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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 3 of 6 Since 2005, a sheen has been observed in well MW-1, and a petroleum odor or sheen has been observed in MW-2. TPH quantified as diesel(TPHd)have been detected in wells MW-3 and WFSMW-1 at concentrations of up to 6,700 micrograms per liter(µg/L) and 970 µg/L, respectively. No dissolved-phase TPH quantified as gasoline(TPHg)or benzene,toluene, ethylbenzene, and total xylenes (BTEX)have been detected in the groundwater from the site wells. TPHg and TPHd were detected in the separate-phase oil(SPO) from well MW-2 in 2005. Low levels of polynuclear aromatic hydrocarbons(PAHs)have occasionally been detected in groundwater from MW-2,MW-3,MW-5, and WFSMW-1. GROUNDWATER MONITORING AND SAMPLING MONITORING Groundwater monitoring and sampling began in 1999 and wells were monitored on an irregular basis. Quarterly groundwater monitoring and sampling began in April 2005. On January 23, 2007,depth to groundwater was measured in wells MW-1,MW-2,MW-4,MW-5, and WFSMW- 1 using a hydrocarbon/water interface probe. Depth to groundwater in these wells ranged from 32.08 feet below top of casing(btoc) in MW-5 to 35.70 feet btoc in MW-4. Calculated groundwater elevations ranged from 71.26 feet(MW-5)to 71.60 feet(MW-2) above MSL. The approximate groundwater flow direction beneath the site is to the east at a calculated gradient of approximately 0.001 feet per foot(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 January 23,2006, following depth-to-groundwater measurements,wells MW-5 and WFSMW-1 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 covered by a vehicle and not accessible during the groundwater monitoring event. 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-1 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-5 and WFSMW-1 were analyzed for the following constituents: