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' Western Slope Carbon, Inc. Page 6 <br />' December 15, 1981 <br />' to the east, the Mancos shale is occasionally capped by Quaternary terrace <br />deposits. These dominately consist of poorly sorted, unstratified clays, <br />' sands, silts, and gravels derived from erosion of the intrusive and volcanic <br />rocks of the West Elk Mountains. To the west, the Mancos shale is overlain <br />' by unconsolidated, unsorted clay silt, sand, and gravel of the North Fork <br />Gunnison River Valley alluvium. The alluvium is likely a 100 feet or more <br />' in thickness and is the probable primary groundwater source in the area. <br />Structurally, the Mancos shale and underlying units form a broad homocline <br />' which dips very gently, three to six degrees, to the north. There are no <br />faults or other significant structural features in the immediate vicinity. <br />' Geologic conditions at the site and its vicinity are depicted on Figure 3, <br />Regional Geologic Map. <br />SOILS <br />Soils within the Pit No. 6 area consist of brown to gray-brown to yellow- <br />brown, medium stiff to very stiff clayey to sandy silts. The soils are re- <br />' sidual in nature, derived from weathering of the underlying Mancos shale and <br />vary in depth from less than five feet in the higher portions of the site to <br />more than 13 feet in the drainage swales. They generally contain fragments <br />' of relatively unweather shale with the percentage of shale fragments in- <br />creasing with depth. At the time of our site investigation, the upper 6 to <br />' 12 inches of soil was saturated while beneath that depth the soil was dry <br />or slightly moist. <br />HYDROLOGY <br />' Ground Water <br />Earth materials underlying the Pit No. 6 site to a depth of more than 500 <br />feet have, for the most part, a very low permeability and specific yield. <br />' Both the Mancos shale and Dakota sandstone likely contain limited quantities <br />of water in fractures and isolated pervious zones of limited extent, or as <br />interstitial pore water. The major groundwater source in the region is prob- <br />ably the Quaternary alluvium of the North Fork Gunnison River Valley. Most <br />