GENERAL40594 - Laserfiche WebLink

Home Browse Search

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