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-25- Two regionally significant aquifers are present in the general area; the Tow Creek Sandstone and the Trout Creek Sandstone. The Tow Creek Sandstone lies approximately 400 feet stratigraphically below the lowest coal seam to be mined. The outcrop of the Tow Creek Sandstone lies along the ridge tops of the mine adjacent area and is not disturbed by any mining activities. Therefore, no impacts to quality or quantity of this regional aquifer are expected to occur from mining at the Grassy Gap Mine. A well drilled by Rockcastle, near the northern permit boundary, bottomed near the top of the Tow Creek Sandstone. The well provides water for operational use. The static water level of the well is about 55 feet with flow of less than 30 gpm under sustained pumping. Water is described as coming from two low permeability sandy shales and three tight sandstones. The drawdown produced by this low rate of withdrawal is not expected to impact any water users outside the mine area. The Trout Creek Sandstone is stratigraphically above the mined section and is not present in the surface affected areas. The Trout Creek outcrops downstream from the Grassy Gap Mine. Grassy Creek could be a source of recharge for this aquifer and as a result, the aquifer could be affected by any impact of the mine on the water quality or quantity of Grassy Creek. Although it does not appear that the mining at Grassy Gap has had an appreciable impact on the surface water downstream to present, it is probable, based on available data, that a slight elevation of iron, manganese, and total dissolved solids may occur as a result of continued mining. No appreciable impacts to the downstream reaches of Grassy Creek are anticipated, due to tributary dilution effects. Further discussion can be found in the Surface Water Section V (C) of this document. Minimal amounts of ground water have been encountered in the mined section at Grassy Gap. Water collecting in the pits at Grassy Gap has never been an operational problem. The major mine sites are located along ridge tops and on the tops of hills. Because of the increased permeability of the reclaimed spoil, it is expected that ground water will collect in the reclaimed sites. This ground water will emanate as seeps along the slopes above Grassy Creek, even in pits where underburden dips away from the creek, due to the permeability of the undisturbed strata being less than the regraded spoil. It is expected that ground water seeping from the reclaimed sites will show elevated levels of iron (Fe), manganese (Mn), boron (B), and total dissolved solids (TDS). The overburden/interburden analyses submitted showed high levels of Fe but not above the suspect levels as recommended in Montana guidelines for overburden analysis. The underburden sample submitted showed elevated levels of B and Mn, with Fe above the suspect level. Elevated levels of these metals have also been noted in the surface water of Grassy Creek and in the alluvial wells.