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Mr.M. Scott Mansholt—CEMC
<br /> Third Quarter 2006 Groundwater Monitoring and Sampling Report October 25,2006
<br /> US Can-Welty Road Page 2 of 5
<br /> Currently,Kinder Morgan Energy Partners,L. P., operates a pipeline that reportedly transports
<br /> gasoline,jet fuel, and diesel; it 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 on 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 Delta-
<br /> Mendota sub-basin on the south.' These sub-basins are located within the larger San Joaquin
<br /> Valley Groundwater Basin.
<br /> The Tracy sub-basin is comprised of continental deposits of Late Tertiary to Quaternary age,
<br /> including the Tulare Formation, Older Alluvium,Flood Basin Deposits, and Younger Alluvium.
<br /> The thickness of these formations ranges from a few hundred feet in the western foothills to about
<br /> 3,000 feet near the eastern margin of the basin. The Tulare Formation is comprised of semi-
<br /> consolidated,poorly sorted,discontinuous deposits of clay, silt, and gravel. The Corcoran clay is
<br /> situated near the top of the Tulare Formation, separating groundwater in the basin in what has
<br /> been reported as two primary aquifers. The upper aquifer is reported to range in thickness from
<br /> 15 to 250 feet below ground surface(bgs), and the lower aquifer is reported at 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 at an approximate gradient of 0.001 feet per
<br /> foot(ft/ft)and is hydraulically controlled by low-permeable,unconsolidated sediments. Based on
<br /> ongoing groundwater monitoring at the site, depth to groundwater at the site varies from 20 to 40
<br /> feet bgs. Soils encountered appear to be fine-grained unconsolidated sediments, consisting
<br /> mainly of lean clays and silts(CL,ML)and clayey and silty sands, (SC, SM)with smaller
<br /> quantities of poorly graded sand and gravel(SP, GP).
<br /> PETROLEUM DISTRIBUTION IN GROUNDWATER
<br /> The RWQCB water quality objectives (WQOs) include total petroleum hydrocarbons (TPH)
<br /> measurements for diesel products,but not for crude oil/Bunker C fuel oil. According to the
<br /> Technical Approach to Site Evaluation and Decision-Making for the Historical Pipeline Portfolio
<br /> (herein referred to as the CTA), diesel products are not associated with the Historical Pipeline
<br /> Portfolio (HPP) sites and typically are not present at these sites.2 However,WQOs are applied to
<br /> "diesel-range hydrocarbons"(extractable TPH, C10—C25)found in HPP site groundwater samples
<br /> because no WQOs are established for crude oil/Bunker C fuel oil, and historical data indicates
<br /> that diesel-range hydrocarbons are often detected at sites affected by crude oil/Bunker C fuel oil.
<br /> Per the CTA, groundwater samples are quantified against a diesel standard so that the comparison
<br /> to the WQOs is as direct as possible.
<br /> 1. California Department of Water Resources,2003. California's Groundwater,Bulletin 118,2003 Update.
<br /> 2. Geomatrix Consultants,Inc.,2005. Technical Approach to Site Evaluation and Decision-Making,Historical
<br /> Pipeline Portfolio,Central Valley Region. February.
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