French American School of New York

Transcription

1 STORMWATER POLLUTION PREVENTION PLAN French American School of New York 400 RIDGEWAY CITY OF WHITE PLAINS, NEW YORK Applicant/Operator/ Owner: French American School of New York 525 Fenimore Road Mamaroneck, NY Prepared by: 120 Bedford Road Armonk, NY JMC Project Date: Revised: Revised: 05/20/ /03/ /05/2014 F:\2010\10170\SWPPP docx

2 TABLE OF CONTENTS SECTION TITLE PAGE I. INTRODUCTION... 1 II. STORMWATER MANAGEMENT PLANNING... 2 III. STUDY METHODOLOGY... 2 IV. EXISTING CONDITIONS... 5 V. PROPOSED CONDITIONS VI. DAM MODIFICATION IMPROVEMENTS VII. SOIL EROSION & SEDIMENT CONTROL VIII. CONSTRUCTION PHASE AND POST-CONSTRUCTION MAINTENANCE IX. CONCLUSIONS APPENDICES FIGURES DESCRIPTION 1. Site Location Map 2. Key Map APPENDIX DESCRIPTION A. Existing Hydrologic Calculations B. Proposed Hydrologic Calculations C. NYSDEC Stormwater Sizing Calculations Runoff Reduction and Water Quality Volume and Stream Channel Protection Calculations StormTech Chambers Sizing Calculations D. Contractor s Certification E. Owner's Certification F. Stormwater Practice Construction Inspection Checklists G. Operation and Maintenance Temporary Erosion and Sediment Control Inspection and Maintenance Checklist Maintenance Inspection Checklists NYSDEC Standard and Green Practice Maintenance Requirements i

3 StormTech Isolator Row O&M Manual CDS Operation and Maintenance Manual H. Drainage Area Drawings DA-1 "Existing Drainage Area Map" DA-2 "Proposed Drainage Area Map" I. Dam Drawings: DIP-1 "Dam Improvement Plan" DIP-2 "Dam Improvement Plan" DIP-3 "Dam Improvement Details" DIP-4 "Dam Improvement Sections" Carlin-Simpson and Associates Drawings and Information: DRP-1 Dam Reconstruction Plan Inspection and Maintenance Plan for Dam ii

4 REFERENCED DRAWINGS FOR SWPPP DESIGN AND DETAILS JOHN MEYER CONSULTING, PC SITE PLANS Dwg. No. Title Date SP-1 Cover Sheet 05/05/2014 SP-2 Overall Existing Conditions Plan 05/05/2014 SP-3 Site Existing Conditions Plan (Area 1) 05/05/2014 SP-4 Site Existing Conditions Plan (Area 2) 05/05/2014 SP-5 Site Existing Conditions Plan (Area 3) 05/05/2014 SP-6 Site Existing Conditions Plan (Area 4) 05/05/2014 SP-7 Site Existing Conditions Plan (Area 5) 05/05/2014 SP-8 Site Demolition Plan (Area 1) 05/05/2014 SP-9 Site Demolition Plan (Area 2) 05/05/2014 SP-10 Site Demolition Plan (Area 3) 05/05/2014 SP-11 Site Demolition Plan (Area 4) 05/05/2014 SP-12 Site Demolition Plan (Area 5) 05/05/2014 SP-13 Overall Site Layout Plan 05/05/2014 SP-14 Site Layout Plan (Area 1) 05/05/2014 SP-15 Site Layout Plan (Area 2) 05/05/2014 SP-16 Site Layout Plan (Area 3) 05/05/2014 SP-17 Site Layout Plan (Area 4) 05/05/2014 SP-18 Site Layout Plan (Area 5) 05/05/2014 SP-19 Site Grading Plan (Area 1) 05/05/2014 SP-20 Site Grading Plan (Area 2) 05/05/2014 SP-21 Site Grading Plan (Area 3) 05/05/2014 SP-22 Site Grading Plan (Area 4) 05/05/2014 SP-23 Site Grading Plan (Area 5) 05/05/2014 SP-24 Site Utilities Plan (Area 1) 05/05/2014 SP-25 Site Utilities Plan (Area 2) 05/05/2014 SP-26 Site Utilities Plan (Area 3) 05/05/2014 SP-27 Site Utilities Plan (Area 4) 05/05/2014 SP-28 Site Utilities Plan (Area 5) 05/05/2014 SP-29 Site Sediment & Erosion Control Plan (Area 1) 05/05/2014 SP-30 Site Sediment & Erosion Control Plan (Area 2) 05/05/2014 SP-31 Site Sediment & Erosion Control Plan (Area 3) 05/05/2014 SP-32 Site Sediment & Erosion Control Plan (Area 4) 05/05/2014 SP-33 Site Sediment & Erosion Control Plan (Area 5) 05/05/2014 SP-34 Preliminary North Street Site Driveway Intersection Improvement Plan 05/05/2014 SP-39 Construction Details 05/05/2014 SP-40 Construction Details 05/05/2014 SP-41 Construction Details 05/05/2014 SP-42 Construction Details 05/05/2014 iii

