SITE INFORMATION AND CORRESPONDENCE

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Mr.M. Scott Mansholt—CEMC Second Quarter 2007 Groundwater Monitoring and Sampling Report July 24,2007 Vernalis Pump Station Page 4 of 5 MW-1 was inspected and replaced. An estimated 1 ounce(0.008 gallon) of SPO was removed. 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 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. CONCLUSIONS AND RECOMMENDATIONS The second quarter 2007 groundwater monitoring and sampling event was completed on May 8, 2007. The second quarter 2007 groundwater elevations ranged from 68.11 feet(MW-1)to 71.29 feet(MW-3 and MW-5) above MSL with a gradient predominantly towards the east at 0.001 ft/ft. Historically,groundwater elevation at the site has ranged from 68.09 to 74.72 feet above MSL, with the average groundwater elevation being 7 1.01 feet above MSL. During the second quarter 2007 sampling event,MW-1 was not sampled due to the presence of SPO in the well. The oleophilic sock in MW-1 was replaced and an estimated 0.008 gallons of 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 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 there were no PAHs detected at concentrations exceeding the most conservative WQOs and/or ESLs. Based on recent and historic site groundwater monitoring data,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, and therefore this well has never been sampled. Wells MW-2 and MW-4 have not been sampled since January 2006. When last sampled, MW-2 had a TPHd detection of 120 gg/1(67 gg/1 after silica-gel cleanup)and MW-4 had a TPHd detection of 290 gg/1(150 µg/1 after silica-gel cleanup). The TPHd WQO/ESL is 100 gg/1. MW-3 was last sampled in November 2006 and TPHd were non-detect below the laboratory method reporting limit of<50 gg/1. MW-5 has had TPHd detections twice since July 2005,with the most recent sampling event having a non-detectable concentration of TPHd. MW- 6 had only a single detection of TPHd since July 2005 and it was below the TPHd WQO/ESL. MW-7 is the only well where TPHd were consistently detected between July 2005 and January 2007,with the last sampling event showing TPHd as non-detect. With the exception of MW-6,PAHs have not been detected at concentrations above WQOs and/or ESLs. PAHs were detected in MW-6 above WQOs and/or ESLs from samples collected during the January 2006 and January 2007 sampling events. These PAH detections were in field duplicate samples and not in the primary sample aliquots. However, several of the reported PAH 3. SAIC,2007. Quality Assurance and Quality Control Sample Collection,Handling,and Analysis. April (Updated).