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SaYiar - 2.04.7 therefore, typically found relatively high in the sequence. Since perched ground water «currences are generally isolated and may be ass«iated with any units in the sequence which meet the bazic 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 Gthologic variatioru. Most of the bedr«k stratigraphic uniu in the sequence have a relatively low permeabihty 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 o[ 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 az recharge points for the perched ground water system Any ground water which accumulates above the relatively impemreable units flows downgradient and laterally along contacu until it eirherencounters 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 u dependent on the relative permeability (primary or secondary of the unit(s) above the confinng 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 searru creates voids and often results in subsidence and fracnrring of the overlying units. Where this «curs, 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, rt may act az a perched aquifer with underlying shale amts limiting further downward migration. In some cazes, coal seams that might be expected to carry water due to their secondary permeability characteristics, do not, az a result of contained coal-bed methane gas and elevated gas pressures. Where the coal seam is relatively impermeable, sandstones in the overlying sequence mayact az perched aquifers to transmit ground water. The D Coal Seam «curs 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 leazt in the outcrop zone) when compared with the other ass«iated units in the sequence, it receives recharge from both overlying unconsolidated macerials and along outcrop/sub-crop exposures in the small drainages when they are Rowing. Where perched ground water occurrences have been identified from surface seeps and springs or through exploration drilling or minhtg, the ass«iated water-bearing units have typically been either sandstones or clastics within the stratigraphic sequence or those coal seattu 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 mirrirrg activiues 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 cLutic sequences overlying the C and B coal seams. Figure 2.04.7-F3, Water Level Hytirograph, D Coal Seam (Well SG3) illustrates the typical minor water level fluctuations for deeper perched ground water. • A summary of perched ground water «currence in the mine area u provided by the report, Geologic Evaluation of Hytlrologrc Regime at Hawk's Nest Mme, Somerset Coal District (Bowman, 1979), included in Exhibit 2.04E3, 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 ass«iated with the E, D, C and B coal PR04 2.04-24 Revised August 2000