5 I. INTRODUCTION This Stormwater Pollution Prevention Plan (SWPPP) has been prepared for the French-American School of New York (FASNY) and is intended to present the physical conditions, planning and engineering criteria as well as demonstrate that the development is designed in accordance with the requirements of the City of White Plains and the New York State Department of Environmental Conservation (NYSDEC) SPDES General Permit for Stormwater Discharges from Construction Activity (Permit No. GP ). The SWPPP has been designed to ensure that the quantity and quality of stormwater runoff during and after development are not substantially altered from pre-development conditions. The project includes a 950 student school/campus on a ±131 acre Site, previously occupied by the Ridgeway Country Club (RCC) at 400 Ridgeway, located between Bryant Avenue and Ridgeway in the City of White Plains in Westchester County, New York (hereinafter referred to as the "Site"). Refer to Figure No. 1 Site Location Map for the general vicinity of the Site and surrounding areas. The Site is divided into four (4) separate parcels A, B, C and D. The parcel designations identified below are for the purpose of describing the proposed development and do not reflect the deed information depicted on the Boundary Survey. Refer to Figure No. 2 "Key Map" for the parcel designations. The majority of the proposed improvements are within the portion of the Site between Ridgeway and Gedney Esplanade, on Parcel A and the southern side of Parcel D. In addition to the residential homes surrounding the property, the Site is also adjoined by: Burke Rehabilitation Hospital on Mamaroneck Avenue, to the west Bryant Gardens, a 409-unit cooperative apartment complex on Bryant Avenue, to the northwest YWCA Activities Center on North Street, to the northeast First Baptist Church on North Street, to the northeast Garden Center on Ridgeway, to the south Westchester Hills Golf Club across Ridgeway, to the south 1

6 FRENCH-AMERICAN SCHOOL OF NEW YORK 400 RIDGEWAY CITY OF WHITE PLAINS, NY SITE LOCATION MAP DATE: 05/05/2014 FIGURE:1 JMC PROJECT: SCALE: 1"=2000'

7 MACY AVE OXFORD RD NORTH ST NEW YORK-PRESBYTERIAN HOSPITAL BRYANT AVE MIDDALE RD LEIR CT BRYANT CRES HEATHERBLOOM RD HATHAWAY LN OXFORD RD GABRIEL CT BRYANT GARDENS YWCA WHITE PLAINS HIGH SCHOOL SECTION , BLOCK 1, LOT 6 PARCEL 'C' (15.58 ± ACRES) HEATHER LN NORTHDALE RD SOUTHDALE RD SECTION , BLOCK 12, LOT 1 PARCEL 'E' (0.70 ± ACRES) ROBINHOOD RD NORTH ST BURKE REHABILITATION HOSPITAL EXISTING POND ANTONY RD HEATHERBLOOM RD ROBINHOOD RD SECTION , BLOCK 2, LOT 3 PARCEL 'B' (14.05 ± ACRES) ROBINHOOD RD HATHAWAY LN SECTION , BLOCK 3, LOT 43 PARCEL 'D' (72.32 ± ACRES) STANLEY RD MONROE DR GEDNEY ESPLANADE HOTEL DR MURCHISON PL SECTION , BLOCK 9, LOT 3 PARCEL 'A' (27.74 ± ACRES) POOL RIDGEWAY EXISTING POND FRENCH-AMERICAN SCHOOL OF NEW YORK 400 RIDGEWAY CITY OF WHITE PLAINS, NY KEY MAP DATE: 05/05/2014 FIGURE: 2 JMC PROJECT: SCALE: 1" = 600'

8 II. STORMWATER MANAGEMENT PLANNING In order to be eligible for coverage under the NYSDEC SPDES General Permit for Stormwater Discharges from Construction Activity (Permit No. GP ), effective January 29, 2010, the SWPPP includes stormwater management practices (SMP's) from the publication "New York State Stormwater Management Design Manual," last revised August A SWPPP has been prepared for this project because it is a construction activity that involves soil disturbances of one (1) or more acres of land. The proposed SMP s have been designed such that the quantity and quality of stormwater runoff during and after construction are not adversely altered or are enhanced when compared to predevelopment conditions. Based on these criteria, the project and its SWPPP are eligible for coverage under SPDES General Permit GP , subject to approval by the City of White Plains as a designated Municipal Separate Storm Sewer System (MS4) under the general permit. Based on the GIS information provided by the website of the New York State Office of Parks, Recreation and Historic Places, the Site does not contain, nor is it immediately adjacent to any properties listed on the State or National Register of Historic Places. III. STUDY METHODOLOGY Runoff rates were calculated based upon the standards set forth by the United States Department of Agriculture Natural Resources Conservation Service Technical Release 55, Urban Hydrology for Small Watersheds (TR-55), dated June The methodology set forth in TR-55 considers a multitude of characteristics for watershed areas including soil types, soil permeability, vegetative cover, time of concentration, topography, rainfall intensity, ponding areas, etc. The 1, 10, 25, 50 & 100 year storm recurrence intervals were reviewed in the design of the stormwater management facilities (see Appendices A & B Existing & Proposed Hydrologic Calculations). 2

9 Anticipated drainage conditions were analyzed taking into account the rate of runoff which will result from the construction of buildings, parking areas and other impervious surfaces associated with the Site development. Base Data and Design Criteria For the stormwater management analysis, the following base information and methodology were used: 1. The Site drainage patterns and outfall facilities were reviewed by John Meyer Consulting personnel for the purpose of gathering background data and confirming existing mapping of the watershed areas. 2. An Existing Drainage Area Map was developed from the topographical survey. The drainage area map reflects the existing conditions within and around the project area. 3. A Proposed Drainage Area Map was developed from the proposed grading design superimposed over the topographical survey. The drainage area map reflects the proposed conditions within the project area and the existing conditions to remain in the surrounding area. 4. The United States Department of Agriculture (USDA) Web Soil Survey of the Site available on its website at 5. The United States Department of Agriculture Natural Resources Conservation Service National Engineering Handbook, Section 4 - Hydrology", dated March The United States Department of Agriculture Natural Resources Conservation Service Technical Report No. 55, Urban Hydrology for Small Watersheds (TR-55), dated June

