STORM WATER MANAGEMENT ANALYSIS

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STORM WATER MANAGEMENT ANALYSIS

for

Church Hill Road

Woodbury, Connecticut

August 31, 2020

Prepared for:

Doug & Heather McAllister

Prepared by:

15 Research Drive

Suite 3

Woodbridge, Connecticut 06525

Phone: (203) 881-8145

www.bbengrs.com

_____________________________________________________________________________________________________________________________________________________________________________

Bryan P. Nesteriak, PE, LS 23556 Job #1026

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APPENDICES

APPENDIX A Figures

• Pre-Development Watershed Area Map

• Post-Development Watershed Area Map

APPENDIX B Hydrograph Data & Calculations

• Hydrograph Return Period Recap

• Graphical Hydrograph Reports

• Pond Reports

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1.0 PROJECT DESCRIPTION

The proposed project includes the construction of a single family dwelling located at the property of Lot 1 of the Applewood Estate Open Space Subdivision located at Church Hill Road in Woodbury, Connecticut. The two lots with areas of 9.1758 acre and 4.5621 acre respectively are both currently vacant with the exception of an old wood driveway that provides access to the property from Church Hill Road. The proposed development includes the construction of a new single family dwelling, a barn, inground pool, and the construction of a gravel and asphalt driveway that will be located on both Lot 1 and Lot 2 as part of a shared accessway. Water and waste service will be provided by a well and an engineered septic system. Storm water from the proposed roofs and a portion of the driveway will be collected, detained and treated on-side with the use of an underground detention system. Runoff from the driveway will be directed to an infiltration trench which has been designed to treat the first inch of runoff.

2.0 SOIL ANALYSIS

The subject parcel was researched and tested for storm water infiltration suitability. According to the Soil Survey of Fairfield County the parcel is underlain with a variety of soils, including Paxton and Montauk fine sandy loams, 8%-15% slope (84 C), Paxton and Montauk fine sandy loams, 3%-8% (84B), Udorthentis-Pits Complex, gravelly (305) which are classified as hydrologic soil group “C”. In addition, the project area is also underlain with Gloucester gravelly sandy loams, (59D) and Ridgebury, Leicester, and Whitman soils (3) which are classified as hydrologic soil groups “A” and “D” respectively.

3.0 METHODOLOGY & ANALYSIS

Watershed

This study was prepared using the Soil Conservation Service (SCS) methodology. This method outlines procedures for calculating peak rates of runoff resulting from precipitation events and procedures for developing runoff hydrographs. The calculations use the unit hydrograph method as described by Technical Release 55 (TR-55). The rates of runoff for the pre and post-development conditions were compared to determine any change as a result of the improvements.

Composite values for area, curve number (CN) and time of concentration (Tc) were calculated for each the pre-development and post-development condition. The curve numbers were calculated using the following values:

Cover Description Hyd. Condition CN

Undeveloped: woods-grass combination Fair “A” 43 Undeveloped: woods-grass combination Fair “C” 76 Undeveloped: woods-grass combination Fair “D” 82

Proposed Lawn: grassland Good “A” 39

Proposed Lawn: grassland Good “C” 74

Proposed Lawn: grassland Good “D” 80

Impervious: house, driveway, improvements - 98

The pre-development condition was modeled as two sub-watersheds, Watershed A and Watershed B, both conditions was modeled as undeveloped land, cover type woods-grass combination, in fair hydrologic condition. The value calculated for the pre-development was as follows:

Description Area CN Tc

Pre-Development Watershed A 3.49 acres 63 14.6 min.

[Undeveloped: woods-grass combo “A” 1.43 43] [Undeveloped: woods-grass combo “C” 1.77 76] [Undeveloped: woods-grass combo “D” 0.29 82]

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2

Pre-Development Watershed B 0.76 acres 56 15.6 min.

