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Mr Jeffrey Wong Page 2 of 7 2.0 BACKGROUND INFORMATION 2.1 Site Description and Hydrogeologic Setting The site is located in east central Stockton approximately one mile west of Highway 99 (Figure 1) The nearest naturally occurring body of surface water is the Calaveras River, located approximately one mile to the north Approximately 1/2 mile north of the property, between the property and the Calaveras River is the Stockton Diverting Canal, a tributary to the Raver Surface elevation at the site is approximately twenty-one feet above sea level Based upon published data from the San Joaquin County Flood Control and Water Conservation District (Spring 1997 Groundwater Report), groundwater was expected to have been encountered at a depth of approximately 55 feet below grade in the site vicinity Data from an adjacent property reveal that historic low groundwater occurred in 1992 at approximately 85 feet below grade Water levels may have reached historic highs in early 1999 when the depth to water in the site vicinity was approximately 36-38 feet below grade According to the Flood Control District reports, groundwater flow has been predominantly toward the northeast although the property is located within an area subject to repeated variations in flow direction and gradient Groundwater flow at the adjacent site has varied from southwesterly to northeasterly over a period of less than ten years 2.2 Underground Storage Tank Removal and Soil Sampling On April 12, 1989, four USTs(one 2,000 gallon, two 550 gallon and one 300 gallon)were removed from the subject site by North Cal Construction of Stockton, California The contents of the USTs apparently had consisted of gasoline One soil sample was collected from beneath each of the smaller USTs at depths ranging from 9 to 10 feet Two samples were collected at depths of 11 5 feet from beneath the 2,000 gallon UST In addition one soil sample was collected from a depth of 3 feet beneath a product line The samples were submitted to State-Certified FGL Environmental Laboratories for analysis Each sample was analyzed for total petroleum hydrocarbons (TPH) using modified EPA Method 8015, for benzene, toluene, ethylbenzene and xylenes (BTEX) and ethylene dibromide(EDB) by EPA Method 8020 and for total lead by EPA Method 7420 Elevated concentrations of TPH and BTEX were detected in the samples collected from beneath Tank#1, Tank#2 and the product line No detectable concentrations of TPH or BTEX were found in the samples collected beneath Tank #3 or Tank #4 No detectable concentrations of EDB were found in any sample Total lead concentrations appear to be within the range of naturally occurring, background concentrations Analytical data are summarized in Table 1 UST and soil sample locations are depicted on Figure 2 The generally good condition of Tank#2 and the lack of significant odor and discoloration noted by the inspector above a depth of 11 feet suggests that the primary source of contamination at the site may have been the adjacent Tank #1 which was noted to have holes Fill and native soil within the Tank #1 excavation were described as having "severe" odor and discoloration from the surface to the sampling depth of 10 feet data\grounzelhwTyslsumrpt doe