10 7. United States Department of Commerce Weather Bureau Technical Release No. 40 Rainfall Frequency Atlas of the United States. 8. The time of concentration was calculated using the methods described in Chapter 3 of TR- 55, Second Edition, June Manning's kinematics wave equation was used to determine the travel time of sheet flow. The 2-year 24 hour precipitation amount of 3.5 inches was used in the equation for all storm events. The travel time for shallow concentrated flow was computed using Figure 3-1 and Table 3-1 of TR-55. Manning's Equation was used to determine the travel time for channel reaches. 9. All hydrologic calculations were performed with the Bentley PondPack software package. 10. The New York State Stormwater Management Design Manual, revised August New York Standards and Specifications for Erosion and Sediment Control, August The storm flows for the 1, 10, 25, 50 & 100 year recurrence interval storms were analyzed for the total watershed areas. The Type III distribution design storm for a 24 hour duration was used and the mass rainfall for each design storm is as follows: 24 Hour Rainfall Amounts Design Storm Recurrence Interval Inches of Rainfall 1 Year Year Year Year Year 7.5 4

11 IV. EXISTING CONDITIONS The Site is currently located in the R1-30 Residential One Family Zoning District (R1-30 District), and is approximately acres in size. It is made up of five separate tax parcels: Section , Block 2, Lot 3; Section , Block 9, Lot 3; Section , Block 1, Lot 6; Section , Block 3, Lot 43; Section , Block 12, Lot 1. Existing conditions on the Site include natural features such as a lake, a creek, state designated wetlands and minimal steep slopes. The Site has been operating as a golf course since The Site is currently used and classified for zoning purposes as a Golf and Country Club with an 18 Hole Golf Course. The site currently includes: (1) an 18 hole golf course; (2) a 53,735 square foot club house and accessory buildings housing, among other things, offices, locker rooms, saunas, a banquet hall and grill room; (3) eight tennis courts; (4) a swimming pool, and (5) parking for approximately 177 vehicles. Parcel A (designated on Tax Maps as Section , Block 9, Lot 3) is ±27.74 acres in size. It is bound by Ridgeway to the south, Hathaway Lane to the east and Gedney Esplanade to the north. The western edge of the parcel is bound by single-family homes. Parcel A contains a majority of the former Country Club facilities, including: Clubhouse Building (main entrance, offices, dining/banquet facilities) Annex Building (locker room, maintenance, cart storage) Pool Paved Parking areas (±123 spaces) 10 Tennis Courts (8 in southwest corner, 2 in northeast corner of parcel) Pro Shop Building Driving Range 4 of 18 Golf Holes (#10, 11, 12 and 18) 5

12 Access to the Club on Parcel A is via three (3) curb cuts on Ridgeway, and one (1) on Hathaway Lane. Parcel B (designated on Tax Maps as Section , Block 2, Lot 3) is ±14.05 acres in size. It is bound by Gedney Esplanade to the south, and Heatherbloom Road to the north. The eastern and western edges of the parcel are bound by single-family homes. Parcel B contains 2 of 18 golf holes on the course (No s 13 and 17). Parcel C (designated on Tax Maps as Section , Block 1, Lot 6) is ±15.58 acres in size. It is bound by Bryant Avenue to the north, and Heatherbloom Road to the east and south. The northern edge is also bound by two (2) single-family homes on Bryant Avenue. The western edge of the parcel is bound by the Burke Rehabilitation Hospital and Bryant Gardens. Parcel C contains 3 of 18 golf holes on the course (No. s 14, 15 and 16). Parcel D (designated on Tax Maps as Section , Block 3, Lot 43) is ±72.32 acres in size; the largest of the four parcels. It is bound by Ridgeway to the south, Hathaway Lane to the west, Bryant Avenue to the north and North Street to the east. The southern edge of the parcel is bound by single-family homes on Ridgeway, as well as a Landscape/Nursery retail business. The eastern edge is bound partly by a "paper street," and by single family homes on Robinhood Road and North Street. The northeastern edges are bound by single-family homes and the YWCA and First Baptist Church on North Street. 557 North Street (designated on Tax Maps as Section Block 12, Lot 1) is approximately 0.70 acres in size. It maintains frontage on North Street and contains a single family residential home. Parcel D consists mainly of 9 of 18 golf holes (No.'s 1 through- 9). The parcel also contains a paved parking area (±54 spaces) at the southern end with access via a curb cut on Hathaway Lane. A small building within the paved area serves as the starter's hut/caddie shack. The parcel includes two (2) connected ponds. These serve as water features for the golf course. 6

13 The Site s topography is varied with elevations ranging between ±246 feet and ±320 feet North American Vertical Datum (NAVD 1988). The Site is located within the Mamaroneck River drainage basin which is within the Lower Long Island Sound drainage basin. The Site straddles an area of higher elevation between Hathaway Lane, Oxford Road and Heatherbloom Road containing single-family homes (between Parcels B, C and D). As previously mentioned, the development area is primarily between Ridgeway and Gedney Esplanade, on Parcel A and the southern side of Parcel D. Stormwater runoff generally drains off of the development area in a southerly direction towards Ridgeway. Runoff from the west side of Hathaway Road (Parcel A) drains south into existing drain inlets throughout the Site and connects into the City of White Plains drainage system along Ridgeway. The drainage system exits the Site through two parallel adjacent 30 inch diameter reinforced concrete pipes (RCP) beneath Ridgeway just east of the existing tennis courts, into a 48 inch by 24 inch concrete box culvert and an existing stream south of Ridgeway. Runoff from the east side of Hathaway Lane (Parcel D) drains east into existing drain inlets within the golf course which discharge to a watercourse and continues into a large pond. The large pond discharges to another watercourse farther east which conveys stormwater to wetlands along the eastern Site boundary. Stormwater from the wetlands eventually discharges to another portion of the City of White Plains drainage system farther northeast along Ridgeway. The following natural features and drainage patterns of the project Site have been identified and utilized to develop Drawing DA-1 Existing Drainage Area Map which is included in Appendix H: Wetlands Watercourses Buffers Forest, vegetative cover Topography (contour lines, existing flow paths, steep slopes, etc.) Soil (hydrologic soil groups, etc.) 7

