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the mine area west of 2700 Road. It is estimated that full irrigation of the <br />reclaimed area will take place by year 2013. Although the pipe will be used to <br />carry the ditch flow until the end of its useful life in 30-50 years, its use is not <br />relevant to the prediction of irrigation recharge since this recharge will occur over <br />99% of the area even when the permanent pipe is in place. <br />From soil information, knowledge of the irrigation practices, discussions with <br />USGS, and the rainfall date for the site, the following recharge data has been <br />calculated: 2" from rain and snowmelt, 13" from irrigation and 1" from <br />underburden recharge and overburden recharge at the uphill spoil/overburden <br />contact. Total long-term recharge is therefore 16" per year. These predictions are <br />approximate but suffice in predicting the behavior of the groundwater in the spoil. <br />The- total affected area is roiighIv 769 arre-, The volume of the reclaim spoil to be <br />recharged below the 5580 spoil spring elevation equals 2,778 ac.ft. as determined <br />from D.T.M. modeling of the spoil area and the pit bottom. Spoil porosity of 15% <br />is determined for the overburden. This yields a pore volume of (0.15)(2778 ac.ft.) <br />= 416 ac.ft. <br />Worst Case Discharge <br />With a pore volume of 416 ac.ft. and assuming a total recharge of 16" per year <br />from all sources over the 768 acres of spoil, annual recharge equals (16/12)(768) <br />= 1024 ac.ft. per year after full irrigation in 2013. It should be noted that a portion <br />of the reclaimed area will be restored to dry land pasture and will therefore will <br />not contribute irrigation recharge, however, other areas will have a greater <br />recharge than 16" total, therefore, the average of 16" over the reclaimed area is <br />reasonable. From the year 2003 to 2013, the expected recharge should only be <br />10% of this amount, since irrigation will not be used on the majority of the area <br />and the fresh-placed spoil will be relatively dry. <br />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 <br />ft. wide seepage area)(0.10 ft. per day seepage velocity)(1/43,560 cu. ft. to ac. <br />ft.)(365 days per year) = 72 ac.ft. <br />Spoil Spring Discharge = (1024 ac.ft. recharge) - (72 ac.ft. seepage into low wall) <br />= 952 ac.ft. In the year 2000, the NPDES 001 discharge at the New Horizon #1 <br />Mine showed an average flow of 271,000 gallons per day or 320 acre-feet per <br />year. The NPDES 001 discharge is for practical purposes composed entirely of <br />spoil water. The New Horizon #2 spoil area is much bigger, therefore the <br />predicted flow of 1024 acre-feet per year for this area is a reasonable maximum <br />flow when compared to what is being observed at the #1 Mine. <br />Worst case time to spring discharge = (Pore Volume)/(Recharge Volume) <br />33