Municipalities and other entities such as universities and prisons that meet certain standards must obtain
NPDES permit coverage for discharges of stormwater from their municipal separate storm sewer systems (MS4s).
In Pennsylvania, there are two Large
MS4s, no Medium MS4s, and 1059 Small MS4s.
MS4s must apply for NPDES permit coverage or a waiver if they are located in an urbanized area as determined by the latest Decennial Census by the U.S. Census Bureau, or if they are designated as needing a permit by DEP. EPA has posted
Urbanized Area Maps from the 2010 Census data. Urbanized Area information from the 2000 Census can also be reviewed at the
U.S. Census Bureau 2000 Urbanized Areas Information website.
For the current permit term, MS4s that discharge to surface waters impaired for certain pollutants or that discharge to waters in the Chesapeake Bay watershed are required to develop Pollutant Reduction Plans (PRPS) or
TMDL Plans. See the
PRP/TMDL Plans webpage for further information.
Small MS4s required to obtain permit coverage may, if eligible, apply for coverage under the 2018
NPDES General Permit for Stormwater Discharges from Small MS4s (PAG-13) (PDF) (3800-PM-BCW0100) which is currently in effect.
Small MS4s that are ineligible for PAG-13 General Permit coverage may apply for an
individual permit (3800-PM-BPNPSM0200).
Permit coverage is generally for a 5-year term. The applicant submits either an Individual Permit application or a "Notice of Intent' (NOI) to discharge under the statewide General Permit at least 180 days prior to the expiration date of coverage. When the statewide PAG-13 General Permit is reissued by DEP, as was done in March 2018, MS4s covered by the previous PAG-13 General Permit are automatically covered by the reissued PAG-13 General Permit if a timely
NOI is submitted by the MS4. New requirements may then apply to the MS4. The MS4 can, if it chooses, elect to apply for an individual NPDES permit in lieu of continued coverage under the reissued General Permit.
DEP has developed a
reporting tool that can be used to generate lists of NPDES-permitted and waived MS4s in Pennsylvania.
DEP's regional offices inspect MS4s to determine whether the MS4 is meeting its permit obligations. The inspections are documented on
DEP's MS4 inspection report (PDF) (3800-FM-BPNPSM0489). DEP also reviews the
Annual Status Report (3800-FM-BCW0491) submitted by MS4s to DEP.
For more information on MS4 NPDES permits and compliance, email the Bureau of Clean Water (BCW) at
RA-EPPAMS4@pa.gov, or contact BCW by phone at 717-787-5017.