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Battle Mountain Resources <br />November 1, 2000 <br />Page 9 <br />4.0 REVISED ESTIMATE OF BACICFILL FLUSHaVG <br />Prior to the re-calculating the saturated pore volume flushing, reconsideration is given to the form <br />of the theoretical equation used to describe the backfill flushing to account for sulfate contained in <br />the groundwater that is flushing the backfill. Specifically, Equation (l) was reevaluated with <br />regard to the correspondence between the theoretical implications of the equation and the <br />observed and anticipated response of the groundwater system. The revised estimate of West Pit <br />backfill flushing will then be presented and discussed. <br />4.l Theoretical Flushing Equation <br />Equation (1) is a first-order exponential decay equation that was first used t~~ describe the <br />observed decreases in concentration of sulfate during batch-leach testing of representative <br />materials from the backfilled West Pit. The form of Equation (1) implies the following <br />characteristics with regard to the backfill flushing process: (I) there is a finite am<wnt of soluble <br />sulfate salt associated with the flushing of the West Pit backfill, i.e., eventually there will no <br />longer be a source of soluble salt and (2) the concentration of sulfate in the rinsing solution is <br />essentially zero. As a result of these implications, the flushing rate predicted using Equation (I ) <br />would represent the maximum expected rate. The actual flushing rate would more likely be <br />influenced by the steady-state concentration of sulfate in the groundwater that will rinse the West <br />Pit backfill. <br />Modifying the form of Equation (1) to incorporate the effects of sulfate in the rinsing <br />groundwater would be represented by the following: <br />where: CP = the concentration at pore volume p <br />Co = the initial concentration at p ° 0 <br />CTM the concentration of sulfate in the rinse water <br />n = a parameter that determines the shape of the decay cu ve <br />p = the number of pore volumes that have passed throul;h the backfill <br />material <br />263G Midporn! Dr., Snile B, For! Co!/u7s, Colorado 80525 <br />Telephone (970) 484-7704 /FAX (970) 484-7789 <br />