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Chevron Products Company • 2
<br />Chevron Service Station #9-2033 508 West Charter Way, Stockton California January IS 2001
<br />butanol, di -isopropyl ether (DIPE), ethyl tertiary -butyl ether (EtBE), tertiary -amyl
<br />methyl ether (TAME), 1,2-dichloroethane, (1,2 -DCA), 1,2-dibromoethane (EDB),
<br />ethanol, and methanol.
<br />In March 1995, Groundwater Technology installed three monitoring wells (MW -1, 2,
<br />and 3) onsite to approximately 50 feet below ground surface (bgs), and one soil boring
<br />(SB -1) to 35 feet bgs. Soil analytical results indicated no detectable levels of TPHg in
<br />soil borings for wells MW -1 and MW -2. Concentrations of TPHg in MW -3 soil were
<br />reported at 3.8 and 250 milligrams per kilogram (mg/kg) at 25 and 35 feet bgs,
<br />respectively. Soil boring SB -1 test results indicated TPHg concentrations of 4.2 and 28
<br />mg/kg at 30 and 35 feet bgs, respectively. Generally, aromatic hydrocarbons including
<br />benzene, toluene, ethylbenzene and xylene were reported for soil samples collected from
<br />the 20 to 25 -foot depth range near the former underground storage tank area (i.e. SB -1)
<br />and in the 30 to 35 foot depth range, (i.e. MW -3) consistent with the first occurrence of
<br />groundwater. Metals analyses results for soil samples from MW -1 indicated
<br />concentrations of chromium, lead, nickel and zinc at 23, 7.8, 21, 50 mg/kg (10 feet bgs)
<br />and 31, 6.5, 42, and 59 mg/kg (35 feet bgs), respectively.
<br />Quarterly sampling of monitoring wells MW -1 through MW -3 has been performed
<br />since May 1995. Dissolved concentrations of TPHg in MW -1 increased from 340 to
<br />5,900 micrograms per Liter (gg/L) during this period. Dissolved benzene
<br />concentrations in MW -1 have also increased from 67 gg/L in May 1995 to 1,100 gg/L
<br />in August 1997. Review of MW -1 analytical results also suggests an increasing trend in
<br />1,2 dichloroethane (DCA). Analytical results for MW -2 have consistently indicated no
<br />detectable concentrations of TPHg, BTEX, and MtBE. Review of analytical results for
<br />MW -3 suggests a decreasing trend of hydrocarbon concentrations between May 1995
<br />and August 1997, from 44,000 gg/L to 7,100 gg/L TPHg, and 2,900 gg/L to 800 gg/L
<br />benzene respectively.
<br />On September 9, 1996, Touchstone Developments oversaw the excavation and removal
<br />of three USTs, three hydraulic hoists, product dispensers, and associated product lines.
<br />Soil samples collected from beneath the former USTs, hydraulic hoists, product piping,
<br />and dispenser locations were analyzed for TPHg and BTEX. Hydrocarbon
<br />concentrations reported for soil samples collected from beneath the former southern
<br />product island (P6) were 3,000 mg/kg TPHg, and 2.6, 20, 47, and 240 mg/kg BTEX
<br />components, respectively, at 3.5 feet bgs. On September 11, 1996, soils near the former
<br />locations of the USTs, product dispensers, and product lines associated with these test
<br />results were removed by excavation. Results for additional samples collected and
<br />analyzed following soil excavation suggest remnant hydrocarbon concentrations
<br />underlying the former southern product island of 1,700 ppm TPHg and 3.2 ppm benzene
<br />at 6 feet bgs, and 1,300 ppm TPHg and 14 ppm benzene at 7 feet bgs west of the
<br />southern product island.
<br />077.41991.0181:\Chevron\92033VdEPORTS\92033 Phase[ISA RevA.doc
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