three county fairgrounds phase 1 stormwater app revised 03-2010.pdf

8/8/2019 Three County Fairgrounds Phase 1 Stormwater App Revised 03-2010.pdf

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Three County Fairgrounds 10/08/09 Stormwater Report Checklist Page 1 of 8

Massachusetts Department of Environmental ProtectionBureau of Resource Protection - Wetlands Program

Checklist for Stormwater Report

A. Introduction

Important: Whenfilling out forms

on the computer,use only the tabkey to move yourcursor - do notuse the returnkey.

A Stormwater Report must be submitted with the Notice of Intent permit application to documentcompliance with the Stormwater Management Standards. The following checklist is NOT a substitute for

the Stormwater Report (which should provide more substantive and detailed information) but is offeredhere as a tool to help the applicant organize their Stormwater Management documentation for theirReport and for the reviewer to assess this information in a consistent format. As noted in the Checklist,the Stormwater Report must contain the engineering computations and supporting information set forth inVolume 3 of the Massachusetts Stormwater Handbook. The Stormwater Report must be prepared andcertified by a Registered Professional Engineer (RPE) licensed in the Commonwealth.

The Stormwater Report must include:

The Stormwater Checklist completed and stamped by a Registered Professional Engineer (seepage 2) that certifies that the Stormwater Report contains all required submittals.

1This Checklist

is to be used as the cover for the completed Stormwater Report.

Applicant/Project Name

Project Address

Name of Firm and Registered Professional Engineer that prepared the Report Long-Term Pollution Prevention Plan required by Standards 4-6

Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan requiredby Standard 8

2

Operation and Maintenance Plan required by Standard 9

In addition to all plans and supporting information, the Stormwater Report must include a brief narrativedescribing stormwater management practices, including environmentally sensitive site design and LIDtechniques, along with a diagram depicting runoff through the proposed BMP treatment train. Plans arerequired to show existing and proposed conditions, identify all wetland resource areas, NRCS soil types,critical areas, Land Uses with Higher Potential Pollutant Loads (LUHPPL), and any areas on the sitewhere infiltration rate is greater than 2.4 inches per hour. The Plans shall identify the drainage areas forboth existing and proposed conditions at a scale that enables verification of supporting calculations.

As noted in the Checklist, the Stormwater Management Report shall document compliance with each ofthe Stormwater Management Standards as provided in the Massachusetts Stormwater Handbook. Thesoils evaluation and calculations shall be done using the methodologies set forth in Volume 3 of theMassachusetts Stormwater Handbook.

To ensure that the Stormwater Report is complete, applicants are required to fill in the Stormwater ReportChecklist by checking the box to indicate that the specified information has been included in theStormwater Report. If any of the information specified in the checklist has not been submitted, theapplicant must provide an explanation. The completed Stormwater Report Checklist and Certificationmust be submitted with the Stormwater Report.

1The Stormwater Report may also include the Illicit Discharge Compliance Statement required by Standard 10. If not included in

the Stormwater Report, the Ill icit Discharge Compliance Statement must be submitted prior to the discharge of stormwater runoff tothe post-construction best management practices.

2 For some complex projects, it may not be possible to include the Construction Period Erosion and Sedimentation Control Plan inthe Stormwater Report. In that event, the issuing authority has the discretion to issue an Order of Conditions that approves theproject and includes a condition requiring the proponent to submit the Construction Period Erosion and Sedimentation Control Planbefore commencing any land disturbance activity on the site.


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Checklist (continued)

LID Measures: Stormwater Standards require LID measures to be considered. Document whatenvironmentally sensitive design and LID Techniques were considered during the planning and design of

the project:

No disturbance to any Wetland Resource Areas

Site Design Practices (e.g. clustered development, reduced frontage setbacks)

Reduced Impervious Area (Redevelopment Only)

Minimizing disturbance to existing trees and shrubs

LID Site Design Credit Requested:

Credit 1

Credit 2

Credit 3

Use of country drainage versus curb and gutter conveyance and pipe

Bioretention Cells (includes Rain Gardens)

Constructed Stormwater Wetlands (includes Gravel Wetlands designs)

Treebox Filter

Water Quality Swale

Grass Channel

Green Roof

Other (describe):

Standard 1: No New Untreated Discharges

No new untreated discharges

Outlets have been designed so there is no erosion or scour to wetlands and waters of theCommonwealth

Supporting calculations specified in Volume 3 of the Massachusetts Stormwater Handbook included.


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Standard 2: Peak Rate Attenuation

Standard 2 waiver requested because the project is located in land subject to coastal storm flowageand stormwater discharge is to a wetland subject to coastal flooding.

Evaluation provided to determine whether off-site flooding increases during the 100-year 24-hourstorm.

Calculations provided to show that post-development peak discharge rates do not exceed pre-development rates for the 2-year and 10-year 24-hour storms. If evaluation shows that off-siteflooding increases during the 100-year 24-hour storm, calculations are also provided to show thatpost-development peak discharge rates do not exceed pre-development rates for the 100-year 24-hour storm.

Standard 3: Recharge Reduction in Impervious Area = Same or greater recharge on site

Soil Analysis provided.

Required Recharge Volume calculation provided.

Required Recharge volume reduced through use of the LID site Design Credits.

Sizing the infiltration, BMPs is based on the following method: Check the method used.

Static Simple Dynamic Dynamic Field1

Runoff from all impervious areas at the site discharging to the infiltration BMP.

Runoff from all impervious areas at the site is notdischarging to the infiltration BMP and calculationsare provided showing that the drainage area contributing runoff to the infiltration BMPs is sufficient togenerate the required recharge volume.

Recharge BMPs have been sized to infiltrate the Required Recharge Volume

Recharge BMPs have been sized to infiltrate the Required Recharge Volume onlyto the maximumextent practicable for the following reason:

Site is comprised solely of C and D soils and/or bedrock at the land surface

M.G.L. c. 21E sites pursuant to 310 CMR 40.0000

Solid Waste Landfill pursuant to 310 CMR 19.000

Project is otherwise subject to Stormwater Management Standards only to the maximum extentpracticable. Redevelopment project with less impervious area proposed

Calculations showing that the infiltration BMPs will drain in 72 hours are provided.

Property includes a M.G.L. c. 21E site or a solid waste landfill and a mounding analysis is included.

180% TSS removal is required prior to discharge to infiltration BMP if Dynamic Field method is used.


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Standard 4: Water Quality (continued)

The BMP is sized (and calculations provided) based on: MASTEP review

The or 1 Water Quality Volume or

The equivalent flow rate associated with the Water Quality Volume and documentation isprovided showing that the BMP treats the required water quality volume.

The applicant proposes to use proprietary BMPs, and documentation supporting use of proprietaryBMP and proposed TSS removal rate is provided. This documentation may be in the form of thepropriety BMP checklist found in Volume 2, Chapter 4 of the Massachusetts Stormwater Handbookand submitting copies of the TARP Report, STEP Report, and/or other third party studies verifyingperformance of the proprietary BMPs.

A TMDL exists that indicates a need to reduce pollutants other than TSS and documentation showingthat the BMPs selected are consistent with the TMDL is provided.

