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1 <br /> Due to the conservative assumptions inherent in these estimates, the estimates are likely to <br /> represent upper bound conditions The actual mass remaining is likely to be less due to rapid <br /> attenuation of mass away from the point of release <br /> ' Techholo used to clean site rf Best Available Technolo BAT was not used ex Iain wh <br /> ' In groundwater, concentrations above water quality goals of gasoline compounds have not been <br /> detected Since groundwater beneath the site is not impacted and beneficial uses are not <br /> impaired, no groundwater remediation is required <br /> In soil, the relatively high ratio of xylene concentrations to benzene concentrations within the area <br /> ' of impacted soil suggests that the gasoline release is relatively aged In addition, approximately <br /> 65 feet of soil between 15 feet bgs and the groundwater table at 80 feet bgs does not contain <br /> ' detectable concentration of TPH-as-gasoline, benzene, and MTBE Since the release appears to <br /> be aged, the site is asphalt capped and not subject to significant surface water infiltration, and a <br /> buffer of approximately 65 feet of relatively non-impacted sod exists above the groundwater table, <br /> ' the gasoline hydrocarbons remaining in shallow soil do not appear to be a threat to groundwater <br /> beneath the site Natural attenuation processes including biodegradation and volatilization <br /> appear to be occurring and may be expected to continue to reduce concentrations of petroleum <br /> hydrocarbons in soil over time <br /> ' Natural attenuation is considered to be the best available technology because (1) it is most cost- <br /> effective, (2) it is protective of human health, and (3) in this case it is protective of present and <br /> ' future beneficial uses of groundwater <br /> Zone of influence calculated for the subsurface remediation system and the zone of capture <br /> ' attained for the soil and ground water remediation system <br /> ' Not applicable No active remedial measures were undertaken <br /> Reasons why "background"_was/is attainable using BAT <br /> The concentrations of gasoline compounds initially detected in the groundwater sample collected <br /> from SB-1 were defined by the four on-site monitoring wells As such, the initially-detected <br /> hydrocarbons do not appear to be migrating Therefore natural attenuation processes are likely to <br />' reduce hydrocarbon concentrations to background over time <br /> 15 <br />