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resulted from mining activity in this area. Since the SWMD has been sealed, measurements of inflows and
<br />discharge indicate that this rate has declined to 15 to 20 gpm. This inflow will be discussed further in the mine
<br />water - balance discussion. The historic inflows can be used to estimate overall inflows to the mine for areas that
<br />• are not near the subcrop of the coal. Based upon the estimated inflow of 55 gpm and an affected mine area of
<br />2,064 acres the estimated inflow per unit area is 0.027 gpm/acre. An area is considered affected when the
<br />entries are mined with the continuous miners.
<br />Hydrologic analysis and information from the existing mine indicate that the undermining and consequent
<br />subsidence would directly impact only the Wadge Coal unit. The Trout Creek Sandstone, located approximately
<br />220 feet below the Wadge Coal Seam, is separated from the mined coal seam by low - permeable shales, and will
<br />not be impacted by the proposed mining operation. The Twentymile Sandstone aquifer is located approximately
<br />680 feet above the Wadge Coal Seam, and is separated from the mined coal by at least 600 feet of low -
<br />permeability shales. Under normal conditions, the Twentymile Sandstone is not expected to be impacted by the
<br />proposed mining operations. However, Monitoring Well 006- 82 -48A, which was completed in the Twentymile
<br />Sandstone, was dewatered when the well casing collapsed after being undermined by longwall operations. It
<br />appears that loss of the well resulted from anomalous subsidence fracturing which intercepted the well bore.
<br />During development of the EMD, only one zone of significant sustained inflow was encountered. While some
<br />faults encountered in high cover areas ( >600 feet) produced initial inflows estimated to be approximately 25
<br />gpm, flows subsequently declined to 5.5 gpm or less in under six months. Beginning in July 1997, however, in
<br />the Southeast Sub -main stub area, particularly near No. 6 Entry Crosscut 1, over 30 gpm was reportedly
<br />produced. Measurements on December 2, 1997 indicated that inflow to this area had declined to less than 10
<br />gpm. The water had a conductivity of approximately 4,000 umhos /cm. In late November 1997, significant
<br />inflows were also encountered in the 6 -Right gateroad, primarily through the roof beginning after Crosscut 25
<br />and continuing to approximately Crosscut 27. These inflows also had a conductivity of approximately 4,000
<br />umhos /cm. The high conductivity of this water indicates that it is derived from the Wadge Overburden near the
<br />old surface mine spoils. All other underlying units have a much lower conductivity. In the 1998 Mine Inflow
<br />Study, the average conductivity of the four sites sampled in the EMD (excluding the 6 Right inflow) was 2,380
<br />µmhos /cm.
<br />The areas of the high inflow, primarily in the 6 -Right area, are on the limb of an anticline with dips to the North -
<br />Northeast. No indication of faulting was observed in either area. The areas of highest inflow are also coincident
<br />with the location of the Foidel Creek liniment. Limited overburden thickness( <400 to <600 feet) and proximity
<br />(less than 3,000 feet) to the subcrop of the Wadge overburden and the spoils, appear to be contributing factors.
<br />The Southeast Submain stub area has a relatively shallow dip. The 6 -Right gateroad was driven in a direction of
<br />increasing dip. The area of highest inflow (near Crosscut 26) is at the intersection of Foidel Creek lineament
<br />and an area of increasing dip. Both of these geologic features can increase the fracturing of the rock, producing
<br />increased permeabilities. When the liniment was penetrated farther downdip in Panel 7- Right, no significant
<br />inflows were encountered. The inflows from 6 -Right appear to be approaching a seasonally variable steady
<br />state condition. The monthly average inflows ranged from 70 to 306 gpm in 1998 and 74 to 234 gpm in the first
<br />six months of 1999 (see Exhibit 51, Table E51 -2).
<br />Future Inflow Estimates Planned future mining will be in areas of high cover, most of which are greater than
<br />1,000 feet, with limited areas with 700 - 1,000 feet of cover. None of the planned future mining will be in areas
<br />of steep dip, and should not encounter major structural features. All future mining areas will be more than 3,000
<br />feet from the coal seam subcrop. Therefore, it is not anticipated that any new significant sustained flows will be
<br />encountered, and inflows are expected to be the same or lower than those measured per unit area in other parts
<br />of the mine. Since the average cover in the NMD and WMD will be greater than 1,000 feet, lower unit inflows
<br />are anticipated. Using the inflow rate of 0.027 gpm/acre developed for the SWMD, anticipated inflows to the
<br />EMD (excluding 6- Right) were projected to increase to 85 gpm due to the additional 400 acres to be affected,
<br />plus 65 gpm from the 6 -Right inflow, for a total of 150 gpm. These estimates were compared with measured
<br />mine discharges and water balance calculations and a good match was found. Approximately 6,500 total acres
<br />had been mined by the end of 2002 (includes 2,050 acres — SWMD, 2,850 acres — EMD, and 1,600 acres —
<br />NMD). For the 2002 inflow study, flows included 20 gpm from the Northeast Mains, 55 gpm from the SWMD,
<br />85 gpm from the EMD, measurements of 25 gpm from the NW -Mains raisebore, and 65 gpm from 6 -Right
<br />(subsequently declined to about 10 gpm), for a total of 250 gpm.
<br />PR09 -08 2.05 -136 04/22/09
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