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