2021-09-03_PERMIT FILE - C1981019A (8)

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RULE 2 PERMITS The stratigraphic thickness of the Williams Fork Formation in the Colowyo revised permit area is about 1,700 feet. Although the formation contains some thick sandstone layers, the Twenty Mile Sandstone Member (within the Williams Fork Formation in the Craig, Hayden, and Steamboat Springs areas) is not present in the Collom permit expansion area. A facies change within the Williams Fork Formation has eliminated the Twenty Mile Sandstone in the Danforth Hills Area. Natural, pre -historic burning of the coal beds has baked (burned) scattered areas of the Williams Fork Formation within the Colowyo revised permit area and the adjacent area. These surface areas are easily distinguished by their red -brown to orange -brown color on the surface. These coal burns are known to extend into the rock for up to several hundred feet. A distinctive bed in the formation is a smectite layer, with an average thickness of two to three feet in the vicinity of the Colowyo permit area. Formed from the deposition of a volcanic ash, Colowyo has identified this bed as the `KM' (this bed may be equivalent to the Yampa Bed in the Williams Fork formation to the north). The lateral continuity of the smectitie layer (KM) is easily discerned by examining downhole geophysical logs of any borehole in the Colowyo drill hole data base that has drilled through this layer. Data on the petrographic and mineralogic analysis (Appendices 2.A and 2.13) and permeability testing (Apendix 5.I) of the KM layer is located in the WMC report (2005). This report is located in Volume 18A, Exhibit 7, Item 21. The KM layer has been identified as an aquiclude. It is approximately 165 feet above the top of the Trout Creek Sandstone, and underlies the lowest seam to be mined by at least 290 feet. Since the KM lies between the Gb and the Trout Creek Sandstone, there should be no impact from the mining operations to the underlying Trout Creek Sandstone. The upper Williams Fork Formation is composed of upper and middle deltaic sediments in the vicinity of the Colowyo Mine. This is evidenced by an increase in mudstone and less continuous sandstone layers than is found at other locations in the region (Kiteley, 1983; Geocid, 1998). Structure The regional geologic structure of the Danforth Hills is a complex of folds dominated by the Axial Basin Uplift to the north of the Colowyo revised permit area and the Piceance Basin on the south. The Axial Basin Uplift, an anticline, or arch, is a southeastward extension of the larger Uinta Mountain Arch to the west, which trends west by northwest. Between the Axial Basin anticline and the basin is a series of synclines, anticlines, and monoclines. The Collom permit expansion area is located between the Axial Basin anticline on the north and the Danforth Hills anticline to the south. Starting on the north end of the Collom permit expansion area, the Axial Basin anticline is an asymmetrical fold, the axis of which trends north 60 degrees (0) west, with strata dipping (inclining) steeper on the south side of the axis than on the north. The rocks of the broad anticline have not been stressed sufficiently to cause them to break severely, but a few discontinuous normal faults trending primarily parallel to the anticlinal axis are found in the area. The south flank of the anticline has several secondary folds trending subparallel and at approximate right angles to the main anticlinal axis. The southern limb of the Axial Basin anticline is shared with the Collom syncline. The Collom Pit will be located on the 3.5° to 8.5° northeastward dipping strata on the southern limb of the Collom syncline and northern limb of the Danforth Hills anticline. The northeast trending Morgan syncline is located on the western boundary of the Collom permit expansion area (Map 7A). Collom — Rule 2, Page 14 Revision Date: 4/2/18 Revision No.: RN -07