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Remedial Investigation Report <br /> -11- 8 March 1991 <br /> DDRW, Sharpe <br /> FINDING <br /> 31. off-site agricultural pumpage causes significant impacts to the ground water flow <br /> pattern at SHAD. Specifically agricultural wells 6, 7, and 10 are affecting both <br /> lateral and vertical movement of Plumes 3, 4, and 7. <br /> RESPONSE <br /> 31. 1 concur with this finding. In addition, based on Figure 9.0-4 in the Report, it <br /> appears that the agricultural supply wells AGW-8 and AGW-9 may also be influencing <br /> the plume migration in the lower water bearing zones. <br /> Because of the pumping influences of these agricultural supply wells are <br /> significant and occur on a seasonal basis, it is important that hydrogeologic <br /> analysis of the site be changed in the future to maximize the efficiency of the <br /> ground water cleanup system. The ground water contour maps need to be revised <br /> from using monthly average ground water elevations over the period from 1987 to <br /> 1989 as the base map to two water level contour maps which represent the maximum <br /> conditions during the wet and dry seasons. In addition, the electrical records <br /> of the agricultural and other supply wells should be obtained to estimate the <br /> pumpage which is then used to quantify the outflow in the system for the model . <br /> If these changes are not made, it can be assumed that the assessment of the plume <br /> migrations and the effectiveness of the treatment system will be sacrificed due <br /> to the incomplete and inaccurate hydrogeologic analysis. <br /> RESPONSES TO RECOMMENDATIONS IN THE REMEDIAL INVESTIGATION REPORT <br /> I have provided responses to each recommendation provided in Chapter 10 of the Report. <br /> However, the recommendations fall short of what is needed to investigate the lateral <br /> and vertical extent of contamination of the ground water and soils. of particular <br /> concern, is that there were no recommendations for the installation of additional <br /> monitor wells. The information in the Report clearly demonstrates that the TCE plume <br /> has migrated into deeper water bearing zones in the down gradient direction. In all <br /> of the plumes, it appears that deeper monitor wells are needed, particularly in the <br /> areas of highest contamination. In addition, as the plumes have migrated off-site and <br /> as influenced by the pumping of the agricultural supply wells, the lateral extent of <br /> many of the plumes is ill-defined in some areas. Plume definition work may be <br /> conducted during the feasibility study. <br /> With respect to soils, the Report indicates that the hazardous concentrations of a <br /> particular constituent may be considered as the cleanup level . This is unacceptable. <br /> The cleanup level must be determined based on the analytical results for soluble <br /> concentrations, particularly for heavy metals and pesticides. An environmental fate <br /> analysis, such as the Designated Methodology, must be performed to determine the <br /> concentrations of the residual waste constituents which pose a threat to water quality. <br /> The Report failed to consider these aspects for the necessary soil remediation work at <br /> the site. <br /> RECOMMENDATION <br /> 1 SoloidkWaste ManagementpUniit (S MU) #3 (BldgalS-119) . d- Thi1saplantshouldsoil <br /> addresaround <br />