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HomeMy WebLinkAboutGrishaj Stormwater Management PlanSTORMWATER MANAGEMENT PLAN Prepared for Nikola Grishaj 3319 Stony Street Town of Yorktown, NY Prepared by: Site Design Consultants 251 F Underhill Avenue Yorktown Heights, New York 10598 914-962-4488 Joseph C. Riina, P.E. NYS Lic. No. 64431 CPESC No. 2670 CPSWQ No. 0073 October 2021 Revised June 2022 Page 1 of 27 r� STORMWATER MANAGEMENT PLAN Prepared for Nikola Grishaj 3319 Stony Street Town of Yorktown, NY Property Owner: John Colangelo 1133 Westchester Ave. Suite N-006 White Plains, NY 10604 347-231-6959 Site Engineer: Joseph C. Riina, P.E. NYS Lic. No. 64431 CPESC No. 2670 CPSQW No. 0073 iriina(�i_)sitedesignconsultants. com Site Design Consultants 251-F Underhill Avenue Yorktown Heights, NY 10598 914-962-4488 www.sitedesianconsultants.com October 2021 Revised June 2022 Page 2 of 27 Table of Contents 1.0 Project Description 2.0 Stormwater Regulatory Requirements 2.1 Stormwater Impacts 2.2 Regulatory Obligation 2.2.1 USEPA/NYSDEC 2.2.2 Local Municipality 3.0 Reducing Pollutant Impacts (update) 3.1 Sources of Impacts 3.2 Stormwater Management During Construction 3.3 Stormwater Management Post -Construction 4.0 Site Characteristics 4.1 Soils 4.2 Hydrology 5.0 Hydrologic Analysis 5.1 Pre -Development Condition 5.2 Post -Development Condition 6.0 Unified Stormwater Sizing Criteria 6.1 Methodology 6.2 Water Quality Volume 6.3 Runoff Reduction (RRv) 6.4 Channel Protection Volume (CPv) 6.5 Overbank Flood (Qp) 6.6 Extreme Flood (Qf) 7.0 Stormwater Management Practices Selection, Justification, and Design 8.0 Erosion and Sediment Control 9.0 Construction Sequence 10.0 Inspection and Reporting 11.0 Installation and Maintenance of Stormwater Management Practices 11.1 During Construction 11.2 After Construction 12.0 Owner / Contractor Responsibilities 12.1 Owner Certification Statement 12.2 Contractor Certification Statement 12.3 Retention of Records 13.0 Conclusion Page 3 of 27 List of Figures 1.1 Location Map 1.2 Vicinity Map 1.3 NYS OPRHP Historic Resource Map 3.1 Stormwater Site Planning and Practice Selection Flow Chart 4.1 Soil Map 5.1 Pre -Development Conditions — Watershed Map 5.2 Post -Development Conditions — Watershed Map 8.1 Soil Restoration Requirements Appendices Appendix A List of Required Approvals and Applications - Town of Yorktown Site Plan Approval — approval pending - Town of Yorktown Building Permit — approval pending; - New York State Department of Environmental Conservation General Permit GP-0-20-001 "Notice of Intent;" - New York State Department of Environmental Conservation SWPPP MS4 Acceptance Form; - New York State Department of Environmental Conservation "Notice of Termination;" Appendix B Regulatory Ordinances - NYS DEC Permit No. GP-0-20-001 - Local Ordinance — Town of Yorktown Chapter 248 of the Town Code Appendix C Owner / Operator Certification Contractor Certification Appendix D Construction Sequence Appendix E Soil Testing Data Appendix F Hydrologic Analysis Appendix G SMP Selection Appendix H Stormwater Management Practices Design: - Rain Garden Sizing Calculations - Stormtech Chamber Sizing Calculations Appendix I This Section Left Blank Appendix J Standard and Specifications for Erosion and Sediment Control Measures Appendix K Sample Inspection Reports Appendix L Schedule "B" Appendix M Project Plans Page 4 of 27 1.0 Proiect Description The subject property is located at 3319 Stony Street in the Town of Yorktown Heights, Westchester County, New York (see Figure 1.1 — Location Map and Figure 1-2 — Vicinity Map). There is one parcel totaling 8.07 acres and is zoned both R1-20 Residential requiring a minimum lot size of 20,000. The site is owned by Mr. Nikola Grishaj. There have been no enforcement actions against the applicant for any violations of law relating to the proposed application. There is an old asphalt driveway that runs from Stony Street and terminates approx. 250 ft into the site. The majority of the site is woodland with some lawn around the existing driveway. There is a small wetland area located near the northeast corner of the site. The northern border and parts of the western border is bounded by an existing drainage channel. This channel is located within the unimproved ROW of Scofield Road. The channel was created from a drainage pipe from high point drive that outlets into the ROW and eroding the area over time. The channel connects to a catch basin off the northeast corner of the site. The site slopes from the southwest corner to the northern and eastern edges of the site. There is an existing sewer and drainage easement along the southern border of the site with a 8" sewer main and drainage line running through the site. It is proposed to subdivide the property into 12 lots. Lots 1 through 10 will be new residential lots which will conform to current zoning. Lot 11 is the north east corner of the site that contains the majority of the existing wetland. This lot is not proposed to be developed. Lot 12 is the proposed road that will connect the site to Highpoint Drive and Shelley Street. The road will terminate in a cul-de-sac. Each lot will have a driveway off of this road. An extension of the watermain in Shelly Street to Stony Street will is also proposed for this project. The proposed watermain will follow the path of the proposed road and connect to the watermain in Stony Street. Each house will have a service connection to the proposed main. A sewer main is also proposed for this project. It will also follow the path of the road, maintaining a 10' setback from the watermain. The residences on lots 1 through 5 will have a service connection to the sewer main. Lots 6 through 10 shall connect to the existing sewer main along the southern border of the site. Stormwater will be managed by filtering and infiltration of the water quality volume and detention of flood storage volumes. Each lot will have its own rain garden system, and the proposed private road will have an infiltration basin for treatment. The total disturbance expected for the project is 4.54 acres. The proposed start date for the project will be June 2022 and will be completed by June 2023. As required by the NYSDEC SPDES General Permit for Stormwater Discharges from Construction Activity, GP-0-20-001, Part IIIA.8, an historic resource screening determination was conducted. This was done using the online tools at the NYS Office of Parks, Recreation and Historic Places (OPRHP) website. This screening determined that there are no areas with historic or archeological sensitivity near the site. Figure 1.3 — NYS OPRHP Historic Resource Map was created from the website showing sensitive areas in Yorktown Heights. The following Report and Plans included in Appendix M describe, in detail, the design and implementation of the Stormwater Management Plan. 2.0 Stormwater Reaulatory Reauirements 2.1 Stormwater Impacts Urban stormwater impacts relate to significant changes to stormwater quantity and quality as a result of land development. "Urban Development has a profound influence on the quality of New York's waters."' This proposed development will change the runoff characteristics of this ' New York State Stormwater Management Design Manual, January 2015, Page 2-1 Page 5 of 27 site altering the quantity and quality of the surface stormwater. The impacts of this must be mitigated by managing the stormwater prior to discharge. This would be accomplished by the capture and treatment of surface runoff prior to discharge. Development of a site alters the hydrology therefore changing the characteristics of the surface and groundwater discharge of runoff. Changing the surface conditions alters a site's natural ability to store, treat, or infiltrate runoff. The change also allows for the discharge of potentially damaging pollutants and sediments to adjoining water bodies. This can occur during the construction phase, and long-term after development. During the construction phase, graded, destabilized, areas are subject to erosion which can cause the displacement of sediment. After development, changes in the surface conditions, such as impervious surfaces, roofs and pavement, or lawn surfaces can generate pollutants which would be collected and discharged through runoff. Some of the pollutants of concern are: Total Suspended Solids (TSS); Biological Oxygen Demand (BOD); Total Phosphorus (TP); and Total Nitrogen (TN), as well as oil or grease, and chloride. The most common sources of these pollutants from developed sites are atmospheric deposition, fertilizers, pesticides, and leaked discharges from vehicle. These pollutants would collect on these impervious surfaces and quickly wash off during even the smallest storm event. In the planning and design of the development, stormwater will be managed to minimize potential impacts. A Stormwater Management and Pollution Prevention Plan will be prepared. This Plan will deal with all aspects of the stormwater management programs such as identifying potential pollutant sources, design of temporary and permanent features, implementation, and maintenance. 