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f <br /> �3 <br /> I rJ v1 <br /> Ann Cerney <br /> Page 2 <br /> lab results it appears soil samples were taken at twenty-five (7.5) <br /> and thirty (30) feet below ground surface. Results indicated that <br /> ;. all other peaks quantitated as Benzene existed at 2 ppm and 6 ppm <br /> at the above respective depths. One water sample was taken from <br /> this monitoring well. The samp3.e. results were non-detect at: twenty <br /> l (20) parts per billion (ppb) . The detection limit recommended for <br /> E` use today is 5 ppb. Given the high detection limit, the need for <br /> confirmation sampling and gradi•rnt determination PHS/EHD does not <br /> feel confident that groundwater has not been impacted. <br /> The lead agency providing oversight at the time the above work was <br /> completed was California Regional Water Quality Control Board, <br /> s Central Valley Region. PHS/EHD has contacted their office and <br /> verified that this site remains on the contaminated site list. <br /> i PHS/EHD is now the lead agency providing oversight for <br /> investigation and remediation of sites contaminated from ,leaking <br /> ' underground storage tanks. The LUFT manual, "Regional Board Staff <br /> Recommendations for Initial Evaluation: and 1'nvestigation of <br /> Underground Tanks" and "Appendix All are guidance documents that <br /> PHS/EHD uses in evaluating sites. Seasonal high groundwater shown <br /> on the San Joaquin County Flood Control Map 1986, is thirty (30) <br /> feet below ground surface for this s.itt- Since soil contamination <br /> _.. appears to exist at twenty-five (25) and thirty (30) feet below <br /> ground surface a groundwater investigation is required. According <br /> to the above documents, if the groundwater gradient for this site <br /> can be documented at an adjacent site, the minimum investigation <br /> would be installation of one monitoring well placed within ten (10) <br /> feet of the tank excavation in a down--gradient position. if the <br /> r' groundwater gradient cannot be documented, a minimum of three (3) <br /> monitoring wells must be installed to determine the gradient. <br /> After review of the results from the minimum investigation PHS/EHD <br /> will comment on whether further investigation is warranted. A <br /> proposal for the above work and a request to be placed in the Local <br /> Oversight Program should be submitted to PHS/EHD. <br /> If you have any questions, contact Margaret Lagorio, Senior REHS, <br /> at (209)468-3449. <br /> Jog- Khanna, m.D. , M.P.H. <br /> Health of a Icer J <br /> e A. C tulla, REHS, Program Manager <br /> ....-Environmental <br /> Division <br /> _._._ <br /> LAC/ML:n2: <br /> ,�: Robertson and Kirsten. <br /> 15312 N E 90th Street <br /> Redmond, WA 98052 <br />