2021-01-28_GENERAL DOCUMENTS - C1982057

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seam, and excessive overburden cover relative to seam thickness over much of the permit area, the operator extracted Wolf Creek and Sage Creek coals within only selected areas of the South Extension Area. The Lennox seam is locally present in the Wadge overburden. It is usually two to five feet thick, and has been eroded away in some areas, and was not recovered by mining operations. The Wolf Creek coal is split into an upper and lower unit. The lower seam is about 16 feet thick, while the upper is about 7.5 feet thick. Above the Wolf Creek seam within portions of the permit area, and separated by 100 to 150 feet of interburden, is the Sage Creek seam. The Sage Creek seam ranges from 2 to 5 feet thick where it occurs in the permit area. SPL initiated mining of selected areas of both the Wolf Creek and Sage Creek seams in the South Extension Area upon approval of PR3, in 2003.Overlying the Sage Creek seam is a 50 to 65 foot thick zone of sandstone interbedded with shales and siltstones. Immediately above this sequence lies the Wadge coal seam. The Wadge coal seam is the most continuous in the area and is the only seam that was extracted prior to 2003. The outcrop strikes about north south,and dips 8 to 14 degrees. The Wadge is also split into upper and lower seams. The lower is two to three feet thick, and separated from the 10 foot thick upper seam by two to five feet of shales and sandstones. Overlying the Wadge is about 560 feet of sandstones, shales and coal, including portions of the Lennox Coal Seam. Overlying this lower unit of the Williams Fork Formation is the 130 foot thick Twenty Mile Sandstone. The upper most unit of the Williams Fork Formation consists of interbedded sandstones, shales, and thin coals. Alluvial deposits are locally present in stream valleys, particularly along the larger streams. Colluvial slides and slumps are also present in canyons and gullies throughout the area. Slide bodies which could potentially affect the stability of mining related structures in the northern portion of the permit area have been identified, and mitigation measures are addressed in Section VII,Back zllin and Grading of this document. Geologic baseline information including local and regional structure, stratigraphy, and information on interburden, overburden and coal geochemistry is provided in Volume 2, Tab 6, of the permit application. Ground Water Bedrock ground water aquifers have been identified as the Wolf Creek coal seam,the Wadge coal seam, the Wadge overburden including the discontinuous Lennox coal seam and the Trout Creek sandstone. Recharge to these and other aquifers in the area is a function of infiltration of snow melt and rainfall at outcrops along the anticline. All aquifers exhibit water table conditions near their outcrops. However, observation wells installed down dip indicate the aquifers are all under artesian conditions with increased pressure related to increased depth. Water quality in all aquifers is poor and undesirable for use as either a drinking or irrigation supply. The Seneca IIW Mine permit area lies on the western flank of the Sage Creek Anticline,a local structure located within the more regional Sand Wash Basin. The Sage Creek Anticline is thought to control local ground water flow, as artesian head increases with distance from the anticlinal axis. Ground water occurs in the alluvium associated with Hubberson Gulch within and adjacent to the permit boundary. Quality of this water prohibits its use for drinking and severely limits its use for irrigation. Surface Water The mine permit boundary encompasses two watersheds. Most of the mine site and the major portion of the disturbed area are in the Dry Creek watershed,draining to Hubberson Gulch and an unnamed tributary to Dry Creek (the Pond 005 Gulch). A small area on the eastern edge of the permit boundary drains to Sage Creek. Page 6 of 37