Element 6 - Antidegradation

Missouri's Water Quality Standards include the EPA "three-tiered" approach to antidegradation, which may be found at 10 CSR 20-7.03(2) .

Tier 1 - Protects existing uses and a level of water quality necessary to maintain and protect those uses. Tier 1 provides the absolute floor of water quality for all waters of the United States. Existing instream water uses are those uses that were attained on or after Nov. 28, 1975, the date of EPA's first Water Quality Standards Regulation.

Tier 2 - Protects and maintains the existing level of water quality where it is better than applicable water quality criteria.
Before water quality in Tier 2 waters can be lowered, there must be an antidegradation review consisting of: (1), a finding that it is necessary to accommodate important economic and social development in the area where the waters are located; (2), full satisfaction of all intergovernmental coordination and public participation provisions; and (3), assurance that the highest statutory and regulatory requirements for point sources and best management practices for nonpoint sources are achieved. Furthermore, water quality may not be lowered to less than the level necessary to fully protect the "fishable/swimmable" uses and other existing uses.

Tier 3 - Protects the quality of outstanding national and state resource waters, such as waters of national and state parks, wildlife refuges and waters of exceptional recreational or ecological significance. There may be no new or increased discharges to these waters and no new or increased discharges to tributaries of these waters that would result in lower water quality.

More information regarding Missouri's antidegradation rule, including the implementation of this rule, can be found on the Water Protection Program web pages.