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iii iiiiiiiiiiiu iii <br />BATTLE MOUNTAIN RESOURCES, INC. <br />September 30, 1993 <br />Mr. Larry Oehler <br />Division of Minerals and Geology <br />1313 Sherman Street, Room 215 <br />Denver, Colorado 80203 <br />Re: Battle Mountain <br />DMG Permit No. <br />Phase II, Raise <br />Dear Mr. Oehler: <br />Resources, Inc <br />iLE MOUNTAIN <br />D COMPANY <br />(BMRI) - San Luis <br />M-88-112 <br />I Embankment Lift <br />This letter is written in response to the Division's <br />August 13, 1993 review letter for the Phase II, Raise <br />embankment lift. <br />Piezometers <br />Simple stand-pipe piezometers were installed to verify that <br />the phreatic level is no higher than 10 ft above the liner. <br />The five existing vibrating wire piezometers were replaced <br />by five stand-pipes spaced at approximately 200 ft intervals <br />across the 8590' crest of the existing main embankment (see <br />attached location map, coordinates and elevation listiing). <br />Stand-pipe piezometers offer the advantage of requiring no <br />data reduction, no data interpretation, and no <br />instrumentation failures. <br />The issue of potential liner damage during installation of <br />the standpipes was addressed through additional modelling <br />efforts. Stability analyses of the critical downstr@am <br />face, sliding wedge failure mode, such as depicted on figure <br />4.2 in the design report, indicates that including a <br />phreatic surface which is 10 feet above the liner ha$ little <br />effect on stability of the structure. Under pseudosikatic <br />loading conditions with a seismic coefficient of 0.1$g the <br />factor of safety decreases from 1.47 to 1.38 when a 10 ft <br />high phreatic surface is included in the analysis. <br />Prior to drilling and installation, the piezometer locations <br />were staked and surveyed. The locations were then plotted <br />on the as-built liner contour map to determine the <br />embankment thickness at each location. Then, each <br />piezometer depth was calculated so that the casing would be <br />placed 10 feet above the liner. <br />• <br />ASUQSIDIARf' OF RA7T! F Af0!/A7AlN GOLD COMPANY <br />N.O. BOX 3111 SAN LUIS, COLORADO NI I S'_ 0310 (7 191 672-3 3G2 FAX (719) 67d-3363 <br />