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• March 2000 -59- 993-2099.150 <br />7.2.3 Water Management <br />The majority of solutions within Phase IV will be directed to the Phase N PSSA. A <br />portion of the Phase IV solution flow will report to the Phase I and Phase II PSSA's. <br />Water balance calculations were conducted to determine the size of the Phase N PSSA and <br />the solution levels in the Phase I and Phase II PSSA's during operation and closure. The <br />water balance calculations were also used to estimate make-up water requirements <br />throughout operations. <br />The water balance model tracks the solution storage volumes in the Phase I PSSA, Phase II <br />PSSA and the Phase IV PSSA on a monthly basis. The water balance model is a <br />probabilistic model that includes operating solution volume (based on hydraulic head), <br />draindown volume (12-hour), precipitation from the 100-year, 24-hour storm, and <br />• precipitation based on seasonal variability (assuming 95 percent confidence interval). <br />7.3 Discussion of Results for Phase N <br />The tabular results of the water balance are presented in Appendix G-3. Golder recomputed <br />the storage volume available for the Phase I PSSA based on the recent ore consolidation <br />testing and the average normal stress within the PSSA from the Phase IV ore plan. Golder <br />used the average ore loading of 305 psi, corresponding to an average ore depth over the <br />PSSA of 400 feet assuming an average wet bulk density of 110 pcf. Using the load- <br />porosity relationship for Cresson ore presented in Appendix B-4-1, this corresponds to a <br />porosity of 0.30, and yields a pore volume of 38.5 MG to an elevation of 9,362 feet. <br />• The results of the water balance model indicates that approximately 44.9 MG will be the <br />required storage for the Phase I PSSA. The 44.9 MG of required storage includes: <br />1:\99120991FINAL REPORT1099MAINt.DOC Golder Associates <br />