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West Elk Mine <br />• S'umn Operations <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 />dischazge standazds. 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 l ONE and 11NE longwall panels (and after the <br />mine water pumping system in Sylvester Gulch is fully operational), the valve on the NW Surnp #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 large inflow emergency) until all mining activities in the western portion <br />• of West Elk Mine are completed and the B West Mains and Lone Pine Gulch portals aze <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 Laree Capaeity Sump 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 lazge, 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 nearly 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 />East Mains fault and east of the LONE Tailgate entries to provide temporary storage while <br />sufficient pumping and pipeline capacity was constructed to remove the water from the mine. <br />Even after developed the capability to pump the unexpected groundwater inflows to the surface, <br />these flows overwhelmed the hydraulic capacity of the treatment processes in the sedimentation <br />ponds. A complicating factor was that water pumped from the NE Tailgate sump caused <br />"treatability" problems (see previous Mine Water Treatment discussions). To assure the safety of its <br />workforce and to continue with mining operations, it was necessary for MCC to take decisive <br />1.05-184 Revised June 2005 PRIO; Rev. March 2006; Rev. May 1006 PRIO <br />