Laserfiche WebLink
tightly cemented sandstones and shales which act as barriers inhibiting vertical percolation. <br />However, field observation of exposed outcrops, mine high- walls, and aquifer analysis data <br />indicate that secondary porosity (weathered and fractured bedrock strata) play a significant role <br />in allowing vertically infiltrating ground water to infiltrate through the unsaturated to the <br />saturated zone. The NHN permit area is impacted by irrigation which is a primary source of <br />infiltrating water Infiltration as a result of precipitation is only a minor component of recharge <br />in the NHN area, but the majority of infiltration comes from irrigation. The large majority of the <br />soils in the mining area have a slow to medium runoff potential. <br />The strata at the NHN permit area and the New Horizon Mine are the same. The lithologic logs <br />indicate that the back fill material will generally be composed of more than 50 percent fragments <br />of blasted sandstone with lesser amounts of shale and siltstone and minor amounts of bentonite. <br />Sections 2.05.3 and 2.05.4 describe the details of the mining and reclamation methods. The <br />recharge capacity and permeability of the back fill material will be increased due to greater <br />porosity and hydrologic conductivities than the undisturbed strata due to increased void volumes. <br />As an example, Peabody conducted a constant discharge pumping test in the backfill (spoils) of <br />the old Peabody Nucla Mine using the formula for the well recovery at GW -N27. The results of <br />the test showed the backfill material to have a transmissivity of 261 ft day, and a hydraulic <br />conductivity of 40 ft/day (about 0.21 gpm /ft which are many times higher than average values <br />of transmissivity and hydraulic conductivity from tests of the overburden , coal and <br />underburden zones in the area, (see Tables 7 -5 and 7 -6, pgs. 7 -22 and 7 -24 of the New Horizon <br />1 Mine Permit copies of which are contained in the Appendix 2.04.7 -2 to this Section). The re- <br />saturation of the back fill material will be greatly limited by its tendency to drain down dip along <br />the floor of the pit to the existing outcrop where it will discharge at Spoil Spring # 1 (SS #1) as it <br />currently does, (see Map 2.04.7 -1 for the location of SS #1 and SS #2). <br />Discharge. Discharge rates from the coal and the under- burden is relatively small compared to <br />the overburden which is more a function of the thickness of the respective zones than it is the <br />difference in lateral permeability. Again, seasonal irrigation is the cause of the saturation of the <br />NHN strata as the monitoring holes show. Without the seasonal irrigation the NHN strata would <br />be dry. The overburden strata is the primary source of discharge to the drainages of Tuttle Draw <br />(to the south) and Coal Canyon (to the west) which help maintain the surface water base flow of <br />the two drainages, (see Map 2.04.5 -1 this application showing coal outcrop). The primary factor <br />of which is the much greater surface area of recharge from the seasonal irrigation for the <br />overburden than for the other two zones. Fourteen aquifer tests have been conducted on the <br />overburden, coal, and underburden strata in the NHN permit area, (see Tables 7 -5 and 7 -6, <br />ppgs.7 -22 and 7 -24 of the New Horizon 1 Mine Permit copies of which are contained in the <br />Appendix 2.04.7 -1 of this Section). These tests show average hydraulic conductivities for: the <br />overburden of 0.72 ft/day; the coal zone of 0.19 ft/day; and the underburden of 1.61 ft/day. One <br />of these tests was at GW -N9 which is located within the NUN Permit area, (see Map 2.04.7 -1). <br />This was a slug test analysed by the McWhorter method on the overburden and coal zone. The <br />results of this test indicated a hydraulic conductivity of 2.1 ft/day for the two zones combined, <br />(see Table 7 -5, pg 7 -22 of the New Horizon 1 Mine Permit a copy of which is contained in the <br />Appendix 2.04.7 -1 to this Section). <br />Estimating discharge from the overburden, coal, and underburden zones into the NHN pit can be <br />based on the average overburden zone aquifer characteristics. For the overburden, the average <br />hydraulic conductivity (or K) is 0.72ft/day. The pit length will be about 2197 ft. long. The <br />Section 2.04.7 Page 5 November 2011 <br />