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The Division has approved surface operations within 100 feet of Hay Gulch <br /> (entrance roads) and within ephemeral streams (tributaries to Hay Gulch) that <br /> have drainage areas greater than one square mile. The Division has determined <br /> that water quality standards will not be violated and environmental resources <br /> shall not be adversely affected due to these operations. (4.05.18(1)). <br /> K. Probable Hydrologic Consequences <br /> The ground water-bearing units having the greatest potential to be affected by <br /> mining at the King I and II Mines are the Hay Gulch alluvium, the Cliff <br /> House Sandstone, and the Menefee Formation. (GCC has stated that the Point <br /> Lookout Sandstone is well beyond the area of influence of the mines because it <br /> is approximately 250 feet stratigraphically below the workings. Monitoring <br /> data show no impacts from mining at the King I and II Mines.). <br /> Hay Gulch Alluvium - The Hay Gulch alluvium has been monitored in the <br /> Wiltse well, downstream from the west sediment pond at the King I Mine. <br /> GCC also monitors alluvial water quality in a well down-gradient of King II. <br /> Monitoring data indicate no significant mining impacts to this unit. <br /> Cliff House Sandstone -It appears unlikely that the King I and II Mines will fill <br /> with water after mining is finished. With the exception of one inflow event, <br /> the mine workings of the King I Mine have been dry. Both mines appear to <br /> underlie the updip, unsaturated portion of the Cliff House Sandstone. <br /> Impermeable shale and siltstone of the Menefee Formation underlie the <br /> workings, and also are unlikely inflow sources for the workings. If the King I <br /> Mine or King II Mine workings were to eventually fill with water, it seems <br /> unlikely the water could be transmitted from the workings to the Cliff House <br /> Sandstone through intergranular porosity in roof rock of the workings because <br /> the roof rock is composed of shale, which probably is impermeable to water. <br /> (Drill hole sample logs in Appendix 4 of the permit show the Upper Coal Seam <br /> of the Menefee Formation, the seam mined at the King I Mine, is bounded above <br /> and below by shale.) Subsidence fractures in the roof rock, however, could <br /> provide a conduit of flow for water from the workings to the overlying Cliff <br /> House. Therefore, if the workings fill with water, and subsidence fractures <br /> convey that water to the Cliff House Sandstone, then impacts could possibly <br /> occur to the water quality in the Cliff House Sandstone aquifer down-dip from <br /> the workings, if mine water is lower quality than ambient ground water. <br /> Significant flow from the workings to the Cliff House through subsidence <br /> fractures is unlikely, however, because head in the overlying (higher elevation) <br /> Cliff House would be greater than the head exerted by the mine water. <br /> Menefee Formation-Like the Cliff House Sandstone, mining impacts to the <br /> Menefee Formation are improbable because it is unlikely the workings of the <br /> King I and II Mines will fill with water. <br /> 17 <br />