2017-08-14_PERMIT FILE - C1981028

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• The thickness of the blow sand overlying the Laramie is variable but is sufficient to hold a large quantity of capillary water. This observation, coupled with the small annual precipitation relative to the potential evapotranspiration, makes it unlikely that significant recharge to the Laramie through the sand exists. This sand is not known to yield water to wells except in conjunction with the stream deposits in Ennis Draw. Subsurface water occurrence in the coal seam of interest and in the overburden are isolated. Lateral movement of this water is toward the northeast in the mine area and apparently discharges into the sands and stream deposits in Ennis Draw to the north and east of the mine site (McWhorter, 1978). Observations of the coal seam indicate only a saturated thickness of 1 to 2 feet at an elevation well below that of the piezometric water surface of Ennis Draw. This suggests that water occurrence in the coal seam is confined and no hydrologic connection exists between the coal seam and Ennis Draw. Ground water in neither the coal nor overburden is known to provide a water supply for any purpose in the vicinity of the mine. Refer to Piezometric Surface Map Appendix I-2 3. Geology Weld County is located in the Colorado Piedmont Section of the Great Plains, • which represents an early Cenozoic erosion surface. The South Platte River is the major erosional agent of the Piedmont Section in Northern Colorado. Rocks of the Precambrian to early Cretaceous age underlie most of the area at great depths. These deposits are in tum overlain by Pierre shale consisting of a thick sequence of fossiliferous marine shale, silt, and clayey sandstone, which contains numerous calcareous concretions. The upper part of the formation is transitional with the overlying Fox Hills sandstone. The zone of contact consists of gray sandy shale and shaley sand. The Fox Hills sandstone is composed of calcareous marine sandstone intermixed with dark -gray to black sandy shale and some massive white sandstone. Together with the sandstones in the Lower Laramie, the Laramie - Fox Hills aquifer is the most important aquifer in the area. Individual Laramie coal beds are often lenticular, do not extend laterally for any great distance and vary considerably in thickness. Areas free of coal were probably channel and channel -margin environments consisting of fine to coarse grained sandstones. Fine, well cemented sandstone boulders encountered in the Keenesburg Mine active pit are representative of channel environments. Light gray claystones (generally massive in the Denver Basin) were deposited • in well drained swamps, and light colored silts and clays deposited on levees. The coal, developed from peat layers, along with dark gray, organic rich fful