2.2 Reaulatory Obligation 2.2.1 USEPA/NYSDEC The Federal Government's Clean Water Act (CWA), Section 402 states "Stormwater discharges from certain construction activities are unlawful unless they are authorized by a National Pollutant Discharge Elimination System ("NPDES") permit or by a state permit program." New York State is a NPDES delegated State. The necessary permitting is administered through the State Pollutant Discharge Elimination System (SPDES) under the General Permit, GP-0-20- 001, for Stormwater Discharges from Construction Activity. The Permit requires that any development meeting the disturbance thresholds listed in Tables 1 and 2 of Appendix B of the General Permit must prepare a SWPPP. Activities listed in Table 1 requires preparation of only an Erosion and Sediment Control Plan. Those listed in Table 2 would additionally require post - construction stormwater management practices. This project requires an E&SC and a SWPPP. This project requires filing a Notice of Intent under the New York State Department of Environmental Conservation General Permit 0-20-001. This project has a disturbance which is more than one acre. It is not located in an Enhanced Phosphorous Watershed (EPW). Therefore this project requires the preparation of a full Stormwater Pollution Prevention Plan. The Plan identifies the potential sources of pollution, and a design prepared and implemented to reduce pollutant loadings. This project will be required to prepare the following to be in compliance: Notice of Intent registered with the NYS DEC; Page 6 of 27 • MS4 SWPPP Acceptance Form signed by an authorized representative of the Municipality; • Prepare an Erosion and Sediment Control Plan; • Design and implement a stormwater quality treatment system to capture and treat the stormwater runoff volume generated by the 1 year rainfall event. • Design and implement a stormwater management system to capture and attenuate all storm events up to the 100-year storm. 2.2.2 Local Municipality In addition, this project requires approval under Chapter 248, Stormwater Management and Erosion and Sediment Control, of the Town of Yorktown Code. The Code requires compliance for projects with a land disturbance activity of 5,000 s.f. or more. The Code requires compliance with the NYS DEC GP-0-20-001 3.0 Reducing Pollutant Impacts 3.1 Sources of Impact For this project, the potential for contamination of stormwater occurs both during construction and after the completion of development. The goal to achieve reduced impacts involves containment and treatment of the various pollutants. Each phase will require temporary sediment and erosion control measures. The greatest source of pollutants during these phases is the potential of soil erosion. The nature of the construction plan is to have exposed soils which can erode and potentially discharge to sensitive areas. During construction, existing vegetation is removed exposing soils. Also, stockpiling of soils takes place. These conditions if not stabilized, are subject to erosion during rainfall events and wind conditions. Sediment discharged to a wetland can destroy vegetation and habitat affecting the function of the wetland. This degradation potential can be irreversible and eliminate its function in the ecosystem. Increases in turbidity to open water bodies such as streams, ponds, etc., are an additional environmental impact. The implementation of proper erosion control measures and sediment containment along with a planned construction sequence can minimize or eliminate these potential impacts. The selection and implementation of erosion and sediment practices are described in a later section of this Report. The post -development state of this project not only will yield a potential for sediment discharges or Total Suspended Solids (TSS), but also other pollutants which can impact the adjacent water bodies. The contaminants of highest concern are Total Phosphorus (TP), Total Nitrogen (TN), and Biochemical Oxygen Demand (BOD). Modification of the surface conditions of the site, specifically increasing the impervious nature of the ground cover, increases the concentration and potential discharge of these pollutants. The development of the site reduces native vegetative cover, and therefore affects the land's natural ability to store, treat or infiltrate runoff. This includes impervious surfaces, such as roads, buildings, and also landscaped areas, specifically lawns. These increases in imperviousness allow for greater concentrations or pollutants to collect and be carried off by runoff. Some of the pollutants are deposited by atmospheric conditions. However, other sources are applied or discharged to the surface of the site. The landscape areas are subject to fertilizers, weed control, and pesticide products. This Page 7 of 27 too is a large potential for pollutants which if discharged untreated could have long term impacts. A full listing of the potential pollutants which can be considered in stormwater can be found in Table 2.1 of the New York State Stormwater Management Design Manual (NYS SMDM). The concentrations are collected in stormwater runoff and rapidly discharge to the adjacent water bodies if not treated properly. The pollutants are collected and conveyed during the initial part of the storm event or the 90% rainfall. This is 90% of the average annual stormwater runoff volume. For this part of the State it is equivalent to approximately 1.2 inches. This is also commonly referred to as the "first flush." The requirement of the NYSDEC SPDES General Permit GP-0-20-001 requires that this volume of runoff is to be collected and treated by the means described in the NYS SMDM. The method to be used is the unified stormwater sizing criteria in which a water quality volume is determined and a practice is selected which best fits the criteria provided. This is described further in Section 6.0. Further treatment is required to enhance the phosphorus removal since this project is located within the NYC Croton Reservoir East of Hudson which is a phosphorus enhanced watershed. As stated earlier, in order to comply with the NYS DEC Enhanced Phosphorus Removal Standards, the WQv to be treated to be the one-year, 24-hour storm. 3.2 Stormwater Management During Construction The Erosion and Sediment Control plan will be implemented during all phases of construction until the completion of the project. This will minimize or eliminate the potential short- term adverse impacts which may occur during construction. After completion, the erosion and sediment control will become a maintenance plan to ensure that permanent erosion and sediment controls continue to function and prevent the transport of sediments. The Erosion and Sediment Control plan includes the Sequence of Construction and designed measures to be installed, operated and maintained during all aspects of construction. The appropriate measures were selected and detailed in plan for implementation by the site contractor. The main objective of the plan is to prevent erosion from occurring by stabilization of the construction site where possible. Sediment controls are to be used as a containment system to allow the removal of sediment from runoff to the greatest extent possible before leaving the work site. Control methods and standards utilized are provided in the NYSSESC. Potential sources of destabilization of the site have been determined so that proper measures will be used. The locations and methods designed for erosion and sediment control measures change as the construction sequence progresses. The priority is to stabilize disturbed areas subject to erosion and use containment and / or filtering practices where sediment may concentrate. Some of the practices and methods that will be used for this project are: • Minimization of open disturbance by use of stabilizers such as seed, mulch, and erosion blankets, stone, etc. Areas not subject to construction traffic for extended periods will be temporarily stabilized. • The work areas will be contained. Down grade perimeters will be lined with barriers such as silt fence, diversions, berms, etc. • Where possible, clean stormwater will be diverted away or around the work site to reduce the amount of runoff requiring treatment. • Sediment traps will be constructed where heavy concentrations of runoff may accumulate. • Dust control measures will be maintained on -site such as water trucks. • Runoff will be prevented from gaining erosive velocities on long slopes. This can be achieved with seed and mulch, erosion control blankets, curb dams and multiple rows of silt fence. Page 8 of 27 • Existing drainage structures will be protected from sediment -laden runoff. • Regular weekly inspections and reports (see Appendix K for report form) to be filed with the Operator and Town. Additional methods of practices may be employed dependent on the situation. The NYSSESC consists of NYS DEC accepted and recommended practices. The design requirements of temporary and permanent erosion and sediment control practices of this Manual have been followed. Prior to completion of the project, all permanent structural features will be cleaned, restored, and re -vegetated as necessary. The erosion and sediment control phase of the project is complete when all work is done and all areas are stabilized. The post -construction Stormwater Management Inspection and Maintenance Agreement (Schedule "B" in Appendix L) will describe the long term inspection schedule, periodic maintenance requirements, and the responsible party. 