14 Based on the United States Department of Agriculture (USDA) Web Soil Survey, the on-site soils are generally moderately drained and belong to hydrological groups B, C & D. The soil types, boundaries and drainage areas/designations are depicted on Drawing DA-1 within Appendix H. Seven separate Design Points (1, 2, 3, 4, 5, 6 & 7) were identified for comparing peak rates and volumes of runoff in existing and proposed conditions. Eleven separate drainage areas were identified in existing conditions based on the existing drainage divides on and off-site. Refer to Drawing DA-1 in Appendix H. The following is a description of each of the drainage areas analyzed in the existing conditions analysis: Design Point #1 Design Point #1 is located at an existing catch basin on the north side of Ridgeway just east of the existing tennis courts near the middle of the frontage of Parcel A. All of the contributing drainage area flows either overland or through existing pipes and eventually meets at the existing catch basin. The following drainage areas ultimately contribute runoff to this design point, as described below: Existing Drainage Area 1A (EDA-1A) is acres in size and consists of a majority of Parcel A bordered by Ridgeway, Gedney Esplanade, Hathaway Lane and several residential homes along Murchison Place, Hotel Drive and Macy Road. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 78 and 27 minutes, respectively. A small portion of the golf course north of Gedney Espalande, designated as Parcel B drains south, across Gedney Espalande and onto Parcel A. EDA-1 drains south from some residential homes along Macy Road, across the golf course and eventually into an existing drain inlet at the northeast corner of the existing tennis courts. The runoff is piped into an existing drainage system with two parallel 30 inch diameter pipes before exiting the Site and connecting to an existing drain inlet within Ridgeway designated as Design Point #1. 8

15 Existing Drainage Area 1B (EDA-1B) is acres in size and consists of many residential homes, roadways and a portion of the golf course north of Gedney Espalande. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 77 and 26 minutes, respectively. EDA-1B drains south across the golf course to the existing drainage system in Gedney Esplanade. Several catch basins in Gedney Espalande collect this runoff at Junction 1B before it is piped to a manhole in Gedney Espalande midway between Macy Road and Oxford Road. The system conveys the runoff south onto Parcel A through a series of pipes and manholes approximately 1,500 linear feet in length which is designated as Reach 1B. There are several underdrains located within the golf course that collect runoff that infiltrates through the fairways, rough areas, etc. and discharge it into the series of pipes travelling across the Site. As the system traverses the Site from Gedney Espalande to Ridgeway, the pipe begins as 30 inch diameter, then increases to 36 inch diameter, then 42 inch diameter and finally two parallel 30 inch diameter pipes before exiting the Site and connecting to an existing drain inlet within Ridgeway designated as Design Point #1. Design Point #2 Design Point #2 is the wetland area at the southeast corner of the property along Ridgeway. This location for Design Point #2 was chosen as a point of analysis because it receives stormwater runoff from the development area under proposed conditions and all upstream areas on-site outside of the developed area as well. The following drainage areas ultimately contribute runoff to this design point, as described below: Existing Drainage Area 2A (EDA-2A) is acres in size and consists of a portion of Parcel D bordered by Ridgeway, Hathaway Lane and several residential homes along Ridgeway and Hathaway Lane. EDA-2 consists of roadways, the RCC golf course, tennis courts, residential homes, driveways, lawns and wooded areas. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 75 and 35 minutes, respectively. A small portion of Parcel A along Hathaway Lane drains east across the roadway and onto Parcel D. Residential homes along Ridgeway drain north onto the Site, across the golf course and into a depressed area with several drain inlets. Residential homes along 9

16 Hathaway Lane and Oxford Road drain east to a portion of a drainage system within Hathaway Lane which runs east through the Site, across the golf course and connects to a manhole within the depressed area of the golf course. The stormwater runoff travels north along the depressed area until being collected by a drain inlet, then it is conveyed north within the drainage system until discharging from the pipe to Junction 2A into an existing swale designated as Reach 2A to Junction 2ACD where it is combined with flows from EDA-2C and the outlet flows from the existing large pond. The flows then travel along another watercourse, designated as Reach 2ACD, which discharges to the wetland area to Design Point #2. Existing Drainage Area 2B (EDA-2B) is acres in size and consists of a portion of Parcel D to the east of the ridge line running north-south along the center of the southern end of Parcel D which divides EDA-2A and EDA-2B. All of the stormwater runoff to the east of the ridge drains east overland, through the wooded area and towards the wetland area. EDA-2B consists of the RCC golf course, some cart paths, lawns, woods and the wetland area. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 65 and 18 minutes, respectively. Runoff drains east off of the ridge, across a portion of the golf course, into the wooded area and into the wetland area where it exits the Site just upstream of the wetland area, designated as Design Point #2. Existing Drainage Area 2C (EDA-2C) is 3.25 acres in size and consists of a small portion of Parcel D along Hathaway Lane and a few residential properties off-site. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 75 and 18 minutes, respectively. Runoff drains east off of the residential properties, across Hathaway Lane, over a portion of the golf course, into an existing swale to Junction 2ACD where it combines with flows from EDA-2A and the large pond. The flows then travel along another watercourse, designated as Reach 4 which discharges to the wetland area, designated as Design Point #2. 10

