NARRATIVE CRITERIA IN THE TMDL PROCESS

Narrative water quality criteria are an integral component of States' water quality standards but they pose special problems when incorporated into the TMDL process. The TMDL process is typically a quantitative activity, defining numeric allowable loads necessary to meet a numeric water quality objective. Narrative criteria confound development of quantitative TMDLs, due to the absence of these numeric criteria. The Water Environment Research Foundation (WERF) sponsored research to improve the methods for addressing narrative water quality criteria in the TMDL process. The problems associated with narrative criteria in the TMDL process are known in general terms but, prior to this research, there has not been a thorough review of the use of narrative criteria in TMDLs nor broad guidance on how to address narrative criteria in the TMDL process. The approach taken for this research was to define the range of problems associated with all types of narrative criteria by means of a comprehensive review of over 120 existing TMDLs, and provide guiding principles to help address these problems. Adherence to these guiding principles is expected to significantly improve the evaluation of water bodies for impairment of a designated use based on non-attainment of narrative water quality criteria, resulting in more accurate 303(d) lists with a greater focus on those water bodies truly impaired. Also, adherence to these guiding principles will contribute to improvements in the TMDL development process, resulting in a greater degree of success in attaining designated uses when a TMDL is implemented.