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<br />- 25 - <br /> <br />Bioassay Studies <br /> <br />The effluent samples for bioassay testing from the Uravan and <br />Slick Rock areas were brought to the State fish hatchery at Durango, <br />Colorado. Facilities were available there for exposing rainbow trout to <br />various dilutions of the wastes under constant temperat~re conditions. <br />Vessels with 2 liters of test solution were placed in hatchery troughs con- <br />taining spring water at a temperature of 520F. Small trout ranging from 2 <br />to 2-1/2 inches in length were used as test fish. Water from the Animas <br />River above Durango was used for dilution. <br /> <br />The fish were exposed to the test solutions for 72 hours, and the <br />individuals surviving this exposure period were counted. A semilogarithmic <br />plot of number surviving versus concentration of waste was made; from this <br />the 72-hour Median Tolerance Limit concentration (TLm) was derived. The <br />72-hour TL is the concentration of effluent in water which causes 50 <br />m <br />percent mortality of the test fish upon exposure for 72 hours. For each test <br />series" control tests were run in which fish were placed in dilution water <br />only. <br /> <br />Chemical analyses made on the test solutions included pH, alkalinity, <br />hardness, and dissolved oxygen. Dissolved oxygen determinations were made <br />at the start of tests and whenever there was reason to believe that the <br />concentrations had lowered to endanger survival. Sufficient oxygen was main- <br />tained by limiting the number of fish in a vessel. <br /> <br />Tables XIV, XV, and XVI show the percentages of wastes in test solu- <br />tions, the survival of fish, and chemical characteristics of these unfiltered <br />waste samples. While the number of fish in anyone sample is not large, it <br />is felt that measurements made on anyone group tend to be representative of <br />the response of test fish in the particular concentration. This is particu- <br />larly true since most test groups showed either all survivals or all deaths. <br />It may therefore be considered that these data give a reasonable representa- <br />tion of the toxici~y to test fish of the various waste streams. <br /> <br />Wastes from Burro Mine were not toxic to fish. These wastes had <br />considerable turbidity due to suspended gray clay, and the pH was greater <br />than that of the receiving stream. Slick Rock plant seepage was toxic with <br />72-hour median tolerance limits ranging from l.5 to 2.4 percent. <br /> <br />The main waste stream at Uravan, uranium and vanadium stripped liquor <br />had TLm values ranging from 0.42 to 0.75 percent. Toxicity of the red cake <br />tails effluent was not as great, with a TLm range of 4.2 to 4.6 percent. <br />Yellow cake tails effluent had a TLm of 2.4 percent. Seepage from the acid <br />leach tailings ponds was toxic to half the fish tested in a lOO percent concen- <br />tration, but was not toxic to the fish tested in any lower concentration. <br />