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tl Y✓ W ...d+ MA, '7 Scptem )Cf 13, 1991 Unocal Station No. 0981, Stockton, California PREVIOUS WORK RESNA (formerly Applied GeoSystems) monitored the removal and installation of underground storage tanks and product lines in May and ,lune 1988. Results of the field work and laboratory analyses indicated gasoline hydrocarbons were present in the soil near the I-orth end and northeast corner of the tank cavity and near the northeast corner of the pump islands (Applied GeoSystenns. 1991). vapor survey a!the site. Results indicated that In December 1988.RESNA performed asoil- low levels of gasoline hydrocarbons were present in soil vapor in probe hole VP-7 near t}te southwest corner of the site; however, the test provided no conclusive data on hydrocarbons below 13 feet (Plate 2). On the basis of these results, Unocal requested an investigation of the soil and ground water beneath the site(Applied GeoSystems, Inc.. February 19, 1991)- In January and February 1990,RESNA conducted an investigation of soil and ground water. Five soil borings were drilled and monitoring wells were installed in the borings. laboratory analyses of soii samples collected from boring B-2 (near the northeast corner of the pump islands) detected benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) above 1.0 part per million (ppm). Labors-ory analyses of soil samples collected from boring B-4 (near the northwest corner of the pump islands) detected BTEX compounds abovA 1.0 ppm at 35 feet below grade and below 1.0 ppm below and above the 35-foot sample interval. Results indicated that samples collected from boring B-5 (near the northeast corner of the tank cavity) contained BTEX compounds below 1.0 ppm. M Borings B-1 and B-3 were sampled at 25 and 45 feet below grade. BTEX compounds were not detected in soil samples collected from these borings, except toluene at 0.13 ppm from ;A B-1 at 25 feet below grade. 3 i