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• Summary of Site Hydrogeologic Assessment Work Five GeoProbe borings and one groundwater monitoring well have been drilled and/or installed at the site Dnlling 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 and References, see the April and November, 2000 reports) The site stratigraphy showed a silty clay to a depth of about b feet This clay was underlain by sand and interbedded sand and clayey silt to depths of about 20 feet The interbedded sand and clayey silt strata compose the aquifer Water levels observed at about 8-9 feet during drilling suggest that this is an unconfined to weakly confined aquifer A clayey sand-sandy silt-clay forms the local leaky confining strata (aquitard) which underlies the uppermost aquifer zone sandy sequence (see Figure 3) These aquitard strata display lateral lithologic variation, and were not observed to yield water in the field, although some strata were very moist Regional lithologic lateral and vertical variations are present in the shallow aquifer strata and underlying confining 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 variations are present in the aquifer strata, these strata form the uppermost waterbearing aquifer (or hydro-) stratigraphy between about 10- to 20 feet in the area explored These aquifer and underlying confining strata display some lateral lithologic variation Very low concentrations of contaminants were observed in Boring 1 and contaminants were not observed in the Iower confuting strata (see Figure 3 and Tables 3 and 4) Groundwater occurred at depths of about 8 feet (depending upon the date drilled) Groundwater rose in the uncased boreholes to a depth of 7 feet, suggesting that this shallow aquifer strata may be unconfined to weakly confined Wright secured permission to enter the Gemehos Property and More for Less Station (also known as Cheaper Gas Station) for casing elevation survey and to collect groundwater level measurements Wright had Triple `B" survey the additional well casings to a known sea-level referenced datum for coordinated groundwater level measurements at the three saes as required by and agreed with PHS-EHD for plotting groundwater gradient (see Table 5 and Figure 5) Historic groundwater data shows a consistent flow to the northeast The groundwater flow direction was to the northeast under a calculated gradient of 0 0027 (March 29, 2001 data), consistent with historically observed trends Wright has supplied all the histonc groundwater flow data to the PHS-EHD in both measurement and plotted format in either assessment or quarterly reports (see References) Groundwater flowhines may change flow directions with changing water levels, and aquifer recharge and discharge One northeastern groundwater flowline trend (about N 15E, toward Cheaper Gas) represents the most historically consistent observed site flow direction (see Figure 5 and Tables 1-3) Discussion of Contaminant Extent, Site Cleanup and Contaminant Mass Groundwater monitonng showed that the dissolved plume remained centered around Borings B-1, B-2 B-3 and monitoring well MW-1 The concentrations fluctuated but • showed an overall slow declining trend to none detected in the last well monitoring The dissolved plume did not show movement with declining contaminant concentrations Since the major source was removed the plume the observed concentrations are interpreted to be Page 3