1992-08-07_REVISION - M1988112 (2)

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' and have conducted modelling exercises using the modified Theis equation for unsteady radial Flow to a well. The input data to the model are as follows: 1 transmissivity = 75 gpd per foot, ' saturated thickness = 20 feet, storage coefficient = 0.001, ' pumping rate of each well: M-9 = 1. gpm, M-12 = 1. gpm, M-13 = 0.4 gpm. 1 Using the existing monitoring well configuration, the model was run to evaluate if these wells ' can hydraulically control the gradient in the Flow window that could potentially be affected by releases from the tailings facility and collection pond (given the current direction of ground ' water flow). The results indicate that, given the current configuration of the monitoring wells and the aquifer hydraulic characteristics obtained from the pump tests, these three monitoring ' wells would not be sufficient, in and of themselves, for all possible remediation eventualities. ~ •° ' However, given the extremely tight nature of the Santa Fe Formation, with the associated very small seepage velocity (approximately 15 feet per year), there is no need to instlall additional wells simply to conUol the hydraulic gradient in the event that remediation may be necessary i some time in the future. If any of the monitoring wells currently installed observe cyanide concentrations indicative of a leak from the tailings facility andlor collection pond, additional wells could be installed at that time, equipped and pumped to control the hydraulic gradient in ' the contaminated area. ' ' Battle Mountain believes that the three existing monitoring wells that are completed in the upper water-bearing strata of the Santa Fe Formation adequately monitor downgradient df the tailings ' facility and collection pond for potential leaks from these facilities. ' CONCLUSIONS AND RECOMMENDATIONS Based on the field investigations and subsequent analyses, we would offer the following ' conclusions and recommendations: ' -8- ,~-x