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Revised Work Plan,Additional Excavation and Confirmation Soil Sampling
<br /> Bulk Transportation Facility, Stockton, California
<br /> Hygienetics Environmental Services,Inc.
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<br /> fi 1.3 Previous Work j
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<br /> A 12,000-gallon UST that contained diesel fuel was located at the site. The UST and associated
<br /> underground and aboveground piping and dispensers were installed in 1988. Fogs excavated and
<br /> removed the dispensers and associated fuel piping during thie week of October 14 through 18,
<br /> 2002 and removed the UST on October 21, 2002. Representatives of the Stockton Fire
<br /> Department and San Joaquin County Department of Environmental Health observed the removal
<br /> of the UST. I
<br /> Hygienetics Environmental Services, Inc. (Hygienetics) collected a total of seven soil samples at
<br /> locations beneath the tank, pipelines, and dispensers shortly after tank removal. These samples
<br /> were submitted to a state-certified laboratory for analysis for totall petroleum hydrocarbons as
<br /> diesel (TPHd) and the aromatic hydrocarbons benzene, toluene, ethylbenzene, and total xylenes
<br /> (BTEX). The results of laboratory analysis showed no detectable concentrations of TPHd or
<br /> BTEX in three soil samples collected from the UST pit and one soil Sample collected beneath the
<br /> former location of the northern satellite fuel dispenser. A total of 42 parts per million (ppm)
<br /> TPHd was detected beneath the former location of the southern satellite fuel dispenser, 1,700 ppm
<br /> f TPHd was detected in soil beneath the former location of the central junction of the fuel.piping
<br /> running to the two satellite fuel dispensers, and 2,400 ppm TPHd was detected in sail beneath the
<br /> location of the fuel supply line. No BTEX was found in the latter three samples. The laboratory
<br /> report notes that oil-range petroleum hydrocarbons were significant',in the three samples, which
<br /> may indicate weathered diesel fuel. Plate 2 presents the configuration of the excavation and the
<br /> locations at which soil samples were collected. Concentrations of TPHd are also noted next to
<br /> each sample. {
<br /> 1.4 Geology and Ground Water
<br /> 1.4.1 Geology
<br /> The site is within the Great Valley Geomorphic Province in central California. Primary
<br /> geomorphic units with the province include dissected uplands, low alluvial plains and fans, river
<br /> flood plains and channels, and overflow lands and Iake bottoms. Stockton and the site lie within
<br /> the river flood plains and channels geomorphic units.
<br /> Rocks and unconsolidated sediments underlying the site and vicinity include Pre-Tertiary-age marine
<br /> rocks and Paleocene- to Oligocene-age (early Tertiary) continental and marine rocks and
<br /> unconsolidated sediments, Oligocene- to Holocene-age (middle to late Tertiary) continental rocks
<br /> and unconsolidated sediments, and Holocene-age (late Ternary) flood basin deposits. The pre-
<br /> Tertiary to early Tertiary marine rocks and deposits include clay,shale;sandstone,and conglomerate
<br /> and the continental rocks and deposits include clay, shale,sand,'sandstone,and conglomerate. These
<br /> units underlie the Stockton area from approximately 3,600 feet;to greater than 9,000 feet below the
<br /> E ground surface. Continental rocks and deposits, which underlie'the site from approximately 100 feet
<br /> to 3,600 feet below the ground surface,include a heterogeneous mix of generally poorly sorted clay,
<br /> silt, sand, and gravel, with some beds of claystone, siltstone, sandstone, and conglomerate. Flood-
<br /> basin deposits, which are from the ground surface to as much-las 100 feet below grade, consist of
<br /> unconsolidated units of clay,silt,and some sand(see Page, 1986).
<br /> Shallow sediments observed during removal of the UST included dark brown, high plasticity, silty
<br /> clay between 1 foot and approximately 4% feet below grade and yellow brown silt between 4'/� and
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