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MS4 Program

Municipal Separate Storm Sewer Systems


Municipalities in the State of Pennsylvania (counties, 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:

  1. owned by a municipality or other public body (created under state law) having jurisdiction over disposal of sewage, industrial wastes, stormwater or other wastes;
  2. designed or used for collecting or conveying stormwater;
  3. not a combined sewer (i.e., not intended for both sewage and stormwater); AND
  4. 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 the Pennsylvania Department of Environmental Protection (PADEP). 


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

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


NPDES permits for MS4s require, in lieu of numeric effluent limitations, implementation of a stormwater management program. There are six program elements designed to reduce the discharge of pollutants to the maximum extent practicable. 


The program elements, titled Minimum Control Measures (MCMs), include: 

1. Public Education and Outreach 

2. Public Involvement / Participation 

3. Illicit Discharge Detection and Elimination 

4. Construction Site Runoff Control 

5. Post-Construction Stormwater Management 

6. Pollution Prevention / Good Housekeeping for Municipal Operations. 


Permit coverage is generally for a 5-year term with a requirement to submit a renewal application or a Notice OF Intent (NOI) at least 180 days prior to the expiration date of coverage.


Lehigh County is considered a non-traditional municipal MS4 and has developed an MS4 Program Plan to identify Lehigh County’s MS4 requirements and to provide an outline as to how the County will comply with these requirements.  This Plan is reviewed annually and revised/updated as needed. 


Lehigh County’s MS4 Program Plan documents the proactive efforts planned by the County under this program. These requirements primarily correspond to the county infrastructure and properties (facilities, parks, athletic fields and drainage infrastructure), but also include public information and outreach on stormwater issues. The ultimate purpose of this plan is to maintain or improve water quality in the area designated as within the MS4 boundary in Lehigh County. The County’s Program Plan has been revised and submitted to PADEP on December 31, 2014. 


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). The County’s MS4 Progress Report was submitted to PADEP on December 31, 2014.


The MS4 program for Lehigh County is administered by the Lehigh County Conservation District (LCCD) through a Memorandum of Understanding between the County and the LCCD. 


The County’s Program Plan and MS4 Reports are available for review through right to know. Copies of the County’s Program Plan and MS4 Reports are kept at the following addresses:


Lehigh County Conservation District  

4184 Dorney Park Road, Suite 105 

Allentown, PA 18104


Lehigh County Government Center

General Services Department

17 S. 7th Street

Allentown, PA 18101-2400