ARCHIVED REPORTS_ANNUAL 2014 GRAOUNDWATER MONITORING AND SAMPLING REPORT

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Mr.C.Dean Hubbard—Central Valley RWQCB Annual 2014 Groundwater Monitoring and Sampling Report April 29,2014 Alden Park Page 5 of 7 • TPHd(Cto—C25),using U.S. Environmental Protection Agency(EPA) Method 8015B; and • PAHs using EPA Method 8270C with selective ion monitoring. The groundwater analytical results are summarized and compared with the numerical water quality objectives(WQOs) and environmental screening levels(ESLs) in Tables 4 and 5.3 Analytical results exceeding the most conservative ESL and/or WQO are shown in bold in Tables 4 and 5. TPHd was not detected in any of the wells. Naphthalene was the only PAH detected in each groundwater sample,but concentrations did not exceed the ESLs and/or WQOs. A copy of the laboratory analytical report and the data usability ' summary are provided as Attachment C. See Attachment C for details regarding data qualifiers. QUARTERLY SPO EXTRACTION AND PRODUCT-THICKNESS MEASUREMENTS Vacuum extraction of SPO was performed quarterly throughout 2013 (March 18,June 20, September 11, and December 5, 2013) and on April 15,2014. Scheduling conflicts prevented the latest event from occurring during the first quarter of 2014. The results of the March 2013 SPO extraction event were reported in the previous annual report dated May 29, 2013. This report covers the second quarter 2013 through the April 2014 SPO extraction events. The customary method of gauging SPO thickness in wells from the top down is made difficult by the highly viscous nature of SPO at the Site. The probe tip becomes coated with SPO as it is lowered, and is thus unable to detect the transition from the bottom of SPO to groundwater. During the second quarter 2013 SPO extraction event, a new SPO measuring process was initiated at the site. The depth to the top of SPO was measured in a conventional way,by lowering the interface probe in the well until it detected SPO. The interface probe was then removed from the well and its sensor cleaned. The next ' step was to place the interface probe at the bottom of the well, inside a capped length of polyvinyl chloride (PVC)pipe. Once the PVC and interface probe reached the bottom of the well,the cap was removed and the bottom of the oil water interface was measured by 1 raising the interface probe until it detected the groundwater/SPO transition. The SPO thickness in the well was then calculated. The SPO column in the wells ranged in thickness from 0.10 foot in MW-3 to 9.5 feet in MW-18 during the second quarter 2013 event. Leidos proposes performing this more accurate method of SPO gauging on an annual basis. This frequency is recommended as site conditions are stable, and more frequent measurements are not warranted. Based on the new measurements, dedicated `stingers' were installed in these wells to minimize the amount of groundwater extracted below the SPO layer. Approximately 72 gallons of SPO were removed from wells MW-1,MW-3,MW-5, MW-6, MW-15, 3. 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." 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.