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HRTTLE MTN. GOLD SL I)~19-672-3363 JUL ~93 12:42 No .008 P.02 <br />STEEPEN ROBERTSON AND KIRSTEN <br />Consulting Engineers and Scientists <br />July 28, 1993 <br />SRK Project No. 14719 <br />Battle Mountain Gold Company, Inc. <br />P.O Boz 310 <br />San Luis, CO 81152-0310 <br />Attn: Ms. Alana Scou <br />RE: SAN LULS PROJECT PHASE II RAISE 1 DESIGN REPORT <br />Dear Ms. Scott: <br />We have reviewed the comments on the above referenced report by the Colot~do Division of <br />Minerals and Geology Division as expressed in the memo from Mr. Allen Sorenson to Mr. <br />Larry Oehler dared July 21, 1993 and offer the following responses. <br />As no seeps have been observed along the downstream face of the main embankment and that <br />the pipes from the underdrain system beneath the embankment exhibit flow; which would <br />indicate that the embankment is not widely saturated and a phreatic surface, if ylresent •ts quite <br />+~~ low. This is in accordance with the original design of the facility. As per the facility design, <br />piezometers were installed at the base of the embankment immediately above the VI,DPE liner <br />which underlies the embankment in order to monitor the phrra6c surface within the <br />embankment. However, these piezometers have produced questionable variations in readings <br />which cast doubt on the validity of the data. Therefore, the State has regttesteU replacing the <br />piewmeters. <br />It is important to consider that the effect of a phreatic surface in the embankment is small unless <br />it develops to a significant height. Based upon accepted theories of saturated flow in porous <br />media, it is not possible, now that the tailings separate the embattlement material from the free <br />water pond, to generate more than a minimal phreade surface in the embattkmertt fill. <br />We do not advocate attempting to replace the current piezometers due to the potential damage <br />to the liner system which could result. Unless installed close to their original pdsidon duectly <br />above the liner, the piezometers are unlikely to detect a phreatic surface sufficit:nt to provide <br />meaningful data, therefore we do not recommend installing them higher in the. embankment. <br />If they must be installed to receive the State's approval for the dam raise, we re ommend that <br />a minimum clearance of f0 ft is maintained above the liner to preclude the poss tlity of liner <br />amage. <br />Steffen Robe~tsen and Kir5lun ~U.S,). Inc. <br />313?. South Vance Sueel. La~•~~:.:~od. Colorado ©U227. U.S,A. <br />Tee. (303) 985.1333 ~ :~::~imde ~3031995~9947 <br />Uihcr ollices m' U.S.A.. Ca~.:•:. Kir.^ydom and /`.Rica <br />