Laserfiche WebLink
The flows are measured at the discharges by totaling flow -meter readings on the dewatering 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, indicated combined <br />inflows of 850 to 1,050 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 the No. 6 Mine was pumped underground to the No. 5 Mine sump and 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 1991 was due to <br />the failure of the pump. The discharge from this sump generally ranges from 250 to 450 gpm when the pump is <br />operating. <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, 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. It is not possible, however, 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 Quality - <br />Fault Zone, indicates that the water is of similar chemistry to the Trout Creek Sandstone. This indicates that much of <br />the inflow to the fault may be derived from the Trout Creek Sandstone. Upward flow from the Trout Creek to the E <br />Coal Seam could also occur if fault zones are encountered. The base of the E Coal Seam in the vicinity of both Trout <br />Creek Sandstone wells is, however, above the current potentiometric level in these two wells, so it is not likely that the <br />fluctuations in potentiometric levels in the Trout Creek Sandstone is related to mine dewatering in the overlying E <br />Coal Seam. <br />Predicted Inflows <br />Ground water inflow analyses were performed on the No. 5 Mine inflow, (RAG Empire, 1983). An additional <br />analysis was also performed on the 2 West Main inflow in the No. 5 Mine. Projections of 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. A <br />less 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 methods of analysis were used to estimate future mine inflows: 1) McWhorter's (1981) methodology for <br />calculating inflow to mines from a coal seam; 2) Jacob & Lohman's (1952) formula for non - steady flow to a well of <br />constant drawdown; and 3) Theim's (1906) steady -state well formula. Because MCM has no direct measurements of <br />the hydrologic properties of the coal, estimates have been made. Transmissivity (T) and storativity (S) values for <br />equivalent coal beds at the nearby Northern Coal Mine were obtained (refer to Table 74, Coal Bed Hydrology Data - <br />Northern Coal Company). Specific yield (Sy) was estimated to be 0.10. Although the coal thickness (b) can vary, an <br />average thickness of 12 feet was used. These values were then applied to the McWhorter method and used to try to <br />duplicate the past measured inflows in the No. 9 Mine. The values of (T) and (S) were varied until a reasonable match <br />to observe flows was obtained. The values of (T) and (S) that produced the best were 30 ft/day (225 gpd/ft.) and <br />0.002 respectively. It was found that the values for transmissivity and storativity used for the No. 9 mine produced a <br />reasonable fit to observed flows in the No. 5 mine as well. <br />TR14 -36 2.05 -37 Revised 03/20/14 <br />