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Mr.M. Scott Mansholt—CEMC First Semi-Annual 2007 Groundwater Monitoring and Sampling Report October 29,2007 Vernalis Pump Station Page 4 of 5 QUARTERLY OIL-ABSORBENT (OLEOPHILIC) SOCK REPLACEMENT An oleophilic sock was installed in well MW-1 in October 2005 due to SPO being observed in this well consistently since 1998. The sock has been monitored and replaced as necessary on a quarterly basis. The oleophilic sock was inspected but not replaced during the third quarter of 2007 due to the observation of only a light stain of SPO on the sock. 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.3 SAIC's evaluation concluded that 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 provided in Table B-1 of Attachment B. Analytical data collected in support of this investigation are considered precise, accurate, representative, complete, and comparable, and may be used for their intended purposes unless noted otherwise. CONCLUSIONS AND RECOMMENDATIONS The first semi-annual 2007 groundwater monitoring and sampling event was completed on August 6,2007. Groundwater elevations ranged from 69.06 feet(MW-1)to 72.24 feet(MW-3) above MSL with a gradient predominantly toward the east at 0.002 ft/ft. Groundwater elevation at the site has historically ranged from 68.09 to 74.72 feet above MSL,with the average groundwater elevation being 71.05 feet above MSL. MW-1 was not sampled during the 2007 monitoring event due to the presence of SPO in the well. The oleophilic sock in MW-1 was not replaced and no SPO was removed. SPO has been consistently observed in this well since 1998. Wells MW-2,MW-3, and MW-4 were not sampled due to insufficient water volume. Groundwater samples were collected from wells MW-5,MW- 6, and MW-7 and analyzed for TPHd and PAHs. TPHd were non-detect below the laboratory method detection limit of<50 gg/L in all the samples, and PAHs were not detected at concentrations exceeding the most conservative WQOs and/or ESLs. Recent and historic site groundwater monitoring data indicate that the TPHd groundwater plume appears to be localized in a small area of the site with wells MW-1 through MW-4 defining the lateral extent of the TPHd groundwater plume. Small amounts of SPO have been observed in MW-1 since monitoring and sampling began in 1998;therefore,this well has never been sampled. Wells MW-2 and MW-4 have not been sampled since January 2006 due to insufficient water volume. MW-2 had a TPHd detection of 120 µg/1(67 gg/l after silica-gel cleanup) and MW-4 had a TPHd detection of 290 µg/1(150 µg/l after silica-gel cleanup)when last sampled,with both these detections exceeding TPHd WQO/ESL of 100 ttg/1. Well MW-3 was last sampled in November 2006 and TPHd were non-detect below the laboratory method reporting limit of <50 µg/1. Well MW-5 had TPHd detections twice since July 2005, and the most recent sampling event(August 2007)had a non-detectable concentration of TPHd. Well MW-6 has never had a detection of TPHd above the WQO/ESL. Well MW-7 is the only well where TPHd have been detected at elevated concentrations, although, during the last two events(second and third quarter 2007),TPHd have been non-detect in well MW-7. 3. SAIC,2007. Quality Assurance and Quality Control Sample Collection,Handling,and Analysis. April (Updated).