17 Existing Drainage Area 2D (EDA-2D) is acres in size and consists of the large pond and portions of the golf course within Parcel D, some cart paths, lawns and wooded areas. A few residential properties also drain to the large pond. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 80 and 19 minutes, respectively. Runoff drains east off of the residential properties along Hathaway Lane, across a portion of the golf course, and into the large pond which has a water surface elevation of There is a defined overflow area that varies in elevation (lowest being ) adjacent to the outlet pipe that conveys outlet flows to the existing watercourse during larger storm events. The maximum water surface elevation of the pond during the 100 year storm is The large pond has an outlet that consists of an 18 inch diameter corrugated metal pipe (CMP) at invert which releases the outlet flows to a catch basin and pipe that discharges to an existing watercourse, designated as Reach 2ACD, which starts at Junction 2ACD and flows down to the wetland area, designated as Design Point #2. Design Point #3 Design Point #3 is an existing pipe which discharges to the municipal drainage system along the northeast property boundary south of Southdale Road. It is hydrologically the point of analysis along the portion of the site that drains off-site in this direction. A low point along the golf course with a drain inlet collects runoff from a majority of EDA-3. The following drainage area ultimately contributes runoff to this design point, as described below: Existing Drainage Area 3 (EDA-3) is acres in size and consists of a portion of Parcel D north of the large pond and residential properties along Hathaway Lane. EDA-3 consists of the golf course, some cart paths, lawns and wooded areas as well as residential properties. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 76 and 23 minutes, respectively. Runoff drains east off of the residential properties, across a portion of the golf course, into the low area and drain inlet along the golf course where it is conveyed through pipes off-site. The area/portion of the property boundary where flows exit the property is designated as Design Point #3. 11

18 Design Point #4 Design Point #4 is at a low point along the northeastern boundary of the Site adjacent to Byrant Avenue. All of the stormwater runoff to the south of Bryant Avenue between Heatherbloom Road and Northdale Road drains onto the golf course overland and towards Bryant Avenue. This location for the following drainage area ultimately contributes runoff to this design point, as described below: Existing Drainage Area 4 (EDA-4) is acres in size and consists of the northeast corner of Parcel D containing, some cart paths, lawns and wooded areas within the golf course as well as surrounding residential properties and roadways. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 76 and 22 minutes, respectively. Runoff drains north off of the golf course to Bryant Avenue which is designated as Design Point #4. Design Point #5 Design Point #5 is at a low point along the northwestern boundary of the Site adjacent to Bryant Avenue. The stormwater runoff from the golf course and a few residential properties along Heatherbloom Road drains to the northwestern property corner along Bryant Avenue. The following drainage area ultimately contributes runoff to this design point, as described below: Existing Drainage Area 5 (EDA-5) is 7.48 acres in size and consists of the northernmost portion of Parcel C to Bryant Avenue containing some cart paths, lawns and wooded area within the golf course as well as residential properties and adjacent roadways. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 76 and 13 minutes, respectively. Runoff drains west off of the residential properties, across a portion of the golf course, where it exits the Site at Design Point #5. 12

19 Design Point #6 Design Point #6 is the point where an existing watercourse exits the site along the western boundary. All of the remaining stormwater runoff within Parcel C north and west of Heatherbloom drains north overland into the watercourse and off-site. The following drainage area ultimately contributes runoff to this design point, as described below: Existing Drainage Area 6 (EDA-6) is acres in size and consists the majority of Parcel C including some cart paths, lawns and wooded areas within the golf course as well as residential properties and adjacent roadways. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 76 and 24 minutes, respectively. Runoff drains north from Heatherbloom Road, across a portion of the golf course and into the watercourse to Design Point #6. Design Point #7 Design Point #7 is at a low point along the south side of Heatherbloom Road. A ridge running east-west along the center of the golf course in Parcel B is the drainage divide between EDA-7 and EDA-1B. All of the stormwater runoff from the golf course to the north of the ridge drains north overland to the low point. This location for Design Point #7 was chosen as a point of analysis because it is the lowest point within the drainage area and stormwater either accumulates and infiltrates into the ground or is conveyed by an underdrain system to an unknown location. The following drainage area ultimately contributes runoff to this design point, as described below: Existing Drainage Area 7 (EDA-7) is 9.41 acres in size and consists of the northern portion of Parcel B which is cart paths, lawns and wooded areas within the golf course as well as few residential properties and a portion of Oxford Road. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 77 and 16 minutes, respectively. Runoff drains west off of the residential properties, across a portion of the golf course and eventually to the low point designated as Design Point #7. 13

20 The peak rates of runoff to the design points from the drainage areas for each storm are shown in the table below: Table 1 Summary of Peak Rates of Runoff in Existing Conditions (Cubic Feet per Second) Storm Recurrence Interval DP-1 DP-2 DP-3 DP-4 DP-5 DP-6 DP-7 1 year year year year year The volumes of runoff to each design point are shown in the table below, as well as the total volume of runoff produced by the entire contributing drainage area: Storm Recurrence Interval Table 2 Summary of Runoff Volumes in Existing Conditions (Cubic Feet) DP-1 DP-2 DP-3 DP-4 DP-5 DP-6 DP-7 Total Volume 1 year 183, ,655 54,782 52,553 23,970 55,425 31, , year 506, , , ,937 68, ,181 89,590 1,854, year 669, , , ,216 91, , ,830 2,435, year 838,504 1,150, , , , , ,117 3,038, year 924,432 1,262, , , , , ,554 3,346,603 14

