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' 47010 lcal Tecluctcs l Page 2 <br /> g g <br /> Site Characterization Report <br /> ' Project No 724 2 <br /> . May 9, 2006 <br /> 1.0 INTRODUCTION <br /> ' In April 1987 the site's two 3,000-gallon gasoline underground storage tanks (UST) and one <br /> 150-gallon waste oil UST were removed (see Figure 1 Area Map & Figure 2 Site Map) <br /> Analyses of soil samples from the UST excavations revealed that a petroleum hydrocarbon <br /> ' release had occurred The San Joaquin County Environmental Health Division (SJC/EHD) <br /> subsequently directed Mr Valentine to begin an investigation to determine the extent of the <br /> petroleum release <br /> ' The following is a summary of work performed at the site to date <br /> ' • In October 1993 four boreholes (SB-1 thru SB-4) were placed around the location of the <br /> former waste oil tank Results showed that all soil samples, except for the 36-foot sample <br /> ' from SB-2, were below detection limits for BTEX and TPH-G <br /> 0 In September 1994 monitoring well MW-1 was installed at the site Soil sample <br /> analytical results indicated the presence of BTEX and TPH-G in the soil to a depth of 56 <br /> ' feet bgs Waste oil was detected in the shallow soil samples <br /> • In June 1995 two additional monitoring wells, MW-2 & MW-3, were installed at the site <br /> Results showed the presence of high levels of BTEX and TPH-G in the soil and <br /> groundwater <br /> 0 In June 1996 three additional monitoring wells (MW-4, MW-5 & MW-6) and soil boring <br /> "SB-B" were installed at the site. Soil sample analytical results indicated the presence of <br />' significant levels of BTEX and TPH-G The results also indicated that the pump-island <br /> was a major source of contamination <br /> • In September and October 1997 five Strataprobe soil borings (SP-1, SP-4 SP-5, SP-5A & <br />' SP-6) were installed at the site Groundwater samples collected from these borings <br /> indicated the presence of low to moderate levels of TPH-G to a depth of 60 feet bgs <br /> • In August 1999, one deep screened monitoring well (MW-101) and one soil boring (SB- <br /> 201) were installed at the site The purpose of these borings was to define the vertical <br /> extent of the groundwater plume Soil samples collected by use of the SimulProbe <br />' Maxitool from the soil borings tested positive for BTEX and TPH-G compounds to a <br /> depth of 111 feet Pore water samples, also collected with the SimulProbe, revealed the <br /> presence of BTEX and TPH-G to a depth of 111 feet bgs <br />' • An abandoned domestic well located at an adjacent residence was destroyed in <br /> accordance with SJC/EHD directives on April 20, 2001 <br /> 0 A discretely screened deep well (MW-201) was installed in October 2001 The results of <br /> this endeavor suggested that the contamination extended to a depth of 128 feet below <br /> grade surface (bgs) This depth was the target of a SimulProbe sampling effort and the <br /> soil sample from this elevation contained detectable TPH-G The well was completed <br />' with a screened interval of 148 — 150 5 feet bgs The amount of contamination in this <br /> well has attenuated to trace levels suggesting that the initial detection was a drilling <br /> artifact <br /> 1 <br />