3.3 Stormwater Management Post -Construction The post -construction design of the project must be included in the Stormwater Pollution Prevention and Stormwater Management Plans to minimize or eliminate potential long-term adverse impacts which might be caused by surface runoff from the site. This will deal with the management of the stormwater upon completion and operation of the site. The plan will be an analysis of all potential impacts due to stormwater and the means of protecting adjoining water bodies. The management plan begins with conceptual designs of the collection and conveyance system and the proposed treatment practices. The treatment practices are subject to different parameters and must be designed to best fit the site including green infrastructure planning. Some of the limitations that may be encountered include soil types and properties, depth to groundwater or bedrock, distance to structures, and maintenance. A list of acceptable practices can be found in Chapters 3, 5, and 10 of the NYS Stormwater Design Manual (SMDM). Chapter 3 states "The Practices on this list are selected based on the following criteria: 1. Can capture and treat the full water quality volume (WQV) 2. Are capable of 80% TSS removal and 40% TP removal 3. Have acceptable longevity in the field 4. Have a pre-treatment mechanism." Green Infrastructure Practices include I. Preservation of Natural Resources II. Reduction of Impervious Cover III. Runoff Reduction Techniques The five broad groups of standard stormwater management practices are: I. Stormwater Ponds II. Stormwater Wetlands III. Infiltration Practices IV. Filtering Practices V. Open -channel Practices These practices "are presumed to meet water quality requirements set forth in this manual if designed in accordance with the sizing criteria presented in Chapter 4 and constructed in Page 9 of 27 accordance with the performance criteria in Chapter 6." 2 This however is modified with the fact that the project must meet the enhanced phosphorus criteria in Chapter 10. Green Infrastructure — Runoff Reduction Chapter 3 of the NYS DEC introduces a planning process for site development which has "increased emphasis on a holistic approach" to urban stormwater runoff management. This is to be done by reducing pollutant -laden runoff by the use of green infrastructure which promotes replication of pre -development hydrology. This is done by designing selected practices which will allow for infiltration, ground water recharge, reuse, recycling and evaporation/evapotranspiration of surface runoff Water Quality Volumes from developed areas. The implementation of this planning process is defined in a five step approach as follows: 1. Preservation of features and reduction of impervious surfaces. 2. Determination of the project's Water Quality Volume. 3. Incorporating green infrastructure and standard stormwater management practices that provide a Runoff Reduction Volume Capacity. 4. Use of standard stormwater management practices to treat Water Quality Volume not addressed by green infrastructure. 5. Design of storage facility for volume and peak rate volumes. This methodology is provided in more detail in Chapter 3 of the SMDM as well as the Flow Chart at the end of Chapter 3 (see Figure 3.1). This process is required for new and redevelopment projects. Chapter 4 Section 4.3 requires the calculation of Runoff Reduction Volume (RRv) and that 100% of post -development Water Quality Volume should be treated on -site using green infrastructure or standard SMP's. If this goal cannot be met, at a minimum, a specific reduction factor(s) based on the hydrologic soil group (HSG) can be applied but justification must be provided as to why the pre -construction condition cannot be met. Enhanced Phosphorus Removal Standards The enhanced phosphorus standards were developed for projects located in phosphorus limited watersheds in order to meet water quality objectives for these watersheds. Enhanced phosphorus removal is required. This will require the implementation of the criteria in Chapter 10 of SMDM where additional performance standards must be implemented. In these standards, the WQv is computed to be the entire one-year 24-hour design storm for the post -development watershed. The one-year storm volume is determined using the SCS Method. The developed volume becomes the basis for treating the WQv as per Chapter 4 of the SMDM including the five steps that apply to runoff reduction. The design will meet enhanced phosphorous removal standards for achieving water quality standards. The guidelines and practices used in selecting and the sizing analyses are found in Chapters 5, 6 and 10 of the NYS DEC Stormwater Management Design Manual January 2015. After the preliminary selection of treatment practices, the water quality volume size will be determined. 2 Pg. 3-7 NYS Stormwater Management Design Manual, January 2015. Page 10 of 27 The treatment methods could be a single practice or a combination of practices. The previously described controlling factors will initially eliminate some treatment methods. The remaining practices will be selected based on feasible locations, functionality, maintenance factors, and cost. An additional factor is to try and select practices which will not only provide an environmental benefit, but also aesthetic value. The practices selected for the project were chosen with these requirements in mind. The treatment practice selected is based off of the six steps enumerated in chapter 3 of the manual. As stated above, the first step in this process is site planning and preservation of features. Due to the nature of this project, this step controlled a good deal of the placing of project infrastructure. On this site, there are several wetland areas It was important to limit any disturbance to these sensitive areas. To prevent disturbance, all of the projects infrastructure was placed outside of the wetlands and the 100' buffer. In addition to this, impervious areas were limited to the greatest extent possible and meet minimum dimensional requirements. Additionally, the majority of the rear of the site contains steep slopes. There is no proposed disturbance in these areas as well. All of the proposed site work has been limited to prevent the disturbance of sensitive features. The second step was to assess the water quality volume for the specific drainage areas of the project. This was done using the one year storm as opposed to the 90% storm event. As there is no existing impervious cover on the site, redeveloped impervious area was not figured into the calculations. This is gone into greater detail in section 6.2 below. The third step in the process is the application of runoff reducing techniques or standard practices with runoff reducing capabilities. The soils testing on the site revealed groundwater at shallow depths. In some tests, ground water was found as shallow as 24". As a result, the use of infiltration practices was infeasible in most locations. Rain Gardens with underdrains have been selected as the primary treatment practice. An infiltration basin is also proposed to provide treatment for the proposed road. These practices are ideal due to the site constraints, their ability to treat runoff, and the runoff reducing capabilities of the rain gardens and infiltration. All stormwater management practices have been designed to maintain the minimum required separation from groundwater. All of the proposed stormwater treatment practices area listed in the 2015 NYS DEC SWDM as either a green infrastructure practice, or a standard practice that contributes towards the RRv. Step four is to address the minimum Runoff Reduction Volume. This volume is based on the proposed site conditions and the existing soil on the site. Depending on the hydrologic soil group of the soil, the minimum runoff reduction will differ. This is provided for by the proposed stormwater treatment practices. The proposed rain gardens are listed in the 2015 NYS DEC SWDM as a Green Infrastructure practice that contributes towards the RRv. The infiltration basin is listed as a standard practice that contributes towards RRv. The calculations for determining this can be found in appendix H of this SWPPP. Step five is the treatment of any of the remaining WQv with standard treatment techniques. This step did not apply to this project as the selected practices provided the full WQv. The sixth and final step in the process is the design of a practice to attenuate peak runoff rates. This is achieved by the primary treatment practices. As such no additional practices are needed. After applying these steps to the design process, the selected treatment practice will be Rain Gardens for the individual lots, and an inflation basin for the proposed private road. They were chosen due to their capacity to hold and treat the water quality volume, and their additional Page 11 of 27 runoff reducing capabilities. They also provide enough storage to attenuate peak flows. The Rain Gardens meet all of the requirements set forth in chapters 3, 5, and 10. They were chosen based on the characteristics and limitations of the site and to satisfy all of the requirements these chapters impose on the stormwater management of a project. 4.0 Site Characteristics 4.1 Soils On -site soils were classified by using the USDA Natural Resources Conservation Service (NRCS) Websoil survey for Westchester County, NY, see Figure 4.1 — Soil Map. The predominant soil types for this project are Charlton loam, Charlton -Chatfield complex, Paxton loam, Woodbridge loam, and Ridgebury loam. These soils are poor to well drained soils that are subject to seasonal groundwater. The Hydrologic classification of these soils are B, C, or D. The erosion hazard level for these soils are slight to moderate. These soil properties are essential in the design and proper construction management of the site. Independent soil tests were performed and the results are located in the Appendix E of this Report. Sect 4.1 • Ridgebury Loam, RgB, RdA, RdB, Hydrologic Soil Group B/D moderate slopes very stony; moderate erosion hazard • Paxton Loam, PnB, PnC, PnD, PoD, Hydrologic Soil Group C moderate slopes very stony; moderate erosion hazard • Woodbridge loam, WdB, WdC Hydrologic Soil Group c/D moderate slopes very stony; moderate erosion hazard Deep Test Soil Logs and soil percolation test data are included in Appendix E of this Report. The locations of these deep soil tests are indicated on the Construction Drawings. On - site soil investigation and knowledge of the soil groups facilitated the selection of coefficient values used for the pre- and post -development pollutant load scenarios. Additionally, curve numbers were determined for use in the analysis. 