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• Spoil spring discharge = (Spoil Spring Recharge) - (Seepage into Low Wall) <br />Seepage into Low Wall = (10 ft. thick permeable sandstone bed in low wall)(8500 ft. wide seepage <br />area)(0.10 ft. per day seepage velocity)(1/43,560 cu. ft. to ac. ft.)(365 days per year) = 72 ac.ft. <br />Spoil Spring Discharge = (557 ac.ft. recharge) - (72 ac.ft. seepage into low wall) = 485 ac.ft. In the <br />year2000,theNPDES001 discharge at the New Horizon#1 Mine showed anaverageflowof271,000 <br />gallons per day or 320 acre-feet per year. The NPDES 001 discharge is for practical purposes <br />composed entirely of spoil water. The New Horizon #2 spoil area is much bigger, therefore the <br />predicted flow of 485 acre-feet per year for this area is reasonable compared to what is being <br />observed at the #1 Mine. <br />Time to spring discharge = (Pore Volume)/(Recharge Volume) <br />_ (227 ac.ft.) / (485 ac.ft.) = 0.5 years to actual spring flow after full irrigation is resumed on the <br />reclaimed land in 2013. <br />It may begin to discharge slightly sooner since irrigation may begin on the eastern portion of the <br />reclaimed area sooner than 2013, thus contributing some discharge. Also, recharge from precipitation <br />• has not been factored in the spoil prior to 2013. Assuming that the permanent pipe is installed in the <br />year 2003 and has a life of 30 years, the pipe would be replaced by the ditch in the year 2033. At this <br />time recharge would increase slightly since water from the ditch would provide additional infiltration, <br />however, the ditch area is so small (0.87 acres) compared to the area of the spoil (418 acres), that the <br />increase in infiltration would be negligible. Water will be seeping from irrigation on the vast majority <br />of the reclaimed spoil regardless of the ditch being in soil or a pipeline. Therefore, the long term <br />predictioh for flow in the spoil spring at the New Horizon #2 Mine is 485 acre feet per year. <br />Overall, there should be no detrimental impacts from the mining operation on groundwater flow and <br />recharge rates. Ii is definite thal ground water flow and recharge in the spoil material will be increased, <br />since the overburden aquifers have historically had very low flow rates and also poor quality. These <br />aquifers have not been used for any wells in the surrounding area and cannot be considered a water <br />resource. The ground wateraquifers below the Dakota coals, in the Burro Canyon Formation, are used <br />in surrounding wells and have better water quality but they will not be affected by the mining and <br />reclamation of this site. Shale layers below the mined coals prevent interaction between the spoil and <br />these aquifers, which get their recharge from long distances away from the mine operation. <br />• (Revised 6/01) 2.05.6(3) - 22 <br />