2021-12-08_GENERAL DOCUMENTS - C1981019

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DocuSign Envelope ID:6BC32598-B737-464E-898A-81 F1 F7131339133 characteristic exposures.The deposition of the Trout Creek Sandstone marked a major regression of the Late Cretaceous seaway over a large region. The resulting clean, well sorted blanket sand formed by this migrating beach and barrier island complex is an aquifer of regional extent in Northwest Colorado. Under the area to be mined within the Colowyo Permit area, the Trout Creek sandstone underlies the lowest surface recoverable seam to be mined by 800 feet. The Iles Formation in the area is estimated to be 1,375 feet thick.The Iles Formation forms most of the cliffs that surround the Axial Basin. The Iles Formation lies approximately 1,700 feet beneath the actual mining area; however, minor folds or faults in the regional trend bring the formation nearer the surface toward the limits. The remaining Mesozoic and Paleozoic sedimentary rocks underlying the Iles Formation have typically been targets for oil and gas exploration and production and have not been used as sources of groundwater in the area. However, several sandstones beneath the Iles formation are potential USDWs. These include the sandstone members of the upper Mancos Shale—the Lloyd Sandstone Member, the Duffy Mountain Member, the Morapos Sandstone Member, and the Meeker Sandstone Member which are the target formations for proposed Colowyo Mine East Taylor Seep INJ#1 UIC well. Other sandstones in the lower Mancos Shale, the lower Cretaceous Dakota Sandstone, the Jurassic Entrada Sandstone, the Triassic Shinarump Formation, and the Pennsylvanian Weber Sandstone have been granted EPA aquifer exemptions in Moffat and Rio Blanco counties and thus, may be USDWs in the sub-basin. Details of these formations and associated confining intervals are described below (from CGS, 2014 and Rowley and Hansen, 1979). Mancos Shale — The Mancos Shale consists of dark gray marine shales and contains mappable sandstones. The upper 1,900 ft of Mancos Shale above the Frontier Sandstone Member consists of light gray calcareous shale and dark gray shaly limestone. Total thickness of the Mancos Shale is approximately 5,100 ft. Lloyd Sandstone Member—The Lloyd Sandstone Member of the Mancos Shale is a massive well sorted, pale olive to yellowish gray, very fine-grained sandstone approximately 45 ft in thickness. The top of the Lloyd Sandstone Member lies about 70 ft below the top of the Mancos Shale. Duffy Mountain Member —The Duffy Mountain Member of the Mancos Shale is a fine-grained sandstone, moderately to well sorted, yellowish gray sandstone approximately 35 ft in thickness. The top of the Lloyd Sandstone Member lies about 245 ft below the top of the Mancos Shale. Moropos Sandstone Member—The Moropos Sandstone Member of the Mancos Shale is a thin bedded, moderately sorted, light gray and tan, fine-grained, slightly calcareous sandstone, shaly near base, approximately 50 ft in thickness. The top of the Moropos Sandstone Member lies about 750 ft below the top of the Mancos Shale. Meeker Sandstone Member — The Meeker Sandstone Member of the Mancos Shale is a thin- bedded, moderately sorted, pale to medium yellowish brown, fine-grained, shaly, calcareous sandstone up to 190 ft in thickness. The top of the Meeker Sandstone Member lies about 1,900 ft below the top of the Mancos Shale. 6