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Del Monte/Disco <br /> Page 2 <br /> PHS/EHD does not agree that the levels of Fe 1 are elevated in the zone of f <br /> significant contamination. The level of Fetes- decreased in MW-DIS-2, MW-DIS-3, <br /> MW-DIS-'SS, as well as MW-DIS-4 (discussed in the report) . <br /> I I <br /> PHS/EHD does not agree that levels of methane are elevated in the zone of <br /> significant contamination. Levels of methane increased in MW-DIS-2 (which is <br /> in the zone of significant contamination) as well as MW-DIS-8S (which is <br /> outside the zone of significant contamination. <br /> Based on these two sampling events for the ITB geochemical indicators PHS/EHD <br /> does not feel any conclusions can be drawn. The petroleum hydrocarbon <br /> contamination has continued to exist at this site for at least 20 years, based <br /> on the information that the tanks were last used in 1976. As discussed <br /> previously in letters and meetings, the variation of depth to water (50 to 100 <br /> feet below rade) , contaminated aminated soil existing above and below groundwater, and <br /> site difficult to evaluate <br /> and <br /> e <br /> sandy, clayey silt type soil makes this <br /> remediate. <br /> It has been demonstrated that vapor extraction is a viable alternative for <br /> remediation at this site. If the radius of influence of a properly screened <br /> and constructed vapor extraction well can be determined, then the number of <br /> vapor extraction wellsjnecessary* to remediate the contamination at this site <br /> can be determined. The cost of the installation of the vapor extraction wells <br /> and conducting vapor extraction until cleanup goals are achieved, must be <br /> evaluated in comparison to some other remedial alternative as discussed in CCR <br /> Section 2725 (d) . A copy is enclosed. The most cost effective alternative <br /> must be performed. <br /> As discussed above it may be necessary to install properly screened wells and <br /> perform vapor extraction tests, if groundwater levels do not decrease. <br /> If you have any questions contact me at (209) 468-3449. <br /> Donna Heran, RENS, Director <br /> Environmental Health Division <br /> Margaret Lagorio, REHS; Supervisor <br /> Site Mitigation Unit <br /> "c: CH2M Hill <br /> c: CVRWQCB - Beth Thayer <br /> c: SWRCB Cleanup Fund <br /> Enc. <br />