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1 <br /> 60 DISCUSSION OF INTERIM SOIL REMEDIAL OPTIONS <br /> Environmental studies performed at the site indicate that a TPHg plume remains in soil generally <br /> beneath the UST excavation Presented below are discussions of the remedial options typically <br /> evaluated for sites with soil impacted with TPHg <br /> ' Remedial options associated with the current groundwater impacts are not discussed herein Source <br /> removal of the residual TPHg in soil should be performed to evaluate potential benefits to <br /> groundwater associated with operation of the VES After removal of the source hydrocarbons from <br /> soil, the remaining groundwater plume can be evaluated from a risk-based perspective for a possible <br /> ' low risk and no further action classification This evaluation should be performed after final policy <br /> relative to low risk site criteria is issued by the state of California Water Resources Control Board <br /> Such policy is currently under development <br /> 1 <br /> 6.1 No Remediation Alternative <br /> ' Due to the plume of TPHg-impacted soil beneath the site contacting groundwater, there exists the <br /> potential for continued leaching of petroleum hydrocarbons from soil to groundwater Such leaching <br /> ' could further degrade the current groundwater quality and contribute to further downgradient <br /> groundwater plume expansion Due to the potential for continued leaching of petroleum <br /> hydrocarbons to groundwater beneath the site, the "no remediation" alternative will not be given <br /> ifurther consideration <br /> 662 ]Excavation of Soil <br /> 1 <br /> The removal of soil impacted with petroleum hydrocarbons would require extensive excavation <br /> ' beneath the UST excavation Due to the depth of soil impacts being on the order of 60 feet, <br /> excavating impacted soil would not be a cost-efficient means of remediation This option is <br /> ' considered non-permissible and will not be given further consideration <br /> 6.3 On-site Soil Aeration, Off-site Soil Treatment <br /> ' These options would require the direct excavation of soil and are not feasible for the same reason <br /> presented in Section 6 2 <br /> ' 64 Bioremediation <br /> The design of an m-situ soil bioremediation system typically includes provisions for the infection of <br /> air, water, and nutrients into the plume for the purpose of enhancing the biological growth of <br /> naturally occurring microorganisms The existence of residual TPHg in soil in proximity to <br /> ' groundwater poses risks associated with the infection of water for bioremediation The leaching of <br /> ' Project No 59100-06-18A -14- December 9, 1996 <br />