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DocuSign Envelope ID:6BC32598-B737-464E-898A-81 F1 F7131339133 <br /> Attachment A. Maps and Area of Review <br /> Attachment Al. Well Location Description <br /> The proposed well is on property owned and operated by Colowyo Coal Company, L.P. (Colowyo) <br /> at the Colowyo Coal Mine in the Axial Basin in Rio Blanco and Moffatt Counties approximately 30 <br /> miles south of Craig, Colorado.Tri-State Generation and Transmission Association, Inc. (Tri-State) <br /> is the parent company through its subsidiary Elk Ridge Mining and Reclamation, LLC. <br /> Seepage from reclaimed areas which were previously mined out and backfilled in the East Taylor <br /> Creek drainage have shown impacts in whole effluent toxicity (WET) testing under the Colorado <br /> Discharge Permit System (CDPS) permit (CDPS #CO-0045161) for surface water discharge from <br /> Outfall 010. Seepage flow rates vary seasonally ranging from less than 100 gallons per minute <br /> (gpm) in fall and winter to approximately 300 gpm during the spring run-off period. Colowyo <br /> intends to dispose of this seepage via underground injection into a deep disposal well. The <br /> proposed UIC Class V disposal well (Colowyo Mine East Taylor Seep INJ#1) will be located in the <br /> SE % of the NW% of Section 4, Township 3N, Range 93W. The well location is shown in Exhibits <br /> Al-1 and A1-2. <br /> The Colowyo Coal Mine operation is located in the northern extent of the Danforth Hills coal field <br /> of the Uinta Region.The Danforth Hills field comprises the coal deposits on the northeast flank of <br /> the Piceance Creek Basin. The northeast flank is a northwest to southeast trending sub-basin of <br /> the Piceance Basin and is defined to the northeast by the Axial Basin Anticline and to the <br /> southwest by the Danforth Hills Anticline. The center of the sub-basin is defined by the Collom <br /> Syncline. <br /> The area of review (AOR) including the well location is shown on the attached maps and consists <br /> of the area within one-half mile of the well bottom-hole location. <br /> Table A-1. Proposed Well Location <br /> Well Name Sec.TWN RNG Surface Hole Location <br /> N/S E/W Lat Long <br /> Colowyo Mine East Taylor Seep INJ#1 Sec.4 T3N R93W 1,900'FNL 1,400'FWL 40°15'40.65"N 107°50'4.22"W <br /> Attachment A2.Area of Review Size Determination <br /> Several methods were evaluated to determine the AOR boundary. Limited site-specific data is <br /> available for the Colowyo UIC location. The maximum anticipated average injection rate and <br /> formation properties based on nearby wells, where available, and best professional judgement <br /> for parameters (when no nearby well information was available)was used in the AOR analysis. <br /> Fixed radius method <br /> The fixed radius method was used to determine the minimum one-quarter mile radius AOR <br /> boundary as mandated by the USEPA. Since the Colowyo UIC facility will consist of only one <br /> injection well,the fixed radius AOR boundary would be a one-quarter-mile radius circle centered <br /> on the proposed UIC well location as shown on Exhibits Al-1 and A1-2. <br /> 1 <br />