SITE INFORMATION AND CORRESPONDENCE

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Mr.M. Scott Mansholt—CEMC First Semi-Annual 2008 Groundwater Monitoring and Sampling Report April 28,2008 Vernalis Pump Station Page 4 of 6 Table 2(TPHd) and Table 3 (PAHs).3 Results exceeding the most conservative ESL or WQO are highlighted in bold-type font. MW-7 had a TPHd detection of 390 micrograms per liter(gg/L;<50 gg/L after silica-gel cleanup)during January 2008 monitoring, and a TPHd detection of 150 gg/L(88 gg/L after silica-gel cleanup)during October 2007 monitoring. None of the other wells had TPHd or PAH detections at concentrations exceeding their respective WQOs/ESLs. The data usability summary with details regarding data qualifiers and a copy of the laboratory analytical report are presented as Attachment B. Well construction details are provided in Table 4. Petroleum distribution maps for January 2008 and October 2007 are presented on Figures 5 and 6,respectively. QUARTERLY OIL-ABSORBENT (OLEOPHILIC) SOCK REPLACEMENT An oleophilic sock was installed in well MW-1 in October 2005 due to the observation of SPO in this well consistently since 1998. The sock has been monitored and replaced as necessary on a quarterly basis. The oleophilic sock was inspected and replaced during the 1 st quarter 2008 event. Less than 0.01 gallon of SPO was removed from the well during this event and a total of approximately 0.02 gallon of SPO has been removed since July 1998 from well MW-1. 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.' 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 4th quarter 2007 groundwater monitoring and sampling event was completed on October 29,2007. The 1St quarter 2008 groundwater monitoring and sampling event was completed between January 28 and January 30, 2008. The groundwater elevation at the site ranged from 69.07 feet(MW-1)to 71.56 feet (MW-6)above AMSL during the 4th quarter 2007. The groundwater elevation at the site ranged from 68.04 feet(MW-1)to 71.11 feet(MW-5)above MSL during the 1St Quarter 2008. The average groundwater elevation at the site is 70.99 feet above MSL based on all groundwater elevation measurements collected to date from these wells. Wells MW-6 and MW-7 were sampled during the 4th quarter 2007 and 1St quarter 2008 monitoring events. The remaining wells(MW-2,MW-3, and MW-5)were sampled during the 1St quarter 2008 monitoring event. MW-1 was not sampled during the 2008 monitoring event due to the presence of SPO in the well. The oleophilic sock in MW-1 was replaced during the 1St quarter 2008 event and approximately 0.01 gallon of SPO was removed. SPO has been consistently observed in this well since 1998 with a total of 0.02 gallon of SPO removed from this well to date. Well MW-4 was not sampled due to a bent well 3. The ESLs(provided as a reference)are a tool based on conservative standard exposure factors for initial human health and the environment screening-level evaluations of analytical results. The WQOs are defined by the Porter-Cologne Act as"the levels or limits of water quality constituents or characteristics which are established for the reasonable protection of beneficial uses of water or the prevention of nuisance within a specific area." 4. SAIL,2007. Quality Assurance and Quality Control Sample Collection,Handling,and Analysis. April(Updated).