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I--------------- <br /> A S S OCIATES I NC . <br /> Fir <br /> = on Smith's Canal upgradient location from the site, it is unlikely that the canal has been impacted <br /> by petroleum hydrocarbons from the site. Based on the distance of the wells from the site, it is <br /> r:• <br /> E s unlikely that they have been impacted by petroleum hydrocarbons from the site. <br /> 6.0 EVALUATION OF LOW RISK CRITERIA <br /> �.i <br /> .'� 6.1 Low Risk Groundwater Case Evaluation <br /> Using the criteria listed in CRWQCB's No Further Action (NFA) requirements, as outlined by <br /> B (Appendix B f h Tri-R Tri-Regional Recommendations conditions at the subject site <br /> CRWQC o the eg }, � <br /> were evaluated to determine if NFA as a "low risk, Groundwater Case" is appropriate for this <br /> site. <br /> Criterion 1: Contaminants remaining in the vadose zone must not reverse or threaten <br /> to reverse the mass reduction rate of groundwater pollutants. <br /> Over the coarse of the investigation, aquifer levels have been measured at depths of <br /> .l` approximately 11 feet. Soil samples collected below 11 feet are generally considered to be <br /> in the saturated zone. Results of samples collected in the vadose zone (above a depth of <br /> 11 feet) appear to not be laterally continuous across the site. The vadose zone <br /> concentrations were measured at lesser concentrations that those collected in the saturated <br /> zone and in very low concentrations. BTEX compounds in the vadose zone were <br /> f measured at very low concentrations and benzene was not detected above the method <br /> detection limit. Approximately 1,600 pounds of petroleum hydrocarbons remain in soil, <br /> but this value is mostly indicative of groundwater contamination as most of the samples <br /> were taken in the saturated zone. Only approximately 116 pounds of petroleum <br /> ` hydrocarbons remain in the vadose zone. Therefore, the likelihood of contaminants in the <br /> vadose zone reversing or threatening to reverse the mass reduction rate of groundwater <br /> L? pollutants is very low. <br /> Criterion 2: Separate phase product has been removed to the extent practicable. <br /> ff <br /> l Floating petroleum product has previously been observed in monitoring well N ff4. Since <br /> December 1997, only a slight, unmeasurable sheen has been observed in monitoring well <br /> MW4. To date, approximately a total of ten gallons of free product has been recovered <br /> from the well. Table 4 summarizes the product thickness measurements and volume of <br /> ':2 product removed from all monitoring events. <br /> Criterion 3: No existing water supply wells, deeper aquifers, surface waters, or other <br /> Lreceptors are threatened by pollutants remaining in the aquifer. <br /> The closest surface water to the site is Smith Canal, approximately 100 feet south of the <br /> •'rri�_� <br /> el site. Historical groundwater gradients measured at the site and regional groundwater <br /> w:162574.021reportslclosure-smith.doc 7 <br /> f <br />