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Underground mining of the "F" coal seam (No. 5 Mine) generated mine inflows on the order of 800 gpm. Fracturing of the <br />coals occurs naturally and as induced by the extraction of the coal seam, may result in a permeability significantly higher <br />than that observed in an undisturbed condition. <br />Faults within the permit boundary have been mapped and are shown on the Geology Map (Map 7). Faults may act a <br />conduits for ground water flow and allow vertical movement of ground water in the immediate locality of the fault. <br />Locally, faults may increase the fracture permeability of the coal bed. A fault system was intersected in the 2 West area of <br />the No. 5 Mine, and increased flows were observed in this area. Mine inflows are discussed in more detail later in Section <br />2.05.6. <br />The Yampa and Williams Fork River valleys contain alluvial material, The Yampa River valley floor reaches widths of up <br />to 9,000 feet. Depths of Yampa River alluvial sediment range from 10 to 18 feet with saturated thickness of up to 18 feet <br />having been measured. The Yampa River alluvium overlies bedrock of the Williams Fork and Lewis shale formations. <br />Permeabilities of the Yampa River alluvium are on the order of 100 gpd/ft. Yields of test wells completed in the Yampa <br />River alluvium within the permit boundary are less than 4 gpm. The width of the Williams Fork valley floor ranges from <br />800 to 1,000 feet. Depths of alluvial sediment range from 10 to IS feet in the valley bottom although saturated thicknesses <br />are generally less than 10 feet. The alluvium overlies bedrock of the Williams Fork and Iles formations within the permit <br />area. Permeabilities of the Williams Fork alluvial sediments are generally on the order of 17 ft/day. Yields of test wells <br />completed in the Williams Fort alluvium are also very low, generally less than 1,0 gpm. The No. 6 Mine will not be located <br />beneath any significant alluvium. Information regarding [he testing program [hat was performed on the Yampa and <br />Williams Fork alluviums is presented in Exhibit 10, Hydrologic Investigation of Williams Fork and Big Bottom (Yampa), <br />Alluvium, March, 1982. <br />Alluvial materials of the Yampa and Williams Fork Rivers are not considered aquifers in the permit area because of their <br />inability to readily transmit water. The alluvial materials may be more significant in terms of their water storage capability <br />and their contribution to base flow of the Yampa and Williams Fork Rivers. <br />Trout Creek Sandstone <br />The Trout Creek Sandstone is the deepest aquifer within the pemvt boundary. It occurs at the top of the Iles formation and <br />marks the contact with the overlying Williams Fork formation. The Trout Creek Sandstone consists of fine to medium <br />grained sands, cemented with calcium carbonate. The thickness of the sandstone ranges from 62 to 91 feet and averages 78 <br />feet. The sandstone outcrops in the valley walls of the Yampa and Williams Fork Rivers on the southern portion of the <br />permit area and dips gently to the north-northeast at 8 to 10 degrees. The stmcture of the Trout Creek Sandstone is <br />presented on the Stntcture Map of the Trout Creek Sandstone (Map 10). <br />The Trout Creek Sandstone reaches depths of as much as 2,350 feet at the northern permit boundary. It is separated from <br />the overlying "E" coal seam, by approximately 250 feet. The intervening strata consist largely of shale, sandy shale, coal, <br />and occasional discontinuous sandstone. <br />Water levels in the Trout Creek Sandstone were initially at ground surface at the No. 5 mine portal. The aquifer is under <br />artesian conditions at the No. 5 mine portal and is probably under artesian conditions over the rest of the permit area, except <br />near the outcrop. <br />Three (3) water supply wells within the permit boundary have been completed into the Trout Creek Sandstone. They are <br />the following: 1) the No. 5 mine well, 2) the No. SA supplemental well, and 3) the Okie Plaza well. The Okie Plaza <br />well was undermined and no longer is used at [he site. The No. SA mine supplemental well was drilled to supplement <br />the No. 5 mine well and was completed in May 1983. For locations of hydrologic monitoring wells, refer to the <br />Hydrologic Monitoring Program Location May (Map 11). <br />Yields of wells on the Trout Creek Sandstone are highly variable. The No. 5 Mine well reportedly flowed at the <br />Permit Revision 04-34 2.04-12 Revised 7/2/04 <br />