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1 <br /> during the total petroleum hydrocarbon testing may be inflated due to naturally occurring <br /> hydrocarbon matter in the soil. <br /> Groundwater, although not tested as part of this investigation, is examined on a quarterly <br /> basis at the site Analytical results obtained from wells MW-1 and MW-2 (located <br /> downgradient from the abandoned tanks) have revealed no detectable petroleum hydrocarbon <br /> concentrations for five consecutive quarterly events <br /> 5.0 Summary/Recommendations <br /> A review of soil data collected to date appears to indicate that while residual petroleum <br /> hydrocarbon concentrations are present at the site, the concentrations which are potentially <br /> leachable are very low. The potential for migration of the residual diesel fuel is additionally <br /> limited since the building which overlies the abandoned tanks impedes the infiltration of <br /> surface water/precipitation and a confining clay/silt layer existings in between the impacted <br /> soils and groundwater Based on the lack of volatile hydrocarbon concentrations and the <br /> decrease in detectable diesel concentrations encountered near the 500 gallon tank, it appears <br /> that the released diesel may be degrading with time A review of groundwater analytical data <br /> collected from downgradient monitoring wells MW-1 and MW-2 appears to indicate a lack of <br /> diesel migration from the soil to groundwater <br /> As discussed in a meeting between IT Corporation, Pacific Bell and San Joaquin County <br /> representatives on July 22, 1994, spatial and technological limitations preclude any removal or <br /> further investigation of the diesel impacted soils surrounding the abandoned basement tanks <br /> As the remaining diesel concentrations appear to be naturally degrading, it was agreed that <br /> quarterly groundwater monitoring only would be continued at this time to identify migration <br /> (if any) of the diesel fuel from soil to groundwater Following the July 22, 1994 meeting, the <br /> quarterly monitoring program was extended to include four additional sampling events Upon <br /> the completion of these events (7/94, 10194, 1/95, 4/95) the necessity of any further actions at <br /> the site will be evaluated. <br /> MZ/09-06-94/UST/940138 mer 9 <br />