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Mr.M. Scott Mansholt—CEMC
<br /> Fourth Quarter 2006 Groundwater Monitoring and Sampling Report and
<br /> Annual Summary Report January 12,2007
<br /> US Can-Welty Road Page 4 of 8
<br /> 2003 Site Investigation.9 On August 4 and 5,2003, Gregg Drilling,under the supervision of
<br /> Geomatrix, advanced three soil borings (GMX-10, GMX-11, and GMX-12) for soil and
<br /> groundwater samples. TPHc were detected in the soil sample from boring GMX-12 collected at
<br /> 41.5 feet bgs at a concentration of 15,000 mg/kg. TPHd were detected in all groundwater
<br /> samples collected from GMX-10, GMX-11, and GMX-12 at concentrations of 210 gg/L,
<br /> 3,600 gg/L, and 110 gg/L,respectively.
<br /> 2005 Site Investigation.10 On March 14 through 16,2005, SAIC supervised the drilling of four
<br /> soil borings (SB-13, SB-14, SB-15, and SB-17) and the installation of one groundwater
<br /> monitoring well(MW-5). A proposed soil boring(SB-16), down gradient of boring GMX-6,was
<br /> not installed due to the presence of a former Union Oil service station at the eastern corner of
<br /> Welty Road and Highway 33. No TPHc, TPHg,BTEX, or methyl tertiary butyl ether(MTBE)
<br /> were detected in the soil samples from SB-13, SB-14, and SB-15, except 120 mg/kg of TPHc in
<br /> SB-14 at I foot bgs. TPHc,TPHg, ethylbenzene, and total xylenes were detected in SB-17 at
<br /> concentrations up to 6,700 mg/kg, 510 mg/kg, 0.2 mg/kg, and 2.9 mg/kg,respectively. Low
<br /> concentrations of polynuclear aromatic hydrocarbons(PAHs)were detected in all of the soil
<br /> borings. No TPHg, BTEX, or MTBE were detected in grab groundwater samples from SB-13
<br /> and SB-14. TPHd were detected in these samples at concentrations up to 450 gg/L. TPHd,
<br /> TPHg, and benzene were detected in the grab groundwater sample from SB-17 at concentrations
<br /> of 150,000 gg/L,,480 gg/L, and 0.6 gg/L,respectively. Low concentrations of PAHs were
<br /> detected in all of the grab groundwater samples,with the exception of 4 gg/L of naphthalene in
<br /> SB-13.
<br /> PETROLEUM DISTRIBUTION IN GROUNDWATER
<br /> The RWQCB water quality objectives (WQOs)include total TPH measurements for diesel
<br /> products,but not for crude oil/Bunker C fuel oil. According to the Technical Approach to Site
<br /> Evaluation and Decision-Making for the Historical Pipeline Portfolio(referred to as the
<br /> Consistent Technical Approach [CTA]), diesel products are not associated with the Historical
<br /> Pipeline Portfolio(HPP) sites and typically are not present at these sites." However,WQOs are
<br /> applied to"diesel-range hydrocarbons" (extractable TPH, CIO—C25) found in HPP site
<br /> groundwater samples because no WQOs are established for crude oil/Bunker C fuel oil, and
<br /> historical data indicates that diesel-range hydrocarbons are often detected at sites affected by
<br /> crude oil/Bunker C fuel oil. Per the CTA, groundwater samples are quantified against a diesel
<br /> standard so that the comparison to the WQOs is as direct as possible.
<br /> Since 2005, a sheen has been observed in well MW-1, and a petroleum odor or sheen has been
<br /> observed in MW-2. TPHd have been detected in wells MW-3 and WFSMW-1 at concentrations
<br /> of up to 6,700 gg/L and 970 gg/L,respectively. No dissolved-phase TPHg or BTEX have been
<br /> detected in the groundwater from the site wells. TPHg and TPHd were detected in the separate-
<br /> phase oil(SPO) from well MW-2 in 2005. Low levels of PAHs have occasionally been detected
<br /> in groundwater from MW-2,MW-3,MW-5, and WFSMW-1.
<br /> 9. Geomatrix Consultants,Inc.,2003. Report of Off-Site Soil and Groundwater Investigation, US Can/Welty Road,
<br /> Vernalis, California.
<br /> 10. SAIC,2005. Soil And Groundwater Investigation Report And Second Quarter 2005 Monitoring And Sampling US
<br /> Can—Welty Road, 35275 Welty Road, Vernalis, California.
<br /> 11. Geomatrix Consultants,Inc.,2005. Technical Approach to Site Evaluation and Decision-Making,Historical
<br /> Pipeline Portfolio, Central Valley Region. February.
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