STORMWATER POLLUTION PREVENTION PLAN

(1)

SWPPP18156.doc

STORMWATER POLLUTION PREVENTION PLAN

For

3622 ROUTE 9 LLC

Philipstown, New York

July 1, 2021 Owner Information: 3622 Route 9 LLC 58 Kingwood Drive Poughkeepsie, NY 12601

Prepared by:

Insite Engineering, Surveying & Landscape Architecture, P.C. 3 Garrett Place

(2)

(3)

3622 Route 9 LLC — SWPPP

Insite Engineering, Surveying & Landscape Architecture, P.C. i 3 Garrett Place, Carmel, New York 10512

The subject property is located at 3622 U.S. Route 9 in the Town of Philipstown. The site is approximately 4± acres in size and is identified as Tax Map No. 17.-1-44. The subject property contains a primary building which has generally been used for contractor offices and storage, and an accessory building to its south. There are currently three access points to the site along its frontage with US-Rt 9, with gravel drives and lawn consuming the front of the property. The rear of the

property is currently largely gravel and lawn area used for tenant storage and parking. There is a well and septic system on site.

The subject project includes the removal of the existing building, associated drives, and storage areas, in order to construct two buildings (11,620 SF and 10,500 SF), new outdoor storage

enclosures, and associated parking. The buildings would house contractor office space and storage. 1.2 Existing Site Conditions

The subject properties are located on the south-east side of Route 9 in the town of Cold Spring, New York. The property is bordered by a vacant commercial lot to the north, a residential lot to the east and two commercial lots to the south-west. The site is currently developed as a contractor offices and storage, and an accessory building. For the purposes of this assessment, one design point was chosen. The design point was chosen to assess the stormwater runoff east of the property and reaching the existing stormwater inlet near the southwest corner of the property. The contributing drainage area to the design point in the existing condition is shown in subcatchment 1.0S on Figure 2 of this report. The existing 19,921SF of impervious areas on the project site are currently not being treated.

1.3 Proposed Site Conditions

The proposed buildings will be located partly in the footprint of the existing building and

extending largely over the west portion of the property, the storage building will be located on the east portion of the lot. The proposed buildings will be 22,120 square feet. The proposed parking will be located largely between the two buildings. The existing slopes in this general area are gently sloped with some steeper slopes east of the existing buildings.

It is proposed to treat the stormwater runoff from new impervious areas. These areas include the proposed buildings and parking area. The drainage areas for the proposed buildings and centrally located parking area are shown in subcatchments 1.1S and 1.2S, located in Figure 3 of this report.

It is proposed to capture and treat the stormwater runoff from the impervious area from two subcatchment areas (1.1S and 1.2S). It is proposed to direct the stormwater runoff from

subcatchment 1.1S towards an infiltration basin (1.1P) for water quality (WQv) and runoff reduction (RRv) purposes. It is proposed to treat the stormwater runoff from subcatchment 1.2S to a pocket pond (1.2P). Stormwater basin designations are shown on Figure 3 of this report.

2.0 STORMWATER MANAGEMENT

The proposed stormwater management system for the project has been designed to meet the requirements of the state stormwater ordinances and guidelines, including but not limited to those of the NYSDEC.

Since the subject re-development project proposes the disturbance of more than one (1) acre,

(6)

requirements relates to treating water quality, while the later pertain to stormwater quantity (peak flow) attenuation. As noted in previous sections of this report, this project is a redevelopment project with an increase in impervious area. Per the requirements of Chapter 9 of the NYSSMDM, all new impervious areas are required to be treated in accordance with the requirements of Chapter 4 for both stormwater quality and quantity. Per Chapter 9, 25% of the water quality from the existing impervious area within the subcatchments reaching the stormwater practice is required to be treated to meet the WQv requirements for redevelopment projects. As shown in the calculations in later sections of this report the 25% of the existing impervious areas were accounted for in the WQv sizing of the stormwater treatment practices.

To address stormwater quantity requirements of the NYSDEC, the “HydroCAD” Stormwater Modeling System,” by HydroCAD Software Solutions LLC in Tamworth, New Hampshire, was used to model and assess the peak stormwater flows for the subject project. HydroCAD is a computer aided design program for modeling the hydrology and hydraulics of stormwater runoff. It is based primarily on hydrology techniques developed by the United States Department of Agriculture, Soil Conservation Service (USDA, SCS) TR-20 method combined with standard hydraulic calculations. For details on the input data for the subcatchments and design storms, please refer to Appendices A and B.

The input requirements for the HydroCAD computer program are as follows: Subcatchments (contributing watershed/sub-watersheds)

• Design storm rainfall in inches

• CN (runoff curve number) values which are based on soil type and land use/ground cover • Tc (time of concentration) flow path information

• Watershed Area in Acres Stormwater Basins

• Surface area at appropriate elevations • Flood elevation

• Outlet structure information

The following is a general description of the input data used to calculate the pre- and

post-development stormwater runoff values. For detailed information for each subcatchment and stormwater management practice, see Appendices A & B.

The precipitation value for the 90% rainfall event is taken from the NYSSMDM. The precipitation values and intensity duration frequency (IDF) curves for the 1-year, 10-year, 100-year, 24-hour design storm events and rainfall distribution curves utilized for this report were obtained from the information provided by Northeast Regional Climate Center (NRCC) and the Natural Resources Conservation Service (NRCS) which is available online at www.precip.eas.cornell.edu. The values provided for all design storms analyzed have been listed below.

Table 2.0.1 – Precipitation Values for Corresponding Design Storms

Design Storm 24-Hour Rainfall

1-Year 2.80”

10-Year 4.82”

100-Year 8.59”

(7)

Table 2.0.2 – Project Ground Cover and Associated Curve Numbers (CN)

Land Use/Ground Cover CN Value

1 ACRE LOTS, 20% IMP, HSG B 68

>75% Grass Cover, Good, A Soil 39 >75% Grass Cover, Good, B Soil 61

Woods, Good, A soil 30

Woods, Good, B soil 55

Paved Parking & Roads 98

The Soil Survey for the project location in Putnam County, New York identifies the soil types on the site as primarily ChB and ChD (Charlton Loam) which are designated in hydrological soil group B, and RhB (Riverhead Loam) which are designated in hydrological soil group A. The onsite soil testing results are shown on Figure 4 of this report.

