Laserfiche WebLink
1 , <br /> 1.0 PROJECT BACKGROUND <br /> This report presents the results of groundwater sampling conducted in March 2005 at the County of San <br /> Joaquin Human Services Agency building located at 145 South Sutter Street,Stockton,California Monitoring <br /> well locations are presented in Figure 1-1 The following section presents a summary of previous <br /> investigations Appendix A presents historical groundwater analytical results <br /> In Apnl 1988,Weston Solutions,Inc (WESTON)supervised the removal ofnme underground storage tanks <br /> (USTs)from 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 Following the <br /> excavation of an additional 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 monitoring wells installed during this <br /> ' investigation(MW-2 and MW-3) The highest concentrations ofpetroleum hydrocarbons were detected in <br /> monitoring well MW-2 <br /> ' A Phase H groundwater investigation was completed m August 1991,and consisted of the installation of five <br /> additional monitoring wells(MW-4 through MW-8),aquifer testing,and a tidal influence study Dunng this <br /> investigation,hydrocarbons were detected mall five new monitoring wells Subsequent quarterly groundwater <br />' monitoring results indicated that the highest concentrations of hydrocarbons were present in downgradient <br /> monitoring wells MW-7 and MW-8 <br /> Following the Phase H investigation,monitoring wells MW-2 and MW-3 went dry due to a drop in the regional <br /> groundwater table Additional deeper wells(MW-2A and MW-3A)were installed in 1995,during the Phase <br /> INN investigation MW-3 was abandoned during this investigation Soil samples were collected from the <br />' boreholes of the new monitoring wells During the installation of monitoring well MW-2A,free product was <br /> observed m soil and groundwater Petroleum hydrocarbons were not detected in soil or groundwater samples <br /> collected from monitoring 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 />' of the Phase IV investigation,San Joaquin County Capital 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(Ray F Weston, Inc,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 /> (upgradient)of the former USTs The fourth quarter of Phase IV groundwater sampling was completed in <br /> May 1997 The CAP was submitted to EHD in January 1998 <br />' Quarterly groundwater sampling has been conducted since 1996 This report is the First Quarter 2005 <br /> Groundwater Monitoring Report, which represents the first report in the current fiscal year groundwater <br /> sampling effort and presents the results of continued groundwater sampling following the schedule presented <br /> in Table 1-1 <br /> 1 <br />