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w..:.,rrl.n~ 1982 and was subsequently purchased by Cyprus Miner- als in 1485. Tn 19R9, Cyprus Coal det:ided to install a longwalt system on the west side of the main entries. The initial Inngwall mining district and first nine panels were re- treated from 2489 to 1946 at an average length of 3.000 m (1QOi10 ft) (Fig. 1). L,ongwail productivity increased it10`.6 during that time because the operation continually improved. And the face was widened from 195 to 256 m (640 to 840 ft) far the last faur panels. In 1492,TCC recognized that to remain competitive In the western coal market, a new mine plan was re- quired because the InngwaTt would move Crnm [he west- ern to the eastern portion of the reserve. The strategy was to prepare the operation for the expiration of a h[ghet priced contract and continue the longwalt mining m the eastern and northern sections of the reserve (Fig, 2) The Inngwall panel configuratians in the eastern area were not conducive to lower cash costs. This was due to the number of longwalt moves, steep grades and the re- yunement to not subside the ailurial valley floor (AVF) and several surface structures. T'he drive to reduce costs and remain competitive in the western coal market led to the development of a cam approach to redesigning the mine plan. The Cyprus Coal ColoradolSouthern Wyoming Business [Jm[ Technical Services Department began looking at the enure underground reserve in a different view,where boundaries were removed. The removal of boundaries and input from the engineering stall within Cyprus Coal led to the concept of 6.700 m (22,000 ft) longwalt panels in the eastern mining district tEMU) of the remaining reserves The key to the new mine plan was that the barriers of the steep grades, AVF, subsidence of surface struc- tures, ventilation and conveyance design, and all the un- dergroundsubsystems for longwalt mining in iongpanels had to be specially designed. Many of these issues re- quired new techniques and engineering that had got been previously attempted in longwalt mines. Design and layout The reserve boundary limits led to the concept that long panels could be physically laid nut for longwalt min- ing (Fig. 3). This was based on the ability to engineer through any barriers established by the steep grades, which decrease to the east. The reserve analysis to the east of the steep grades showed good thickness along with coat quality tar 4,875 m (16,0(10 Ft) before tapering into a parting agd fauhed area. TCC had struggled with grnund conditions through- out the western portion of the reserve. The roof rock there wus 0.3 to 0.6 m (i to 2 ft) of weak shale.and would tat! in on continuous miner development. Tl was deteo- mined that certain entries and x-cuts developed in the western bh:cders at a 45° angle off the principal horizon• tat stress held up the mnf rock. Therefore, when laying out the panels in the EMD, an orientation of. 45` oft the principal horizontal stress was used to maximize recov- ery in the reserve. Another advantagt of the proposed layout was the use of existing main entries for pane! gateroads This re- duced contiguous miner and capital costs. The panel layout was first proposed and reviewed by engineering and aperations. Obstacles were then listed and timelines established for engineering and permitting. The obstacles included surface features for subsidence. coat leases, ventilation and escapeways, conveyance and equipment design life. A gantt chart was established listing alt the criteria for the startup of the first longwaU panel. 't'ile criteria were then assigned responsibility for completion andJnr management of the tasks This step was critical because it established all of the key dates far the completion of major issues, such as permitting, mine plan sequencing. engineering subsystems and equipment design. It was realized early nn that many of the issues or criteria were new eon• cepts that required additional time and analysis. Surface features The key surface features of structures that were going to be sub sided included a set of two AVP ar eas, three major power lines, th railroad spur to the mine, a county read and a few smaII structures (Pig 4). astern mining district at Twentymila Coal. Cyprus Twentymiie Coal's surface feeilitiez near Oak Creek, CO..