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Municipal Stormwater


Important News!



Municipalities (cities, boroughs, and townships) that meet certain standards must obtain NPDES permit coverage for discharges of stormwater from their municipal separate storm sewer systems (MS4s).

A municipal separate storm sewer is any conveyance or system of conveyances (including but not limited to streets, ditches, and pipes) that is:

  • owned by a municipality or other public body (created under state law) having jurisdiction over disposal of sewage, industrial wastes, stormwater or other wastes;
  • designed or used for collecting or conveying stormwater;
  • not a combined sewer (i.e., not intended for both sewage and stormwater); AND
  • not part of a publicly owned treatment works (POTW).

MS4s are categorized as Large, Medium and Small based on criteria in the federal regulations at 40 CFR 122.26. Large and Medium MS4s must apply for NPDES permit coverage.

Small 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 Bureau of the Census, 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.

Waivers may be granted in lieu of permit coverage if the criteria in 40 CFR 122.32(d) or (e) are met.


NPDES Permits

Large and Medium MS4s must apply for individual NPDES permits in Pennsylvania, as no NPDES General Permit exists for these MS4s.

Small MS4s required to obtain permit coverage may, if eligible, apply for coverage under the NPDES General Permit for Stormwater Discharges from Small MS4s (PAG-13) (3800-PM-BPNPSM0100). Small MS4s that are ineligible for PAG-13 General Permit coverage may apply for an individual permit (3800-PM-BPNPSM0200).

If the Small MS4 believes that the criteria for a waiver are met, the MS4 may submit an application for a waiver. Waiver applications must be submitted in conjunction with the PAG-13 Notice of Intent (NOI) or the individual permit application, as applicable. An MS4 that would be ineligible for PAG-13 coverage should submit the individual permit application, rather than a PAG-13 NOI, with their waiver application.

NPDES permits for MS4s require, in lieu of numeric effluent limitations, implementation of a stormwater management program that contains six Minimum Control Measures (MCMs), which include:

  • Public Education and Outreach on Stormwater Impacts
  • Public Involvement/Participation
  • Illicit Discharge Detection and Elimination
  • Construction Site Stormwater Runoff Control
  • Post-Construction Stormwater Management in New and Re-Development Activities
  • Pollution Prevention/Good Housekeeping

In addition, permits require the submission of periodic reports (annual reports or progress reports every other year); submission of Total Maximum Daily Load (TMDL) plans that document how an MS4 will reduce pollutants discharged in stormwater to achieve wasteload allocations (WLAs) in TMDLs (if the MS4 discharges to waters with an EPA-approved TMDL with WLAs); and submission of Chesapeake Bay Pollutant Reduction Plans that document the steps MS4s will take to reduce the discharge of nitrogen, phosphorus and sediment to the Chesapeake Bay (if the MS4 discharges to waters that drain to the Bay).

Permit coverage is generally for a 5-year term with a requirement to submit a renewal application or NOI 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 2013, 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.

For more information on NPDES permits, see the MS4 Frequently Asked Questions (PDF) document, email BPNPSM at, or contact BPNPSM's Division of Planning and Permitting at 717-787-8184.



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). To facilitate compliance and ensure consistency in the reporting of information in periodic reports, TMDL plans and Chesapeake Bay Pollutant Reduction Plans, DEP has posted the following templates that should be used by permittees:

For more information on NPDES permit compliance, see the MS4 Frequently Asked Questions (PDF) document, email BPNPSM at, or contact BPNPSM's Division of Operations, Monitoring and Data Systems at 717-787-6744.

DEP has also provided links to additional MS4 resources, including documents and sites for maps, modeling and MCM implementation.


Program Updates

DEP is planning to make several changes to the NPDES MS4 program in the next few years, as described in the recorded webinar listed below. The changes will not take effect until 2018, but DEP is proposing the changes now to provide ample opportunity for review and feedback from MS4s.

DEP solicited input on a draft of the PAG-13 NPDES General Permit for Discharges from Small MS4s, which would become effective in March 2018. Notice of the availability of the official draft PAG-13 General Permit was published in the Pennsylvania Bulletin on May 30, 2015. DEP is now in the process of finalizing this draft permit.

For the next permit term, DEP anticipates that MS4s that discharge to surface waters impaired for certain pollutants or that discharge to waters in the Chesapeake Bay watershed will need to implement specific best management practices or develop TMDL Plans or Pollutant Reduction Plans. To assist MS4s with understanding their obligations regarding impaired waters, DEP has prepared a draft MS4 Requirements Table.  The Table consists of two parts – one for Municipal MS4s (PDF) and one for Non-Municipal MS4s (PDF). (Note – the Non-Municipal component of the Table is new as of March 2016)." See also the Instructions (PDF) for understanding and using the Table and for methods to provide comments. DEP is soliciting comments on this table to ensure that all discharges to impaired waters are accurately represented prior to the effective date of the PAG-13 General Permit (see instructions in the document for methods to provide comments).

Many MS4s have responsibilities under the current PAG-13 General Permit, or an individual NPDES permit, to develop TMDL Strategies and TMDL Design Details. An option, where applicable, when developing these plans is to modify the total pollutant load the MS4 is responsible for achieving by "parsing" the TMDL-assigned wasteload allocation (WLA) based on land area, land use, or other methods. DEP has developed draft guidelines for parsing WLAs from TMDLs (PDF) to assist MS4s with this process, if elected.



DEP will be offering two series of MS4 workshops across the State starting the summer of 2016.

The first series of one day workshops will help prepare current and future permittees for the next permit application or NOI (Notice of Intent). Registration for the first series of workshops is now open and limited to 50 participants each workshop (details on registration form). The official Registration Form and payment must be received by DEP via mail 30 days before each workshop begins.

The second series of one day workshops will cover how to prepare the Pollutant Reduction Plans and TMDL Plans that must be submitted as part of the application or NOI for some permittees. Registration information for these workshops will be coming soon.