2012-01-06_PERMIT FILE - C1982057 (24)

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- are minimized. .The_designed, structures constructed and proposed at the -Seneca II-W and II-W South complex (sediment ponds, diversions, culverts, etc.), and the establishment of reclaimed areas within each mining area were determined to have no significant affect on surface water quantity (see Tab 17, PHC). All sediment ponds have been designed according to acceptable engineering criteria to contain the 10- year, 24-hour runoff volumes. SCC will ensure that each pond maintains this capacity by dewatering and/or excavating excessive sediment accumulated according to plans outlined in Tab 13 (Facilities). The bottom and sides of sediment ponds will be compacted to a sufficient density to prevent excessive leakage of pond water to the shallow aquifers. The diversions have been designed to pass the 10-year, 24-hour runoff volumes in accordance with approved engineering design criteria. Culverts and road drainageways will ensure that runoff originating within or outside each mining area will be controlled and adequately routed through to minimize changes-in surface water quantities. The postmining landscape is designed to protect the hydrologic balance by establishing slopes that generally will not exceed 5:1. Any highwall reductions will result in maximum slopes not to exceed 5:1. Reclaimed hillslopes established at the Seneca II-W mining area approximate the original premining contours. Topsoil material will exhibit infiltration rates generally similar to or slightly greater than premining soils. The proposed reclaimed areas will be disked and adequately reseeded in a timely manner to minimize overland flow rates and volumes. Surface Water Monitoring. SCC has developed a network of surface water monitoring sites at NPDES sediment pond discharge sites (005, 006, 009, 015, 016, and 017), and in the drainages of Sage Creek, Dry Creek, and Hubberson Gulch. Monitoring instrumentation, parameters, and monitoring frequencies are described in detail in Tab 15, Hydrologic Monitoring Program. Surface water monitoring sites will be maintained for the life of the mining operation or until such time as DMG may agree that they are no longer necessary. All surface water monitoring installations will be removed upon completion of the postmining phase of the Hydrologic Monitoring Program. All surface water data collected at each monitoring site in each future water year will be compiled and submitted to the DMG in the form of the Seneca II-W Annual Hydrology Report (AHR) by March 1 following the end of each water year. Quarterly NPDES discharge monitoring reports for each NPDES monitoring site are submitted to the Colorado Department of Health and the DMG. 0, 5 Revision 9/96