For a detailed description of construction responsibilities to mitigate stormwater run-off read the Township's ordinance regarding "Suspension and Revocation of Permits and Approvals."
From Chester County Water Resource
"Poorly managed stormwater runoff is one of the principal causes of impairment throughout the watersheds of Chester County. The ultimate and collective purpose of comprehensive stormwater management is to accommodate planned growth in a manner that protects public safety and maintains the natural hydrologic characteristics of the watersheds and sustains groundwater recharge, stream baseflows, stable stream channel processes, and geomorphology conditions, the flood-carrying capacity of streams and their floodplains, and groundwater and surface water quality -to the maximum extent practicable."
The following sources provide further information on managing stormwater in a more sustainable manner. Note, that the link opens a separate window.