[Undeveloped: woods-grass combo “A” 0.45 43] [Undeveloped: woods-grass combo “C” 0.31 76]

The post-developed condition utilized three watersheds, one of which will be detained, and the other two that will flow overland and naturally off-side. Pond Inflow, the detained sub-watershed, consists of runoff from the proposed dwelling, barn, part of the driveway and a portion of the surrounding lawn area. Undetained area consists of runoff from the remaining driveway and vegetated land that will be allowed to flow offsite naturally as it does today. Values used for the post-development condition were as follows:

Description Area CN Tc

Watershed A Undetained Area 3.41 acres 65 14.6 min.

[Impervious: driveway 0.25 acres 98]

[Proposed Lawn: grassland “A” 0.76 acres 39] [Undeveloped: woods-grass combo “A” 0.50 acres 43] [Proposed Lawn: grassland “C” 0.10 acres 74] [Undeveloped: woods-grass combo “C” 1.56 acres 76] [Undeveloped: woods-grass combo “D” 0.16 acres 82] [Proposed Lawn: grassland “D” 0.08 acres 80]

Watershed B Undetained Area 0.67 acres 57 15.9 min.

[Proposed Lawn: grassland “A” 0.22 acres 39] [Undeveloped: woods-grass combo “A” 0.14 acres 43] [Proposed Lawn: grassland “C” 0.09 acres 74] [Undeveloped: woods-grass combo “C” 0.22 acres 76]

Pond Inflow Area 0.17 acres 74 6.0 min.

[Proposed Lawn: grassland “A” 0.07 acres 39] [Impervious: Building, driveway 0.10 acres 98]

The design storm used for this study is the 24 hour SCS Type III cumulative rainfall distribution. All of the watersheds were analyzed by the computer program Hydraflow Hydrographs Extension for AutoCAD Civil 3D 2019; the results of which are located in Appendix B. For convenience and to conserve resources, the drainage calculations included in the appendices of this report were limited to the 25 year storm event.

Detention System

The detention system has been designed to contain, infiltrate the 25 year runoff of the building, barn and a portion of the driveway. A 1’x3’ stone infiltration trench has been designed to collect and treat Infiltration rates were used as part of the design; however, the values used were twice the measured rates for a factor of safety.

Results

The calculated storm water peak flows are as follows:

2-YEAR 5-YEAR 10-YEAR 25-YEAR

CONDITION FLOW FLOW FLOW FLOW

Watershed A Pre-Development 1.44 CFS 2.93 CFS 4.48 CFS 7.27 CFS Watershed B Pre-Development 0.12 CFS 0.34 CFS 0.61 CFS 1.12 CFS Watershed A Undetained Area 1.71 CFS 3.28 CFS 4.87 CFS 7.70 CFS Watershed B Undetained Area 0.18 CFS 0.51 CFS 0.87 CFS 1.54 CFS Pond Inflow Area 0.22 CFS 0.35 CFS 0.47 CFS 0.68 CFS

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3

Pond Route 0.00 CFS 0.00 CFS 0.09 CFS 0.33 FS Watershed A Final Combined 1.71 CFS 3.28 CFS 4.87 CFS 8.03 CFS

In order to accurately analyze the post-developed condition, the pre-development hydrographs were compared to their respective combined hydrographs of Pond Inflow and Undetained.

Watershed A Pre-Development 1.44 CFS 2.93 CFS 4.48 CFS 7.27 CFS Watershed A Final Combined 1.71 CFS 3.28 CFS 4.87 CFS 8.03 CFS PROPOSED CHANGE 0.27 CFS 0.35 CFS 0.39 CFS 0.76 CFS

Watershed B Pre-Development 0.12 CFS 0.34 CFS 0.61 CFS 1.12 CFS Watershed B Undetained Area 0.18 CFS 0.51 CFS 0.87 CFS 1.54 CFS PROPOSED CHANGE 0.06 CFS 0.17 CFS 0.26 CFS 0.42 CFS

The proposed change has been calculated to show that the stormwater peak flow rates for each watershed are expected to nominally increase from the development. Due to the large size of the watershed and sparse development in the area, this increase is not expected to create any issues downstream of the proposed improvement.

