Summary

The Clean Water Act (CWA) was enacted in 1948 and expanded and amended in 1977 and 1987.  The CWA establishes the structure to regulate pollutant releases into waters of the United States. The purpose of the CWA is to maintain and restore the chemical, physical and biological integrity of the nation’s surface waters. Pollutants regulated under the CWA include toxic pollutants (those that directly harm the environment), nutrients when in excess (such as nitrogen and phosphorus), suspended solids (such as sediment), and many other substances that affect water quality. The Environmental Protection Agency (EPA) is the primary Federal agency that administers and enforces the CWA.

Background

Under the CWA, pollutants fall into two categories: point sources and nonpoint sources. A point source is an entity that directly discharges pollutants to surface waters through a pipe or specific discharge location. Examples of point sources include manufacturing facilities, wastewater treatment plants and Concentrated Animal Feeding Operations (CAFOs).

A nonpoint source is a source of pollution without a specific location of discharge but rather discharges come from runoff from the land.  Examples of nonpoint sources are row crop production, animal feeding operations without a CAFO designation, lawns and golf courses. Examples of pollutants often discharged by nonpoint sources are excess nutrients, herbicides, and sediment.

Total Maximum Daily Loads

Impaired waters not meeting their designated use are listed on the Federal section 303(d) list as not meeting standards.  These waters are then assessed and assigned a Total Maximum Daily Load (TMDL) for the pollutant(s) responsible for the water not meeting its designated use.  The TMDL is determined by the state but must be submitted to EPA for approval where it may be revised. Discharges from both point sources and NPS are considered when establishing a TMDL. Once a TMDL has been established, strategies to reduce the discharging pollutant(s) are developed.  These strategies include revisions to discharge permits for point sources and state led initiatives to reduce pollutant discharges from NPS. 

What is the difference between TMDLs and Water Quality Criteria?

Although TMDLs and Water Quality Criteria are both aimed at improving or maintaining water quality, there are important distinctions between the two. The key difference is the timing of implementation. Water quality criteria, whether numeric or narrative, are determined once the designated use of the water body is determined.  A TMDL is only implemented once it has been determined that a water body is not meeting its designated use.