County-wide Act 167 Stormwater Management Plan and 2022 Model Ordinance Update

On August 17, 2022, the Chester County Board of Commissioners adopted Resolution 55-22 to amend the County-wide Act 167 Stormwater Management Plan for Chester County, PA to replace the 2013 model ordinance with the 2022 County-wide Act 167 Stormwater Management Model Ordinance. This updated ordinance incorporates PA DEP's comments from their review of the Model Ordinance to improve consistency with their state-wide 2022 Stormwater Management Model Ordinance. In January 2024, the 2022 model ordinance was officially incorporated into the Watersheds 2045 plan, which serves as the updated County-wide Act 167 Stormwater Management Plan. 

Under the Pennsylvania Stormwater Management Act (PA Act 167), all Chester County municipalities, both MS4 and non-MS4 permittees, were required to adopt stormwater ordinances consistent with the County's Model Ordinance by May 31, 2023.

It is recommended that municipalities adopt the Model Ordinance as a stand-alone ordinance. After the ordinance has been adopted, we ask that an electronic copy, along with the completed Certification of Ordinance Adoption, be submitted to the Chester County Water Resources Authority (CCWRA) at [email protected]. Municipalities do not need to submit their draft updated ordinance to CCWRA or the Chester County Planning Commission (CCPC) prior to adoption. 

Model Ordinance Workshops

In May of 2022, the Chester County Water Resources Authority hosted two implementation workshops to assist municipalities with updating their stormwater ordinances. Links to the recordings and PDFs of presentations delivered at both workshops can be found at this page.

Implementation Workshop 1 Presentation


County-wide Act 167 Stormwater Management Model Ordinance Documents 

The updated County-wide Act 167 Model Ordinance is the culmination of and was significantly shaped by nearly three years of collaboration between Chester County, its municipalities, residents, and other stakeholders. It was designed to meet the needs of Chester County’s municipalities, fulfill the standards set forth in the Pennsylvania Storm Water Management Act (“Act 167”), and comply with the regulatory requirements of PA DEP’s National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) program. The updates incorporated into the Model Ordinance were also designed to comply with the provisions included in PA DEP's 2022 Model Stormwater Management Ordinance.

Links to updated versions of the adopted Model Ordinance and supporting documents can be found below. The following documents were also updated for consistency with the changes to the Model Ordinance: Appendix B, Appendix E, the Matrix of Minimum Standards, Summary of Changes, and Summary of Options. Municipalities should reference these latest documents when updating their ordinance to be consistent with PA DEP’s 2022 Model Ordinance and the County-wide Act 167 Model Stormwater Ordinance. 

Model Ordinance Implementation Resources 

Below are additional resources to assist Municipalities with updating their ordinances to be consistent with the County-wide Model Ordinance. 

Additional Historic County-wide Act 167 Plan Resources

The Pennsylvania Department of Environmental Protection approved the “County-wide Act 167 Stormwater Management Plan for Chester County, PA” on July 2, 2013. The State, through Act 167, requires that all Chester County municipalities adopt the updated ordinance requirements included in the Plan amendment.

Please note, the Plan is more than just the model ordinance (Appendix D) and the components of the Plan are comprised of the following, as shown in the bulleted list below.

Precipitation Resources

Section 706 of the updated Model ordinance requires inspections of BMPs installed after the adoption of this ordinance to be inspected during or immediately after the cessation of a 25-year or greater storm (for inspections conducted by the municipality) or 10-year or greater storm (all other inspections). Municipalities and those with BMP inspection responsibilities should reference NOAA Atlas 14 when assessing when inspections are required. The chart below provides information on average return intervals for Chester County. 

NOAA Atlas 14 Precipitation Estimates
Average of seven locations throughout Chester County, PA


1-Hour2-Hour6-Hour12-Hour24-Hour
2-Year Storm1.441.722.312.803.24
5-Year Storm1.792.142.873.514.07
10-Year Storm2.032.462.873.514.07
25-Year Storm2.352.893.954.805.75
50-Year Storm2.583.234.465.646.58
100-Year Storm2.823.575.006.427.47

Links to subscribe to real-time precipitation data from the seven USGS precipitation gages in the County are below:  

Additional precipitation data for Chester County can be found at the following links: