2018-02-05_PERMIT FILE - C1981019

Home Browse Search

October 19, 2017 Page 1 1.0 INTRODUCTION 1.1. Project Background and Setting As requested by Colowyo, Agapito Associates Inc. (AAI) performed a detailed dewatering and depressurization study for the Collom Pit at the Colowyo Mine. Similar to past and currently active pits at Colowyo, several coal seams at the Collom Pit will be mined using an updip approach. A dewatering study has been performed for this operation previously, primarily by Water Management Consultants, Inc. (WMC) (2005). The objective of the present study was to assess the usefulness of the previous study and to develop an optimal dewatering plan for the Collom Pit. 1.1.1 Project Location and Topography The Colowyo Mine is located approximately 24 miles south of Craig, Colorado, adjacent to and west of Colorado State Highway 13. Surface coal mining is currently active in the South Taylor Pit, located in Rio Blanco and Moffat Counties. Mining in the South Taylor Pit is expected to be completed in approximately 2022. The Collom Pit represents the long-term future of the Colowyo Mine. The Collom Pit is located approximately 4 miles northwest of the South Taylor Pit. The Collom Pit Project Area (the Project Area) is located on the southern edge of the Yampa River Basin, northwest of the Danforth Hills. Elevations range from approximately 8,100 feet (ft) above mean sea level (amsl) on the southern end of the Project Area to 6,900 ft on the northern end. The area consists of gently sloping interfluvial ridges divided by deeply entrenched gulches and drainage valleys. Major drainages include Jubb Creek, various forks of the Collom Gulch and Little Collom Gulch, and Straight Gulch. All drainages flow northeast and ultimately to the Yampa River. The ridge surfaces are characterized by shallow tan to gray - brown silts or silty loams locally covered with sandstone slabs and angular gravels. Large bedrock outcrops also occur in some locations. Valley bottoms are generally narrow with very steep canyon walls. Ridgetops are wide and gently sloping. 1.1.2 Geologic Setting The coal seams in the Project Area are contained within the Upper Cretaceous Williams Fork Formation of the Mesaverde Group (Bureau of Land Management [BLM] 2006, Brownfield et al. 2008). The Mesaverde Group generally consists of a thinly to thickly interbedded succession of shale, siltstone, and sandstone that was deposited largely in a terrestrial environment. The Mesaverde Group is categorized into two formations: the overlying Williams Fork Formation and the underlying Iles Formation (Brownfield et al. 2008). The Williams Fork Formation has been subdivided into five stratigraphic units. In ascending order, these are the Fairfield coal group, barren interval, Goff coal group, Lion Canyon Sandstone, and Lion Canyon coal group. The Iles Formation has been subdivided into three stratigraphic units: in ascending order, these are the Lower coal group, the Black Diamond coal group, and the Trout Creek Sandstone Member (Brownfield et al. 2008). The Williams Fork and Iles Formations comprise a sedimentary rock sequence that originated from a deltaic and marginal marine depositional environment. The Trout Creek Sandstone Member consists of Agapito Associates, Inc.