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most panel first, then proceeds to the next panel to the west. Retreat longwall mining in the first panel (completely removing the coal in the panel with the longwall, allowing the roof to cave and settle, subsiding (or lowering) the ground surface above) was begun in late July 1992. Presently, MCC is retreat mining the third longwall panel from the east. Approximately ten percent (southeast segment) of the fourth longwall panel, and even less of one Jumbo Mountain panel in Section ]9 T13S, R90W, are beneath U.S.F. S. surface lands. Retreat mining of the fourth longwall panel will begin approximately February 1994, and will enter beneath U.S.F.S. surface a few months later. Development and retreat mining will continue to the west beneath private surface and aze projected to be completed approximately July 1998 (including the proposed Jumbo Mountain panels). Development of longwall panels in the B seam planned to the south and east of the current permit area could begin as early as 1996. Mining in the E seam is also planned to occur in these areas. Specific information will be available for your review and approval in future revision applications. Subsidence is the lowering of the above ground surface after retreat mining occurs and is greatest directly above the mined areas. The amount of subsidence (or lowering) is less with lower mining heights and with greater amounts of overburden (all soil and rock material above the mined coal). Generally, no apparent effects of subsidence are anticipated in areas where the overburden above the F seam is 300 feet or greater and where the overburden above the B seam is 375 feet or greater. More than 80 percent of the overburden above these seams that have been or are planned to be mined exceeds these amounts. On the basis of more than four years of subsidence monitoring data, MCC's 1989 study projected that approximately 2.25 feet of subsidence (or lowering of the ground surface above) would occur as a result of retreat mining the F seam. Approximately 8.0 feet of additional subsidence was projected after retreat mining the B seam. Total subsidence was thus projected to be 10.2 feet in areas where both the B and F seams were mined. Actual subsidence to date has been measured to be approximately two feet for the F seam and six feet for B seam, for a total of eight feet, which is less than projected. This study and MCC's approved subsidence monitoring control program are contained within MCC's approved permit document and are available for review in your file copy at the U.S.F.S. Supervisor's Office in Delta, Colorado. Please feel free to call me or Phil Schmidt, Engineering Manager, should you have questions. Sincerely, ~-~~ ~~ Kathleen G. Welt, Environmental Supervisor Attachments cc: Gene DiClaudio, MCC fPhil Schmidt, MCC ,/ Christine Johnston, DMG, OMLR Henry Austin, OSM