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 porous pavement parking lot has been coupled with adjoining bioretention areas and infiltration trenches. The minimum calculated infiltration rate recorded in the area was 2.84 inches per hour. Construction on the project commenced in 2004.
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.
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.
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.
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.
Horstman Associates (Civil Engineering & Environmental Consulting)
D.S. Guest Excavating, Inc. (Contractor)
Boy Scouts of America
Pennsylvania Department of Environmental Protection
Total project cost: $114,060.99
Site work: $52,238.00
Porous & standard pavement: $41,742.00
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
Director of Welkinweir
1368 Prizer Road
Pottstown PA 19465