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w N"we 2.0 EXPLORATORY DRILLING AND SOIL SAMPLING _ 2.1 Preliminary Activities A soil boring permit was obtained from the SJCPHS and a borehole grouting inspection was scheduled through Spectrum Exploration, the drilling contractor. A copy of the San Joaquin County boring permit is provided as Appendix B. Due to the limited scope of this investigation, the safety plan requirements of the OSHA Hazardous Waste Operations Standard (29 CFR 1910.120) were satisfied by the preparation of a record of the site safety meeting held prior to commencement of fieldwork. All employees of RES and drilling contractor personnel have received the training and certification to meet the 40-hour initial and on-the-job proficiency level required by the Standard. _ 2.2 Soil Boring and Sampling On 28 September 1994, the subsurface soil investigation was conducted by RES under the direction of Christopher B. White, RG. Four (4) exploratory boreholes were advanced through the UST backfill material and into native soils surrounding the abandoned UST pit. One borehole was advanced through the center of the abandoned UST pit and three boreholes were advanced along the perimeter of the pit. A single borehole was advanced at the northeastern corner of the abandoned UST pit instead of the two proposed in the investigation work plan. The borehole proposed for the northern edge of the pit was relocated to the northeastern corner to remain well clear of the underground sewer and water pipelines (because their exact locations were not known) and the second borehole in this area was deemed unnecessary. The locations of exploratory boreholes Bl through B4 are shown on Figure 2. Drilling was accomplished using a CME-75 truck mounted drill rig operated by Spectrum Exploration of Stockton, California. The drill rig was equipped with 8-inch diameter hollow- stem augers. Auger flights were steam cleaned prior to the start of drilling and separate auger _ Rights were used for each borehole to reduce the possibility of cross-contamination. The native soils encountered at the site consisted primarily of silts and silty sands. Sandy gravel _ backfill material was encountered within the abandoned UST pit. Soils containing hydrocarbon odors or staining were not encountered during the drilling investigation. All boreholes were advanced to a depth of 20 feet below grade. The concrete tie-down slab was encountered from a depth of 14 to 15.5 feet below grade in borehole B3. Boring logs describing the soils encountered in each borehole are provided in Appendix C. Samples of the native soils were obtained from the boreholes using a hammer driven, 18-inch long, split barrel sampler fitted with three 2-inch diameter by 6-inch long brass tubes. Samples were retrieved from three intervals from each borehole (10 to 11.5 feet, 15 to 16.5 feet, and 20 to 21.5 feet below grade) except borehole B3, where samples were obtained below the concrete tie-down slab at intervals of 16 to 17.5 and 20 to 21.5 feet below grade. The soil sampling intervals are shown on the boring logs. _ 4185\CBW4\SPRINr.RP7\70CT94 3 .r