4.0 STORM WATER QUALITY ANALYSIS

Since the accessway and driveways will be limited to mostly residential traffic, the observance of any oils, grease or particulates in the storm water runoff is remote. All trench drains and infiltration trenches should be cleaned periodically in order to remove accumulated sediment. Salts and other dissolved matter will infiltrate to the ground via the detention systems and infiltration trench where the soil will encourage filtering.

The system was planned in accordance with design considerations found in the 2004 Connecticut Stormwater Quality Manual. As stated in the manual it should be enabled to infiltrate the full Water Quality Volume (WQV). The underground detention system was designed to handle 161.7% of the WQV of the pond inflow. Calculations for the system are located in Appendix B.

The homeowners will be responsible to implement an annual maintenance program which should include pavement sweeping, gutter and trench drain cleaning and pipe maintenance. Proper fertilizer and pesticide management and household pet waste management should be observed.

5.0 CONCLUSION

The proposed storm water collection system has been designed to adequately convey the required storm event with nominal increase from the development. No adverse impacts are expected due to the proposed improvement and the system has been designed to adequately maintain water quality.

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6.0 REFERENCES

1. Urban Hydrology for Small Watersheds, Technical Release No. 55, USDA Soil Conservation Service Publication, June 1986.

2. Rainfall Frequency Values for Connecticut with 24-Hour Storm Duration, United States Department of Commerce and Weather Bureau, T.P. 40, May 1961.

3. 2002 Connecticut Guidelines for Soil Erosion and Sediment Control, The Connecticut Council on Soil and Water Conservation.

4. Debo, Thomas N. and Reese, Andrew J., Municipal Stormwater Management, Second Edition, Boca Raton, Lewis Publishers, 2003

5. 2004 Connecticut Stormwater Quality Manual, Connecticut Department of Environmental Protection.

6. Web Soil Survey. 8/1/2006. National Resources Conservation Service <http://websoilsurvey.nrcs.usda.gov/app/>

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WATERSHED B PRE-DEVELOPMENT AREA WATERSHED A PRE-DEVELOPMENT AREA

SOIL TYPE: PAXTON AND MONTAUK FINE SANDY LOAMS, 3%-8% SLOPE (84B)

HYD. GROUP: C

SOIL TYPE PAXTON AND MONTAUK FINE SANDY LOAMS, 8%-15% SLOPE (84C)

HYD. GROUP: C

SOIL TYPE: GLOUCESTER GRAVELLY SANDY LOAM, 15%-35% SLOPE,

EXTREMELY STONY (59D) HYD. GROUP: A

SOIL TYPE RIDGEBURY, LEICESTER AND WHITMAN SOILS, 0%-8% SLOPES,

EXTREMELY STONY (3) HYD. GROUP: D

CHURCH

HILL SOIL TYPE: UDORTHENTS-PITS COMPLEX,

GRAVELLY (305) HYD. GROUP: C

EXISTING WATERSHED AREA MAP

OF

CHURCH HILL ROAD WOODBURY, CT

Land Surveying, Professional Engineering &

Land Use Consultants

15 Research Drive

Woodbridge, CT 06525

P: (203) 881-8145

www.bbengrs.com

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WATERSHED B UNDETAINED AREA

WATERSHED A UNDETAINED AREA

SOIL TYPE: PAXTON AND MONTAUK FINE SANDY LOAMS, 3%-8% SLOPE (84B)

HYD. GROUP: C

SOIL TYPE PAXTON AND MONTAUK FINE SANDY LOAMS, 8%-15% SLOPE (84C)

