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DocuSign Envelope ID:6FE5F752-9229-4969-B8B6-9154B88CD3C4 <br /> TRI-STATE GENERATION AND TRANSMISSION ASSOCIATION, INC.D <br /> HEADQUARTERS: P.Q. BOX 33695 ❑ENVER, COLORADO 80233-0695 303-452-6111 <br /> November 11, 2020 <br /> Submitted via email iacob.dysteii►ytate.co.us and cdphe.wgrecordscentel(a state.co.us <br /> Mr. Jacob Dyste <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—4Q 2020 <br /> Dear Mr. Dyste: <br /> The third party laboratory, The SeaCrest Group, recently provided the enclosed analytical <br /> report containing the fourth quarter 2020 Whole Effluent Toxicity(WET)test results for Outfall <br /> 010 at the Colowyo Coal Company, LP (Colowyo) Colowyo Mine (CDPS Permit#CO- <br /> 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 LD.I.b. of the permit. <br /> Outfall Species Reproduction/Growth Results IWC <br /> NOEL* IC25** <br /> 010 Ceriodaphnia dubia 20% 22% 100% <br /> 010 Pimephales promelas (fathead 100% 99.9% 100% <br /> minnow) <br /> *NOEC 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 /> The facility's Colorado Discharge Permit System (CDPS)permit was recently amended <br /> on May 29, 2020 to remove the automatic compliance responses (Toxicity Identification <br /> Evaluation and Toxicity Reduction Evaluation). Therefore,we will be continuing the progress on <br /> addressing site conditions by the 2023 deadline. <br /> AN FOUAL OPPORTUNITYIAFFIRMATIVE ACTION EMPLOYER CRAIG STATION ESCALANTE STATION NUCLA STATION <br /> P.O.BOX 1307 P.O.BOX 577 P.O.BOX 696 <br /> A Touchstone Energy'Cooperative K�"A CRA IG,CO 81626.1307 PREWITT,NM 67045 NU CLA,CO 91424.0698 <br /> 970.824.4411 505.876.2271 970-864.7316 <br />