4.2 Hydrology The proposed improvements will not significantly change the surface runoff patterns. Runoff flows from the Southwest corner of the site to the northern border where it enters the drainage channel, or eastern borders where it enters the drainage system in Stony Street. The surface runoff pattern is a combination of sheet flow and concentrated flow. The majority of the site is woods with moderate to steep slope. Under the proposed condition the general direction of the surface runoff will not be altered. Almost the entire amount of surface runoff from the impervious areas will be collected and treated. The proposed improvements as shown will result in an increase in the imperviousness of the drainage area. Therefore, there will be an increase in the volume of runoff as well as the pollutant loads generated by the site for a given rainfall event. This will be mitigated with stormwater management practices. In the planning, design and construction of the development, stormwater will be managed to minimize or eliminate potential off -site impacts. The proper implementation of temporary sediment and erosion control measures are used to achieve this goal. An Erosion and Sediment Control Plan has been established and will be implemented during all phases of construction until the completion of the project. The Erosion and Sediment Control Plan incorporates the sequence Page 12 of 27 of construction and designed measures to be installed, operated and maintained during all aspects of each phase. The erosion and sediment controls are designed in accordance with the NYS Standards and Specifications for Erosion and Sediment Control. 5.0 Hydrologic Analysis The method used to compute project runoff was the Soil Conservation Service TR-55. The basis for the analysis was the Type III, 24-hour storm, for the 1 year, 2 year, 10 year, 25 year, and 100-year storm event. The rainfall depth for the respective storm events are 3.1, 3.5, 5.0, 6.0, and 7.5. The runoff coefficient "CN" and Time of Concentration for existing and post - development conditions were computed using Standard TR-55 criteria. 5.1 Pre -Development Condition As stated, the portion of the site to be developed with new homes is wooded and lawn areas. Therefore, the only change in surface conditions will be the proposed impervious surfaces of the road, the houses and driveways. The remainder will continue to be woods and lawn. Therefore, the analysis for stormwater increases has been done for these individual impervious components. The contributing watersheds are shown on Figure 5.1 — Pre -Development Watershed Map. The site has been divided into two distinct watersheds. There is a catch basin in stony street about midway along the property. This serves as the main drainage divide for the site. The flow that does not enter this catch basin enters on further down stony street that is connect to the drainage channel. Drainage area 1 is the portion of the site that flows to the first catch basin in stony street. The majority of this area is woods and lawn. Drainage area 2 is the area directly to the north of this area and flows to the catch basin at the northeast corner. Runoff either flows to stony street and then into this catch basin or to the channel to the north and into the catch basin from there. The majority of the area is woodlands, with some open space and impervious cover. The Drainage Basin sizes, curve numbers and travel times used in the analysis are summarized in the Table below: Pre -Development Conditions Watershed Analysis Variables Drainage Basin Area Curve Number Travel Time, Tc (acres) CN hrs DA-1 3.70 71 0.345 DA-2 4.92 71 0.336 5.2 Post -Development Condition A hydrologic analysis has been done for each of the new lots and the proposed private road to determine the expected runoff depth for each storm event. The results of this analysis were used to calculate the Rain Garden sizes required for each lot. Additional detention basins were sized to accommodate the 100-year storm event. The contributing watersheds are shown on Figure 5.2 — Post -Development Watershed Map. The hydrologic analysis assumes that full soil restoration as required in Chapter 5 (Table 5.3) of SMDM will be implemented. The areas of soil restoration will be shown on the E&SC Plan if required (See Figure 5.3). Page 13 of 27 The post developed watersheds have been further broken down into 13 drainage areas. The general path of runoff is the same with all areas draining to one of the two catch basins adjacent to the site. The first two drainage areas are the same as they are in the predeveloped condition less the areas to be developed. They are the areas that flow unhindered towards the streams on site. Drainage areas 3 — 12 are the individual lots created by subdividing the site. Each lot will have its own rain garden for treatment of the water quality volume. On most lots, runoff will sheet flow into the rain garden and be treated therein. The Rain Gardens in Lots 1, 2, 3, 7, 9, and 10 will also have additional detention beneath the system. These rain gardens will have a riser pipe for overflow to the detention so that ponding will not exceed 6" in the rain garden. The detention systems will outlet downstream to the proposed bypass structure for the infiltration chambers for Drainage area 13. The Rain Gardens in lots 4, 5, 6, and 8 will have a weir overflow downstream. Drainage areas 13 includes the proposed road, and any other adjacent areas that are captured. Runoff will sheet flow to the road, where it will enter the proposed storm sewer which will direct it into the proposed infiltration basin. This will provide treatment as well as detention. The infiltration basin will have an emergency overflow outlet to provide controlled release of runoff exiting the infiltration basin. Flows from storms in excess of the 1 year storm will be bypassed to detention chambers which will outlet to a rip rap stabilized outlet. There will be no discharges associated with industrial activities other than construction as a result of the development. The Drainage Basin sizes, curve numbers and travel times used in the analysis are summarized in the Table below: Post -Development Conditions Watershed Analysis Variables Drainage Basin Area Curve Number (acres) CN Travel Time, Tc hrs DA-1 1.440 73 0.302 DA-2 2.799 72 0.363 DA-3 0.181 83 0.171 DA-4 0.225 81 0.087 DA-5 0.194 84 0.178 DA-6 0.169 85 0.083 DA-7 0.288 82 0.159 DA-8 0.472 80 0.102 DA-9 0.403 81 0.123 DA-10 0.444 80 0.128 DA-11 0.150 82 0.083 DA-12 0.191 84 0.083 DA-13 1.868 81 0.226 6.0 Unified Stormwater Sizing Criteria 6.1 Methodology To satisfy the requirements of the NYS DEC General Permit and the Town of Yorktown a combination of Green Infrastructure Techniques and standard practices have been selected. These practices meet attenuation as well as stormwater quality goals. The guidelines and practices used in selecting and the sizing analyses are found in Chapters 4, 5, and 6 of the NYS DEC Stormwater Management Design Manual. Page 14 of 27 6.2 Water Qualitv Volume (WQv The Treatment volumes are determined as prescribed by the standard methods as outlined in the NYS DEC SMDM. This Water Quality Volume WQv requirement is normally based on the 90% rainfall event. This equates to 90% of the average rainfall for the specific region. However, for this project the treatment volumes exceed that requirement by treating the 1-year storm event. This site is located in the Croton Watershed which is an enhanced phosphorous basin. This requires implementation of the enhanced phosphorus standards for the capture and treatment of the runoff from the 1-year, 24-hour rainfall event, which represents the water quality volume. The 1-year, 24-hour runoff volume required to be captured and treated has been further defined as the runoff volume from the contributing drainage areas for the proposed project. The volume proposed to be captured will be that volume generated by a 1-year, 24-hour storm or greater. With the design provided, this entire volume will be captured and retained for an extended period of 24-hours for pollutants to settle out of the contained runoff. Excess stormwater above the water quality volume will be diverted to subsurface storage for the larger storm events. The volumes to be treated have been calculated as shown in the following table. Water Qualitv Volume Drainage WQv based on 90% Pretreatment WQv Provided Storm Area Rainfall Event Provided Treatment Treated DA-3 352.44 --- 534.3 90% DA-4 372.76 --- 497.9 90% DA-5 410.63 --- 258.7 90% DA-6 385.98 --- 460.2 90% DA-7 512.27 ---- 526.5 90% DA-8 673.37 --- 538.2 90% DA-9 646.68 --- 490.1 90% DA-10 634.23 ---- 509.6 90% DA-11 280.53 --- 429 90% DA-12 409.86 --- 461.5 90% DA-13 3090.87 --- 3,989.0 90% These volumes meet the requirements of the NYS DEC and Town of Yorktown Heights for the limitation of phosphorous export. Page 15 of 27 The water quality volume required to be captured and treated has been further defined as the runoff volume from the impervious surface that will result from the proposed project. The volume proposed to be captured will be that volume generated by the 1 year rainfall event or greater. With the design provided, this entire volume will be captured and detained for an extended period of 24-hours for pollutants to settle out of the contained runoff. Excess stormwater above the water quality volume will be released at a controlled rate providing attenuation of larger storm events. The volumes to be treated have been calculated as shown in the following table. 