2014-02-05_REPORT - C1981014 - Laserfiche WebLink

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Southfield Mine 2013 Subsidence Monitoring Report Page 3 2.0 South Subsidence Monitoring Grid The South Subsidence Monitoring Grid consists of 23 monuments constructed in two lines that cross perpendicular to each other. Established in 1983, prior to mining, the pattern of the monuments was designed as a "high resolution grid" for the purpose of determining the angle of draw resulting from retreat mining of a typical room and pillar mining panel. Subsidence surveys were conducted following construction of the grid on a quarterly basis in order to establish pre - mining conditions. Subsequent surveys provided subsidence data during the time that the panel was developed and then retreat mined. Subsidence data provided in previous Annual Subsidence Reports indicated subsidence occurring soon after retreat mining operations in the subject panel. Subsequent retreat mining in a second adjacent mining panel resulted in subsidence in the area around the monuments comprising the north limb of the South Subsidence Monitoring Grid. Based on information provided in previous reports, most of the measured subsidence occurred within approximately one year following retreat mining operations, with minimal additional subsidence occurring thereafter. A review of the data obtained during the 2013 subsidence survey, summarized on Exhibit B, South Subsidence Monitoring Grid, shows measured subsidence ranging from 0.000 to 2.213 feet at monuments 18 and 15 respectively. Monument 15 situates above the second mining panel mentioned above. Measured subsidence of 2.213 feet at Monument 15 is within both the predicted probable subsidence range of 1.46 to 5.85 feet, and projected worst case vertical subsidence range of 2.60 to 4.36 feet, as documented in the approved permit application. Additional subsidence in the area of South Subsidence Monitoring Grid is unlikely since no mining operations have occurred in the vicinity of the monuments since 1983 to potentially cause additional subsidence. No visual indications of subsidence in the grid area were noted in previous reports, and none were reported during the 2013 subsidence survey. Visual Observations and Subsidence Repair A minor surface tension crack was found and reported on the former Newlin Creek Mine property, the location being over the Moose Panel situated immediately south of the Main Entries. During 2011, the crack was backfilled with a small dozer and water bars were installed to divert surface water away from the crack. The landowner also installed some rock in the crack that was inaccessible for the dozer. Six subsidence holes were reported in the vicinity of the abandoned Canon National Mine portal area located in the NE' /. of Section 25. In order to repair the subsidence features, EFCPs contractor cleared debris from the holes, then backfilled and compacted the sites. Topsoil that had been tested for suitability and approved by the DRMS was hauled in and distributed on the hole footprints, followed by seeding the footprints with the approved seed mix, and finally mulching the seeded areas with wood chips acquired by chipping wood removed from the disturbed area. The mitigation of the subsidence holes was completed during October 2012.