As previously discussed, one (1) design point has been selected to analyze the stormwater runoff from the proposed improvements across the site. The proposed onsite improvements will be directed to an infiltration basin or a pocket pond. The proposed stormwater practices will provide both stormwater quality and quantity mitigation. The systems have been designed in general accordance with the NYSSMDM and are proposed to treat the Water Quality Volume for the respective drainage areas. The proposed practices have been designed to meet the Stream Channel Protection,

Overbank Flood Control, and Extreme Flood Control requirements set forth in the design manual. 2.1 NYSDEC Water Quality Volume, WQv

The stormwater management practices have been designed in accordance with the

Performance Criteria (Chapter 4) of the NYSSMDM. As outlined in Chapter 4, the WQv is the runoff

volume produced during the 90% storm. The proposed infiltration, water quality swale, and pocket pond practices have been designed to treat the WQv in accordance with the NYSSMDM. The following equation, per Chapter 4, was used to determine the water quality volume for the 90% storm for each of the contributing areas to the treatment practices:

The water quality volume shall be WQv = (P)(Rv)(A)

12 Where,

WQv = water quality volume (in acre-feet) P = 90% Rainfall Event Number

Rv = 0.05 + 0.009(I), where I is percent impervious cover A = site area in acres

The equation above, per Chapter 4, was used to determine the water quality volume for the 90% storm for each of the contributing areas to the treatment practices as summarized below:

Table 2.2.1 - Water Quality Volume Calculation Summary Subcatchment WQv1,2

(cf)

1.1S 7,605

1.2S 2,864

1

For detailed calculations see Appendix C

2 _{As per Chapter 9 of the NYSSMDM, for redevelopment projects with an increase in}

(8)

The stormwater management practices consist of an Infiltration Basin (NYSDEC Design I-2), and a Pocket Pond (NYSDEC Design P-5) proposed as part of the redevelopment of the site to meet both the WQv and RRv requirements as well as provide the necessary peak flow attenuation to satisfy the Overbank (Qp) and Extreme (Qf) Flood Control requirements.

Tables 2.1.2 and 2.1.3 below provide a summary of the water quality volume of the NYSDEC compliant practices, and its satisfaction of the NYSDEC WQv requirements: It should be noted the calculated WQv shown above for the subcatchment was used in the sizing calculation for the Infiltration Basin and Wet Ponds summarized in the tables below.

The infiltration basin has been sized to capture and infiltrate 100% of the RRv / WQv for new impervious and 25% of the RRv/WQv for existing surfaces. Storage for 100% of the contributing RRv / WQv to the infiltration basin is provided below the outlet of the infiltration basin. Pretreatment for the infiltration systems is to be provided by a hydrodynamic separator. The HydroCAD accounts for infiltration in the infiltration system (known as exfiltration in the HydroCAD output). The exfiltration rate utilized in the HydroCAD was confirmed by field testing as required by the design manual. Table 2.1.2 summarizes the required WQv and Proposed WQv.

Table 2.1.2 Infiltration Pond Water Quality Volume Treatment Summary

Subcatchment Treatment Practice NYSDEC Design Practice Designation Required WQv (c.f.) Proposed WQv (c.f.) 1.1S 1.1P I-2 7,605 9,663

It should be noted that the above table illustrates the water quality volume storage requirements set forth in the NYSSMDM have been met for the infiltration system design.

As noted in the NYSSMDM, the pocket pond (P-5) practices are sized for water quality treatment by providing a percentage of the water quality volume in the permanent pool. The

proposed pond contains a minimum 4-foot-deep permanent pool meeting the required percentage of storage as noted in Table 2.1.3 below. The pond is also required to have a pretreatment forebay with a permanent pool greater than 10% of the WQv. The table below summarizes the sizing of the proposed stormwater management ponds to meet the WQv requirements.

Table 2.1.3 Pond Sizing Summary

Sub-catchment Required WQv (c.f.) NYSDEC Practice Designation Required Pre- Treatment Volume (10% WQv) (c.f.) Provided Pre-treatment Volume) (c.f.)1 Minimum Storage Volume Required WQv (c.f.) Storage Volume Provided Below Permanent Pool (c.f.)2 1.2 2,864 P-5 286 3,600 50% 1,432 4,000

1_{The storage volume is calculated as the volume between the bottom of the forebay to the natural water level.}

2_{Refer to HydroCAD output in Appendix B for pond volume calculations.}

(9)

The site currently contains untreated impervious surfaces. Some of these impervious surfaces are proposed to be removed as part of the re-development of the site. Where existing impervious surfaces are removed the NYSSMDM allows for the re-development criteria of Chapter 9 to be applied. It is not practical to provide treatment to all impervious areas, so the re-development criteria are proposed for these areas. The untreated impervious areas have reduced by greater than 25% to meet this criteria.

2.2 NYSDEC Runoff Reduction Volume, RRv

The Runoff Reduction Volume (RRv) criterion is intended to replicate pre-development hydrology by maintaining preconstruction infiltration, peak flow runoff, discharge volume, as well as minimizing concentrated stormwater flow. As stated in Chapter 4 of the NYSSMDM, RRv may be treated with standard stormwater management practices (SMP’s) sized in accordance with the Chapter 4/6 requirements, or with green infrastructure practices (GIP’s) sized in accordance with the requirements set forth for each practice in Chapter 5. This requirement is addressed on the subject project by providing infiltration practices, specifically infiltration systems designed as an SMP in accordance with the latest design standards. Runoff reduction is achieved when runoff from a

percentage of the impervious area on the site is captured, routed through an SMP or a GIP, infiltrated to the ground, reused, reduced by evapotranspiration, and eventually removed from the stormwater discharge from the site.

