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Revised April 5, 1985 <br />• Div) The quality of the subsurface water. <br />(b) The application shall contain additional information which <br />describes the recharge, storage, and discharge characteristics of aquifers <br />and the quality and quantity of ground water, according to the parameters <br />and in the detail required by the Division. <br />RESPONSE: <br />Depth and Extent of Aquifers <br />The proposed permit and adjacent areas are situated in Twentymile <br />Park, as shown on Map 3, Twentymile Park Hydrology. Twentymile Park <br />contains an enclosed ground water basin formed by several synclinal <br />folds. Ground water occurrence in the basin is controlled by <br />structure, topography and lithology. There are two types of aquifers <br />which occur within the basin in the proposed permit and adjacent <br />areas: confined bedrock aquifers and unconfined alluvial aquifers. <br />• In the Twentymile Park area, ground water occurs in confined bedrock <br />aquifers within several formations. The rocks which compromise major <br />aquifers are the Twentymile and Trout Creek Sandstones of the Williams <br />Fork Formation an'd the Iles Formation, respectively. Wells finished <br />in these thick, massive, fine-to-medium-grained sandstones can yield <br />as much as 100 gallons per minute (Srogden and Giles, 1977). However, <br />these aquifers are stratigraphically separated from the minor aquifers <br />affected by mining. <br />Minor aquifers in the Williams Fork Formation include thin layers of <br />fine-grained sandstone, siltstone, and, where locally fractured, coal <br />beds. Minor aquifers in the general area yield an average of 10 gpm. <br />The combination of saturated permeable layers confined by impermeable <br />layers results in artesian aquifer conditions. Artesian pressures <br />within the confined aquifers in the heart of the ground water basin <br />have been found to exceed 700 pounds per square inch at a depth of <br />• 1630 feet. Almost all of the wells drilled into confined aquifers in <br />2.04-20 <br />