2014-02-05_REPORT - C1981014 - Laserfiche WebLink

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Southfield Mine 2013 Subsidence Monitoring Report Page 2 It should be noted that the previous Subsidence Report (Period: Year 2006) mentioned a variance in previous horizontal coordinates. The reason is because the monuments were relocated when the survey method changed to a high resolution GPS survey and the previous monument points were located under the eaves of the structures where the GPS receiver could not receive signals from the satellites. Accordingly, data for the structures in this summary are compared to the original survey data and data obtained from the 2006 survey. As mentioned above, measured vertical changes were negligible. No survey data was obtained at the south house survey point in October due to recent construction activities on the house that blocked view of the survey point. The most recent survey data, obtained in 2006, indicated that no subsidence was occurring at this structure. 1.2 Newlin Creek Point Survey data for the Newlin Creek point indicates 0.287 feet of subsidence as compared to the original survey data through the period of this report. Similar to the survey data for the ranch structures, it is unlikely that any subsidence has occurred at this monument due to advance mining only in this area. In addition, no mining operations have occurred in the vicinity of this survey point since 1982 to potentially cause additional subsidence. 1.3 Florence Water Line The number of surveyed subsidence monuments along the Florence Water Line was reduced from eight to five upon approval of above referenced TR -36. The three monuments eliminated, designated "G ", "H" and "I ", lie along a section of the water line that was abandoned in the 1990's when new water line was constructed that followed the alignment of County Road 15. Survey data obtained at the five monuments along the Florence Water Line indicate minor or no additional subsidence occurring in the area of the water line during the reporting period. Only minor additional subsidence is anticipated along the water line since no mining has been done in the vicinity of any of the monitoring points after May 1996. The amount of measured subsidence found at the water line monuments, as compared to original data, ranged from 0.071 to 2.228 feet. The maximum measured subsidence along the water line occurs at Monument "F", with a current deflection of 2.228 feet as compared to the original survey. This value is well within the predicted probable maximum vertical subsidence range of 1.46 to 5.85 feet as documented in the approved permit application. There have been no known breaks in the water line or interruption of service reported by the City of Florence through the period of this report. No potential damage is anticipated to the water line resulting from subsidence since no additional mining in the vicinity has occurred since 1996.