Standard 5: Land Uses With Higher Potential Pollutant Loads (LUHPPLs) Not Applicable Proposed project site is not expected to yield high potential pollutant loads.

The NPDES Multi-Sector General Permit covers the land use and the Stormwater PollutionPrevention Plan (SWPPP) has been included with the Stormwater Report.

The NPDES Multi-Sector General Permit covers the land use and the SWPPP will be submitted priortothe discharge of stormwater to the post-construction stormwater BMPs.

The NPDES Multi-Sector General Permit does notcover the land use.

LUHPPLs are located at the site and industry specific source control and pollution preventionmeasures have been proposed to reduce or eliminate the exposure of LUHPPLs to rain, snow, snowmelt and runoff, and been included in the long term Pollution Prevention Plan.

All exposure has been eliminated.

All exposure has notbeen eliminated and all BMPs selected are on MassDEP LUHPPL list.

The LUHPPL has the potential to generate runoff with moderate to higher concentrations of oil andgrease (e.g. all parking lots with >1000 vehicle trips per day) and the treatment train includes an oilgrit separator, a filtering bioretention area, a sand filter or equivalent.

Standard 6: Critical Areas Not Applicable The project site does not discharge to a critical area.

The discharge is near or to a critical area and the treatment train includes only BMPs that MassDEPhas approved for stormwater discharges to or near that particular class of critical area.

Critical areas and BMPs are identified in the Stormwater Report.


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Standard 7: Redevelopments and Other Projects Subject to the Standards only to the maximumextent practicable

The project is subject to the Stormwater Management Standards only to the maximum ExtentPracticable as a:

Limited Project

Small Residential Projects: 5-9 single family houses or 5-9 units in a multi-family developmentprovided there is no discharge that may potentially affect a critical area.

Small Residential Projects: 2-4 single family houses or 2-4 units in a multi-family developmentwith a discharge to a critical area

Marina and/or boatyard provided the hull painting, service and maintenance areas are protectedfrom exposure to rain, snow, snow melt and runoff

Bike Path and/or Foot Path

Redevelopment Project

Redevelopment portion of mix of new and redevelopment.

Certain standards are not fully met (Standard No. 1, 8, 9, and 10 must always be fully met) and anexplanation of why these standards are not met is contained in the Stormwater Report.

The project involves redevelopment and a description of all measures that have been taken toimprove existing conditions is provided in the Stormwater Report. The redevelopment checklist foundin Volume 2 Chapter 3 of the Massachusetts Stormwater Handbook may be used to document thatthe proposed stormwater management system (a) complies with Standards 2, 3 and the pretreatmentand structural BMP requirements of Standards 4-6 to the maximum extent practicable and (b)improves existing conditions.

Standard 8: Construction Period Pollution Prevention and Erosion and Sedimentation Control

A Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan must include thefollowing information:

Narrative;

Construction Period Operation and Maintenance Plan;

Names of Persons or Entity Responsible for Plan Compliance;

Construction Period Pollution Prevention Measures;

Erosion and Sedimentation Control Plan Drawings;

Detail drawings and specifications for erosion control BMPs, including sizing calculations;

Vegetation Planning;

Site Development Plan;

Construction Sequencing Plan; Sequencing of Erosion and Sedimentation Controls;

Operation and Maintenance of Erosion and Sedimentation Controls;

Inspection Schedule;

Maintenance Schedule;

Inspection and Maintenance Log Form.

A Construction Period Pollution Prevention and Erosion and Sedimentation Control Plan containingthe information set forth above has been included in the Stormwater Report.


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Standard 8: Construction Period Pollution Prevention and Erosion and Sedimentation Control(continued)

The project is highly complex and information is included in the Stormwater Report that explains whyit is not possible to submit the Construction Period Pollution Prevention and Erosion andSedimentation Control Plan with the application. A Construction Period Pollution Prevention andErosion and Sedimentation Control has notbeen included in the Stormwater Report but will besubmitted beforeland disturbance begins.

The project is notcovered by a NPDES Construction General Permit.

The project is covered by a NPDES Construction General Permit and a copy of the DRAFT SWPPPis in the Stormwater Report.

The project is covered by a NPDES Construction General Permit but no SWPPP been submitted.The SWPPP will be submitted BEFORE land disturbance begins.

Standard 9: Operation and Maintenance Plan

The Post Construction Operation and Maintenance Plan is included in the Stormwater Report andincludes the following information:

Name of the stormwater management system owners;

Party responsible for operation and maintenance;

Schedule for implementation of routine and non-routine maintenance tasks;

Plan showing the location of all stormwater BMPs maintenance access areas;

Description and delineation of public safety features;

Estimated operation and maintenance budget; and

Operation and Maintenance Log Form.

The responsible party is notthe owner of the parcel where the BMP is located and the StormwaterReport includes the following submissions:

A copy of the legal instrument (deed, homeowners association, utility trust or other legal entity)that establishes the terms of and legal responsibility for the operation and maintenance of theproject site stormwater BMPs;

A plan and easement deed that allows site access for the legal entity to operate and maintainBMP functions.

Standard 10: Prohibition of Illicit Discharges

The Long-Term Pollution Prevention Plan includes measures to prevent illicit discharges;

An Illicit Discharge Compliance Statement is attached;

NO Illicit Discharge Compliance Statement is attached but will be submitted prior tothe discharge ofany stormwater to post-construction BMPs.


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Three County Fairgrounds - Phase 1 March 18, 2010

Northampton, Massachusetts Stormwater Drainage Report

The Berkshire Design Group, Inc. Page 1

Table of Contents

Introduction 2

Site Terrain and Soils 3

Existing Conditions 3

Proposed Conditions 5

Calculations and Design 6

Stormwater Standards 7

Summary 9

Figures

Figure 1 Pre- Development Drainage Area Map

Figure 2 Post Development Drainage Area Map

Figure 3 USDA Soils Map

Appendices

Appendix A Pre- and Post Development Hydrologic Calculations

Appendix B Soil Test Pit Information

Appendix C Operation &Maintenance Plan

Appendix D Long Term Pollution Prevention Plan

Appendix E Stormwater Pollution Prevention and Erosion Control Plan

Appendix F Water Quality Information


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I. Introduction

The following report presents an analysis of the stormwater management systemfor the proposed Phase 1 redevelopment the Three County Fairgrounds, located

off Route 9 in Northampton, Massachusetts which is located in the SC zoning

district.

Locus Map (site outlined in red)

The proposed project involves the redevelopment of a small portion of the site.

The 15 existing horse barns and 2 other small buildings will be demolished and 3

new barns are proposed to be constructed.

