SITE INFORMATION AND CORRESPONDENCE

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Mr.M. Scott Mansholt—CEMC First Semi-Annual 2007 Groundwater Monitoring and Sampling Report October 29,2007 Vernalis Pump Station Page 3 of 5 • Approximate Groundwater Flow Direction/Gradient: East at 0.002 feet per foot (ft/ft). Data from both the site and the adjacent US Can—Welty Road site were used in calculating the groundwater flow gradient. Wells that were found to contain SPO were not used in the groundwater flow-gradient calculations. SAMPLING Wells MW-6 and MW-7 were purged using the regulatory-accepted, low-flow minimal drawdown method following depth-to-groundwater measurements. Well MW-5 was purged using the three well casing-volume purge method due to a slow recharge rate. A low-flow submersible pump with dedicated polyethylene tubing was used. Measurements of pH, specific conductance,temperature, oxygen-reduction potential,turbidity, and dissolved oxygen water- quality parameters were recorded during the purge process. Groundwater samples were collected at wells MW-6 and MW-7 after water-quality parameters stabilized. Stabilization criteria are presented on field data sheets (Attachment A). Groundwater samples were collected at well MW-5 following the three well casing-volume purge and after the groundwater recharged to 80 percent of the static depth-to-groundwater level. Well MW-1 was not sampled due to the presence of SPO and wells MW-2,MW-3, and MW-4 were not sampled due to insufficient groundwater recovery for sample collection. Laboratory-provided bottles were used to preserve the samples. The bottles were labeled, sealed, and placed immediately into an ice-cooled container for delivery to Lancaster Laboratories, Inc. (Lancaster),under SAIC chain-of-custody protocol. Lancaster is a California-certified laboratory (ELAP#2116). GROUNDWATER ANALYTICAL RESULTS The groundwater samples from wells MW-5,MW-6, and MW-7 were analyzed for the following constituents: • 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 801513; and • Polynuclear aromatic hydrocarbons(PAHs)using EPA Method 8270C with selective ion monitoring. 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 (TPHd)and Table 3 (PAHs).2 Results exceeding the most conservative ESL or WQO are highlighted in bold-type font. TPHd were non-detect below the laboratory method detection limit of<50 micrograms per liter(µg/L) in all the samples, and PAHs were not detected at concentrations exceeding the most conservative WQOs/ESLs. The data usability summary with details regarding data qualifiers and a copy of the laboratory analytical report are presented as Attachment B. Well construction details are provided in Table 4. A petroleum distribution map is presented on Figure 5. 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."