Chapter 4 of the NYSSMDM notes the RRv applies to the water quality volume from impervious surfaces resulting from the 90% rain fall event. Again, it shall be the intent to provide RRv equivalent to the entire WQv. Section 4.3 of the NYSSMDM states for sites that do not achieve runoff reduction to pre-construction condition must, at a minimum reduce a percentage of the runoff from impervious areas to be constructed on the site a minimum RRv. The following equation can be used to determine the minimum runoff reduction volume:

The minimum runoff reduction volume shall be RRvminimum = (P)(Rv)(Ai) 12 Where,

S = Hydrologic Soil Group (HSG) Specific Reduction Factor = 0.50

Aic = Total Area of New Impervious Cover

Ai = Impervious cover targeted for Runoff Reduction = (S)(Aic)

Rv = 0.95

For detailed calculations of the runoff reduction for the proposed stormwater infiltration practices see Appendix C. Listed in Table 2.2.1 below is a summary of the NYSDEC compliant practice, and its satisfaction of the NYSDEC RRv requirements:

Table 2.2.1 Runoff Reduction Volume Summary 100% RRv WQv (c.f.) Sum of Table 2.1.1 RRv Minimum (c.f.) Calculated in Appendix C NYSDEC Practice Designation Allowable % of WQv provided to be applied towards RRv

Storage Volume Provided Below Outlet Weir / System

Overflow (c.f.) (From Appendix C) Total RRv Provided (c.f.) 10,469 5,118 I-2 100%* 9,663 9,178

(10)

As shown in the table above the RRv provided is greater than the RRv minimum. There were

several factors as to why the site could not provide the 100% RRv. Soil testing indicated some areas contained soils that would prevent water from infiltrating into the ground. These conditions limit the effectiveness or disallow standard SMP’s with RRv capacity like infiltration or bioretention in many locations. The same is the case for green infrastructure practices such as rain gardens. The neighbors well to the south also limits areas where infiltration is allowed. The use of infiltration practices where soils are conducive to infiltration have been used to achieve RRv to the greatest extent practical. Where soils are not conducive to infiltration, wet ponds have been provided for water quality treatment as a more appropriate stormwater practice, however wet ponds do not provide RRV.

Due to site conditions the project will not be able to provide 100% RRv. The soils in some locations of the site require practices like wet ponds that do not provide RRv. However, the RRv minimum will be achieved through infiltration where possible and be supplemented with GIP’s when practical. By providing RRv to the greatest extent practical and achieving the RRv minimum, it is assumed that the requirements of the NYSDEC for RRv have been met.

2.3 NYSDEC Stream Channel Protection Volume, CPv

The Stream Channel Protection (CPv) criterion is intended to protect stream channels from erosion and is accomplished by the 24-hour center of mass detention or plug flow detention of the 1-year, hour design storm event. CPv can also be achieved through fully infiltrating the 1 1-year, 24-hour design storm. The project will achieve the required CPv through both 24-24-hour detention and by fully infiltrating the 1-year, 24-hour design storm. The table below summarizes how CPv is achieved through the different SMP’s.

Table 2.3.1: Channel Protection Volume Plug Flow Detention Time / Infiltration for 1-Year, 24 Hour Design Storm

NYSDEC

Water Quality Volume, WQ

V

2.4 NYSDEC Overbank Flood Control, Qp, and Extreme Flood Control, Qf

The Overbank Flood Control (Qp) requirement is intended to prevent an increase in the

frequency and magnitude of out-of-bank flooding events generated by urban development. Overbank control requires storage to attenuate the post-development 10-year, 24-hour peak discharge to pre-development rates. The Extreme Flood Control (Qf) requirement is intended to prevent the increased risk of flood damage from large storm events, maintain the boundaries of the pre-development 100-year flood plain, and protect the physical integrity of stormwater management practices. Extreme flood control requires storage to attenuate the post-development 100-year, 24-hour peak discharge to pre-development rates. As shown in Table 2.4.1 attenuation for both the 10-year and 100-year 24-hour storms has been provided, thus satisfying the Qp and Qf requirements.

Subcatchment Treatment

Practice

NYSDEC Practice Designation

Plug Flow Detention (Hrs)

Infiltration of the 1-Year, 24-Hour Storm

1.1S 1.1P I-2 N/A Yes

(11)

Table 2.4.1– Pre and Post-Development Peak Flows at the Design Line 24-HOUR DESIGN STORM PEAK FLOWS (c.f.s.)

10-YEAR (Overbank Flood Control)

100-YEAR (Extreme Flood Control)

Pre Post Pre Post

Design Point 9.9 7.3 33.3 32.4

As shown in the above table the peak flows discharging to the design point in the proposed condition have been mitigated to the existing condition levels, therefore the receiving downstream drainage systems and resources will see no change in peak flows during the storm events shown above.

3.0 STORMWATER CONVEYANCE SYSTEM

The proposed stormwater conveyance systems for the project will consist of precast concrete drainage structures and grass swales. The storm drainage collection system will be sized utilizing the Rational Method for the 10-year 1-hour design storm. The Rational Method is a standard method used by engineers to develop flow rates for sizing collection systems.

The stormwater conveyance system will discharge to rock outlet protection at the outlet of the

proposed ponds and all pipes. Rock outlet protection will be provided at discharge points within the site and will be designed in conformance with the New York State Standards and Specifications for Erosion and Sediment Control (Blue Book).

4.0 EROSION AND SEDIMENT CONTROL

Erosion and sediment control will be accomplished by three basic principles: containment of sediment, treatment of dirty water, and stabilization of disturbed areas. Sediment will be contained with the use of silt fence at the toe of disturbed slopes. Disturbed areas will be permanently stabilized within 14 days of final grading to limit the required length of time that the temporary facilities must be utilized.