The drainage areas analyzed total 56.80 acres of which approximately 6.62 acres

will be disturbed by construction activities. The impervious area on site will

decrease by approximately 620sf due to the demolition of many of the existing

buildings. The existing stormwater management system is sufficient to minimize

proposed peak flows to reduce or match the existing flows off the site, recharge

appropriate volumes of stormwater, and treat stormwater to the maximum extent


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E-1

E-1 is approximately 24.06 acres and contains a large area of the existing track,

horse barns, other miscellaneous buildings, grassed areas, paved areas, and gravel

areas. The area drains to existing catch basins which direct the stormwater to the

existing detention basin at the east end of the site (shown as E-Pond1 on Figure

1). The easterly detention pond has 2 outlets: The first outlet is a 12 CMPlocated on the north edge of Fair Street which discharges water across the street to

the property line located at the southeastern area of the site (shown as E-CP1 on

Figure 1). The second outlet is a catch basin located just south of Horse Barn H &

C. When the level of water in the pond exceeds elevation 117, it overflows out

of the catch basin and spills over Cross Path Road into the adjacent property

(shown as E-CP3 on Figure 1) causing standing water in the spring and summer

and frozen ponding in the winter. Occasionally when a large fairgrounds event is

planned, the detention pond is pumped to the other existing pond on the west side

of the site (shown as E-Pond2 on Figure 1) in order to drain the adjacent area.

The westerly basin discharges to the Williams Street Brook system (shown as E-

CP2 on Figure 1) which is undersized in most storms.

E-2

E-2 is approximately 10.75 acres and contains a portion of the existing track,

buildings, grassed areas, paved areas, and gravel areas. This area sheet flows into

existing catch basins which discharge into the westerly retention basin (E-Pond2).

The detention pond discharges into the Williams Street Brook drainage system

through a 12 pipe (E-CP1).

E-3

E-3 is approximately 10.38 acres and contains adjacent houses, buildings, grassed

areas, paved areas, and gravel areas. This area sheet flows into existing catchbasins which discharge directly into the Williams Street Brook drainage system

(E-CP1).

E-4

E-4 is approximately 7.52 acres and is located south of the main area and contains

a portion of Fair Street, existing buildings, grassed areas, and gravel areas. This

area sheet flows overland to the southern property line (E-CP2).

E-5

E-5 is approximately 3.41 acres and is located north of the main area and contains

a portion of Ferry Road, a basketball court, and grassed areas. This area sheet

flows over Ferry Road where it begins to pond until it enters the existing westerly

detention basin which drains to the Williams Street Brook system (E-CP1).

E-6

E-6 is approximately 0.68 acres and is located north of the main area and contains

a portion of Ferry Road, abutting houses, and grassed areas. This area sheet flows


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toward existing catch basins where it is directed to the easterly detention basin

which drains to the south eastern area of the site (E-CP2).

IV. Proposed Conditions

The proposed project does not alter the site significantly and it retains the general

flow patterns of the existing stormwater patterns. The proposed site contains 6

drainage areas (P-1 through P-6) and 3 different control points used for

determining peak runoff rates, and the site has an average curve number of 74 (the

same as existing conditions). The drainage areas and control points are shown on

the Post-Development Drainage Area Plan (see Figure 2). The following is a brief

description of each drainage area:

P-1

P-1 is approximately 24.06 acres and contains the 3 new horse barns, a large area

of the existing track, other miscellaneous buildings, grassed areas, paved areas,and gravel areas. The 3 new horse barns will generally drain to a new drain

system installed under 2 new concrete pads between the barns. Each pad contains

5 drain inlets with 2 sumps. Before horse manure is permitted to be stockpiled

on the pads, the drains inlets are replaced with covers to prohibit potential

contamination of the drainage system. The drains are all designed with sumps and

they are directed to a deep sump hooded catch basin which discharge to a

StormCeptor 2400 unit prior to discharging to the detention basin to maximize

TSS removal. The horse barn roof areas are piped directly into the drain system to

allow for separation of roof runoff which will increase the water quality entering

the detention basin. The rest of the existing area within P-1 drains to existing

catch basins or sheet flows to the existing detention basins on the east side of thesite (shown as P-Pond1 on Figure 2). The detention pond has 2 outlets. The first

outlet is a 12 CMP located on the north edge of Fair Street which discharges

water across the street to the property line located at the south eastern area of the

site (shown as P-CP1 on Figure 2). The second outlet is a catch basin located just

south of Horse Barn H & C (which will be removed in proposed conditions).

When the level of water in the pond exceeds elevation 117, it overflows out of

the catch basin and spills over Fair Street into adjacent property (shown as P-CP3

on Figure 2) causing standing water in the spring and summer and frozen ponding

in the winter. Occasionally when a large fairgrounds event is planned, the

retention pond is pumped to the other existing pond on the west side of the site

(shown as P-Pond2 on Figure 2) in order to drain the adjacent area. The westerly

basin discharges to the Williams Street Brook system (shown as P-CP2 on Figure

2) which is undersized in most storms.

P-2

P-2 is approximately 10.75 acres and contains a portion of the existing track,

buildings, grassed areas, paved areas, and gravel areas. This area sheet flows into

existing catch basins which discharge into the westerly retention basin (P-Pond2).


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The detention pond discharges into the Williams Street Brook drainage system

through a 12 pipe (P-CP1).

P-3P-3 is approximately 10.38 acres and contains adjacent houses, buildings, grassed

areas, paved areas, and gravel areas. This area sheet flows into existing catch

basins which discharge directly into the Williams Street Brook drainage system

(P-CP1).

P-4

P-4 is approximately 7.52 acres and is located south of the main area and contains

a portion of Fair Street, existing buildings, grassed areas, and gravel areas. This

area sheet flows overland to the southern property line (P-CP2).

P-5P-5 is approximately 3.41 acres and is located north of the main area and contains

a portion of Ferry Road, a basketball court, and grassed areas. This area sheet

flows over Ferry Road where it begins to pond until it enters the existing westerly

detention basin which drains to the Williams Street Brook system (P-CP1).

P-6

P-6 is approximately 0.68 acres and is located north of the main area and contains

a portion of Ferry Road, abutting houses, and grassed areas. This area sheet flows

toward existing catch basins where it is directed to the easterly detention basin

which drains to the south eastern area of the site (P-CP2).

V. Calculations and Design

Drainage calculations were performed on Hydrocad Stormwater Modeling System

version 8.0 using Soil Conservation Service (SCS) TR-20 methodology. The SCS

method is based on rainfall observations, which were used to develop the

Intensity-Duration-Frequency relationship, or IDF curve. The mass curve is a

dimensionless distribution of rainfall over time, which indicates the fraction of the

rainfall event that occurs at a given time within a 24-hour precipitation event. This

synthetic distribution develops peak rates for storms of varying duration and

intensities. The SCS distribution provides a cumulative rainfall at any point in

time and allows volume dependent routing runoff calculations to occur. These

calculations are included in the appendices.

The watershed boundaries for calculation purposes are divided according to the

proposed site grading and the natural limits of the drainage areas. The curve

numbers (CNs) and times of concentration for the existing and proposed


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subcatchment areas are based on the soil type and the existing and proposed cover

conditions at the site. The soil hydrologic group assumed for the site is noted in

Figure 3. Watershed subcatchment areas, runoff coefficients and watercourse

slopes are based on survey information.

Calculations were performed for the 2-, 10-, and 100-year frequency storms underexisting and proposed conditions. The results of the calculations are presented in

Table 1 below. Appendix A presents the Hydrocad calculations.

