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based on the potentiometric elevation of the presumed highest source of mine inflow. The portals aze approximately 75 ft. than higher than 7350 ft.; therefore, the mine will not discharge water to the ground surface from the portals. The regional aquifers, Tow Creek and Trout Creek sandstones, will not be affected by the Apex No. 2 Mine; the Tow Creek is a few hundred feet below the mine workings, and the Twentymile is several hundred feet higher in the stratigraphic section. The only bedrock aquifer that could be affected by the Apex Mine is a sandstone bed in the basal Williams Fork aquifer. The basal Williams Fork aquifer was defined by Robson and Stewart (1990, USGS Water-Resources Investigations Report 90-4020, page 54). Domestic wells yielding less than 10 gpm have been developed in this aquifer near the Apex Mine, but no wells have been completed in the specific sandstone bed that could potentially be affected by the Apex No. 2 Mine. The basal Williams Fork sandstone bed is approximately 40 feet thick and is about 90 feet above the lower Pinnacle coats. The sandstone bed probably is low porosity based on the absence of a density anomaly on the density log. Drilling depth from the ground surface to this sandstone bed would be at least 450 feet at the northeast end of the Apex No. 2's workings. At that location, the workings extend across a fault, a few feet into the sandstone bed. The fault has juxataposed the sandstone bed against the Pinnacle coal at that location. A plume of mine water may form in the basal Williams Fork sandstone bed down-gradient from the none's workings as described on pages 190.3 and 190.4 of the permit application. The plume could possibly occupy an 8-acre azea. The plume probably would take a few hundred years to develop owing to the low permeability of the sandstone. The water quality of the plume would probably be no worse than the ambient quality of ground water in the sandstone. The plume would constitute a minor hydrologic impact, and would not result in material damage. The mine does not dischazge to alluvial ground water. Ground water in Trout Creek alluvium has commonly exceeded iron and manganese table values for agricultural use, but the exceedances occur both in the upstream and the downstream monitoring wells, thus indicating mining is not the cause. Other pazameters have not been exceeded in the downstream alluvial well. Colorado's Basic Standards for Ground Water aze set forth in Section 41.S.C.6 of the regulations of the Colorado Water Quality Control Commission. The standard that is applicable at the Apex Mine is the less restrictive of either the 1994 ambient quality, or the table values listed in the regulation. In either case, the Apex Mine complies. Bedrock ground water can be expected to have only the minor impact described above. Alluvial ground water has shown no impacts, also as described above. Apex No. 2 Mine Page 12 January 24, 2003 Phases I, II, and III Bond Release