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Mr.M. Scott Mansholt—CEMC First Quarter 2007 Groundwater Monitoring and Sampling Report April 24,2007 US Can-Welty Road Page 4 of 6 • TPHd(C107-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 selected ion monitoring. In Tables 2 and 3,the groundwater analytical results are summarized and compared with the RWQCB Region 2 Environmental Screening Levels(ESLs)and the numerical State WQOs;3 those 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 390 gg/L of TPHd in WFSMW-1. It should be noted that TPHd were detected in the laboratory method blank sample at 34 gg/L. A petroleum-hydrocarbon distribution map is presented on Figure 4. The laboratory analytical report and data usability summary, as well as details regarding data qualifiers, are presented as Attachment B. A fuel-fingerprint sample was collected from WFSMW-I due to apparent increasing TPHd concentrations in quarterly results and the close proximity of the well to the location of a former underground storage tank(UST)complex associated with operations at Western Farm Services. The sample was analyzed by Chevron Energy Technology Company(ETC)to identify the range of hydrocarbons present. The results of the analysis show that the sample contained 1,300 gg/L of iso-octane,mono-aromatics (BTEX), and some constituents of gasoline(Attachment B). No diesel-range hydrocarbons were detected. The approximate percentages of each carbon range detected were C6 at 20.1 percent, C7-C10 at 79.7 percent, C11-C4 at 0.2 percent, and C15+at 0 percent. The TPHd analysis routinely conducted on the groundwater samples uses a carbon range of C10-C25, overlapping the analysis done by ETC in the C11-C14 range. Applying the 2- percent C11-C14 carbon range to the total concentration of 1,300 gg/L yields 260 gg/L,which approximates the 390 gg/L TPHd detected during the routine analysis. It is possible that the 390 gg/L detected was actually heavier-end,gasoline-range hydrocarbons associated with the former WFS UST complex. However, additional investigation regarding this finding is necessary. 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. Analysis of major dissolved-ion species (Na+, Ca2+, K+,Mg2+, Cl-, S042-,HCO3-)were expressed by plotting relative concentrations on a trilinear diagram(Piper Diagram), displaying the percentage composition of the cation/anion groups (Attachment Q. As shown in Attachment C,the groundwater sample indicates that the water-bearing zone is not controlled by a specific ionic type.4 A cation-anion balance was conducted to validate the laboratory analysis(Attachment Q. The percent error calculated from the charge balance for MW-5 is 2.3 percent. Less than 5 percent is considered an acceptable error for analysis.5 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. C.W.Fetter, 1994.Applied Hydrogeology Third Edition,Prentice Hall Inc.,p.421-3. 5. R.Freeze,J.Chevy, 1979. Groundwater,Prentice Hall Inc.,p.97