2018-07-02_PERMIT FILE - C2010089A (19)

Home Browse Search

than average values of transmissivity and hydraulic conductivity from tests of the overburden, coal and underburden zones in the area (please see Tables 7-5 and 7-6 in Appendix 2.04.7-1). The resaturation of the back fill material will be greatly limited by its tendency to drain down dip along the floor of the pit to the existing outcrop where it will discharge at Spoil Spring # 1 (SS #1) as it currently does (see Map 2.04.7-1 for the location of SS #1). Discharge Discharge rates from the coal and the underburden is relatively small compared to the overburden which is more a function of the thickness of the respective zones than it is the difference in lateral permeability. Again, seasonal irrigation is the cause of the saturation of the NHN permit area strata as the monitoring wells show. Without the seasonal irrigation the NHN permit area strata would be dry. The overburden strata is the primary source of discharge to the drainages of Tuttle Draw (to the south) and Coal Canyon (to the west and north) which help maintain the surface water base flow of the two drainages (see Map 2.04.5-1 this application showing coal outcrop). The primary factor of which is the much greater surface area of recharge from the seasonal irrigation for the overburden than for the other two zones. Fourteen aquifer tests have been conducted on the overburden, coal and underburden strata in the NHN permit area (see Tables 7-5 and 7-6, ppgs.7-22 and 7-24 of the New Horizon 1 Mine Permit copies of which are contained in the Appendix 2.04.7-1 of this Section). These tests show average hydraulic conductivities for: the overburden of 0.72 ft/day; the coal zone of 0.19 ft/day; and the underburden of 1.61 ft/day. One of these tests was at GW -N9 which is located within the NHN Permit area (see Map 2.04.7-1). This was a slug test analysed by the McWhorter method on the overburden and coal zone. The results of this test indicated a hydraulic conductivity of 2.1 ft/day for the two zones combined, (please see Table 7-5 in Appendix 2.04.7-1). Estimating discharge from the overburden, coal, and underburden zones into the NHN pit can be based on the average overburden zone aquifer characteristics. For the overburden, the average hydraulic conductivity (or K) is 0.72ft/day. The pit length will be about 2,197 feet long. The average saturated thickness of the overburden zone just north of the highwall is about 16 feet. The average gradient in the overburden just north of the highwall is about 0.05. Based on the existing overburden characteristics, the annual discharge from the highwall is calculated using Darcy's Law Q = (K)(gradient)(cross sectional area of discharge). Therefore, Q (or discharge) for the overburden zone is equal to 0.72ft/day x 0.05 x (16.0 ft x 2197 ft) or about 911 ft3 per day or 323,515 ft3 per year. The average thickness of the coal zone is about 9.0 feet and the average K value is 0.19 ft/day. The hydraulic gradient averages about 0.051 and the pit length is the same at about 2,197 feet long. Using the same methodology, the discharge from the coal zone is about 192 ft3 per day or about 70,080 ft3 per year. The average hydraulic conductivity for the underburden is 1.61 ft/day and the average hydraulic gradient is 0.056. The thickness of the underburden is about 6.0 feet. Discharge from the underburden into the pit using the same methodology would be about 1188 ft3 per day or about 433,620 ft3 per year. Based on these calculations, the annual discharge into the pit would be about 836,215 ft3 per year or an average Section 2.04.7 Page 6 March 2018 (TR -16)