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1 <br /> IUFINfERS OESIElIEF5Cd19lTA1R$ <br /> SECTION 1 <br />' INTRODUCTION <br /> This report presents the results of the phase IV site investigation and first quarter of groundwater <br /> sampling at The County of San Joaquin Human Services Agency building located at 145 South <br /> Sutter Street, Stockton, California <br />' 1.1 PROJECT BACKGROUND <br /> In April 1988, WESTON supervised the removal of nine underground storage tanks (USTs) from <br /> a former gasoline station located on the northwest corner of Washington and Sutter Streets <br />' Petroleum hydrocarbons were detected in soil samples collected from beneath the tanks <br /> Following the excavation of an additional 2,000 cubic yards of contaminated soil, the pit was <br />' backfilled with clean soil <br /> An initial soil and groundwater investigation (Phase I) was performed at the site by WESTON <br /> in late 1988 Dissolved hydrocarbons were detected in two of three monitor wells installed <br /> during this investigation (MW-2 and MW-3) The highest concentrations of petroleum <br /> hydrocarbons were detected in monitor well MW-2 <br /> A Phase II groundwater investigation was completer) in August 1991 which consisted of the <br /> installation of five additional monitor wells (MW-4 through MW-8), aquifer testing, and a tidal <br /> influence study During this investigation, hydrocarbons were detected in all five new monitor <br /> wells Subsequent quarterly groundwater monitoring results indicated that the highest <br /> concentrations of hydrocarbons were present in downgradient monitor wells MW-7 and MW-8 <br /> Following the Phase II investigation, monitor wells MW-2 and MW-3 went dry due to a drop <br /> in the regional groundwater table These wells were abandoned and replaced with deeper wells <br /> (MW-2A and MW-3A) in 1995 during the Phase III investigation Soil samples were collected <br />' from the bore holes of the new monitor wells During the installation of monitor well MW-2A <br /> free product was observed in soil and groundwater Petroleum hydrocarbons were not detected <br /> in soil or groundwater samples collected from monitor well MW-3A <br /> A meeting was held on 12 January 1996 with Ms Mary Meays of the San Joaquin County <br />' Public Health Services Environmental Health Division (EHD) to discuss additional site activities <br /> LFaneraaulUC'1SICFiSA IS[' 1 October 096 <br />