Flow Rates & Water Quantity

In the post development conditions the runoff from the proposed site will be

reduced due to a reduction of impervious area. Table 1 below presents the

comparison of flow rates and water quantity at both existing and proposed control

points.

Table 1 Peak Flow and Volume

Summary

*Names in parentheses refer to HydroCad model and calculations.

I. MADEP Stormwater Standards Compliance

Condition

& Point of

Analysis

Peak Flow

Rate(cfs)

Volume

(acre-ft)

Peak Flow

Rate(cfs)

Volume

(acre-ft)

Peak Flow

Rate(cfs)

Volume

(acre-ft)

Existing

Control Pt.

(E-CP1)*

Proposed

Control Pt.

(P-CP1)*

Existing

Control Pt.

(E-CP2)*

Proposed

Control Pt.

(P-CP2)*

Existing

Control Pt.

(P-CP3)*

Proposed

Control Pt.

(P-CP3)*

2.899

0.00 0.000 1.29 0.162 33.55 2.792

0.00 0.000 1.79 0.241 35.24

33.55 7.003

6.83 1.669 17.62 3.798 32.57 6.908

6.86 1.697 17.66 3.854

2-Year Storm 10-Year Storm 100-Year Storm

3.00 4.50 6.50

22.81 4.596

3.85 1.024 10.21 3.237 22.72 4.590

3.85 1.091 10.37 3.256


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The following section details how the project will meet DEP Stormwater

Management Policys ten stormwater management standards. This project is a

Redevelopment Project and Volume 2 Chapter 3 of the MA DEP Stormwater

handbook was utilized to ensure that the project will comply with the standards to

the maximum extent practicable.

Standard 1 - Untreated Stormwater

The proposed redevelopment will utilize the existing stormwater management

system and will not create any new discharges as the runoff from the new barns

will be directed to the existing easterly detention basin. The impervious area on

site will be reduced in proposed conditions and the majority of the new

impervious area will be directed to 2 drain systems between the barns, which are

equipped with sumps to remove potential solids the may enter the system. The

roof runoff will be directly piped into the system as MA DEP recommends. In

addition, measures have been taking to ensure manure from the barns does not

enter the drainage system as it does in existing conditions by enforcing employeesto cover the drain system prior to moving and disposing of any manure. Do to the

improved water quality and reduction in impervious area, the project site will

comply with Standard 1 as required for a redevelopment project

Standard 2 - Post-Development Peak Discharge Rates

The proposed project will have a net loss of 620sf of impervious area so the site

will generate less runoff in proposed conditions. The existing stormwater system

is sufficiently designed to ensure that post-development peak discharge rates are

equal or less than pre-development peak discharge rates leaving the site. Refer to

Table 1 Peak Flow and Volume Summary and Appendix A for HydroCAD

calculations.

Standard 3 - Recharge to Groundwater

The proposed project will improve the recharge opportunities on site by reducing

the impervious area from existing conditions as the proposed project will have a

net loss of 620sf of impervious area. Redevelopment projects require that

proposed sites approximate the annual recharge from the existing site. The net

loss in impervious area provides the site with the equal or greater opportunity for

water to infiltrate into the ground and recharge the groundwater to the maximum

extent practicable as required for redevelopment projects.

Standard 4 Water Quality

The proposed redevelopment will utilize the existing detention basin at the east

end of the site and a series of drains located within new concrete pads between the

new barns. There are 5 drains per pad and all contain a 2 sump system which

directs the stormwater to a deep sump hooded catch basin which providing

additional pretreatment for the stormwater. The new catch basin will discharge to

a StormCeptor 2400 unit allowing prior to entering the existing detention basin,


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achieving a combined TSS removal rate of approximately 83% improving water

quality to the maximum extent practicableas required for redevelopment

projects. The proposed manure management system will also increase the water

quality as the existing site does not have measures in place to prevent manure

from entering the stormwater system and causing contamination.

To ensure that the water quality on site will improve and be maintained at the

proper level of performance, an operation and maintenance plan has been

incorporated into the plans to ensure that the existing catch basins and detention

basins are maintained in order to ensure that they will function efficiently. The

reduction in impervious area will also allow the stormwater management system

to function more efficiently. Based on the improvements to the existing

conditions and treatment capabilities of the new and existing stormwater BMPs,

the project effectively meets the standard 4 and improves existing conditions.

Note that a Long Term Pollution Prevention Plan will be implemented to maintain

a clean site and ensure that all BMPs are functioning to their maximum potential.See Appendix D for Long Term Pollution Prevention Plan.

Standard 5 - Higher Potential Pollutant Loads

The proposed project is not expected to yield high potential pollutant loads.

Standard 6 - Protection of Critical Areas

The project site does not discharge to critical areas as defined in MA DEP

Stormwater Policy Handbook.

Standard 7 - Redevelopment ProjectsThe proposed project is a redevelopment project as per the MA DEP Volume 2

Chapter 3 definition: A Redevelopment is defined to include: Development

rehabilitation, expansion and phased projects on previously developed sites,

provided the redevelopment results in no net increase in impervious area. The

project has a proposed reduction in impervious area and has incorporated the

redevelopment checklist as guidance for the design.

Standard 8 - Erosion/Sediment Control

Erosion and sediment controls have been incorporated into the project design to

prevent erosion, control sediments, and stabilized exposed soils during

construction and land disturbance. See Appendix E for Construction Period

Pollution Prevention and Erosion Sedimentation Control.

Standard 9 - Operation/Maintenance Plan

An Operation and Maintenance Plan for the proposed project is included in

Appendix C. It includes general controls for construction and long term

maintenance of the stormwater management system.


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Standard 10 Prohibition of Illicit Discharges

No Illicit Discharge Compliance Statement is included with this report however

one will be submitted prior to the discharge of any stormwater to post-

construction BMPs.

VII. Summary

The impervious area from existing to proposed conditions will decrease by

approximately 620sf from the demolition of existing buildings and construction of

the 3 new barns. The combination of the new drain systems adjacent to the barns

along, the StormCeptor unit, and the existing stormwater management system

improves the site stormwater system and will meet the required standards for an

MA DEP Redevelopment project.


