SITE INFORMATION AND CORRESPONDENCE

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I 1 Mr. M. Scott Mansholt—CEMC Fourth Quarter Groundwater Monitoring and Sampling Report and 2005 Annual Summary December 22,2005 Vernalis Pump Station, Vernalis,California Page 6 of 7 QUARTERLY PETROLEUM-ABSORBENT (OLEOPHILIC) SOCK REPLACEMENT An oleophilic sock has been installed in well MW-1 due to the presence of SPO observed in the well. The sock has been monitored and replaced as necessary on a quarterly basis. During the fourth quarter 2005, the sock was weighed but not replaced, and four ounces (approximately 0.03 gallon)of SPO had been absorbed. A summary of SPO thickness measurements is included in Table 1. QUALITY ASSURANCE/QUALITY CONTROL (QA/QC) All field procedures were conducted in accordance with SAIC's Quality Assurance and Quality Control Sample Collection, Handling, and Analysis procedures. No sample was received by the 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), a duplicate (MW-3D), matrix spike (MW-41v[S), and matrix spike duplicate(MW-4MWD). 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 surrogate quality control, matrix spike, and matrix spike duplicate samples results were within acceptable ranges, except for benzo(a)anthracene used in the matrix spike/duplicate. The laboratory considers the sample results acceptable and useable. ANNUAL SUMMARY Quarterly groundwater monitoring and sampling began at the Vernalis Pump Station site in the second quarter 2005. DTW recorded during 2005 ranged between approximately 33.71 (MW-6) to 38.09 (MW-5) feet btoc (Table 1). Groundwater flow during 2005 remained 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 map is presented as Figure 5. The site wells are constructed with screen lengths of approximately 10 feet for wells MW-1 through MW-4(28 to 38 feet bgs)and 20 feet for wells MW-5 through MW-7 (approximately 30 to 50 feet bgs). DTW has ranged from approximately 24 to 38 feet bgs, indicating that wells MW-5 though MW-7 are appropriately screened to monitor the upper water-bearing zone beneath the site. Wells MW-1 though MW-4 are shallow and will need to be replaced if future groundwater levels become lower. A summary of well construction details is presented in Table 5. SPO has been observed in well MW-1. Oleophilic socks are currently used in MW-1 to extract the SPO. Approximately 0.03 gallon has been extracted by the absorbent sock. A summary of the SPO thickness measurements is presented in Table 1. No TPHg, BTEX, or MTBE concentrations were detected in the any groundwater samples during 2005 (Table 2). TPHd was detected in the samples from well MW-7 at concentrations of up to 620 µg/L. Low PAH concentrations were detected in wells MW-2, MW-3, MW-6, and MW-7 (Table 3). The EPA Region 9 Preliminary Remediation Goals (PRGs)9 for direct exposure to residential tap water for PAH levels were slightly exceeded by naphthalene. The PRG for naphthalene is 0.093 µg/L. The highest naphthalene concentration detected in the site wells was 9. The PRGs are risk-based tools for evaluating potential exposure risk to human health at the screening level and for establishing preliminary cleanup goals.