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Mr.M. Scott Mansholt—CEMC
<br /> Third Quarter 2005 Groundwater Monitoring and Sampling Report October 25,2005
<br /> US Can-Welty Road,Vernalis,CA Page 2 of 6
<br /> The former Tidewater Associated Oil Company(TAOC)pipeline was also present between the
<br /> site and Highway 33. The TAOC pipeline was used to transport heated heavy petroleum(crude
<br /> oil and Bunker C fuel oil) from the Central Valley to the San Francisco Bay Area and operated
<br /> from the early 1900s until it was decommissioned in the 1970s. (Hereinafter,the two former
<br /> pipelines, OVP and TAOC, shall be collectively referred to as OVP.)
<br /> Currently,Kinder Morgan Energy Partners,L. P. (KM), operates a pipeline that reportedly
<br /> transports gasoline,jet fuel, and diesel and is located between the site and Highway 33. Western
<br /> Farm Service (WFS)is located directly northeast of the site across Highway 33 and has stored
<br /> and distributed bulk liquid and dry fertilizers since 1969. In addition, a former Union Oil gas
<br /> station,reportedly located northeast of the site, operated from approximately 1972 until the mid
<br /> 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. (California Department of Water Resources, 2003,
<br /> California's Groundwater,Bulletin 118.) 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. (California Department of Water Resources,2003, California's
<br /> Groundwater,Bulletin 118.)
<br /> Locally,the site is situated at an approximate elevation of 103 to 105 feet above MSL and has a
<br /> relatively flat topography that slopes gently downward to the northeast. Groundwater in the
<br /> upper water-bearing zone flows in a northeasterly direction and is hydraulically controlled by
<br /> low-permeable,unconsolidated sediments. Generally, depth to groundwater near the site varies
<br /> from 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. ERM, Inc. collected 11 surface soil samples (S-1 through S-11)in the
<br /> vicinity of the can fabrication plant waste/bum pit area. Oil and grease(O&G)was detected in
<br /> four of the soil samples (S-4, S-5, S-6, and S-8) in concentrations ranging from 1,500 milligrams
<br /> per kilogram(mg/kg)to 5,200 mg/kg. Gasoline was detected in two of the soil samples(S-4 and
<br /> 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 /> can fabrication plant. Petroleum-affected soil was identified in three borings. Benzene,toluene,
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