4.1 Temporary Erosion and Sediment Control Facilities

Temporary erosion and sediment control facilities will be installed and maintained as required to reduce the impacts to off-site properties. In general, the following temporary methods and materials will be used to control erosion and sedimentation from the project site:

• Dust Control

• Stabilized Construction Entrance • Silt Fence Barriers

• Storm Drain Inlet Protection

(12)

Siltation barriers constructed of geosynthetic filter cloth (silt fence) will be installed liberally at the toe of all disturbed slopes. The intent of these barriers is to contain silt and sediment at the source and inhibit its transport by stormwater runoff. The siltation barriers will also help reduce the rate of runoff by creating numerous filters through which the stormwater must pass. Siltation barriers will also be installed around drain inlets. The intent of these barriers is to prevent silt and sedimentation from entering the stormwater collection system.

4.2 Permanent Erosion and Sediment Control Facilities

Permanent erosion and sediment control will be accomplished by controlling/reducing stormwater runoff velocities and volumes, and vegetative and structural surface stabilization. All of the permanent facilities are relatively maintenance free and only require periodic inspections.

Other than impervious surfaces, the primary method for permanently stabilizing disturbed surfaces at the subject site is with vegetation. The vegetation will control stormwater runoff by preventing soil erosion, reducing runoff volume and velocities, and providing a filter medium. Permanent seeding should optimally be undertaken in the spring from March 21st_{through May 20}th and in late summer from August 15th_{to October 15}th_.

5.0 IMPLEMENTATION AND MAINTENANCE 5.1 Construction Phase

Details associated with the implementation and maintenance of the proposed stormwater facilities and erosion control measures during construction are shown on the project drawings. A Construction Sequence has been provided to guide the contractor in the installation of the erosion control measures as well as the site plan features. The erosion control plan includes associated details and notes to aid the contractor in implementing the plan.

During construction, a Site Log Book, Appendix E, is required to be kept per NYSDEC SPDES General Permit GP-0-20-001. Erosion and sediment control inspections are required to be conducted as necessary under coverage of the permit (minimum once a week) and an updated logbook and a copy of the SWPPP is required to be kept on site for the duration of the construction activities. The Construction Site Log Book is an appendix taken from the New York Standards and Specifications for

Erosion and Sediment Control (Blue Book).

In addition to the proposed erosion and sediment control facilities, the following good

housekeeping best management practices shall be implemented to mitigate potential pollution during the construction phase of the project. The general contractor overseeing the day-to-day site operation shall be responsible for the good housekeeping best management practices included in the following general categories:

• Material Handling and Waste Management • Establishment of Building Material Staging Areas • Establishment of Washout Areas

• Proper Equipment Fueling and Maintenance Practices • Spill Prevention and Control Plan

All construction waste materials shall be collected and removed from the site regularly by the general contractor. The general contractor shall supply waste barrels for proper disposal of waste materials. All personnel working on the site shall be instructed of the proper procedures for construction waste disposal.

(13)

data sheets, material inventory, and emergency contact numbers will be maintained in the office trailer. All personnel working on the site shall be instructed of the proper procedures for hazardous waste disposal.

Temporary sanitary facilities (portable toilets) shall be provided on site during the entire length of construction. The sanitary facilities shall be located in an alternate area away from the construction activities on the site. The portable toilets shall be inspected weekly for evidence of leaking holding tanks.

All recyclables, including wood pallets, cardboard boxes, and all other recyclable construction scraps shall be disposed of in a designated recycling barrel provided by the contractor and removed from the site regularly. All personnel working on the site shall be instructed of the proper procedures for construction waste recycling.

All construction equipment and maintenance materials shall be stored in a designated staging area. Silt fence shall be installed down gradient of the construction staging area. Shipping containers shall be utilized to store hand tools, small parts, and other construction materials, not taken off site daily. Construction waste barrels, recycling barrels and if necessary hazardous waste containers shall be located within the limits of the construction staging area.

Throughout the construction of the project, several types of vehicles and equipment will be used on-site. Fueling of the equipment shall occur within the limits of the construction staging area. Fuel will be delivered to the site as needed, by the general contractor, or a party chosen by the general contractor. Only minor vehicle equipment maintenance shall occur on-site, all major maintenance shall be performed off-site. All equipment fluids generated from minor maintenance activities shall be disposed of into designated drums and stored in accordance with the hazardous waste storage as previously discussed.

Vehicles and equipment shall be inspected on each day of use. Any leak discovered shall be repaired immediately. All leaking equipment unable to be repaired shall be removed from the site. Ample supplies of absorbent, spill-cleanup materials, and spill kits shall be located in the construction staging area. All spills shall be cleaned up immediately upon discovery. Spent absorbent materials and rags shall be hauled off-site immediately after the spill is cleaned for disposal at a local landfill. All personnel working on the site shall be instructed of the proper procedures for spill prevention and control. Any spill large enough to discharge to surface water will be immediately reported to the local fire / police departments and the National Response Center 1-800-424-8802.

5.2 Long Term Maintenance Plan

The owner will be responsible for the maintenance of the permanent erosion control and stormwater facilities. Initially the stormwater facilities will require an increased maintenance and inspection schedule until all portions of the site are stable. The Monitoring and Maintenance will require that each spring, the paved areas (roads, parking areas, and sidewalks) will be swept clean to remove the winters accumulation of traction sand. After this is completed, all drain inlet sumps should be cleaned. All pipes should be checked for debris and blockages and cleaned as required. During the cleaning process, the drain inlets and pipes should be inspected for structural integrity and overall condition; repairs and/or replacement will be made as required.

Once the desired vegetative cover is established in the basins, only limited maintenance is required. The basins and outlet structures should be inspected after major storm events and semi-annually. During the inspections, the following should be checked:

• Evidence of clogging of outlet structures.

• Erosion of the flow path through the stormwater basins.

• Subsidence, erosion, cracking or tree growth on the embankment/berms. • Condition of the emergency spillways.

• Accumulation of sediment around the outlet structures.

• Adequacy of upstream/downstream channel erosion control measures. • Erosion of the basin bed and banks.

