EVALUATION OF THE RESIDENT-SPECIES PROCEDURE FOR DEVELOPING SITE-SPECIFIC WATER-QUALITY CRITERIA FOR COPPER IN BLAINE CREEK, KENTUCKY

Acute toxicity tests were performed on each of nine different organism s in Blaine Creek (Lawrence County, KY) water to determine 48-h LC50 v alues for copper (Cu). Blaine Creek is the receiving stream for Kentuc ky Power Company's Big Sandy Plant fly-ash pond discharge. Selection o f the nine tested species and integration of the results were based on the U.S. Environmental Protection Agency's (EPA's) resident-species p rocedure. The following LC50 (mug Cu/L) values were obtained (hardness 100-120 mu/L as CaCO3): Daphnia pulex 37; Physella sp. 109; Isonychia bicolor 223; Pimephales promelas 284; Stenonema sp. 453; Eurycea bisl ineata 1,120; Chironomus riparius 1,170; Orconectes sp. 2,370; Lepomis macrochirus 4,300. A final acute value (FAV) of 10.1 mug Cu/L (hardne ss 50 mg/L as CaCO3) was derived using the Blaine Creek database, whic h is lower than the EPA's national FAV (18.5 mug/L). The differences i n FAVs were due to the effect of database size, not differences. in th e relative sensitivity of test organisms. Our findings provide caution for dischargers who may choose to use the resident-species procedure for future site-specific water-quality-criteria demonstrations. The re sident-species procedure, because of the inherent conservative bias of the calculation process, tends to produce more stringent criteria whe n used on a site-specific basis. A modified recalculation procedure, i n conjunction with site-specific metal bioavailability data, was judge d to be the most appropriate method for deriving site-specific Cu crit eria for Blaine Creek.