Water quality‐based criteria for toxics: Scientific, regulatory, and political considerations: Site‐specific water quality criteria from in‐stream monitoring data

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Abstract
The determination of site‐specific water quality criteria generally involves the recalculation of national criteria using laboratory‐derived toxicity data or the conducting of bioassays using site water. Because of uncertainty of predictions of in‐stream biological responses to contamination, an alternative procedure using stream benthic surveys and water quality data was applied at the Appalachian Power Company Clinch River Plant on the Clinch River in southwestern Virginia. Benthic surveys of riffle transects at four stations located upstream and downstream of the plant showed no significant differences among sites, except just below the effluent discharge site. During low‐flow periods there were significant decreases at this site in the percentage of mayflies in the organisms collected.Effluent and ambient chemical data were examined statistically with respect to the biological data. Increased copper concentrations were significantly associated with decreases, from reference levels, in percent mayflies at the impacted area. A linear equation was derived relating decreased percent mayflies to increased copper concentrations. A no effect level based on the least detectable difference in percent mayflies produced a total recoverable copper criterion of 34.2 μg/L. Criteria or impact estimates derived from in‐stream data possess many advantages; they are a valuable tool for reducing uncertainty through integrated field‐laboratory assessments.