(14)

The graded basin and the side slopes and berms of the basins should be mowed annually to prevent the establishment of woody plants within the swales, access, or basin berm. The bottom of the basins should not be mowed. During the mowing operations, debris and litter should be removed from all parts of the access, and basin. Removal of sediment from the permanent pool shall be done every 5 to 10 years or when the permanent pool depth is decreased to less than 3’.

(15)

SWPPP18156doc Insite Engineering, Surveying & Landscape Architecture, P.C.

APPENDIX A

(16)

(17)

1.0S

Ex. Conditions

Routing Diagram for 3622 Route 9 LLC, Existing Cond

(18)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Existing Cond

Printed 2/4/2021

Prepared by Insite Engineering, Surveying & Landscape Architecture , P.C.

Page 2

Summary for Subcatchment 1.0S: Ex. Conditions

Runoff

=

0.9 cfs @ 12.64 hrs, Volume=

0.270 af, Depth= 0.22"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

Area (ac)

CN

Description

0.600

98 Paved parking, HSG B

0.700

61 >75% Grass cover, Good, HSG B

6.000

55 Woods, Good, HSG B

0.100

39 >75% Grass cover, Good, HSG A

2.100

30 Woods, Good, HSG A

4.300

68 1 acre lots, 20% imp, HSG B

0.900

98 Paved parking, HSG A

14.700

60 Weighted Average

12.340 83.95% Pervious Area

2.360 16.05% Impervious Area

Tc Length

Slope Velocity Capacity Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

11.3 100 0.0900

0.15 Sheet Flow,

Woods: Light underbrush n= 0.400 P2= 3.50"

7.7 550 0.0560

1.18 Shallow Concentrated Flow,

Woodland Kv= 5.0 fps

6.9 550 0.0360

1.33 Shallow Concentrated Flow,

(19)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Existing Cond

Printed 2/4/2021

Prepared by Insite Engineering, Surveying & Landscape Architecture , P.C.

Page 3

Subcatchment 1.0S: Ex. Conditions

(20)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Existing Cond

Printed 2/4/2021

Prepared by Insite Engineering, Surveying & Landscape Architecture , P.C.

Page 4

Summary for Subcatchment 1.0S: Ex. Conditions

Runoff

=

9.9 cfs @ 12.36 hrs, Volume=

1.467 af, Depth= 1.20"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

Area (ac)

CN

Description

0.600

98 Paved parking, HSG B

0.700

61 >75% Grass cover, Good, HSG B

6.000

55 Woods, Good, HSG B

0.100

39 >75% Grass cover, Good, HSG A

2.100

30 Woods, Good, HSG A

4.300

68 1 acre lots, 20% imp, HSG B

0.900

98 Paved parking, HSG A

14.700

60 Weighted Average

12.340 83.95% Pervious Area

2.360 16.05% Impervious Area

Tc Length

Slope Velocity Capacity Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

11.3 100 0.0900

0.15 Sheet Flow,

Woods: Light underbrush n= 0.400 P2= 3.50"

7.7 550 0.0560

1.18 Shallow Concentrated Flow,

Woodland Kv= 5.0 fps

6.9 550 0.0360

1.33 Shallow Concentrated Flow,

(21)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Existing Cond

Printed 2/4/2021

Prepared by Insite Engineering, Surveying & Landscape Architecture , P.C.

Page 5

Subcatchment 1.0S: Ex. Conditions

(22)

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

3622 Route 9 LLC, Existing Cond

Printed 2/4/2021

Prepared by Insite Engineering, Surveying & Landscape Architecture , P.C.

Page 6

Summary for Subcatchment 1.0S: Ex. Conditions

Runoff

=

33.3 cfs @ 12.33 hrs, Volume=

4.633 af, Depth= 3.78"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

Area (ac)

CN

Description

0.600

98 Paved parking, HSG B

0.700

61 >75% Grass cover, Good, HSG B

6.000

55 Woods, Good, HSG B

0.100

39 >75% Grass cover, Good, HSG A

2.100

30 Woods, Good, HSG A

4.300

68 1 acre lots, 20% imp, HSG B

0.900

98 Paved parking, HSG A

14.700

60 Weighted Average

12.340 83.95% Pervious Area

2.360 16.05% Impervious Area

Tc Length

Slope Velocity Capacity Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

11.3 100 0.0900

0.15 Sheet Flow,

Woods: Light underbrush n= 0.400 P2= 3.50"

7.7 550 0.0560

1.18 Shallow Concentrated Flow,

Woodland Kv= 5.0 fps

6.9 550 0.0360

1.33 Shallow Concentrated Flow,

(23)

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

3622 Route 9 LLC, Existing Cond

Printed 2/4/2021

Prepared by Insite Engineering, Surveying & Landscape Architecture , P.C.

Page 7

Subcatchment 1.0S: Ex. Conditions

(24)

(25)

SWPPP18156.doc Insite Engineering, Surveying & Landscape Architecture, P.C.

APPENDIX B

(26)

(27)

1.1S

1.2S

1.3S

DP1

1.1P

1.2P

Routing Diagram for 3622 Route 9 LLC, Proposed Cond-Revised

Prepared by {enter your company name here}, Printed 7/1/2021

(28)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 2

Summary for Subcatchment 1.1S:

Runoff

=

4.2 cfs @ 12.04 hrs, Volume=

0.260 af, Depth= 1.52"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

Area (ac)

CN

Description

0.750

98 Paved parking, HSG B

0.490

61 >75% Grass cover, Good, HSG B

0.810

96 Gravel surface, HSG B

2.050

88 Weighted Average

1.300 63.41% Pervious Area

0.750 36.59% Impervious Area

Tc

Length

Slope

Velocity

Capacity

Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

(29)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 3

Summary for Subcatchment 1.2S:

Runoff

=

1.4 cfs @ 12.05 hrs, Volume=

0.091 af, Depth= 0.95"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

Area (ac)

CN

Description

0.560

98 Paved parking, HSG B

0.590

61 >75% Grass cover, Good, HSG B

1.150

79 Weighted Average

0.590 51.30% Pervious Area

0.560 48.70% Impervious Area

Tc

Length

Slope

Velocity

Capacity

Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

(30)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 4

Summary for Subcatchment 1.3S:

