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<br /> <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman Sl., Room 215 <br />Denver, CO 80203 <br />Phone: (303) 866-3567 <br />FA%: (303) 832-8106 <br />August 6, 1993 <br />TO: Larry Oehler <br />STATE OF COEORADC~ <br />pFfO~ <br />~~ ~~ <br />~` O <br />~• <br />1B'!6 ~ <br />Roy Romer <br />Governor <br />Michael B. Long <br />Division Director <br />FROM: Allen Sorenson ~~~~ <br />RE: San Luis Project Phase II Raise 1 Design Report, Battle <br />Mountain Resources, Inc., File No. M-88-112 <br />Based on review of the memorandum dated July 28, 1993, from Mr. <br />David Hallman of Steffen, Robertson, and Kirsten (SRK) to Ms. Alana <br />Scott of Battle Mountain Gold (BMG), and on discussio#ls with Mr. <br />James Pendleton, who has met with SRK and BMG regarding this <br />matter, I offer the following clarifications and addresLs lingering <br />concerns. <br />PIEZOMETERS <br />The Division shares SRK's concern for the potential fop damage to <br />the liner that could occur during replacement of the malfunctioning <br />piezometers within the main embankment, however, monitoring of the <br />phreatic surface within the embankment is a permit requirement, and <br />a standard practice industry-wide to assess dam stability. Prior <br />to placement of the proposed raise, BMG must submit results of <br />testing or monitoring adequate to define the phreatic surface <br />within the embankment. Such testing may include electrical and <br />seismic geophysical methods which will provide the necessary <br />information without the potential of damaging the liner. Based on <br />the results of initial testing to determine the location of a <br />phreatic surface, BMG would have to provide the Divislion with a <br />strategy for on-going monitoring of the phreatic surface, such as <br />installation of one or more piezometers, or continuing geophysical <br />evaluations. <br />TAILING CONSOLIDATION <br />The operator has indicated, that to further assure the strability of <br />the proposed raise, material founded on the tailing surface will be <br />placed in an initial l0 foot lift, and that the foundatign material <br />would be allowed to consolidate over time prior to placement of <br />additional material. This procedure would then be repeJated until <br />the design elevation is reached. The Division should require the <br />operator to commit to this scheme as a design parameter, and <br />further require that the rate and magnitude of consolidation be <br />closely monitored through placement of consolidation plates on the <br />