2014-02-26_REVISION - C1996083 (2)

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Page 2of10 The Division's question regarding elevated pore pressures, and any effect this may have on the stability of Gob Pile #2 with the addition of the proposed drying area, has not been satisfactorily addressed. Please submit a thorough stability analysis of the proposed configuration, with all inputs and assumptions clearly identified, establishing that the required minimum FoS of 1.5 will be maintained at all times. Certain earlier Buckhorn analyses (Feb -2006, Feb -2007, and Mar -2007) analyzed Total Stress as well as Effective Stress. Later reports eliminated the Total Stress model under the assumption that moisture was draining from the compacted waste and pore pressures were reducing with time. As demonstrated by quarterly measurements at vibrating wire piezometers VWP -06 and VWP -08, that assumption may not be valid. Please incorporate Total Stress analyses, if appropriate, or include a detailed explanation of why this approach is not applicable to the current evaluation of Gob Pile #2. b) A response to this question was provided by Buckhorn, but it may be more appropriately addressed within the permit text. It seems apparent, based on the photo of revised page 14a, that VWP -06 is located well within the proposed footprint of the storage area. BRL's intention should be clearly stated: either damage to VWP -06 will be avoided (may require a vertical extension of the pipe), or damage to this instrument is likely or expected. If the latter is true, then plans and commitments for its replacement should be made at this time. There are only two functioning piezometers remaining in the upper reaches of Gob Pile No. 2. Given the slow rate at which the pile is dewatering, it is imperative that collection of pore pressure data not be interrupted. Please clarify whether damage to VWP -06 is anticipated, and whether it will be protected or replaced when gob is placed in the temporary drying area. 3. Buckhorn responded that BRL's surface operations staff will maintain the 25 -foot buffer, and that no changes to the design are proposed. That may be the case. However, the stability analysis assumes a 25 -foot setback. If there is a chance that material may encroach upon the buffer, please evaluate the effect on the stability of the pile as a whole if the setback is not maintained. 4. Buckhorn's response includes the proper citation. This item is resolved. However, a new, related issue is incorporated here: a) For permanent inclusion into Volume IX of the permit, the two documents submitted by Buckhorn (05- Dec -2013 and 04- Feb -2014) should be replaced by a single comprehensive report which also addresses the issues raised in this latest adequacy review. 5. The TOC was updated, as requested, but the date of the latest Buckhorn report was listed as February 4, 2012. The date should be February 4, 2014, however the TOC will require an additional revision (see Item 4a, above) that will correct this error.