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1 <br /> cores,calcite is almost ubiquitous. Calcite serves two functions. First, it buffers <br /> the pH of the water, which tends to slow the oxidation of pyrite, reducing the <br /> production of acid. Second, it will neutralize the acid that is produced. The core <br /> samples that exhibited low paste pH's are surrounded by non-acid producing, <br /> calcite-bearing rocks. The water that contacts the low-paste pH materials will <br /> have first reacted with calcite, and therefore developed a pH-buffer capacity of <br /> its own. The groundwater monitoring data indicate that mixed overburden and <br /> interburden waters have near neutral pH's. Sample pH's less than 6 are associated <br /> only with the lower Dakota coal. Where the coal's permeability is high enough <br /> to produce about 5gpm daring sampling, the acid-producing reactions do not <br /> appear to be fast enough to maintain the pH of the water less than 5. Oxidation <br /> rates may increase due to the mining process, however, other conditions which <br /> inhibit acid production include the quantity of calcite present, and the reactivity <br /> of the pyrite. In conclusion, the paste-pH test, conducted under oxidizing <br /> conditions, indicates that only a small proportion of the overburden is likely to <br /> produce acid. Acid that is produced will quickly be neutralized. During the <br /> mining process, WFC tests the overburden. If and when acidic layers are <br /> encountered, they will be mixed with non-acidic layer to neutralize any acid <br /> forming effects. <br /> Potential impacts of replaced spoil on groundwater quality: The analysis of <br /> geochemical controls on groundwater quality suggests that the water chemistry <br /> and concentrations of most elements of concern are controlled by mineralogic <br /> reactions that will resist changes in water chemistry. Production of acid may <br /> occur in very local settings and is probably most prevalent in the coal which will <br /> be reined. Calculations indicate that neutralization of the acid will occur rapidly <br /> with mixing of water, or with movement of acidic water into calcite-bearing <br /> rocks. Also, the analysis conducted indicates that chemical changes are not likely <br /> to occur. <br /> Effects of mining on the local geomorphology: Impacts from mining on the local <br /> geomorphology will be long term, but appear to be of minimal significance. The <br /> reestablished reach of the drainage which will be mined will result in a shorter, <br /> slightly stepper stream channel. The potential for increased sediment loads in the <br /> drainage (once pond 007 is removed) should be offset by the stable banksides and <br /> the relatively small change in overall gradient. The increased runoff and <br /> consequent erosion potential on disturbed basins in the mining area due to the <br /> temporary loss of topsoil stricture should be of minimal significance. Contour <br /> ripping, mulching and revegetation have been demonstrated to minimize soil <br /> erosion and will be used to mitigate the increased runoff potential until the <br /> topsoil structure is developed. <br /> Effects of sediment ponds on channel characteristics and downstream users: <br /> Potential impacts of sediment pond 007 on downstream users will involve <br /> 22 <br />