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ASSlcl \T: m <br /> O C I ATE S I N C . <br /> 4�2 Petroleum Hydrocarbons in Groundwater <br /> ' The grab groundwater sample collected from angle soil boring SB2A and groundwater sample <br /> collected from well MW4 contained no detectable concentrations of TPHg, TPHd, TPHss, <br /> ' BTEX, or oxygenate fuel additives. Analytical results of groundwater samples are summarized <br /> in Table 2. Laboratory data sheets and chain-of-custody documentation for groundwater samples <br /> are contained in Appendix C. <br /> 5.0 DISCUSSION <br /> Based on the analytical results and field observations, the soil and groundwater in the immediate <br /> vicinity beneath the location of the former 1,000-gallon UST are impacted by TPHss. <br /> ' Groundwater and soil samples collected from borings MWl, MW3, SB2A, and MW4 indicate <br /> that impacted soil and groundwater have been defined to the north, east, south, and west of the <br /> former UST. The soil samples from boring S132 indicate the vertical extent of impacted soil is <br /> ' limited to less than 65 feet bgs. <br /> ATC recommends performing three quarters of groundwater monitoring at the site to confirm the <br /> groundwater gradient and monitoring petroleum hydrocarbon concentrations in wells MWI <br /> through MW4. if concentrations of petroleum hydrocarbons remain the same during the next <br /> three quarters of groundwater monitoring, ATC will prepare a site closure report according to the <br /> guidelines contained in the Tri-Regional Board Appendix A Guidelines. <br /> w:1172951reponslsumiii.doc 6 <br />