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Mr.M. Scott Mansholt—CEMC
<br /> Fourth Quarter 2005 Groundwater Monitoring and Sampling Report and
<br /> 2005 Annual Summary January 5,2006
<br /> US Can-Welty Road,Vernalis,California Page 2 of 7
<br /> operated from the early 1900s until it was decommissioned in the 1970s. (Hereinafter,the two
<br /> former pipelines,OVP and TAOC, shall be collectively referred to as OVP.)
<br /> Currently,Kinder Morgan Energy Partners,L. P., operates a pipeline that reportedly transports
<br /> gasoline,jet fuel, and diesel and is located between the US Can-Welty Road site and Highway 33.
<br /> Western Farm Service(WFS) is located directly northeast of the site across Highway 33 and has
<br /> stored and distributed bulk liquid and dry fertilizers since 1969. In addition, a former Union Oil
<br /> gas station,reportedly located northeast of the site, operated from approximately 1972 until the
<br /> mid 1980s.
<br /> REGIONAL/LOCAL HYDROGEOLOGY
<br /> Regionally,the site is encompassed within the Tracy Sub-basin(Groundwater Basin Number
<br /> 5-22.15)and is defined by unconsolidated to semi-consolidated sedimentary deposits that are
<br /> bounded by the Diablo Range on the west,the Mokelumne and San Joaquin rivers on the north,
<br /> the San Joaquin River to the east, and the San Joaquin-Stanislaus County line on the south. The
<br /> Tracy Sub-basin is located adjacent to the eastern San Joaquin Sub-basin on the east and the
<br /> Delta-Mendota Sub-basin on the south.' The above-mentioned sub-basins are located within the
<br /> larger San Joaquin Valley Groundwater Basin.
<br /> The Tracy Sub-basin is comprised of continental deposits of Late Tertiary to Quaternary age,
<br /> which include the Tulare Formation,Older Alluvium,Flood Basin Deposits, and Younger
<br /> Alluvium. The thickness of these formations ranges from a few hundred feet in the western
<br /> foothills to about 3,000 feet near the eastern margin of the basin. The Tulare Formation is
<br /> comprised of semi-consolidated,poorly sorted,discontinuous deposits of clay, silt, and gravel.
<br /> The Corcoran clay is situated near the top of the Tulare Formation, separating groundwater in the
<br /> basin in what has been reported as two primary aquifers. The upper aquifer is reported to range
<br /> in thickness from 15 to 250 feet below ground surface(bgs), and the lower aquifer is reported at a
<br /> depth of 600 feet bgs.'
<br /> Locally,the site is within the Central Valley Physiographic Province of California, is situated at
<br /> an approximate elevation of 103 to 105 feet above mean sea level, and has a relatively flat
<br /> topography that slopes gently downward to the northeast. Groundwater in the upper
<br /> water-bearing zone flows in a northeasterly direction and is hydraulically controlled by low-
<br /> permeable,unconsolidated sediments. Generally, depth to groundwater near the site varies from
<br /> 20 to 40 feet bgs. Soils encountered appear to be fine-grained unconsolidated sediments,
<br /> consisting mainly of lean clays and silts (CL,ML)and clayey and silty sands, (SC, SM)with
<br /> smaller quantities of poorly graded sand and gravel(SP, GP).
<br /> PREVIOUS ENVIRONMENTAL ACTIVITIES
<br /> 1995 Site Investigations.2'3 ERM,Inc. collected 11 surface soil samples(S-1 through S-11) in
<br /> the vicinity of the can fabrication plant wasteibum pit area. Oil and grease(O&G)was detected
<br /> in four of the soil samples(S-4, S-5, S-6, and S-8) in concentrations ranging from 1,500
<br /> milligrams per kilogram(mg/kg)to 5,200 mg/kg. Gasoline was detected in two of the soil
<br /> samples(S-4 and S-5) in concentrations ranging from 20 to 6,000 mg/kg.
<br /> ERM, Inc. conducted four hand borings(HB-3,HB-4,HB-5, and HB-6)to 10 feet bgs in order to
<br /> establish the lateral and vertical extent of petroleum-affected soil near the northeastern side of the
<br /> 1. California's Groundwater,Bulletin 118,California Deparhnent of Water Resources,2003 Update.
<br /> 2. ERM-West,Inc., 1995,Letter to ERM,Inc.,Hunter Container Corporation Soil Sampling.
<br /> 3. ERM-West,Inc., 1995,Letter to US Can Company regarding lab analysis data.
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