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3 .4 System 'Effectivenes <br /> As an interim remediation system, the system was somewhat effective <br /> during its operation There were, however, significant problems <br /> First, the system was extremely expensive to operate During the <br /> operation, the system cost an average of $14,230 per month or a total of <br /> $1,854 per gallon of gasoline removed This is not considered a cost- <br /> effective means of operation, especially compared to the cost of the <br /> ASNE system, which costs $297 per gallon of gasoline removed <br /> Second, the hydrocarbon concentrations in groundwater showed little <br /> change during the period of P&T system operation, although free-floating <br /> hydrocarbon present at the site during this period may have skewed the <br /> results <br /> Third, as the operation of the system continued, significant bio-fouling of <br /> the recovery wells occurred, interfering with the system operation <br /> During the final months of operation, the bio-fouling became excessive <br /> and the P&T system became extremely inefficient Since the bio-fouling <br /> slime consisted of hydrocarbon degrading bacteria, it would have been <br /> counterproductive to kill the bacteria, even though it was interfering with <br /> the system operation As a result, ASE redeveloped the wells to remove <br /> the slime on a regular basis, but still encountered decreasing groundwater <br /> flow with time and decreased pumping efficiency This slime is still <br /> present in these wells and is likely more effective in site remediation than <br /> the operation of the P&T system <br /> Fourth, the P&T system did not remove any hydrocarbon mass from the <br /> vadose zone, which like all pump and treat systems, minimizes the long- <br /> term effectiveness of the system without vadose zone remediation <br /> 3 . 5 Recommendations lRegardina the "Pump and Treat" Sys <br /> Since only very low hydrocarbon concentrations remain in groundwater <br /> on-site, and since the "pump and treat" system will not be able to pull <br /> back contaminated groundwater that has already impacted wells across <br /> West Yosemite Avenue, ASE does not recommend any further use of the <br /> "Pump and treat" remediation system at the site <br /> Frank's One Stop interim Effectiveness Report -- November 2003 <br /> -3- <br />