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Subsurface Investigation and Well Installation Report ARCO Facility No 6100 Tracy, California Page 4 purpose of soil sampling were completed using the mud rotary drilling method Hollow stem augers were not used to advance any soil borings due to difficult drilling conditions and to permit wireline geophysical logging within the boreholes Electrical methods were used to conduct borehole geophysical logging Delta was unable to obtain a special use permit to conduct neutron and gamma-gamma logging in an open borehole Exploratory Soil Borings Delta oversaw Western Strata Exploration, Inc of West Sacramento (C-57 #552198) advance six onsite soil borings (B-33 through B-38) between August 29 and September 7, 2001 Soil boring locations are shown on Figure 2 The borings were advanced to depths ranging from approximately 135 to 140 feet bgs using the mud rotary drilling method Each soil boring was continuously sampled in five-foot intervals using a 3-inch diameter core barrel advanced ahead of a 5 5-mch diameter drill bit The drilling mud consisted of water and powdered bentonite On reaching total depth of each borehole, anA electnc log was performed on the boring Following removal of the logging tool, the drilling mud was removed and the borehole backfilled to surface grade with neat cement Soil recovered from the core barrel was placed into core boxes and labeled according to borehole ID and sampling interval The soil was logged onsite using the Unified Soil Classification System Geologic logs of the soil borings and a copy of the drilling permit are presented in Appendix B Soil collected from selected intervals was field screened for volatile organic compounds using a photoionization detector (PID) Soil types and PID results were used to determine sampling depths Soil samples from selected intervals were collected by dnving a pre-cleaned brass tube into the soil core The ends of each sample tube were covered with Teflon TM sheets, capped, and sealed Each sample tube was subsequently labeled, placed in a resealable plastic bag, and stored in an ice-chilled cooler Wireline Geophysical Logging Delta retained Dewey Data Down Hole Surveys of Acampo, California, to conduct open- hole geophysical logging of borings B-33 through B-38 Following removal of the drill rods from the borehole, a sonde was lowered through the drilling mud to the total depth of the borehole Logging was conducted as the sonde was pulled up the borehole at a fixed rate of speed using a winch Electrical conductivity/resistivity of the formation, spontaneous potentials, and natural gamma radiation emitted from the formation were measured Copies of the borehole geophysical logs are presented in Appendix C Electneal conductivity/resistivity measurements were collected using electrode spacings of 16 inches, 64 inches, and from focused electrode logging (lateral logging) The largest contrasts in electrical conductivity/resistivity of the formation around the borehole were observed in the lateral log measurements The Dewey Data representative indicated that lateral logging is often the most effective downhole electrical method for observing P 1ARCO\61001REPORTS16100-well install report doc