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until the coal has been removed. Following the short-term water level decline on the groundwater <br />system as a result of pumpage of groundwater inflow to the pit, a potential long-term impact to the <br />local groundwater flow is the period of time necessary for resaturation of the spoil material and <br />reestablishment of a flow gradient. Spoil material at the New Horizon 2 mine will be replaced using <br />techniques which will restore permeabilities of the material. Thus, the mining operation will not <br />diminish vertical or horizontal permeabilities but may increase these permeabilities. As a result, <br />there should be no significant impacts from the mining operation on groundwater flow and recharge <br />rates. The time period required for the spoil material to resaturate should be greatly reduced <br />because of the irrigation recharge as the mined area will be revegetated for an irrigation type of post <br />mining land use. <br />Containment of pit inflow and impacts on water guality. All runoff and pit pumpage from <br />disturbed areas will be routed through sedimentation pond 007. The pond is designed and <br />constructed to impound runoff and pit pumpage from areas disturbed by mining and provide <br />sufficient residence time to insure that the pond discharge water chemistry meets the effluent <br />requirements specified in the NPDES Permit. A review of the chemical and flow data indicates that <br />the potential for any discharge from Pond 007 to exceed receiving stream or federal standards is <br />minimal. Past history of mine operations at the Nucla Mine indicate very few exceedances of the <br />standards over the years of operations. As previously discussed, highest pit inflow is predicted to <br />occur in year 5 at approximately 5,600 cubic feet per day. To assess the impact of this inflow on <br />Calamity Draw and the San Miguel water quality, it was assumed that the entire flow was discharged <br />and that the TDS level for the overburden aquifer was representative of the chemical load. The <br />duration of the water quality impacts is relatively short term (5 years) and the significance of the <br />impact is negligible as TDS increases in the range of 0.08 to 1.5 percent are projected on the San <br />Miguel River and Calamity Draw, respectively. These increases in TDS will be additional <br />magnesium/sodium-sulfate type water which may result in a slight increase in salinity. These <br />projected changes in TDS levels will in no way affect the present and potential uses of the surface <br />water and are so small that they may not be measurable. <br />Impact of spoil water quality on the ground and surface water quality. The available data <br />indicate that a small proportion of the overburden may produce acid through the oxidation of pyrite. <br />Based on laboratory tests on overburden cores, calcite is almost ubiquitous. Calcite serves two <br />functions. First, it buffers the pH of the water, which overall tends to slow the oxidation of pyrite, <br />2.04.7-57