Developers have a responsibility to manage their stormwater both during and after construction for most types of earth disturbance activities (i.e. single family residential, multi-family housing, mixed use, commercial, industrial, new construction for agricultural operations). Erosion and Sedimentation (E&S) Control BMPs (i.e. erosion control blanketing, straw mulch) help control erosion from areas with disturbed soils, collect sediment in engineered catchment areas (sediment traps or sediment basins) and limit that amount of sediment that leaves the construction site (i.e. compost filter socks, silt fence). Chapter 102 of the PA Code is an important regulation for defining the E&S requirements.
For projects that will disturb less than one acre, E&S plans can be reviewed by the municipality or through the Chester County Conservation District. Post Construction Stormwater Management (PCSM) for projects under an acre is also regulated through the municipality through a grading permit or subdivision and land development application. Projects applying for permits under these programs are reviewed for compliance with the municipality’s stormwater management ordinance. Municipal stormwater management ordinances are at least as stringent as the County’s Act 167 Model Ordinance, which satisfies all requirements in DEP’s statewide model ordinance.
For projects that will disturb more than one acre over the course of the project, another type of National Pollutant Discharge Elimination System (NPDES) Permit is required for Discharges of Construction Associated with Construction Activities. This permit is intended to ensure that all Chapter 102 regulations are being met for the construction activities during (E&S) and after construction (PCSM). For the NPDES Construction Stormwater permit, the developer is the responsible party (as opposed to the NPDES MS4 permit for which the municipality is responsible).
PA DEP issues NPDES Permits pursuant to a legal delegation from the US EPA, and then most County Conservation Districts, including Chester County, have a delegation agreement with PA DEP for some or all of the NPDES Reviews. Similar to MS4 permits, the applicant can apply under either a General NPDES Construction Stormwater Permit (PAG-02) or an Individual Permit. An Individual Permit is required for projects located in special protection (HQ or EV) watersheds or for projects that do not meet the eligibility criteria for the PAG-02. There are additional requirements for NPDES Permitted Projects in special protection watersheds, including antidegradation implementation requirements under Chapter 93 of the PA Code and riparian buffer requirements. Additional resources for residents or developers on the NPDES Construction Stormwater Permits can be found here.