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Remedial Investigation Report -2- 8 March 1991 <br /> DDRW, Sharpe <br /> RESPONSES TO FINDINGS IN THE REMEDIAL INVESTIGATION REPORT <br /> FINDING <br /> 1. SHAD is underlain by a geometrically complex sequence of interbedded sand, silt, <br /> and clay. Individual lithologic units tend to be discontinuous over small <br /> distances. <br /> RESPONSE <br /> 1. I concur with this finding except that it is technically inaccurate to state that <br /> sediments are deposited in geometric patterns. I assume that the term "geometric" <br /> refers the lenticular lenses which are typical of the nature of alluvial <br /> sediments. <br /> FINDING <br /> 2. Based on relative moisture of sediments recovered during drilling and results of <br /> the seismic reflection survey, it appears that most of the sediments underlying <br /> SHAD are not saturated with water. It is estimated that only 25 percent of the <br /> subsurface materials are saturated with water. The saturated units are generally <br /> cleaner sands and represent potential flow paths for ground water contaminant <br /> movement. <br /> RESPONSE <br /> 2. I do not concur with the finding. Cleaner sands generally are the preferential <br /> flow paths for ground water contaminant movement. However, the finding that only <br /> 25 percent of the subsurface materials are saturated is not supported by the data <br /> generated from the RI and is based on the highly questionable soils information <br /> and misinterpretations of the seismic reflection data. The soils information is <br /> questionable because the depth of the soils borings samples were never related to <br /> the depth of the ground water table and if the samples were obtained using mud <br /> rotary, then the relative soil moisture cannot be determined. The seismic <br /> reflection data indicates the relative densities of the different lithologic <br /> units, but does not indicate relative moisture content. In addition, it is <br /> unclear how the different water bearing zones (assumed to be the saturated, <br /> cleaner sandy sediments) can be interconnected if only a small portion of the <br /> subsurface is saturated. <br /> FINDING <br /> 3. Because the relative proportion of saturated sediments is low, the total quantity <br /> of potential contaminated ground water is less than originally estimated. <br /> RESPONSE <br /> 3. This finding should be deleted from the final RI because it is based on the <br /> finding that most of the subsurface is unsaturated (refer to response above) . <br /> FINDING <br /> 4. The aquifer system (i .e. ,aquifer and aquitards) can best be described as a <br /> non steady-state, anisotropic, multiple, discontinuous, leaky artesian system. <br />