Write TMDLs with the Right Water Quality Standards

Abstract

More than 20,000 water bodies nationally do not meet state water quality standards. The Clean Water Act requires states to list these impaired water bodies and develop a Total Maximum Daily Load (TMDL) for each. Historically, states were directed to list impaired water bodies promptly due to imminent court actions. Across the U.S. emphasis has focussed on the cost, feasibility, efficiency, and necessity of developing TMDLs based on the scope of the policy. A TMDL is a policy instrument for states to meet their own water quality standards. Most often state water quality standards are not site- or state-specific and may not even be intended for the designated use of the impaired water body. A more sensible approach would be to undertake an integrated assessment of the physical, biological, and economic impacts of the designated use of the water body to ascertain the appropriate designated use and associated water quality standards. Then, if ambient water quality standards are not met, a TMDL can be established. This approach will ensure that state resources are targeted towards water bodies where the TMDL approach is most effective and most appropriate. For example, most surface waters are designated for recreational use under the primary contact standard (fishable and swimmable). In many instances a state may demonstrate to EPA after performing a Use Attainability Analysis (UAA) that the intended use is not appropriate, thus satisfying the Clean Water Act because a lesser use (fishable only) is the best use that is attainable. Findings of a UAA may merit a use downgrade due to declining economic or social conditions associated with improving water quality. A second outcome of a UAA may warrant antidegradation, which is lowering the water quality standard to accommodate economic or social development in the area. Guidelines for conducting UAA have already been developed by EPA and the Water Environment Research Foundation. This study outlines the steps and procedures necessary for states to target and use UAA in conjunction with TMDL development and implementation. The objective of this analysis is to critically assess how UAAs can be used by states to establish, review, or modify designated uses and water quality standards. Previously conducted UAAs will be reviewed to estimate the effectiveness of developing site-specific designated uses and water quality standards. A national overview of the potential impacts of UAA on TMDL development and implementation will be presented. This analysis suggests that states should consider conducting UAAs to comprehensively assess pollution-impaired water bodies and to aid in cost-effectively applying the TMDL approach to meet water quality standards.