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V. COLORADO <br />AMIIVDivision of Reclamation, <br />Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />December 8, 2020 <br />Tony Tennyson <br />Tri-State Generation and Transmission Association <br />1100 West 116th Avenue <br />Westminster, CO 80234 <br />Re: Colowyo Coal Company, Permit No. C-1981-019 <br />2018 and 2019 Annual Hydrology Reports (AHRs) — Second Review <br />Dear Mr. Tennyson: <br />The Colorado Division of Reclamation, Mining and Safety (the Division) received your response <br />regarding the 2018 and 2019 AHRs for the Colowyo Mine (letter dated November 24, 2020). No <br />further action is requested by the Division regarding the 2018 and 2019 AHRs. Below are the <br />Division's comments based on Colowyo's responses to the Division's initial review. <br />• Regarding monitoring sites EFGSC and LWFGSC, the Division acknowledges that the <br />2018 and 2019 AHRs are in compliance with the monitoring requirements in Section <br />4.05.13 of the Permit Application Package (PAP). <br />• It is noted that future AHRs, beginning with the 2020 AHR, will include additional <br />analyses of the data as the Division has requested in the past per Rule 4.05.13(4)(c)(iii). <br />The Division believes that this exercise will provide a more thorough review of the AHRs <br />with additional understanding of potential impacts on the hydrology at the Colowyo Mine <br />and on adjacent receiving waters. <br />• The Colowyo response letter states, "The Division infers that Colowyo is attempting to <br />circumvent applicable regulatory standards ..." related to Colowyo's legal use of its <br />water. In the Division's review of the subject AHRs, it is stated that "When considering <br />the impacts of the Colowyo Mine on uses of the receiving waters, Colowyo's own use of <br />the water was not considered relevant." This statement is not meant to infer as to the <br />motives of the Colowyo; rather, the statement describes an underlying basis for the <br />Division's methodology in reviewing AHRs. One of the factors that the Division <br />considers in the review of AHRs is the potential impact on the use of surface water (and <br />groundwater) by other entities. <br />• Regarding the use of the term "total dissolved metals," it is noted that Colowyo states that <br />the utilization of this term was a typographical error, and will be corrected in future <br />AHRs. <br />• Regarding concentrations of total recoverable iron in Jubb Creek, the provided discussion <br />OF COlO <br />�4�= <br />.n O <br />1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us * <br />* Jared S. Polis, Governor I Dan Gibbs, Executive Director I Virginia Brannon, Director * 1876 <br />