2009-02-10_PERMIT FILE - C1981022 (5)

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Seam - 2.04.7 therefore, typically found relatively high in the sequence. Since perched ground water occurrences are generally isolated and may be associated with any units in the sequence which meet the basic criteria previously noted, thickness, lateral extent, and aquifer characteristics vary significantly. With the numerous deeply incised drainage valleys, which are characteristic of the locally rugged topography, stratigraphic outcrops are common. The lateral continuity of most near-surface units is, therefore, limited by the bounding drainage valleys, the cross-bedding which is common within the Mesa Vence Formation, and other localized depositional and lithologic variations. Most of the bedrock stratigraphic units in the sequence have a relatively low permeability therefore, any limited infiltration percolating downward through unconsolidated surface materials and any low permeability layers stops at the first relatively impermeable unit, thus creating a perched water table. Regionally, average infiltration rates are estimated at approximately four percent of available precipitation (0.68 inches based on average annual precipitation of 16.94 inches) although infiltration in the mine and adjacent areas may be somewhat less due to the rugged terrain and rapid runoff. Outcrop exposures in flowing drainages which have differentially higher permeabilities may also serve as recharge points for the perched ground water system Any ground water which accumulates above the relatively impermeable units flows downgradient and laterally along contacts until it eitherencounters a zone of increased secondary permeability allowing downward percolation to another confining layer, or discharges where the confining layer outcrops at the ground surface. The rate and extent of downgradient and lateral ground water movement is dependent on the relative permeability (primary or secondary) of the unit(s) above the confining layer. Dependent on coal characteristics and outcrop exposures, several of the coal seams are burned (weathered and severely oxidized) from outcrop or sub-crop downdip for distances of up to several hundred feet. Burning of the coal seams creates voids and often results in subsidence and fracturing of the overlying units. Where this occurs, increased secondary permeability results in increased • percolation down through the stratigraphic sequence. Where the coal seam is relatively permeable due to natural joint and fracture patterns, it may act as a perched aquifer with underlying shale units limiting further downward migration. In some cases, coal seams that might be expected to cant' water due to their secondary permeability characteristics, do not, as a result of contained coal-bed methane gas and elevated gas pressures. Where the coal seam is relatively impermeable, sandstones in the overlying sequence may act as perched aquifers to transmit ground water. The D Coal Seam occurs relatively high in the stratigraphic sequence and outcrops or sub-crops in most of the small tributary drainages on the north side of the North Fork Valley. Because it is high in the sequence and has somewhat higher permeability (at least in the outcrop zone) when compared with the other associated units in the sequence, it receives recharge from both overlying unconsolidated materials and along outcrop/sub-crop exposures in the small drainages when they are flowing. Where perched ground water occurrences have been identified from surface seeps and springs or through exploration drilling or mining, the associated water-bearing units have typically been either sandstones or clastics within the stratigraphic sequence or those coal seams having a more pronounced cleat or fracture pattern. The lower limiting units are typically claystones or shales. In all cases, perched aquifer units are characterized by un-confined or semi-confined flow with no evidence of artesian pressures or flows. Exploration drilling and mining activities have encountered perched ground water below the E seam, in the D Coal Seam below its outcrop/sub-crop with Elk Creek, and in the clastic sequences overlying the C and B coal seams. Figure 2.04.7-F3, Water Level Hydrograph, D Coal Seam (Well SG3) illustrates the typical minor water level fluctuations for deeper perched ground water. • A summary of perched ground water occurrence in the mine area is provided by the report, Geologic Evaluation of Hydrologic Regime at Hawk's Nest Mne, Somerset Coal District (Bowman, 1979), included in Exhibit 2.04-E3, Geologic Information. This report is based on observations from four drillholes (WSGS, 6, 7, and 8) drilled from the Hawk's Nest Mine downward from the E coal seam through the Rollins sandstone. For the clastic sequences associated with the E, D, C and B coal PR04 2.04-24 Revised August 2000