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'I I 6.0 FIELD INVESTIGATIONS 6.1 Site Description The subject site is located on West Hammer Lane in Stockton, California (Figure 1). The site is currently operating as a retail gasoline station and mini market. Approximate locations of the existing onsite gasoline USTs and other pertinent site features are shown on Figure 2. 6.2 Soil Borings ATC retained the services of Environmental Probing (EnProbe), Oroville, California for 1 advancing the boreholes. The field investigation was performed on July 9, 2000. Underground Services Alert (USA) was notified of the proposed drilling activities to ensure that no utility lines were located within the immediate vicinity of the soil borings, and Cruz Brothers Sub-Surface Locators, Inc. of Milpitas, California provided a subsurface survey of utility lines and other buried objects in and around the borehole locations. All soil borings were advanced to a total depth of between approximately 27 feet to 32 feet bgs. Groundwater was encountered at depths ranging from approximately 10 to 17 feet bgs in the upper aquifer and 24 to 29 feet in the lower aquifer. The soil borings locations are shown on Figure 2. Each soil boring was terminated at a depth sufficient to collect a groundwater sample. All soil borings were backfilled to the surface with neat cement slurry after sampling was completed. Backfilling was completed under the supervision of San Joaquin County Public Health Services Inspector. An ATC geologist logged the soil in the field in accordance with Unified Soil Classification System (USCS), under the supervision of a California Registered ' Geologist. Boring logs are included in Appendix B. Copies of the approved San Joaquin County Public Health Services Application for Well/Pump Permits are included in Appendix C. A copy ' of the approved Site Access Agreement from Taco Bell Property Owner is included as Appendix D. 5.3 Soil Sampling Soil cores were obtained by pushing a GeoprobeTM sampler with 4-foot long acrylic liners into the subsurface. The borings were cored continuously. Upon retrieval of the 4-foot long acrylic liner from the borehole, the sample was screened using a photoionization detector(PID). Based on the PID readings, a section of the liner was cut out at the selected sampling depth for submittal to the j:w prV= KSTX)MQs 132(0003)%KEP0K SV000L4ddDrfl0M.doe 10 ATC Associates Inc.