REP42542 - Laserfiche WebLink

Home Browse Search

preceeding survey. The maximum subsidence continues to be at Monument 4 (1.09 total feet) which is comparable to the maximum expected subsidence, as predicted by RMG, in the Mining Permit. It is anticipated that future subsidence above "A" Panel will continue to be minimal. Citv of Florence Water Line Data collected for the water line monuments, as shown on the summary table, are compared to a survey conducted during May, 1985. Data collected prior to 1985 by contract surveyors were inconsistent and inconclusive, apparently due to errors in the benchmark elevations that were used. The maximum subsidence detected occurs at Monument "E" with a total displacement of 0.21 feet. Of this, 0.17 feet of subsidence occurred between Septem- ber, 1985 and April, 1986. During this time retreat mining passed under Monument "E" in the 5 South Section. The observed subsi- dence is probably a result of mining activities although its magnitude is much less than the RMG prediction of 2.79 feet. It is expected that minor subsidence will continue to occur but at a decreasing rate with time. The remaining monuments displayed insignificant movement (+0.02 to -0.04 feet) due to no undermining taking place. it should he noted that Monument "A" is no longer monitored. Due to the align- ment change made by the City of Florence during the spring of 1985, Monument "A" is located approximately 300 feet away from the water line, and its continued monitoring would not represent subsidence effects to the line. Newlin Creek Streambed The single subsidence monument established along Newlin Creek in May, 1985, has subsided a total of 0.6 feet to present. The entire displacement occurred during the period between May through September, 1985. Mining in this area, which was completed in 1982, was development mininy only. The above mentioned subsidence would not be expected to have occurred as a result of this mining activity. The mining section under the Monument (1 North) is situated under an abandoned mine, separated by 20 to 30 feet of interburden. The 1 North Section (along with the old works) were allowed to fill with water until early 1985, when efforts began to dewater this area. It is possible that roof collapse in the old works, due to dewatering, manifested as subsidence. Continued monitoring of the Newlin Creek Monument should indicate only minor additional subsidence of this area. Tliomoson Ranch Structures Subsidence monitoring stations were established on the three structures existing on the property during May, 1985. Survey data collected to date indicate minor subsidence ranging from 0.2 to 0.5 total feet. The data from the preceediny survey indicate that no subsidence occurred. It is anticipated that only minor subsi-