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2.3 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 duinig the November 1992 monitomig Tills direction may be a one-time anomaly or, more likely, may be erroneous (Harlin Knoll - PHS/EHD, personal communication, 1994) Petroleum hydrocarbons were detected in groundwater samples froin the monitoring wells during each monitoring event (Table 3) Concentrations have varied over time, but no clear pattern has emerged Benzene, toluene and xylenes were detected during the November 1992 groundwater monitoring event 2.4 UST Removai The UST's and product lines were piessuie tested for leaks in 1987 The tanks and piping passed the pressure tests, however, a faulty vapor recovery valve was discovered and repaired Four 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 hydiocaibons Very low concentrations of volatile aromatics were 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. Four-inch diameter PVC casing was installed around the bottom of the excavation Slotted casing was used on the noithein and southern sures of the excavation and blank PVC was used on the eastern and western sides Blank piping was installed vertically to the surface and extended to a point behind the northern corner of the building Approximately S niches ' of pea gravel were placed in the excavation to cover the piping Plastic sheeting was placed over this gravel, and the new USTs were installed over the plastic sheeting 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 fiend (SB 2004) I Mr Phillips therefore retained GeoAudit to per foi nn additional subsui face 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 Owieyvl Ando Se-,Inc A IL—i ru d Swed.QR331 KSM S Y I ,