HYD. GROUP: C

SOIL TYPE: GLOUCESTER GRAVELLY SANDY LOAM, 15%-35% SLOPE,

EXTREMELY STONY (59D) HYD. GROUP: A

SOIL TYPE RIDGEBURY, LEICESTER AND WHITMAN SOILS, 0%-8% SLOPES,

EXTREMELY STONY (3) HYD. GROUP: D

CHURCH

HILL SOIL TYPE: UDORTHENTS-PITS COMPLEX,

GRAVELLY (305) HYD. GROUP: C

POND INFLOW AREA

PROPOSED WATERSHED AREA MAP

OF

CHURCH HILL ROAD WOODBURY, CT

Land Surveying, Professional Engineering &

Land Use Consultants

15 Research Drive

Woodbridge, CT 06525

P: (203) 881-8145

www.bbengrs.com

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Hydrograph Return Period Recap

Hyd. Hydrograph Inflow Peak Outflow (cfs) Hydrograph

No. type hyd(s) Description

(origin) 1-yr 2-yr 3-yr 5-yr 10-yr 25-yr 50-yr 100-yr

1 SCS Runoff --- --- 1.436 --- 2.928 4.478 7.272 --- --- Watershed A Pre Development

3 SCS Runoff --- --- 0.123 --- 0.342 0.606 1.121 --- --- Watershed B Pre Development

5 SCS Runoff --- --- 1.712 --- 3.283 4.872 7.704 --- --- Watershed A Undetained Area

7 SCS Runoff --- --- 0.184 --- 0.505 0.867 1.540 --- --- Watershed B Undetained Area

9 SCS Runoff --- --- 0.218 --- 0.348 0.472 0.682 --- --- Pond Inflow Area

10 Reservoir 9 --- 0.000 --- 0.000 0.091 0.329 --- --- Pond Route

12 Combine 5, 10, --- 1.712 --- 3.283 4.872 8.027 --- --- Watershed A Final Combined

Proj. file: 1021 Hydraflow.gpw Friday, 08 / 28 / 2020

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Hydrograph Summary Report

Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph No. type flow interval Peak volume hyd(s) elevation strge used Description

(origin) (cfs) (min) (min) (cuft) (ft) (cuft)

1 SCS Runoff 7.272 2 732 30,389 --- --- --- Watershed A Pre Development

3 SCS Runoff 1.121 2 732 4,944 --- --- --- Watershed B Pre Development

5 SCS Runoff 7.704 2 732 31,937 --- --- --- Watershed A Undetained Area

7 SCS Runoff 1.540 2 724 4,562 --- --- --- Watershed B Undetained Area

9 SCS Runoff 0.682 2 724 2,039 --- --- --- Pond Inflow Area

10 Reservoir 0.329 2 730 481 9 662.29 565 Pond Route

12 Combine 8.027 2 732 32,419 5, 10, --- --- Watershed A Final Combined

1021 Hydraflow.gpw Return Period: 25 Year Friday, 08 / 28 / 2020

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Hydrograph Report

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® 2019 by Autodesk, Inc. v2020 Friday, 08 / 28 / 2020

Hyd. No. 1

Watershed A Pre Development

Hydrograph type

= SCS Runoff

Peak discharge

= 7.272 cfs

Storm frequency

= 25 yrs

Time to peak

= 732 min

Time interval

= 2 min

Hyd. volume

= 30,389 cuft

Drainage area

= 3.490 ac

Curve number

= 63*

Basin Slope

= 0.0 %

Hydraulic length

= 0 ft

Tc method

= TR55

Time of conc. (Tc)

= 14.60 min

Total precip.

= 6.40 in

Distribution

= Type III

Storm duration

= 24 hrs

Shape factor

= 484

* Composite (Area/CN) = [(1.430 x 43) + (1.770 x 76) + (0.290 x 82)] / 3.490 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 Q (cfs) Time (min)

Watershed A Pre Development

Hyd. No. 1 -- 25 Year

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Hydrograph Report

Hyd. No. 3

Watershed B Pre Development

Hydrograph type

= SCS Runoff

Peak discharge

= 1.121 cfs

Storm frequency

= 25 yrs

Time to peak

= 732 min

Time interval

= 2 min

Hyd. volume

= 4,944 cuft

Drainage area

= 0.760 ac

Curve number

= 56*

Basin Slope

= 0.0 %

Hydraulic length

= 0 ft

Tc method

= TR55

Time of conc. (Tc)

= 15.60 min

Total precip.

