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~ III IIIIIIIiilllllll ~ <br />STATE OF ~OLOIZADO <br />DIVISION OF MINERALS AND GEOLOGY _ <br />Department of Natural Resources ~,oe coto-0 <br />hP <br />1313 Sherman St., Room 215 ~ ~ <br />Denver, CO 80203 ~ ~„ ~ , <br />Phone: 13031 856-3 56 7 ' re~e' <br />FAX: p031 832-8106 <br />Ruy Romer <br />Gwernur <br />Michael B. Lung <br />July, 21 1993 Division Dvenor <br />TO: Larry Oehler <br />FROM: Allen Sorenson <br />RE: Design Report for the First Upstream Raise at t1Re San Luis <br />Mine Tailing Impoundment, Battle Mountain Resources, Inc., <br />File No. M-88-112 <br />Battle Mountain Gold (BMG) and their consultants, Steffen, <br />Robertson, and Kirsten (SRK), have prepared and submitted a design <br />report which addresses the suitability of the in-situ tailing as a <br />foundation for the phase II upstream raises. Submittal of this <br />report is a result of commitments made by BMG in the approved mine <br />plan to verify design assumptions through monitoring, testing, and <br />analysis as the tailing impoundment was developed. <br />PIEZOMETERS <br />As part of the monitoring program incorporated into the San Luis <br />Project mine plan, BMG was to install and monitor piezometers <br />within the tailing embankment. Readings of the five vibrating wire <br />piezometers installed in the embankment indicate that the structure <br />is unsaturated, as designed, however, inconsistencies in <br />temperature readings provided by the piezometers demonstrate that <br />the instruments are not functioning properly, and the piezometric <br />data cannot be used with reliability. <br />It is critical, in terms of embankment stability, that the phreatic <br />surface, or lack thereof, within the embankment be monitored. BMG <br />should be required to install properly functioning piezometers <br />within the embankment sufficient to fully characterize the <br />saturated or unsaturated state of embankment materials prior to <br />construction of the phase II raises. Installation of the <br />piezometers must be carefully supervised to preclude the <br />possibility of damaging the synthetic liner beneath the embankment. <br />LIQUEFACTION AND STABILITY ANALYSES <br />In adequacy responses submitted during consideration of the San <br />Luis Project permit amendment, the operator stated: <br />The Phase 2 raises will be founded upon unsaturated tailings <br />sand and the embankment itself, therefore, the design has <br />assumed liquefaction in this area cannot occur. <br />