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Groundwater Monitoring Well Installation and Ozone Microsparge System Installation and Startup Report— ConocoPhillips(76)Service Station No. 11195,Lathrop,California May 20,2003 6.0 RESULTS 6.1 Subsurface Conditions. Soil encountered during drilling consisted primarily of silty sand, poorly to well graded sand, and silt. In well borings MW-19 and MW-20, silty sand was encountered from approximately 0.5 feet bgs to depths ranging from approximately 8 to 13 feet bgs. Underlying the silty sand is poorly graded sand to approximately 15 feet bgs, followed by silty sand to the total depth of the borings (20 feet bgs). In boring MW-18, silty sand with gravel was observed from approximately 0.5 to 13 feet bgs, underlain by clay to approximately 17 feet bgs and silt to the total depth of the boring. In boring MW-21, silty sand with gravel and poorly graded sand with silt was observed from approximately 0.5 to 9 feet bgs, underlain by poorly graded sand and well graded sand to the total explored depth of the boring (20 feet bgs). Detailed descriptions of the soil encountered during this investigation can be found in the boring logs in Appendix B. Groundwater was encountered in the well borings during drilling at approximately 15 feet bgs. Groundwater subsequently stabilized in each boring between approximately 9 and 10 feet bgs. 6.2 Soil Analytical Results I Soil samples analyzed were reported as not detectable for concentrations of the hydrocarbon constituents analyzed, except for soil sample MW-19-S(10), which contained a concentration of MtBE at 0.0067 ppm. The stockpile soil sample, Comp-1 (A,B,C,D), contained a concentration of lead that was acceptable for disposal at Allied Waste's Forward Landfill. The analytical results from the soil samples are summarized in Table 3. Laboratory analytical reports are included in Appendix E. 6.3 Groundwater Analytical Results Groundwater samples collected from MW-19 contained 60 ppb of TPHg reported by the laboratory as in the gasoline range but not matching the laboratory standard for gasoline, and 200 ppb of MtBE- Groundwater samples collected from MW-18, MW-20 and MW- 21 did not contain detectable concentrations of hydrocarbon constituents analyzed. Groundwater chemical analytical data are summarized in Tables 1 and 2. 6.4 Waste DisDosal On, January 8, 2003, Tim Manley Trucking, of Sacramento, California, removed approximately 8.56 tons of soil cuttings from the site and transported it to Allied Waste's Forward Landfill in Manteca, California. The soil cuttings were accepted at the landfill under approval number 2819. A copy of the landfill waste acceptance letter is included in Appendix D. 1 140193.14-2 8