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Energy Fuels Coal, Inc. <br />Southfield Mine <br />Semi-Annual Subsidence Monitorine Renort <br />(May I , 1992 -October 31, 1992) <br />Introduction <br />This report presents summarized field survey data and discussion of subsidence predictions in <br />accordance with the requirements of Colorado Coal Mining and Reclamation Permit No. C-81-014. <br />The following discussion of tureen[ subsidence data includes comparing measured subsidence to <br />predicted values, documented by three summary data tables of survey data for the montunents and structures <br />with accompanying cross section diagrams of the high resolution monument grid. <br />Discussion <br />I) Monitored structures include the following: <br />Thompson Ranch (3 buildings) <br />Florence Water Line (8 monuments) <br />Newlin Creek (I monument) <br />Survey monitoring data for the above structures for the reporting period are summarized on Table 2, <br />Florence Water Line and Table 3, Thompson Ranch Structures and Newlin Creek Point. <br />The survey data obtained from the two quarterly monitoring field surveys indicate that nu <br />measurable subsidence has occured at any of the above structures during the period of this report. This <br />condition corcelates to the fact that no recent retreat mining has been done below the monitored structures. <br />1\4easured subsidence at monument 'E' along the Florence Water Line remains at 1.50 feet, well within the <br />maximum predicted value of 2.79 documented in the permit application. <br />2) The high resolution monitoring grid includes the following: <br />South Subsidence Grid (23 monuments) <br />Survey monitoring data for the above monuments are summarized on Tnl~le I, South Stthsiclence <br />Grid and are presented in cross section format on Figures 1 and 2. <br />A review of the survey data obtained from the one semi-annual field survey indicates that no <br />additional subsidence has occured in the area of the monitoring grid. These data continue ut verify that <br />ground strata have almost completely consolidated since the period of retreat mining. In addition, the <br />maximum measured subsidence of 2.31 feet (monument 15) is only 43 percent of the maximum predicted <br />subsidence value of 5.40 feet. <br />The estimated angle of draw is depicted on Figure I indicating an angle of approxim:uely 25 <br />degrees. This draw angle is comparable to the 20 to 25 degree angle of draw predicted in the approved <br />permit application. <br />