PROJECT AREA:

Pawling

HUDSON VALLEY REGIONAL COUNCIL

3 Washington Center, Newburgh NY 12550 http://www.hudsonvalleyregionalcouncil.com

GREEN INFRASTRUCTURE PLAN FOR DUTCHER GOLF COURSE PARKING LOT

Project type: Parking Lot Retrofit June 2011 Proposed practices: Permeable Paving, Bioretention Area

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The following draft report describes a schematic landscape design proposal using green infrastructure practices for stormwater management. The illustrated plan and report are intended to give practical guidance for the owner, design professionals, contractors, and other interested parties to use in developing a final design. They are not intended to be used as final design and construction documents.

LOCATION

Street Address: 135 East Main St., Pawling (Village), NY 12564 Grid # 134001-7056-05-157752-0000

OWNERSHIP

The Dutcher Golf Course is owned and operated by the Town of Pawling, though the land is within the Village of Pawling.

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PROJECT DESCRIPTION

The Dutcher Golf Course is located within the watershed of the East Branch Croton River, part of the New York City Watershed. There is a paved parking lot adjacent to the clubhouse building. Beyond the paved lot, to the north, is a gravel and dirt area used as overflow parking. There is also a strip of turf and bare earth to the west side of the paved lot that is used for parking. The proposed green infrastructure retrofit of this site focuses on adding permeable paving to the unpaved parking areas to reduce erosion and facilitate infiltration. Bioretention areas would treat the remaining runoff.

PROJECT RATIONALE, SUPPORT, AND FUNDING

The golf course parking lot was identified as a site for improvement by committee members because it is eroding and dusty. The bare earth and gravel sections of the parking area are contributing to polluted runoff as well as aesthetic concerns. Runoff from the Clubhouse building and the paved parking lot all appears to flow northward toward the bare areas, contributing to the erosion and pollution issues. The existing paved parking area is in reasonably good condition, so the recommendation is to leave that mainly as-is and simply improve the unpaved parking areas with permeable paving. A bioretention area would be added to treat the runoff from the existing paved area so that it doesn’t flow onto the permeable paving and overload its capacity. Overflow would be piped to a vegetated filter strip area north of the parking area. Representatives of the Town of Pawling will be consulted to see if they support this approach.

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EXISTING CONDITIONS

SURFACE COVER/CONTRIBUTING AREA

There is approximately 8,000 SF of paved parking lot and a 1,600 SF building directly uphill of the unpaved parking areas. The surrounding areas are grassed and do not appear to slope toward the project area.

SOILS & TOPOGRAPHY

The topography is gently sloping northward. According to maps, the soils on the site consist of Farmington-Galway complex (FcG). Farmington is considered hydrologic group C and Galway is hydrologic group B. It will be critical to test infiltration capacity in the field to determine whether porous paving will drain adequately. The NYS Stormwater Design Manual specifies that underlying parent soils should have a minimum infiltration rate of 0.5 inches per hour, and that organic content of the underlying soils is important to nutrient removal.

SOLAR AND WIND EXPOSURE

There is a border of trees and vegetation on the east edge of the site, and a stone and tree hedgerow to the north. Overall solar exposure is strong.

VEGETATION

Aside from the trees bordering the parking area to the east, most of the area is surrounded by golf course turf grass.

SITE CONSTRAINTS

There are no known constraints to accessing the site. There is a protective net installed just west of the northern parking area that would need to be considered in siting a bioretention area, and a stone wall to the north. Also, utilities would need to be investigated.

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SITE PHOTOS

Facing north (down hill)

Facing south (up hill)

proposed bioretention area site

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OVERALL SCHEMATIC PLAN

Vegetated filter strip for overflow Two areas of permeable paving:

1. Approximately 220’ x 41’ 2. Approximately 240’ x 18’

Bioretention Area

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PLAN FOR PERMEABLE PAVING

DESIGN

The primary recommendation is to stabilize the unpaved areas using permeable paving. Area 1 is approximately 220’ x 41’, and Area 2 is approximately 240’ x 18’. (Measured in the field.)

In order to keep runoff from the existing paved area from flowing onto the permeable pavement, some minor re-grading of the paved area is recommended. Runoff would be redirected northwest to a bioretention area. It may be preferable to prevent runoff from the impervious paving from entering the permeable pavement to avoid overloading the infiltration capacity of the soil and to prevent particulate matter from clogging the pores. Two types of permeable paving could be considered for this site (descriptions from NYS Stormwater Management Design Manual 2010): “Porous pavement is a permeable asphalt or concrete surface that allows stormwater to quickly infiltrate to an underlying reservoir. Porous pavement looks similar to conventional pavement, but is formulated with larger aggregate and less fine particles, which leaves void spaces for infiltration.”

