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• 5 • <br />but the presence of large voids in the Eagle Valley Evaporite can not be totally ruled out. <br />The presence of hourglass-shaped rubble zones in the final pit walls are not expected to <br />have a significant influence on stability of the final pit wall slopes. Also, the potential for <br />subsurface voids in the subsurface is not considered to be a major reclamation issue, but <br />voids could require backfilling and stabilization as part of the reclamation program. If <br />large subsurface voids aze encountered during mining operations, they could create a <br />safety problem. The pit operator should be aware of this potential and systematic <br />observations of the excavated areas should be made as mining proceeds. If critical <br />conditions appear then exploratory drilling could be performed ahead of mining <br />operations to help identify possible subsurface voids. <br />ESCARPMENT EROSION <br />In the northwestern part of the Phase 2 area the river is actively undercutting and <br />over-steepening the terrace escarpment along the outside of a sharp river channel bend. <br />This is a slow, natural geologic process and with time the erosion could reach the <br />reclaimed gravel pit area. The erosion potential does not present a safety issue to the <br />proposed mining operations and mining and reclamation should not increase the natural <br />erosion rates. In our opinion, special remedial actions are not necessary unless occupied <br />or critical structures are located near the top of the escarpment. <br />SUBSURFACE EXPLORATION <br />The subsurface exploration for the project was conducted on November 19 & <br />20, 1997. Thirteen exploratory borings were drilled at the approximate locations <br />shown on Fig. 1 to evaluate the subsurface conditions. The borings were advanced <br />with 4 inch diameter continuous flight augers powered by atruck-mounted C.ongyear <br />BK-SiHD drill rig. The borings were logged by a representative of Hepworth-Pawlak <br />Geotechnical, Inc. <br />Samples of the subsoils were taken with 13/e inch and 2 inch [.D. spoon <br />samplers. The samplers were driven into the subsoils at various depths with blows <br />H-P GEOTECH <br />