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December 1986 7 863-2060 <br />• <br />A well-cemented, silty, fine sandstone underlies the black shale <br />unit described above. This sandstone ranges in color from gray <br />to black, is well indurated, and typically of medium strength. <br />The unit contains abundant shale partings dipping 5 to 10 degrees <br />and is slightly weathered to fresh in the vicinity of Area 9/10 <br />boreholes. <br />Historic mine data include joint and fault measurements made in <br />the Wadge seam and adjacent units exposed in the Area 51 high- <br />wall. Joint measurements indicate very consistent jointing in <br />these units. Steeply-dipping joints which strike to the north- <br />west and dip 70 to 90 degrees northeast and southwest are <br />dominant. Joint surfaces in the sandstone and Wadge seam are <br />generally tight, relatively smooth, contain minor quantities of <br />pyrite, and are typically longer than 8 feet. <br />Faults and shears observed in the Area 51 highwall also dip <br />steeply (63 to 90 degrees to the northeast and southwest) and <br />strike northwest. The shears contain up to 0.2 feet of clayey <br />gouge, while the faults contain 1 to 2 feet of gouge/breccia. <br />4.3 Ground Water <br />Ground-water recharge in Area 9/10 is through mine spoil infil- <br />tration, as well as through the Flesaverde strata which outcrop <br />along the ridge located immediately south of the site. Observa- <br />tion of the Area 51 highwall during the spring season indicates <br />that ground-water discharge is primarily through the Wadge seam. <br />Such observations also indicate that ground-water distribution in <br />the Wadge seam and overburden units is Controlled by the major <br />faults exposed in the Area 51 cut. These faults appear to act as <br />barriers to down-dip (northwesterly) ground-water flow in the <br />• Mesaverde units in the vicinity of Area 9J10. <br />Golder Associates <br />