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West Elk Mine <br />• Since the Box Canyon longwall panels aze yet to be mined, the specifics about how the water will <br />flow and/or be pumped to and stored in them is not yet know. However, based on the mining layout <br />and projected mining plan, the available storage volume will progressively increase as mining of <br />panels continues to the south (and up-dip). The estimated storage capacity within the entire Box <br />Canyon longwall panels is in excess of 325 million gallons or more than 1,000 acre-feet. This <br />estimate is based on the volume created by removing a 12-foot thickness of coal in the longwall <br />panels plus the associated development mining. Additionally, a porosity of 20 percent was applied <br />to the volume within the panels to account for caving of the immediate overburden. <br />Sum~Onerations <br />As discussed previously and below, MCC has been successful in managing large volumes of <br />sediment-laden mine water in the NW Panels sealed sump. Good quality water has consistently <br />emerged from the NW Panels sealed sump at the northern-most Lone Pine Gulch ventilation seals <br />(on the 7NW longwall panel), and has been pumped from the mine in compliance with NPDES <br />discharge standards. As such, this sealed sump is a proven and crucial element of MCC's mine <br />water management system. <br />With the majority of MCC's future mining being to the east and south, similarly the primary use of <br />the future sealed sumps (i.e., the NE and Box Canyon Panels sealed sumps) will shift to the east. <br />Prior to the completion of the ventilation seals on the lONE and 11NE longwall panels (and after the <br />mine water pumping system in Sylvester Gulch is fully operational), the valve on the NW Sump #1 <br />. horizontal drill hole will be opened, tying the two sealed sumps together. At that time, the water <br />level within the NW Panels sealed sump at the Lone Pine Gulch seals will likely drop below the <br />level necessary to flow from the seals for pumping from the mine to Lone Pine Gulch. The primary <br />mine water storage and handling will then be the NE Panels sealed sump and the Sylvester Gulch <br />mine dewatering facility. This sealed sump and pumping facility will likely remain as a significant <br />component of the mine water management system until the Box Canyon sealed sump is operational. <br />The NW Panels sealed sump, along with the Lone Pine Gulch discharge point will remain available <br />for use (particulazly for a lazge inflow emergency) until all mining activities in the western portion <br />of West Ells Mine aze completed and the B West Mains and Lone Pine Gulch portals are <br />permanently sealed. Even then, the NW Panels sealed sump will continue its benefit to the system <br />through the NW Sump # 1 horizontal drill hole connection to the NE Panels sealed sump. <br />Basis for Large Caoacitv Sumu Use <br />Historically, F and B Seam combined inflows have been approximately 12 gpm on an average <br />annual basis. On the few occasions that large, discrete inflows were experienced (inflows ranging <br />from 50 to 100 gpm), these inflows dropped off to low levels (<5 gpm) within a matter of days and <br />would eventually dry. In 1996, by contrast, due primarily to inflows through the BEM fault, the <br />average annual groundwater inflow increased to neazly 200 gpm, with a peak day inflow rate of <br />2,500 gpm, and peak monthly inflow rate of approximately 650 gpm (see previous section entitled <br />Mine Inflows). <br />. Initially, it was infeasible to pump the inflows to the surface as quickly as water was entering the <br />mine. Therefore, an operational sump (NE Tailgate sump) was constructed to the north of the B <br />2.05-144 RevisedNwem6er 1004 PRIG <br />