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1994 Subsidence Report Page 6 approximately 2100 feet of overburden. The monitoring point established at this site was surveyed December 8, 1993 at elevation 8812.23. This station was not surveyed in 1994 because mining was not advanced in the 1st West Mains so it is not in the angle of draw of the active mine workings. Station 98: Station 98 was newly established in 1993 and is located at the Grosse-Rhode bunkhouse identified as structure 34 on permit No. C-81-038; Map No. 9-7. Advance mining of Panel Y in the vicinity of this location occur=ed during December 1993 and retreat m;n;ng occurred in early 1994. This station overlies approximately 2050 feet of overburden. The monitoring point established at this site was surveyed December 8, 1993 at elevation 8757.50. The October 1994 survey indicates an minor elevation gain of 0.08 feet compared to the December 8, 1993 survey. Station 99: Station 99 is located at the Northwest corner of Section 15. The elevation of Station 99 was defined by satellite survey in July 1992 at 7921.9 feet. Station 99 was re-surveyed in 3anuary 1994 and showed a 0.96 foot elevation loss. It is not apparent whether this elevation change is associated with subsidence or the difference in survey techniques. Cover in • the vicinity of Station 95 is approximately 1200 feet. No mining occurred in the vicinity of station 99 during 1994. Pitkin Mesa Pipeline Subsidence Monitorin4 Sum~rV Seven subsidence monitoring stations were established at locations along the Pitkin Mesa Pipeline which overlies Panel C. Panel C development ccsrmenced in October with twenty four crosscuts completed by January 1, 1993. Panel C was mined utilizing a partial extraction design intended to preclude the development of subsidence in order to protect the pipeline. The subsidence monitoring stations along the pipeline are depicted on Map No. 2-SA, Permit No. C-81-038. The stations were surveyed twice in 1994; May 18 and September 22. Results of the surveys are appended to this report. The 1994 survey established new minitmnn elevations for survey points PL~fl, PI#3, Pl~k4, & Pl~k7. PL#1 was 0.01 feet; PIa~3 was 0.05 feet; PI~f9 was 0.08 and PI~7 was 0.14 feet lower than their respective historic minimun elevations. Surveys will continue approximately semi-annually until stability is docimiented. Visual Monitoring 1994 Visual subsidence monitoring is acca~lished by periodic "walkovers" of recently mined areas within the present permit area. Walkovers are generally done in conjunction with survey monitoring due to the seasonal accessibility of the • area. Visual mronitoring is concentrated over areas of retreat mining with particular emphasis on areas mined under lw+ overburden.