21 V. PROPOSED CONDITIONS The project includes a 950 student school/campus for Nursery, Pre-School, Kindergarten and Grades 1 through 12 consisting of the following proposed buildings and facilities: Nursery, Pre-School, Kindergarten and Grades 1 through 5 are proposed together in one building on Parcel D Multipurpose Playing Field, Play Areas for the Nursery, Pre-K, Kindergarten and Grades 1 through 5 on Parcel D Middle School for Grades 6 through 8, High School for Grades 9 through 12 and a Performing Arts, Gymnasium and Auditorium for the Middle and High Schools all together on Parcel A Tennis Courts, Running Track, Multipurpose Playing Fields, Softball/Baseball Field, Basketball Court, etc. on Parcel A Parking areas, access driveways, sidewalks, landscaping and stormwater management basins throughout the Site The parcel designations identified below are for the purpose of describing the proposed development and do not reflect the deed information depicted on the Topographic and Utilities Survey. In addition to the Parcels previously identified, Hathaway Lane, between Gedney Esplanade and Ridgeway is proposed to be abandoned. Parcels A and D will be merged together as a result of the abandonment. Parcels A and D includes the construction of a High School, Middle School, Gymnasium and Performing Arts Building. A portion of the existing building adjacent to Ridgeway will remain. Bus and vehicle drop-off traffic loops will be constructed adjacent to the new buildings. Parking will be provided in multiple areas on Parcel A and D, primarily to serve the Middle and High Schools needs. Athletic fields will occupy the western portion of Parcel A. The existing tennis courts will be removed and six new tennis courts will be constructed as hard surfaces. Stormwater management facilities will occupy the area adjacent to Ridgeway south of the Tennis Courts. 15

22 The Lower School which includes the Nursery to Kindergarten program, and the Grades 1 through 5 program will be constructed on Parcel D. Bus and vehicle drop-off loops will be provided, with short-term parking nearby for parents dropping off the youngest children adjacent to the lower school. Staff, teacher, and visitor parking will also be located nearby. Play areas, with play structures and a youth Athletic Field, will be located on the southern half of Parcel D. The vast majority of Parcel D, including the pond area, surrounding wetlands, and wooded area will remain open space and included in the proposed Greens to Green Conservancy. The main access to the Campus will be provided from North Street via an asphalt driveway which traverses Parcel D. Parcel B is proposed as open space and included in the proposed Greens to Green Conservancy with the exception of the FASNY Gardens which will be located on the southern side of Parcel C. Parcel C is proposed as open space and included in the proposed Greens to Green Conservancy. Under future conditions, stormwater runoff from the impervious surfaces on the developed Site, including roadways, parking areas, driveways, sporting facilities and sidewalks will be collected and conveyed by vegetated swales, riparian buffers, catch basins and underdrains drains and conveyed by a network of high density polyethylene (HDPE) drain pipe installed underground which discharge to the proposed stormwater management basins. Runoff from a portion of the building rooftops will be collected into roof drains which will discharge into stormwater practices including green roofs and subsurface infiltration system which treat stormwater prior to entering the underground storm pipes which will convey stormwater to the proposed stormwater management basins. Runoff from portions of the landscaped areas will either continue to flow offsite similar to existing conditions or be conveyed into the stormwater management basins. Vegetated swales, catch basins and underdrains will be installed at strategic locations and the Site will be graded to direct runoff into these facilities for collection, treatment and conveyance to the stormwater management basins. 16

23 The existing golf course lawns in the fairways, greens and rough areas shall be converted and maintained meadow and gardens. Some of the existing paved golf cart paths will remain and others will be converted to eco-sensitive trails which will form a network of biking and walking trails throughout the Conservancy. All wooded areas shall remain. As a result of the above changes to the land cover types throughout the property and the proposed stormwater management practices, the total runoff rates and volumes of all areas in proposed conditions, draining off-site will be decreased. This section describes the design and analysis of the proposed conditions used to demonstrate that the SWPPP meets the requirements of the General Permit. The Five Step Process For Stormwater Site Planning and Practice Selection The project s design and its SWPPP have been developed in accordance with the NYSDEC s Five Step Process for Stormwater Site Planning and Practice Selection of the New York State Design Manual, as described below: Step 1: Site Planning The project has been designed to protect natural resources, minimize disturbances and restore golf course surfaces to natural land coverage types. The majority of the project is within the portion of the Site in between Ridgeway and Gedney Esplanade (Parcels A & D) with the exception of the main driveway which traverses Parcel D to North Street. Hathaway Lane between Gedney Esplanade and Ridgeway is proposed to be abandoned. The Site s slopes vary throughout the property and there is a minimal amount of undisturbed land coverage. The existing wetlands at the southeast corner of the site, their respective regulated wetland buffers and any existing wooded areas have been respected by the proposed design. The access driveways onto the campus will be provided from a new driveway from North Street. The design of the proposed Site topography will minimize earthwork cuts and fills to the 17

24 maximum extent practicable, and utilize a significant amount of erosion controls and stabilization. Significant portions of the Site will remain undeveloped in proposed conditions. The following practices and Site features were incorporated in the Site design: Preserving hydrology - Maintaining drainage divides Wetlands and buffers The Site includes approximately 8.9 acres of wetlands, however the project does not propose any disturbance to the NYSDEC regulated wetlands or wetland buffers. Floodplain considerations - The Site is not located within the 100 year flood zone. Watercourses (intermittent) The location, setback, cross section, etc. of the existing watercourses have been maintained. Forest, vegetative cover The amount of existing forest has been maintained and the maximum amount of existing vegetative cover has been provided. Topography (contour lines, existing flow paths, steep slopes, etc.) has been maintained or disturbed to the minimum extent practicable. Soil (hydrologic soil groups, etc.) Depths to groundwater and other restrictive layers of soil. Step 2: Determine Water Quality Treatment Volume (WQv) This initial calculation of WQv must be revised after green infrastructure techniques are applied. The following method has been used to calculate the WQv. 90% Rule - According to the New York State Stormwater Design Manual, Section 4.1, the water quality volume is determined by the 90% rule. The method is based on 90% of the average annual stormwater runoff volume which must be provided due to impervious surfaces. The WQv is directly related to the amount of impervious cover created at a site. The rainfall depth depends on the location of the site within the state. From this depth of rainfall, the required water quality volume is calculated. 18

