A MINI-PRIMER ON UAAs By Allison Wiedeman Technology Coordinator EPA, Chesapeake Bay Program 7/2001 What is a UAA?? As defined in the Water Quality Standards Regulation (40 CFR 131.3), a use attainability analysis is: a structured scientific assessment of the factors affecting the attainment of a use which may include physical, chemical, biological, and economic factors as described in section 131.10(g). Reference: Water Quality Standards Handbook: Second Edition. EPA-823-B-94-OOEa, August 1994 When does a UAA have to be performed? Under section 131.10(J) of the Water Quality Standards Regulation, states are required to conduct a use attainability analysis whenever: 1) the State designates or has designated uses that do not include the uses specified in section 101a2 of the Act; or 2) the state wishes to remove a designated use that is specified in section 101 (a)(2) of the Act or adopt subcategories of uses specified in section 101(a)(2) that require less stringent criteria. States are not required to conduct UAAs when designating uses that include those specified in section 101a2 of the Act, although they may conduct these or similar analyses when determining the appropriate subcategories of section 101a2 goal uses. What factors must be considered in conducting UAAs? Designated uses may be removed, or subcategories of a use established, only under the conditions given in section 131.1 Og. The state must be able to demonstrate that attaining the designated use is not feasible because: 1) naturally occurring pollutant concentrations prevent the attainment of the use; 2) natural, ephemeral, intermittent, or low-flow conditions or water levels prevent the attainment of the use, unless these conditions may be compensated for by the discharge of sufficient volume ------- of effluent discharges without violating state water conservation requirements to enable uses to be met; 3) human-caused conditions or sources of pollution prevent the attainment of the use and cannot be remedied or would cause more environmental damage to correct than to leave in place; 4) dams, diversions, or other types of hydrologic modifications preclude the attainment of the use, and it is not feasible to restore the water body to its original condition or to operate such modification in a way that would result in the attainment of the use; 5) physical conditions related to the natural features of the water body, such as the lack of a proper substrate, cover, flow, depth, pools, riffles, and the like, unrelated to chemical water quality, preclude attainment of aquatic life protection uses; or 6) controls more stringent than those required by sections 30 lb 1A and B and 306 of the Act would result in substantial and widespread economic and social impact. What questions should be asked in performing a UAA?? Reference: A Suggested Framework for Conducting UAAs and Interpreting Results: Use Attainability Analysis. Water Environment Research Foundation, Final Report, 1997. 1. Which uses are existing uses (attained on or after November 28, 1975) and which are goal uses (designated but not yet attained)? 2. Which goal uses can be attained (attainable uses)? 3. Do water quality criteria protect designated uses? 4. How do habitat, flow, or physical factors affect attainment? 5. To what extent does water quality preclude the attainment of designated uses? 6. What levels of water quality are necessary to protect designated uses? 7. Is the level of water quality necessary to protect designated uses present in effluents from point source discharges? 8. What level of treatment is required to achieve the water quality necessary to support designated uses? 9. What are the social and economic impacts of the treatment levels required to achieve the water quality necessary to support designated uses? As a practical matter, federal regulations require that a UAA be conducted to justify a change to ------- less stringent standards. Designated uses and water quality criteria are not the same, and technically the UAA requirement is directly linked only to use changes. In practice, agencies responsible for water quality management often rely on redundant conservative assumptions. They assume that acceptable water quality can only result from restrictive standards and that any increase in concentrations of water quality constituents must impair designated uses. Because such assumptions ignore safety factors built into water quality criteria, the requirement for UAA is triggered by any change toward less restrictive standards involving either uses or criteria. Unless a proposed change would result in more restrictive standards, proponents of change are required to demonstrate continued protection of all designated uses. The practical effect is that whenever less restrictive standards could result from a proposed change, a UAA is required to justify the change. ------- |