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Municipal Stormwater


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.

NPDES Permits

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, or contact BCW by phone at 717-787-5017.


Please visit DEP’s Clean Water Academy to access online MS4 courses that are available to the public. More courses will be added over time.

Program Updates

DEP published the final NPDES General Permit for Stormwater Discharges from Small MS4s ("PAG-13") in the Pennsylvania Bulletin on June 4, 2016. That General Permit is effective as of March 16, 2018. DEP received over 600 comments on the draft PAG-13 General Permit that was published on May 30, 2015, and has prepared a comment-response document.

DEP also published individual NPDES permit application documents for small MS4s on its website for those MS4s that cannot use the PAG-13 General Permit, such as MS4s with a requirement to develop a TMDL Plan or discharge to special protection waters. Periodic updates to the MS4 "Frequently Asked Questions (FAQ) (PDF)" document are published. The FAQ provides good general background information as well as concepts relevant to Pollutant Reduction Plans and TMDL Plans.

Related Information

Perspectives from Four PA Municipalities

Leaders from Lemoyne Borough, Harrisburg, and Lower Paxton and Susquehanna Townships share their perspectives on the stormwater management challenge.