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TRI-STATE GENERATION AND TRANSMISSION ASSOCIATION, INC. HEADQUARTERS: P.O. BOX 33695 DENVER, COLORADO 80233-0695 303-452-6111 January 27, 2016 Mr. Zach Trujillo Environmental Protection Specialist Colorado Division of Reclamation, Mining & Safety Department of Natural Resources 1313 Sherman Street, Room 215 Denver, CO 80203 RE: Colowyo Coal Company L.P. Permit No. C-1981-019, Permit Revision No. 04 (PR -04) Third Preliminary Adequacy Response, Adequacy Item 70 Dear Mr. Trujillo: RECEIVED JAN 2 9 Z016 DIV1S!0N 0`7 ?ECLAMATIC" M Nit,G;.ND SAFETY Tri-State Generation and Transmission Association, Inc. (Tri-State), is the parent company to Axial Basin Coal Company, which is the general partner to Colowyo Coal Company L.P. (Colowyo). Tri-State received your adequacy letter dated October 14, 2015, and Tri-State on behalf of Colowyo has the below response to Item 70. Adequacy responses to all other outstanding items were submitted to the Division previously. ITEM 70. Of the six drill holes that were sampled for overburden/interburden analysis, only one falls within the 1.4 square mile (approximate) footprint of the newly proposed Collom pit (C-04-25). The guidelines call for a minimum of three sampling locations with a spacing of approximately one hole per square mile (from reference I below). In the geochemical analysis, CCC has also cited a guideline published by the Wyoming Department of Environmental Quality (from reference 2 below), which calls for an initial sample spacing of one hole per 80 acres (which is equivalent to eight holes per square mile). The geochemical data from the six holes is presented in Exhibit 6, Item 9, and summarized in table 2.04.6-7 and in the text. The data shows that hole C-04-25 contains a greater proportion of unsuitable overburden material than the other five holes. For example: • A significant proportion of the overburden sampled at this point (27%) contains Molybdenum at greater than 1 ppm. • The deeper horizons are notably high in Arsenic, with a maximum value of 39.8 ppm (compared to the WY DEQ criteria of <2.0 ppm). • The deeper horizons also have elevated levels of Sodium, as indicated by the high SAR values. In summary, the data provided are not sufficient to adequately characterize the material that will be disturbed by the proposed Collom pit. The analysis, as currently presented, underestimates the proportion of material thatfails to meet the suitability criteria. AN EQUAL OPPORTUNITY/ AFFIRMATIVE ACTION EMPLOYER CRAIG STATION ESCALANTE STATION NULLA STATION P.O. BOX 1307 P.O. BOX 577 P.O. BOX 698 CRAIG, CO 81676-1307 PREMTT, NM 87045 NUCLA. CO 81424-0698 AToUChsCOrie Energy* Cooperative 970-824-4411 505-972-5200 970-864-7316