Water Quality Standards - Authorities, Definitions and Considerations | Region 10 | US EPA

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Water Quality Standards - Authorities, Definitions and Considerations


Under section 303(a)-(c) of the Clean Water Act, states are required to establish water quality standards. EPA is responsible for reviewing standards adopted by the states to ensure their consistency with the requirements of the Act.

  • EPA’s regulations at 40 CFR Part 131 describe the minimum requirements for water quality standards.
  • Any new or revised water quality standards adopted by states and submitted to EPA after May 30, 2000 must be approved by EPA in order for those standards to be effective (40 CFR 131.21(c)(2)).
What are Water Quality Standards?

Water quality standards (WQS) are legally binding norms that describe the desired ambient condition (i.e., level of protection) for a waterbody and consist of the following three principle elements:
  1. the “designated uses” of the state’s waters, such as public water supply, recreation, propagation of aquatic life and wildlife, or navigation;
  2. “criteria” specifying the amounts of various pollutants, in either numeric or narrative form, that may be present in those waters without impairing the designated uses (note - criteria include any one or more of three components: magnitude, duration, and frequency); and,
  3. antidegradation requirements providing for protection of existing water uses and limitations on degradation of high quality waters.
Frequently asked questions about new or revised water quality standards under CWA 303(c)(3)

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URL: https://yosemite.epa.gov/r10/water.nsf/Water+Quality+Standards/Whats-a-WQS

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