National Pollutant Discharge Elimination System (NPDES)

EPA's Residual Designation Authority

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 can use its "residual designation" authority under 40 CFR 122.26(a)(9)(i)(C) and (D) (PDF)(23 pp, 224 K, About PDFto 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,
  • 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)(2 pp, 135 K, About PDF).

In addition, designation can be requested by petition.

Stormwater discharges pose a serious threat to the nation’s water bodies. EPA is committed to working with the states and its partners to ensure that effective programs and activities are implemented to meet water quality objectives. Residual designation is one tool for achieving necessary pollutant reductions.

2015 Petitions

In September 2015, EPA Regions 3 and 9 received petitions requesting that they designate categories of stormwater discharges from privately-owned commercial, industrial, and institutional sites that contribute pollutants for which TMDLs had been prepared in four water bodies: Dominguez Channel and the Alamitos Bay/Los Cerritos Channel in the Los Angeles area, and Army Creek in New Castle County, Delaware and Back River, in Baltimore City and Baltimore County, Maryland.

EPA Regions' Responses to the 2015 Petitions

In October 2016, EPA Regions 3 and 9 denied the petitions for designation in each watershed, after evaluating the petitions and considering relevant factors, including:

  • The likelihood that the pollutants would be exposed to precipitation at sites in the source categories specified in the petition,
  • Whether sufficient data were available to evaluate the contribution of stormwater discharges to water quality impairment from the specified sources,
  • Whether the specified sources already were adequately addressed by other environmental programs.

View more information about the 2015 petitions and 2016 responses:


2013 Petitions

In July 2013, EPA Regions 1, 3, and 9 received petitions requesting EPA to use its residual designation authority to regulate stormwater discharges from commercial, industrial, and institutional sites that discharge certain pollutants to waters listed as impaired for those pollutants. The identified pollutants were lead, zinc, copper, phosphorus, nitrogen, sediment, biological oxygen demand, and chemical oxygen demand. The petitions requested designation of stormwater discharges from sites located throughout each Region.

EPA Regions’ Responses to 2013 Petitions

In March 2014, the three Regions responded to the petitioners after evaluating the petitions and considering relevant factors, including those listed above.

Regions 3 and 9 declined to designate the stormwater discharges for NPDES permitting. Region 1 neither granted nor denied the petition, but committed to evaluate specific watersheds to determine whether site specific information will support such designations.

View more information about the 2013 petitions and 2014 responses:

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