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TRI-STATE GENERATION AND TRANSMISSION ISSIO ASSOCIATION, INC, <br /> HEADQUARTERS: P.O. BOX 33695 DENVER, COLORADO 80233-0695 303-452-6111 <br /> July 12, 2018 <br /> Submitted via email eric.mink a),,,vtate.co.us <br /> Mr. Eric Mink <br /> Water Quality Control Division <br /> Colorado Department of Public Health and Environment <br /> 4300 Cherry Creek Drive South <br /> Denver, Colorado 80246-1530 <br /> RE: CDPS Permit#CO-0045161 <br /> Colowyo Mine, Outfall 010 <br /> Notification of Chronic WET Results—2Q 2019 and Commencement of TIE <br /> Dear Mr. Mink: <br /> On June 28, 2019, the third party laboratory, The SeaCrest Group, provided the enclosed <br /> analytical report containing the second quarter 2019 Whole Effluent Toxicity(WET) test results <br /> for Outfall 010 at the Colowyo Coal Company, LP (Colowyo) Colowyo Mine (CDP S Permit <br /> #CO-0045161). Tri-State Generation and Transmission Association (Tri-State) is the parent of <br /> Colowyo. Therefore, we are providing the required notification of WET results, in accordance <br /> with Part I.D.Lb. of the permit. <br /> Outfall Species Reproduction/Growth Results IWC <br /> NOEC* IC25** <br /> 010 Ceriodaphnia dubia 20% 47.5% 100% <br /> 010 Pime.hales (fathead minnow) 100% >100% 100% <br /> *NOEL means"no observed effect concentration"at which concentration there are no observable adverse effects on <br /> the organisms. <br /> **IC25 means inhibition concentration causing a 25%reduction in the biological measurement. <br /> In accordance with the permit, the facility is commencing a targeted Toxicity <br /> Identification Evaluation (TIE) with The SeaCrest Group,based on the Q4 2018 and Q1 2019 <br /> TIE, for the most sensitive species (Ceriodaphnia dubia) for this outfall location. We will also be <br /> submitting the initial WET test summary and chains of custody with the June 2019 Discharge <br /> Monitoring Report (DMR)by July 28, 2019. <br /> AN EOUA.OPPORTUNfTY1AFFIRM 477VEACTION EMPLOYES CRAIG STATION ESCALANTE STATION NUCLA STATION <br /> P.O.BOX 1307 P.O.BOX 577 P.O.BOX 698 <br /> A Touchstone EnereCcx)perative stt� ,#, CRAIG,CO 81626-1307 PREWITT,NM 87045 NUCLA,CO 81424-0698 <br /> .00* 970-824-4411 505-876-2271 970-864-7316 <br />