1997-06-10_REVISION - M1981302 (7)

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Memo to File M-81-302 -5- June 5, 1997 gpd/ft2 and averages about 200 gpd/ft2. Using the average value for hydraulic conductivity, the capture zones for the dewatering trenches were analyzed and platted in the Leonard Rice report . These plats show that the captur3 zones extend no more than 260 feet from the deep dewatering trenches . The presence of only a 260 foot lateral extent for the ground water capture zone during aggressive pit dewatering leads to the conclusion that the capture zone of evaporating ground water lakes would cause only a slight cone of depression resulting in negligible impacts on the elevation of the ground water table . Subsequent to the submittal of the Leonard Rice report, the Division required that justification be provided for the hydraulic conductivity values used in the determinations made . The operator conducted direct measurements of inflows to dewatering trenches and calculated hydraulic conductivities of between 73 .4 gpd/ftz and 80 . 7 gpd/ft' . These hydraulic conductivity values are lower than the values input to the analysis in the Leonard Rice report . Lower hydraulic conductivities would result in a smaller capture zone with a steeper slope to the cone of depression. The current approved reclamation plan for the Deepe Farm Pit calls for the construction of a chain of 4 ponds, within the perimeter berm, that would be excavated into ground water and could also be fed by ditch water. The creation of additional water surface at the site by excavating ponds to expose ground water would tend to cause additional depression of the water table elevation, which would be a greater threat to Ute ladies' tresses orchid habitat than the current condition and the proposed reclaimed condition with a lesser area of ground water exposed to the atmosphere . During times when the chain of ponds in the currently approved reclaimed configuration were being fed by ditch water, an increase in the elevation of the surrounding ground water table could result, and the higher ground water table could potentially be an enhancement of habitat for the Ute ladies' tresses orchid and for the Preble' s mouse . However, since the chain of ponds approved in the current plan have not been constructed, the prevailing mouse and orchid habitat does not rely on any increase in water table elevation that the chain of ponds may create, so there would not be a negative off-site impact in terms of lowering the ground water table by deleting the chain of ponds from the plan. In fact , the impact to mouse and orchid habitat in the surrounding Open Space by deleting the chain of ponds could be positive, because, as discussed above, during periods when the chain of ponds would not be fed by ditch water, the ponds would tend to cause a depression of the water table . Although, as is also discussed above, the depression in the water table as it would affect surrounding lands would be negligible under either the currently approved reclamation plan or under the proposed reclamation plan. It follows from the analysis presented above that relative to what