2020-12-14_PERMIT FILE - C1981019A (2)

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RULE 2 PERMITS 2.04.7 Hydrology Description The objective of this section is to meet the requirements of Rule 2.04.7 et seq. by furnishing hydrological information for the Collom permit expansion area in sufficient detail to describe the following: • Character of surface and groundwater resources; • Baseline groundwater quantity and quality; • Baseline surface water quantity and quality; • Seasonal variations in surface and groundwater quantity and quality; and • Ownership and use of surface and groundwater resources. To meet the requirements of Rule 2.04.7 et seq. both general and detailed groundwater and surface water resource information was collected, compiled, and analyzed. Groundwater resource information will be provided first followed by surface water resource information. 2.04.7 (1) Groundwater Resource Information First general and then detailed information regarding groundwater in the vicinity of the mining areas will be presented in the following subsections. General Groundwater Resource Information General Groundwater Characteristics — Colowyo Coal Company's area of operation lies within the Danforth Hills coal field. The Collom permit expansion area is in the north -central part of the coal field. The "general area", as defined in Section 1.04 (Definitions) of the Coal Regulations, is located north of the Danforth Hills on the south margin of the Axial Basin Anticline. Geologic structure in the area is dominated by the Collom Syncline and the Danforth Hills Anticline, both of which trend about west- northwest through the area. The axis of the Danforth Hills Anticline is south of the Colowyo revised permit area, and the axis of the Collom Syncline is in the northern part of the revised permit area. The rock strata dip generally northward at gentle angles (2° to 8°) off the Danforth Hills Anticline to the axis of the Collom Syncline. The north limb of the Collom Syncline turns steeply upward, however, and the strata dip steeply (up to 40°) toward the south. The principal geologic units in the area include the upper Cretaceous Iles and Williams Fork Formations. Both are part of the Mesaverde Group, which Brownfield et al. (2000) characterize as a thinly to thickly interbedded succession of shale, siltstone and sandstone commonly containing carbonaceous rocks. A more detailed description of the geologic units in the area is provided in Section 2.04.6. The Iles Formation consists of about 1,300 to 1,500 feet (ft.) of fine- to medium -grained, poorly sorted, calcareous sandstone interbedded with sandy and silty carbonaceous shale, siltstone, mudstone, claystone and coal (Brownfield and Johnson, 2008). At the top of the Iles Formation is the Trout Creek Sandstone member, which is up to 75 ft thick and consists of white, fine-grained, well -sorted, massive, marine sandstone deposited along a regressing shoreline. The Trout Creek Sandstone is considered to be a regional aquifer (Robson and Stewart, 1990). The overlying Williams Fork Formation consists of up to 1,700 ft of alternating beds of sandstone, sandy shale, mudstone, and coal. The Williams Fork Formation includes the Twentymile Sandstone member, which is considered to be a regional aquifer (Robson and Stewart, 1990). However, the Twentymile Sandstone is not present in the Danforth Hills area (Camp, Dresser & McKee (CDM), 1985a). Collom — Rule 2, Page 20 Revision Date: 4/7/17 Revision No.: RN -07