1

2

Regrade to direct runoff

this way

Bioretention

area

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“Permeable pavers include reinforced turf, interlocking concrete modules, and brick pavers (Figure 5.59). Often, these designs do not have an underground stone reservoir, but can provide some infiltration and surface detention of stormwater to reduce runoff velocities.” Parking lot managers should be consulted to select the most appropriate type of pavement considering usage and maintenance. A key consideration is winter time usage. Our understanding is that this lot is not plowed or salted during the winter. This makes permeable pavers a more viable option since they will not be subject to damage by snow plows. Example of permeable pavers adjacent to asphalt:

Figure 5. 59 Asphalt, Permeable Pavers, Porous Concrete, Albany, NY (from NYS Stormwater Design Manual)

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SIZING COMPUTATIONS /RUNOFF REDUCTION

Total Drainage Area 13,750 Ft2

Available Surface Area 13,750 Ft2

Step 1: Calculate Water Quality Volume (WQv) WQv = (P) (Rv) (A) / 12

P = 90% rainfall number = 1.1 inches

Rv = 0.05+0.009 (I), if Rv < 20%, use Rv = 20% 95% I = percent impervious of area draining to practice = 100% % of Total area that drains to practice 100%

A = Area draining to practice = 13750 Ft2

WQv = 1197.4 Ft3

Step 2: Calculate the available storage volume in the storage reservoir: Storage Volume = Ap*n*dt where: n = assumed porosity = 0.4

dt = gravel bed/reservoir depth = 0.25 Ft

Reservoir Storage Volume = 1375 cf

CONSTRUCTION STEPS AND MATERIALS

Typical construction steps for interlocking concrete pavers are as follows:

Excavate to proposed depth and level the bottom of infiltration bed.

Place geotextile if required

Place sub base and base aggregrates as required by final design

Place setting setting bed aggregate

Install edge restraint

Place permeable interlocking pavers

Place joint aggregate Specific steps would be prescribed in final engineering plans.

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MAINTENANCE

According to the Design Manual, the following activities would typically be required to maintain permeable pavers:

Maintenance Activity Schedule

Ensure that paving area is clean of debris Monthly

Ensure that paving dewaters between storms Monthly and after storms >0.5 in.

Ensure that the area is clean of sediments Monthly

Mow upland and adjacent areas, and seed bare areas As needed

Vacuum sweep frequently to keep surface free of sediments Typically 3 to 4 times a year

Inspect the surface for deterioration or spalling Annual

Two excellent fact sheets on permeable and porous paving Research Update and Design

Implications and Maintaining Permeable Pavements are available from the NC State University Stormwater Engineering Group at http://www.bae.ncsu.edu/stormwater/pubs.htm:

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COST

For installation, maintenance costs and lifespan data for the practices discussed here, the Cost Sheet developed by the Center for Neighborhood Technology (CNT) in collaboration with the US EPA Office of Wetlands, Oceans, and Watersheds (OWOW), Assessment and Watershed Protection Division, Non-Point Source Branch, provides useful information based on examples from various locations. It may be found at their website. http://greenvalues.cnt.org/national/cost_detail.php Another useful source of cost data can be found in the Center of Watershed Protection's Urban Subwatershed Restoration Manual Series. Manual 3: Urban Stormwater Retrofit Practices, pages E-1 though 14, includes a discussion of costs in terms of the amount of stormwater treated. http://www.cwp.org/categoryblog/92-urban-subwatershed-restoration-manual-series.html

1 Urban Waterways, NC State University and A&T State University Cooperative Extension.2011.

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PLAN FOR BIORETENTION AREA

DESIGN

A bioretention area is recommended to collect and treat the runoff from the existing asphalt parking area. The pavement would need to be partially re-contoured to drain runoff to the northwest corner of the existing paved area, rather than flowing into the new porous paved areas. A bioretention area would be constructed of about 800 ft

2.

An underdrain would need to be designed, and soil permeability would need to be field tested. Specifications for the soil to fill the bioretention area would be detailed in the engineering design. The DEC Stormwater Manual recommends a mixture of sand, topsoil and peat.

