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Remedial System Enhancement Plan—Former-Tosco(Unocal)Service Station No 6981 <br /> !' August 8,2001 <br /> depth to groundwater has risen from approximately 51 to 53 feet bgs in 1993 to 27 to 29 feet bgs on March <br /> 7,2001 Groundwater flow has been to the northeast with the hydraulic gradient ranging from 0 002 to 0 013 <br /> feet/feet <br /> I <br /> REMEDIATION OPTIONS <br /> The VES at the site has been in operation since September 1994 and is currently operating in pulse mode The <br /> data indicates that asymptotic levels were reached in February 2000 No petroleum hydrocarbon concentrations <br /> have been detected in the influent since December 2000 This indicates that VES is no longer an effective <br /> treatment method for this site <br /> GR has evaluated the site data and reviewed various remedial enhancements or modifications that are still <br /> available for the subject site,considering prior remediation activities and current conditions The following <br /> is a brief description and comparison of those options reviewed <br /> Option#1 - No Remedial Action/Long Term Monitoring <br /> COST Low <br /> TIME FRAME Long term <br /> . ADVANTAGES 1) Low annual cost <br /> 2) Minimal disruption of site operations <br /> DISADVANTAGES 1) Potential liability <br /> 2) No defined project completion/closure <br /> 3) Potential migration of contamination <br /> CONCLUSION Not a suitable approach for this site at this time <br /> Option#2 -Excavation Of Impacted Soil <br /> COST , Medium to high <br /> TIME FRAME Short term <br /> ADVANTAGES 1) Potential for quick efficient source removal if site conditions <br /> are favorable <br /> DISADVANTAGES 1) Excavation does not address groundwater contamination, <br /> therefore,contamination in the capillary fringe zone would be <br /> expected to return <br /> 2) Equipment limits depth of potential excavation <br /> 14012A 10 3 <br />