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Green Valleys Association’s
(GVA) expansion of
programs at Welkinweir and the addition of a brand new open air
classroom prompted an increase in estate visitors. Because of tight
parking capacity, people were required to park in a meadow area adjacent
to the 8-space parking lot which resulted in runoff, erosion and
over-compacted soils. A gully began to form down the hill across Prizer
Road and through a neighbor’s property. Showing a commitment to the
environment through sustainable practices, GVA installed a combination
of natural and structural stormwater best management practices (BMPs) in
line with the Pennsylvania BMP Handbook to counteract the
environmental impacts associated with its expansion of facilities. GVA’s mission has been to intercept all runoff and achieve utmost
groundwater recharge, which is why the 1) porous pavement parking lot
has been coupled with adjoining 2) bioretention areas and 3)
infiltration trenches. The minimum calculated infiltration rate
recorded in the area was 2.84 inches per hour. Construction on the
project commenced in 2004.
1) Porous pavement and subsurface storage bed
This parking expansion
effort replaces 8 parking spaces with accommodations for 50 vehicles, in
addition to a school bus circle. While the main entry road is composed
of standard pavement, the parking bays are porous pavement. Without the
use of curbs and gutters, stormwater is directed towards the parking lot
bays where it percolates into a subsurface storage bed, which stores
water and controls discharge rates during storm events. The porous
pavement captures 29,621 square feet of drainage area, or .68 acres. The depth of the subsurface stone reservoir is 1.2 feet and its volume
is 6,200 cubic feet.
The porous pavement was
kept as level as possible to absorb a maximum amount of water from
adjoining areas. The project contractor,
D.S. Guest Excavating, was concerned that the underlying infiltration
bed’s tilt, due to the grade of the landscape, would cause all
runoff to concentrate towards the lower side of the
infiltration storage bed. To resolve this issue, the contractor and the
engineer, Horstman Associates, decided to leave intact soil in the
middle of the infiltration bed, called a soil key. This soil key
permits stormwater recharge on the side of the storage bed where
infiltration occurs.
2) Bioretention Areas
Water that is not able
to percolate fast enough into the subsurface storage bed will flow into
the two bioretention areas that front the porous pavement bays. They
absorb excess water in the vicinity, maximizing area groundwater
recharge. Native plants were planted in the bioretention areas and in
other parts of the landscaping. Native plants help purify stormwater
affected by nonpoint source pollution consisting of brake dust, oil,
antifreeze and other pollutants generated by automobiles. Native
plants’ long roots not only absorb more pollutants than regular
traditional planted sod, but they also soak in and consume more water to
reduce flooding. The native plants have provided food and shelter for
endemic animal species, including painted turtles, various frogs and
toads, red-winged blackbirds, cedar waxwings, and robins. For a list
the native plants, click
here.
The first bioretention
basin’s drainage area is .2 acres, with a maximum depth of 2.2 feet and
a storage volume of 5,200 cubic feet. The second bioretention basin’s
drainage area is .37 acres, with a maximum depth of 3 feet and a storage
volume of 9,000 cubic feet. Because impervious surfaces were found
under the second bioretention basin, no measurable permeation occurs and
a small pond or wetland has formed on the site.
3) Infiltration Trenches
An infiltration trench
measuring 30 feet long, 2 feet wide and 3 feet deep was constructed to
catch any excess water from the porous pavement parking lot and the
nearby bioretention basins. The drainage area for the infiltration
trench is about a tenth of an acre. The addition of this BMP
contributes to GVA’s goal of obtaining zero
percent runoff from the site, even during the 100-year storm.
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County:
Chester
Watershed:
Schuylkill River
Located within the
French Creek Watershed, Welkinweir, Green Valleys Association’s
headquarters, is a 197-acre arboretum and nature preserve located at Prizer
and Murray School Roads in Pottstown, Pennsylvania. GVA
advocates watershed conservation through educational activities and aids
local municipalities with updating their stormwater ordinances.
GVA is
in stewardship of 155 square miles of watershed within northern Chester
County, comprising parts of Stoney Run, and Valley, Pickering, French and
Pigeon Creeks.
View
all
TVSSI BMPs in a larger map
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Total project cost $114,060.99
Including:
Site work $52,238.00
Porous & standard pavement $41,742.00
Funding Sources:
Pennsylvania DEP Growing Greener Grant (2002) $86,000.00
Chester County Conference & Visitors Bureau
$24,000.00
Green Valleys Association (Brewster Bequest) $4,222.00
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