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Three County Fairgrounds March 18, 2010

Northampton, Massachusetts Stormwater Drainage Report Appendix

The Berkshire Design Group, Inc. Figures

Figures


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Three County Fairgrounds March 18, 2010

Northampton, Massachusetts Stormwater Drainage Report Appendix

The Berkshire Design Group, Inc. Appendix

Appendix A Pre- and Post Development

Hydrologic Calculations


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E-1

Area to Easterly BasinE-2

Area To W esterly Basin

E-3

Direct to Road DrainageInfrastructure

E-4

Southeast Area of Siteto South Property Line

E-5

Area north of site(includes basketball

court)

E-6

Northeast of Site (Roadand abutting property)

P-1

Area to Easterly Basin

P-2

Area To W esterly Basin

P-3

Direct to Road DrainageInfrastructure

P-4

Southeast Area of Siteto South Property Line

P-5

Area north of site(includes basketball

court)

P-6

Northeast of Site (Road

and abutting property)

E-CP1

Williams St. BrookInfrastructure

E-CP2

South Property Line

E-CP3

Cross Paths Road

P-CP1

Williams St. BrookInfrastructure

P-CP2

South Property Line

P-CP3

Cross Paths RoadE-Pond1

Existing East DetentionBasinE-Pond2

Existing West DetentionBasin

P-Pond1

Existing East DetentionBasin

P-Pond2

Existing West DetentionBasin

Drainage Diagram for Three Country Fairgrounds Phase 1- ActivePrepared by The Berkshire Design Group 3/22/2010

HydroCAD 8.00 s/n 000752 2006 HydroCAD Software Solutions LLC

Subcat Reach Pond Link


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Type III 24-hr 2 YRS Rainfall=3.00"Three Country Fairgrounds Phase 1- ActivePage 3Prepared by The Berkshire Design Group

3/22/2010HydroCAD 8.00 s/n 000752 2006 HydroCAD Software Solutions LLC

Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 pointsRunoff by SCS TR-20 method, UH=SCS

Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method

Runoff Area=1,048,195 sf Runoff Depth>0.80"Subcatchment E-1: Area to Easterly BasinFlow Length=888' Tc=17.0 min CN=72 Runoff=14.69 cfs 1.613 af

Runoff Area=468,308 sf Runoff Depth>1.12"Subcatchment E-2: Area To Westerly BasinFlow Length=1,136' Tc=16.9 min CN=78 Runoff=9.89 cfs 1.007 af

Runoff Area=451,921 sf Runoff Depth>0.85"Subcatchment E-3: Direct to Road Drainage InfrastructureFlow Length=100' Slope=0.0050 '/' Tc=19.5 min CN=73 Runoff=6.47 cfs 0.737 af

Runoff Area=327,415 sf Runoff Depth>0.71"Subcatchment E-4: Southeast Area of Site to South PropertyFlow Length=750' Tc=17.3 min CN=70 Runoff=3.85 cfs 0.445 af

Runoff Area=148,626 sf Runoff Depth>0.90"Subcatchment E-5: Area north of site (includes basketball cFlow Length=545' Tc=22.7 min CN=74 Runoff=2.15 cfs 0.257 af

Runoff Area=29,661 sf Runoff Depth>1.19"Subcatchment E-6: Northeast of Site (Road and abutting propFlow Length=625' Tc=12.3 min CN=79 Runoff=0.74 cfs 0.067 af

Runoff Area=1,062,120 sf Runoff Depth>0.76"Subcatchment P-1: Area to Easterly BasinFlow Length=888' Tc=17.0 min CN=71 Runoff=13.74 cfs 1.538 af

Runoff Area=454,383 sf Runoff Depth>1.12"Subcatchment P-2: Area To Westerly BasinFlow Length=1,136' Tc=16.9 min CN=78 Runoff=9.59 cfs 0.977 af

Runoff Area=451,921 sf Runoff Depth>0.85"Subcatchment P-3: Direct to Road Drainage InfrastructureFlow Length=100' Slope=0.0050 '/' Tc=19.5 min CN=73 Runoff=6.47 cfs 0.737 af

Runoff Area=327,415 sf Runoff Depth>0.71"Subcatchment P-4: Southeast Area of Site to South PropertyFlow Length=750' Tc=17.3 min CN=70 Runoff=3.85 cfs 0.445 af

Runoff Area=148,626 sf Runoff Depth>0.90"Subcatchment P-5: Area north of site (includes basketball cFlow Length=545' Tc=22.7 min CN=74 Runoff=2.15 cfs 0.257 af

Runoff Area=29,661 sf Runoff Depth>1.19"Subcatchment P-6: Northeast of Site (Road and abutting propFlow Length=625' Tc=12.3 min CN=79 Runoff=0.74 cfs 0.067 af

Inflow=6.86 cfs 1.697 afReach E-CP1: Williams St. Brook InfrastructureOutflow=6.86 cfs 1.697 af

Inflow=3.85 cfs 1.091 afReach E-CP2: South Property LineOutflow=3.85 cfs 1.091 af

Inflow=0.00 cfs 0.000 afReach E-CP3: Cross Paths RoadOutflow=0.00 cfs 0.000 af


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Inflow=6.83 cfs 1.669 afReach P-CP1: Williams St. Brook InfrastructureOutflow=6.83 cfs 1.669 af

Inflow=3.85 cfs 1.024 afReach P-CP2: South Property Line Outflow=3.85 cfs 1.024 af

Inflow=0.00 cfs 0.000 afReach P-CP3: Cross Paths RoadOutflow=0.00 cfs 0.000 af

Peak Elev=116.49' Storage=49,652 cf Inflow=15.33 cfs 1.680 afPond E-Pond1: Existing East Detention BPrimary=0.91 cfs 0.646 af Secondary=0.00 cfs 0.000 af Outflow=0.91 cfs 0.646 af

Peak Elev=117.23' Storage=25,436 cf Inflow=11.84 cfs 1.264 afPond E-Pond2: Existing West Detention B12.0" x 55.0' Culvert Outflow=1.76 cfs 0.960 af

Peak Elev=116.46' Storage=48,428 cf Inflow=14.38 cfs 1.605 afPond P-Pond 1: Existing East Detention BPrimary=0.82 cfs 0.578 af Secondary=0.00 cfs 0.000 af Outflow=0.82 cfs 0.578 af

Peak Elev=117.21' Storage=24,919 cf Inflow=11.54 cfs 1.234 afPond P-Pond 2: Existing West Detention12.0" x 55.0' Culvert Outflow=1.71 cfs 0.932 af

Total Runoff Area = 113.596 ac Runoff Volume = 8.149 af Average Runoff Depth = 0.86"78.99% Pervious Area = 89.724 ac 21.01% Impervious Area = 23.872 ac


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Subcatchment E-1: Area to Easterly Basin

Runoff = 14.69 cfs @ 12.26 hrs, Volume= 1.613 af, Depth> 0.80"

Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrsType III 24-hr 2 YRS Rainfall=3.00"

Area (sf) CN Description

10,000 98 Basins574,174 61 >75% Grass cover, Good, HSG B25,182 98 Road90,593 98 Roof

348,246 80 Gravel/Stone Dust

1,048,195 72 Weighted Average922,420 Pervious Area125,775 Impervious Area

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)

14.6 100 0.0080 0.11 Sheet Flow,Grass: Short n= 0.150 P2= 3.00"

2.4 788 0.0100 5.36 4.21 Circular Channel (pipe),Diam= 12.0" Area= 0.8 sf Perim= 3.1' r= 0.25'n= 0.011 Concrete pipe, straight & clean

17.0 888 Total

Subcatchment E-2: Area To Westerly Basin




29,666 98 Basin190,948 61 >75% Grass cover, Good, HSG B56,968 98 Road69,608 98 Roof


468,308 78 Weighted Average

312,066 Pervious Area156,242 Impervious Area


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7.3 100 0.0050 0.23 Sheet Flow,

Fallow n= 0.050 P2= 3.00"7.5 376 0.0070 0.84 Shallow Concentrated Flow,Nearly Bare & Untilled Kv= 10.0 fps


