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Mr.M. Scott Mansholt—CEMC Annual 2009 Groundwater Monitoring and Sampling Report April 3,2009 US Can-Welty Road Page 4 of 5 GROUNDWATER ANALYTICAL RESULTS The groundwater samples from MW-3 were analyzed for the following constituents of potential concern: • Total petroleum hydrocarbons quantified as diesel (TPHd; Clo—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 8015B; and • Polynuclear aromatic hydrocarbons (PAHs)using EPA Method 8270C with large- volume injection. Tables 2 and 3 summarize the groundwater analytical results, and compare them with the RWQCB Region 2 Environmental Screening Levels (ESLs) and the numerical State Water Quality Objectives (WQOs)3. Results exceeding the most conservative ESL or WQO are highlighted in bold in the tables. Analyte detection limits were elevated for the PAHs due to matrix interference. The groundwater sample from MW-3 had a TPHd detection of 3,000 micrograms per liter(gg/L), with a detection of 1,800 gg/L after silica-gel cleanup, and a chrysene detection of 0.97 µg/L. A duplicate sample from MW-3 also reported the following PAHs exceeding their respective screening levels: benzo(a)anthracene at 0.038 gg/L, chrysene at 1.0 µg/L, and pyrene at 2.3 gg/L. A petroleum-hydrocarbon distribution map is shown on Figure 4. The laboratory analytical report and data usability summary, as well as details regarding data qualifiers, are provided as Attachment C. QUARTERLY OIL-ABSORBENT (OLEOPHILIC) SOCK REPLACEMENT Oleophilic socks were installed in MW-1 (due to the presence of SPO) and MW-2 (due to petroleum odor) in 2005. The socks were monitored and replaced as necessary on a quarterly basis until August 2007, when monitoring and replacement was reduced from a quarterly basis to an annual event with the concurrence of the RWQCB. The oleophilic sock in MW-1 was replaced during the February 2009 event. The weight of the removed sock was 8 ounces, and a calculated volume of 0.06 gallon of SPO was removed from MW-1. The sock in MW-2 exhibited no staining from SPO, so it was not changed. A total of approximately 0.51 gallon of SPO has been removed since June 1999 from MW-1 and MW-2. SPO has not been detected in the other site wells. A summary of SPO thickness measurements is included in Table 1. 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."