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KLEINFEIDER . 1 EXECUTIVE SUMMARY Unocal Corporation has leased a site at the Port of Stockton since 1974 from Southern Pacific Pipelines Since 1979, Unocal has subleased the northeast corner of this site to ST Services ST Services operates an incinerator on this portion of the site and had a small underground tank removed from that area in 1985. Unocal's facilities are located on the west half of the property. Unocal installed two underground tanks, a 20,000-gallon diesel tank and a 10,000-gallon stoddard solvent tank, under the Ioading dock on the west side of the property in 1974 According to Unocal records, no other tanks were installed or removed by Unocal, (with the exception of above ground bulk oil tanks installed in 1988), and no gasoline has been sold at the Unocal facility Kleinfelder installed seven morutoring wells at the Unocal site in 1988 One of these wells, MW-5, is located on the eastern side of the property that is leased by ST-Services. All seven wells were sampled in July 1988 and in June 1989 In July 1988, benzene, toluene, ethylbenzene, xylene, and total petroleum hydrocarbons (TPH) as gasoline were detected in MW-5 Low concentrations of benzene, toluene, and TPH (as diesel) were detected in MW-3 and a low concentration of TPH (as diesel) was detected in MW-6. In June 1989, no hydrocarbon constituents were detected in the monitoring wells, with the exception of MW-5 Benzene, toluene, ethylbenzene, xylene, and TPH (identified as an unknown hydrocarbon) were detected in the sample from MW-5. The local ground water gradient in July 1988 was to the east-southeast under the Unocal site The local ground water gradient in June 1989, based on measurements in wells and piezometers on and around the Unocal site, was also to the east-southeast No sigruficant variations in the ground water gradient over a 12-hour period on June 2, 1989 were observed Therefore, tidal influences of the San Joaquin River did not appear to affect the general gradient on the date of observation Floating product was observed in six piezometers (P11 through P16) installed along Stork Road, east of the Unocal site On June 2, 1989, samples of the floating product were collected from P12 (northeast of the Unocal facility) and P16 (east of the Unocal facility) and were submitted for analysis of TPH by GC-FID The analytical laboratory characterized both samples as being largely composed of gasoline, with some diesel 194-89-1112 1