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'r <br />SOUTHFIELD MINE <br />SEMI-ANNUAL SUBSIDENCE MONITORING REPORT <br />MAY, 1990 THROUGH OCTOBER, 1990 <br />INTRODUCTION <br />This report presents a discussion of survey data collected <br />during two monitoring surveys during the above referenced semi <br />annual period. A review of the data indicates that maximum <br />subsidence occuring at any of the monitored stations is less than <br />values predicted in the approved permit application. Attached to <br />this report for reference are Tables 1-3; survey data for <br />monitored structures and monuments, and Figures 1 and 2; cross <br />section of the high resolution monument grid. <br />Following are discussions <br />semi annual period as compared to <br />in the permit application. <br />of subsidence observed for this <br />subsidence informatlon contained <br />HIGH RESOLUTION GRID <br />Field survey data for the grid monuments are summarized on <br />Table 1 and portrayed in cross sectional form on Figures 1 and 2. <br />A review of the data indicates total subsidence ranging from <br />0.04 to 2.29 feet within the grid defined by the 23 monuments. <br />The magnitude of vertical subsidence compares favorably with the <br />maximum 5.40 feet predicted in the permit application. The actual <br />value being less than the worst case prediction may indicate the <br />elastic nature of the overburden strata as suggested in the <br />permit. Only minor additional subsidence has occured for the <br />period of this report, consistent with previous semi-annual <br />reports. <br />Also consistent with previous reports is the measured angle <br />of draw (from the cross-sections) of 20 to 29 degrees as compared <br />to the predicted range of 20 to 25 degrees. Since only minor <br />additional subsidence is anticipated, the indicated angle of draw <br />is not expected to change. <br />FLORENCE WATER LINE MONUMENTS <br />Field survey data for the eight monuments along the water <br />line are summarized on Table 2. The survey data indicate <br />measurable subsidence continuing to occur at Monument 'E' <br />totalling 1.46' through the period of this report. This <br />displacement is approximately half of the maximum value of 2.79 <br />feet predicted in the permit. Only minor additional subsidence is <br />expected at Monument 'E' as mining was completed some five <br />yearsago. Subsidence, within the amount predicted in the permit, <br />