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The remoteness of the traverse stations and the extremely rough terrain <br /> will require helecopter transport to accomplish the control traverse survey. <br /> Subsidence Monitoring Net: <br /> Mine Subsidence Engineering Company proposes to install a network of <br /> surveying monuments over panels 301 and 302 to obtain subsidence data. This <br /> network will include three lines of monuments perpendicular to panel center- <br /> lines and a partical line of monuments over each panel centerline (Figure 3) . <br /> All subsidence monuments will be installed on 200-ft centers. This <br /> monument spacing is-well within the 0. 1h to 0. 15h (h = overburden depth) <br /> spacing recommended by the British National Coal Board for spacing of monu- <br /> ments. In addition, perpendicular subsidence lines will extend 1250 ft <br /> beyond the panel ribside to determine the angle of draw. <br /> • It should be noted that much of panel 301 and the ground surface to the <br /> northeast of panel 301 can not be instrumented because of the extremely steep <br /> topography and dense tree cover. Extensive clearing of timber in this area <br /> for subsidence monitoring and monument construction ;;ould probably not be <br /> acceptable to county or U.S. Forest Service officials. <br /> The proposed monument construction is similar to that utilized in a sub- <br /> sidence study at the York Canyon Mine, New Mexico. Subsidence monuments will <br /> be S-in diameter concrete pylons approximately 6 to 10 inches nigh . Construc- <br /> tion details are outlined in Appendix B along with a detailed drawing . <br /> The proposed monuments will minimize the impact to the environment both <br /> during construction and during the monitoring program. The small monument <br /> ten+ <br /> size will also minimize the time and amount of materials required for <br /> • construction in the remote location. The remoteness of the monitoring area <br />