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Sandstone's outcrop area +vhere it is probably not saturated. The White Sandstone overlies the mine by approximately 125 feel and outcrops approximately 1,000 feet north of the portal. The historic +vater levels in [he White Sandstone • were probably not affected by [he mining (1985 Annual Hydrology Report, Permit G81-044. Figures 12-14) indicating that there is not a good connection between the aquifer and the mine. Also. the mine was driven in a do+vrt gradient directron so al] of the +vorkings are in lower head areas than the portal. The vertical groundwater gradient, based upon a comparison of the piezometric surfaces to the overlying and underlying sandstones, indicates [hat it is downward in the No. 9 Mine area. Even if there is a good connection between either aquifer, and the mine, the downward gradient indicates that the mine would not till to the surface. Instead, it would refill to an equilibrium level that would be between the levels of the two aquifers. None of the historic underground mines in the area are unknown to discharge. This includes the Wisehill No. 4, which had opening in a "bottom area" and was filled with discharge from the No. 5 Mine. It discharged when water from water from the No. 5 Mine was injected; however, when injection stopped, it ceases to discharge. • The piezometric surface in the aquifer below the mined seam is lower than [he portal elevation. • The piezometric surface in [he aquifer above the mined seam is lower than the ground surface at the portal site. • Where there was measured inflow to the No. 9 Mine, the highest piezometric head in the overlying aquifer was lower than the portal elevation. • The vertical component ofthe gradient in the area is downward. • The mine was driven in a down-dip and down-gradient direction. • The mine portal is located at the crop line. There are no historic springs in the area. • None of the historic underground mines in the area are known to discharge, and the No. 9 Mine portal is at a higher elevation than any of the old mines. Effects of Seepage from No. 9 Portal Backfil] • The No. 9 Mine portal backfill will have surface area of approximately five(5) acres. Using an infiltration rate of three-(3) inches per year, the annual infiltration will be less than 1 gpm, This amount is insignificant and will therefore have no measurable effect on nearby aquifers. Also the backfill area is stratigraphically separated from the nearest aquifer, the Twentymile Sandstone, by 360 feet of very low permeability interbedded claystone, siltstones, and sandstones. Water Quality lmpacts of Mine Discharge Mine discharge rates were discussed under the subsection Mine Inflows. Plot of total dissolved solids concentrations versus time for the two discharge points, 5 Mine Discharge and 7 North Angle, are presented in Exhibit 42, Figures 58AE and 58AF, respectively. One [rend appazent in the plots is an initial increase in the concentrations of total dissolved solids in the 7 North angle dischazge. The source of this initial increase in dissolved solids in 7 North Angle discharge is unknown. Observed Impacts Quarterly data from the Williams Fork River gauging stations (WF] and WF-2) were reviewed to ascertain actual impacts to the Williams Fork River resulting from mine discharges. Summaries of the water quality data are presented in Tables 26 and 27, in Section 2.04.7, Hydrology Information. Plots of field electrical conductivity measurements for tte Williams Fork River are presented in Figure SSd and Exhibit 42, Figures 58AG and 58AH, respectively. The comparisons of these data from the upstream and downstream stations on the Williams Fork River indicate that conductivity levels are nearly identical upstream and downstream of the mine. Likewise, plots of total dissolved solids measurements for the Williams Fork River are presented in Figures • 58AI and SSAJ for upstream station WF-1 and downstream station WF-2, respectively. The -T('+ 3 3 Midterm Response 2.05-47 _ _ 7/30/01