2013-04-05_PERMIT FILE - C1981019A

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RULE 2 PERMITS 2.04.7 Hydrology Information Groundwater Occurrence of Groundwater General Area Colowyo Coal Company's general area of operation is defined by the area bounded by Goodspring and Wilson Creeks, both of which are tributaries to the Yampa River. The mine permit area and its relationship to Goodspring and Wilson Creeks are shown on Map 32. Colowyo Coal Company's, mining operations are in an area of limited hydrology. Precipitation averages 21.5 inches for the drainages in the "general area" and runoff is limited. Flows in Wilson, Taylor and Goodspring Creeks are mostly from snowmelt or thunderstorm events. Groundwater resources on and adjacent to the mine property are also limited. Base flows observed in Goodspring and Wilson Creeks are mostly groundwater discharged from the thin and limited alluvial/colluvial aquifers that can be found in the valleys of both creeks. There are no known places of groundwater discharge from bedrock units to Goodspring, Taylor, or Wilson Creeks from the sandstones between the coals to be mined. Rocks on the property are part of the Mesa Verde Group. These rock units are almost entirely interbeds of sandstones and shales. The uppermost geologic unit in the permit area is the Williams Fork Formation. The coals to be mined on the property are part of the Fairfield Group, the principle coal-bearing zone in the area. The sandstones are predominately fine to medium-grained, poorly sorted and calcareous. In the upper part of the formation they are generally channel sandstones and exhibit unilateral and vertical continuity. In the lower part of the formation the sandstones are more continuous than in the upper part. The thickness of the Williams Fork Formation, in the general area, is estimated to be about 1600 feet. Underlying the Williams Fork Formation is the Iles Formation. Little data are available to describe the characteristics of the Iles Formation, principally because of its great depth. However, based on information from adjacent areas, the general characteristics of the Iles Formation can be described. The Iles Formation is continuous and can be correlated over a large area. Trout Creek Sandstone, the upper member of the Iles Formation, has been mapped to be 75 feet thick. This sandstone is easily recognized and is considered a marker bed for the top of the Iles formation. Trout Creek Sandstone is a white, fine- grained and well sorted sandstone. It is fairly uniform in thickness in the general area. Beneath the Iles Formation lies the Mancos Shale. The Mancos Shale is a marine shale with thin interbeds of siltstones and limestones and is estimated to be over 5,000 feet thick in this area. This shale forms the base of the regional groundwater system in the area. These shales are relatively impermeable and do not store or transmit appreciable quantities of groundwater. The Mancos Shale is exposed north of the permit area and is found at depth beneath the permit site. The permit area straddles the southern limb of the Collura Syncline. The syncline is a regional structure trending in a southeast northwest direction parallel to the major geologic structure of the area in the Axial Basin. The Williams Fork and the Iles Formations are truncated north of the permit area and the Mancos Shale is exposed as a result of the regional geologic structure. Goodspring, Taylor and Wilson Creeks are tributaries to the Yampa River, a major surface water feature located some distance from the mine property. Water resources on the mine property are connected to the Yampa River only by surface water discharge and then only during periods of infrequent snowmelts and thunderstorm events. A second major surface water feature in the area is the Williams Fork River. However, the Williams Fork River, which is a tributary to the Yampa River, does not receive discharge Rule 2 Permits 2.04.7-1 Revision Date: 6/23/08 Revision No.: MR-91