6.3 Runoff Reduction (RRv) Green infrastructure design as part of the planning process enables the reduction of runoff from a project. These practices in turn reduce the requirements of water quality treatment and flood protection. The selection of green infrastructure practices is developed using a five -step process detailed in Section 3 of the SMDM. A flow chart of this process is included as Figure 3.1 of this Report. Design of the practices can be found in Appendix H of this Report. The selection and justification of green practices can be found in Appendix G of this Report. 6.4 Stream Channel Protection Volume Reauirements (CPv) This requirement is for the protection of stream channels from receiving erosive velocities. This goal is accomplished by providing 24-hour extended detention of the one-year, 24-hour storm event that remains after runoff reduction is applied to the project. Trout waters may be exempted to only provide 12-hour detention. It is also not required if the discharge is to a pipe or hardened channel. The detention time is measured by the center of mass method or plug flow calculation method. Further criteria for the application of the Cpv can be found in Section 4.4 of the SMDM. 6.5 Overbank Flood Control (Qp) The purpose of this sizing criteria for overbank flood control is to avoid an increase in the frequency and magnitude of out -of -bank flooding that may be the result of development. These are flow events where channel capacity is exceeded and spill over to flood plains. To meet the criteria the proposed stormwater management system for the project must attenuate the 10-year, 24-hour storm event to pre -development peak discharge rate. Detailed criteria can be found in Section 4.5 of the SMDM. 6.6 Extreme Flood Control Criteria (Qf The purpose of the extreme flood analysis is to prevent flood damage from large storm events by maintaining predevelopment 100-year flood plain boundaries and protecting the integrity of stormwater management practices. The basis of the analysis is to maintain pre - development peak rates of runoff for the 100-year, 24-hour storm event with proper stormwater management. Detailed criteria can be found in Section 4.6 of the SMDM. A summary of peak discharge rates at each design point for the pre and post -developed storm events analyzed for each drainage basin is summarized in the tables below: Page 16 of 27 Design Point 1: Storm Event Pre -Developed Post- Developed Net Change of Percent (year) Peak Flow Peak Flow Peak Flow Reduction (cfs) cfs (cfs) 1 1.58 1.08 -0.50 -31.6% 2 2.42 1.93 -20.2% -0.49 10 5.86 5.25 -0.61 -10.4% 25 9.05 9.10 +0.05 +0.6% 100 15.34 14.30 -1.04 -7.3% Design Point 2: Storm Event Pre -Developed Post- Developed Net Change of Percent (year) Peak Flow Peak Flow Peak Flow Reduction (cfs) cfs (cfs) 1 2.12 1.28 -0.84 -39.6% 2 -40.3% 3.25 1.94 -1.31 10 7.90 5.10 -2.8 -35.4% 25 12.19 9.07 -3.12 -25.6% 100 20.64 15.75 -23.7% -4.89 As can be seen by the results, peak discharge rates are decreased for all scenarios. Therefore, the overall post developed peak flow has been reduced. From this it can be determined that there will be no impacts on downstream receiving waters as all peak flows have been attenuated. 7.0 Stormwater Management Practices Selection. Justification and Design The stormwater management practices selection process detailed in Chapters 3 and 7 of the NYS Stormwater Management Design Manual was followed to help select the practices chosen. These Chapters provide a series of matrices which allows logical selection of treatment practices based on several factors. The factors are as follows: 1. Land Use - rural; 2. Physical Feasibility - location, slope, drainage area, groundwater table; 3. Watershed / Regional Factors - near Croton Reservoir; 4. Stormwater Management Capability - can meet all requirements; 5. Community and Environmental Factors - meets all requirements. The matrices are provided in Appendix G of this Report. The matrices have been commented on or redacted to show elimination criteria through this stepped approach and eventual possible alternatives for treatment. Thermal impacts are not a major concern on this project due to the lack of impervious surfaces. Surface water flows will travel mostly over or through vegetated cover whether through the woods or swales prior to discharge into the Water Quality Basins. Therefore, the stormwater collection and management will not contribute to the heating of stormwater where it will have a downstream thermal impact. Page 17 of 27 Rain Garden NYSDEC SMDM: A Water Quality Volume was determined for each of the treatment areas and discharged into the associated Rain Garden. The Stormwater Management Practice selected is a Rain Garden as described in the NYS DEC SMDM. This design is a combination of an extended detention and peat/sand filter bed for the treatment of water. The basin is supplemented with plantings and blended into the landscape features of the project. The Basin has been located at the lowest possible hydraulic location to intercept and treat runoff. As described in earlier sections of this report, the required Water Quality Volume has been exceeded in the design. The Water Quality Volumes are summarized in Section 6.2. A typical cross section of the proposed Rain Garden can be found in the Plan Set. The Rain Garden is designed to have runoff sheet flow directly into the system. The water quality volume is treated by providing extended detention to temporarily store the WQv and pass it through a filter bed of top soil, and a peat/sand mix. Filtered runoff is then collected in an underdrain system and discharged to the main collection system before reaching the discharge point. Partial exfiltration into the surrounding soils may also occur. This will provide the necessary storage for channel and flood protection. The bottom of the pond should maintain a 2 foot separation from the ground water table. The soil logs noted above indicate that sufficient depth is available at the proposed location to provide the required separation. The following is the size criteria for the practice as per Chapter 6 of the NYS SMDM: - Typical length to width ratio of 1.5:1; - Filter media shall be a peat/sand mix (reed -sedge hemic peat shall be used); - Underdrain system; - Provide the required minimum filter bed surface area; The selection of the treatment practice was based on evaluating the site to determine what would best fit the conditions providing maximum benefits. The goal was to select practices which would meet treatment and attenuation standards and minimize the disturbance footprint. The selection of Stormwater Practices was based on the surface and subsurface conditions of the site. In addition, the site design concept is to create a natural and environmentally sensitive setting. The high groundwater table made practices with an underdrain a necessity. See Routing Calculations in Appendix F and H for sizing calculations. Infiltration — Subsurface Chambers (1-3) NYS DEC SMDM: Stormwater Infiltration Practices capture and temporarily store stormwater. The stormwater is then infiltrated into the existing soil strata over an extended period of time allowing recharge into the groundwater. Required Elements: Pre -Treatment Volume Provided If Fc for underlying soils is less than 2.0 in/hr minimum pre-treatment volume of N/A 25% is required. If Fc for underlying soil greater than 2.0 in/hour, minimum pretreatment volume N/A of 50% is reauired Page 18 of 27 If Fc for underlying soil greater than 5.0 in/hour,100% of WQv must be 100% Exit velocities from pretreatment volume shall be non -erosive (3.5 to 5.0 fps) during the 2-year storm event Required Exit velocities are not a concern since there are no significant surface discharges. Treatment Volume Provided Infiltration practice designed to exfiltrate All criteria have been met. The subsurface entire WQv through floor of practice infiltration system has been designed to exfiltrate (side walls not included in sizing); the entire WQv and has been sized based solely on the surface area of the bottom. Installation shall carefully follow the construction sequence. The surface area of the infiltration practice shall be sized based on Ap = Vw / ndt Ap = surface area (SF) Vw = Water Quality Volume (cf) n = porosity (one used since open cavity) dt = depth of practice Landscaping: Does not apply. Required All criteria have been met. system has been designed WQv and has been sized surface area of the bottom. All criteria have been met. system has been designed WQv and has been sized surface area of the bottom. Maintenance The surface infiltration to exfiltrate the entire based solely on the The surface infiltration to exfiltrate the entire based solely on the Provided Infiltration practice shall never serve as This Erosion and Sediment Control Plan includes a temporary sediment trap during separate locations for temporary sediment traps construction. which do not coincide with the practice locations. An observation well shall be installed in every practice and shall have lockable caD. Direct access shall be provided to the practice for maintenance and rehabilitation. The subsurface stormwater management system will have access manholes. Direct access and observation will be served by a manhole cover. See Routing Calculations in Appendix F and H for sizing calculations. In General: Controls should be inspected periodically for the first few months after construction and on a semi-annual basis thereafter. They should also be inspected after major storm events (greater than 0.5 inches). All stormwater controls shall be inspected and cleaned of any debris or sediment. Any erosion shall be repaired and stabilized with seeding and mulch or stone. Page 19 of 27 Please note that additional notes regarding maintenance activities are contained on the project Construction Drawings and should be adhered to during and after construction. The selection and justification of green practices can be found in Appendix G of this Report. The design of the practices can be found in Appendix H of this Report. 