The use of bioassays and toxicity identification evaluation (TIE) procedures to assess recovery and effectiveness of remedial activities in a mine drainage-impacted stream system

Effluents from Walker Mine and its tailings pile have resulted in toxic con centrations of metals in Dolly and Little Grizzly Creeks. Recent remedial s tructures have greatly reduced metal loading, however the need to assess re covery of the receiving aquatic ecosystem exists so that future remediation priorities can be established. The objective was to contribute to this ass essment using Toxicity Identification Evaluation procedures. Water samples were collected at several sites in Dolly and Little Grizzly Creeks. Untreat ed samples and samples passed through ion exchange columns, which remove ca tionic metals, were compared in side-by-side bioassays using Pimephales pro melas, Ceriodaphnia nubia, and Selenastrum capricornutum. Samples were anal yzed for total and dissolved copper, cadmium, zinc, and iron. Copper was th e element responsible for toxicity. Toxicity was detected in the mine disch arge and immediately downstream from the tailings where dissolved copper co ncentrations were 250 mu g/L and 415 mu g/L, respectively. Toxicity decreas ed at downstream sites but extended at least 6.4 km downstream. Improvement in bioassay performance by the treated waters verified metal toxicity. The results indicate that the mine effluent and tailings pile currently have t he heaviest impact on Dolly and Little Grizzly Creeks and should be given t he highest priority in future remedial programs.