Point Source Pollution: NPDES


The National Pollutant Discharge Elimination System (NPDES) permit program controls water pollution by regulating point sources that discharge pollutants into surface waters of the United States. NPDES permits establish discharge limits for facilities (e.g., power plants, wastewater treatment plants, and concentrated animal feeding operations) to meet state water quality standards. Permit limits are either based on:

  • Technology-based effluent limitation guidelines, which are industry-specific standards based on performance of treatment and control techniques, or;
  • Water quality-based effluents limitations (WQBEL) guidelines, which are developed when technology-based limits are not sufficient to attain state water quality standards.

WQBELs are numeric discharge limits calculated on the basis of allocating, to the discharger, a share of the total allowable cumulative discharge of pollutants that will achieve water quality standards (for further discussion on aspects of the Water Quality Standards program, see sections on water quality criteria, designated uses, TMDL, and monitoring and assessment). 

How can I use National Point Discharge Elimination System permits to protect drinking water sources?

Significant potential exists for writing NPDES permits that are more protective of drinking water sources, and particularly in development and application of WQBELs. A starting point is bringing the contaminants of concern to drinking water sources to the attention of state water agencies and NPDES permit writers. Even when aware of a certain pollutant, permit writers often face challenges when developing WQBELs for pollutants of concern because many states exclusively rely on narrative water quality criteria, rather than numeric necessary for WQBELs, and are therefore required to interpret narrative criteria on a case-specific basis, a process that can be limited by available data and access to analytical tools. In either case, public drinking water stakeholders can contribute to development of NPDES permits protective of drinking water sources by providing water quality data (from source water quality data, Maximum Contaminant Level (MCL) violations, source water assessments, etc.) that characterize pollutant threats in relation to downstream water sources and provide for basis of numeric water quality criteria. 

  • Encourage states and permit writers to include NPDES effluent limits for pollutants that are regulated as drinking water contaminants under state or federal law or that are otherwise identified as contaminants of concern to drinking water
  • Encourage states to adopt numeric water quality criteria (or numeric “translators” for narrative criteria) for each contaminant of concern for every drinking water source
  • Share source water quality information with state NPDES permit writers to assist in analyzing the relationship between discharge effluent limits and source water quality

Opportunities for involvement

All existing permits must be renewed on a regular basis and are open to public notice and comment. Many states NPDES authorities issue permits on a watershed basis to ensure that all point source discharges to a watershed are considered at the same time. Stakeholders may request renewal schedules from their permitting authority—either a state environmental agency or an EPA Regional office—or be added to public notices mailing lists. Read more about the NPDES program, here.

For further discussion on protecting drinking water through the Clean Water Act, see Opportunities to Protect Drinking Water and Advance Watershed Goals through the Clean Water Act: A Toolkit for State, Interstate, Tribal, and Federal Water Program Managers.