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Subsidence Impacts - 1997 • Subsidence survey monitoring of selected wide-spaced monuments in the vicinity of active mine workings was conducted during June, 1997 and November, 1997. Surveying of these selected stations was conducted in accordance with the projected monitoring addressed in the 1996 Annual Subsidence Report. Selected subsidence monitoring stations established over the Pitkin Mesa pipeline were monitored in June and November of 1997. Wide-Spaced Monitoring Grid Station Summary Fourteen wide-spaced monitoring grid stations were surveyed for the 1997 reporting yeaz. The station locations aze shown on Map No. 2-5. The following discussions present a station by station assessment of survey results generated for 1997. Monitoring station data sheets are appended to this report for reference (Tab 7). Station 6 Surveys were initiated m August 1982 and continued biannually through July 1984. Surveys were re-initiated m 1987 and conducted annually through 1991 and biannually 1992 - 1994. Station 6 is located on approximately 350 feet of overburden and lies approximately 300 feet north of the 1st North, 2 '/z West Panel retreat mined from May through June, 1983. Station 6 lies adjacent to the II West Submaa~ development advanced in 1987. The 1997 average survey data indicates an elevation gam of 0.03 feet. Station 6 is located within a mapped landslide area and may be exhibiting movement associated with this feature. No mining anticipated to produce subsidence has occurred in the vicinity of Station 6 since 1983. • Station 14 Station 14 is located in the Stevens Gulch alluvium protective buffer zone over approximately 750 feet of overburden. The station was initially surveyed in June, 1982. Subsequent surveys have been conducted annually since 1988. Panel G was advanced under this station in September, 1988. Retreat mining occurred outside the buffer zone in the vicinity of this site in February, 1989. Panel C was advanced adjacent to this site in December, 1992. An elevation adjustment of - 0.55 feet was detected at this site in October 1989 but was perhaps influenced by control station coordinates being redefined. January 1991 data indicated 0.31 feet were subsequently gained but again, new control point coordinates were generated. No mining activity took place in the vicinity of station 14 during 1997, The June 1997 measurements were within the historic maximum and minimum elevation values for this station. Station 15 Station 15 was established for the 1991 surveying year. Station 15 overlies approximately 700 feet of overburden and is located within the 600 - 800 foot overburden depth Stevens Gulch alluvium protective buffer zone. Panel B was retreat mined with partial floor extraction during May, 1992 m the immediate vicinity of station 15. The 1997 survey results show an elevation loss of 0.3 feet when compazed to the January 1992 elevation. • -2