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d SUMMARY OF PREVIOUS INVESTIGATIONS Former Chevron Service Station 9-8632 575 West Grant Line Road, Tracy, California 1994 Underground Storage Tank (UST), Piping, Sump, and Hoist Removal: In May 1994, Touchstone Developments (TD) removed three single-walled fiberglass gasoline USTs and one used-oil UST, associated product lines, sump, and hoists. As approved by San Joaquin Public Health Services, approximately 300 cubic yards of slightly impacted soil generated from the fuel UST and piping removal was aerated until hydrocarbons were non-detect and reused onsite as backfill material. Approximately 100 cubic yards of soil generated from the used-oil UST and sump removals were disposed at Browning-Ferris Industries in Livermore, California. Excavation activities are detailed in TD's June 20, 1994, UST and Product Line Removal Report. 1994 Used-Oil UST and Sump Overexcavation: In August 1994, TD overexcavated the former used-oil UST and sump locations until soil was non-detect, or exhibited low concentrations of oil and grease. Approximately 150 to 200 cubic yards of impacted soil were removed and disposed. No report is available for reference. 1995 Monitoring Well Installation: In May 1995, Groundwater Technology Inc. (GTI) installed groundwater monitoring wells MW-1 through MW-4 to a depth of 20 feet below grade (fbg) . The maximum concentration of total petroleiun hydrocarbons as diesel (TPHd) was detected in the southwest corner of the site at 190 milligrams per kilogram (mg/kg) in boring MW-4 at 6 fbg. Elevated concentrations of total petroleum hydrocarbons as gasoline (TPHg) and benzene in soil were detected in the area of the former pump islands at 7,600 mg/ kg and 24 mg/kg, respectively, in boring MW-3 at 6.5 fbg. This work is detailed in GTI's June 29, 1995, Environmental Assessment Report. 20 1 Cone Penetration es ing (CPT) Soil Borings; In MayGT,SEC0R_ nt�tional c. (SECOR) advanced 15 CPT soil borings to depths of 30 to 40 fbg. TPHd was detected in all soil samples at concentrations ranging from 1 .4 mg/ kg in CPT-1 at 23 fbg to 14 mg/kg in CPT-2 at 7 fbg. The soil sample collected from CPT-2 at 7 fbg also detected concentrations of TPHg, benzene, toluene, ethylbenzene, and xylenes (BTEX) at 400 mg/ kg, 2.1 mg/ kg, 1 .1 mg/kg, 10 mg/ kg, and 5 mg/ kg, respectively. No methyl tertiary-butyl ether (MTBE) was detected in the soil samples. Thirteen out of the fifteen grab-groundwater samples detected concentrations of TPHg, BTEX, and/ or MTBE. Details of this work are included in SECOR's July 16, 2001, Site Assessinent Report. 2001 Well Survey: In June 2001, SECOR performed a water well search to identify the locations of permitted water supply wells within a 1-mile radios of the site. According to California Department of Water Resources (DWR) files, the nearest well, used for irrigation, was located near the intersection of West Grant Line Road and Tracy Boulevard, though the exact location could not be determined . SECOR also conducted a door-to-door survey of businesses, commercial buildings, and residences within a 2,000-foot radius of the site. No wells were Ma 77 (4) 1 CONESTOGA-ROVERS & ASSOCIATES