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tt � <br /> CAMBRIA <br /> • <br /> to 215 ppb TPHg and 0 60 ppb benzene during the first quarter 2002 sampling event MTBE was not <br /> detected in this well <br /> REGULATORY STATUS REVIEW AND RECOMENDATIONS <br /> The site appears to meet the CVRWQCB cntena for a low-nsk groundwater designation As outlined <br /> in Appendix B of the "Tri-Regional Board Staff Recommendations for Preliminary Investigation and <br /> Evaluation of Underground Tank Sites" a low-nsk groundwater case has the following general <br /> characteristics <br /> 1 Contaminants remaining in the vadose zone must not reverse or threaten to reverse the mass <br /> (9 1 <br /> reduction rate of groundwater pollutants, <br /> 2 Separate phase product has been removed to the extent practicable, <br /> 3 No existing water-supply wells, deeper aquifers, surface waters, or other receptors are threatened <br /> • by pollutants remaining in the aquifer, and <br /> 4 The total pollutant mass remaining in the groundwater is decreasing at predicted rates and neither <br /> creates,nor threatens to create, a risk to human health and safety or future beneficial use(s)of the <br /> aquifer <br /> Contaminants remaining in the vadose zone must not reverse or threaten to reverse the mass <br /> reduction rate of groundwater pollutants. An estimate of initial mass of petroleum hydrocarbons <br /> in soil indicates that up to 759 pounds of TPHg and 3 pounds of benzene may have been present in <br /> soil prior to vapor extraction(Attachment G) It is unknown how much of this hydrocarbon mass was <br /> removed during the extended pilot vapor extraction test However, groundwater analytical data <br /> indicate that any hydrocarbon mass remaining in soil is not impacting groundwater quality Due to <br /> a rising groundwater table beneath the site, groundwater has come into contact with this potentially <br /> impacted vadose soil If there was a significant residual hydrocarbon mass in the vadose soil, we <br /> would expect the hydrocarbon concentrations in groundwater to increase as the water table rose Since <br /> hydrocarbon concentrations in groundwater have remained stable and/or decreased,this suggests there <br /> is little, if any,residual hydrocarbon mass in vadose soil <br /> Separate phase product has been removed to the extentpracticable: Separate-phase hydrocarbons <br /> have never been observed at this site <br /> • <br /> 0837 5 <br />