PERMFILE108142 - Laserfiche WebLink

Home Browse Search

West E!k Mine Subsidence Monitoring Plan - 2.05.6 (6)(b){ii), (6)(c)(i) and (6)(e)(iii) Until 1999, subsidence monitoring at the West EIk Mine was accomplished using conventional survey methods of a monument grid. The grid was laid out over the first three longwall panels to be mined (panels 1-3NV~, and successfully verified MCC's prediction about the amount of subsidence. The grid is shown on Map 29. As subsidence of the three Iongwall panels was completed. and the surveys no longer showed movemem, monitoring of the grid was discontinued in 1999. However, the monuments will remain in place to be surveyed in the event that any unanticipated ground surface displacement occurs in the vicinity of the monuments. In the Jumbo Mountain permit revision application (PRNOS), MCC proposed measuring subsidence using aerial photogratnntetric methods. MCC had been collecting data from aerial flights since 1995. Areas were flown prior to, during, and following mining. MCC has evaluated this data and determined that measuring subsidence using aerial methods is not feasible for a number of reasons. The first is the rugged topography of the azeas that is undermined makes it difficult to place survey panels and interpret the data. In addition, placing an adequate number of survey panels has also been difficult due to limited access and thick vegetation. Another difficulty, particularly on Jumbo Mountain, is that it is difficult to distinguish between actual subsidence and ground movement due to landsliding. I • The monitoring of MCC's subsidence grid established the amount of subsidence that occurs over a longwall panel, when it occurs, where it occurs, and when it is complete; therefore, there is no longer a need for additional grids. Instead, MCC will visually inspect the ground over the azeas that have been undermined to document any disturbance that may have occurred. MCC will also visit new mine areas prior to any subsidence occurrence to document pre-existing conditions, and will also visit locations where cracks have previously been documented to verify that the cracks are healing. MCC will uti]ize traditional survey methods, as necessary, to evaluate structures of concern, for example Deep Creek. MCC will conduct these visual surveys, and any necessary traditional surveys, in the summer months of each year and provide the information in a written report by the end of September each year. Monitoring of Deep Creek will be more frequent as mining approaches the stream. A summary of the observations and monitoring will be provided in a quarterly letter report to CDMG and to the USFS. If any mechanical response is detected during these visual inspections that is not consistent with what has been previously observed, MCC will notify CDMG within ten working days of our observations. The annual reports of the visual surveys will include photographs to document any subsidence features, including cracks; rockfalls, landslides, revegetation, and other relevant features. A map will also be included that identifies the location of the photographer and the aspect of the image for each photograph. An additional map will be prepared that identifies the location and extent of the observed features. MCC will attempt to revisit previously identified subsidence features to note any changes that have occurred since the previous visit. MCC will also attempt to replicate the aspect of the photographs taken greviously to document the progression 2.05-134 ReviaedJun. 7995 PR06; IN6 RN03; RwiudMay 7999 7889: RwisedJmt. 2000 PR08