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SUBSIDENCE IMPACTS 1988 Cyprus Orchard Valley completed mainly advance development of Sub-Mains and a panel section in conjunction with some pillar extraction of Panel G. The following are discussions of monitoring and impacts divided into survey and visual observations respectively. Subsidence monitoring data is contained in Appendix G. Survey Monitoring The COVCC Survey Monitoring Program within the present permit area consists of a wide-spaced grid of survey monuments and three high-resolution grids. The main emphasis has been placed on wide-spaced grid stations with the drainage buffer zone areas of East Roatcap and Steven's Gulch and also the close-spaced grids overlying 9th Fast, 5 North 1 West, and the 11-12 North area of undermining, The monitoring stations were surveyed once during 1988 due to a request and ap- proval by MLRD for reduction of subsidence monitoring frequency to once a year, This request was a result of what COVCC felt as a reduction of subsidence-induc- ed movement within pillar extraction areas of the Orchard Valley Mine. Field surveying employed a double angle/double distance method to increase accuracy. Data reduction was [hen completed by the surveyor and entered on cumulative data sheets. Tabulated survey sheets were computed for the grid stations overlying 11 and 12 North. Using these results a graph was developed plotting time past undermining versus percent of maximum subsidence to date. • Survey data indicated that subsidence has virtually ceased within the close- spaced grid points 28-69 except for a couple of stations. Calculations of the maximum theoretical subsidence <using National Coal Board Methods) expected over the 11 and 12 North panels were compared to the actual center or most close to centerline grid point subsidence induced movement. No .38 grid station which overlies the 11 North panel had an actual movement of 397, of the estimated val- ue. This was compared to 1f60 close-spaced station which overlies 12 North panel and had an actual 507, of the theoretical value. High-resolution grid stations 201-224 showed upward movement of between ,30'- 1.0' indicating residual cantilevered subsidence is still occurring within this area. Observed movement is still occurring adjacent to the 9th East panel through what appears to be possible instrument control station movement. The movement within high-resolution grids 42-51 has been uniform for the past several surveys indi- cating that the control station elevation could be changing, The control sta- tion elevations will be checked during the 1489 survey to verify original on differing elevations to allow evaluation of grid stations 42-51, As expected, little if any subsidence occurred over the Orchard Valley West Mine area during 1988. Survey results of stations 6, 14, 89, 90, 92 and 93 verified this conclusion. Visual Monitoring . Visual subsidence monitoring is accomplished by periodic "walkovers" of mined areas within the present permit area, Walkovers are generally done in conjunc- tion with survey monitoring due to the seasonal accessibility of the area.