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I <br /> Geological TeclMSInc Page 2 <br /> Additional Site Characterization Report <br /> Project No 662 2 <br /> February 20,2004 <br /> ' contamination is localized to an area beneath the former underground storage tank (UST) <br /> excavation <br /> ' Groundwater samples obtained from the boreholes reveal that the residual contamination is <br /> sourcing a submerged plume that is migrating to the location of CPT-7 A sand layer is <br /> ' present at a depth of 38 — 48 feet across the site and it appears to act as a preferential <br /> pathway for contaminant migration <br /> ' On December 12, 2003, a single, groundwater extraction well EW-1 was installed in the <br /> vicinity of the former UST excavation This well will be used to perform an aquifer <br /> pumping test GTI is in the process of developing a work plan addendum for the installation <br /> of additional monitoring wells for plume definition and for the aquifer-pumping test <br /> 1.0 SITE HISTORY <br /> ' In March of 1998 a total of six angle boreholes were hand augered beneath the three <br /> existing 8,000 gallon USTs at the site Minor amounts of MTBE, Toluene, and Xylene were <br /> detected in soil samples <br /> On April 29 and May 26, 1998, Cardoza Enterprises was directed by San Joaquin County <br /> Environmental Health Department (SJC/EHD) to submit a work plan to deterinine if <br /> ' residual soil or groundwater contamination exists beneath the tanks (see Figures 1 & 2) <br /> Two direct push soil borings were installed in August of 1998 Results showed the presence <br /> of fuel oxygenate compounds in the soil and BTEX, TPH-G and the fuel oxygenate <br /> ' compounds in the groundwater <br /> ' In March of 1999, the three underground fuel storage tanks and associated product lines and <br /> vent lines were removed At that time soil samples were collected and tested according to <br /> the regulator's discretion A new storage tank and dispenser system was installed and the <br /> ' station returned to operation <br /> On January 5, 2000, three soil borings were drilled at the site and converted into <br /> ' groundwater monitoring wells Sixteen quarterly sampling/monitoring events have been <br /> completed since the installation of wells MW-1 through MW-3 Groundwater samples <br /> collected from MW-1 and MW-3 have contained elevated concentrations of the gasoline <br /> oxygenate MTBE Well MW-2 has not contained contaminant concentrations above the <br /> laboratory reporting limits since its' installation <br /> ' On May lb & 17, 2001, Geological Technics Inc (GTI) advanced seven (7) GeoProbe <br /> boreholes (GP-3 through GP-9), collected soil and groundwater samples, and analyzed these <br /> samples for petroleum hydrocarbon compounds The results of the laboratory analyses did <br /> 1 <br />