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Mr.M. Scott Mansholt—CEMC Second Quarter 2006 Groundwater Monitoring and Sampling Report July 11,2006 US Can-Welty Road Page 3 of 5 Since 2005, a sheen has been observed in well MWA, and a petroleum odor or sheen has been observed in MW-2. TPH as diesel-range organics(TPHd)have been detected in wells MW-3 and WFSMW-1 at concentrations of up to 6,700 and 240 micrograms per liter(gg/L),respectively. No dissolved-phase TPH as gasoline-range organics(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 PAHs have occasionally been detected in groundwater from MW-2,MW-3,MW-5, and WFSMW-1. GROUNDWATER MONITORING AND SAMPLING MONITORING On May 3 and 4,2006, depth to water(DTW)was measured in wells MW-3 through MW-5 and WFSMW-1 using a hydrocarbon/water interface probe. DTW in these wells ranged from 33.14 feet below top of casing(btoc)in MW-5 to 36.76 feet btoc in WFSMW-1. The approximate groundwater flow direction beneath the site is to the east at a calculated gradient of approximately 0.001 ft/ft. Cumulative DTW 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 in Attachment A. SAMPLING Following DTW measurements,groundwater samples were collected from wells WFSMW-1 (duplicate sample also collected) on May 3,2006 and from MW-5 on May 4,2006. Wells WFSMW-1 and MW-5 were purged of approximately three casing volumes using 2-inch disposable polyethylene bailers. Wells MW-3 and MW-4 were purged dry using a low-flow submersible pump and were not sampled due to insufficient groundwater recovery for sample collection in the wells. During purging activities,pH, specific conductance, dissolved oxygen, turbidity,and temperature water-quality parameters were recorded. After water-quality parameters stabilized(i.e., a minimum of three consecutive readings with values within 10 percent for each parameter), groundwater samples were collected using 2-inch disposable polyethylene bailers. 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 State-certified laboratory (ELAP#2116). No samples were collected from wells MW-1 and MW-2 due to the presence of SPO in these wells and the presence of petroleum-absorbing oleophilic socks. Field data sheets are included as Attachment A. GROUNDWATER ANALYTICAL RESULTS The groundwater samples from WFSMW-1 and MW-5 were analyzed for the following: • TPHd: C,o—C25,using U.S. Environmental Protection Agency(EPA)Method 8015M and TPHd with silica-gel preparation for samples with detectable concentrations of TPHd using EPA Method 8015M; • TPHg: C6—C,0,using EPA Method 8015M; • BTEX using EPA Method 802113; and • PAHs using EPA Method 8270C SIM.