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• S ECOR —� — — d..
<br /> Mrs. Kristi Shelton
<br /> April 17, 2008
<br /> Page 2
<br /> PREVIOUS INVESTIGATIONS
<br /> A partially buried 5,000-gallon tank was removed from the southwestern portion of the site in
<br /> December 1989. The tank was reportedly primarily used for the storage of transmission fluid
<br /> but had also historically contained heating oil. Details of the excavation of this tank are
<br /> described in a Pacific Environmental Group, Inc (PEG) letter to Unocal dated March 20, 1990.
<br /> Two soil samples collected after tank removal indicated the presence of total petroleum
<br /> hydrocarbons as diesel (TPHd), toluene, and ethylbenzene. The tank was underlain by a
<br /> concrete pad, which was not removed during the excavation.
<br /> In October 1990, PEG installed three groundwater monitoring wells (U-1, U-2, and U-3) to
<br /> evaluate the distribution of fuel-related hydrocarbons in groundwater beneath the site. The
<br /> wells were screened from 7 to 27 feet below ground surface (bgs). Soil samples collected
<br /> during the well boring installations indicated elevated concentrations of total petroleum
<br /> hydrocarbons as gasoline (TPHg), TPHd, and/or benzene, ethylbenzene, and xylenes in the
<br /> three borings, with maximum concentrations of 1800, 710, 2.7, 52, and 66 parts per million
<br /> (ppm), respectively, in the 61/2-foot sample from well U-1. TPHg and BTEX (the collective
<br /> abbreviation for benzene, toluene, ethylbenzene, and total xylenes) compounds were detected
<br /> in groundwater from U-1 and U-2. Static groundwater levels of approximately 9.5 feet bgs and
<br /> a northerly flow direction were reported (Soil and Groundwater Investigation Report, PEG,
<br /> February 13, 1991).
<br /> In May 1991, PEG installed three additional groundwater monitoring wells (U-4, U-5, and U-6)to
<br /> evaluate the lateral extent of dissolved-phase hydrocarbons detected in wells U-1 and U-2.
<br /> Wells U-5 and U-6 were screened from 5 to 20 feet bgs; well U-4 was screened from 5 to 18
<br /> feet bgs. Soil samples collected during the well boring installations indicated elevated
<br /> concentrations of TPHg, TPHd, and/or BTEX in borings U-5 and U-6, with respective maximum
<br /> concentrations of 620, 340, 3.9, 24, 18, and 89 ppm in the 6'/z-foot sample from well U-5. In
<br /> addition, PEG drilled three soil borings near the ASTs and former semi-buried tank. Analytical
<br /> results indicated elevated concentrations of hydrocarbon constituents in the 61/2-foot samples of
<br /> the three borings, with maximum concentrations in the boring located just west of the ASTs (Soil
<br /> and Groundwater Investigation Report, PEG, September 30, 1991).
<br /> In March 1992, PEG installed four additional groundwater monitoring wells (U-7, U-8, U-9 and
<br /> U-10) to further delineate groundwater impacts detected in previously installed wells. Each well
<br /> was screened from 4'h to 15 feet bgs. Soil samples collected during the well boring installations
<br /> indicated no fuel-related hydrocarbons in samples from the four borings, except minor
<br /> concentrations of TPHd and total petroleum hydrocarbons as oil (TPHo) in the 6%2-foot sample
<br /> from boring U-7. Static groundwater levels of approximately 9.5 feet bgs and a northerly flow
<br /> direction were reported (Soil and Groundwater Investigation Report, PEG, June 11, 1992).
<br /> In September 1994, thirteen test pits were excavated at the site to further evaluate soil impacts.
<br /> Twenty-seven soil samples were collected from the test pits at depths ranging from 5 to 15 feet
<br /> bgs. Analytical results of these samples indicated significant soil impact in the vadose and
<br /> saturated zones near the ASTs, near the underground piping between the loading rack and
<br /> loaders, and near the former semi-buried transmission fluid tank. Maximum TPHo, TPHd, and
<br /> TPHg concentrations of 890, 690, and 1500 ppm, respectively, were reported in an 8-foot bgs
<br /> sample from the test pit located just north of the ASTs. Maximum ethylbenzene and xylenes
<br /> concentrations of 18 and 95 ppm, respectively, were reported in the 8-foot bgs sample from the
<br /> SECOR International Incorporated
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