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M. Scott Mansholt—CEMC Second Semi-Annual 2008 Groundwater Monitoring and Sampling Report September 26,2008 Vernalis Pump Station Page 4 of 7 GROUNDWATER ANALYTICAL RESULTS The groundwater analytical results are summarized and compared with the RWQCB Region 2 Environmental Screening Levels (ESLs) and the numerical State Water Quality Objectives(WQOs)in Table 2(for TPHd)and Table 3 (for PAHs)2. The results are as follows: • MW-1:Not sampled due to presence of SPO. • MW-2: TPHd detected at 110 micrograms per liter(gg/L; <50 gg/L after silica-gel cleanup) from the July 2008 monitoring event. • MW-3 and MW-5: TPHd not detected at<50 gg/L from the July 2008 monitoring event. • MW-4:Not sampled due to a damaged casing. • MW-6: TPHd detected at 74 gg/L(<50 gg/L after silica-gel cleanup) from the July 2008 monitoring event, and<50 gg/L from the April 2008 monitoring event;naphthalene detected at a concentration of 0.031 gg/L(April 2008). • MW-7: TPHd detected at 320 gg/L; (170 gg/L after silica-gel cleanup)from the July 2008 monitoring event; a duplicate sample indicated TPHd at 230 gg/L(68 gg/L after silica-gel cleanup. TPHd detected at 150 gg/L (120 gg/L after silica-gel cleanup) from the April 2008 monitoring event. Naphthalene detected at 0.018 gg/L,and acenaphthene detected at 0.018 gg/L (April 2008). A data usability summary with details regarding data qualifiers and the laboratory analytical report are provided as Attachment B. Well construction details are provided in Table 4. Petroleum distribution maps for July 2008 and January 2008 (and April 2008 for MW-6 and MW-7) are shown on Figures 5 and 6,respectively. QUARTERLY OLEOPHILIC SOCK REPLACEMENT An oleophilic sock was installed in well MW-1 in October 2005 due to the consistent observation of SPO 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 2008 event. Less than 0.01 gallon of SPO was removed from well MW-1 during this event and a total of approximately 0.02 gallon of SPO has been removed from the well since July 1998. A summary of SPO thickness measurements is provided 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.s SAIC's evaluation concluded that all analytical data are 2. 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(Interim Final November 2007,[Revised May 2008])." 3. SAIL,2007. Quality Assurance and Quality Control Sample Collection,Handling,and Analysis. April(Updated).