EPA's Residual Designation Authority

Stormwater discharges can contain pollutants from a variety of sources and convey them to waters of the United States. EPA and the authorized states regulate stormwater discharges from regulated municipal separate storm sewer systems (MS4s), industrial activities, and construction sites under section 402(p) of the Clean Water Act. These stormwater discharges require NPDES permits. For details, see the NPDES stormwater program.

In addition, EPA and authorized states are given an authority to designate other stormwater discharges to control stormwater pollutants. Called "residual designation" authority under 40 CFR 122.26(a)(9)(i)(C) and (D) (pdf)(224 KB), EPA and authorized states can require NPDES permits for other stormwater discharges or category of discharges on a case-by-case basis when it determines that:

• the discharges contribute to a violation of water quality standards,
• the discharges are a significant contributor of pollutant to federally protected surface waters, or
• controls are needed for the discharge based on wasteload allocations that are part of "total maximum daily loads" (TMDLs) that address the pollutant(s) of concern.

Small MS4s that are not already required to have NPDES permit coverage can be designated for regulation under 40 CFR 123.35(b) (pdf)(135 KB).

Additionally, designation can be requested by petition.

Stormwater Discharges from MS4

EPA has designated small MS4 systems for permitting in the following locations:

• Region 6: Los Alamos County, New Mexico
  • EPA Region 6 received a petition from Amigos Bravos requesting that EPA designate certain stormwater discharges in Los Alamos County, New Mexico as needing NPDES permits due to contributions to exceedances of state water quality standards in receiving waters. A copy of the petition is available on Regulations.gov, Docket ID EPA-R06-OW-2023-0566, see Appendix 1 of Docket item EPA-R06-OW-2023-0566-0002.
• Region 1: Long Creek, Maine
• Region 9:
  • Department of Public Works, Tamuning, Guam
  • Department of the Navy, Island of Guam (Federal Facility) (pdf) (1.23 MB)
• Region 10:
  • Moscow, Idaho (pdf) (935.43 KB)
  • Joint Base Lewis-McChord, Washington (Federal Facility) (pdf) (610 KB)
  • Whidbey Island, Washington (Federal Facility) (pdf) (248.54 KB)

In addition, EPA is reviewing the following petition for designation:

• Region 3: Delaware Inland Bays Watershed
  • On April 4, 2016, EPA received a petition filed by the Inland Bays Foundation (pdf) (415.28 KB) to designate and permit resort towns as MS4s in the Delaware Inland Bays Watershed.

Stormwater Discharges from Commercial, Industrial, and Institutional Sources

EPA has received petitions for the designation of commercial, industrial, and institutional sources for stormwater permitting in the below locations. Follow the links for additional details and information on EPA’s actions in response to the petitions.

• Region 1: Watershed-Based Residual Designation Actions in New England
  • Residual Designation in the Charles River Watershed, Mystic River Watershed and Neponset River Watersheds (Massachusetts)
  • Petition to Designate Certain Properties in the Great Bay Estuary Watershed (New Hampshire)
• Region 9: Petition to Designate Certain Stormwater Discharges in two Los Angeles Watersheds - Los Cerritos Channel/Alamitos Bay and Dominquez Channel/Los Angeles/Long Beach Harbor (California)
• Region 3: Petition to Designate Certain Privately Owned CII Sites in Back River Watershed in Baltimore City and Baltimore County (Maryland) (pdf) (233.03 KB)
  • EPA is preparing a proposed designation in accordance with a 2019 court decision. See Blue Water Baltimore, Inc. v. Wheeler, 2019 WL 1317087 (17-cv-1253, Mar. 22, 2019).