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Recently, the TMDL program has become one of the most discussed and debated environmental programs in the nation, primarily because of EPAs drafting of final rules for the program. These rules follow several years of intense activity, including the formation of a Federal Advisory Committee devoted to this topic. In October 2000, Congress suspended EPAs implementation of these rules until further information could be gathered on several aspects of the program. In particular, Congress requested that the National Research Council (NRC) form a committee to examine the scientific basis of the TMDL program. This committee found that substantial improvements could be made in a number of areas to strengthen the scientific basis of the TMDL program. The committee also identified several policy issues that are restricting the use of the best science in the TMDL program.

Using the information gathered during the study and the NRC committees collective experience, it was felt that the data and science have progressed sufficiently over the past 35 years to support the nations return to ambient-based water quality management. In addition, the need for this approach is made apparent by the inability of a large percentage of the nations water to meet water quality standards using point source controls alone. Given reasonable expectations for data availability and inevitable limits on our conceptual understanding of complex systems, statements about the science behind water quality management must be made with acknowledgment of uncertainties. The committee also concluded that there are creative ways to accommodate this uncertainty while moving forward in addressing the nations water quality challenges. These broad conclusions will be elaborated upon throughout this presentation.