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Introduction This report presents the results of the reconnaissance site investigation required by the County of San Joaquin County Public Health Services Environmental Health Division (PHS-EHD) for the site as discussed in the Wright work plan dated October 3, 1995. The information contained herein is for initial site assessment and would be used in future site interim remedial cleanup as needed. The site had underground storage tanks removed and soil and groundwater contamination revealed by initial site studies by other consultants for this site (see References). The work presented herein was reviewed and approved by PHS-EHD representatives, and slightly modified in the field by a PHS-EHD representative. Background Two underground storage tanks (one 1000 gallon gasoline and one 5000 gallon aviation gasoline) were removed on May 11, 1990 by Crisp Tank Testing of Stockton, CA. The tanks were removed under approved permits of the PHS-EHD. Soil samples under the tanks revealed that contaminants were not detected under the regular gasoline tank. Soil samples collected under the aviation gasoline tank showed 610 parts per million (ppm) Total Petroleum Hydrocarbons as Gasoline (TPHG), Benzene at 6,500 parts per billion (ppb), Toluene at 62,240 ppb, Ethylbenzene at 41,450 ppb and Xylenes at 169,250 ppb. A groundwater sample from the 5000 gallon tank pit revealed TPHG was not detected, Benzene at 3.9 ppb, ,. Toluene at 18.4 ppb, Ethylbenzene at 7.5 ppb and Xylenes at 31.9 ppb. Ethylene dibromide and organic lead were not detected in the groundwater sample. Field Methods - Exploratory Soil Borings Six exploratory borings were drilled at the locations shown on Figure 1. Drilling permits were secured from the PNS-EHD prior to doing the field work. Boreholes were drilled with truck mounted GeoProbe(tm) drilling equipment. All drilling equipment and sampling tools were cleaned prior to arriving, and before leaving the site. The push tools were advanced to the desired sampling depth interval, and a continuous acetate liner was driven. The sampler was then retrieved and dissembled, and the soil samples retained for chemical analysis were cut from the soil filled acetate liner, sealed with foil and plastic endcaps, labeled, logged onto chain- of-custody forms and placed in a chilled ice chest. 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. The samples were continuously collected at intervals of obvious contamination and at stratigraphic features of interest. Depth of static groundwater levels in boreholes were measured to the nearest one-one hundredth of one foot to the existing grade. Upon completion of the borehole drilled and collection of information, the boreholes were backfilled with grout, placed from the bottom to top of the borehole under approval of the PHS-EHD. Haley Flying Services Project No. 4111 Page 3