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Remedial Investigation Report -3- 8 March 1991 <br /> DDRW, Sharpe <br /> RESPONSE <br /> 4. This description of the aquifer system needs to be revised. The aquifer is not <br /> discontinuous. The lithologic units are discontinuous because of the nature of <br /> the alluvial depositional environment. However, the aquifer is continuous across <br /> the site. The Report did not define any boundary conditions which would cause the <br /> aquifer to be discontinuous. Additionally, if the aquifer is artesian, then it <br /> is not leaky. The term artesian generally implies confined conditions. The use <br /> of the term leaky generally implies semi-confined conditions. Furthermore, the <br /> storage coefficients determined from aquifer test data do not support the finding <br /> that confined conditions exist across the site. The description of the aquifer <br /> system is confusing. <br /> FINDING <br /> 5. Data from the 72-hour pump test on Lathrop well No. 5 and other subsequent tests <br /> indicate that some areas of SHAD apparently exhibit relatively high values of <br /> vertical permeability. <br /> RESPONSE <br /> 5. This finding is confusing. 1 concur that the aquifer test data indicated that <br /> some of the water bearing zones exhibited relatively high values of hydraulic <br /> conductivity (K) . However, the use of the term "vertical" confuses the matter. <br /> The aquifer parameters derived from a aquifer test are usually in reference to <br /> horizontal K. One of the major assumptions of the most common methods of aquifer <br /> test analyses is that the vertical flow components are neglected and that the flow <br /> is considered to be horizontal and uniformly distributed with depth (Dupuit- <br /> Forchheimer assumption) . <br /> The use of the term "vertical " is confusing because vertical flow components <br /> become important when there are thick clayey sediments within the aquifer. When <br /> these units are stressed, downward vertical gradients will be increased because <br /> of the low hydraulic conductivity of these type units. Therefore, the term <br /> vertical should be deleted from the finding. <br /> FINDING <br /> 6. More than 6,200 environmental samples consisting of more than 3,700 ground water <br /> samples, 1,800 soil gas samples (see Fig. 9.0-1) , 200 air samples, and 500 soil <br /> samples have been analyzed from SHAD. <br /> RESPONSE <br /> 6. I concur with the finding. A significant data base has been developed at this <br /> site. However, my review of the Report has revealed that a large portion of the <br /> data may have been used inaccurately, may not have been used to its fullest extent <br /> or may not have been used at all in the interpretation and presentation of the <br /> data. The inaccurate and incomplete hydrogeologic analysis has been a long <br /> standing problem at this site. <br /> FINDING <br /> 7. TCE is the dominant VOC in both soil and ground water at SHAD. <br />