2008-09-17_REVISION - M1980244 (28)

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• Y. According to the model, it is supposed to predict when a solution applied onto the pad will report to the pregnant solution collection ponds. At present the DRMS has in place hydrostatic head measuring transducers in the pregnant solution collection ponds. Based on the total water balance for the Valley Leach Facility, each pond level cannot exceed 80% of total capacity during normal operation as measured in feet of hydrostatic head. That is not expected to change under the current proposed dynamic water balance proposal. Under the current amendment, CC&V is proposing to increase the total pumping rate in the valley leach facility from the current 14,900 gpm, to 29,000 gpm, which is double the current pumping rate. Granted the ADR will still process at the current rate of 14,900gpm so no additional processing facility is proposed at this time. The additional pumping rate will go through the enrichment tanks located west of the ADR and will be applied somewhere on to the pad. The model is supposed to predict when that solution will report to the pregnant pond and allow some lag time so when it does report to the pregnant ponds, it will still be under the 80 % maximum operational capacity. Can CC&V explain why this model is any different than applying solution on to the pad and waiting for the solution to report as pregnant solution in to the ponds and be pumped to the ADR, for gold recovery? Even under the current pumping rates,(14,900gpm) on numerous occasions in the past, CC&V had to take emergency pumping measures to transfer solution from one pond area to another pregnant pond area, due to the levels getting closer to the 80% maximum operating permit condition. In order to satisfy the Divisions concerns, the DRMS would like to see how the wettest years on record as reported in the Rigi station ( the station should have good recorded data since 2000) correlate with the pregnant pond levels.. The data for the pond levels should be available because CC&V keeps a good record of such data in the • ARD building control room for the ponds. The pond levels should mimic the results from the model projections. The model assumes a 30% porosity for the ore to derive the pore volume yield. Dori t the lower lifts have an already established preferential path flow? If not, is each time a lift added and solution applied, does a different flow path become established? Please explain Response. In terms of water balance models, a dynamic water balance model is generally considered more protective of the environment and facility operation as it takes into account time lag for solution recovery and precipitation which can impact the overall solution management for a heap leach operation. Experience has shown that with large heap leach facilities, there may be a considerable time lag between solution application and recovery of solution at the PSSAs. The time lag is a combined effect of ore uptake (wetting of the ore to exceed the field capacity) and the hydraulic properties of the partially saturated ore which affect travel time through the heap. The time lag for solution recovery is often referred to as "dynamic inventory," which is the quantity of solution moving through the heap as a function of time. Traditional (non-dynamic) water balance models cannot track or address the dynamic inventory. These models simply assume the solution instantaneously reports to the PSSA. Under this assumption, the solution level in the PSSA would reflect the instantaneous condition when solution is applied. This is a non-conservative assumption, as it can lead to • over-application of solution onto the heap and high solution levels in the PSSA. For example, a low solution level in the PSSA may lead the operator to believe more solution should be added to the ore heap, not realizing there is a time delay for solution reporting to the PSSA. However, by adding more solution onto the heap, the dynamic inventory is increased. Once 44