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• Probable Hydrologic Impacts <br />The following surface-water and ground-water impacts summaries are based on <br />CPiLRD's proposed decision document. During mining operations, the disturbed <br />areas experience a slight decrease in peak runoff because of flow into the <br />mine pit and storage in the sediment ponds. The total suspended solids (TSS) <br />levels observed at the surface water monitoring sites are significantly higher <br />than premising levels. The maximum pre-mining concentration at one site (S-5) <br />was 230 mg/1 whereas the maximum mining level was 20,900 mg/1. However, the <br />higher TSS levels may be natural (TSS concentration of 20,900 mg/1 would not <br />be unreasonable for thunderstorm runoff in an undisturbed ephemeral <br />watershed). The mining operation uses a series of diversions, sixteen <br />sediment ponds, and one inactive pit to control runoff and sediment generated <br />at the mine. <br />Samples of runoff from the Trapper minesite, collected before mining started <br />indicated that most surface flow exceeded the drinking water standards for <br />TDS, sulfate, iron, and manganese. Irrigation standards for iron, manganese, <br />lithium, molybdenum, and sodium adsorption ratio frequently were exceeded. <br />Runoff from areas disturbed by mining generally is similar .in quality to the <br />pre-mining samples, although iron and manganese concentrations were higher in <br />some samples, apparently in relation to the increases in suspended sediment. <br />Runoff from the disturbed area is still suitable for watering livestock and <br />wildlife, the only pre-mining uses. <br />Seepage of water into the active mine pits (10 to 70 gpm) will lower water <br />• levels up to 1 mile from the mine. Only two domestic wells (both more than <br />0.5 miles from the mine) could be affected. idater level de=lines in those <br />wells should not be large enough to affect their use, and would last only for <br />a few years. <br />The quality of water in the third White Sandstone could be degraded as a <br />result of leachate from replaced spoils material, and from utility and <br />municipal wastes that are disposed of in the mined-out pits. The applicant <br />estimates that as many as 15 existing wells could be affected if this quality <br />change occurs. <br />. -11- <br />