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Mr.M. Scott Mansholt—CEMC First Quarter 2006 Groundwater Monitoring and Sampling Report April 18,2006 US Can-Welty Road Page 3 of 5 GROUNDWATER MONITORING AND SAMPLING MONITORING On February 14, 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 32.67 feet below top of casing(btoc)in MW-5 to 36.20 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 MW-3,MW-5, and WFSMW-1 on February 14,2006. Well MW-4 was purged dry using a low-flow submersible pump and was not sampled because there was insufficient groundwater recovery in the well for sample collection. Well MW-3 was purged of only one well casing volume of water because of slow recharge in the well. Well WFSMW-1 was purged of approximately four casing volumes. Well MW-5 was redeveloped and was purged of approximately 25 gallons or 12 casing volumes. The wells were purged using a low-flow submersible pump. In these wells,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. The TPHd with silica gel-cleanup result for the sample collected from MW-3 on February 14, 2006(22,000 gg/L)appeared anomalous and significantly higher than the TPHd result(1,500 gg/L). The laboratory noted that the normal reporting limit(50 gg/L) could not be obtained for the TPHd analysis with silica-gel cleanup because of sample matrix interference observed during extraction. The surrogate quality control did not meet quality control requirements for the TPHd with silica gel-cleanup analysis. PAH concentrations detected in the sample collected on February 14,2006 from MW-3 were four to eight times greater than historical results. Because of potential matrix effects due to sediments in the samples collected on February 14,2006, and the anomalous TPHd with silica gel-cleanup result,MW-3 was re-sampled on March 30,2006. No samples were collected from 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 Groundwater samples were collected on February 14 and March 30,2006. All samples were collected using a low-flow submersible pump using new polyethylene tubing through which groundwater was extracted. As discussed in the above paragraph,MW-3 was re-sampled on March 30,2006 and the samples where analyzed for TPHd and PAHs. 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). The samples were analyzed for the following: • TPHd: CIO—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—Clo,using EPA Method 8015M;