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Remedial Action Plan-Tosco 76 Branded Facility No. 11195 June 2.1_ 1999 Five on-site groundwater monitoring wells (MW-1 through MW-5) were installed in December 1992. Soil samples collected from the borings were reported to contain petroleum hydrocarbons at concentrations of up to 120 parts per million (ppm) of Total Petroleum Hydrocarbons as gasoline (TPHg), and 16 ppm of benzene. The initial groundwater samples collected from MW-3 and MW-4 contained concentrations of up to 10,000 parts per billion(ppb) of TPHg (Alisto, 1999). Two additional wells (MW-6 on-site and MW-7 off-site) were installed in September 1993. Soil samples collected at a depth of 6 feet below ground surface (bgs) were reported as not detected for petroleum hydrocarbons (Alisto, 1999). One 550-gallon fiberglass waste oil UST and associated remote fill line were removed in 1997. One soil sample was collected from the bottom of the waste oil UST excavation at 10 feet bgs. A second soil sample was collected from beneath the remote fill line at 3 feet bgs. Both samples were reported as not detected for all petroleum hydrocarbons (GeoStrategies, Waste Oil UST and Remote Fill Line Soil Sampling Report, dated August 6, 1997). In July 1998, an abandoned water well, located north of the former UST pit adjacent to Louise Avenue, was properly destroyed by perforating the steel casing and grouting the well with neat cement placed by the use of a grout pump and tremie pipe. The well destruction was permitted and observed by the San Joaquin County Environmental Health Division(SJCEHD). Five off-site wells (MW-8 through MW-12) were installed and one off-site well MW-7 was destroyed in September 1998. Soil samples collected during the investigation at depths of 4 to 6 feet bgs contained petroleum hydrocarbon concentrations of up to 1.5 ppm of TPHg and 0.0034 ppm of benzene. Five oxygenate compounds or methyl tert-butyl ether (MtBE) were not detected in any soil samples (Alisto, 1999). A sensitive receptor survey and a 1h-mile water well survey were performed by Alisto. No basements or subways were found within a 300-foot radius of the subject site. An off-site subsurface utility survey revealed the presence of a sanitary sewer trench adjacent to the subject site which may influence the transport of petroleum hydrocarbons in groundwater. A search of California Department of Water Resources (DWR) and Banks Information Solutions files determined that seven water wells had been installed within 1h-mile of the subject site, but only two could be definitively located. A visual reconnaissance of the area did not identify any water wells (Alisto, 1999). One 10,000-gallon, one 8,000-gallon, and one 6,000-gallon single-wall fiberglass gasoline USTs, two dispenser islands, related product lines, and one canopy were replaced with two 12,000-gallon double-wall gasoline USTs, two dispenser islands, related product lines, and one canopy in December 1998. The new USTs were installed in an excavation located immediately adjacent to the former UST complex. These excavations are hydraulically connected with pea gravel backfill material encountered in the northeast corner of the former UST pit. 140193.07-1 2