Runoff

=

0.3 cfs @ 12.74 hrs, Volume=

0.156 af, Depth= 0.13"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

Area (ac)

CN

Description

0.300

98 Paved parking, HSG B

7.500

55 Woods, Good, HSG B

0.200

39 >75% Grass cover, Good, HSG A

1.800

30 Woods, Good, HSG A

4.300

68 1 acre lots, 20% imp, HSG B

14.100

56 Weighted Average

12.940 91.77% Pervious Area

1.160 8.23% Impervious Area

Tc

Length

Slope

Velocity

Capacity

Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

11.3

100 0.0900

0.15 Sheet Flow,

Woods: Light underbrush n= 0.400 P2= 3.50"

5.8

410 0.0560

1.18 Shallow Concentrated Flow,

Woodland Kv= 5.0 fps

3.2

258 0.0360

1.33 Shallow Concentrated Flow,

Short Grass Pasture Kv= 7.0 fps

2.1

530 0.0100

4.27

34.15 Channel Flow,

Area= 8.0 sf Perim= 10.0' r= 0.80'

n= 0.030 Earth, grassed & winding

1.2

336 0.0113

4.82

3.79 Pipe Channel,

(31)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 5

(32)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 6

Summary for Reach DP1:

Inflow Area =

17.300 ac, 14.28% Impervious, Inflow Depth > 0.17" for 1-yr event

Inflow

=

0.4 cfs @ 12.74 hrs, Volume=

0.244 af

Outflow

=

0.4 cfs @ 12.74 hrs, Volume=

0.244 af, Atten= 0%, Lag= 0.0 min

Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

(33)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 7

Summary for Pond 1.1P:

Inflow Area =

2.050 ac, 36.59% Impervious, Inflow Depth = 1.52" for 1-yr event

Inflow

=

4.2 cfs @ 12.04 hrs, Volume=

0.260 af

Outflow

=

0.2 cfs @ 14.00 hrs, Volume=

0.260 af, Atten= 95%, Lag= 117.4 min

Discarded =

0.2 cfs @ 14.00 hrs, Volume=

0.260 af

Primary

=

0.0 cfs @

0.00 hrs, Volume=

0.000 af

Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

Peak Elev= 266.59' @ 14.00 hrs Surf.Area= 4,335 sf Storage= 5,366 cf

Plug-Flow detention time= (not calculated: outflow precedes inflow)

Center-of-Mass det. time= 289.4 min ( 1,124.5 - 835.1 )

Volume

Invert

Avail.Storage

Storage Description

#1

265.00'

44,050 cf

Custom Stage Data (Prismatic) Listed below (Recalc)

Elevation

Surf.Area

Inc.Store

Cum.Store

(feet)

(sq-ft)

(cubic-feet)

265.00 2,100

0

266.00 3,800

2,950

268.00 5,600

9,400

12,350

270.00 7,900

13,500

25,850

272.00 10,300

18,200

44,050

Device

Routing

Invert

Outlet Devices

#1

Primary

269.70'

0.5' long x 0.5' breadth Broad-Crested Rectangular Weir

Head (feet) 0.20 0.40 0.60 0.80 1.00

Coef. (English) 2.80 2.92 3.08 3.30 3.32

#2

Discarded

265.00'

2.000 in/hr Exfiltration over Surface area

#3

Primary

267.50'

4.0" Vert. Orifice/Grate C= 0.600

Discarded OutFlow Max=0.2 cfs @ 14.00 hrs HW=266.59' (Free Discharge)

2=Exfiltration (Exfiltration Controls 0.2 cfs)

Primary OutFlow Max=0.0 cfs @ 0.00 hrs HW=265.00' TW=0.00' (Dynamic Tailwater)

1=Broad-Crested Rectangular Weir ( Controls 0.0 cfs)

(34)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 8

(35)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 9

Summary for Pond 1.2P:

Inflow Area =

1.150 ac, 48.70% Impervious, Inflow Depth = 0.95" for 1-yr event

Inflow

=

1.4 cfs @ 12.05 hrs, Volume=

0.091 af

Outflow

=

0.0 cfs @ 24.04 hrs, Volume=

0.088 af, Atten= 98%, Lag= 719.4 min

Primary

=

0.0 cfs @ 24.04 hrs, Volume=

0.088 af

Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

Starting Elev= 266.00' Surf.Area= 5,300 sf Storage= 7,600 cf

Peak Elev= 266.53' @ 24.04 hrs Surf.Area= 6,202 sf Storage= 10,651 cf (3,051 cf above start)

Plug-Flow detention time= (not calculated: initial storage exceeds outflow)

Center-of-Mass det. time= 1,665.6 min ( 2,539.1 - 873.5 )

Volume

Invert

Avail.Storage

Storage Description

#1

262.00'

21,600 cf

Custom Stage Data (Prismatic) Listed below (Recalc)

Elevation

Surf.Area

Inc.Store

Cum.Store

(feet)

(sq-ft)

(cubic-feet)

262.00

100

0

264.00 1,100

1,200

266.00 5,300

6,400

7,600

268.00 8,700

14,000

21,600

Device

Routing

Invert

Outlet Devices

#1

Primary

266.80'

1.0' long x 0.5' breadth Broad-Crested Rectangular Weir X 2.00

Head (feet) 0.20 0.40 0.60 0.80 1.00

Coef. (English) 2.80 2.92 3.08 3.30 3.32

#2

Primary

266.00'

1.1" Vert. Orifice/Grate C= 0.600

Primary OutFlow Max=0.0 cfs @ 24.04 hrs HW=266.53' TW=0.00' (Dynamic Tailwater)

1=Broad-Crested Rectangular Weir ( Controls 0.0 cfs)

(36)

NY-Downey 24-hr S1 1-yr Rainfall=2.66"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 10

(37)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 11

Summary for Subcatchment 1.1S:

