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<br />t BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT <br />CMLRD ADEQUACY LETTER RESPONSES <br />Page 9 of 28 <br />15. In order for the Division to make a more adequate determination of <br />' the long-term stability of the tailings disposal facility, a <br />Liquefaction potential investigation should be conducted. The <br />stability of Phase 2 raises 1 and 2 in relation to the tails <br />undergoing acceleration sufficient to produce this event should be <br />specifically evaluated. <br />Liouifaction Potential <br />' Liquifaction potential has been evaluated for the tailings facility <br />in terms of the foundation, embankment, and tailings themselves. The <br />facility is designed to retain the tailings solids and allow drainage <br />of solution from the facility throughout operations. <br />Liquefaction potential of a specific site is primarily governed by <br />' the moisture content, grain size, and density of the materials and <br />the intensity and duration of the seismic loading. No ~iiquefaction <br />will occur if the material is not saturated or is at a sufficient <br />density to inhibit collapse during seismic loading. At the San Luis <br />tailings disposal area, the embankment will be constructed of <br />permeable gravel materials with a drainage blanket on the upstream <br />' face and perforated pipes in a gravel blanket drain, throughout the <br />impoundment and beneath the embankment itself. No phreatic surface <br />will exist in the critical area of the embankment constructed for <br />Phase 2 of the facility. The tailings depositional sequence will <br />result in the deposition of relatively free draining sand adjacent <br />to the embankment and will force the free water pool well away from <br />the embankment. The deposition sequence and drainage system will <br />1 result in a very low phreatic surface at the upstream toe of the <br />embankment. The Phase 2 raises will be founded upon unsaturated <br />tailings sand and the embankment itself, therefore, the design has <br />assumed liquefaction in this area cannot occur. <br />In order to monitor the actual field performance of the drain system <br />and stability of the embankment, pneumatic piezometers will be <br />installed to measure the phreatic surface during actual operation <br />of the facility. These piezometers will be installed at the base of <br />the embankment, the upstream face of the embankment and within the <br />tailings "beach" sands. Prior to construction of the Phase 2 raises, <br />the location of the phreatic surface and density of tailing material <br />will be established and its affect on stability evaluated to verify <br />that liquifaction in this area will not occur. <br /> <br /> <br />It <br />