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' yielded a 20% moisture content for ore at near saturation levels. This number would not be realistic under field conditions in a heap leach situation. Under field conditions, the ore near the upper surface of the heap will be near the field capacity moisture content while the ore in direct contact with the pad will be nearly saturated. Averaging the two values yields a 16% 1 overall leaching moisture content which represents about a 68% degree of saturation. The difference between the leaching moisture content (16%) and the field capacity (12%) represents the 10 gallons per ton draindown used in the water balance. This number is considered to be a reasonable assumption for the San Luis Project. Exhibit D, Section D.8.2 has been clarified 4/20/89. 45. In the water balance mode] output, a draindown of 2 acre-feet from the deactivated part of the heap is shown. What pad area, ore volume and denaturation rate corresponds to this draindown volume? Response: The 2 acre-feet draindown referred to should not be confused with the "power failure-induced" draindown. The 2 acre-feet represents the draindown from one month of ore production as the application system is advanced to newly placed ore. This volume is simply the net difference between leaching moisture and field capacity moisture contents for 75,000 tons of ore (one month production). Any lift(s) of ore beneath a newly stacked lift has already been leached and is therefore at field capacity moisture content. The amount of moisture required to bring this ore back up to leaching moisture content is derived directly from the draindown of the adjacent cre just deactivated. Thus only the uppermost lift experiences the net wetup versus draindown, i.e. the numbers shown in the water balance table. No application change necessary. 46. At the time of detoxiri~ation and decommissioning of the heap, it appears that only the solution volume contained in circulation from the final stage of 700,000 tons is available for use in rinsing the heap. As the entire 6,500,000 tons on the pad will need to be rinsed, please address the volume of water required, where will this come from and what amount of time will be necessary to rinse the entire heap. It is also impor*. ant to document whether the ponds will provide sufficient storage capacity during this operation? Please include these volumes in the water balance calculation in Appendix G. Response: The revised water balance contained in Appendix G provides information on the rinsing of the heap over a two year period. In two years the equivalent of more than ten draindown volumes will be passed through the heap. This amount is believed to be I sufficient to neutralize the ore. The source for the rinse water will initially be solution I existing in circulation at the close of leaching which will be