00 0.00 0.3 0.00 0.33 - 7.2 2.4 7.3 5.4 0.012 1.1 HDS 2.1 DI 5 DI 5 DI 4 0.15 0.9 0.14 0.00 0.3 0.00 0.69 - 7.2 5.0 7.7 6.7 0.012 1.2 DI 5 DI 4 CB 6B CB 6A 0.05 0.9 0.05 0.00 0.3 0.00 0.05 - 7.2 0.4 3.0 2.6 0.012 0.6 CB 6B CB 6A CB 6A DMH 6 0.05 0.9 0.05 0.00 0.3 0.00 0.10 - 7.2 0.7 3.7 3.6 0.012 0.9 CB 6A DMH 6 CB 6C DMH 6 0.05 0.9 0.05 0.00 0.3 0.00 0.05 - 7.2 0.4 3.7 3.0 0.012 0.9 CB 6C DMH 6 DI 5A DI 5 0.05 0.9 0.05 0.57 0.3 0.17 0.22 - 7.2 1.6 3.0 3.9 0.012 0.6 DI 5A DI 5 STRUCTURE STRUCTURE IMPERVIOUS AREA PERVIOUS AREA TIME OF CONC. (min.) JOB NUMBER: 24154.100 I CA DATE: 4-30-2025 PROJECT: Croton Point DRAINAGE SYSTEM CALCULATIONS CHK: JWM PIPE DESIGN DATE: 4-30-2025 BY: CMS Q (cfs) Y:\Insite Forms\Design\Stormwater\Pipe Sizing\Pipe Sizing Calc.xls 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. APPENDIX H OPRHP/SHPO Determination Letter KATHY HOCHUL Governor RANDY SIMONS Commissioner Pro Tempore September 03, 2024 Jan Johannessen, RLA, AICP Principal KSCJ Consulting 500 Main Street Armonk, NY 10504 Re: SEQRA 1 Croton Point 1 Croton Point Ave, Croton On Hudson, NY 10520 24PR07889 Dear Jan Johannessen, RLA, AICP: Thank you for requesting the comments of the Office of Parks, Recreation and Historic Preservation (OPRHP). We have reviewed the project in accordance with the New York State Historic Preservation Act of 1980 (Section 14.09 of the New York Parks, Recreation and Historic Preservation Law). These comments are those of the OPRHP and relate only to Historic/Cultural resources. They do not include potential environmental impacts to New York State Parkland that may be involved in or near your project. Based upon this review, it is the opinion of OPRHP that no properties, including archaeological and/or historic resources, listed in or eligible for the New York State and National Registers of Historic Places will be impacted by this project. If further correspondence is required regarding this project, please be sure to refer to the OPRHP Project Review (PR) number noted above. If you have any questions, please contact Chelsea Towers at the following email address: Chelsea.Towers@parks.ny.gov Sincerely, R. Daniel Mackay Deputy Commissioner for Historic Preservation Division for Historic Preservation New York State Office of Parks, Recreation and Historic Preservation Division for Historic Preservation, Peebles Island, PO Box 189, Waterford, New York 12188-0189 (518) 237-8643 • https://parks.ny.gov/shpo 1 Croton Point — SWPPP SWPPP24154.doc Insite Engineering, Surveying & Landscape Architecture, P.C. FIGURES LANDSCAPE ARCHITECTURE, P.C. Z:\E\24154100 WBP Croton Point Ave\Stormwater\Figures\Figure 1 - Location Map.dwg, 4/28/2025 6:33:37 PM, jmcmanus, 1:1 ENGINEERING, SURVEYING & LANDSCAPE ARCHITECTURE, P.C. Z:\E\24154100 WBP Croton Point Ave\Stormwater\Figures\Figure 2 - Pre Development Map.dwg, 4/28/2025 6:35:14 PM, jmcmanus, 1:1 ENGINEERING, SURVEYING & LANDSCAPE ARCHITECTURE, P.C. · · Z:\E\24154100 WBP Croton Point Ave\Stormwater\Figures\Figure 3 - Post Development Map.dwg, 5/1/2025 10:24:50 AM, cstepkoski, 1:1