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The porosity of a unit containing groundwater is the principle control of the <br />• quantity of water the unit can hold. The porosities of fine-grained sandstones, <br />such as those in the Mesa Verde group overlying the Cameo coal zone, <br />typically range from less than 5 percent to a maximum of 30 percent. (Davis and <br />DeWeist, 1965). The cementation, type and degree of fracturing and other <br />factors may significantly alter the original porosity of an aquifer. Based on these <br />factors an estimated range of porosity of the sandstone located with the permit <br />are is 5 to 20 percent. <br />According to the Collins report in Appendix 7-2, Pitman et.al. (1989) found the <br />porosity of the Mesa Verde sandstones to be 1.6 to 8.9 percent when evaluating <br />their potential natural gas reservoirs. Collins discusses the geologic makeup of <br />the sandstone which limits porosity. <br />Of the water contained in an aquifer, only that quantity available for gravity <br />• drainage will be affected by mining operations. The fine-grained, tight nature of <br />the Mesa Verde formation indicates that its specific yield is very low. Price and <br />Waddle (1973) provided a specific yield from 0.' ' Fo 0.70 percent for units in the <br />permit area. J.F. Sata and Associates (1983) d'. .study of the Cameo B seam <br />and the overlying strata in Coal Gulch, 25 miles northwest of the Roadside <br />Mines. In their study, they found the coal seam to have a transmissivity of 3 feet= <br />per day with a hydraulic conductivity of 0.11 feet per day, and the overburden to <br />have a transmissivity of 4 feet2 per day with a hydraulic conductivity of 0.007 <br />feetz per day. Fractured sandstones in the overburden were found to have a <br />transmissivity of 538 feetz per day with a hydraulic conductivity of 19.39 feet per <br />day. Transmissivity and hydraulic conductivity were calculated for the Rollins <br />Sandstone, Appendix 7-3. The transmissivity ranged from 1.30 feet2 per day to <br />412 feetz per day with the 1.30 believed to be a typical formation value and the <br />• 7-6a (New 9117197) <br />