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Municipal Separate Storm Sewer Systems



Stormwater runoff from urban and industrial areas can contain harmful pollutants. To help keep these pollutants from being washed or dumped into surface waters, operators of municipal separate storm sewer systems (known as MS4s) must get a permit and develop a stormwater management program.

Pollutants found in stormwater runoff include nutrients, heavy metals, pesticides, herbicides and synthetic organic compounds such as fuels, waste oils, solvents, lubricants and grease. These can have damaging effects on both human health and aquatic ecosystems if not treated.

Municipal Stormwater NPDES Permits

The national program of NPDES MS4 Individual and General Permits was first introduced into the EPA’s NPDES program in 1990. It tackled larger municipal governments with the Phase I permits. Phase II permits, for smaller communities in Census-designated Urbanized Areas and some non-governmental stormwater systems, came in 1999.

Since then, DNREC has worked with the Delaware’s public entities to ensure the compliance of both the Phase I and Phase II permits. The Department has also introduced a more encompassing Phase II General Permit.

Phase I Permits in Delaware

The Phase I Individual Permit provides coverage to Principal Permittees New Castle County (NCC) and Delaware’s Department of Transportation (DelDOT), including co-permittees the City of Delaware City, the City of New Castle, the City of Wilmington, the Town of Elsmere and the Town of Newport.

NCC and DelDOT Phase I MS4 Permit (2013)

NCC and DelDOT Phase I MS4 Permit Fact Sheet (2013)

Phase II Permits in Delaware

The Phase II General Permit provides coverage to multiple permittees. The new cycle of the Phase II General Permit was broken into two tiers; Tier I and Tier II.

The Tier I General Permit provides coverage to those who currently work under an Individual Phase II MS4 permit. The Tier II General Permit provides coverage to those who seek a new MS4 permit.

The Tier I General Permit will cover the City of Newark/University of Delaware, the Town of Middletown, the City of Dover and DelDOT in Kent County.

DRAFT Phase II Tier I MS4 General Permit (2020)

DRAFT Phase II Tier I MS4 General Permit Fact Sheet (2020)

The Tier II General Permit will cover the Town of Smyrna, the Town of Camden, the Town of Laurel and the City of Seaford.

DRAFT Phase II Tier II MS4 General Permit (2020)

DRAFT Phase II Tier II MS4 General Permit Fact Sheet (2020)

Resources

National Municipal Stormwater Alliance/EPA MS4 Resource Guide

EPA NPDES Stormwater Discharges from Municipal Sources

EPA NPDES Urbanized Area Maps (Phase II)

DelDOT Stormwater Page

University of Delaware Stormwater

Penn State Extension – What is an MS4?




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