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velocity)(1/43,560 cu. ft. to ac. ft.)(365 days per year) = 72 ac.ft. per year. <br />The seepage velocity could be as high as 0.3 feet per day, depending upon the <br />sandstone permeability. Using a worst case of 0.3 feet/day, this results in a travel <br />of 1000 feet every 10 years. <br />It is strongly ;believed that spoil water seepage into the low-wall will not have any <br />significant impact on water quality, flow rates, well usage etc. due to four reasons: <br />1) As described in this section, the water quality of the spoil water will be at a <br />maximum 6% to 10% higher in TDS than the existing overburden water <br />quality, which is relatively poor. Therefore, regardless of the seepage rates <br />into the sandstone zones, the water quality will be very similar to what has <br />been cons 1J Lelltly 'pLed 111 file over bur den, ?'V?lth a TDlcl from 2VVV LV 35VV <br />ppm- <br />2) Due to the low seepage rates, the movement is very slow (1000 feet every 10 <br />years). <br />3) The sandstones above the Dakota coals have historically been poor in quality <br />and too low in flow rates to provide useful wells. Apparently, for this reason, <br />no known wells in the vicinity of the mine area have been completed in the <br />Dakota sandstone. It is very unlikely that any new wells will be completed in <br />the Dakota sandstone in the vicinity since the Burro Canyon Formation <br />provides significantly better water quality and flow and is located only 50 to <br />100 feet deeper than the Dakota sandstone. <br />4) The local wells are completed in the Burro Canyon Formation, which is below <br />the Dakota coals. Although this zone has significantly better quality water, <br />these sandstones are separated from the spoil by shale layers with very low <br />permeability, therefore these aquifers should not be affected by the spoil <br />water. <br />4. Impact of spoil water quality on surface water quality. <br />Spoil Water Quality <br />The chemistry of the water interacting with the spoil is described in the previous <br />section. In order to determine the impact of the spoil water quality on the surface <br />water, it is first necessary to predict the expected quality of the spoil leachate for <br />the New Horizon #1 mine. The principal impact from a quality perspective is that <br />irrigation water will seep rapidly through the spoil, increase in TDS and then <br />discharge through a spoil spring at the lower part of the mine area. Since the <br />pre-mine site did not have spoil springs, there is a potential impact to the quality of <br />the receiving waters. The spoil spring at the New Horizon #1 Mine enters Tuttle <br />Draw. Increases or decreases in pH have never been observed on the site. The <br />33