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Mr.M. Scott Mansholt—CEMC Fourth Quarter 2005 Groundwater Monitoring and Sampling Report and 2005 Annual Summary January 5,2006 US Can-Welty Road,Vernalis,California Page 6 of 7 laboratory outside of acceptable temperature or pH limits. In addition to routine laboratory QC sample analysis, four field QC samples were analyzed for this event in accordance with SAIC's standard field procedures: a trip blank(QA-T); duplicate(MW-5D); a matrix spike(MW-5MS); and matrix spike duplicate(MW-SMSD). No indication of potential cross contamination was identified in the sample analyses. No THPd,TPHg,BTEX, or PAHs were detected in the laboratory blank sample. The field duplicate, surrogate quality control,matrix spike, and matrix spike duplicate sample results were within acceptable ranges, except for the TPHd(with silica-gel preparation) surrogate recovery for MW-3 that was slightly out of the specification range. The laboratory considers the sample results acceptable and useable. ANNUAL SUMMARY Quarterly groundwater monitoring and sampling began at the US Can-Welty Road site in the second quarter 2005. DTW recorded during 2005 ranged between approximately 31.50 (MW-5) to 36.60(MW-4) feet btoc (Table 1). Groundwater flow during 2005 ranged from northeast to east-southeast at an average gradient of 0.001 ft/ft. A summary of groundwater flow directions and gradients is presented in Table 4, and the previous 2005 quarterly potentiometric surface maps are presented as Attachment C. The site wells are constructed with screen lengths of approximately 25 to 45 feet bgs. DTW has ranged from approximately 31 to 37 feet bgs, indicating that the site wells are appropriately screened to monitor the upper water-bearing zone beneath the site. A summary of well construction details is presented in Table 5. SPO has been observed in wells MW-1 and MW-2. Oleophilic socks are currently used in MW-1 and MW-2 to extract the SPO. Approximately 0.07 gallon has been extracted by the oleophilic sock in MW-1. An oleophilic sock was placed in MW-2 during the fourth quarter 2005. A summary of the SPO thickness measurements is presented in Table 1. No dissolved-phase TPHd, TPHg, or BTEX were detected in any groundwater samples during 2005, except 6,700 and 240µg/L in wells MW-3 and WFSMW-1,respectively(Table 2). TPHg- and TPHd-range hydrocarbons have been detected in the SPO from MW-2. Well MW-2 has had measurable SPO in the past and currently has a sheen and a petroleum odor. TPHd levels appear to have increased during 2005 in WFSMW-1; however, additional analytical data is required to confirm that this is an upward trend and not the result of natural concentration fluctuations. Low PAH concentrations were detected in all the site wells(Table 3). The EPA Region 9 Preliminary Remediation Goals (PRGs)' for direct exposure to residential tap water for PAHs were slightly exceeded by benzo(a)anthracene in the second quarter in MW-3, and by several PAHs in a sample collected from well MW-2. The tap water PRG for benzo(a)anthracene is 0.092µg/L. Benzo(a)anthracene was detected in well MW-3 at 0.1 µg/L. A distribution map for 2005 of petroleum in groundwater is presented as Figure 4. CONCLUSIONS AND RECOMMENDATIONS Groundwater elevations from the site wells indicate that groundwater flow ranged from the northeast to east-southeast at an approximate gradient of 0.001 ft/ft during 2005. No dissolved- phase TPHg,BTEX, or MTBE appears to be present at the site. Dissolved-phase TPHd-range hydrocarbons were detected in two of the wells (MW-3 and WFSMW-1)during 2005 at 1. The PRGs are risk-based tools for evaluating potential exposure risk to human health at the screening-level and for establishing preliminary cleanup goals.