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C A B R I A <br /> solvent concentrations in site groundwater have increased,these contaminants did not originate from <br /> an onsite source <br /> Separate phase product has been removed to the extent practicable- Separate-phase hydrocarbons <br /> have never been observed at this site <br /> No existing water-supply wells,deeper aquifers,surface waters,or other receptors are threatened by <br /> pollutants remaining in the aquifer- With the exception of very low levels of benzene and toluene <br /> detected in well MW-4, no BTEX or TPHg were detected in site groundwater during the most recent <br /> monitoring event In addition, the shallow soils beneath the site are predominantly clays,and would <br /> be expected to have a very low hydraulic conductivity Therefore, it is unlikely that dissolved <br /> hydrocarbons would migrate downward and impact a deeper aquifer The potential for extensive <br /> offsite migration of hydrocarbons in groundwater is minimal based on the low permeability and high <br /> adsorptive capacity of the clayey soils and the high potential for the shallow groundwater to be oxygen <br /> rich and capable of biodegrading any remaining hydrocarbons Therefore, fuel hydrocarbons <br /> originating from the site and remaining in the aquifer do not threaten water-supply wells, deeper <br /> aquifers, surface waters, or other receptors As noted previously, the HVOCs detected in site <br /> monitoring wells appear to have originated offsite <br /> 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 orfuture beneficial use(s)ofthe <br /> aquifer As shown on the following graphs, TPHg and benzene levels in well MW-3, located in the <br /> area of greatest groundwater impact, have decreased to below detection limits as a result of site <br /> remediation Furthermore,since 1996,only trace levels of TPHg or BTEX have been detected in any <br /> of the site monitoring wells Therefore,the total pollutant mass remaining in the groundwater does not <br /> create or threaten to create a risk to human health and safety or future beneficial use(s)of the aquifer <br /> TPHg Concentrations in Groundwater(MVV-3) <br /> 50000 100 2 <br /> 40000 t 80 m <br /> CL 30000 60 w <br /> y " E <br /> = 20000 40a. <br /> 3 <br /> 10000 L + 20 <br /> 0 + + t + 1 }moi f + + } + + 0 0 <br /> tib LD (O (D r— r— M CO C37 M O 0 <br /> CA Cn T CA C3 C3 CA CA CA T T O T O O <br /> [J3 -0CA -0 CA .0 "-' Cn C C C <br /> Q ti Q ii Q ti O 2 Q -' `� <br />