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~. • • <br />• Ms. Kathleen G. Weit - 2 - July 22, 1987 <br />5. A list of monitoring stations and the geologic formations and water <br />parameters monitored should be presented in the AHR. <br />Subsidence <br />Jim Pendleton offers the following comments with respect to the subsidence <br />portion of the annual report: <br />The visual and survey subsidence data appears properly gathered and <br />tabulated. The data shows subsidence response over the 11 North Panel to have <br />been very similar to that of the 12 North Panel, which was retreat mined the <br />previous year. A maximum elevation change of 1.57' was recorded at <br />Station 38. The majority of the subsidence was observed to occur within the <br />first 3 1/2 months. <br />I have one concern regarding the operator's determination of the <br />representative angle of draw. Three observations have been made of the angle <br />of draw adjoining Panels 11 North and 12 North. Based on the observations to <br />date the operator has determined three angles of draw: <br />East side of Panel 11 North = 16.1 degrees from vertical <br />West side of Panel 12 North = 15.8 degrees from vertical <br />East side of Panel 12 North = 20.0 degrees from vertical <br />Based on these three determinations and the rationale that "it is difficult to <br />determine the exact location at which possible subsidence could actually be <br />surveying instrument or human incapacity", the operator proposes that the <br />angle of draw be assumed to equal 16.0 degrees. With a sample of only three <br />observations I do not believe that this assumption is warranted. I believe <br />that it would be more appropriate to conservatively assume that the angle of <br />draw is 20.0 degrees, until more definitive information becomes available. <br />The Division accepts the visual and survey subsidence monitoring data as <br />reported. However, for purposes of determining buffer zone boundaries in the <br />future, I believe the data only warrants the assumption of 20.0 degrees from <br />vertical as the projected angle of draw. <br />If you have any questions or comments, please contact me. <br />Sincerely, <br />~~ c <br />Tho~ma~s A-.-Schreiner <br />Reclamation Specialist <br />TAS/srs <br />1274E <br />