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  <br />   <br />   <br />  <br />  <br /> <br />  <br /> 715 Horizon Drive, Suite 340 1536 Cole Blvd., Suite 310, Bldg. 4   <br /> Grand Junction, CO 81506 USA Lakewood, CO 80401  <br /> +1 970.242.4220 +1 303.271.3750  <br />www.agapito.com  <br />September 22, 2022 227-27 <br /> <br /> <br />Mr. Lee Sampson, P.E. <br />Senior Mining Engineer <br />Colowyo Coal Company <br />5731 State Hwy 13 <br />Meeker, CO 81641-9119 <br /> <br />Re: The Adequacy of the Natural Sorted Spoil Material for the Purpose of a Rock Drain <br />in Little Collom Draw <br /> <br />Dear Mr. Sampson: <br /> <br />This letter report provides an assessment of the adequacy of the natural sorted spoil material for <br />the purpose of a rock drain and a natural filter for the underdrain in Little Collom Draw. The <br />location of the assessment area is showing in Figure 1. This assessment draws on the results of <br />previous analyses conducted at the mine, photographs of the active spoil end dumping in Little <br />Collom Draw, and site observations made during a September 13, 2022, site visit by Ry Stone of <br />Agapito Associates, Inc (Agapito). <br /> <br />Colowyo Mine has indicated that prior to dumping spoil in the Little Collom Draw, the <br />southernmost 820 feet (ft) of the draw had a 24-ft-wide rock drain constructed in 2021 (see <br />Figure 1). The constructed drain was filled with large sandstone rock sorted on-site from existing <br />spoil dumps. The sorted rock was placed in the drain with loaders and dozers. Following <br />construction of the rock drain, excess spoil was end dumped into the draw and over the drain. This <br />resulted in a dump height of approximately 130 ft above the valley floor at the north end of the <br />draw. <br /> <br />Immediately north of the constructed rock drain, natural sorting from end dumping of the spoil <br />material was utilized to create a rock drain for an additional 1,500 ft down the draw (see Figure 1). <br />The cumulative volume of spoil dumped in the draw to date is estimated to be in the order of <br />4,200,000 cubic yards. <br /> <br />Following re-evaluation of the planned life of the mine, Colowyo have indicated that no additional <br />spoil would be dumped in the draw and that the existing valley fill would be permitted as “Post <br />Mine Topography”. Agapito understands that this will result in a change in classification of the <br />valley fill from temporary to permanent. Section 4.09.02, Part 2 from the Department of Natural <br />Resources, Division of Reclamation, Mining and Safety (DRMS) Code of Colorado Regulations <br />stipulates that a subdrainage system for the valley fill shall be constructed for permanent <br />conditions. This assessment will therefore demonstrate that the natural sorting of the spoil material <br />from end dumping will be sufficient for facilitating a free-draining environment in the valley fill <br />in Little Collom Draw. <br />