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t <br /> . 1.0 PROJECT BACKGROUND <br /> This report resents the results of groundwater sampling conducted in October 2003 at the Count of San <br /> P �' p g y <br /> I Joaquin Human Services Agency building located at 145 South Sutter Street,Stockton,California Monitoring <br /> fi well locations are presented on Figure 1-1 The following section presents a summary of previous <br /> investigations Appendix A presents historical groundwater analytical results <br /> In April 1 <br /> p 988,WESTON supervised the removal of nine underground storage tanks{USTs}from a former <br /> gasoline station located on the northwest comer of Washington and Sutter Streets Petroleum hydrocarbons <br /> were detected in soil samples collected from beneath the tanks Following the excavation of an additional <br /> 2,000 cubic yards of contaminated soil, the pit was backfilled with clean soil <br /> An initial soil and groundwater investigation(Phase 1)was performed at the site by WESTON in December <br /> 1988 Dissolved hydrocarbons were detected in two of three monitor wells installed during this investigation <br /> (MW-2 and MW-3) The highest concentrations of petroleum hydrocarbons were detected in monitor well <br /> MW-2 <br /> A Phase II groundwater investigation was completed in August 1991 which consisted of the installation of <br />[ five additional monitor wells(MW-4 through MW-8),aquifer testing,and a tidal influence study During this <br /> investigation,hydrocarbons were detected in all five new monitor welts Subsequent quarterly groundwater <br /> monitoring results indicated that the highest concentrations of hydrocarbons were present in downgradient <br /> 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 in the regional <br /> groundwater table An additional deeper well (MW-2A) was installed in 1995, during the Phase III <br /> investigation MW-3 was abandoned during this investigation Soil samples were collected from the boreholes <br /> of the new monitor wells During the installation of monitor well MW-2A,free product was observed in soil <br /> and groundwater Petroleum hydrocarbons were not detected in soil or groundwater samples collected from <br /> monitor well MW-3A <br /> A Phase IV investigation was conducted in August 1996 to collect additional soil contaminant concentration <br /> data in the vicinity of MW-2A and to collect upgradient groundwater analytical data As part of the planning <br /> I of the Phase IV investigation,San Joaquin County Capitol Projects and the San Joaquin County Public Health <br /> Services Environmental Health Division(EHD)agreed that one year of quarterly groundwater monitoring <br /> would be performed according to the schedule presented in Table 1-1 It was also agreed that a corrective <br /> action plan (CAP) would be prepared following the completion of one year of quarterly groundwater <br /> monitoring (Roy F Weston, Work Plan for Phase IV Site Investigation and Quarterly Groundwater <br /> Sampling, February 1996) The Phase IV investigation of groundwater sampling confirmed that soil <br /> ITR O]ECfSISA1110Q1HSAll Q01RPT WPD 1 <br /> I <br />