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~. <br />,_ <br />STATE OF COLORADO <br />Rov Romer, Governor <br />Patti Shwayder. Acting Executive Director [[~~ <br />Dedicated to pro[ecung and improving the health and em•ironment of the people of CocJt~ Ell /r~ n <br />4300 Cherry Creek Dr. S. Laboratory BuJdmg 1 C1J <br />Denver, Colorado b0?2?-7530 4?70 C 11th Avenue Md~ ~ C <br />Phone (303) 69?-?000 Denver, Colorado BO??0-371G /1 J 1995 <br />(303) 69t -4700 <br />April ] 0, 1995 <br />Division of Minerals & Geology <br />OF COQ. <br />~~,~, <br />Me ;. ~ <br />~.~. , <br />t816 ~ <br />Colorado Deparvnent <br />of Public Health <br />and FJttvtrotvnent <br />Mr. Walter L. Wright, Mine Manager <br />Somerset Mining Company <br />P.O. Box 535 <br />Somerset, CO S 1434 <br />°EC=(V~~J APR 1 7 ;005 <br />Re: Aquatic Impairment Studv Report Dated February 1, 1995 <br />CDPS Permit No. CO-0000132 <br />Gunnison County, Colorado <br />Dear Mr. Wright: <br />The Division has reviewed the subject Aquatic Impairment Study Report. As you are aware, the <br />study was to assess the impacts of the efrluent on the receiving stream's aquatic life; since Somerset <br />experienced persistent Whole Effluent Toxicity test failures at Outfall Ol 1 for ceriodaphnia dubia <br />and identified Total Dissolved Solids ("TDS"), especially bicarbonates, as the toxicant. The report is <br />complete and generally fulfills the requirements set forth by the Division for such a study. <br />The Division agrees the study shows that the Sanborn Creek Mine effluent has a minima] effect on <br />stream macroinvertebrates. Therefore, we have developed several options from which you can <br />choose to proceed: <br />1) Propose a method to modify the acute WET test to remove onlt, the TDS from the effluent <br />prior to testing, perhaps b}' aeration; <br />2) Conduct a Toxicity Identification Evaluation ("TIE") every quarter that the effluent fails the <br />WET test for ceriodaphrua dubia to confirm TDS as the toxicant; <br />3) Request the Division amend the permit to change the macroinvertebrate test species from <br />ceriodaphnia dubia to daphnia magna, using the EPA method for testing this species, and <br />possibl}~ verifying the toxicant as TDS on the occasions the effluent fails with daphnia <br />magna; <br />4) Treat Outfall O1 ]'s effluent to remove the TDS (e.g. ion exchange, reverse osmosis) to a level <br />non-toxic to the ceriodcrphnra dubia; <br />5) Combine two or more of the above options; or <br />