8.0 Erosion and Sediment Control Erosion and sediment control practices were selected and designed in accordance with the NYSSESC. The practices proposed for this project are described below. Standard details and specifications are included in Appendix J as well as on the Construction Plans. Initial locations of each practice are shown on the Plans as construction progresses it may become necessary to repair, replace or relocate these practices as conditions warrant. Stabilized Construction Entrance: This has been specified for the entrance of the driveway. The installation will occur at the beginning of the project as described in the Suggested Construction Sequence. It will be maintained so as to prevent the tracking of sediment off -site. Silt / Sediment Fence and Haybales: Silt fence and haybales have been specified to control and contain sediment from leaving areas under disturbance to undisturbed areas. The fence shall be installed as best as possible following the contours and will be spaced in accordance with the NYSSESC. The fence will be inspected daily, repaired, and sediment removed as necessary. Soil Stockpile: Areas are provided for temporary stockpiling of delivered soil material for the construction. These areas will be contained with sediment fence to prevent the movement of sediment. The stockpiles, if not active for more than seven (7) days, will be seeded and mulched. The stockpile areas were placed to best suit the proposed construction activity. The stockpile will be installed as described in the Construction Sequence. Temporary and Permanent Vegetative Cover: This stabilization measure may be temporary and in other cases permanent vegetative cover is used. The vegetative cover specifications are based on the NYSSESC Manual. On the Constructions Plans are notes, locations, and specifications as to the vegetative cover requirements. In the notes, there are specific situations and time constraints related to stabilization of disturbed areas. The specifications give seed and fertilizer mixes as well as placement. Any disturbed area expected to remain exposed for more than seven (7) days shall receive temporary vegetative cover. Storm Drain Inlet Protection: The inlet protection is specified to provide a permeable barrier around drainage inlets to reduce sediment content in runoff before entering the storm drain system. Erosion Blankets: Erosion blankets and seeding shall be used for the stabilization of slopes 3:1 or greater or as otherwise specified. The blankets shall be installed as per the Plans and Details, and the Page 20 of 27 manufacturer's specifications. They shall be stapled or staked in place as per the manufacturer's specifications. The blankets may be installed at locations other than those shown on the Plans as directed by the Town Engineer, Project Engineer, or other persons inspecting the site under the direction of the aforementioned. Soil Restoration: Soil restoration is a required practice for construction projects where soil compaction occurs to soils which will be permanently vegetated. This compaction is typically a result of heavy vehicle traffic, cutting or filling, and areas which may receive heavy surcharges. This becomes more pronounced in soils with greater fines content specifically when wet. These actions can change soil properties which affect its ability to drain or absorb surface water and will also affect the survivability of vegetation. In order to maintain the integrity of the stormwater management plan these areas must receive soil restoration. See Figure 8.1 taken from the NYSSMDM for requirements. This project has soils which fall in the hydrologic soil group HSG "C." Therefore, for most instances, soil restorations are required for the development areas subject to permanent vegetation. Soil restoration can be done by tilling or aerating the soil to a depth of 12-inches. In heavy traffic areas, 3-inches of compost shall be placed over the compacted areas prior to the tilling. After the restoration, a 3/8" metal bar should be able to be hand pushed into the soil. Areas within the drip -line of trees should not be tilled. Rock Outlet Protection: Rock outlet protection is specified at discharge points of pipes and channels to reduce depth, velocity, and the energy of water to avoid downstream erosion. The sizing criteria used is from the NYSSESC Manual. Water Bars: Water bars shall be used for diversion of surface runoff to limit the accumulation of erosive velocities of water. The water bars shall be installed as per the Plans and Details. The water bars may be installed at locations other than those shown on the Plans as directed by the Town Engineer, Project Engineer, or other persons inspecting the site under the direction of the aforementioned. Other Controls: Waste Disposal: Solid, sanitary and toxic waste must be disposed of in a proper manner in accordance with applicable local, state and federal regulations. It is prohibited to burn, bury or pour out onto ground or into the storm sewers any solvents, paints, stains, gasoline, diesel fuel, used motor oil, hydraulic fluid, anti -freeze, cement curing compounds, or other toxic or hazardous wastes. The Contractor shall be responsible for disposal of all waste off site. Concrete Truck Washout: Wash out of cement trucks should occur in a designated diked area where the washings can be collected and disposed of properly when they harden. Page 21 of 27 Dust Control: Generation of dust shall be minimized by limiting the extent of exposed soils and re- establishing vegetative cover in these areas as soon as possible. Additional and/or temporary methods to minimize dust may include wetting, mulching, spray adhesives, stone covering and wind barriers. Stabilization: The Contractor shall initiate stabilization measures as soon as practicable in portions of the site where construction activities have temporarily or permanently ceased, but in no case more than seven (7) days after the construction activity in that portion of the site has temporarily or permanently ceased. This requirement does not apply in the following instance: Where the initiation of stabilization measures by the 7" day after construction activity temporarily or permanently ceased is precluded by snow cover or frozen ground conditions, stabilization measures shall be initiated as soon as practicable. All areas not designated as buildings, roads, driveways, parking lots, walks, or aprons shall be established as lawn or vegetative areas. Permanent planting and vegetation shall be provided per approved the landscaping plan. 9.0 Construction Sequence A key objective of the SWPPP is to reduce erosion and sedimentation potentials for the project. As a means to accomplish this, a suggested construction sequence was developed to assist the developer with incorporating, into the project, various controls designed to reduce such potentials. The sequence considers the performance of development activities in a phased approach, in conjunction with the installation, construction and monitoring of erosion and sedimentation control devices prior to and during construction. Appendix D contains the project specific Suggested Construction Sequence. Essentially, the sequence has been broken down into various activities designed to ensure that certain erosion/sedimentation controls are in place, prior to and during construction, in recognition of site development. Prior to any construction activities, the Owner, Engineer and any Contactors to perform land -disturbing activities shall meet to review this SWPPP to insure a thorough understanding of its contents and overall intent. Certifications to this effect shall be signed by the Owner and Contractor. Certifications are provided on the Construction Plans and in Appendix C. The Responsible Party during and after Construction is as follows: Nikola Grishaj 11 Mudrock Road New City, NY 10596 845-406-0426 10.0 Insoection and Reportin Unless notified by the NYSDEC, the Owner or Operator shall have a qualified inspector conduct site inspections in accordance with the Permit requirements; for a site with on -going soil disturbance activities, a qualified inspector shall conduct a site inspection at least once every seven (7) calendar days. If a project has received prior written approval by the NYSDEC for the Page 22 of 27 disturbance of greater than five (5) acres of soils at any one time, the inspection frequency shall be increased to a minimum of two (2) per seven (7) calendar day period separated by two (2) calendar days for as long as the five (5) acre threshold is exceeded. The qualified inspector, as defined in SPEDES General Permit guidelines, shall prepare an inspection report subsequent to each and every inspection. At a minimum, the inspection report shall include and/or address the following: Date and time of inspection. 