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INTEROFFICE MEMORANDUM <br />Date: 07 July 2014 <br />To: Susan Burgmaier, Lead Specialist <br />From: Marcia Talvitie, P.E. <br />Subject: Bowie No. 2 Mine — Permit No. C- 1996 -083 <br />Review of May 2014 VWP Monitoring Report <br />Vibrating Wire Piezometers (VWPs) installed to measure pore water pressures within Coal Mine Waste Disposal <br />Area No. 2 (Gob Pile #2) at the Bowie No. 2 Mine have been historically monitored on a quarterly basis. Results <br />are submitted with the quarterly monitoring report for coal mine waste piles at the Bowie No. 2 Mine. <br />During the adequacy review process for TR -85, the Division developed concerns about the slow rate at which <br />pore pressures were dissipating from the upper central portions of CMWDA No. 2. In particular, pressures <br />reported for VWP -08 were within just 3 psi of the level at which the pile's Factor of Safety (FoS) might fall below <br />the minimum required value of 1.5. <br />Given the operator's plan to increase the volume of wet coal mine waste being stored atop the pile, the Division <br />required Bowie Resources, LLC (BRL) to commit to a temporary increase in the frequency of VWP monitoring. A <br />commitment to monitor the VWPs monthly from April through October 2014 was provided by J.E. Stover & <br />Associates, on behalf of BRL, in a letter dated April 11, 2014. <br />To date, two monthly VWP monitoring reports have been submitted. Data is collected in the field by Buckhorn <br />Geotech, the company that originally installed the various VWPs. Buckhorn's report is attached to a cover <br />report prepared by Huddleston -Berry Engineering & Testing (HBET). The HBET report is then submitted to the <br />Division by J.E. Stover & Associates. <br />The VWP report for April, dated May 8, 2014, showed little change (compared with those for the 1St Qtr 2014) in <br />the values reported for the five VWPs that are currently functioning. For May, however, historic values for VWP - <br />08, -09, and -10 were revised to reflect corrections made by Buckhorn to the calibration factors used in that <br />company's spreadsheet. The correction is significant for VWP -08, and results in there being a much larger <br />margin of safety at this installation. Specifically, the pore pressure reported for 4/21/2014 is now reduced from <br />12.6 psi to 8.7 psi. An increase of 7 psi rather than just 3 psi would now be required to push the pile to an <br />unacceptably low FoS. <br />With the May 2014 VWP monitoring report, HBET recommends that quarterly monitoring be re- implemented, <br />and does not believe that ongoing monthly monitoring is warranted. I recommend that the Division review the <br />VWP monitoring data for June when it is submitted. If the data trends appear to be consistent with what was <br />reported for April and May, then reverting to quarterly monitoring is likely an appropriate response. <br />In the June 11, 2014 HBET cover to BRL, certain table entries have not been copied faithfully from the Table 2 of <br />the May 27, 2014 Buckhorn attachment. Values dated 4/21/14 for VWP -05, -06 and -10 and 5/21/14 for VWP - <br />06 are not consistent with the Buckhorn values, and should be revised. <br />Please let me know if you have any questions or concerns. <br />Cc: David Berry, DRMS <br />