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extension of the Panel 6 bleeders and start room under the AVF area. In compliance with applicable regulations and in order to provide an objective basis for future subsidence projections and mine planning, TCC established and has surveyed on a regular basis, a network of three lines of subsidence monuments. The first two lines overlie and parallel the centerlines of Panels 1 and 3, while the third line of monuments is perpendicular to and extends across Panels 1 and 2. TCC's ongoing subsidence monitoring program has been supplemented by US Bureau of Mines (USBM) on-site research using Multiple Point Borehole Extensometers (MPBX) to measure the effects of subsidence on overlying strata. Data reflecting subsidence monitoring to date has been utilized to project potential future mining related subsidence. In order to evaluate potential subsidence effects or. the portion of the designated Fish Creek AVF overlying the Panel 5 and 6 extensions proposed under the revised mine plan, a Subsidence Effects Study Area has been delineated and is the focus of the reports presented in the technical revision. This area encompasses all projected areas of subsidence within the designa~ed Fish Creek AVF, as well as adjacent upstream and downstream areas. The area immediately to the east of the study area was previously disturbed by surface coal mining activities end has been effectively reclaimed. Both the study area and adjacent undisturbed and reclaimed lands are semi-arid rangeland used for seasonal livestock grazing. The study area, as shown on Drawing 1, Twentymile Coal Company Longwall Layout Plan, of Exhibit 7B, Fish Creek AVF/Stream Study Subsidence Predictions, includes a segment approximz.tely 3,000 long of the Fish Creek drainage. This area can be described as a low to moderate gradient perennial stream valley and is typical of small drainages in this area. Within this area, the Fish Creek floodplain is relatively flat with a distinct slope break at the valley margins. There are two general terrace levels within the floodplain. The main terrace, extending across the entire floodplain supports a sagebrush-meadow vegetation community. The lower terrace, which is limited to the margins of the current flow channel and abandoned channel segments, supports a more mesic vegetation community including rushes and sedge species. Fish Creek, within the study area, is a dynamic stream system with a constantly changing channel and general stream configuration. The dynamic nature of the stream system is evidenced by ongoing channel and bank erosion, a number of abandoned meander segments, and the new upper channel segment established by unusually high spring runoff in 1984. Bank and channel materials appear to be relatively fine grained alluvial/colluvial materials mixed with weathered sediments derived from slope wash and mass wasting. The flow regime is typical of small perennial drainages in the area, with high volume flows resulting from snowmelt runoff in late