Laserfiche WebLink
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 Lennox seam is locally present in the Wadge overburden. It is usually two <br />to five feet thick, but has been eroded away in some areas, and is not recovered by mining <br />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 Area, <br />upon approval of PR -3, in 2003. Neither seam was previously mined at Seneca II -W. Overlying <br />the Sage Creek seam is a 50- to 65 -foot thick zone of sandstone interbedded with shales and <br />siltstones. Immediately above this sequence is the Wadge coal seam. The Wadge coal seam is the <br />most continuous in the area and is the only seam that was extracted prior to 2003. The outcrop <br />strikes about north -south, and dips 8 to 14 degrees. The Wadge is also split into upper and lower <br />seams. The lower is two to three feet thick, and is separated from the 10 foot thick upper seam by <br />two to five feet of shales and sandstones. Overlying the Wadge is about 560 feet of sandstones, <br />shales, and coal, including the Lennox Coal Seam, which has been eroded away in places. <br />Overlying this lower unit of the Williams Fork Formation is the 130 -foot thick Twenty Mile <br />Sandstone. The upper most unit of the Williams Fork Formation consists of interbedded <br />sandstones, shales, and thin coals. <br />The surficial geology of the area is composed chiefly of sedimentary rocks, of marine and <br />non -marine origin. These sedimentary rocks were formed through the transgression and regression <br />of an epicontinental sea. <br />Alluvial deposits are locally present in stream valleys, particularly along the larger streams. <br />Colluvial slides and slumps are also present in canyons and gullies throughout the area. Slide <br />bodies which could potentially affect the stability of mining related structures in the northern <br />portion of the permit area have been identified, and mitigation measures are addressed in Section <br />VII., 'Backfilling and Grading" of this document. <br />Geologic baseline information including local and regional structure, stratigraphy, and information <br />on interburden, overburden and coal geochemistry is provided in Volume 2, Tab 6, of the permit <br />application. <br />viii <br />