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The Seneca II -W Mine is situated in the southeastern synclinal portion of the Sand Wash <br />Structural Basin of northwestern Colorado and south central Wyoming. Exposed strata near the <br />mine site vary in age from Late Cretaceous to Quaternary. Most units in the area are <br />sedimentary. However, some Miocene extrusives are locally present. Many faults and folds <br />modify the regional synclinal structure; however, no faults have been identified at the site. The <br />most significant local fold is the Sage Creek Anticline, located just east of the mine. Rock units <br />dip 8 to 14 degrees to the west. The Seneca II -W Mine lies on the western flank of this anticline. <br />The largest local structure is the Tow Creek Anticline, located about 10 miles northeast of the <br />permit area. <br />The local stratigraphic sequence, in ascending order, is the Mancos Shale; the Mesaverde Group, <br />which is subdivided into the Iles and Williams Fork Formations; and the Lewis Shale. See the <br />Exhibit 6 -GX geologic cross section map series in the permit application package for further <br />detail. <br />The Iles Formation is divided into three members. The basal Tow Creek Sandstone is a massive, <br />fine grained, well sorted sand. The Tow Creek varies from 35 to 125 feet thick. Overlying the <br />Tow Creek are 1200 feet of interbedded shales, sandstones, and coals. The coals, while mined in <br />the vicinity, are too deep to be considered economically recoverable at the Seneca II -W Mine. The <br />massive, fine grained, 100 feet thick Trout Creek Sandstone is the uppermost unit of the Iles <br />Formation. <br />Conformably overlying the Iles is the Williams Fork Formation. The lower unit of the Williams <br />Fork Formation is a series of interbedded shales, sandstones, sandy shales and coal. The middle <br />coal group contains the seams of economic importance. Four coal seams of economic importance <br />are found in the Williams Fork Formation. These seams are, in ascending order, the Wolf Creek, <br />Sage Creek, Wadge, and Lennox coals. Due to discontinuous occurrence of the Sage Creek seam, <br />and excessive overburden cover relative to seam thickness over much of the permit area, the <br />operator extracted Wolf Creek and Sage Creek coals within only selected areas of the South <br />Extension Area. The Wadge coal was mined in both the North and South parts of the operation. <br />The Lennox seam is locally present in the Wadge overburden. It is usually two to five feet thick, <br />but has been eroded away in some areas, and was not recovered by mining operations. <br />The Wolf Creek coal is split into an upper and lower unit. The lower seam is about 16 feet thick, <br />while the upper is about 7.5 feet thick. Above the Wolf Creek seam within portions of the permit <br />area, and separated by 100 to 150 feet of interburden is the Sage Creek seam. The Sage Creek <br />seam ranges from 2 to 5 feet thick where it occurs in the permit area. SCC initiated mining of <br />selected areas of both the Wolf Creek seam and the Sage Creek Seam in the South Extension <br />Area, upon approval of PR -3, in 2003. Neither seam was previously mined at Seneca II -W. <br />Overlying the Sage Creek seam is a 50 to 65 foot thick zone of sandstone interbedded with shales <br />and siltstones. Immediately above this sequence is the Wadge coal seam. The Wadge coal seam <br />is the most continuous in the area and is the only seam that was extracted prior to 2003. The <br />outcrop strikes about north - south, and dips 8 to 14 degrees. The Wadge is also split into upper <br />and lower seams. The lower is two to three feet thick, and is separated from the 10 foot thick <br />Seneca II -W Findings Document 7 C- 1982 -057 <br />Permit Revision No. 6 January 6, 2012 <br />