Clean Water Act, Water Quality Criteria/Standards,TMDLs, and Weight‐of‐Evidence Approach for Regulating Water Quality

Abstract

AbstractThe Clean Water Act (PL 92–500, the 1972 amendments to the Federal Water Pollution Control Act) established a water quality standards‐based approach for regulating water quality. The U.S. EPA was to develop national water quality criteria that would serve as the basis for state water quality standards. Those standards are the legally enforceable limits that evaluate water quality impairment. It was specified in the Clean Water Act that violation of the water quality standards was to lead to the listing of the waterbody as “impaired” and trigger the establishment of a total maximum daily load (TMDL) of the pollutant in violation. Significant problems have developed in the implementation of the Clean Water Act. The most important of these problems is use of the numeric U.S. EPA national criteria and state water quality standards without waterbody‐specific adjustment for characteristics that influence the toxicity/availability of potential pollutants. This problem has led to inappropriate listing of waterbodies as “impaired” and the establishment of TMDLs with inappropriate water‐quality‐standard goals. It is becoming recognized that a “best professional judgment” (BPJ) triad weight‐of‐evidence approach should regulate water quality in the United States. The key component of this approach is the “best professional judgment” evaluation of a triad of key parameters: aquatic life toxicity/bioaccumulation of the contaminant(s); aquatic organism assemblage information in the aquatic system of concern; and chemical kinetic/thermodynamic information pertaining to the contaminant(s) of interest and the aquatic system of concern. This evaluation by consensus of a panel of experts in a public, interactive, peer‐review process is crucial for the technically valid, cost‐effective control of pollutants in aquatic systems.