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The net impact of seepages can be estimated using the mass balance technique. The estimated net effect will be an <br />increase in the SAR from 3.6 to 9.4. This is a worst -case calculation and will only occur after the mine is refilled. <br />Since the bottom areas in the vicinity of the mine that are used for agricultural purposes are flood - irrigated, the fields <br />would be irrigated with low SAR water. <br />Since the alluvial water is naturally higher in metals and dissolved solids than the mine discharge water, no other <br />impacts on water quality are expected. Development mining beneath Big Bottom is not anticipated to impact the AVF <br />since pillars would be retained for long -term support, there would be no associated subsidence, and water inflow <br />discharge would be handled utilizing the existing system and outfalls. <br />Postmining Discharge — No. 9 Mine <br />The "P" seam was mined from the No. 9 Mine from March 1978 to August 1981. The mine was driven northward in <br />a down -dip direction. The approximate elevation of the bottom of the No. 9 mine portal was 6,305 ft., and present <br />ground surface is approximately 6,350 ft. No significant full- extraction mining was performed in the mine. <br />The water level in the Twentymile Sandstone is estimated to be approximately 6,260 ft. at the point which has the <br />highest piezometric level in the Twentymile Sandstone anywhere it underlies the No. 9 Mine. This estimate is based <br />on the water level contour map for water levels measured in November 1995 (1995 Annual Hydrology Report, Permit <br />C -81 -044, Figure 12). The Twentymile Sandstone underlies the "P" seam by approximately 350 ft. The historic <br />water levels in the Twentymile Sandstone have apparently not been effected by mining in the area, as they have been <br />constant since 1981 (ibid., Figure 10) indicating a limited hydrologic connection between the aquifer and the mine. <br />The maximum piezometric level of the White Sandstone is estimated to be approximately 6,300 feet where it overlies <br />a location in the No. 9 Mine where measurable flow was encountered. This is based on the mine inflow study (Eagle <br />No. 9 Mine Inflow Study, Map IV -I la, 5/8/83) and the December 1985 water level measurements (1985 Annual <br />Hydrology Report, Permit C -81 -044, Figure 17). In addition, the maximum projected piezometric level of the White <br />Sandstone where it overlies any portion of No. 9 Mine is less than 6,320 feet, however, this is at the White <br />Sandstone's outcrop area, where it is probably not saturated. The White Sandstone overlies the mine by <br />approximately 125 feet and outcrops approximately 1,000 feet north of the portal. The historic water levels in the <br />White Sandstone were probably not affected by mining (1985 Annual Hydrology Report, Permit C -81 -044, Figures <br />12 -14) indicating a limited hydrologic connection between the aquifer and the mine. <br />The vertical groundwater gradient, based upon a comparison of the piezometric surfaces in the overlying and <br />underlying sandstones, indicates that it is downward in the No. 9 Mine area. Even if there is a good connection <br />between either aquifer and the mine, the downward gradient indicates that the mine would not fill to the surface. <br />Instead, it would refill to an equilibrium level that would be between the levels of the two aquifers. <br />None of the historic underground mines in the area are known to discharge. This includes the Wise Hill No. 4, with <br />portals in a "bottom area ", and which filled with discharge from the No. 5 Mine. There was temporary discharge from <br />the Wise Hill No. 4 workings when water from the No. 5 Mine was injected; however, when injection stopped, the <br />discharge ceased. <br />• The piezometric surface in the aquifer below the mined seam is lower than the portal elevation <br />• The piezometric surface in the aquifer above the mined seam is lower than the ground surface at the portal <br />• Where there was measured inflow to the No. 9 Mine, the highest piezometric head in the overlying aquifer <br />was lower than the portal elevation <br />• The vertical component of the gradient in the area is downward <br />• The mine was driven in a down -dip and down- gradient direction <br />• The mine portal is located at the crop line. There are no historic springs in the area <br />• None of the historic underground mines in the area are known to discharge, and the No. 9 Mine portal is at a <br />higher elevation than any of the old mines <br />TR14 -36 2.05 -46 Revised 03/20/14 <br />