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• (Page 2) • MINE ZD # OR PROSPECTING ID # M-94-117 INSP cCTIOIy DATE 10/07/98 INSPECTOR'S INITIALS CLK OBSERVATIONS The following observations were made during the removal of organics and some tailings from the Phase II (old pond) area of the pond expansion project. 1) The liner placement was checked, since the burial of the liner in the anchor trench above the pond took place over the weekend. The liner was solidly tucked in around the entire perimeter, with no gaps or loose areas. The edge of the liner/soil interface did not crumble or slough when stepped on, and there appeared to be a flat 6" of liner around the entire edge prior to its burial. The liner anchoring appears to be acceptable. The liner itself appeared to be in adequate shape, with no new rips and no sliding apparent. 2) A.t 10 a.m., tailings and organics began being scooped out of the pond with a hydraulic excavator with a flat-toothed bucket (placed on the top of the dam). The reeds and cattails needed to be removed prior to any other action regarding liner placement or removal. The tailings were placed in a D9 Cat front-end loader, which then dumped the tailings into the newly-lined portion of the pond. The inspector observed this process in order to be sure that no new rips were made in the liner or damage done to the dam during th.e tailings removal. Old rips, which would probably need to be repaired, were noted. 3) At 11 a.m., Allen Sorenson of the Division arrived, and a discussion regarding the disposition of the tailings in Phase II. The design engineers of McCulley, Frick, and Gilman, had expressed a wish to place the liner directly over the tailings (not previously included in the design specifications or Technical Revision), so as to prevent any dam failure due to a lack of support at the toe of the dam, which might occur if the tailings were removed. Larry Owen then mentioned two possible modes of failure: one from a slip between the old liner and the tailings which are now part of the dam (interstitial failure) and one from a block failure (the dam tailings slumping into the pond and taking part of the dam face with it) if the tailings were removed. Christina Kamnikar had previously stated to both MFG engineers that consolidation tests on the tailings would be needed, as well as a new factor of safety analysis for this new case, prior to any Division decision regarding a different liner design. 4) Upon examination of the tailings and a check of the previously submitted application, it was thought that the main tailings material at the bottom of the pond was too fine and too water-logged to be suitable lining subgrade material. It was also mentioned that this material was not the same as that used in the lower dam construction (checking the grain size distribution report and the text of the application which described the sampling areas led to this conclusion). 5) Jon Friedman of MFG then stated that no previous block failure analysis had been done, and Larry Owen explained that the rotational shear analysis was done under the assumption that all of the tailings in the pond would be left in place, buttressing the dam. MFG stated that they believed dam stability would be significantly compromised if all of the tailings were removed. This seemed in conflict with parts of the application submitted to DMG in August. Allen Sorenson then mentioned his fear that the fine tailings would be subject to differential settlement (solids and water settling out separately) as well as vertical settlement. The vertical settlement factor of the tailings used in the dam was said to be close to 1.5 inches/foot of tailings; however, the material at the bottom of the pond, not having been previously tested, could settle to a larger degree. 6) It was decided that a back-calculation of the tailings stability would be done, assuming that the current dam case with the tailings in place had a Factor of Safety equal to 1.05.