Runoff

=

8.3 cfs @ 12.04 hrs, Volume=

0.598 af, Depth= 3.50"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

Area (ac)

CN

Description

0.750

98 Paved parking, HSG B

0.490

61 >75% Grass cover, Good, HSG B

0.810

96 Gravel surface, HSG B

2.050

88 Weighted Average

1.300 63.41% Pervious Area

0.750 36.59% Impervious Area

Tc

Length

Slope

Velocity

Capacity

Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

(38)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 12

Summary for Subcatchment 1.2S:

Runoff

=

3.6 cfs @ 12.04 hrs, Volume=

0.254 af, Depth= 2.65"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

Area (ac)

CN

Description

0.560

98 Paved parking, HSG B

0.590

61 >75% Grass cover, Good, HSG B

1.150

79 Weighted Average

0.590 51.30% Pervious Area

0.560 48.70% Impervious Area

Tc

Length

Slope

Velocity

Capacity

Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

(39)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 13

Summary for Subcatchment 1.3S:

Runoff

=

7.0 cfs @ 12.34 hrs, Volume=

1.117 af, Depth= 0.95"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

Area (ac)

CN

Description

0.300

98 Paved parking, HSG B

7.500

55 Woods, Good, HSG B

0.200

39 >75% Grass cover, Good, HSG A

1.800

30 Woods, Good, HSG A

4.300

68 1 acre lots, 20% imp, HSG B

14.100

56 Weighted Average

12.940 91.77% Pervious Area

1.160 8.23% Impervious Area

Tc

Length

Slope

Velocity

Capacity

Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

11.3

100 0.0900

0.15 Sheet Flow,

Woods: Light underbrush n= 0.400 P2= 3.50"

5.8

410 0.0560

1.18 Shallow Concentrated Flow,

Woodland Kv= 5.0 fps

3.2

258 0.0360

1.33 Shallow Concentrated Flow,

Short Grass Pasture Kv= 7.0 fps

2.1

530 0.0100

4.27

34.15 Channel Flow,

Area= 8.0 sf Perim= 10.0' r= 0.80'

n= 0.030 Earth, grassed & winding

1.2

336 0.0113

4.82

3.79 Pipe Channel,

(40)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 14

(41)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 15

Summary for Reach DP1:

Inflow Area =

17.300 ac, 14.28% Impervious, Inflow Depth > 1.02" for 10-yr event

Inflow

=

7.3 cfs @ 12.35 hrs, Volume=

1.466 af

Outflow

=

7.3 cfs @ 12.35 hrs, Volume=

1.466 af, Atten= 0%, Lag= 0.0 min

Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

(42)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 16

Summary for Pond 1.1P:

Inflow Area =

2.050 ac, 36.59% Impervious, Inflow Depth = 3.50" for 10-yr event

Inflow

=

8.3 cfs @ 12.04 hrs, Volume=

0.598 af

Outflow

=

0.5 cfs @ 13.38 hrs, Volume=

0.598 af, Atten= 93%, Lag= 80.6 min

Discarded =

0.3 cfs @ 13.38 hrs, Volume=

0.498 af

Primary

=

0.3 cfs @ 13.38 hrs, Volume=

0.100 af

Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

Peak Elev= 268.11' @ 13.38 hrs Surf.Area= 5,722 sf Storage= 12,950 cf

Plug-Flow detention time= (not calculated: outflow precedes inflow)

Center-of-Mass det. time= 421.4 min ( 1,231.2 - 809.8 )

Volume

Invert

Avail.Storage

Storage Description

#1

265.00'

44,050 cf

Custom Stage Data (Prismatic) Listed below (Recalc)

Elevation

Surf.Area

Inc.Store

Cum.Store

(feet)

(sq-ft)

(cubic-feet)

265.00 2,100

0

266.00 3,800

2,950

268.00 5,600

9,400

12,350

270.00 7,900

13,500

25,850

272.00 10,300

18,200

44,050

Device

Routing

Invert

Outlet Devices

#1

Primary

269.70'

0.5' long x 0.5' breadth Broad-Crested Rectangular Weir

Head (feet) 0.20 0.40 0.60 0.80 1.00

Coef. (English) 2.80 2.92 3.08 3.30 3.32

#2

Discarded

265.00'

2.000 in/hr Exfiltration over Surface area

#3

Primary

267.50'

4.0" Vert. Orifice/Grate C= 0.600

Discarded OutFlow Max=0.3 cfs @ 13.38 hrs HW=268.11' (Free Discharge)

2=Exfiltration (Exfiltration Controls 0.3 cfs)

Primary OutFlow Max=0.3 cfs @ 13.38 hrs HW=268.11' TW=0.00' (Dynamic Tailwater)

1=Broad-Crested Rectangular Weir ( Controls 0.0 cfs)

(43)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 17

(44)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 18

Summary for Pond 1.2P:

Inflow Area =

1.150 ac, 48.70% Impervious, Inflow Depth = 2.65" for 10-yr event

Inflow

=

3.6 cfs @ 12.04 hrs, Volume=

0.254 af

Outflow

=

0.3 cfs @ 12.96 hrs, Volume=

0.250 af, Atten= 91%, Lag= 54.7 min

Primary

=

0.3 cfs @ 12.96 hrs, Volume=

0.250 af

Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

Starting Elev= 266.00' Surf.Area= 5,300 sf Storage= 7,600 cf

Peak Elev= 266.94' @ 12.96 hrs Surf.Area= 6,906 sf Storage= 13,367 cf (5,767 cf above start)

Plug-Flow detention time= 3,278.0 min calculated for 0.075 af (30% of inflow)

Center-of-Mass det. time= 1,172.0 min ( 2,014.8 - 842.8 )

Volume

Invert

Avail.Storage

Storage Description

#1

262.00'

21,600 cf

Custom Stage Data (Prismatic) Listed below (Recalc)

Elevation

Surf.Area

Inc.Store

Cum.Store

(feet)

(sq-ft)

(cubic-feet)

