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Battle Mountain Resourc~ • <br />January 31, 2000 <br />Page 2 <br />The general trend of the data produced from the batch leach testing was consistent with an <br />aggregate geochemical process that yielded initially greater quantities of salts and thereafrer <br />monotonically decayed to aquasi-steady state value. The flushing characteristics of the backtill <br />materials was represented usine a first order exponential decay equation of the form: <br />CP = Co eCpl-nP) <br />where: Cp = the concentration at pore volume p <br />C, = the initial concentration at p = 0 <br />n =a parameter that determines the shape of the decay curve <br />p =the number of pore volumes that have passed through the backfill <br />material <br />Equation (1) can be solved for p, the number of pore volumes required to reach ~. concentration <br />of CP. The initial concentration, Co, and the tinal target concentration, CP, influence the <br />magnitude of the number of pore volumes, p. In November 1999 when the Response Plan was <br />developed, the only geochemical data available in the backtill groundwater system came from <br />BF-2 and BF-l. At that time. the concentration of sulfate in BF-2 was appro~.imately 1.370 <br />mg/L. In contrast, the concentration of sulfate in BF-1 was approximately 200 mg/L. The <br />greater concentration value was chosen to ensure conservatism in the calculation. to reflect the <br />small data se[ used in the calculation. The resulting value ofp, assuming an initial concentration <br />of 1,370 mg/L and a final value of 2~0 mg/L (the groundwater quality standard), was <br />approximately 10 pore volumes of flushing. <br />The estimated number of pore volumes, as calculated in the Response Plan, was combined with <br />the results of the hydrological evaluation that was conducted in support of development of TR- <br />26. The estimated residence time of eroundwater in the West Pit backtill is a veais, based on an <br />~~.~ <br />outflow rate of approximately 80 ;w~ar3. Ten pore volumes of flushing at 4 years pcr pore volume <br />results in 40 years, as was presented in TR-26 (pp. 38). <br />3801 Automation Way, S'aite 100, Fort Collins', Colorado 80~1~ <br />Telephone (970)123-9600 / FA.Y (970) 113-7171 <br />