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IT Corporation <br /> July 13, 1999 A Member of The IT Group <br /> Page 4 <br />. 9 Reasons why "background"was/as unattainable using BAT <br /> Hydrocarbon staining and odor were still apparent after the limited excavation <br /> beneath PD-1, PD-2 and PD-3 However, over-excavation was terminated to <br /> protect the structural integrity of the canopy supports <br /> Additional investigation in the downgradient direction is not possible due to the <br /> presence of Highway 120 It is unlikely that the low concentrations of benzene <br /> once reported in MW-2 would migrate the full distance across Highway 120 <br /> Therefore the installation of a monitoring well at that location would not be <br /> beneficial <br /> 10 Rationale why conditions remaining at the site will not adversely impact water <br /> quality, health or other beneficial uses <br /> The following are rationale why conditions remaining at the site will not adversely <br /> impact water quality, health or other beneficial uses <br /> Site assessment has been completed Although there are residual <br /> hydrocarbons in soils in the immediate vicinity of the dispenser islands, the <br /> observed reductions in hydrocarbon concentrations in the soil samples <br /> collected from the borings indicate that their lateral and vertical extent have <br />. been defined <br /> • Dissolved hydrocarbons have historically only been detected in one well on <br /> site, MW-2 Dissolved hydrocarbon concentrations in groundwater have <br /> declined steadily since wells were installed in August 1998 Separate phase <br /> hydrocarbon has never been present in site wells Benzene has never been <br /> detected in monitoring wells MtBE has not been detected in the <br /> groundwater above 16 ppb, which is below accepted California action <br /> levels Neither benzene nor MtBE were detected in site wells during the <br /> first quarter 1999 <br /> • The closest water supply well to the site is approximately 1,500 feet north <br /> (downgradient) of the site This well is screened from 90 to 150 feet bgs <br /> indicating that there is greater than 70 feet of separation between impacted <br /> groundwater and the usable aquifer <br /> 9110071B/01 02/Closure <br />