262.00

100

0

264.00 1,100

1,200

266.00 5,300

6,400

7,600

268.00 8,700

14,000

21,600

Device

Routing

Invert

Outlet Devices

#1

Primary

266.80'

1.0' long x 0.5' breadth Broad-Crested Rectangular Weir X 2.00

Head (feet) 0.20 0.40 0.60 0.80 1.00

Coef. (English) 2.80 2.92 3.08 3.30 3.32

#2

Primary

266.00'

1.1" Vert. Orifice/Grate C= 0.600

Primary OutFlow Max=0.3 cfs @ 12.96 hrs HW=266.94' TW=0.00' (Dynamic Tailwater)

1=Broad-Crested Rectangular Weir (Weir Controls 0.3 cfs @ 1.07 fps)

(45)

NY-Downey 24-hr S1 10-yr Rainfall=4.82"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 19

(46)

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 20

Summary for Subcatchment 1.1S:

Runoff

=

14.8 cfs @ 12.04 hrs, Volume=

1.221 af, Depth= 7.15"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

Area (ac)

CN

Description

0.750

98 Paved parking, HSG B

0.490

61 >75% Grass cover, Good, HSG B

0.810

96 Gravel surface, HSG B

2.050

88 Weighted Average

1.300 63.41% Pervious Area

0.750 36.59% Impervious Area

Tc

Length

Slope

Velocity

Capacity

Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

(47)

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 21

Summary for Subcatchment 1.2S:

Runoff

=

7.3 cfs @ 12.04 hrs, Volume=

0.581 af, Depth= 6.06"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

Area (ac)

CN

Description

0.560

98 Paved parking, HSG B

0.590

61 >75% Grass cover, Good, HSG B

1.150

79 Weighted Average

0.590 51.30% Pervious Area

0.560 48.70% Impervious Area

Tc

Length

Slope

Velocity

Capacity

Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

(48)

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 22

Summary for Subcatchment 1.3S:

Runoff

=

28.7 cfs @ 12.30 hrs, Volume=

3.891 af, Depth= 3.31"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

Area (ac)

CN

Description

0.300

98 Paved parking, HSG B

7.500

55 Woods, Good, HSG B

0.200

39 >75% Grass cover, Good, HSG A

1.800

30 Woods, Good, HSG A

4.300

68 1 acre lots, 20% imp, HSG B

14.100

56 Weighted Average

12.940 91.77% Pervious Area

1.160 8.23% Impervious Area

Tc

Length

Slope

Velocity

Capacity

Description

(min)

(feet)

(ft/ft)

(ft/sec)

(cfs)

11.3

100 0.0900

0.15 Sheet Flow,

Woods: Light underbrush n= 0.400 P2= 3.50"

5.8

410 0.0560

1.18 Shallow Concentrated Flow,

Woodland Kv= 5.0 fps

3.2

258 0.0360

1.33 Shallow Concentrated Flow,

Short Grass Pasture Kv= 7.0 fps

2.1

530 0.0100

4.27

34.15 Channel Flow,

Area= 8.0 sf Perim= 10.0' r= 0.80'

n= 0.030 Earth, grassed & winding

1.2

336 0.0113

4.82

3.79 Pipe Channel,

(49)

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 23

(50)

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 24

Summary for Reach DP1:

Inflow Area =

17.300 ac, 14.28% Impervious, Inflow Depth = 3.48" for 100-yr event

Inflow

=

32.4 cfs @ 12.30 hrs, Volume=

5.011 af

Outflow

=

32.4 cfs @ 12.30 hrs, Volume=

5.011 af, Atten= 0%, Lag= 0.0 min

Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

(51)

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 25

Summary for Pond 1.1P:

Inflow Area =

2.050 ac, 36.59% Impervious, Inflow Depth = 7.15" for 100-yr event

Inflow

=

14.8 cfs @ 12.04 hrs, Volume=

1.221 af

Outflow

=

1.4 cfs @ 12.88 hrs, Volume=

1.221 af, Atten= 90%, Lag= 50.6 min

Discarded =

0.4 cfs @ 12.88 hrs, Volume=

0.677 af

Primary

=

1.1 cfs @ 12.88 hrs, Volume=

0.544 af

Routing by Dyn-Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.05 hrs

Peak Elev= 270.12' @ 12.88 hrs Surf.Area= 8,042 sf Storage= 26,793 cf

Plug-Flow detention time= (not calculated: outflow precedes inflow)

Center-of-Mass det. time= 376.6 min ( 1,164.0 - 787.4 )

Volume

Invert

Avail.Storage

Storage Description

#1

265.00'

44,050 cf

Custom Stage Data (Prismatic) Listed below (Recalc)

Elevation

Surf.Area

Inc.Store

Cum.Store

(feet)

(sq-ft)

(cubic-feet)

265.00 2,100

0

266.00 3,800

2,950

268.00 5,600

9,400

12,350

270.00 7,900

13,500

25,850

272.00 10,300

18,200

44,050

Device

Routing

Invert

Outlet Devices

#1

Primary

269.70'

0.5' long x 0.5' breadth Broad-Crested Rectangular Weir

Head (feet) 0.20 0.40 0.60 0.80 1.00

Coef. (English) 2.80 2.92 3.08 3.30 3.32

#2

Discarded

265.00'

2.000 in/hr Exfiltration over Surface area

#3

Primary

267.50'

4.0" Vert. Orifice/Grate C= 0.600

Discarded OutFlow Max=0.4 cfs @ 12.88 hrs HW=270.12' (Free Discharge)

2=Exfiltration (Exfiltration Controls 0.4 cfs)

Primary OutFlow Max=1.1 cfs @ 12.88 hrs HW=270.12' TW=0.00' (Dynamic Tailwater)

1=Broad-Crested Rectangular Weir (Weir Controls 0.4 cfs @ 1.90 fps)

(52)

NY-Downey 24-hr S1 100-yr Rainfall=8.59"

3622 Route 9 LLC, Proposed Cond-Revised

Printed 7/1/2021

Prepared by {enter your company name here}

Page 26

STORMWATER POLLUTION PREVENTION PLAN