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<br />Semi-Annual Subsidence Report <br />Southfield Mine <br />March 14, 1995 <br />Page 3 <br />maximum vertical subsidence will range between 1.46 feet and <br />3.22 feet and the worst-case vertical subsidence will range <br />between 1.46 feet and 6.48 feet. These predictions are based <br />on the Rocky Mountain Geotechnical report prepared in 1983 for <br />Dorchester, the previous operator of the mine. In addition, <br />the angle of draw had been determined to range from 20° to <br />25°. , <br />1. In the subsidence report under the discussion of <br />the high-resolution grid, the third paragraph <br />states that the maximum predicted value of 5.40 <br />feet is presented in the permit application. <br />Please explain how this prediction was developed <br />and why it differs from information contained in <br />the permit. <br />Irregardless of the maximum predicted, the total <br />amount of subsidence has not exceeded 2.65 feet. <br />This maximum amount of subsidence was measured at <br />Monument I on the Florence water line. <br />2. During the last few subsidence reports the Division <br />has noted that the actual angle of draw has been <br />between 26° and 29°. EFCI has submitted a technical <br />revision (TR#18) to extend the permit boundary to <br />include the higher angle of draw. <br />The data collected for the report periods continues <br />to be within the 26° to 29° range. <br />IV. Structure Monitoring <br />The subsidence survey, subsidence monitoring, and subsidence <br />control plan in the permit identifies all structures which may <br />be potentially affected by mining. If these structures are <br />damaged, it is expected that minor mitigation will be <br />necessary. The structures are the: <br />^ County Road 92 <br />^ County Road 115 <br />^ Freshwater Pond No. 3 <br />^ Sedimentation Pond No. 4 <br />EFCI goes on further to list the structures which may be <br />significantly impacted. This list is also included in the <br />Rocky Mountain Geotechnical report. The structures include: <br />