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• Mining has marginally influenced the values of pH from the surface water runoff. High pH readings (>9.0) <br />are annually reported at NPDES 001, 002 and less frequently at other sites. The high values are <br />attributed to algae growth during the summer and is addressed in our NPDES permit with the WQCD. <br />Total iron and manganese concentrations are above pre-mine conditions for some of the operational <br />monitoring results. Some of the higher operational concentrations of iron and manganese are thought to <br />be natural, while some are likely the result of mining. <br />4.8.1.6 Not Assigned <br />4.8.1.7 Dozer Basins <br />Dozer basins are small sediment control structures constructed only in disturbed portions of the mine <br />permit area. They are temporary structures and function to provide secondary sediment control. Dozer <br />basins are designed to augment the function of designed sedimentation ponds, which provide primary <br />sediment control, to achieve and maintain all applicable water quality standards. Dozer basin density will <br />not exceed an average of one structure per ten acres of disturbed land. <br />Dozer basins are constructed as total excavation or "dugout" structures. They are built either with no <br />embankment or, if they contain a minimal embankment, they are built with a notched spillway that <br />originates at ground level. Maintenance requirements are minimal, consisting of periodic removal of <br />accumulated sediment, insuring that spillways are functional, and, in certain applicable situations, using <br />rock structures at inlets or outlets to discourage excessive headcutting or downcutting. Sediment removal <br />from dozer basins is conducted only when the continued use of a particular dozer basin is deemed <br />necessary. In many situations, dozer basins will either be removed by mechanical means or simply <br />allowed to fill up with sediment and abandoned until the area is permanently reclaimed. <br />is Figure 4.8-7 presents a typical dozer basin design. Dozer basins at Trapper Mine will typically be smaller <br />than approximately one acre-foot in volume. Locations of dozer basins are given in the "Livestock Ponds <br />and Dozer Basins" map which is found in the Trapper Mine annual report document. As such, dozer basin <br />locations are updated on an annual basis on this annual report map. <br />4.8.2 Imoacts and Res :)ration of Groundwater <br />This section consists of use of ground water, groundwater inflow to the pits, aquifer restoration, opera- <br />tional and postmine groundwater quality. A discussion of postmine recharge is also presented in this <br />section. The information presented in Appendix W includes narratives for the permit renewal terms, 1987- <br />present, and operational groundwater data recorded during 1981-present. <br />Ar?CL/ e _" c? <br />4.8.2.1 Use and Potential Uses of Groundwater in the Trapper Mine Area <br />The Trapper Mine has two water supply wells, GD-1, (see Map M52 for location and Appendix Q for well <br />permit) and GD-1(2), both located in the Twentymile Sandstone. GD-1 is a backup well to the main water <br />well GD-1(2)(see MR-1 ^.15). The GD-1 and GD-1(2) groundwater wells are used as a supply for the office <br />and shop. Water from these wells may also be used occasionally for dust suppression. Well permit <br />#22140-F allows use of water from pit dewatering related to coal mining operations. <br />L J <br />4-223 <br />7-1