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• The values of pH from the surface water runoff have been marginally influenced by mining. High pH <br />readings (>9.0) are annually reported at NPDES 001, 002 and less frequently at other sites. The high <br />values are attributed to algae growth during the summer and is addressed in our NPDES permit with the <br />WQCD. Total iron and manganese concentrations are above pre-mine conditions for some of the <br />operational monitoring resuks. Some of the higher operational concentrations of iron and manganese are <br />thought to be natural, while some are likety the resuh of mining. <br />4.8.1.8 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 fundion to provide secondary sediment control. Dozer <br />basins are designed to augment the fundion 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 censtructed as total excavation or 'dugout' structures. They are built either with no <br />embankment or, 'rf they contain a minimal embankment, they are built with a notched spillway that <br />originates al 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 <br />removal from dozer basins is conducted only when the continued use of a particular dozer basin is <br />deemed necessary. In many situations, dozer basins will either be removed by mechanical means or <br />simply allowed to fill up with sediment and abandoned until the area is permanently reclaimed. <br />• 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 Impacts and Restoration 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 Append'a W includes naratives for the pernrt renewal terms, <br />1987-1996, and operational groundwater data recorded during 1981-1996. <br />4.8.2.1 Use and Potential Uses of Groundwater in the Trapper Mine Area <br />The Trepper Mine has two water suppty wells, GD-1, (see Map M52 for location and Append'oc Q for well <br />permit) and GD-1(2), both located in the Twentymile Sandstone. GD-1 is a backup well to the main <br />water well GD-1(2)(see MR-115). The GD-1 and GD-1(2) groundwater wells are used as a suppty for the <br />office and shop. Water from these wells may also be used occasionally for dust suppression. Well <br />pernil #22140-F allows use of water from pit dewatering related to coal mining operations. <br />4-223 <br />• <br />PK-~} <br />MAY 1 3 199$ <br />