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<br /> <br />The Santa Fe formation has a very high acid neutralization potential. <br />Both the Santa Fe and the Pink Gneiss units have the potential to release selenium in quantities <br />exceeding drinking water and agriculture standards. The Pink Gneiss has the potential also to release <br />manganese in quantities exceeding drinking water and agriculture standards. However, high Se and <br />Mn are characteristic of the local waters, so it appears that the generation and release of either of these <br />metals would not appreciably affect the ambient groundwater conditions. <br />Most of the Pink Gneiss will be stored below the water table and below the water table <br />fluctuation zone. In that configuration, acid cannot be generated in significant gtiatttities. Most of <br />the Santa Fe will be stored at or above the water table, but because the Santa 'Fe is a net alkali <br />generator, the potential for acidification of groundwater is nil. <br />A minor quantity of the Pink Gneiss will be stored above the water table and within the water <br />table fluctuation zone. Acid may be generated, locally, from the Pink Gneiss stored here, but the <br />presence of the alkaline Santa Fe formation around it should serve to neutralize such acid in very short <br />order. <br />It is likely that any release of manganese or selenium from either of the units will be <br />indistinguishable from the presence of these metals already in local waters. <br />CONCLUSIONS AND RECOMMENDATIONS <br />After the West Pit is filled and after groundwater pumping ceases, groundwater around the pit <br />will rise to some equilibrium level similar to the pre-mining condition. It seems very unlikely that <br />the water quality, which will evolve as the West Pit re-equilibrates with the local surface and <br />groundwater, will differ appreciably from that which existed prior to filling the West Pit. <br />The current monitoring well configuration seems adequate to detect and intercept contaminated <br />groundwater, if such ever develops -which seems unlikely. The monitoring plan should assure that <br />water from the pit area has had the chance to flow to the measurement wells before the monitoring <br />program is curtailed. <br />A:~TRIBBMRI.REV <br />9 <br />