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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 <br />discharged and that the TDS level for the overburden aquifer was representative of the chemical <br />load. The duration of the water quality impacts is relatively short term (5 years) and the <br />significance of the impact is negligible as TDS increases in the range of 0.08 to 1.5 percent are <br />projected on the San Miguel River and Calamity Draw, respectively. These increases in TDS will <br />be additional magnesium/sodium-sulfate type waterwhich may result in a slight increase in salinity. <br />These projected changes in TDS levels will in no way affect the present and potential uses of the <br />surface 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 tyres, 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 />slowing the production of acid. Second, it will neutralize the acid that is produced. The core <br />samples that exhibited low paste pH's are surrounded bynon-acid producing, calcite-bearing rocks. <br />The waterthat contacts the low-paste pH materials will have first reacted with calcite, and therefore <br />developed a pH-buffer capacity of its own. The groundwater monitoring data indicate that mixed <br />overburden and interburden waters have near neutral pH's. Sample pH's less than 6 are <br />associated only with the lower Dakota coal. Where the coal's permeability is high enough to <br />produce about 5 gpm during sampling, the acid-producing reactions do not appear to be fast <br />enough to maintain the pH of the water less than 5. Oxidation rates may increase because of the <br />mining process. However, the supply of oxidation is only one of the constraints on the production <br />of acid. Other constraints are imposed by the quantity of calcite present, and the reactivity of the <br />pyrite. The paste-pH test, conducted under oxidizing conditions, indicates that a very small <br />proportion of the overburden is likely to produce acid. The acid that is produced will be quickly <br />neutralized. During the mining process, WFC will test the overburden and if acidic layers are <br />encountered, they will be mixed with non-acidic layers to neutralize any acid forming effects. <br />(REVISED 25 Jul 2002) 2.04.7-48 <br />