2. Name and title of person(s) performing inspection. 3. A description of the weather and soil conditions (e.g. dry, wet, saturated) at the time of inspection. 4. A description of the condition of the runoff at all points of discharge from the construction site. This shall include identification of any discharges of sediment from the construction site. Include discharges from conveyance systems (i.e. pipes, culverts, ditches, etc.) and overland flow. 5. A description of the condition of all natural surface waterbodies located within, or immediately, adjacent to, the property boundaries of the construction site which receive runoff from disturbed areas. This shall include identification of any discharges of sediment to the surface waterbody. 6. Identification of all erosion and sediment control practices that need repair or maintenance. 7 Identification of all erosion and sediment control practice that were not installed properly or are not functioning as designed and need to be reinstalled or replaced. 8. Description and sketch of areas that are disturbed at the time of the inspection and areas that have been stabilized (temporary and/or final) since the last inspection. 9. Current phase of construction of all post -construction stormwater management practices and identification of all construction that is not in conformance with the SWPPP and technical standards. 10. Corrective action(s) that must be taken to install, repair, replace or maintain erosion and sediment control practices; and to correct deficiencies identified with the construction of the post -construction stormwater management practices. 11. Digital photographs, with date stamp, that clearly show the condition of all practices that have been identified as needing correction actions. The qualified inspector shall also take digital photographs, with date stamp, that clearly show the condition of the practice(s) after the corrective action has been completed. Within one business day of the completion of an inspection, the qualified inspector shall notify the Owner or Operator and appropriate Contractor (or Subcontractor) of any corrective actions that need to be taken. The Contractor (or Subcontractor) shall begin implementing the corrective action within one business day of this notification and shall complete the corrective actions in a reasonable time frame. All inspection reports shall be signed by the qualified inspector. A sample inspection report is included in Appendix K. Page 23 of 27 The Owner or Operator shall maintain a record of all inspection reports in a site log book until all disturbed areas have achieved final stabilization and the N.O.T. has been submitted to the DEC. The site log book shall be maintained on site and be made available to the permitting authority upon request. Prior to filing of the Notice of Termination or the end of permit term, the Owner or Operator shall have the qualified professional perform a final site inspection. The qualified professional shall be provided with a certified final asbuilt survey. The survey shall locate and provide detailed information for the permanent stormwater facilities. The information provided shall include and not be limited to the following: rim and invert elevations of all structures, outlets, weirs, etc.; pipe material and sizes; basin dimensions, elevations and topography; and any other pertinent information specific to the stormwater practice constructed. Upon final review of the asbuilt survey and completed site improvements, the qualified professional shall certify that the site has undergone final stabilization 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. The qualified professional shall then complete the Notice of Termination (NOT) to be signed by the Owner. The NOT with the required supporting documentation shall be submitted to the MS4 for signature of approval which will then be forwarded to the NYS DEC. 11.0 Installation and Maintenance of Stormwater Management Practices 11.1 During Construction The Contractor shall be responsible for the installation and maintenance of all temporary erosion control measures. The Contractor shall also be responsible for the installation of permanent control measures. The Operator shall be responsible for the maintenance of all permanent control measures. All temporary erosion control measures installed on the project site shall be observed and maintained to ensure that they are operating as intended as follows: 1. Temporary measures will be inspected by the trained Contractor daily. Any necessary repairs, replacements, or upgrades will be made immediately. 2. Accumulated sediments will be removed as required to keep the measures functional. In the case of silt fencing and haybales (if applicable), remove deposits where accumulations reach half the height of the fence or bale. In the case of sediment basins, remove deposits whenever their capacity has been reduced by fifty percent (50%) from the design capacity. 3. All erosion of the silt fence will be repaired immediately with compacted backfill materials. 4. Disturbed areas, stockpile areas, areas used for storage of materials that are exposed to precipitation shall be inspected for evidence of, or the potential for, pollutants entering the drainage system or downstream. 5. Where discharge locations or points are accessible,they shall be inspected to ascertain whether erosion control measures are effective in preventing significant impacts to receiving waters. Page 24 of 27 6. Locations where vehicles enter or exit the site shall be inspected for evidence of off -site sediment tracking. 7. The permanent storm drainage system shall be inspected and cleaned of all sediment prior to completion of project. 11.2 After Construction The long-term operation and maintenance of the stormwater management system will be the responsibility of the Owner. A legally binding document will be signed detailing the responsible parties and required actions. A sample of the Stormwater Management Inspection and Maintenance Agreement is included, as Schedule "B" in Appendix L. The following is the proposed Inspection and Maintenance Schedule: Control to be Inspectec' Swales an Channels Infiltration Detention Ba Rain Garde In CiPnArni- Inspection Maintenance Maintenance Frequency I Threshold Criteria I Procedure >emi-Annually Bi-annually Bi-annually Quarterly Debris and leaves and Sediment at 5% Debris and leaves and Sediment at 5% Debris and leaves And Sediment at 5% Ponding for more than 48 hours Remove debris and sediment semi-annually Cut Grass — Remove debris and leaves Cut Grass — Remove debris and leaves Remove accumulated sediment and debris; weed and replace plants and mulch as needed. • Controls should be inspected periodically for the first few months after construction and on a semi-annual basis thereafter. They should also be inspected after major storm events (greater than 0.5 inches). • All stormwater controls shall be inspected and cleaned of any debris or sediment. • Any erosion shall be repaired and stabilized with seeding and mulch or stone. • Maintenance and access shall comply with all local, State and Federal safety codes and guidelines. Please note that additional notes regarding maintenance activities are contained on the project Construction Drawings and should be adhered to during and after construction. Page 25 of 27 12.0 Owner / Contractor Responsibilities 12.1 Owner / Operator Certification Statement The is the Owner/Operator of the project for the purpose of this Permit (see Appendix A). The Owner must sign a copy of the Owner's Certification Statement before construction commences (see Appendix C). 12.2 Contractor Certification Statement The Owner is responsible for ensuring all Contractors and Subcontractors associated with site work construction activities identified within this SWPPP agree to implement applicable provisions of the SWPPP and sign a copy of the Contractor Certification Statement (see Appendix C) before construction commences. In addition, the Owner/Operator is responsible to make sure that all Contractors and Subcontractors shall identify at least one person representing the Company at the site will be responsible for implementation of the SWPPP. This person will be known as the Trained Contractor and will have the required 4-hour Certification. This Certification is available through the NYS DEC. The listing of courses can be found at the NYS DEC Website. 12.3 Retention of Records The Owner shall retain a copy of the most current SWPPP at the construction site from the date construction is initiated at the site until the date of construction at the site is completed and the N.O.T. has been filed. Once work is completed, the Owner shall submit to the NYSDEC a Notice of Termination (see Appendix A). The Owner shall retain copies of the N.O.I, N.O.T., Acknowledgement Letter, MS4 SWPPP Acceptance Form, SWPPP and all reports required by the General Permit for a period of five (5) years from the date that the site achieves final stabilization unless the NYSDEC specifies another time period in writing. 