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23 Groundwater Monitoring Groundwater monitoring of the site was performed by AGS and Nations Groundwater Associates (NGA) on seven occasions between June of 1987 and November 1992 AGS and NGA reported that groundwater flowed consistently to the southwest between June 1987 and April 1991 However, in a report dated February 2, 1993, NGA calculated a northeasterly groundwater flow during the November 1992 monitoring This direction may be a one-time anomaly or, more likely, may be erroneous (Harlin Knoll - PHS/EHD, personal communication, 1994) Hydrocarbons were detected in groundwater samples from the monitoring wells during each monitonng event (Table 2) Concentrations have vaned over time, but no clear pattern has emerged Benzene, toluene and xylenes were detected during the November 1992 groundwater monitoring event 2.4 LIST Removal The UST's and product lines were pressure tested for leaks in 1987 The tanks and piping passed the pressure tests, however, a faulty vapor recovery valve was discovered and repaired Two UST's were removed from the site In March of 1990 Eight samples were analyzed by EPA methods 8240 and 8260 for volatile and semi-volatile hydrocarbons Gasoline contamination was detected in soil samples collected beneath the tanks According to the San Joaquin County Public Health Services - Environmental Health Division (PHS/EHD), approximately 800 cubic yards of gasoline-contaminated soil were removed from the tank excavation and stockpiled on-site 2.5 Further Investigation As a result of the continued evidence of groundwater contamination, PHS/EHD notified Mr Phillips that failure to take corrective action to remove the contamination would jeopardize his eligibility for reimbursement from the state underground tank cleanup fund (SB 2004) Mr Phillips therefore retained GeoAudit to perform additional subsurface investigation of the extent of soil and groundwater contamination From January 11 to 17, 1994, four soil borings were drilled at the site Borings MW-5 and MW-6 were advanced to a depth of 85 feet and completed as groundwater monitoring wells Borings B7 and B8 were advanced to a depth of 65 feet and backfilled in the entire depth with Portland cement No petroleum hydrocarbons were detected in any of the 14 samples analyzed The stratigraphy appears to vary considerably across the site Clayey to sandy silts are present from the surface to d to 12 feet The silt overlies moderately-sorted to well-sorted Geological Audit Services, Inc ' Lockeford Beacon QR2/5 941860 S 4