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2002 -8- <br />2.3 VLF Storage Contingencies <br />003-2203 <br />The VLF internal PSSAs and External Storage Pond are sized not only to contain solution <br />inflows, as described above, but contingency storage is also provided to contain 12-hour <br />draindown, and the 100-year, 24-hour design storm event. This provision is consistent with <br />Amendment No. 7 and Amendment No. 8. The 12-hour draindown is conservatively based <br />on the maximum pumping rate and assumes instantaneous draindown with solution reporting <br />to the PSSAs. The design storm event also conservatively assumes instantaneous reporting <br />to the PSSA. Under actual conditions, draindown solutions and storm event precipitation <br />enters dynamic storage within the ore heap and may take several days to weeks to report to <br />the PSSA. <br />2.4 Solution Management <br />Within the water balance model, solution management routing has been integrated to <br />simulate actual conditions within the VLF. Both the Phase I and Phase IV PSSAs aze <br />operated in the water balance without freeboard, because solution outflow from either of <br />these PSSAs will report directly to the Phase II PSSA via gravity flow. The Phase II PSSA is <br />operated with a freeboard. If the solution levels within the Phase II PS5A exceeds the 9305 <br />elevation, then the solution is pumped to the External Storage Pond. <br />The water balance model tracks the solution storage volumes in the Phase I, Phase II, and the <br />Phase IV PSSA on a monthly basis. The water balance model is a probabilistic model that <br />includes operating solution volume (based on hydraulic head), draindown volume (12-hour), <br />precipitation from the 100-yeaz, 24-hour storm, and precipitation based on seasonal <br />variability (assuming 95 percent confidence interval). The water balance calculations also <br />estimate make-up water requirements throughout operations. <br />Golder Associates <br />