13.0 Conclusion The Stormwater Management Plan has been established for this project in accordance with the requirements of NYS DEC GP-0-20-001 and the Town Code of Yorktown. This plan will effectively control stormwater generated by this project during and after construction. The management of the stormwater is based on controlling increases in peak runoff as well as water quality. The design of the water quality component not only will treat runoff due to the project, but also that which is currently not treated. Overall it would improve even the existing conditions. The final design of the project will detail the proposed practices and will establish the method with which they will be constructed. The detail will include layout, grading, plantings, outlet structures, and any other component as required for the design based on the Erosion and Sediment Control established in this Report. These will be part of the project Construction Drawings. The Sequence of Construction and required maintenance will also be set forth as part of the final construction plan. The full Construction Plan shall be considered part of the Stormwater Management Plan or Stormwater Pollution Prevention Plan. The effectiveness of the stormwater practices selected in design will be insured by implementing a maintenance plan. The maintenance plan details specific activities, safeguards Page 26 of 27 and provisions to be monitored and performed by specified frequencies. By adhering to the maintenance plan, optimum performance of the stormwater practices can be expected. Based on the results of the analysis and recommended maintenance practices for the collection and treatment system, the proposed stormwater control designs will provide maximum control efficiency, high effectiveness for removal of pollutants of concern, and the best attainable post -development pollutant loading scenario. In conclusion, the Stormwater Management Plan will not create negative downstream impacts as a result of this project. Joseph C. Riina, RE June 2022 Page 27 of 27 FIGURES GRISHAJ VICINITY MAP 'Nmnrul f'ra Fak , Shrli _ Jar ul• ak ro•^6 SITE s H titrheya H landf Lake ark u.�h Lair Lake Mohegan as Monegaq .blsepan T Fnn _ IL R r.� RaMt F art �:• r�t� i B.- h F kllR�nl ill _i eR, �l Neniamm FranMn ptr411� :>. h� il Jet%, 1 klrrr 1 ,YYILwb7 oFrr r_l J lanrlon r :'flint F'arw SrH an Gkn �� To am Pw.ar.� 1 � art O 'rorktrn+n Falrah •:� f'. CrornP and I/ r F ark �.Ga 4,."1 F.Ii-J44 01 S��r April 15, 2024 1:36,112 0 023 045 09 mi 1 0 0.35 07 1 "4 km County of Weslchesler. Esri HERE, Gamin INCREMENT R USGS. META NASN EPA USDA NYS Department of EnNromrenlal Cc—agon Not a legal do —I NOTE: 0 1. Map Source: USGS 7.5 Minute Series Topographic Quadrangle Map (1:24,000 scale) for Yorktown Heights, Westchester County, New York. NOTE: UNAUTHORIZED ALTERATIONS OR ADDITIONS TO THIS DRAWING IS A VIOLATION OF SECTION 7209 (2) OF THE NEW YORK STATE EDUCATION LAW. t•,;li" - =n IF=r'T V) y ��l �l L 1 NOTE: 1. Map Source: Google Maps Image. FIG 1.2 -VICINITY MAP Site Design Consultants PREPARED Gishaj Nikollr Civil Engineers •Land Planners 251 F Underhill Avenue Yorktown Heights, NY 10598 (914) 962-4488 - Fax (914) 962-7386 NOT TO SCALE Town of Yorktown Westchester County, New York www.sitedesignconsultants.com ilk DATE; 5/7,21 NOTE: UNAUTHORIZED ALTERATIONS OR ADDITIONS TO THIS DRAWING IS A VIOLATION OF SECTION 7209 (2) OF THE NEW YORK STATE EDUCATION LAW. Q m, N. N z r -- m � 0 gunny Ridge Rd joC'y Rd Count•4 of'vVesfchest NOTE: 1. Map Source: NYS Historic Preservation Office, GIS Public Access. FIG 1.3 - HISTORIC MAP Site Design Consultants PREPARED FOR Nikolla Grishaj Civil Engineers •Land Planners 251 F Undm hi I I Avenue Yoi ktown Heights, NY 10598 (914) 9624488 - Fax (914) 962-7386 NOT TO SCALE Town of Yorktown Westchester County, New York www.sitedesignconsultants.coin DATE: 5rn2i NOTE: UNAUTHORIZED ALTERATIONS OR ADDITIONS TO THIS DRAWING IS A VIOLATION OF SECTION 7209 f2) OF THE NEW YORK STATE EDUCATION LAW New York State Stormwater Management Design Manual Chapter 3: Stormwater Management Planning Section 3.6 The Six Step Process for Stormwater Site Planning and Practice Selection Figure 3.1: Stormwater Site Planning and Practice Selection Flow Chart Step 1: Site PlannlnL Refer to Chapter 5 section 5.1-5.2 Step 2: Determine Water Uuallh• Volume (\Wt)v) Refer to Chapter 4 Section 4.1 Steil 3: Runuff Reduction hv.\pnlsing Runoff Reduction Techniques anti S\IP% with RRv Canackv Refer to Chapter 5 Section 5.3 and Chapter 6 Section 6.3-6.5 Yes Step 6: APPIV volume and peak rate control oractices Refer to Chapter 4 Section 4.44.6 Are Quantity control requirements met Yes Complete Plan No Is RRv 2 WQv No Ate there site limitnrions din exaru 1000/6reduction of wQv Yes No las all newly created Has a justification of impervious been NO iofensibifin� been made directed to an RRv for those m eas not ttac6cc 5:en 4: Determine dpecled Yes minimum RRv renuitrd No IS RRv z Min. RRv No 1 Yes Sten 5: Apply SNIP% to address remaining 1Wpv Refer to Chapter 6 3-1 NOTE: 1. Source: NYS DEC Stormwater Design Manual - August 2010 FIGURE 3.1 - STORMWATER SITE PLANNING AND PRACTICE SELECTION FLOW CHART PREPARED FOR Nikolla Grishaj Town of Yorktown Westchester County, New York Site Design Consultants Civil Engineers • Land Planners 251 F Underhill Avenue Yorktown Heights. NY 10598 (914) 962.4488 - Fax (914) 962-7386 NOT Tit SCAT F www.sitedcsigncensuitonts.com nAtl•� i NOTE: UNAUTHORIZED ALTERATIONS OR ADDITIONS TO THIS a m v 09WL9V OlWL9V OWN9V OCLVL90 09WL9V 019*L9V 09WL9V N �_ M V9 66 =U M V9 fib aU N O 01 m W N _ a JaN 4. M 3 m Z ! z m Z m � F �jN m h tR ma 35 01 Z U Cn s � S x v gy 0 mF Z� 0 M9c O9" M9T09 eFL 4� 09w4w O.WLO OacrLV O.LVM fQ811N O.Wn.> tT�:>:p t5OL5 a � a NOTE: 1. Map Source: USDA National Resources Conservation Service, National Cooperative Soil Survey, Web Soil Survey Map. FIG 4.1.1 -SOIL MAP Site Design Consultants PREPARED FOR Civil Engineers .Land Planners Nikolla Grishaj 251 F Underhill Avenue Yorktown Heights, NY 10598 TOWD of Yorktown Westchester County, New York (914) 962-4488 -Fax (914) 962-7386 www.si[edesignconsul[ants.com NOT TO SCALE DATE: 111/21 NOTE: UNAUTHORIZED ALTERATIONS OR ADDITIONS TO THIS DRAWING IS A VIOLATION OF SECTION 7209 (2) OF THE NEW YORK STATE EDUCATION LAW. z O Q O U. Z a Q G z W c� W J IL m N `m mm G_G O y v u y m i42m`o n E Z m �3 cLi mo�0 m <h m o 5 O- m Of J m E O 3 m 9 ° Y 0- O N m m y m e c _ $ 2 m i3 ayi J y L) wo U so E 3 m E�mo °cry a m y N d v�2�m rs m5 z ZN 3 cLio�',v_ Q m N0 rX U m t m E L U W N �m tE C n m m N c� C m 0 N O a ). Ory@ ad .0� O E T fm0 N - a 0c 0v32 m a: 29 a g .O.. m E E o my —12 3 m a-- m �— 5 m m anc m m E � E... �o�L `m a �� z� rn m c V m c d 3> m m o� oa £ y n m E m F y r E as as o ryry L m N Ol lO m � m m m O m N O C r0 f0 Z N m m L A lQ '- C iii=° Q ._. lC m 0 :5 0 9 a N m mNEoi �.E it%lm E3��tinm.v_iE E'camm Nm am t7v Eo w pac�ic m� E m b— �" mm uNv `o '�,�12 n. L° J %£ —i= —n �r 0Em lE� 3 c wEmS� aE t°A3U .aa¢m �`o rn rn t°n- �N ,0.Ew V 3 � = o ¢ ¢ a 4 2! a: 5 — U �V Z W 3 ar c '1 m 0 a V a n C C O m £ _ °a o a a o o �a J e o m o €a a m m U U O Z ❑ate❑❑❑❑❑❑❑❑�--� Z Z y ■ ■ ■ ■ 4 w NOTE: 1. Map Source: USDA National Resources Conservation Service, National Cooperative Soil Survey, Web Soil Survey Map. F4v N w N ° N Of W a O z 11 FIG 4.1.2 - SOIL MAP Site Design Consultants PREPARED r Nikolla Grii shaj Civil Engineers .Land Planners 251 F Underhill Avenue Yorktown Heights, NY 10598 (914) 962-4488 - Fax (914) 962-7386 NOT TO SCALE Town of Yorktown Westchester County, New York wwwsitedesignconsultants.corn )ItDATE: 1171-1 NOTE: UNAUTHORIZED ALTERATIONS OR ADDITIONS TO THIS DRAWING IS A VIOLATION OF SECTION 7209 (2) OF THE NEW YORK STATE EDUCATION LAW. Hydrologic Soil Group —Westchester County, New York Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long -duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows; Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink -swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie -break Rule: Higher Natural Resources i Conservation Service Web Soil Survey National Cooperative Soil Survey NOTE 1. Map Source: USDA National Resources Conservation Service, National Cooperative Soil Survey, Web Soil Survey Map. FIG 4.1.3 - SOIL MAP PREPARED FOR Nikolla Grishaj Town of Yorktown Westchester County, New York Site Design Consultants Civil Engineers • Land Planners 251 F Underhill Avenue Yorktown Heights, NY 10598 (914) 962-4488 - Fax (914) 962-7386 www.s i tedes ignconsu I tants.com 9/1 /2021 Page 4 of 4 NOT TO SCALE DATE: 5/7/31 NOTE: UNAUTHORIZED ALTERATIONS OR ADDITIONS TO THIS DRAWING IS A VIOLATION OF SECTION 7209 (2) OF THE NEW YORK STATE EDUCATION LAW. Hydrologic Soil Group —Westchester County, New York Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI PnB Paxton fine sandy loam, 3 to 8 percent slopes C 11.0 40.2% PnC Paxton fine sandy loam, 8 to 15 percent slopes C 4.9 17.8% PnD Paxton fine sandy loam, 15 to 25 percent slopes C 1.2 4.2% RdB WdB Ridgebury complex, 3 to 8 percent slopes Woodbridge loam, 3 to 8 percent slopes D C/D 2.2 8.2 7.9% 29.9% Totals for Area of Interest 27.4 100.0% us�DDAA Natural Resources Web Soil Survey 9/1/2021 Conservation Service National Cooperative Soil Survey Page 3 of 4 ' / \ _ r/iW 1100 f I I I u 1 1 �—�.000 175U e TP#5 TP#4 -� ' 2 U N o w o \ gCOF1ELOW o•OwA � r — � �� alp � ' / � •N ¢ � m TP#8 1 1 \ U s i l teary o DA— 2 1 �� TP#2 0 \ l �i ---------------T�*° Lu TERSHED� \ ♦ 1 1 ♦ 1 / 000 r„ 1 y Concrete Curb POINT DRIVE peare a •`Ir \ .\ TP#9 \ /000 ' \�� '��� -, s ►` [ FLOW PATH - TIME OF CONCENTRATION / t �— I '.4 B/ ' V I WCATIONIN j7ll / ,� � s \•\ — — —� \ \ s s �s\ I I / LOCATION /B TP#8 I \ ,...... 00 z o Cn ' 0 15 30 80 .00 LrL=l ' 1 SCALE1"=30'4" SAFE DIG NOTE: y ' ' ' \ 13*1" YOU 1111, Ora a 0111r I THISISNOTASURVEY ALL SURVEY INFORMATION SHOWN ON THIS PLAN HAS BEEN 1 \ FIG - 5.1 TAKEN FROM SURVEY MAP PREPARED BY NAME OF SURVEYOR, DATEDXWXYJXX LAST®4�W�T R EVISEDXXIXXIXX THE ENGINEER ASSUMES NO RESPONSIBILITY FOR ITS ACCURACY 1