= 6.40 in

Distribution

= Type III

Storm duration

= 24 hrs

Shape factor

= 484

* Composite (Area/CN) = [(0.450 x 43) + (0.310 x 76)] / 0.760 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 Q (cfs) Time (min)

Watershed B Pre Development

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Hydrograph Report

Hyd. No. 5

Watershed A Undetained Area

Hydrograph type

= SCS Runoff

Peak discharge

= 7.704 cfs

Storm frequency

= 25 yrs

Time to peak

= 732 min

Time interval

= 2 min

Hyd. volume

= 31,937 cuft

Drainage area

= 3.410 ac

Curve number

= 65

Basin Slope

= 0.0 %

Hydraulic length

= 0 ft

Tc method

= TR55

Time of conc. (Tc)

= 14.60 min

Total precip.

= 6.40 in

Distribution

= Type III

Storm duration

= 24 hrs

Shape factor

= 484

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 Q (cfs) Time (min)

Watershed A Undetained Area

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Hydrograph Report

Hyd. No. 7

Watershed B Undetained Area

Hydrograph type

= SCS Runoff

Peak discharge

= 1.540 cfs

Storm frequency

= 25 yrs

Time to peak

= 724 min

Time interval

= 2 min

Hyd. volume

= 4,562 cuft

Drainage area

= 0.670 ac

Curve number

= 57*

Basin Slope

= 0.0 %

Hydraulic length

= 0 ft

Tc method

= TR55

Time of conc. (Tc)

= 15.90 min

Total precip.

= 6.40 in

Distribution

= Type II

Storm duration

= 24 hrs

Shape factor

= 484

* Composite (Area/CN) = [(0.220 x 39) + (0.140 x 43) + (0.090 x 74) + (0.220 x 76)] / 0.670 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 1.00 1.00 2.00 2.00 Q (cfs) Time (min)

Watershed B Undetained Area

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Hydrograph Report

Hyd. No. 9

Pond Inflow Area

Hydrograph type

= SCS Runoff

Peak discharge

= 0.682 cfs

Storm frequency

= 25 yrs

Time to peak

= 724 min

Time interval

= 2 min

Hyd. volume

= 2,039 cuft

Drainage area

= 0.170 ac

Curve number

= 74*

Basin Slope

= 0.0 %

Hydraulic length

= 0 ft

Tc method

= User

Time of conc. (Tc)

= 6.00 min

Total precip.

= 6.40 in

Distribution

= Type III

Storm duration

= 24 hrs

Shape factor

= 484

* Composite (Area/CN) = [(0.100 x 98) + (0.070 x 39)] / 0.170 0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 0.10 0.10 0.20 0.20 0.30 0.30 0.40 0.40 0.50 0.50 0.60 0.60 0.70 0.70 0.80 0.80 0.90 0.90 1.00 1.00 Q (cfs) Time (min)

Pond Inflow Area

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Hydrograph Report

Hyd. No. 10

Pond Route

Hydrograph type

= Reservoir

Peak discharge

= 0.329 cfs

Storm frequency

= 25 yrs

Time to peak

= 730 min

Time interval

= 2 min

Hyd. volume

= 481 cuft

Inflow hyd. No.