16.9 1,136 Total

Subcatchment E-3: Direct to Road Drainage Infrastructure




0 98 Basin292,465 61 >75% Grass cover, Good, HSG B85,542 98 Road53,870 98 Roof20,044 80 Gravel/Stone Dust

451,921 73 Weighted Average312,509 Pervious Area139,412 Impervious Area


19.5 100 0.0050 0.09 Sheet Flow,Cultivated: Residue>20% n= 0.170 P2= 3.00"

Subcatchment E-4: Southeast Area of Site to South Property Line



Area (sf) CN Description0 98 Basin

207,984 61 >75% Grass cover, Good, HSG B36,840 98 Road19,517 98 Roof27,926 80 Gravel/Stone Dust35,148 74 >75% Grass cover, Good, HSG C



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1.8 100 0.0080 0.92 Sheet Flow,Smooth surfaces n= 0.011 P2= 3.00"15.5 650 0.0100 0.70 Shallow Concentrated Flow,

Short Grass Pasture Kv= 7.0 fps

17.3 750 Total

Subcatchment E-5: Area north of site (includes basketball court)




50,138 61 >75% Grass cover, Good, HSG B27,807 98 Paved parking70,681 74 >75% Grass cover, Good, HSG C




4.7 270 0.0040 0.95 Shallow Concentrated Flow,Grassed Waterway Kv= 15.0 fps

1.3 125 0.0060 1.57 Shallow Concentrated Flow,Paved Kv= 20.3 fps


22.7 545 Total

Subcatchment E-6: Northeast of Site (Road and abutting property)




15,016 61 >75% Grass cover, Good, HSG B14,645 98 Paved parking



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1.7 100 0.0100 1.01 Sheet Flow,

Smooth surfaces n= 0.011 P2= 3.00"6.3 345 0.0020 0.91 Shallow Concentrated Flow,Paved Kv= 20.3 fps

4.3 180 0.0100 0.70 Shallow Concentrated Flow,Short Grass Pasture Kv= 7.0 fps

12.3 625 Total

Subcatchment P-1: Area to Easterly Basin


Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs

Type III 24-hr 2 YRS Rainfall=3.00"





Tc Length Slope Velocity Capacity Description

(min) (feet) (ft/ft) (ft/sec) (cfs)14.6 100 0.0080 0.11 Sheet Flow,

Grass: Short n= 0.150 P2= 3.00"2.4 788 0.0100 5.36 4.21 Circular Channel (pipe),

Diam= 12.0" Area= 0.8 sf Perim= 3.1' r= 0.25'n= 0.011 Concrete pipe, straight & clean

17.0 888 Total

Subcatchment P-2: Area To Westerly Basin








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7.3 100 0.0050 0.23 Sheet Flow,Fallow n= 0.050 P2= 3.00"

7.5 376 0.0070 0.84 Shallow Concentrated Flow,Nearly Bare & Untilled Kv= 10.0 fps


16.9 1,136 Total

Subcatchment P-3: Direct to Road Drainage Infrastructure









Subcatchment P-4: Southeast Area of Site to South Property Line




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0 98 Basin207,984 61 >75% Grass cover, Good, HSG B

36,840 98 Road19,517 98 Roof27,926 80 Gravel/Stone Dust35,148 74 >75% Grass cover, Good, HSG C



1.8 100 0.0080 0.92 Sheet Flow,Smooth surfaces n= 0.011 P2= 3.00"

15.5 650 0.0100 0.70 Shallow Concentrated Flow,

Short Grass Pasture Kv= 7.0 fps17.3 750 Total

Subcatchment P-5: Area north of site (includes basketball court)




50,138 61 >75% Grass cover, Good, HSG B

27,807 98 Paved parking70,681 74 >75% Grass cover, Good, HSG C







22.7 545 Total


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Subcatchment P-6: Northeast of Site (Road and abutting property)










12.3 625 Total

Reach E-CP1: Williams St. Brook Infrastructure

Inflow Area = 24.538 ac, Inflow Depth > 0.83" for 2 YRS eventInflow = 6.86 cfs @ 12.32 hrs, Volume= 1.697 afOutflow = 6.86 cfs @ 12.32 hrs, Volume= 1.697 af, Atten= 0%, Lag= 0.0 min

Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs

Reach E-CP2: South Property Line



Reach E-CP3: Cross Paths Road

Inflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 afOutflow = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af, Atten= 0%, Lag= 0.0 min



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Reach P-CP1: Williams St. Brook Infrastructure

Inflow Area = 24.218 ac, Inflow Depth > 0.83" for 2 YRS event



Reach P-CP2: South Property Line



Reach P-CP3: Cross Paths Road



Pond E-Pond1: Existing East Detention Basin

Inflow Area = 24.744 ac, Inflow Depth > 0.81" for 2 YRS eventInflow = 15.33 cfs @ 12.26 hrs, Volume= 1.680 af

Outflow = 0.91 cfs @ 17.12 hrs, Volume= 0.646 af, Atten= 94%, Lag= 291.7 minPrimary = 0.91 cfs @ 17.12 hrs, Volume= 0.646 afSecondary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af

Routing by Dyn-Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrsPeak Elev= 116.49' @ 17.12 hrs Surf.Area= 47,597 sf Storage= 49,652 cf

Plug-Flow detention time= 387.7 min calculated for 0.646 af (38% of inflow)Center-of-Mass det. time= 245.3 min ( 1,125.1 - 879.8 )

Volume Invert Avail.Storage Storage Description

#1 112.00' 432,726 cf Custom Stage Data (Prismatic) Listed below (Recalc)

Elevation Surf.Area Inc.Store Cum.Store(feet) (sq-ft) (cubic-feet) (cubic-feet)

112.00 6,800 0 0113.00 7,463 7,132 7,132114.00 8,704 8,084 15,215115.00 10,000 9,352 24,567116.00 11,362 10,681 35,248117.00 85,524 48,443 83,691118.00 272,423 178,974 262,665118.50 407,822 170,061 432,726


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Device Routing Invert Outlet Devices

#1 Secondary 117.00' 100.0' long x 5.0' breadth Broad-Crested Rectangular Weir

Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.002.50 3.00 3.50 4.00 4.50 5.00 5.50Coef. (English) 2.34 2.50 2.70 2.68 2.68 2.66 2.65 2.65 2.652.65 2.67 2.66 2.68 2.70 2.74 2.79 2.88

#2 Primary 116.00' 12.0" Vert. Invert of 12" CMP Outlet on Fair Street C= 0.600

Primary OutFlow Max=0.91 cfs @ 17.12 hrs HW=116.49' TW=0.00' (Dynamic Tailwater)2=Invert of 12" CMP Outlet on Fair Street (Orifice Controls 0.91 cfs @ 2.38 fps)

Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=112.00' TW=0.00' (Dynamic Tailwater)1=Broad-Crested Rectangular Weir ( Controls 0.00 cfs)

