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Municipal Separate Storm Sewer Systems



Urban stormwater runoff is commonly transported through Municipal Separate Storm Sewer Systems (known as MS4s) and is often discharged, untreated, into local waterbodies. To prevent harmful pollutants from being washed or dumped into these systems, operators must obtain a NPDES permit and develop a stormwater management program.

The national program of MS4 General NPDES Permit was phased-in, over time, with the first phase covering larger municipal governments. The second phase covers smaller communities, in Census-designated Urbanized Areas, and some non-governmental stormwater systems.

Phase I, first issued in 1990, requires medium and large cities or certain counties with populations of 100,000 or more to obtain NPDES permit coverage for their stormwater discharges.

Phase II, first issued in 1999, requires regulated small municipal systems in Urbanized Areas, as well as some outside of Urbanized Areas that are designated by a permitting authority, to obtain NPDES permit coverage for their stormwater discharges.

Phase I Permits in Delaware

New Castle County and Delaware Department of Transportation MS4 Permit (Includes Appendix A & B)
Appendix C
Appendix D

New Castle County and Delaware Department of Transportation MS4 Fact Sheet

Phase 2 Permits in Delaware

Town of Middletown Interim Phase II MS4 Permit

Town of Middletown, Interim Phase II MS4 Fact Sheet

NPDES Permit for Small Phase II Municipal Separate Storm Sewer Systems

The Phase II Final Rule established under the Federal Clean Water Act requires nationwide coverage of all small MS4s that are located within the boundaries of Census-designated Urbanized Areas, based on the latest decennial Census. The 2010 Census results expanded the Urbanized Areas area within Delaware. That requires DNREC to expand the universe of municipalities requiring NPDES Phase II MS4 permit coverage. Currently the four Phase II MS4 permits in Delaware are individual permits; however, as our permitted universe continues to expand DNREC has decided to move Phase II MS4 coverage to a General Permit Program.

 




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