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P � <br /> WQOs was TBA in groundwater samples collected from RW-1 and RW-3 <br /> i <br /> Other than the TBA, only TPH-G and TPH-D remain on-site at <br /> concentrations above WQOs However, the influent air samples collected <br /> at the site have decreased significantly, and no TPH-G was detected in t h e <br /> air samples collected in September and October 2003 This indicates that <br /> there are no longer enough hydrocarbons present in soil and groundwater <br /> beneath the site for the system to operate efficiently <br /> 4.4 RecOromendations Regarding the ASIVE System QAtrauan <br /> Although this system has proven highly effective in soil and groundwater <br /> remediation at the site, its effectiveness has now decreased due to the low <br /> hydrocarbon concentrations remaining at the site As shown in Table <br /> Two, hydrocarbon concentrations on-site are now relatively low and the <br /> system will no longer be able to remove a significant mass of <br /> hydrocarbons This observation corresponds with the decrease in <br /> hydrocarbon concentrations in the influent air concentrations as shown in <br /> Table Four as well as on the graph in the Graph section of this report <br /> During the months of September and October 2003, no measurable TPH-G <br /> was removed from the site due to the low remaining hydrocarbon <br /> • concentrations at the site <br /> Based on (a) the low hydrocarbon concentrations remaining at the site in <br /> both soil and groundwater, (b) the decrease in efficiency of the AS/VE <br /> system due to the decrease in hydrocarbon concentrations in soil an d <br /> groundwater, and (c) the presence of hydrocarbon degrading bacteria in <br /> groundwater in the vicinity of the recovery wells where the highest total <br /> petroleum hydrocarbon concentrations are detected, it appears <br /> appropriate that the AS/VE system be turned off at this time <br /> ASE recommends that the operation of this system be discontinued ASE <br /> recommends, however, that quarterly groundwater monitoring continue <br /> at the site to verify that the hydrocarbon concentrations at the site <br /> continue to decrease due to natural attenuation <br /> 5 . 0 DOMESTIC WELL WELLHEAD TREATMENT SYSTEMS <br /> -5 . 1 System Description and Operation <br /> ASE operates individual wellhead treatment remediation systems on 1 1 <br /> domestic wells downgradient of the site Untreated water from these <br /> wells contains, or has contained, detectable concentrations of MTBE or <br /> Frank's One Stop Interim Effectiveness Report — November 2003 <br /> -5- <br />