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Hydrologic analysis and information from the existing mine indicate that the undermining and consequent
<br />subsidence would directly impact only the Wadge and Wolf Creek coal units. Tlie Trout Creek Sandstone,
<br />located approximately 220 feet below the Wadge Coal Seam and 70 -100 feet below the Wolf Creek Coal Seam.,
<br />is separated fronn the mined coal seams by low - permeable shales, and will not be directly affected by the mining
<br />operations. The Twentymile Sandstone aquifer is located approximately 680 feet above the Wadge Coal Seam,
<br />and is separated from this upper coal seam by at least 600 feet of low- permeability shales. Linder normal
<br />conditions, the Twentymile Sandstone is not expected to be impacted by the proposed mining operations.
<br />Monitoring Well 006- 82 -48A, which was completed in the Twentymile Sandstone, was however dewatered
<br />when the well casing collapsed after being undermined by longwall operations. It appears that loss of the well
<br />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 Iess 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 gate -road, 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(c400 to X600 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, WMD, and WCR will be greater than 1,000 feet, lower unit .
<br />inflows are anticipated. Using the inflow rate of 0.027 gpm /acre developed for the SWMD, anticipated inflows
<br />to the EMD (excluding 6- Right) were projected to increase to 85 gpm due to the additional 400 acres to be
<br />affected, plus 65 gpm from the 6 -Right inflow, for a total of 150 gpm. These estimates were compared with
<br />measured mine discharges and water balance calculations and a good match was found. Approximately 6,500
<br />total acres had been mined by the end of 2002 (includes 2,050 acres — SWML), 2,850 acres — EMD, and 1,600
<br />acres — NMD). For the 2002 inflow study, flows included 20 gpm from the Northeast Mains, S5 gpin from the
<br />SWMD, 85 gpm from the EMD, measurements of 25 gpm from the NW -Mains raisebore, and 65 gpm from 6-
<br />Right (subsequently declined to about 10 gpm), for a total of 250 gpm.
<br />Based on historic groundwater inflow studies (2006 and 2009), measured mine inflows were approximately 55
<br />gpm for the SWMD and WMD, 32 to 65 gpm for the EMD, 63 to 95 gpm for the NMD, and roughly 10 gpm
<br />from other mine sources, for a total of approximately 155 to 290 gpm. Additional system inputs include
<br />approximately 5 gpm from the potable water well and approximately 165 acre -ft for operational use annually
<br />from Pond A. Projected maximinn annual water inputs total approximately630 acre -ft, although the
<br />TRI3 -83 2.05 -136 11/03/14
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