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National Pollutant Discharge Elimination System (NPDES)

Permit Limits-Nutrient Permitting

Excess nutrient loading to water bodies beyond levels needed to maintain the health of an indigenous aquatic ecosystem is commonly referred to as nutrient pollution. The effects of nutrient pollution are diverse and far-reaching. Among the most significant and widespread effects of nutrient pollution are accelerated eutrophication and the resulting impacts on water quality.

Nitrogen and phosphorus are transported to water bodies in rain, surface runoff, including urban and agricultural ground water drainage, and municipal and industrial wastewater. Once in a water body, nitrogen or phosphorus can occur in dissolved organic, dissolved inorganic or particulate forms with transformations occurring among these forms. Because nutrients cycle among various forms, nitrogen and phosphorus pollution in water bodies generally is measured in terms of total nitrogen and total phosphorus.

Visit EPA's Nutrient Pollution website for more information about nutrient pollution.

The Clean Water Act (CWA) section 402 and Code of Federal Regulations (CFR) § 122.1(b) establishes the framework for the NPDES program, requiring permits for any point source discharge of pollutants to waters of the United States. Point sources regulated by the NPDES program that discharge nutrients include municipal and industrial wastewater treatment plants, concentrated animal feeding operations (CAFOs), Municipal Separate Storm Sewer Systems (MS4s), stormwater associated with industrial activity, and various other potential sources of nutrient pollution. Return flows from irrigated agriculture and agricultural stormwater runoff are not considered point sources and, therefore, are not regulated under the NPDES program (§ 122.2).

EPA Resources

  • Compilation of Cost Data Associated with the Impacts and Control of Nutrient Pollution -- A compilation of data collected from a range of sources including published, peer-reviewed journals, government-funded research and reports, academic studies and other data sources. This report is a collection of research data from 2000 through 2012 including references to the literature cited. 
  • Municipal Facilities with Permit Requirements for Nutrients -- Counts and percentages, by state or territory, of municipal wastewater treatment facilities that have NPDES permits with effluent limits or monitoring requirements for nutrient parameter(s). Setting permit limits for nitrogen and phosphorus from municipal wastewater treatment facilities can substantially reduce nutrient loadings to waterbodies, protecting local and downstream water quality as a result.
  • Nutrient Recycling Challenge -- EPA is partnering with pork and dairy producers, the U.S. Department of Agriculture, and environmental and scientific experts to find affordable technologies that recycle nutrients from livestock manure and create valuable products.
  • Watershed-based Permitting -- Watershed-based permitting is a process that produces NPDES permits that are issued to point sources on a geographic or watershed basis. Since nutrient pollution often has far-field, cumulative impacts on a waterbody, stakeholders may wish to pursue a watershed-based permitting approach to NPDES permits.
  • Water Quality Trading -- Water quality trading under the Clean Water Act is an option for compliance with a water quality based effluent limitation (WQBEL) in a NPDES permit.
  • Discharge Monitoring Report (DMR) Pollutant Loading Tool -- The DMR Pollutant Loading Tool helps determine which facilities are discharging, what pollutants they are discharging and how much, and where they are discharging. The tool calculates pollutant loadings from permit and DMR data from EPA's Integrated Compliance Information System for the National Pollutant Discharge Elimination System (ICIS-NPDES). Data are available from the year 2007 to the present.
  • National Study on Nutrient Control and Water Treatment Technologies -- EPA is considering a national study on nutrient removal at municipal wastewater treatment plants, also called water resource recovery facilities (WRRFs). This study would be a multi-year effort and fill crucial and fundamental information gaps that exist for nationwide nutrient contribution from WRRFs, and the nutrient control measures and practices available for these facilities. In the fall of 2016, EPA plans to collect basic information from all facilities nationwide to identify the secondary treatment facilities that should be surveyed.

Non-EPA Resources

  • Nutrient Modeling ToolkitExit-- Developed by the Water Environment Research Federation (WERF), the Nutrient Modeling Toolkit is used to quantitatively link nutrient loads to water quality and ecological response indicators on a site-specific basis.

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