SIZING COMPUTATIONS /RUNOFF REDUCTION

Total Drainage Area 10,000 Ft2

1: Calculate Water Quality Volume (WQv)

WQv = (P) (Rv) (A) / 12

P = 90% rainfall number = 1.1 inches

Rv = 0.05+0.009 (I), if Rv < 20%, use Rv = 20% 91%

I = percent impervious of area draining to planter = 95%

% of Total area that drains to planter 100%

A = Area draining to practice = 10000 Ft2

WQv = 830 Ft3

2 Bioretention Details

WQv*df/k(hf+df)(tf)

df = depth of soil medium = 2.5 ft

k = Coefficient of permeability of planting soils 0.5 ft/day

hf = Average ponding depth (max depth/2 0.25 ft

tf = filter time (days) = 2 days

3. Calculation Af = Required surface area for bioretention 754 Ft2

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CONSTRUCTION STEPS

Before construction can take place, surveying and engineering design would be necessary. The Town would also need to ensure no permits are needed. The bioretention area would initially be dug to 36” depth, and then backfilled with approximately 6” of stone and then filled with 30” of design soil mix. A planting plan for the bioretention area should be developed based on the soil mix selected. Maintenance for the plants should also be pre-arranged.

MATERIALS

Plants

Plants adapted to the periodically wet and dry conditions of bioretention areas would be selected, and native plants are recommended. See Appendix H of the DEC Manual for list of recommended plants. Soil and mulch

Components and proportions would be specified in the final design. Recommendations in the Design Manual for bioretention area soils and mulch are as follows:

Planting Soil Bed Characteristics The characteristics of the soil for the bioretention facility are perhaps as important as the facility location, size, and treatment volume. The soil must be permeable enough to allow runoff to filter through the media, while having characteristics suitable to promote and sustain a robust vegetative cover crop. In addition, much of the nutrient pollutant uptake (nitrogen and phosphorus) is accomplished through adsorption and microbial activity within the soil profile. Therefore, the soils must balance soil chemistry and physical properties to support biotic communities above and below ground. The planting soil should be a sandy loam, loamy sand, loam (USDA), or a loam/sand mix (should contain a minimum 35 to 60% sand, by volume). The clay content for these soils should by less than 25% by volume. Soils should fall within the SM, or ML classifications of the Unified Soil Classification System (USCS). A permeability of at least 1.0 feet per day (0.5"/hr) is required (a conservative value of 0.5 feet per day is used for design). The soil should be free of stones, stumps, roots, or other woody material over 1" in diameter. Brush or seeds from noxious weeds. Placement of the planting soil should be in lifts of 12 to 18", loosely compacted (tamped lightly with a dozer or backhoe bucket). Mulch Layer The mulch layer plays an important role in the performance of the bioretention system. The mulch layer helps maintain soil moisture and avoid surface sealing which reduces permeability. Mulch helps prevent erosion, and provides a micro-environment suitable for soil biota at the mulch/soil interface. It also serves as a pretreatment layer, trapping the finer sediments which remain suspended after the primary pretreatment. The mulch layer should be standard landscape style, single or double, shredded hardwood mulch or chips. The mulch layer should be well aged (stockpiled or stored for at least 12 months), uniform in color, and free of other materials, such as weed seeds, soil, roots, etc. The mulch should be applied to a maximum depth of three inches. Grass clippings should not be used as a mulch material (Appendix H, page 6).

COST

For installation, maintenance costs and lifespan data for the practices discussed here, the Cost Sheet developed by the Center for Neighborhood Technology (CNT) in collaboration with the US EPA Office of Wetlands, Oceans, and Watersheds (OWOW), Assessment and Watershed Protection Division, Non-Point Source Branch, provides useful information based on examples from various locations. It may be found at their website. http://greenvalues.cnt.org/national/cost_detail.php

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Another useful source of cost data can be found in the Center of Watershed Protection's Urban Subwatershed Restoration Manual Series. Manual 3: Urban Stormwater Retrofit Practices, pages E-1 though 14, includes a discussion of costs in terms of the amount of stormwater treated. http://www.cwp.org/categoryblog/92-urban-subwatershed-restoration-manual-series.html Diagram of a typical bioretention area:

Plan created by: JoAnne Daley, Town of Pawling John Watson, PE, Community Volunteer Mike Purcell, Town of Pawling Conservation Advisory Board Shari Chertok, Community Volunteer Emily Svenson, Hudson River Watershed Alliance Marcy Denker, Hudson Valley Regional Council