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i by PHS/EHD as "Site Code 1282-10." The site had a 2,000-gallon steel tank (PHS/EHD ID # 39-1282-10), which, according to the "UGST Worksheet for Site Closure Evaluation," (Appendix A) contained regular gasoline. No information is available as to the age of the tank. The tank and associated piping were removed on July 15, 1991 by Jim Thorpe Oil, Inc. The PHS/EHD inspection report indicates that the tank was constructed of steel and was in "poor" condition upon removal. No visible holes were reported. The inspection report indicates that the tank was originally installed on a "slab" that was present under the tank at 8 feet below ground surface (bgs), and that no piping was associated with the tank. The slab was removed during excavation. Approximately 55 yards of soil were excavated during the tank removal, and the tank excavation was reportedly extended to a depth of 8 feet bgs. Two soil samples were collected by Roy F. Weston, Inc. (Weston) from a depth of 11.5 bgs, one beneath the north end and one beneath the south end of the former tank. No groundwater was encountered during excavation or sampling. Soils beneath the tank were reported by PHS/EHD to be "clay loam" and contained "no odor and discoloration." 2.2 SUMMARY OF PREVIOUS SITE CHARACTERIZATION WORK The two soil samples collected from beneath the tank were submitted to Weston for analysis of total petroleum hydrocarbons as gasoline(TPHg) and total petroleum hydrocarbons as diesel (TPHd) by the LUFT method; benzene, toluene, ethyl benzene, and total xylenes (BTEX) by EPA method 8020; total lead by EPA method 6010; and ethylene dibromide (EDB) by EPA method 504. Analytical results (Table 1) indicated that none of the above constituents were detected in either sample with the exception of benzene, which was detected at a concentration of 2.4 mg/kg from the sample collected at the south end of the former tank. 2.3 GEOLOGIC AND HYDROLOG C I CHARACTERISTICS - C The subject site is located on the delta of the San Joaquin River, approximately 2 miles east of the confluence of the San Joaquin and Calaveras Rivers. The subsurface geology consists of a thick sequence of alluvial deposits of late Tertiary to Holocene Age, overlying sedimentary rocks of Cretaceous to Tertiary age, which in turn overlie crystalline basement rocks (Bartow and Nilsen, 1990). Based on data from nearby studies within the Port area, the soil profile at the site to a depth of about 20 feet bgs consists of interbedded, sands and clays, mostly under reduced conditions (Sierra-Pacific Groundwater Consultants [SPGC], 1994). i 2 95117%s4usr1Nv.wrN