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REQUEST FOR SITE CLOSURE <br /> General MWs Facwcy <br /> 2000 West Turner Road <br /> Lodi, CAIdornla <br /> Delta Project Yo 40-92-708 <br /> Page 7 <br />' 5.0 CONCLUSIONS AMD RECOMMENDATIONS <br /> Delta recommends that no further action be taken at the site for the following reasons. volatile <br />' hydrocarbon constituents in soil have only been detected at trace concentrations in the base of the former <br /> underground storage tank basin, TPH as diesel No 6 is restricted to a small volume of soil beneath one <br />' of the former underground heating oil tanks, diesel No 6 is relatively immobile in soil and has not <br /> migrated vertically more than a few feet in the 45 years since storage tanks have been located at the site, <br /> and ground water has not been impacted as indicated by four quarters of monitoring <br />' The County has incorrectly applied the leaching potential analysis screening table by requiring further <br /> site investigation, but it is Delta's opuaion that further site investigation should not be conducted unless <br />' the results of General Risk Appraisals warrant Delta performed General Risk Appraisals for toluene, <br /> xylenes, and athylbenzene A General Risk Appraisal for benzene was not necessary because it has not <br /> been detected at the site The results indicate that the acceptable concentration at 15 feet tar toluene is <br /> S ppm, for xylenes is 30 ppm, and for ethylbenzene is 40 ppm The actual concentrations detected at <br /> 15 feet (the base of the tank excavation) were 0.006 for toluene, 0 045 for xylenes, and 0.01 for <br /> ethylbenzene Therefore, soil remediation is not necessary <br /> Finally, to further support our recommendation, Delta performed theoretical General Risk Appraisals. <br /> For these appraisals, we assumed that toluene, xylenes, and ethyibenzene have migrated vertically in the <br /> soil to 30 feet beneath the surface at the concentrations in which they were detected in the base of the <br /> tank excavation. This simulates a worst-case scenario Even with worst-case assumptions, the results <br /> of these appraisals indicate that acceptable concentrations of toluene range from 4 ppm at 20 feet to <br /> I ppm at 30 feet, xylenes range from 20 ppm at 20 feet to 7 ppm at 30 feet, and ethylbenzene range from <br />' 40 ppm at 20 feet to 10 ppm at 30 feet. AIthough we do not believe that these constituents have migrated <br /> undiluted to these depths, if they had, the acceptable concentrations based on General Risk Appraisals <br /> are still well above concentrations actually found !n soil at the site. <br /> R M6 TA <br /> r <br />