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s d PROBLEM ASSESSMENT REPORT Moore Petroleum, Inc. 1399 E. Yosemite Avenue, Manteca, CA NGA Project No. 10-0rl•4$0 Page 11 TABLE 4 Ground-water Analytical Results Sample Ethyl- ID Date Benzene Toluene Benzene Xylenes EDB EDC TPH MPI--1 08/24/88 2.3 NF NF 3.0 NF 1.2 80.0 04/28/59 NF NF NF NF NF NF <50.0 MW-1A 07/06/90 72.0 20.0 14.0 380.0 NF NF 4800.0 MW-2 04/28/89 8.4 NF 4.0 4.0 0.3 NF 200.0 07/06/90 NF NF NF NF NF 0.3 NF MW-3 04/28/90 0.4 NF 2.0 10.0 1.0 NF <50.0 07/28/90 NF NF NF NF NF NF NF NOTES: all values in ppb NF = Not Found TPH = Total Purgeable Petroleum Hydrocarbons EDC = 1r2-Dichloroethane EDB =Ethylene Dibromide 4.0 DISCUSSION OF RESULTS 4.1 Extent of Petroleum Constituents in Soil Analyses of soil samples taken from soil borings and beneath USTs and fuel product lines at the site indicate that the areal extent of petroleum constituents in soil is confined primarily to the vicinity of the former tank basin. A smaller area where site soils contain petroleum constituents appears to extend from the Southern end of the tank basin to the vicinity of MW-1A. The highest TPH concentration was detected at MW-1A (40,000 ppm) . Soil sample analyses indicate that TPH concentrations in site soils are highest in the vicinity of the former tank basin and MW-1A and decrease rapidly away from these areas. Figure 5 presento the interpreted areal extent of petroleum constituents in site soils. The interpreted vertical extent of petroleum constituents in site soils is shown on the geologic cross-sections of Figures 4. 'These figures (based upon soil analytical results) indicate that --- ----- --- ----- -------------appreciable-concentrations- limited oncentrations limited to a depth of about 25 feet beneath the surface of the site: