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~, <br />~ _,, <br />Energy Fuels Coal, Inc. <br />Southfield Mine <br />Semi-Annual Subsidence Monitoring Report <br />May, 1991 through October, 1991 <br />ntroduction <br />This report presents summarized subsidence monitoring data <br />from surveys conducted in accordance with Colorao Coal Mining and <br />Relcamation Permit No. C-81-014. <br />Discussions of the survey data obtained during the above <br />period of record compose measured subsidence a the monitored <br />structures and the high-resolution grid with subsidence <br />predictions in the approved permit application. In addition, <br />three summary data tables of survey data for the monitored <br />structues and monuments are attached, and are accompanied by two <br />cross section subsidence plots of r.he high resolution grid. <br />Discussion <br />A. Florence water line, Newlin Creek, and Thompson Ranch <br />Structures <br />Survey monitoring data for tl~e above referenced structures <br />(12 monitoring poiints total) are shown on Table 2: Florence <br />Water Line and Table 3: Thompson Ranch Structures and Newlin <br />Creek Point. <br />A review of the data indicates that no significant subsidence <br />has occured at any of the sturcture monitoring points through the <br />period of this report. The greatest magnitude of displacement has <br />occured at Monument 'E' along the Florence Water Line near the <br />west end of the permit area. The total measured displacement is <br />1.41 feet, which is approximately 50 percent of the maximum <br />predicted value of 2.79 feet. The total displacement at Monument <br />'E' has changed little in r.he past three years, as documented in <br />previous semi-annual reports, and only minor additional subsidence <br />is expected to occur. The other water line monuments and the <br />ranch stuuctures are not expected to have measurable subsidence <br />until retreat mining has been completed below the monitored <br />locations. <br />B. High-resolution grid <br />Survey data for the 23 monuments within the high resolutio <br />grid are provided on attached Table 1: South Subsidence Grid. .`The <br />same data is shown in cross-section format on Figure 1 and 2. <br />::i~~6~::x:tna... ., ,., . .::vi,:x•. <br />