SITE INFORMATION AND CORRESPONDENCE (2)

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Mr.M. Scott Mansholt—CEMC Fourth Quarter 2006 Groundwater Monitoring and Sampling Report and Annual Summary Report January 12,2007 Vernalis Pump Station Page 6 of 7 QUARTERLY OIL-ABSORBENT (OLEOPHILIC) SOCK REPLACEMENT An oleophilic sock was installed in well MW-1 due to SPO observed in the well. The sock has been monitored and replaced as necessary on a quarterly basis. During the fourth quarter of 2006,the sock was weighed but not replaced, and 2 ounces(approximately 0.017 gallon)of SPO had been absorbed. A summary of SPO thickness measurements is included in Table 1. QUALITY ASSURANCE/QUALITY CONTROL All field procedures were conducted in accordance with SAIC's Quality Assurance and Quality Control Sample Collection, Handling, and Analysis.10 Based on SAIC's evaluation, all analytical data are usable as qualified for the purpose of determining chemical concentrations in groundwater at the site. Qualified data with applicable reason codes are shown in Table B-1 of Attachment B. Unless noted otherwise,analytical data collected in support of this investigation are considered precise, accurate,representative, complete, and comparable, and they may be used for their intended purposes. ANNUAL SUMMARY 2006 Quarterly groundwater monitoring and sampling began at the site in the second quarter of 2005. Depth to groundwater recorded during 2006 ranged between approximately 33.46 (MW-6)to 38.92 (MW-4) feet btoc (Table 1). Groundwater flow during 2006 varied east to northeast 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 2006 quarterly potentiometric surface maps are presented as Figure 5 through 7. 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). Depth to groundwater has ranged from approximately 31 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 0.012 gallon has been extracted by the sock. A summary of the SPO thickness measurements is presented in Table 1. No TPHg or BTEX were detected in the any groundwater samples during 2006(Table 2). TPHd were detected in the samples from wells MW-2 through MW-5 and MW-7 at concentrations up to 930µg/L. Low PAH concentrations were detected in wells MW-5,MW-6, and MW-7 (Table 3). The RWQCB Region 2 ESLs and the numerical State WQOs were slightly exceeded by benzo(b)fluoranthene. The WQO and ESL for benzo(b)fluoranthene are 0.04 and 0.014 pg/L,respectively. The highest benzo(b)fluoranthene concentration detected in the site wells was 0.044 pg/L in MW-6. A distribution map for 2006 of petroleum in groundwater is presented on Figure 4. CONCLUSIONS AND RECOMMENDATIONS The groundwater elevation and gradient remained relatively consistent during 2006. The groundwater elevation fluctuated between 68.83 and 72.04 feet above MSL with a gradient predominantly towards the east at 0.001 ft/ft. Dissolved-phase TPHg and BTEX do not appear to be present beneath the site. While dissolved-phase TPHd concentrations fluctuated between non-detect levels to 930 µg/L,the 10. SAIL,2006. Quality Assurance and Quality Control Sample Collection,Handling,and Analysis. January(Updated).