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pumped to the surface <br />• The flows are measured at the discharges by totaling flow meer readings on the de~vatering sump pumps. The mean <br />flow rate did not exceed the mine inflow predictions from the Probable Hydrologic Consequences (PHC) evaluation. <br />Year four of the PHC prediction, which corresponds most closely with the 1991 mining year ndicated, combined <br />inflows of 850 to 1050 gpm for the No. 5 and No. 6 Mine operations. The 1991 average discharge was 454 gpm from <br />the No. 5 Mine sump, and 219 gpm from the 7 North Angle. The combined average discharge was 673 gpm. The <br />water produced in [he No. 6 Mine is pumped underground to the No. 5 Mine sump and is accounted for at the <br />discharge from that point. <br />The low discharge from the 7 North Angle sump during the first quarter and the decline at the end of 199] was due to <br />the failure of the pump. The discharge from this sump generally ranges from 250 to 450 gpm when [he pump is <br />working. <br />A mine inflow study performed for the No. 5 Mine in 1985 is presented in Exhibit 30, 1985 Mine Inflow Study. The <br />results of this study indicated that almost half of the inflow to the No. 5 Mine was coming from a fault zone in the 2 <br />West Main. A report on the fault zone inflows in the 2 West area is presented in Exhibit 33, a Review of the Geology <br />and Geohydrology of the 2 West area, RAG Empire No. 5 Mine. <br />Based upon the observed flows in the mine, it appears that a significant portion of the inflow is coming from <br />dewatering of the coal beds. Additional flows are coming from fault zones and from overlying and underlying zones. <br />Because water level declines are being observed in the overlying Middle Sandstone unit, it can be assumed that some <br />of the inflow to the mines is from this unit. However, it is not possible to determine whether the Middle Sandstone <br />water reaches the mine through existing faults, through general seepage or through subsidence induced fractures. As <br />indicated in Figure 21, in Section 2.04.7, Hydrology Information, the No. 5 Mine discharge has declined slightly since <br />• 1986 despite the advance of mining into the E seam associated with the No.6 Mine. <br />The water quality data for the fault zone inflow in the No. 5 Mine presented on Table 73, Ground Water Qualiry- <br />Fault Zone, indicates that the water is of similar chemistry to the Trout Creek Sandstone. In addition, mine inflow <br />study data (Exhibit 30) indicated that the inflow from the 2 West Main fault zone was about ]7° to 18° C while most <br />of the inflow had a temperature of ] 0° to 14° C. This indicates that some of the inflow may be coming from a deeper <br />formation. This indicates that much of the inflow to the fault may be derived from the Trout Creek Sandstone. <br />Upward flow from the Trout Creek to the E coal seam could also occur if fault zones are encountered. However, as <br />the base of the E coal seam in the vicinity of both Trout Creek Sandsbne wells is above the current potentiometric <br />level in these two wells, it is not likely that the fluctuations in potentiometric levels in the Trout Creek Sandstonewas <br />related to mine dewatering in the overlying E coal seam. Since the Trout Creek wells used for water supply purposes <br />the fluctuations were most likely due to pumping of the wells. <br />Since the water quality data seems to indicate some the inflow from the 2 West Main fault may be from underlying <br />formations and the water level data indicates that some of the inflow may be coming from overlying Middle <br />Sandstone, it is likely that both are at least partial sources of the inflow. <br />Predicted Inflows / t^ ~~ e:k 3 ~ <br />QrA,.~ k (Ground water inflow analyses were performed on the No. 5 Mine inflow, (RAG Empire, 1983). An additional <br />.3~ analysis was also performed on the 2 West Main inflow in the No. 5 Mine. The projected mine inflows were made <br />assuming an aggressive mining sequence in both mines with completion of all mains in the No. 5 mine in 1984. Less <br />aggressive mining sequence would produce smaller maximum inflows for the mines. This prediction was <br />subsequently altered to take into account longwall mining and the acquisition of additional land (RAG Empire, 1984). <br />• Three (3) types of analysis were performed to estimate future mine inflows. These were: 1) Theim's (]906) steady <br />state well formula, 2) Jacob & Lohman's (1952) formula for non-steady flow to a well of constant drawdown, 3) <br />McWhorter's (1981) methodology for calculating inflow to mines from a coal seam. Because RPG Empire has no <br />-T~ 3 3 <br />Midterm Response z.os-37 APPROVED MAR 15 2002 7i3oiol <br />