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DocuSign Envelope ID:6BC32598-B737-464E-898A-81 F1 F7131339133 <br /> Attachment B. Geological and Geophysical Information <br /> Geology Description <br /> General location <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 /> Stratigraphy <br /> The area is underlain by as much as 13,500 feet of sedimentary rock consisting of approximately <br /> 4,500 feet of Paleozoic quartzite, limestone, shale, sandstone, and gypsum and 9,000 feet of <br /> Mesozoic limestone, shale, mudstone, sandstone, and conglomerate. The coal seams mined at <br /> the Colowyo operation are in the upper Cretaceous Age Mesaverde Group. The proposed <br /> Colowyo East Taylor Seep INJ#1 injection intervals are sandstone members of the Cretaceous <br /> Mancos Shale which underlies the Mesaverde Group. A generalized stratigraphic column of the <br /> Piceance Basin is shown in Exhibit B-1. <br /> The two main geologic formations which serve as groundwater sources in the sub-basin for <br /> drinking water, irrigation, and industrial use within the area are the upper Cretaceous Iles and <br /> Williams Fork Formations of the Mesa Verde Group. Details of each formation are set forth below. <br /> Williams Fork Formation -The Williams Fork Formation consists of alternating beds of sandstone, <br /> sandy shale and coal. It is distinguished from the Iles Formation by its thick zones of brick red <br /> sandstone and shale, which have been colored from adjacent naturally-burning coal beds, a <br /> common occurrence in the Axial area.The coal beds in the formation are uniformly distributed in <br /> the vicinity of the mine but generally vary greatly within the regional extent of the unit. The <br /> stratigraphic thickness of the Williams Fork Formation in the area has been estimated to be about <br /> 1,600 feet; its degree of areal extent in the Axial Basin is similar to that of the Iles Formation. <br /> The Williams Fork Formation is the predominant coal-bearing formation in the Mesa Verde Group. <br /> Mesa Verde coals associated with the Fairfield Group, the coal-bearing zone above the Trout <br /> Creek Sandstone, rank in quality about midway between bituminous and sub-bituminous. <br /> Although the Twenty Mile Sandstone Member is a regional aquifer noted within the Williams Fork <br /> Formation in the Craig, Hayden and Steamboat Springs area, a facies change within the Williams <br /> Fork Formation has eliminated the Twenty Mile Sandstone in the Danforth Hills Area. <br /> Iles Formation - In general,the Iles Formation consists of light brown-to white, fine-to medium- <br /> grained, poorly-sorted calcareous sandstone interbedded with red and dark maroon sandy and <br /> silty carbonaceous shale. Thin lenticular coal beds are found in this formation. The uppermost <br /> sandstone of the Iles Formation, the Trout Creek Sandstone Member, appears to be reliable <br /> marker horizon at the base of the principal coal beds within the Williams Fork Formation. The <br /> 75-foot thick Trout Creek member is a white,fine-grained,well-sorted, massive sandstone that is <br /> fairly uniform in thickness over a large area. The Trout Creek Sandstone Member, a common <br /> ridge-forming unit in the Danforth Hills, has been called the "White Rock" because of its <br /> 5 <br />