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the backfill. <br />The hydraulic conductivity of the spoil, as measured in well GW-N27, 40 ft/day, which is far <br />greater that any measurement made in the overburden. K values in the overburden generally <br />range from 3.0 to 5.5 ft/day. GW-N27 is located in the old New Horizon #1 Mine northwest <br />of the release area. <br />Based on rainfall data for the site, soil information, and irrigation practices, recharge for the <br />release area has been determined to be 2" from rain and snowmelt, 13" from irrigation, and <br />1" from underburden recharge and overburden recharge at the uphill spoil/overburden contact. <br />Total long-term recharge is therefore 16" per year. The total long-term recharge in the <br />Dryland Pasture areas will be less than 16" since there is no irrigation in those areas. These <br />predications are approximate, but are accurate enough in predicting the behavior of the <br />groundwater in the spoil. <br />Water could build up against the southern mining limit and begin to surface as a spoil spring, <br />since the strata below the mined out area tilts gently to the southwest. As of June 2009, no <br />springs have developed anywhere in this area. Well GW-N40 is located immediately down dip <br />from the release areas, and will show any changes in ground water quality before any spring <br />developed on the surface. <br />Overall, there should be no detrimental impacts from the mining operation on groundwater <br />flow and recharge rates. It is definite that ground water flow and recharge in the spoil <br />material will be increased, since the overburden aquifers have historically had very low flow <br />rates and also poor quality. These aquifers have not been used for any wells in the <br />surrounding area and cannot considered a water resource. The ground water aquifers below <br />the Dakota coals, in the Burro Canyon Formation, are used in surrounding wells and have <br />better water quality but they will not be affected by the mining and reclamation of this site. <br />Shale layers below the mined coals prevent interaction between the spoil and these aquifers, <br />which get their recharge from long distances away from the mine operation. <br />C) Potential impacts of replaced spoil on groundwater quality <br />Since the operation has disturbed the overburden above the Dakota coal seam and has <br />removed the Dakota coal, these are the only two stratigraphic zones that have been affected <br />by this operation. The water quality of the overburden is usually poor with a TDS of over <br />3000 ppm. The primary potential for impacts to ground water quality occurs from increased <br />water infiltration causing an accelerated oxidation of pyrite in the spoil. Other salts may also <br />dissolve more readily in the highly permeable spoil. The minor amounts of sulfuric acid <br />produce can cause lower pH, which then results in higher rates of dissolution of other <br />chemical compounds in the spoil, resulting in higher TDS. Also, the spoil water can infiltrate <br />into the low wall strata of the Dakota Sandstone formation. <br />SL-12 CURRENT 11MAR11.wpd 41