25 Step 3: Runoff Reduction Volumes (RRv) by Applying Green Infrastructure Techniques and Standard SMP's Handling of the Runoff Reduction Volume (RRv) is required for the project since it is new development. As permitted in the NYS Stormwater Design Manual, green infrastructure techniques and standard stormwater management practices with RRv capacity can be credited towards the required WQv discussed above when implemented in accordance with the Manual. Green infrastructure techniques are grouped into two categories: Practices resulting in a reduction of contributing area such as preservation/restoration of conservation areas, tree planting, riparian buffers, etc. Practices resulting in a reduction of contributing volume such as vegetated swales, pervious pavers, bioretention systems and infiltration systems. Apply a combination of green infrastructure techniques and standard SMPs with RRv capacity to provide 100% of the WQv calculated in Step 2. If the RRv calculated in this step is greater than or equal to the WQv in Step 2, the RRv requirement has been met and Step 4 can be skipped. If the RRv provided cannot meet or exceed 100% of the WQv, the project must, at a minimum, reduce a percentage of the runoff from impervious areas to be constructed on the Site which is referred to as the Minimum RRv. The percent reduction is based on the Hydrologic Soil Group(s) (HSG) of the Site and is defined as Specific Reduction Factor. The following green infrastructure techniques and practices are provided in the Design Manual: Conservation of Natural Areas o The majority of the Site will remain undeveloped and undisturbed. Much of the area to be left undisturbed consists of the existing golf course holes that will be converted to meadows as previously described. These areas are planned to be included within a conservation easement as most of the area is not within the contributing drainage area 19

26 to the stormwater practices. Therefore, a majority of the undisturbed area cannot be subtracted from the contributing area for the WQv calculation. Sheet flow to Riparian Buffers or Filter Strips o There are areas of the Site that proposes improvements upstream and outside of a well vegetated area with acceptable slopes. A portion of the proposed driveway and the undisturbed off-site areas located on the western side of the existing pond will utilize riparian buffers as an area reduction practice and to provide WQv. Vegetated Swales o The use of sheet flow into vegetated swales has been implemented for smaller drainage areas wherever possible on the southern portion of the site throughout the parking lots and along the shoulders of the roadways instead of using catch basins and pipes. Tree Planting / Tree Pits o The project includes extensive tree planting as part of the proposed landscaping plan. Disconnection of Rooftop Runoff o This practice is not practical for this project since these items are typically used in a residential application. Stream Daylighting o This practice is limited to redevelopment projects as defined in Chapter 9. Rain Gardens o This practice is not practical for this project since a contributing drainage area is limited to 1,000 square feet of rooftop. This practice is typically used in a residential application. Green Roofs o This practice is utilized for portions of the rooftops of the middle school and black box theater, performance arts center, gymnasium and high school buildings. Stormwater Planters o Rooftop runoff from the proposed buildings are treated in other green practices more suitable for the proposed site conditions. 20

27 Rain Barrels and Cisterns o Rain barrels and cisterns are more suitable for residential buildings. More appropriate green practices are utilized for rooftop runoff from the proposed buildings. Porous Paving o This practice is utilized for walkways around the middle school, high school areas and the campus greenhouse as well as certain parking areas. Standard Practices with RRv Capacity o Bioretention Systems This practice is provided for the proposed driveway/drop off area located on the northern side of the lower school building. o Infiltration Practices A subsurface infiltration system is proposed to treat and retain runoff from the rooftop of the lower school building. This practice is located in an area where the existing grade is being raised and the groundwater was identified at a lower depth. The Minimum RRv capacity required must be provided by green infrastructure techniques to verify that the RRv requirement has been met. The RRv that is provided by the green infrastructure techniques can then be subtracted from the Total Required WQv that must be provided by the SMP s. Step 4: Apply Standard Stormwater Management Practices to Address Remaining Water Quality Volume The standard SMP's must be designed to meet additional water quality volume requirements that cannot be addressed by applying the green infrastructure techniques by themselves. The standard SMP's proposed are: Ponds Wet Extended Detention Ponds (P-3) 21

28 Description Pond that treats a portion of the Water Quality Volume by detaining storm flows above a permanent pool for a specified minimum detention time. Each Wet Extended Detention Pond has a forebay for pretreatment, an aquatic bench and a permanent pool for treatment, a 12 foot wide maintenance access path, 4 foot horizontal to 1 foot vertical side slopes for added safety and ease for maintenance and outlet control structures to slowly release the water quantity storms to reduce the peak flow rates and provide channel protection. Pocket Pond (P-5) Description A stormwater pond design adapted for the treatment of runoff from small drainage areas that has little or no baseflow available to maintain water elevations and relies on ground water to maintain a permanent pool. Infiltration Systems Manufactured Infiltration System o StormTech Chamber System Description An infiltration practice that stores the water quality volume in subsurface chambers before it is infiltrated. Manufactured Infiltration Systems (StormTech Chambers) provide infiltration for the stormwater runoff contributing 90% towards the runoff 22

