Maryland's Municipal Separate Storm Sewer System (MS4) Permit Program
The National Pollutant Discharge Elimination System (NPDES) permit program was established in 1972 under the federal Clean Water Act (CWA). The CWA requires point sources that discharge pollutants into waters of the United States (U.S.) to obtain coverage under an NPDES permit. An NPDES permit establishes certain terms and conditions to discharge pollutants to receiving waters in order to protect water quality. Congress added Section (402)p to the CWA in 1987 in response to the need to address pollution from stormwater discharges from municipal systems.
The U.S. Environmental Protection Agency (EPA) promulgated NPDES municipal separate storm sewer system (MS4) regulations in two phases beginning in 1990. The Phase I regulations established requirements for stormwater discharges for 11 categories of industrial activity and for MS4s serving populations of 100,000 or greater. In Maryland, ten jurisdictions and the Maryland Department of Transportation, State Highway Administration (MDOT-SHA) are covered under individual Phase I MS4 stormwater permits. These permits require the implementation of best management practices and various programs to reduce pollution discharges. The permits are effective for five-year terms unless administratively continued. Reissued permits establish requirements that build upon previous progress and help Maryland to reach its Chesapeake Bay total maximum daily load (TMDL) pollution reduction requirements. Learn more about Maryland’s Chesapeake Bay Clean Up Plan here.
In December 1999, the EPA promulgated the Phase II MS4 regulations to address pollution discharges from small MS4s in urbanized areas (UA). The Phase II Final Rule also required the NPDES permitting authority to evaluate additional small MS4s located outside of UA’s that should be regulated. Maryland expanded its MS4 permit program by issuing two general permits, one for municipalities (2003) and one for state and federal agencies (2004) operating small MS4s. These permits were reissued in 2018.
Maryland’s Phase II program now covers over 90 small MS4 operators. The Phase II MS4 permits are similar to Phase I permits in that they require implementing stormwater best management practices and programs to reduce pollution discharges and to protect water quality. The work of Maryland’s Phase I and Phase II MS4 programs demonstrate a significant commitment to stormwater management and improving local water quality and the Chesapeake Bay.
- Notices of Final Determination to Issue NPDES MS4 Permits to Carroll, Charles, Frederick, Harford, and Howard Counties (December 30, 2022)
- Notice of Final Determination to Issue NPDES MS4 Permit to Prince George's County (December 2, 2022)
- Notices of Final Determination to Issue NPDES MS4 Permits to Anne Arundel, Baltimore, and Montgomery Counties, Baltimore City (November 5, 2021)