Department of
Environmental Quality

Use Attainability Analysis

The designated use of a water body that is shown to not be an existing use may be changed if it is not attainable. A use attainability analysis (UAA) is a structured scientific assessment of the beneficial uses a water body could support, given application of required effluent limits and implementation of cost-effective and reasonable best management practices.

A UAA is required anytime a state or tribe designates a use that does not include the "fishable/swimmable" goals of the Clean Water Act or changes a use to one that would apply less stringent criteria than the current use. If a use is designated that does not include the "fishable/swimmable" goals, that use designation and the rationale behind it need to be revisited every three years to see if circumstances have changed. In Idaho, two UAAs have been done where aquatic life use designations were set to “none.” These designations are reviewed every three years to determine if the designation is still appropriate.

Waters must be protected for the most sensitive of their uses. Most streams have overlapping or competing uses. When this is the case, the most sensitive use is that which requires better water quality (the use with the most stringent criteria). If an existing use is "better" than the designated use, the existing use must be protected and that use must become the designated use. Uses that currently exist, or have existed since November 25, 1975, cannot be removed or downgraded.

Process for Changing a Use Designation

The process for changing a use designation requires rulemaking by DEQ. Therefore, parties interested in changing designated uses should involve the agency early in the process. Simply put, the first part of the process is to determine what the existing uses for the water body segment are. If the existing uses have associated criteria that are less stringent than the designated uses, then the next step is determining if the designated uses are attainable if all cost-effective and reasonable best management practices are in place and effective and that all effluent limits are being met. If the designated use is shown to be unattainable, the final step is to determine what the highest attainable use would be if all those practices and effluent limits were in place. This process constitutes the body of the UAA and is followed by the agency’s rulemaking process to change the designated use(s).

• Use Attainability Analysis Flow Charts

According to federal regulations, only six allowable reasons exist for changing a current use designation:

1. Naturally occurring pollutant levels prevent attainment of the use.
2. Natural ephemeral, intermittent, or low flow prevents attainment of the use.
3. Human-caused pollution prevents attainment and cannot be remedied without causing worse environmental harm.
4. Dams, diversions, and other hydrologic modifications prevent attainment and it is not feasible to restore the water or operate the modification in a way that would result in attainment.
5. Natural physical features prevent attainment.
6. Controls more stringent than required effluent limitations or new source performance standards would be necessary to attain the use and would result in substantial and widespread social and economic hardship.

In Idaho, rulemaking is, at a minimum, a several-month process that requires public comment and response, Board of Environmental Quality approval, and legislative approval. Use changes are subject to EPA review and approval before becoming effective for Clean Water Act purposes (e.g., discharge permits, total maximum daily loads, §303(d) listing decisions). The entire process—developing the UAA and undergoing rulemaking—could take at least two years and possibly more to craft a structured scientific assessment to change a designated use.

In some instances, the criteria for determining if a designated use is fully supported are not appropriate for a particular water body. A state may reduce the stringency of the criteria for use attainment assigned to a water body by revising its water quality criteria (site-specific or statewide). This action can only occur where scientific understanding supports the position that a less stringent criterion is still fully protective of the designated uses. This can occur in instances where natural background conditions that support designated uses exceed the water quality criteria.

DEQ has successfully removed designated uses from two water body segments in Idaho: Blackbird Creek and Bucktail Creek. Both of these water bodies were significantly impacted by mining activities in the late 1940s through 1950s. The mine has been the site of significant cleanup activities over the past two decades to reclaim and restore the water bodies. Progress has been made in this area and DEQ continues to review data on a triennial basis to support and assess the continued use designation of “none” for aquatic life uses in these water bodies. Other successful UAAs include two UAAs to remove salmonid spawning as a designated use. Both proceeded to rulemaking to remove the use based on reason five (natural physical features prevent attainment).

• The first UAA removed salmonid spawning as a designated use for the portion of the Snake River inundated by Brownlee, Oxbow, and Hells Canyon Reservoirs (rulemaking docket 58-0102-0002, approved by EPA in March 2006). Salmonid spawning was found to be unattainable due to unsuitable habitat conditions; salmonids require suitable substrate (gravels) and sufficient water velocity to move water through the gravels, neither of which is a prevalent condition in a lake or reservoir.
• The second UAA removed salmonid spawning from a small headwaters segment of Butcher Creek above a natural barrier to fish passage (rulemaking docket 58-0102-0204, approved by EPA in January 2006). 

Separate reports were not prepared for these UAAs. Support of the use change was incorporated in the rulemaking packages.