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I I
<br /> Mr. M. Scott Mansholt—CEMC
<br /> Fourth Quarter Groundwater Monitoring and Sampling Report and
<br /> 2005 Annual Summary December 22,2005
<br /> Vernalis Pump Station, Vernalis,California Page 2 of
<br /> approximately 4 to 5 feet below ground surface (bgs)during 1985, was constructed of 0.25-inch
<br /> thick wrapped steel, and was under the control of a subsidiary of Southern Pacific Pipeline
<br /> Company.
<br /> From 1902 to 1935 Standard Oil (predecessor to Chevron)operated the Vernalis Pump Station,
<br /> which was the part of former Old Valley Pipeline (OVP) system that transported heated heavy
<br /> petroleum(crude oil and Bunker C fuel oil) from San Joaquin Valley oil fields in Bakersfield to a
<br /> refinery in Richmond, California. The OVP was located along the northeastern side of the site
<br /> and parallel to the existing UPRR tracks and Highway 33. Site features included a boiler house, a
<br /> pump house, a sump, an incinerator, a rubbish pit, cottages, and three bulk-storage tanks with
<br /> secondary containment structures. These surface structures were located within the Arcos
<br /> property. The property located immediately southeast of the Arcos property was a former
<br /> Tidewater Associated Oil Company(TAOC) (predecessor to Texaco and now Chevron) pump
<br /> station. According to the 1995 Environmental Site Assessment,the former pump station was
<br /> owned by Vernalis Enviropur-West in 1995, and was used for bulk storage of petroleum and oil
<br /> products.
<br /> REGIONAL/LOCAL HYDROGEOLOGY
<br /> Regionally, the study area is encompassed within the Tracy Sub-basin(Groundwater Basin
<br /> Number 5-22.15) and is defined by unconsolidated to semi-consolidated sedimentary deposits
<br /> that are bounded by the Diablo Range on the west,the Mokelumne and San Joaquin rivers on the
<br /> north, the San Joaquin River to the east, and the San Joaquin-Stanislaus County line on the south.
<br /> The 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 2 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 bgs, and the lower aquifer is reported at a depth of 600 feet bgs.'
<br /> Locally, the site is within the Central Valley Physiographic Province of California, has a
<br /> relatively flat topography that slopes gently downward to the northeast, and is situated at an
<br /> elevation of approximately 107 feet above mean sea level. 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), clayey and silty sands (SC, SM) with smaller
<br /> quantities of poorly graded sand and gravel (SP, GP).
<br /> I. Geological Technics, Inc.,February 1995,Preliminary Environmental Site Assessment: Vernalis Property,35500
<br /> Welty Road,Vernalis,California.
<br /> 2. California's Groundwater,Bulletin 1 18,California Department of Water Resources,2003 Update.
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