Biological Approach to Use Attainability
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The 1987 Clean Water Act amendments placed greater emphasis on toxicity-based approaches to improving surface water quality. To guide states having NPDES authority, a number of criteria documents have been prepared by the USEPA for specific metals that describe numerical limits for metals in effluents. The primary objective of these numerical limits is the protection of 95 percent of the aquatic species present in a receiving stream. Georgia has the responsibility for issuing National Pollutant Discharge Elimination System (NPDES) permits for release of treated effluents into surface waters of the state. Lacking any other guidance, the state has used these national criteria to set new discharge limits on metals for NPDES permits up for renewal in Gwinnett County. The objective of these limits presupposes that the more restrictive newer toxicity based limits are necessary to protect the designated uses of the stream. The determination of whether the new limits are required to protect the designated uses of specific water bodies is discussed in 40 CPR 131.10(g). Under this section of the regulations, where it can be demonstrated that other conditions not related to the applicant preclude the attainment of the designated uses, procedures are provided for a variance from specific standards. The objective of this study was to determine if the state designated uses of the upper segment of the Yellow River in Gwinnett County would be affected by proposed changes in discharge permits for selected Waste Water Treatment Plants (WWTPs). This paper describes a biological approach for evaluating the factors affecting the designated uses for the upper segment of the Yellow River.