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, . SCD f <br /> Color Spot, Inc. <br /> March. 19, 1991 (M88168F) 7 <br /> Therefore, it is our opinion, the trace concentrations of benzene detected in the <br /> local wells is the result of a source other than the former UST. <br /> SGD recommends that no additional site characterization of <br /> hydrocarbon contaminated ground water be conducted at the site by Color Spot, <br /> Inc. , the existing ground water monitoring well be abandoned, and the site be <br /> granted closure status, in regards to ground water contamination, by PHS-EHD. <br /> Additionally, according to PHS-EHD's most recent letter, paragraph <br /> no. 3 indicates that "San Joaquin County Flood Control maps document regional <br /> ground water gradient to the southwest at depths of 50 to 60 feet during the <br /> seasonally high year of 1986". Given the fact that the effective base of any <br /> soil contamination documented at the site was at a depth of less than 15 feet <br /> below the ground surface, and that ground water was not encountered at a depth <br /> of less than 90 feet below the ground surface during October 1990, there exist <br /> a 75-foot-thick zone of uncontaminated material between the ground water table <br /> and any former soil contamination, at a minimum. The worst case considered, <br /> there existed a 35-foot-thick zone of uncontaminated material between the ground <br /> water table and any previously existing soil contamination in the "seasonally <br /> high year of 1986" . <br /> { CLOSURE <br /> i <br /> We trust this information will be of use. If you have any questions, <br /> please contact one of the undersigned. <br /> i <br /> Sincerely, <br /> STAAL, GARDNER & DUNNE, INC. <br /> a <br /> Jerome K. Summerlin David A. Gardner <br /> Staff Geologist President <br /> JKS:DG:av/12 <br /> I <br /> I <br /> i <br /> t <br /> a <br />