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v Introduction This report presents the results of the subsurface contamination investigation requested by the San Joaquin County Public Health Services Environmental Health Division for the site as discussed in the Wright workplan dated September 16, 1996. The site had an underground storage tank removed in November of 1995. The last use of the tank is not known, but it had apparently been used for gasoline storage. The tank was estimated to be approximately of 500 gallon capacity, and was observed to have several small holes in the bottom. Soil samples analyses from the former tank pit bottom revealed low levels of degraded petroleum compounds. Analyses of water samples collected from the tank pit and soil samples collected from the side walls revealed no detectable concentration levels of petroleum hydrocarbons (see Wright report dated June 21, 1996) PHS-EHD specifically requested this investigation to collect additional data on the lateral extent of the soil contamination noted at six feet below ground surface (bgs). PHS-EHD indicated it will use the data presented herein to ascertain a potential threat to the aquatic ecosystem and users of nearby surface waters. Field Activities and Methods - Exploratory Sal Borings Five exploratory borings were drilled at the locations shown on Figure 3. Drilling and well installation permits were secured from the PHS-EHD prior to doing the field work. Boreholes were drilled with van 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 drive. The sampler retrieved and dissembled, and the soil samples retained for chemical analysis were cut from the soil filled acetate liner, sealed with Teflon® paper and plastic endcaps, labeled, logged onto chain-of-custody forms and placed in a chilled ice chest. The boreholes were lithologically 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. Upon completion of the borehole drilling 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. Ground Water Sampling Each exploratory boring was sampled. The ground water samples collected from the boreholes were used for a rapid reconnaissance of the site groundwater contamination. The temporary wells were sampled using the Wright Geoscience Sampling Protocol, a brief summary of which follows: • Each borehole was advanced about 4-feet into the aquifer. • Temporary well was installed in four locations (B1, B2, B3 and 64) by pushing 10-feet of 0.20-inch slotted 1-inch diameter schedule 40 PVC casing to the bottom of each boring. • Depth of static groundwater levels in boreholes was measured to the nearest one- one hundredth of one foot from the existing grade. • The water entering the borehole was sampled using a clean bailer, and carefully poured into the appropriate container with minimum cavitation. • Depth to groundwater measurements were made to the nearest one-one hundredth of one foot, and also checked for the presence of separate phase product • Each water sample was labeled, logged onto a chain-of-custody form, and placed in a chilled ice chest. Naornie King Trust Project No. 4131 Page 3