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,I ATTACHMENT A d SUMMARY OF PREVIOUS INVESTIGATIONS Chevron 9-8632, 575 Grant Line Road, Tracy, CA 3 In 1964 the product lines and an unspecified number of steel underground storage tanks (USTs) were installed at the site. In 1984, the steel USTs and product lines were removed. They were replaced with three 10,000-gallon capacity gasoline USTs, and one 1 ,000-gallon capacity waste oil UST, all of single-wall fiberglass construction. In May 1994, the USTs, product lines, hoists, sand/grease trap, and approximately 400 cubic yards of impacted soil generated during excavation activities were removed from the site. As approved by San Joaquin County Public Health Services (SJCPHS), slightly impacted soil was aerated to non-detect levels and reused onsite. Groundwater was encountered during excavation activities at approximately 8 feet below ground surface (bgs). In August 1994, the waste-oil UST and sump excavations were over-excavated until soil exhibiting low to non-detect levels of oil and grease were encountered. Approximately 150 to 200 cubic yards of oil and grease impacted soil was removed and hauled offsite. In May 1995 , wells MW- 1 through MW-4 were installed at the site. Maximum concentrations of TPHg and benzene in wet soil were reported in the area of the former pump islands (boring MW-3) at 7,600 mg/kg at 6. 5 feet below ground surface (bgs) and 24 mg/kg at 6.5 feet bgs, respectively. On May 22 through 24, 2001 , SECOR supervised Gregg Drilling & Testing, Inc. (Gregg) of Martinez, California as they advanced 15 direct push borings (CPT-1 through CPT- 15) and the collection of depth-discrete soil and groundwater samples. TPHd was detected in all eight soil samples collected with concentrations ranging from 1.4-milligrams-per-kilogram-(mg/kg)-at CPT=1--(23-feet-bgs)-to 14 mg/kg at-CPT-Z- , feet bgs) . The sample collected from CPT-2 at 7 feet bgs also contained TPHg and BTEX at 400 mg/kg, 2. 3 mg/kg, 1 . 1 mg/kg, 10 mg/kg, and 5 mg/kg, respectively. MtBE was not detected in any of the soil samples collected. TPHg was detected in eight groundwater samples at concentrations ranging from 55 micrograms per liter (µg/L) (CPT- 12 at 16 feet bgs) to 3900 µg/L (CPT-7 at 9 feet bgs) . Benzene was detected in ten groundwater samples at concentrations ranging from 0 . 51 µg/L (CPT- 11 at 18 feet bgs) to 31 µg/L (CPT-7 at 9 feet bgs). Toluene was detected in five groundwater samples at concentrations ranging from 0. 58 µg/L (CPT-4 at 18 feet bgs) to 1 .4 µg/L (CPT- 10 at 18 feet bgs). Ethylbenzene was detected in thirteen groundwater samples at concentrations ranging from 0. 66 µg/L (CPT-2 at 15 feet bgs) to 110 µg/L (CPT-6 at 23 feet bgs) . Xylenes were detected in twelve groundwater samples at concentrations ranging from 0.68 µg/L (CPT- 12 at 34 feet bgs) to 76 µg/L (CPT- 14 at 16 feet bgs). MtBE was detected in seven groundwater samples at concentrations ranging from 4. 8 µg/L (CPT40 at 24 feet bgs) to 56 µg/L (CPT-9 at 16 feet bgs) . EtBE, TBA, TAME, DIPE, EDB, 1 ,2-DCA, methanol, and ethanol were not detected above laboratory reporting limits in any of the groundwater samples collected.