2011-08-26_REVISION - M1981185 - Laserfiche WebLink

Home Browse Search

• May Day /Idaho Mine — Geotechnical Stability Exhibit Comments to August 2011 Submittal Page 2 August 19, 2011 is the "Analysis of the Effect of Blasting Operations on Structures Associated with Mining Activity at the May Day Mine. The "New Access Road Stability Report" is not to be found. 5. Page 6, Embankments. The reader is directed to Attachment D -5 for the Augmentation Pond embankment discussion. Attachment D -5 is the Dry Stack Tailings Work Plan. The Augmentation Pond work plan is presented in Attachment D -4. 6. Page 8, Augmentation Pond, second to last paragraph. The last line of this paragraph references the work plan, Attachment D -5, Figure D -5 -1 for illustration of the embankment slopes. Attachment D -5 is the Dry Stack Tailings Work Plan, Attachment D -6 is the Augmentation Pond work plan. Furthermore, it is Figure D -2 in Attachment D -6, not Figure D -1 that presents sections of the Augmentation Pond. Finally, there are no embankment side slopes labeled in cross section A, and the downstream embankment is cut off in the cross section. There is no horizontal scale provided from which to estimate a side slope on the cross section. 7. Page 9, La Plata River Bridge. The first bullet references Attachment 6.5 -3 with respect to the bridge. The "Geotechnical reconnaissance report" in Attachment 6.5 -3 does not mention the bridge. 8. Page 10, Blasting Impacts. The first sentence references Attachment 6.5.5 for the blasting analysis. The blasting analysis is in Attachment 6.5.4. Technical Comments (pursuant to Rules 6.4.21 and 6.5): 9. Page 6, Bench Stability. DRMS commented on this in the May 25, 2011 Memorandum from Tim Cazier to Wally Erickson. Neither the comment, nor the response from the applicant has changed: the applicant states "Existing mine benches were created in the early 1900's with no signs of failure or instability." Furthermore, it is stated that "the angle of repose of the benches range from 30 to 35 degrees..." and that "in the future operating and reclaimed bench and waste rock slopes of 1.5 (H) to 1(V) will be used as design criteria." The stated angle of repose (30 to 35 degrees) equates to 1.4H:1V to 1.7H:1 V. Please note that the proposed design criteria (1.5H:1 V) is steeper than the flatter angle of repose (1.7H:1 V). Also, during the June 30, 2010 inspection, tension cracks in the May Day 1 bench were observed by the two DRMS inspectors present, who pointed out the fracture and discussed their concern with the Wildcat representative. As such, DRMS believes there to be sufficient evidence of potential instability to necessitate analyses to demonstrate otherwise. Therefore, DRMS requires the operator to submit stability analyses to demonstrate that the proposed benches will be stable under the proposed design criteria while loaded with the expected mining/construction equipment. These analyses shall have appropriate materials test data to support assumptions used for analysis, including, but not limited to: unit weight, cohesion, and friction angle. 10. Page 7, Chief Portal and Reclaimed Drainage Channel. The third bullet references Attachment U -3 and Table U -12 for channel geometry and estimated flow velocity. Both are in consistent with the information in Attachment U -3. The side slopes in the F1owMaster® computer output following Table U -12 indicate 3H:1V side slopes (not 2H:1 V) and the estimated velocity is greater than 10 fps, not 7.5 fps. 11. Page 7, May Day No. 2 Operational Area Reclaimed Drainage Channel. The first bullet references Attachment U -3 and Table U -11 for channel geometry and estimated flow c: \documents and settings \sssuocaI settings \temporary internet files \content.outlook \a5ghsruj \exh6 5geotechstabcomments_mem 19augl l .docx