Department of
Environmental Quality

Federal Water Quality Standards (40 CFR 131.12) require states to develop antidegradation policies to protect existing and designated uses of surface waters. Antidegradation is one of three required regulatory elements. (The other two are assignment of beneficial uses and adoption of narrative and numeric water quality criteria, both of which Idaho has met.)

Idaho's antidegradation policy, contained in Section 051 of Idaho's Water Quality Standards (IDAPA 58.01.02.051), establishes three tiers of water quality protection.

Tier 1

Tier 1 maintains and protects existing uses and water quality conditions necessary to support such uses. Where an existing use is established, it must be protected even if it is not listed in the water quality standards as a designated use. Tier 1 requirements are applicable to all surface waters. Waters that just meet the numeric criteria are tier 1.

Tier 2

Tier 2 maintains and protects "high quality" waters – water bodies where existing conditions are better than necessary to support Clean Water Act "fishable/swimmable" uses. Water quality may be lowered in tier 2 waters, but only with public review of the social and economic tradeoffs. In no case may water quality be lowered to a level that would interfere with existing or designated uses. Most of the waters in Idaho are likely tier 2.

Tier 3

Tier 3 maintains and protects water quality in outstanding resource waters (ORWs). Except for certain temporary changes, water quality cannot be lowered in such waters. Outstanding resource waters generally include the highest quality waters of the United States. However, the ORW classification also offers special protection for waters of exceptional ecological significance, such as those that are important, unique, or sensitive ecologically. Decisions regarding which water bodies qualify to be ORWs are made by states and authorized tribes. Though several waters in Idaho have been considered for ORW recognition, none have been legislatively approved.

Antidegradation Guidance Development

DEQ began developing its antidegradation guidance in 2010. During ensuing months, several comment opportunities were held on individual chapters and appendices. Based on comments received, the draft document underwent various revisions, culminating in a public comment draft in January 2012. The comment period on the public comment version of the draft guidance closed March 12, 2012. Previous draft versions and comments received may be viewed below.

Previous Draft Versions

Documents Distributed

Written Public Comments Received

Revisions Made Based on Meeting Discussions and Review of Written Comment Received

Meeting Schedule

Antidegradation guidance development meetings were held on the following dates:

• December 10, 2010
• January 13, 2011
• January 27, 2011
• February 17, 2011
• March 10, 2011 (Meeting Cancelled)
• March 17, 2011
• May 6, 2011
• May 19, 2011
• June 17, 2011
• July 22, 2011 (Meeting Cancelled)
• August 5, 2011