Pond E-Pond2: Existing West Detention Basin

Inflow Area = 14.163 ac, Inflow Depth > 1.07" for 2 YRS eventInflow = 11.84 cfs @ 12.26 hrs, Volume= 1.264 afOutflow = 1.76 cfs @ 13.47 hrs, Volume= 0.960 af, Atten= 85%, Lag= 72.5 minPrimary = 1.76 cfs @ 13.47 hrs, Volume= 0.960 af



Volume Invert Avail.Storage Storage Description#1 116.00' 98,409 cf Custom Stage Data (Prismatic) Listed below (Recalc)


116.00 19,210 0 0117.00 21,276 20,243 20,243118.00 35,033 28,155 48,398119.00 64,989 50,011 98,409


#1 Primary 116.26' 12.0" x 55.0' long Culvert CMP, projecting, no headwall, Ke= 0.900Outlet Invert= 116.13' S= 0.0024 '/' Cc= 0.900n= 0.011 Concrete pipe, straight & clean

Primary OutFlow Max=1.76 cfs @ 13.47 hrs HW=117.23' TW=0.00' (Dynamic Tailwater)1=Culvert (Barrel Controls 1.76 cfs @ 2.89 fps)


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Pond P-Pond 1: Existing East Detention Basin


Inflow = 14.38 cfs @ 12.26 hrs, Volume= 1.605 afOutflow = 0.82 cfs @ 17.46 hrs, Volume= 0.578 af, Atten= 94%, Lag= 311.9 minPrimary = 0.82 cfs @ 17.46 hrs, Volume= 0.578 afSecondary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 af






112.00 6,800 0 0113.00 7,463 7,132 7,132114.00 8,704 8,084 15,215115.00 10,000 9,352 24,567116.00 11,362 10,681 35,248117.00 85,524 48,443 83,691118.00 272,423 178,974 262,665118.50 407,822 170,061 432,726

Device Routing Invert Outlet Devices#1 Secondary 117.00' 100.0' long x 5.0' breadth Broad-Crested Rectangular Weir




Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=112.00' TW=0.00' (Dynamic Tailwater)1=Broad-Crested Rectangular Weir ( Controls 0.00 cfs)

Pond P-Pond 2: Existing West Detention Basin




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Peak Elev= 117.21' @ 13.49 hrs Surf.Area= 24,111 sf Storage= 24,919 cf

Plug-Flow detention time= 227.4 min calculated for 0.932 af (76% of inflow)

Center-of-Mass det. time= 137.5 min ( 1,001.8 - 864.3 )




116.00 19,210 0 0117.00 21,276 20,243 20,243118.00 35,033 28,155 48,398119.00 64,989 50,011 98,409



Primary OutFlow Max=1.71 cfs @ 13.49 hrs HW=117.21' TW=0.00' (Dynamic Tailwater)1=Culvert (Barrel Controls 1.71 cfs @ 2.86 fps)


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Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 pointsRunoff by SCS TR-20 method, UH=SCS

Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method

Runoff Area=1,048,195 sf Runoff Depth>1.81"Subcatchment E-1: Area to Easterly BasinFlow Length=888' Tc=17.0 min CN=72 Runoff=35.96 cfs 3.637 af

Runoff Area=468,308 sf Runoff Depth>2.29"Subcatchment E-2: Area To Westerly BasinFlow Length=1,136' Tc=16.9 min CN=78 Runoff=20.70 cfs 2.047 af

Runoff Area=451,921 sf Runoff Depth>1.89"Subcatchment E-3: Direct to Road Drainage InfrastructureFlow Length=100' Slope=0.0050 '/' Tc=19.5 min CN=73 Runoff=15.35 cfs 1.632 af

Runoff Area=327,415 sf Runoff Depth>1.67"Subcatchment E-4: Southeast Area of Site to South PropertyFlow Length=750' Tc=17.3 min CN=70 Runoff=10.14 cfs 1.044 af

Runoff Area=148,626 sf Runoff Depth>1.96"Subcatchment E-5: Area north of site (includes basketball cFlow Length=545' Tc=22.7 min CN=74 Runoff=4.96 cfs 0.558 af

Runoff Area=29,661 sf Runoff Depth>2.37"Subcatchment E-6: Northeast of Site (Road and abutting propFlow Length=625' Tc=12.3 min CN=79 Runoff=1.53 cfs 0.135 af

Runoff Area=1,062,120 sf Runoff Depth>1.74"Subcatchment P-1: Area to Easterly BasinFlow Length=888' Tc=17.0 min CN=71 Runoff=34.76 cfs 3.535 af

Runoff Area=454,383 sf Runoff Depth>2.29"Subcatchment P-2: Area To Westerly BasinFlow Length=1,136' Tc=16.9 min CN=78 Runoff=20.08 cfs 1.986 af

Runoff Area=451,921 sf Runoff Depth>1.89"Subcatchment P-3: Direct to Road Drainage InfrastructureFlow Length=100' Slope=0.0050 '/' Tc=19.5 min CN=73 Runoff=15.35 cfs 1.632 af

Runoff Area=327,415 sf Runoff Depth>1.67"Subcatchment P-4: Southeast Area of Site to South PropertyFlow Length=750' Tc=17.3 min CN=70 Runoff=10.14 cfs 1.044 af

Runoff Area=148,626 sf Runoff Depth>1.96"Subcatchment P-5: Area north of site (includes basketball cFlow Length=545' Tc=22.7 min CN=74 Runoff=4.96 cfs 0.558 af

Runoff Area=29,661 sf Runoff Depth>2.37"Subcatchment P-6: Northeast of Site (Road and abutting propFlow Length=625' Tc=12.3 min CN=79 Runoff=1.53 cfs 0.135 af

Inflow=17.66 cfs 3.854 afReach E-CP1: Williams St. Brook InfrastructureOutflow=17.66 cfs 3.854 af

Inflow=10.37 cfs 3.256 afReach E-CP2: South Property LineOutflow=10.37 cfs 3.256 af

Inflow=1.79 cfs 0.241 afReach E-CP3: Cross Paths RoadOutflow=1.79 cfs 0.241 af


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Inflow=17.62 cfs 3.798 afReach P-CP1: Williams St. Brook InfrastructureOutflow=17.62 cfs 3.798 af

Inflow=10.21 cfs 3.237 afReach P-CP2: South Property Line Outflow=10.21 cfs 3.237 af

Inflow=1.29 cfs 0.162 afReach P-CP3: Cross Paths RoadOutflow=1.29 cfs 0.162 af

Peak Elev=117.04' Storage=87,154 cf Inflow=37.30 cfs 3.771 afPond E-Pond1: Existing East Detention BPrimary=2.78 cfs 2.212 af Secondary=1.79 cfs 0.241 af Outflow=4.57 cfs 2.453 af

Peak Elev=118.19' Storage=55,628 cf Inflow=25.28 cfs 2.605 afPond E-Pond2: Existing West Detention B12.0" x 55.0' Culvert Outflow=3.57 cfs 2.222 af

Peak Elev=117.03' Storage=86,444 cf Inflow=36.09 cfs 3.669 afPond P-Pond 1: Existing East Detention BPrimary=2.76 cfs 2.192 af Secondary=1.29 cfs 0.162 af Outflow=4.04 cfs 2.354 af

