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INTEROFFICE MEMORANDUM <br />Date: April 7, 2014 <br />To: Susan Burgmaier, Lead Specialist <br />From: Marcia L. Talvitie, P.E. <br />Subject: Bowie No. 2 Mine — Permit No. C- 1996 -083 <br />TR -85 — Gob Pile #2 Drying Area <br />Review of April 7, 2014 Response <br />J.E. Stover & Associates has submitted a package in response to the TR -8S adequacy comments <br />I made in a March 25, 2014 email. The response, received electronically today, successfully <br />addresses each of my comments: <br />Page 19 —the text was revised to reflect the current status of the Vibrating Wire Piezometers at <br />Gob Pile #2. <br />Huddleston- Berry's (HBET's) stability evaluation has been revised to include the Feb. 15, 2006 <br />Buckhorn study in the list of referenced materials. <br />The HBET report now evaluates the computed stability's sensitivity to the angle of internal <br />friction of compacted coal mine waste (gob). A friction angle of 32 degrees results in a Factor <br />of Safety (FoS) of 1.502. HBET (on page 5) believes that since one of the shear strength tests <br />show a drained friction angle as low as 30 degrees, that value is not representative of the <br />material, and conducting a sensitivity analysis using that value is not warranted. <br />The Table of Contents was updated to reflect the April 4 date of the new HBET stability <br />evaluation. <br />NOTE: HBET's analysis does indicate that the FoS for Gob Pile #2 is sensitive to the pore <br />pressures present at VWP -08, which is located downslope from the proposed drying area. The <br />most recent quarterly coal mine waste report shows that a value of 13.4 psi was measured at <br />VWP -08 on Dec. 17, 2013. HBET notes that an increase of just 3 psi in this area of the pile <br />would result in the FoS falling below the required 1.5. 1 interpret this to mean that the pore <br />pressure should probably be monitored at an increased frequency, once dumping of gob <br />commences in the drying area. <br />Cc: Sandy Brown, DRMS <br />