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. 1.0 PROJECT BACKGROUND <br /> This <br /> sampling re ort resents the results of groundwaterconducted in December,2002 at the County of San <br /> P P <br /> Joaquin Human Services Agency building located at 145 South Sutter Street,Stockton,California Monitor <br /> well locations are presented Figure 1-1 The following section presents a summary of previous investigations <br /> Appendix A presents historical groundwater analytical results <br /> In <br /> April 1988,WESTON supervised the removal of rime underground storage tanks{USTs}from a former <br /> gasoline station located on the northwest corner 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 I)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 wells Subsequent quarterly groundwater <br />' monitoring results indicated that the highest concentrations of hydrocarbons were present in down gradient <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 These wells were replaced with deeper wells(MW-2A and MW-3A)in 1995 during the <br />' Phase III investigation Soil samples were collected from the boreholes of the new monitor wells During <br /> the installation of monitor well MW-2A free product was observed in soil and groundwater Petroleum <br /> hydrocarbons were not detected in soil or groundwater samples collected from monitor well MW-3A <br /> 1 <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 up gradient groundwater analytical data As part of the planning <br /> 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 />' contamination is present in the vicinity of MW-2A and that groundwater contamination is not present south <br /> L%PR01FCJ'SISANJ0Q\H5Al2Q04RPr WPD 1 <br />