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The boreholes were drilled with truck mounted direct push drilling equipment All drilling equipment and sampling tools were cleaned prior to arriving, between driving samples and before leaving the site The augers were advanced to the desired sampling depth interval, and a drive split spoon sampler were driven ahead of the drill bit The sampler was then retrieved and dissembled, and the soil filled brass or acetate liners retained for chemical analysis, were sealed with Teflon® paper and plastic end caps, labeled, logged onto chain- of-custody forms and place in a chilled ice chest on crushed ace Drill cuttings were drummed and left on-site The boreholes were logged using the Unified Soil Classification System under the supervision of a registered geologist Additional lithologic information was collected to describe the subsurface geology Soil samples were field screened for presence of contaminants by checking for presence of odor and staining, and a photoionization meter was _used for reconnaissance soil field vapor measurement use Soil samples were ; collected at minimum five-foot intervals, with additional samples collected at intervals of obvious contamination and at stratigraphic features of interest using field discretion In addition, Boreholes PB-15, PB-16, PB-17, and PB-1 S were continuously cored Upon completion of the borehole dulling and collection of information, ail boreholes were backfilled with cement grout, placed from the bottom to top of the borehole by tremae line •+ Field Modifications of Work plan The PHS-EHD representative and field geologist discussed the sampling as the borehole drilling, sampling and borehole sealing progressed on April 25, 2000 Field observations during drilling indicated that contaminants were not widespread at the originally selected MW-9 and MW-3 locations, hence a modification to the fieldwork and sampling was approved by PHS-EHD in the field The modifications included the following, advancing five boreholes near the originally selected locations, returning to the site at a later date to mark utilities for borehole drilling and to search for additional possible contaminant sources both at the original tank pit and elsewhere. and a discussion with PHS-EHD regarding a review of previous work and the revision of the work plan prior to returning to the field to continue assessment Wright met with the PHS-EHD representative in late April, 2000 and discussed the amended approach to additional plume definition • Conducting a surface geophysical survey with ground penetration radar to search for anomalous indications of possible contaminant sources (discussed above) • Performing utility location with the City of Tracy and Westside irrigation line owner to locate lines so that borings can be advanced to collect more lateral and vertical assessment data near MW-9 • Inspecting the welding building for indications of potential contaminant sources (such as oil/water separators and sand traps) None were observed • Advancing exploratory borings through the former tank pit and east and south of MW- 9 for additional vertical and lateral subsurface assessment in those areas (see Figure 1) I Page 4