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Soil and Groundwater Investigation Report and Second Quarter 2005 Monitoring and Sampling,US Can-Welty Road October 2005 10. GROUNDWATER MONITORING AND SAMPLING 10.1 HISTORICAL MONITORING AND SAMPLING DATA Historically,the site wells were monitored and sampled only occasionally during from October 1996 to August 2003. Depth to groundwater in the wells has ranged from 30.12 feet below the top of casing (btoc)in MW-2 in June 1999 to 34.81 feet btoc in MW-4 in May 2002. The approximate groundwater flow direction beneath the site varies from northeast to east. The site wells were sampled for TPHg, TPHd, TPH quantified as motor oil(TPHmo),BTEX,MTBE, PAHs, TCE, and cis-1,2-dichloroethene (cis-1,2-DCE). Petroleum constituents were never detected in wells MW-4 and WFSMW-1. No petroleum constituents, except TPHd,were ever detected in MW-3. TPHg and TPHd concentrations have been detected in wells MW-1 and MW-2. Furthermore,residual petroleum sheen had been noted in well MW-2 along with concentrations of TPHmo,BTEX, and PAHs. Historical soil and groundwater analytical results are presented in Appendix B. 10.2 MONITORING On April 21,2005, site wells MW-1 through MW-4 and off-site wells WFSMW-1 and MW-5 were monitored for depth to water(DTW)using a hydrocarbon/water interface probe. DTW ranged between 32.94 feet btoc in MW-5 and 36.60 feet btoc in MW-4. The approximate groundwater flow direction beneath the site is towards the northeast at a calculated gradient of 0.0008 feet/foot(ft/ft),consistent with historical flow directions and gradients. Separate-phase oil or hydrocarbon sheen was observed in MW-1 and MW-2. Wells MW-3 and MW-4 contained only limited quantities of water and were not sampled. A summary of DTW measurements and groundwater elevations is presented in Table 6. A potentiometric map showing groundwater elevation contours and flow direction across the site is presented on Figure 7. 10.3 SAMPLING Following DTW measurements,wells WFSMW-1 and MW-5 were purged of four casing volumes of groundwater using a 2 inch-diameter disposable polyethylene bailer. During the purge process pH, specific conductance, 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 into laboratory-provided bottle ware. The bottles were labeled, sealed, and placed immediately into an ice-cooled chest for delivery to under SAIC chain- of-custody protocol. Groundwater samples collected from wells WFSMW-1 and MW-5 were analyzed for the following: • TPHg: C6-C12 using N. CA LUFT Gasoline Method, • TPHd: C10-C25 using CALUFT-DRO/EPA Method 8015B Modified, • BTEX using EPA Method 8260B, and • PAHs using EPA Method 8270C SIM. TPHd were detected in sample WFSMW-1 at 71 (gg/L),phenanthrene was detected at 0.011 (gg/L), and naphthalene was detected at 0.025 (gg/L). Only naphthalene was detected at 0.012 (µg/L), in a sample from MW-5. Other petroleum constituents were not detected in any of the samples collected during the April 21,2005 quarterly monitoring and sampling event. Groundwater elevation data are presented in Table 6; analytical results are summarized in Table 7 and Table 8. A potentiometric elevation map is presented as Figure 7 and second quarter 2005 groundwater concentration map is presented as Figure 8. Copies of the laboratory analytical reports are included in Appendix F. Field data sheets are included in Appendix H. 8 From Science to Solutions-