Peak Elev=118.16' Storage=54,241 cf Inflow=24.67 cfs 2.544 afPond P-Pond 2: Existing West Detention12.0" x 55.0' Culvert Outflow=3.53 cfs 2.166 af

Total Runoff Area = 113.596 ac Runoff Volume = 17.942 af Average Runoff Depth = 1.90"78.99% Pervious Area = 89.724 ac 21.01% Impervious Area = 23.872 ac


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Subcatchment E-1: Area to Easterly Basin










17.0 888 Total

Subcatchment E-2: Area To Westerly Basin









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1.8 100 0.0080 0.92 Sheet Flow,Smooth surfaces n= 0.011 P2= 3.00"15.5 650 0.0100 0.70 Shallow Concentrated Flow,

Short Grass Pasture Kv= 7.0 fps

17.3 750 Total

Subcatchment E-5: Area north of site (includes basketball court)




50,138 61 >75% Grass cover, Good, HSG B27,807 98 Paved parking70,681 74 >75% Grass cover, Good, HSG C







22.7 545 Total

Subcatchment E-6: Northeast of Site (Road and abutting property)







48/105




1.7 100 0.0100 1.01 Sheet Flow,

Smooth surfaces n= 0.011 P2= 3.00"6.3 345 0.0020 0.91 Shallow Concentrated Flow,Paved Kv= 20.3 fps


12.3 625 Total

Subcatchment P-1: Area to Easterly Basin


Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs

Type III 24-hr 10 YRS Rainfall=4.50"





Tc Length Slope Velocity Capacity Description

(min) (feet) (ft/ft) (ft/sec) (cfs)14.6 100 0.0080 0.11 Sheet Flow,

Grass: Short n= 0.150 P2= 3.00"2.4 788 0.0100 5.36 4.21 Circular Channel (pipe),

Diam= 12.0" Area= 0.8 sf Perim= 3.1' r= 0.25'n= 0.011 Concrete pipe, straight & clean

17.0 888 Total

Subcatchment P-2: Area To Westerly Basin








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7.3 100 0.0050 0.23 Sheet Flow,Fallow n= 0.050 P2= 3.00"

7.5 376 0.0070 0.84 Shallow Concentrated Flow,Nearly Bare & Untilled Kv= 10.0 fps


16.9 1,136 Total

Subcatchment P-3: Direct to Road Drainage Infrastructure









Subcatchment P-4: Southeast Area of Site to South Property Line




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0 98 Basin207,984 61 >75% Grass cover, Good, HSG B

36,840 98 Road19,517 98 Roof27,926 80 Gravel/Stone Dust35,148 74 >75% Grass cover, Good, HSG C




15.5 650 0.0100 0.70 Shallow Concentrated Flow,

Short Grass Pasture Kv= 7.0 fps17.3 750 Total

Subcatchment P-5: Area north of site (includes basketball court)




50,138 61 >75% Grass cover, Good, HSG B

27,807 98 Paved parking70,681 74 >75% Grass cover, Good, HSG C







22.7 545 Total


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Subcatchment P-6: Northeast of Site (Road and abutting property)










12.3 625 Total

Reach E-CP1: Williams St. Brook Infrastructure



Reach E-CP2: South Property Line



Reach E-CP3: Cross Paths Road




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Reach P-CP1: Williams St. Brook Infrastructure




Reach P-CP2: South Property Line



Reach P-CP3: Cross Paths Road



Pond E-Pond1: Existing East Detention Basin

Inflow Area = 24.744 ac, Inflow Depth > 1.83" for 10 YRS eventInflow = 37.30 cfs @ 12.24 hrs, Volume= 3.771 af

Outflow = 4.57 cfs @ 13.73 hrs, Volume= 2.453 af, Atten= 88%, Lag= 89.2 minPrimary = 2.78 cfs @ 13.73 hrs, Volume= 2.212 afSecondary = 1.79 cfs @ 13.73 hrs, Volume= 0.241 af






112.00 6,800 0 0113.00 7,463 7,132 7,132114.00 8,704 8,084 15,215115.00 10,000 9,352 24,567116.00 11,362 10,681 35,248117.00 85,524 48,443 83,691118.00 272,423 178,974 262,665118.50 407,822 170,061 432,726


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#1 Secondary 117.00' 100.0' long x 5.0' breadth Broad-Crested Rectangular Weir




Secondary OutFlow Max=1.79 cfs @ 13.73 hrs HW=117.04' TW=0.00' (Dynamic Tailwater)1=Broad-Crested Rectangular Weir (Weir Controls 1.79 cfs @ 0.46 fps)

Pond E-Pond2: Existing West Detention Basin



Plug-Flow detention time= 218.7 min calculated for 2.222 af (85% of inflow)Center-of-Mass det. time= 155.6 min ( 998.8 - 843.3 )

Volume Invert Avail.Storage Storage Description#1 116.00' 98,409 cf Custom Stage Data (Prismatic) Listed below (Recalc)


116.00 19,210 0 0117.00 21,276 20,243 20,243118.00 35,033 28,155 48,398119.00 64,989 50,011 98,409



Primary OutFlow Max=3.57 cfs @ 13.31 hrs HW=118.19' TW=0.00' (Dynamic Tailwater)1=Culvert (Inlet Controls 3.57 cfs @ 4.55 fps)


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Pond P-Pond 1: Existing East Detention Basin


Inflow = 36.09 cfs @ 12.25 hrs, Volume= 3.669 afOutflow = 4.04 cfs @ 14.02 hrs, Volume= 2.354 af, Atten= 89%, Lag= 106.5 minPrimary = 2.76 cfs @ 14.02 hrs, Volume= 2.192 afSecondary = 1.29 cfs @ 14.02 hrs, Volume= 0.162 af






112.00 6,800 0 0113.00 7,463 7,132 7,132114.00 8,704 8,084 15,215115.00 10,000 9,352 24,567116.00 11,362 10,681 35,248117.00 85,524 48,443 83,691118.00 272,423 178,974 262,665118.50 407,822 170,061 432,726

Device Routing Invert Outlet Devices#1 Secondary 117.00' 100.0' long x 5.0' breadth Broad-Crested Rectangular Weir




Secondary OutFlow Max=1.28 cfs @ 14.02 hrs HW=117.03' TW=0.00' (Dynamic Tailwater)1=Broad-Crested Rectangular Weir (Weir Controls 1.28 cfs @ 0.41 fps)

Pond P-Pond 2: Existing West Detention Basin




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Peak Elev= 118.16' @ 13.29 hrs Surf.Area= 39,717 sf Storage= 54,241 cf

Plug-Flow detention time= 217.7 min calculated for 2.166 af (85% of inflow)

Center-of-Mass det. time= 154.0 min ( 997.4 - 843.4 )




116.00 19,210 0 0117.00 21,276 20,243 20,243118.00 35,033 28,155 48,398119.00 64,989 50,011 98,409


#1 Primary 116.26' 12.0" x 55.0' long Culvert CMP, projecting, no head

three county fairgrounds phase 1 stormwater app revised 03-2010.pdf

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