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DocuSign Envelope ID:6BC32598-B737-464E-898A-81 F1 F7BB39B3 <br /> OF <br /> TRI-STATE <br /> November 12, 2021 <br /> Submitted electronically only to Brown.Christopher.T(a,,epa.gov <br /> Chris Brown, P.G. <br /> Physical Scientist <br /> U.S. EPA Region 8,UIC Section <br /> 8WD-SDU <br /> 1595 Wynkoop Street <br /> Denver, Colorado 80202 <br /> RE: Colowyo Coal Mine—East Taylor Seep <br /> UIC Class V Permit Application <br /> Dear Mr. Brown, <br /> On behalf of Colowyo Coal Company LP, Tri-State Generation and Transmission Association, <br /> Inc. (Tri-State) is applying for a Class V underground injection control (UIC)well to dispose of East <br /> Taylor Seep water on the Colowyo Coal Company, L.P. —Colowyo Coal Mine. Tri-State is the facility's <br /> parent company. Colowyo Coal Mine currently discharges this seep water originating from reclaimed <br /> areas under the Colorado Discharge Permit System (CDPS) individual wastewater and stormwater <br /> permit CDPS #CO-0045161. The East Taylor Seep water has been studied under the CDPS permit after <br /> whole effluent toxicity (WET) impacts from total dissolved solids (TDS)were identified. The treatment <br /> system chosen for this seep water is a Class V UIC well. <br /> Tri-State identified the sand zones of the Mancos Shale as the proposed receiving aquifer for this <br /> UIC well application. The project area is located in southern Moffat County in northwestern Colorado, <br /> between Meeker and Craig, CO. The facility is rural, and agriculture and mining are the primary <br /> industries in the area. Consequently,there are little data available for potential receiving aquifers, and <br /> water quality must be interpreted from wells located along the extents of the basin. These data suggest <br /> marginal water quality in the Mancos Shale sand zones, but the actual water quality can only be <br /> estimated from these wells. Tri-State proposes to permit and drill the Class V injection well, and then <br /> procure detailed water quality analyses from the receiving aquifer to confirm compliance with Class V <br /> rules and regulations. Tri-State has also discussed with you the potential for permitting a deeper Class V <br /> or Class I injection well depending on the outcome of water quality analyses. <br /> The enclosed application contains the required exhibits and data for a Class V UIC application. <br /> In addition, the application has been designed to meet well construction specifications for either Class V <br /> or Class I injection wells. Please identify if any well specifications are not sufficient for Class I <br /> requirements. <br /> P.O.BOX 33695 <br /> DENVER,CO 80233-0695 A Touchstone Energy <br /> 303-452-6111 Cooperative <br /> WWW.TRISTATE.COOP <br />