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TCC reviewed historic records and personnel working at the mine to detemune the extent of•mine inflow into <br />the short-lived Middle Creek Mine. The information obtained from this process indicates that the inflow into <br />the mine was approximately 60 gallons per minute. This infomtation was obtained from a 1981 memorandum <br />from Mike Ludlow to J. Weston. In addition to the mine flow rates, there was additional information addressing <br />dewatering wells that had been installed aY the site. The memorandum indicates that the wells produced <br />anywhere from 0.5 to ] 20 gallons perm minute. Therefore, it appears that the maximum inflow into the mine in <br />this area was 60 gallons per minute, while the maximum pumping rate for a dewatering well tvas 120 gallons per <br />minute. The outline of the mine is shown on Map 5. As is noted, the mine only advanced approximately 900 feet <br />before the decision was made to abandon the project. <br />Based on the historic record, it appears the inflow came into the mine from the roof strata. The Middle Creek <br />~ mine was under a low overburden height of 300-650 feet and the overburden was highly fractured from the <br />previous surface mine operations at the highwall and its location in a fault zone. It was always the intent of the <br />Middle Creek mine plan to cross the fault located in Section 12, TSN, R86W where mining conditions on the west <br />side of that fault were anticipated to be much improved for both groundwater inflow and dip of coal slam. It is <br />known that this water came into the mine from the Wadge overburden by means of roof bolting drillholes, the <br />mine portals were aligned close to parallel with the local and regional faults, cleats, joints, and fractures. <br />Twentymile has drilled exploration holes (2) in Section 14, TSN, R86W with no evidence of significant <br />groundwater flows. Twentymile has also mined entries in the Wadge coal seam and currently maintains <br />ventilation through the East Mine District bleeder shafts in Section 14, TSN, R86W. Again there is no <br />groundwater water inflow in these mined out areas. Based on these observations and the experiences in the Wadge <br />coal seam for both the western and eastem mining districts, no major groundwater inflow is anticipated for the <br />development mining proposed for the Wadge Coal Seam in Sections 11 and 14, TSN, R86W. The proposed <br />development will be mining in areas of a minimum 700 feet of overburden which has not led to groundwater <br />inflow in comparable areas of the western and eastern mining districts. The 6 Right out-by section of the East <br />Mine District was developed in an area of less than 500 feet of overburden where groundwater inflow was <br />experienced. If groundwater inflow were to be encountered in the development mining of Sections 11 and 14, <br />TSN, R86W, Twentymile Coal would use local sumps driven into the floor of the gatemad section to collect the <br />water and pump it downdip to the Northeast Mains section whereby it would then be collected in the existing sump <br />and pumped through the present mine dewatering system. <br />NMD (Panels 17-Right through 25-Right, PR03-06 and PR06-07) <br />The general geology and hydrology of the remaining NMD segment has been described in the previous No. 4 and <br />No. 5 permit revisions. Exploration drilling in 2002 was used to establish mining limits related to steep grades <br />neaz the eastern flank of the Tow Creek Anticline. Combined results of the 1999 and 2002 surface 2D seismic <br />exploration further helped to define the eastern and northern regional fault trends which control the mining <br />boundary for the remaining NMD district longwall panels. Revised steep grade and fault limits are displayed on <br />the Surface Geology and Wadge Seam Structure maps (Maps 5 and 6). <br />WMD (Panels 12-Left through 17-Left, PR06-07) <br />The general geology and hydrology of the WMD is described under 2.04.5. The majority of the exploration <br />drilling for this area was completed in the 1980's (1981 through 1989), as indicated by the drillhole locations and <br />numbers shown on Map 6. Drilling information, along with more recent seismic work in the azea, have helped to <br />delineate stmctural controls and coal seam occurrence and characteristics for the NWMD, as shown on Maps 5 and <br />6. TCC does anticipate completing some supplemental fill-in drilling and seismic work for this azea, which will be <br />permitted separately under the CDRMS's Notice of Intent process. <br />• <br />PR06-07 2.04-16.3 11 /07/06 <br />