The Yeadon Borough Hall building is surrounded by parking lots and some landscaped areas, but constitutes 70% impervious surfaces. The Borough also owns a vacant parcel filled with some trees and turf grass, which is nearby, just southeast of the Borough Hall. There are few drains on-site connecting to the Borough’s sewer system off of Baily Road. As with most traditional stormwater facilities, these drains quickly convey runoff without really managing it.
These recommended stormwater Best Management Practices (BMPs) coincide with basic site improvements the Borough has planned, which include the repaving of the parking lots and the installation of a new recreation space for a vacant parcel. The rate, quantity, and quality of stormwater runoff around Yeadon Borough Hall will be improved with the addition of the following BMPs: Porous Paving with Subsurface Infiltration, Infiltration Trenches, and Bioretention Basin.
Porous Pavement with Subsurface Infiltration
Porous paving is recommended to replace the .4 acres of parking lot at the rear of Yeadon Borough Hall. Subsurface infiltration beds can catch this percolated runoff, as well as runoff from installed and existing stormwater inlets along Baily Road. The storage bed will have an average depth of 18 to 36 inches and will be wrapped in geotextile. Porous material creates a ground surface for the complete system. A “positive overflow” allows for excess water to overflow into the existing sewers if the system reaches capacity during a storm event. Permeability rates on the soil will need to be tested before constructing this BMP. For a diagram of a typical porous pavement section with subsurface infiltration bed, created by Cahill Associates, Inc., click here.
The vacant lot can be enhanced to better accommodate runoff from the east-end parking lots and the Borough building driveway. This can be done by installing a subsurface infiltration trench and/or a shallow bioretention basin. A picnic area and children’s playground may also be designed in accordance with these attractive and efficient stormwater management practices.
An infiltration trench is a long and narrowly-shaped stormwater management system lying subsurface in this case, on a sloped topography. If an infiltration trench is constructed on this site, it would be underlying a sidewalk, playground or picnic area and would not be visible or interfere with recreational activities. Infiltration trenches are pits lined with geotextile, filled with stone, and back filled with soil. A perforated pipe both distributes water throughout the infiltration bed and conveys positive overflow into the municipal stormwater system. Series of infiltration trenches can maximize space and manage the greatest volume of stormwater. Click here for an infiltration trench diagram drawn by Cahill Associates, Inc.
A bioretention basin can complement an infiltration trench, or it can be the main method of stormwater management on the parcel site. If a basin is built in addition to infiltration trenches, then the trenches’ overflow water would be conveyed to the basin.
Adding a bioretention basin would further reduce stormwater runoff, but would also improve water quality through evapotranspiration and vegetative filtering. The basin would fill up 6 to 10 inches during a storm event before a domed riser outlet would dispel overflow water off-site. The bioretention basin would be planted with native plants tolerant of all moisture conditions. A rain garden like this one would bring an important amenity to this public space by adding interesting features to the landscape. For a bioretention diagram by Cahill Associates, Inc. click here.
Watershed: Darby-Cobbs Creek
Yeadon Borough Hall is located off of the corner of Church Lane and Baily Road in Yeadon Borough. The site is 1.2 acres and is surrounded by both mixed density residential and commercial areas.
The estimated costs include porous pavement parking at $44,706, which is comprised of excavation, stone, pipes, fabric, and overflow control structure. A rain garden/bioretention area could cost about $1,500, while infiltration trenches may cost $7,500. The total costs for all these additions and engineering fees are about $72,000.
The concept design was prepared by Cahill Associates, Inc. as part of the Pennsylvania Environmental Council’s (PEC’s) Stormwater Retrofit Technical Assistance Program, which is funded through a Pennsylvania DEP Coastal Zone Management Program Grant and through the William Penn Foundation.