SITE INFORMATION AND CORRESPONDENCE

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Mr. M. Scott Mansholt—CEMC First Quarter 2006 Groundwater Monitoring and Sampling Report April 10,2006 Vernalis Pump Station Page 5 of 5 inadequately spiked. The sample results for MW-5 were not consistent with historical results for PAHs. Because the MS/MSD failed to meet the QC requirements, MW-5 was re-sampled on March 16, 2006, and another set of MS/MSD samples were collected. The March 16, 2006 MS/MSD results, lab control sample results, and surrogate recoveries met QC requirements. Because the MS/MSD QC requirements were not met during the January analysis, the March 16, 2006 results for MW-5 are reported instead. The laboratory considers the sample results acceptable and useable. CONCLUSIONS AND RECOMMENDATIONS Groundwater elevations from the site wells indicate that groundwater flow was to the east at an approximate gradient of 0.041 ft/ft during the first quarter of 2006. No dissolved-phase TPHg or BTEX appear to be present at the site. Dissolved-phase TPHd were detected in MW-2, MW-3, MW-4, MW-6, and MW-7 during the first quarter of 2006 at concentrations of 120, 930, 290, 95, and 480 �tg/L, respectively. Low concentrations of PAHs were detected in the samples from wells MW-6 (field duplicate only) and MW-7 and were below the PRGs for direct exposure to tap water. SPO has been observed in well MW-1 since 1998. SAIC recommends continued quarterly groundwater monitoring and sampling of wells MW-1 through MW-7. The absorbent sock in well MW-I will be monitored quarterly and replaced as necessary. When the petroleum sheen has been removed, SAIC recommends that well MW-1 be incorporated into the quarterly monitoring and sampling program. Due to the lack of water and poor sample quality in wells MW-1 through MW-4, SAIC recommends that these wells be destroyed and new wells installed with a more suitable screen interval. A work plan for this scope of work will be submitted to the RWQCB. CLOSING If you have any questions regarding this report, please call Chris Dennis at(916) 979-3866. Sincerely, SCIENCE APPLICATIONS INTERNATIONAL CORPORATION c4vv�//"� �� G St Zet e Villanueva Christopher B. Dennis, P.G. Staff Scientist Senior Geologist NAL Enclosures: �� Figure 1: Site Vicinity Map O CHRISTOPHER Figure 2: Site Map with Monitoring Well Locations d B Figure 3: Potentiometric Surface Map—First Quarter 2006 DENNIS Figure 4: Petroleum Distribution in Groundwater First Quarter 2006 Table 1: Groundwater Elevation Data and SPO Thickness Measurements IV°'79 84 Table 2: Groundwater Analytical Results—THPd,TPHg, and BTEXQF CAS-tF� Table 3: Groundwater Analytical Results—PAHs Attachment A. Field Data Sheets Expires August 31 =7 Attachment B: Laboratory Analytical Report ...................... .............. . ................ ....... ......... ........... .. ...... . .. ... ..... ..... .... ... .... ....... . . .......