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<br /> ATTACHMENT B
<br /> SUMMARY OF PREVIOUS INVESTIGATIONS
<br /> Chevron Service Station 9-2033, 508 West Charter Way, Stockton, California
<br /> In March 1995, Groundwater Technology installed three monitoring wells (MW-1, 2, and 3)
<br /> onsite to approximately 50 feet below ground surface (bgs), and one soil boring (SB-1) to 35
<br /> feet bgs Soil analytical results indicated no detectable levels of TPHg in soil borings for
<br /> wells MW-1 and MW-2 Concentrations of TPHg in MW-3 soil were reported at 3 8 and 250
<br /> milligrams per kilogram (mg/kg) at 25 and 35 feet bgs, respectively Soil boring SB-1 test
<br /> results indicated TPHg concentrations of 4 2 and 28 mg/kg at 30 and 35 feet bgs,
<br /> respectively Generally, aromatic hydrocarbons including benzene, toluene, ethylbenzene
<br /> and xylene were reported for soil samples collected from the 20 to 25-foot depth range near
<br /> the former underground storage tank area (i a SB-1) and in the 30 to 35 foot depth range,
<br /> (i e MW-3) consistent with the first occurrence of groundwater Metals analyses results for
<br /> soil samples from MW-1 indicated concentrations of chromium, lead, nickel and zinc at 23,
<br /> 7 8, 21, 50 mg/kg (10 feet bgs) and 31, 6 5, 42, and 59 mg/kg(35 feet bgs), respectively
<br />. On September 9, 1996, Touchstone Developments oversaw the excavation and removal of
<br /> three USTs, three hydraulic hoists, product dispensers, and associated product lines Soil
<br /> samples collected from beneath the former USTs, hydraulic hoists, product piping, and
<br /> dispenser locations were analyzed for TPHg and BTEX Hydrocarbon concentrations
<br /> reported for soil samples collected from beneath the former southern product island (P6)
<br /> were 3,000 mg/kg TPHg, and 2 6, 20, 47, and 240 mg/kg BTEX components, respectively, at
<br /> 3 5 feet bgs On September 11, 1996, soils near the former locations of the USTs, product
<br /> dispensers, and product lines associated with these test results were removed by excavation
<br /> Results for additional samples collected and analyzed following soil excavation suggest
<br /> remnant hydrocarbon concentrations underlying the former southern product island of 1,700
<br /> ppm TPHg and 3 2 ppm benzene at 6 feet bgs, and 1,300 ppm TPHg and 14 ppm benzene at
<br /> 7 feet bgs west of the southern product island
<br /> On August 30 and 31, 2000, SECOR supervised Precision Sampling (Precision) of
<br /> Richmond, California as they advanced three soil borings Analytical results reported no
<br /> detected benzene, toluene, xylenes or fuel oxygenates in soil samples submitted TPHg and
<br /> ethylbenzene concentrations of 130 mg/kg and 0 026 mg/kg were reported in the soil sample
<br /> SB-2 at 27-feet bgs
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