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the original overburden. The hydraulic conductivity (K) of the spoil, as measured in <br />well GW-N27, is 40 ftlday, which is far greater than any measurement made in the <br />overburden. K values in the overburden generally range from 3.0 to 5.5 fUday. The <br />New Horizon #1 site has had continued seasonal irrigation from the North Lateral <br />ditch and a secondary ditch that flows immediately north of the New Horizon #1 <br />reclaimed azeas. Water from irrigation and some added precipitation has moved <br />through the spoil and saturated it until it discharges at the low point of the base of the <br />coal at the Spoil Spring and the Pond 001 discharge, Flow From this point fluctuates in <br />response to the use of irrigation. <br />Utilizing several resources, the following recharge data has been calculated: 2" from <br />rain and snowmelt, 13" from irrigation and 1" from underburden and overburden <br />recharge at the uphill spoil/overburden contact. Total long-term recharge is therefore <br />16" per year. These predictions are approximate but suffice in predicting the behavior <br />of the groundwater in the spoil. <br />A spoil porosity of 15% was determined for the overburden. <br />Spoil spring discharge (Spoil Spring Recharge) - (Seepage into Low Wall) <br />Seepage into the Low Wall is approximately 18% of the total recharge. Spoil Spring <br />Discharge is approximately 82% of the total rechazge. In the year 2000, the NPDES <br />001 discharge at the New Horizon #1 Mine showed an average flow of 271,000 <br />gallons per day or 320 acre-feet per year. The NPDES 001 discharge is for practical <br />purposes composed entirely of spoil water. <br />Overall, there should be no detrimental impacts from the mining operation on <br />groundwater flow and recharge rates. Ground water flow and rechazge in the spoil <br />material will be increased, since the overburden aquifers have historically had very <br />low flow rates and also poor quality. These aquifers have not been used for any wells <br />in the surrounding area and cannot be considered a water resource. The ground water <br />aquifers below the Dakota coals, in the Burro Canyon Formation, are used in <br />surrounding wells and have better water quality but will not be affected by the mining <br />and reclamation of this site. Shale layers below the mined coals prevent interaction <br />between the spoil and these aquifers, which get their recharge from long distances <br />away from the mine operation. <br />3) Potential impacts of replaced spoil on groundwater quality. The operation has <br />disrupted the overburden above the Dakota coals and has removed the Dakota coals, <br />therefore, these aze the only two stratigraphic zones that have been affected. As <br />described in the section on overbuden water quality, the pre-mine quality of the <br />overburden water is poor with TDS generally in the 3000 ppm range and some ions <br />exceeding limits for most water uses. The primary potential for impacts to ground <br />water quality occurs from increased water infiltration causing an accelerated oxidation <br />23 <br />