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~~ ~ ~~~~iiii~iiiiiiiiii • DATE: November 16, 982 999 T0: Sandy Emrich ~~ DRAFT FROM: David Craig RE: Foidel Creek Mine - Geology!Frirtdings GEOLOGY Description of the Environment Three recognizable geologic formations exist in the vicinity of the proposed Foidel Creek underground mine. They are, in ascending order, the Iles and Williams Fork Formations of the P1esa Verde Group, and the Lewis Shale Formation (see Figure 2 of the permit application). These strata were all deposited during the late Cretaceous Period. The proposed mining operation will mine the Wadge Coal Seam of the Williams Fork Formation (see Map 8 of the permit application for stratigraphic relationships). Generally, the strata dip to the northwest at about 5.7°. Overburden depths in the proposed permit area range from outcrop at the portal area to approximately 1,100 feet at the northwest corner (see Map 7 of the permit application). For a more detailed description of geology see Section 2.04.6 of the permit application and the following discussion. The Iles Formation underlies the Williams Fork Formation and outcrops southeast of the proposed mine workings. The strata generally consist of a massiver marine shale and a massive fine-grained sandstone. The massive sandstone unit, the Trout Creek Sandstone, is a marker bed in the area forming the top of the Iles Formation. Approximately 250 feet of interbedded sandstones, siltstones, shales, and coals separate the Trout Creek Sandstone from the proposed mine workings. The Williams Fork Formation is stratigraphically located between the Iles Formation and the Lewis Shale Formation. Consisting primarily of sandstone, siltstones, shales, and coals, the Williams Fork Formation contains most of the coal seams which are economically mineable in the Yampa Coal Field. A key marker bed in the Williams Fork Formation is the massive Twentymile Sandstone. The proposed mine workings are separated from the Twentymile Sandstone by a 700 foot thick massive shale member. The strata in the Williams Fork Formation are generally laterally discontinuous. Generally, the only laterally persistent strata in the formation are the Twentymile Sandstone, the underlying massive shale member, and the coal seams. The Wadge Coal Seam, of the Williams Fork Formation, ranges from 9.0 to 11.5 feet in thickness in the proposed mine area. It has a relatively low sulfur content and high BTU value, and is upper sub- bituminous in rank. iY L I~ ...i l