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Clint Rogers <br /> Page 2 <br /> PHS/EHD stated in correspondence dated October 17, 1991 that further confirmatory <br /> soil sampling would be necessary to evaluate the effectiveness of the vapor extraction <br /> system. Subsequently, on May 12, 1992 three soil borings were drilled, two converted to <br /> monitoring wells, MW10 and MW11, and one converted to a vapor extraction well, VW6. <br /> Soil sample results detected residual soil contamination which may act as a source to <br /> further contaminate groundwater. The vapor extraction well, VW6, was terminated at <br /> 27.8 feet and analysis detected residual contamination, 120 ppb benzene and 730 ppm <br /> total petroleum hydrocarbon - gasoline. Only two samples, at 50 and 60 feet, were <br /> analyzed from each monitoring well, MW10 and MW11, and these samples detected <br /> toluene contamination up to 60 ppb. Additional investigation of the extent of soil <br /> contamination will be necessary. <br /> Since the VETS system was installed as an interim remedial measure, PHS/EHD does <br /> not object to the removal of the system prior to the complete remediation of soil <br /> contamination. Further soil investigation to define the extent of soil contamination is <br /> necessary prior to the installation and operation of a final remedial system. <br /> Once soil and groundwater contamination has been defined, a problem assessment report <br /> should be submitted, followed by a final remediation plan to mitigate residual soil and <br /> groundwater contamination. <br /> If you have any questions or to schedule a site inspection, please contact Mary Meays, <br /> REHS, of my staff at (209) 468-0337. <br /> Jogi Khanna, M.D., M.P.H. <br /> Health Officer _ <br /> Laurri�otulla, REHS, Program Manager <br /> (environmental Health Division <br /> LAC/MM:lb <br /> c: Elizabeth Thayer, CVRWQCB <br /> c: Richard Blewett <br /> c: Geoffrey Bain <br /> c: John Borkovich, GTI <br /> c: David Thomas, Geraghty and Miller <br />