= 9 - Pond Inflow Area

Max. Elevation

= 662.29 ft

Reservoir name

= 48in concrete galley

Max. Storage

= 565 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 120 240 360 480 600 720 840 Q (cfs) 0.00 0.00 0.10 0.10 0.20 0.20 0.30 0.30 0.40 0.40 0.50 0.50 0.60 0.60 0.70 0.70 0.80 0.80 0.90 0.90 1.00 1.00 Q (cfs) Time (min)

Pond Route

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Pond Report

Pond No. 1 - 48in concrete galley Pond Data

UG Chambers -Invert elev. = 658.00 ft, Rise x Span = 4.00 x 2.83 ft, Barrel Len = 40.00 ft, No. Barrels = 1, Slope = 0.00%, Headers = No Encasement -Invert elev. = 657.50 ft, Width = 3.83 ft, Height = 5.00 ft, Voids = 40.00%

Stage / Storage Table

Stage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cuft) Total storage (cuft)

0.00 657.50 n/a 0 0 0.50 658.00 n/a 31 31 1.00 658.50 n/a 65 95 1.50 659.00 n/a 65 160 2.00 659.50 n/a 65 224 2.50 660.00 n/a 65 289 3.00 660.50 n/a 65 354 3.50 661.00 n/a 65 418 4.00 661.50 n/a 65 483 4.50 662.00 n/a 65 548 5.00 662.50 n/a 31 578

Culvert / Orifice Structures Weir Structures

[A] [B] [C] [PrfRsr] [A] [B] [C] [D] Rise (in) = 4.00 0.00 0.00 0.00 Span (in) = 4.00 0.00 0.00 0.00 No. Barrels = 1 0 0 0 Invert El. (ft) = 661.50 0.00 0.00 0.00 Length (ft) = 30.00 0.00 0.00 0.00 Slope (%) = 5.00 0.00 0.00 n/a N-Value = .013 .013 .013 n/a Orifice Coeff. = 0.60 0.60 0.60 0.60 Multi-Stage = n/a No No No Crest Len (ft) = 0.00 0.00 0.00 0.00 Crest El. (ft) = 0.00 0.00 0.00 0.00 Weir Coeff. = 3.33 3.33 3.33 3.33 Weir Type = --- --- --- ---Multi-Stage = No No No No

Exfil.(in/hr) = 4.000 (by Wet area) TW Elev. (ft) = 0.00

Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s).

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Stage (ft) 0.00 657.50 1.00 658.50 2.00 659.50 3.00 660.50 4.00 661.50 5.00 662.50 Elev (ft) Discharge (cfs) Stage / Discharge Total Q

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Hydrograph Report

Hyd. No. 12

Watershed A Final Combined

Hydrograph type

= Combine

Peak discharge

= 8.027 cfs

Storm frequency

= 25 yrs

Time to peak

= 732 min

Time interval

= 2 min

Hyd. volume

= 32,419 cuft

Inflow hyds.

= 5, 10

Contrib. drain. area

= 3.410 ac

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 Q (cfs) 0.00 0.00 2.00 2.00 4.00 4.00 6.00 6.00 8.00 8.00 10.00 10.00 Q (cfs) Time (min)

Watershed A Final Combined

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I = 58.8 % R = = 0.05 + 0.009 ( 58.8 ) = 0.579 1" (0.5792) (0.17) A = =

=

CF

= CF 578 CF, EQUATES TO OF THE WQV. 0.17 12 161.7%

THEREFORE, THE SYSTEMS COMPLY WITH THE REQUIREMENTS OF THE 2004 CONNECTICUT STORMWATER QUALITY MANUAL FOR UNDERGROUND INFILTRATION SYSTEMS.

357

Volume of designed basin 578

PER THE MANUAL, THE INFILTRATION SUTRUCTURES SHOULD BE DESIGNED TO MAINTAIN AT LEAST THE WATER QUALITY VOLUME (WQV)

AS DESIGNED, THE DETENTION SYSTEM HAS A TOTAL CAPACITY OF which 0.008 Acre-Feet

= site area in acres =

STORM WATER QUALITY CALCULATIONS

Underground Detention System

as defined by "2004 Connecticut Stormwater Quality Manual"

Determine "Water Quality Volume" (WQV)

percent impervious cover = Watershed:

WQV = 1" (R)(A) volumetric runoff coefficient = 0.05 + 0.009(I) 12

STORM WATER MANAGEMENT ANALYSIS