29 reduction volume. The total runoff reduction volume achieved utilizing the underground infiltration practice listed above is 6,097 cubic feet. The combination of the green infrastructure techniques and extended detention practices combine to exceed the WQv requirements as demonstrated in Appendix C. Step 5: Apply Volume and Peak Rate Control Practices to Meet Water Quantity Requirements All of the proposed stormwater management practices combine to meet the volume and peak rate water quantity requirements as required in the General Permit and Stormwater Design Manual. The Channel Protection Volume (CPv), Overbank Flood Control (Qp) and Extreme Flood Control (Qf) must be met for the plan to be completed. This is accomplished by using standard SMP's such as Micropool Extended Detention Ponds (P-1) to meet water quantity requirements. The following standards must be met: 1. Stream Channel Protection (CPv) Stream Channel Protection Volume Requirements (CPv) are designed to protect stream channels from erosion. This goal is accomplished by providing 24-hour extended detention of the one-year, 24-hour storm event, remained from runoff reduction. Reduction of runoff for meeting stream channel protection objectives, where Site conditions allow, is encouraged and the volume reduction achieved through green infrastructure can be deducted from CPv. Detention time has been calculated using the plug flow calculation method. 1. Overbank Flood (Qp) which is the 10 year storm. Overbank flood control (10-year storm) are met by the design of the SWPPP to provide storage to attenuate the post development 10-year, 24-hour peak discharge rate (Qp) below predevelopment rates. 23

30 2. Extreme Storm (Qf) which is the 100 year storm. Extreme Flood Control (100-year storm) requirements are met by the design of the SWPPP to provide storage of runoff to attenuate the post development 100-year, 24-hour peak discharge rate (Qf) below predevelopment rates. Based on the foregoing, this project is eligible for coverage under NYSDEC SPDES General Permit No. GP All practices exceed the required elements of SMP criteria as outlined in Chapter 6 of the NYS Stormwater Management Design Manual. A summary of each category is provided below. 1. Feasibility Ponds are designed based upon unique physical environmental considerations noted in the NYS Stormwater Management Design Manual (NYSSMDM) Table 7.2 "Physical Feasibility Matrix". 2. Conveyance The design conveys runoff to the designed pond in a manner that is safe, minimizes erosion and disruption to natural drainage channel and promotes filtering and infiltration. 3. Pretreatment All ponds provide pretreatment in accordance with NYSSMDM design guidelines. 4. Treatment Geometry The plan provides water quality treatment in accordance with NYSSMDM guidelines noted Table 6.1 "Water Quality Volume Distributing in Pond Design". 5. Environmental/Landscaping Extensive landscaping has been provided for each proposed practice to enhance pollutant removal and provide aesthetic enhancement to the Site. 6. Maintenance Maintenance for the environment practices has been provided and is detain the SWPPP Report as required. Maintenance access is provided in the design plans. 24

31 In order to determine the post-development rates of runoff generated on-site, the following drainage areas were analyzed in the post-development conditions. These areas are graphically depicted on Drawing DA-2 "Proposed Drainage Area Map" located in Appendix "H". Similar to existing conditions, seven separate Design Points (1, 2, 3, 4, 5, 6 & 7) were identified when comparing peak rates of runoff in existing and proposed conditions. Unlike existing conditions, several sub-drainage areas were identified in proposed conditions based on the proposed drainage divides and specific contributing drainage areas to different SMP s and green infrastructure techniques. However, the Design Points remain the same. The following is a description of each of the drainage areas analyzed in the proposed conditions analysis: Design Point #1 Design Point #1 is the existing catch basin on the north side of Ridgeway just east of the existing tennis courts near the middle of the frontage of Parcel A. The contributing drainage area flows through the proposed network of HDPE drain pipe to Stormwater Management Basin 1A which discharges through a proposed 36 inch diameter pipe to a new structures that will replace the existing catch basin on Ridgeway. The following drainage areas ultimately contribute runoff to this design point, as described below: Sub drainage areas contributing to this design point employ numerous source control Runoff Reduction Volume Methods. The required Minimum RRv is provided by green practices for all improvement areas as demonstrated in Appendix C and described below. Design Point #1 WQv / RRv Calculations Summary See Appendix C Initial WQv 32,652 c.f. Adjusted WQv (Area Practices) 32,652 c.f. Minimum RRv 3,808 c.f. RRv Provided 4,603 c.f. Net WQv 28,049 c.f. 25

32 The entire WQv could not be provided solely by green practices for Design Point #1 due to the various site constraints. However, standard SMP's are implemented to treat the remaining Net WQv. The following drainage areas ultimately contribute runoff to this design point, as described below: Proposed Drainage Area 1A (PDA-1A) is acres in size and includes the majority of Parcel A bordered by Ridgeway, Gedney Esplanade, Hathaway Lane. PDA-1A consists of portions of the converted proposed High School, tennis courts, running track, multipurpose turf playing field, basketball court, parking areas, access driveways, sidewalks, landscaping, roadways, driveways and lawns areas. The Curve Number (CN) and Time of Concentration (Tc) for this drainage area are 81 and 6 minutes, respectively. It should be noted that the field area within the running track which will be constructed of a pervious artificial turf material has been modeled as grass areas with a curve number of 74. However, John Meyer Consulting performed a sensitivity analysis with the field area being modeled as impervious area with a curve number of 98 to confirm that the Stormwater Management Basin designed for this drainage area can meet the water quantity standards regardless of the coverage type at Design Point #1when compared to existing conditions. Green Practices / RRv o Vegetated Swales Portions of the parking lot and roadway north of the performing arts, gymnasium and Middle School buildings, are graded to sheet flow into Vegetated Swales 1A-1, 1A-2, 1A-3 and 1A-4 instead of using catch basins and pipes to promote infiltration through the grass and to provide a longer Tc for the runoff. The vegetated swales are in HSG C soils and are therefore eligible for a 15% reduction of the required RRv. o Pervious Pavers/Flexipave The walkways surrounding the High school, Gymnasium, Performing Arts Center and the Middle school buildings are proposed as Pervious 26