2010-01-25_PERMIT FILE - C1981044A (4)

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The final cover placement will consist of a minimun-i of two feet of suitable, non-toxic cover material, including spoil or other cover material and topsoil or best available plant-growth media (in accordance with Rule 4.11.4). These areas will then be revegetated by seeding with a cropland seed mix (Table 65) appropriate to the approved postmining land-use as shown on the Reclamation Plan Map (Map 29). All seeded areas will be straw mulched at a rate of two tons/acre. Postmining Discharge - No. 9 Mine The "P" seam was mined from the No. 9 Mine from August 1988 to March [985. Tl:~ iiai:i~. ~~ as uriver~ northward in a downdip direction. The approximate elevation of the bottom of the No.9 mine portal was 6,305 ft., and present ground surface is approximately 6,350 ft. No significant full-extraction mining was occurred in the mine. The water level in the Twentymile Sandstone is estimated to be at approximately 6,260 ft., at the point which has the highest piezometric level in the Twentymile Sandstone anywhere it underlies the No.9 Mine. This estimation is based on the water level contour map for water levels measured in November 1995 (1995 Annual Hydrology Report, Permit C-81-044, Figure 12). The Twentymile Sandstone is approximately 350 feet below the "P" seam. The historic water levels in the Twentyrnile Sandstone have apparently not been effected by mining in the area, as they have been constant since 1981 (ibid., Figure ] 0), indicating the lack of an effective hydrologic connection between the aquifer and the mine. The maximum piezometric level of the White Sandstone is estimated to be approximately 6,300 feet, where it overlies a location in the No.9 Mine where measurable flow was encountered. This is based on the mine inflow study (Eagle No.9 Mine Inflow Study, Map IV-1 l a, 5/8/83) and the December 1985 water level measurements (1985 Annual Hydrology Report, Permit C 81-044, Figure 17). In addition, the maximum projected piezometric level of the White Sandstone where it overlies any portion of No. 9 Mine ~s less than 6,320 feel; however, this is at the outcrop of the White Sandstone where it is probably not saturated. The White Sandstone overlies the mine by approximately 125 feet and outcrops approximately 1,000 feet north of the portal. Based on .available hydrologic monitoring information, historic water levels in the White Sandstone were not effected by mining (1985 Annual Hydrology Report, Permit C-81- 044, Figure 12 -14), indicating the lack of an effective hydrologic connection between the aquifer and the mine. The indicated vertical groundwater gradient, based upon a comparison of the piezometric surfaces in the overlying and underlying sandstones, is downward in the No.9 Mine area. Even if there were an effective hydrologic connection between either of the aquifers and the mine, the ground water gradient indicates that the mine would not fill 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 known to discharge. This includes the Wise Hill No.4, which had an opening in a "bottom area" and had gradually filled with discharge from the No.S Mine. It discharged briefly when additional water from the No. 5 Mine was injected; however, when injection stopped, discharge ceased. The following summarizes key hydrologic considerations: • The piezometric surface in the aquifer below the mined seam is lower than the portal elevation • The piezometric surface in the 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 of the gradient in the area is downward • The mine was driven in a down-dip and down-gradient directions TRd7-34 2.05-30 10/31107