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M. Scott Mansholt - 3 - 14 December 2005 <br /> Chevron Environmental <br /> US Can-Welty Road <br /> Soil boring SB-17, was advanced approximately 150 feet east-northeast of the site to evaluate offsite soil <br /> and groundwater in that area. However, the boring is closer to the adjacent former Vernalis Pump <br /> Station/Roberts OVP site (now referred to as Bellini). Low TPHc concentrations (17 to 60 mg/kg) were <br /> reported in shallow soil and 6,700 TPHc and 510 mg/kg TPHg was reported in the 42-foot sample from <br /> SB-17. Benzene and MTBE were ND and the PAHs were ND to low concentrations at or above the <br /> respective method detection limits (MDLs). <br /> Groundwater <br /> Groundwater samples were obtained from three of the four borings, except SB-15 that was converted to <br /> monitoring well MW-5 which was sampled as part of the second (and third) quarterly groundwater <br /> monitoring events (discussed in this report). <br /> TPHd concentrations of 450, 200, and 150,000 µg/L, were reported in borings SB-13, 14, and 17 <br /> groundwater samples, respectively. In addition, TPHg in SB-17 was 480 µg/L and ND in SB-13 and <br /> SB-14. BTEX and MTBE results were ND; the PAH compounds were ND and at or slightly above their <br /> respective MDLs. <br /> Quarterly groundwater monitoring was conducted during July 2005 as part of the third quarter sampling <br /> evaluation. Review of the analytical results indicates an increase of TPHd in three of the four on-site <br /> monitoring wells previously reporting low concentrations. MW-1 remains unchanged with a sheen; <br /> MW-2, located on the northwestern portion of the site,has increased from 2,300 µg/L in 1998 to <br /> 150,000 µg/L TPHd and from ND to 310 µg/L TPHg; concentrations of PAH compounds were also <br /> detected. Similarly,TPHd in MW-3, located on the east portion of the site, has increased from 300 µg/L <br /> in 1998, ND in 2002, 86 in 2003, to 6,700 µg/L during July 2005. TPHg and PAHs were essentially ND <br /> in MW-3. Upgradient well MW-4 (SE corner of the site) remains unchanged with TPH compounds ND <br /> for the same monitoring period. <br /> Based on our review, we have the following comments: <br /> • Petroleum-impacted soil appears to occur in close proximity to the OVP at a variety of locations <br /> and depths from approximately five to greater than 40-feet, but generally is present at higher <br /> concentrations beginning at 10 to 12 feet or deeper. However, according to the findings to date, <br /> it appears that there are two separate areas of affected soil (MW-2/GMX-8 and MW-1/MW-3 <br /> [next to the waste/bum pit])that are more heavily impacted as result of leaks from the OVP. <br /> However, it appears that impacts contributed from historic site activities have affected conditions <br /> in the area of the waste/bum pit. <br /> • The report suggests that impacted soil in an area southeast of former boring GMX-11 (east to <br /> northeast of MW-3) has yet to be delineated. The vertical extent of impacted soil appears to be <br /> defined at approximately 50 feet by on-site borings MW-2 and GMX-1B and off-site borings <br /> GMX-11 and 12. The extent of impacted soil beneath the on-site structures is unknown, but soil <br /> boring samples south and upgradient were ND for TPH compounds. <br />