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Mr.M. Scott Mansholt—CEMC First Quarter 2007 Groundwater Monitoring and Sampling Report April 24,2007 Vernalis Pump Station Page 4 of 5 • TPHd(CIO—C25),using U.S. Environmental Protection Agency(EPA)Method 8015B and TPHd with silica-gel preparation for samples with detectable concentrations of TPHd using EPA Method 801513; and • PAHs using EPA Method 8270C selective ion monitoring(SIM). The groundwater analytical results are summarized and compared with the RWQCB Region 2 Environmental Screening Levels (ESLs) and the numerical State WQOs in Tables 2 and 3;5 results exceeding the most conservative ESL or WQO are highlighted in bold-type font. No TPHd or PAHs were detected at concentrations exceeding the most conservative WQO or ESL, except possibly 150 gg/L TPHd in MW-5 and MW-7, and several PAHs detected in MW-6. No PAHs were detected in the duplicate sample for MW-6 collected at the same time. It should be noted that TPHd were detected at a concentration of 110 gg/L in the equipment blank sample; therefore,the TPHd detection at MW-7 may be attributed to cross contamination. A petroleum hydrocarbon-distribution map is presented on Figure 4. The data usability summary and a copy of the laboratory analytical report are presented as Attachment B. Please see Attachment B for details regarding data qualifiers. The groundwater sample from MW-5 was analyzed for General Minerals as suggested by the RWQCB during a semi-annual project meeting in August,2006. The results of the analyses are presented in Attachment C. Analyses of major dissolved-ion species(Na+, Ca 2+,K+,Mg2+, Cl-, S042-,HCO3-)were expressed by plotting relative concentrations on a trilinear diagram(Piper Diagram), and displaying the percentage composition of the cation/anion groups6 (Attachment C). As shown in Attachment C,the groundwater sample indicates that the water-bearing zone is not controlled by a specific ionic type.5 A cation-anion balance was conducted to validate the laboratory analysis. The percent error calculated from the charge balance for MW-5 is 2.7 percent. Less than 5 percent is considered an acceptable error for analysis.' QUARTERLY OIL-ABSORBENT (OLEOPHILIC) SOCK REPLACEMENT An oleophilic sock was installed in well MW-1 due to SPO observed in the well. The sock has been monitored and replaced as necessary on a quarterly basis. During the first quarter of 2007,the sock was weighed but not replaced. 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.S 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 groundwater elevation ranged between 68.09 and 71.24 feet above MSL with a gradient predominantly towards the east at 0.001 ft/ft. Dissolved-phase TPHd concentrations have historically 5. 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." 6. C.W.Fetter, 1994. Applied Hydrogeology,Third Edition,Prentice Hall Inc.,p.421-3. 7. R.Freeze,J.Cherry, 1979. Groundwater,Prentice Hall Inc.,p.97. 8. SAIL,2007. Quality Assurance and Quality Control Sample Collection,Handling,and Analysis. April(Updated).