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-$30 million coal prep plant has been constructed and began operation. The source <br />followed appropriate permitting requirements for this modification. <br />-Missile doors have been replaced with chain curtains. This change has not resulted in <br />an increase in emissions from this point. Run of mine ('ROM') stockpile missiles were <br />operating at the time of the inspection and no visible emissions were observed. <br />Longwall mining began at this facility in 1991 (replaced room and pillar mining). The longwall <br />panels that are currently being worked are approximately 1,000' wide and 14,000' long. The <br />current seam being mined is approximately 8.5-13 feet thick. The longwall removes a three (3) <br />foot cut of material with each pass as it travels along the 1,000' wide cut, and can complete 20 <br />passes per day. The current panels take approximately one year to complete before needing to <br />completely dismantle and move the longwall. As the wall slowly advances, large hydraulic panels <br />hold the ceiling up above the mining face. As the longwall completes a pass and panels progress <br />forward, the remaining material collapses behind the active face. As material collapses, the <br />ground and rock above are usually fractured at a thickness approximately 10 times that of the <br />area to be filled. This fracturing results in additional release of methane into the mine, especially <br />considering that the strata directly above a coal seam often contains a large amount of trapped <br />gas. The collapsed materials consisting of rock and coal residue are together referred to as 'gob'. <br />Along with the longwall, mine sections performing 'development work' also produce coal from the <br />mine as they prepare the roads and access routes to new longwall panels. Development work <br />uses a method called continuous mining, and leaves large pillars behind for structural support <br />between roadways. MCC's conveyor system removing coal from the mine has a capacity of <br />3,000 tph. The longwall and mine development operations are capable of meeting that rate at <br />best operating conditions, but likely do not operate near that rate on a continuous basis as the <br />breaker plant has a 1,650 tph maximum operational rate. <br />For the safety of the workers, the atmosphere in the mine must be carefully maintained such that <br />methane and coal dust are not present in explosive concentrations. In all finished areas of the <br />mine, inert 'rock dust' is used to coat walls, floor, and ceiling, to provide a non-flammable barrier <br />between active work areas/equipment and the flammable coal dust. Rock dust is applied wet <br />such that it forms an inert cake once dried. The rock dust at the MCC mine is pulverized <br />limestone, and is stored aboveground in one silo, which has a pipe that feeds directly into the <br />underground mine. The silo has been present and operated at this mine for many years, but does <br />not appear to have been included in the facility -wide permit or been reported to the Division on an <br />Air Pollutant Emission Notice (APEN). Opacity was observed during silo loading at the <br />inspection. See 'Rock Dust Silo' discussion section on page 5 of this report for details. <br />To prevent the buildup of methane gas to explosive concentrations (5-15% in air is extremely <br />explosive), MSHA requires that methane within the mine is kept below 1 %. This is accomplished <br />using several methods: <br />Methane Drainage Wells (MDWs) are drilled from the surface, through 600-1,200 feet <br />of cover, into the strata directly above the coal seam just in front of the longwall. The <br />strata directly above the coal seam contains high amounts of gas. As this strata is <br />high porosity, low permeability, MDWs at this facility are not used to pre -drain the <br />gas, but instead control gas levels after the gob collapses and the strata is fractured. <br />After drilling to within 20 feet above the coal seam, casing is added to the well, and a <br />'floating' slotted pipe is inserted. Portable pumps, powered originally by propane but <br />fired by mine gas after startup, are attached to the well and release almost all <br />removed mine gas uncontrolled (some gas is controlled through combustion in the <br />pump - See Picture #1). Once the longwall passes under the well and the gob <br />collapses, the floating pipe is able to drop with the gob and will continue to pull <br />methane from that area of the mine. MCC reported that their MDWs can pull 600- <br />1000 cfm of gas, which varies in methane concentration. For most current E seam <br />panels, MCC will drill three (3) wells at the start of a new panel, and then drill the <br />remaining MDWs with an approximately 700 foot spacing down the longwall face. <br />2012 Air Pollution Inspection <br />0510015-INSP-2012.docx Page 2 of 30 <br />