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Mr.M. Scott Mansholt—CEMC Fourth Quarter 2006 Groundwater Monitoring and Sampling Report and Annual Summary Report January 12,2007 US Can-Welty Road Page 5 of 8 GROUNDWATER MONITORING AND SAMPLING MONITORING On November 8, 2006, depth to groundwater was measured in wells MW-1 through MW-5 and WFSMW-I using a hydrocarbon/water interface probe. Depth to groundwater in these wells ranged from 31.08 feet below top of casing(btoc)in MW-5 to 35.70 feet btoc in MW-4. The approximate groundwater flow direction beneath the site is to the east at a calculated gradient of approximately 0.001 ft/ft. Cumulative depth-to-groundwater measurements, groundwater elevations, and product thickness are presented in Table 1. A map showing the potentiometric surface is presented on Figure 3. Field data sheets are included as Attachment A. SAMPLING On November 8, 2006, following depth-to-groundwater measurements,wells MW-5 and WFSMW-I were purged using the regulatory-approved, low-flow minimal drawdown method. A low-flow submersible pump with dedicated polyethylene tubing was used. During the purge process,pH, specific conductance,temperature, oxygen-reduction potential,turbidity, and dissolved oxygen water-quality parameters were recorded. After water-quality parameters stabilized(stabilization criteria is presented on field data sheets), groundwater samples were collected. Well MW-3 was sampled using the three-volume purge method because the drawdown requirements using the low-flow minimal drawdown method could not be sustained. Three well casing volumes were purged from MW-3 prior to sample collection. Well MW-4 was not sampled due to insufficient groundwater recovery for sample collection in this well. Laboratory-provided bottles were used to preserve the samples. The bottles were labeled, sealed, and placed immediately into an ice-cooled chest for delivery to Lancaster Laboratories,Inc. (Lancaster)under SAIC chain-of-custody protocol. Lancaster is a California-certified laboratory (ELAP#2116). Samples were not collected from wells MW-I and MW-2 due to the presence of SPO in these wells. Field data sheets are included as Attachment A. GROUNDWATER ANALYTICAL RESULTS The groundwater samples from MW-3,MW-5, and WFSMW-1 were analyzed for the following constituents: • 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; • TPHg(C6—C12)using EPA Method 801513; • BTEX using EPA Method 8021B; and • PAHs using EPA Method 8270C selected ion monitoring(SIM). In Tables 2 and 3,the groundwater analytical results are summarized and compared with the RWQCB Region 2 Environmental Screening Levels(ESLs)12 and the numerical State WQOs; 12. 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."