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• Additional excavation of the former tank pit was performed to remove contaminated soil and groundwater (see report dated October 10, 1999) This work removed some of the residual contanunants in and around the capillary fringe area Well MW-1 was destroyed during this work since it had been placed within the excavation area A calculated estimate of residual contaminants suggests that only limited concentrations remained following this excavation work Subsurface Site Assessment Hydrogeologic Summary A total of fourteen exploratory borings and four groundwater-monitoring wells were drilled and installed Drilling permits were secured from and all work was performed under the review of the PHS EHD (see attached exploratory boring logs and monitoring well details) Silty clay underlies the backfill to a depth of 14-feet, which was stained gray and displayed petroleum vapor and odor in the immediate former tank pit area This strata as underlain by a clayey sand to sand to a depth of about 21-feet The staining and vapors decreased with depth, with none observed by 19-feet Sand and silty sand strata underlie the clayey sand below about 19 feet Thin clay interbeds occurred in the silty sand at depths of 31- to 32-feet (see Figures 1, 2 and 3) Regional lithologic lateral and vertical variation are present in the shallow aquifer strata, which are typical for river and floodplain deposits in this portion of the San Joaquin Valley (see Geologic . Cross Section, Figure 3) While lateral and vertical variation are present in the aquifer strata, these strata as a whole form the uppermost water bearing aquifer and discontinuous confining beds forming the hydrostratigraphy to depths of about 10- to 30-feet in the area explored Groundwater occurred at depths of about 11- to 15-feet (depending upon the date drilled) Groundwater rose in the encased boreholes to a depth of 9 3 5 feet, suggesting that these shallow aquifer strata may vary from unconfined to weakly confined Historic groundwater data shows a consistent flow to the north-northeast (see Table 3 and Figure 3) Wright has forwarded all the historic groundwater flow data and maps to the PHS-EHD in both measurement and plotted format in quarterly reports Groundwater flow lines and flow nets may change azimuth directions with changing water levels, and aquifer recharge and discharge One groundwater flow line trend (ME) represents the most historically consistent observed site flow direction (see Figure 2 and Tables 1, 2, and 3) I Page 2 1