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• Potential storage volumes of individua] expansions together with the surface area of future disturbance are tabulated in Table 2. The yardage calculations presented in this table show that a total of about 600,000 yd3 could be deposited in the valley for tF~e remaining lifetime of the mine operation. The mine management could Selectively choose any of the proposed expansion schemes. 4.2 Stability Analyses To perform stability analyses of the existing waste piles on the property, it was necessary to identify configurations where a potential failure was most probable. For this purpose, all sections recently sur- veyed by Cotter Corporation were evaluated carefully. Additional in- formation that is necessary for the assessment of potential stab- ility problems (i.e. geologic conditions, ground water conditions, etc.) was also considered. Pre-mining topographic conditions werer also taken • into account so that both the present topographic surface and the surface prior to waste piles deposition could be identified. Based in the fore- going and the best engineering judgement, the representati~ie stability analyses can be performed on stability sections that coincide with sur- veyed Section Nos. 4 and 5, as they are shown on Plate 4. These two typical sections across the waste piles are shown on Plates 10 and 11. Both sections show the existing topography, the ground surface prior to waste Dile deposition and an approximate interpretation of geologic conditions. The interpretation of geologic cam ditions is based on geotechnical mapping; the thicknesses of colluvial and alluvial soils are approximate only as they have not been verified by drilling or excavation of test pits. The interpretation of geologic conditions was made to provide a conservative approach for the stabili~:y analyses. Important geotechnical units in the vicinity of they waste piles consist of the following: • - 18 -