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Mr.M. Scott Mansholt—CEMC
<br /> Fourth Quarter 2005 Groundwater Monitoring and Sampling Report and
<br /> 2005 Annual Summary January 5,2006
<br /> US Can-Welty Road,Vernalis,California Page 4 of 7
<br /> samples. TPHc were detected in borings GMX-8 and GMX-1B at maximum concentrations of
<br /> 8,000 and 5,100 mg/kg,respectively.
<br /> 2003 Site Investigation! 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, 3,600, and
<br /> 110 gg/L,respectively.
<br /> 2005 Site Investigation.9 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 MTBE were detected in the soil
<br /> samples SB-13, SB-14, and SB-15, except 120 mg/kg TPHc in SB-14 at 1 foot bgs. TPHc,
<br /> TPHg, ethylbenzene, and xylenes were detected in SB-17 at concentrations up to 6,700, 510, 0.2,
<br /> and 2.9 mg/kg,respectively. Low concentrations of PAHs were detected in all of the soil borings.
<br /> No TPHg,BTEX,or MTBE were detected in grab groundwater samples from SB-13 and SB-14.
<br /> TPHd was detected in these samples at concentrations up to 450 gg/L. TPHd, TPHg, and
<br /> benzene were detected in the grab groundwater sample from SB-17 at concentrations of 150,000,
<br /> 480, and 0.6 gg/L,respectively. Low concentrations of PAHs were detected in all of the grab
<br /> groundwater samples, except 4 gg/L naphthalene in SB-13.
<br /> PETROLEUM DISTRIBUTION IN GROUNDWATER
<br /> During 2005, a sheen was observed in well MW-1 and a petroleum odor observed in MW-2.
<br /> Dissolved-phase crude oil was indicated by TPHd analyses. TPHd has been detected in wells
<br /> MW-3 and WFSMW-1 at concentrations of up to 6,700 and 240 gg/L,respectively. No
<br /> dissolved-phase TPHg or BTEX were detected in the groundwater from the site wells during
<br /> 2005. TPHg and TPHd range hydrocarbons were detected in the separate-phase oil(SPO)from
<br /> well MW-2. Low levels of PAHs were detected in groundwater from all of the site wells.
<br /> GROUNDWATER MONITORING AND SAMPLING
<br /> MONITORING
<br /> On October 18, 2005, depth to water(DTW)was measured in wells MW-1 through MW-5 and
<br /> WFSMW-1 using a hydrocarbon/water interface probe. DTW in these wells ranged from 31.50
<br /> feet below top of casing(btoc)in MW-5 to 35.02 feet btoc in MW-4. The approximate
<br /> groundwater flow direction beneath the site is to the east-southeast at a calculated gradient of
<br /> approximately 0.001 feet/foot(ft/ft). Cumulative DTW measurements, groundwater elevations,
<br /> and product thickness are presented in Table 1. A map showing the potentiometric surface is
<br /> presented on Figure 3. Field data sheets are included in Attachment A.
<br /> 8. Geomatrix Consultants,Inc.,2003,Report of Off-Site Soil and Groundwater Investigation,US Can/Welty Road,
<br /> Vernalis,California.
<br /> 9. SAIC,2005,Soil And Groundwater Investigation Report And Second Quarter 2005 Monitoring And Sampling Us Can—Welty
<br /> Road,35275 Welty Road,Vernalis,California.
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