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INTEROFFICE MEMORANDUM <br />Date: 26 May 2015 <br />From: Marcia L. Talvitie, P.E. <br />To: Jason D. Musick, Lead Specialist <br />Subject: Bowie No. 2 Mine (Permit No. C-1996-083) <br />TR -98 Gob Pile No. 2 — Footprint Enlarged and Borrow Areas <br />Second Adequacy Review— Engineering & Geotechnical <br />I have reviewed the adequacy response for TR -98 prepared by J.E. Stover and Associates on behalf of <br />Bowie Resources, LLC (BRL). My initial adequacy comments (and the number assigned in the Division's <br />Mar. 11, 2015 adequacy review to BRL) are repeated below, and are updated to reflect my review of the <br />revised information. Only two items, highlighted in yellow, remain to be addressed. <br />Geotechnical Reports/Stability Analyses <br />1 (7) DRMS 03/11: In a report dated July 29, 2013, submitted with TR -81, BRL's geotechnical <br />consultant analyzed the stability of a proposed expansion of Gob Pile #2. Results for Sections A- <br />A' and F -F' were presented, showing that the minimum static Factor of Safety (FoS) of 1.5 could <br />be achieved. With TR -98, a somewhat different configuration for the pile is being proposed, and <br />although the peak elevation will not change, the thickness of material proposed for placement <br />along the axis of the original valley is increasing (as shown on revised Section E -E' of Volume IX <br />Figure 1). Material parameters utilized in 2013's TR -81 analysis differ slightly from those used in <br />later analyses (for TR -84, MR -171, and TR -94) which were conducted by a different geotechnical <br />consultant. Please analyze the stability of the proposed configuration depicted on Section A -A' <br />of Volume IX Figure 1, to determine whether a minimum static safety factor of 1.5 can be <br />achieved, in accordance with 4.10.4(2). If material properties used in this new analysis differ <br />from those assumed in the recent revisions listed above, please provide a justification for the <br />change, such as the coal mine waste's being blended with coverfill material to reduce the <br />moisture content. <br />DRMS 05/26: The response includes a new Stability Analysis, dated July 30, 3014, prepared by <br />Huddleston -Berry Engineering & Testing (HBET). Material parameters used are consistent with <br />those assumed in other recent analyses conducted by HBET. The requisite FoS was achieved for <br />a continuous slope of 3h:1v (which is steeper than the benched configuration that will be <br />constructed), and the sensitivity to pore pressures was evaluated. This item has been <br />satisfactorily addressed. <br />2 (8) DRMS 03/11: During the Division's 2014 review of TR -89, the question was raised whether a <br />stability analysis for ditch side slopes / borrow areas was needed, where cut slopes of 1.5h:1v <br />were proposed. Rules 2.05.3(4)(a) and (d); 4.05.3(3) and (5); and 4.14.2(1), (1)(b) are pertinent <br />to this situation. While 1.5h:1v slope is roughly equivalent to 33°, which is typical angle of <br />