2005-01-03_REVISION - M1999120 (5)

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Ms. Lynn Mayer January 3, 2005 Page 7 3. Mitigation. If the trigger is reached based on post-mining data, the following actions should be undertaken: • An evaluation of the data to confirm that LGE is responsible for the change should be completed. • Implementation of mitigation measures. Mitigation measures that could be implemented (not necessarily in the order listed) include: • Construction of a pipe/drain to equalize groundwater levels. Preliminary modeling and calculations indicate that it would be possible to construct a gravity drain or pipeline to equalize groundwater levels to mitigate impacts from the proposed expansion. Such a drain or pipe could be constructed along County Road 18, or between lined cells in the proposed amendment area, where it would convey water from the upgradient side of the operation to the downgradient side. • Release of water in ditchesflaterats. Water could be released in ditches/laterals to provide irrigation, increase recharge, and/or raise groundwater levels. • Well improvements. Affected water wells could be deepened or modified to increase yield. Alternatively, new alluvial well(s) could be constructed to provide a new water supply. LGE should provide temporary replacement, if needed, while studies to determine fault are being conducted, or while mitigation measures are in the process of being implemented. The exact mitigation measure or combination of measures would be determined based on additional investigations and consultations with the affected party. Costs for implementation and maintenance of mitigation measures needed from LGE operations should be borne by LGE. #9 Effects on stability of wells, wetlands, and cottonwood trees. As described in the previous response and shown on Drawing 5, the cumulative impact study completed shows that the amendment area reduces groundwater levels by a maximum of 5 feet north of the pit. Potential impacts from this drawdown were addressed in #8. The following addresses potential impacts from mounding. The impact study shows a rise in groundwater, or mounding, of 3 feet on the west side of the operation due to the proposed amendment.