As part of an expansion project to construct several new buildings on its 10-acre property in the Somerton section of Northeast Philadelphia, Cranaleith Spiritual Center undertook a stormwater management project beginning in July 2011. It involved the creation of five bio-retention basins, two of which became operational during the first phase of the development project. Basins 1 and 2 are designed to handle a water depth of 9 inches, and to infiltrate a water volume of 4802 cubic feet in basin 1 and 3054 cubic feet in basin 2. Future Phase 2 completion of the three remaining basins will handle an additional volume of 4613 cubic feet.
However, current conditions in the first two basins do not allow for timely infiltration (as a result of damaged and non-percolating soil types), requiring remediation currently underway that will facilitate drainage within 72 hours. The remediation will be accomplished by removing and setting aside soil within the basin that is not draining, and continuing to excavate to depths required for 30 inch well-draining planting-soil depth. After excavation of the entire area, perforated pipe underdrains will be installed in the subgrade. These will connect to a discharge pipe that drains into an existing pond which feeds the Poquessing Creek. Upon completion of the sub-drain, a soil mix with a high ratio of compost and sand will be added to the floor of the basins. The basin bottom will be finished with the addition of river stones, wet-tolerant plants, and a leaf-compost mulch.
The completed basin remediation will allow for stormwater infiltration volumes previously discussed; plants in the basin will also assist with evapotranspiration. Water quality will be improved through: plants filtering stormwater, reduction in temperature of stormwater, settling of sediments, and decreasing the rate of runoff and erosion.
Although testing was done on the basins in advance of the project with recorded infiltration rates of 0.5 inches per hour at 36 inch depth (basin 1) and 0.88 inches per hour at 30 inch depth (basin 2), underdrains were not allowed following PA’s BMP manual guidelines. (Pennsylvania’s infiltration threshold is 0.1 inches per hour, whereas Delaware’s threshold is 1.02 inches for an underdrain). Pennsylvania’s standards discourage underdrains unless other methods do not work; because ours did not work, an additional $160,000 is required to remediate with underdrains.
Watershed: Poquessing Creek
Renew Design Group
Cranaleith Spiritual Center
13475 Proctor Road
Philadelphia, PA 19116