ARCHIVED REPORTS_XR0007462 CASE 1

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REQ[JEST FOR SITE CL SURE Ganeral dills Facuiry 2000 West Turner Road . Lodi, CaL for= Delta Project No 40-92-708 Page 7 5.0 CONCLUSIONS -SND RECOMMENDATIONS Delta recommends that no further action be taken at the site for the following reasons volatile hydrocarbon consutuents in soil have only been detected at trace concentrations in the base of the former underground storage tank basin, TPH as diesef No 6 is restricted to a small volume or soil beneath one of the former underground heating oil tanks, diesel No 6 is relatively immobile in soil and has not migrated vertically more than a few feet in the 45 years since storage tanks have been located at the site, and ground water has not been impacted as indicated by four quarters of monitoring The County has mcorreedy applied the leacning potential analysis screening table by requirmg further site investigation, but it is Delta's opinion that further site investigation should not be conaucted unless the results of General Risk Appraisals warrant. Delta performed General Risk Appraisals for toluene, xylenes, and ethyibenzene. A General Rask Appraisal for benzene was not necessary because it has not . been detected at the site. The results indicate that the acceptable concentration at 15 feet for toluene is S ppm. for xylenes is 30 ppm, and for erhyibenzene is 40 opal. The actual concentrations detected at 15 feet (the base of the tank excavation) were 0 006 for toluene, 0 045 for xylenes, and 0 01 for ethyibenzene Therefore, soil remediation is not necessary Finally, to further support our recommendation, Delta performed theoretical General Risk Appraisals For these appraisals, we assumed that toluene, xylenes, and ethyfbenzene have migrated vertically in the soil to 30 feet beneath the surface at the concentrations in which they were detected in the base of the tank excavation_ This simulates a worst-case scenario. Even with worst-case assumptions, the results of these appraisals indicate that acceptable concentrations of toluene range from 4 ppm at 20 feet to I ppm at 30 feet, xylenes range from 20 ppm at 20 feet to 7 ppm at 30 feet, and ethylbenzene range from 40 ppm at 20 feet to 10 ppm at 30 feet. Althougn we do not believe that these constituents have migrated undiluted to these depths, if they had, the acceptable concentrations based on General Risk Appraisals are still well above concentrations actually found in soil at the site R PTCr76.TA