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purposes composed entirely of spoil water. The New Horizon #2 irrigated spoil area is bigger, <br />therefore the predicted flow of 490 acre-feet per year for this area is a reasonable maximum flow <br />when compared to what is being observed at the #1 Mine. <br />Realistic case time to spring discharge = (Pore Volume)/(Recharge Volume) <br />_ (416 ac.ft.) / (490 ac.ft.) = 0.8 years to actual spring flow after full irrigation is resumed on the <br />reclaimed land in 2013. This is the most realistic case of when the spoil spring will begin to flow. <br />In both the worst case and the more realistic discharge scenario, it may begin to discharge slightly <br />sooner since irrigation may begin on the eastern portion of the reclaimed area sooner than 2013, <br />thus contributing some discharge. Also, recharge from precipitation has not been factored in the <br />spoil prior to 2013. Assuming that the permanent pipe is installed in the year 2003 and has a life <br />of 30 years, the pipe would be replaced by the ditch in the year 2033. At this time recharge would <br />increase slightly since water from the ditch would provide additional infiltration, however, the <br />ditch area is so small (0.87 acres) compared to the area of the spoil (768 acres) and the area of <br />irrigation (422 acres), that the increase in infiltration would be negligible. Therefore, the worst case <br />prediction for flow in the spoil spring at the New Horizon #2 Mine is 952 acre feet per year, <br />while the most realistic flow for the spoil spring is 490 acre feet per year. This is a potential flow <br />of 1.31 cfs (worst case) and 0.68 cfs (realistic case). <br />In both cases, the flow is higher than the previously calculated spoil spring flow from when the New <br />Horizon #2 Mine covered a smaller area. That flow was 0.57 cfs. The greater flow at New Horizon <br />#2 Mine will lead to a lower impact on area water quality due to dilution. <br />Overall, there should be no detrimental impacts from the mining operation on groundwater flow <br />and recharge rates. It is definite that ground water flow and recharge in the spoil material will be <br />increased, since the overburden aquifers have historically had very low flow rates and also poor <br />quality. These aquifers have not been used for any wells in the surrounding area and cannot be <br />considered a water resource. The ground water aquifers below the Dakota coals, in the Burro <br />Canyon Formation, are used in surrounding wells and have better water quality but they will not be <br />affected by the mining and reclamation of this site. Shale layers below the mined coals prevent <br />interaction between the spoil and these aquifers, which get their recharge from long distances away <br />from the mine operation. <br />The locations of nine monitoring wells designed to evaluate water quality, groundwater flow <br />conditions, and saturated thickness in the backfilled pit in areas upgradient of the Trench Drain <br />are provided in Attachment 2.05.3(3)-4. Design information for the Trench Drain which serves <br />as a collection structure for spoil spring water is included in Attachment 2.05.3(3)-26. <br />July 2016 (TR -74) 2.05.6(3)-18 <br />