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1.0 INTRODUCTION/BACKGROUND <br /> This report is being submitted in response to a request by the San Joaquin County Public Health <br /> Services Environmental Health Division for a subsurface investigation at the Gardner property, <br /> 26056 Thornton Road, Thornton, California (Figure 1) <br /> On September 6, 1989, three underground gasoline storage tanks were removed at the project <br /> site by Western Meter Service of Stockton, California (Figure 2) Soil samples were collected <br /> beneath each tank and the associated piping The soil samples were analyzed for benzene, <br /> toluene, ethylbenzene, xylenes (BTEX), total petroleum hydrocarbons as gasoline (TPHG), tetra <br /> ethyl lead (TEL), and ethylene dibromide (EDB), by California Water Labs utilizing appropriate <br /> EPA and DHS methodologies Soil samples collected from beneath two of the tanks contained <br /> moderate to high levels of ethylbenzene and xylenes (1.2 to 70 parts per million (ppm) as well <br /> as TPHG (470-830 ppm) The analytical results are summarized in Table 1 The laboratory <br /> ' data sheets and chain-of-custody documentation from the tank removal are included in Appendix <br /> I The presence of elevated concentrations of petroleum hydrocarbons in the tank pit soil <br /> samples indicated further investigation would be required <br /> 2.0 SITE DESCRIPTION <br /> 2.1 Topographic and Cultural Features <br /> 1 The project site is situated on level terrain in the City of Thornton, California, near Interstate <br /> Highway 5, in San Joaquin County (Figure 1) The primary industry of the area is light <br /> ' industrial and farming <br /> I2.2 Geology and Hydrology <br /> The project site is situated at the southern end of the Sacramento Valley, part of the large <br /> ' northwest trending sedimentary trough termed the Central Valley of California The Sacramento <br /> Valley contains a thick sequence of sediments which reach a depth of 10 miles in some places <br /> tThese sediments range in geologic age from Jurassic to Holocene and include both marine and <br /> continental deposits. Near surface deposits are derived from flood and overbank river deposits <br /> consisting of irregularly interbedded and discontinuous layers of fine to coarse grained <br /> unconsolidated sediments <br /> ' GPR1227 JPL 1 <br />