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March 18,2002 <br /> Former Beacon Station No. 12474 <br /> Problem Assessment Re ort/Corrective Action Alan <br /> Stockton California <br /> - groundwater to this extent would protect human health and the environment because the <br /> groundwater resource that is encompassed by the groundwater plume is not used and is not <br /> likely to be used in the foreseeable future. Additionally, the plume can be controlled by <br /> moderate levels of remedial action. It is Horizon's professional opinion that remediation of <br /> the groundwater to the extent which will cause the plume to remain stable and allow natural <br /> attenuation to progress should be adequate to protect human health and the environment. <br /> 10.0 PROPOSED CORRECTIVE ACTIONS <br /> Horizon recommends operation of SVE and air sparging systems as the most cost-effective <br /> and expeditious approach to site remediation. Results of feasibility testing indicate that this <br /> remedial approach would be effective in removing petroleum hydrocarbons from soil and <br /> groundwater and facilitate natural attenuation processes. The option of adding groundwater <br /> extraction in a staged approach to the remedial effort should be considered after evaluation <br /> of the effectiveness of SVE and air sparging operations. The extraction of groundwater <br /> would have the effect of additional control on the migration of the plume, if necessary, as <br /> well as lowering the groundwater table and aiding in SVE effectiveness. <br /> Operation of an SVE system would act to remove volatile gasoline constituents from the <br /> vadose zone and, together with air sparging, enhance volatilization of gasoline constituents <br /> in groundwater into the vadose zone. Operation of VES and air sparge systems would <br /> facilitate bio-attenuation of fuel constituents by inducing flow of soil gases, including <br /> oxygen, into the impacted vadose zone. The installation of an additional air sparge well <br /> should be considered after evaluation of the effectiveness of SVE and air sparging with <br /> existing installations. <br /> The recommended remediation will result in a reduction of the hydrocarbon mass in soil and <br /> groundwater plumes, increase plume stability, facilitate the progression of natural <br /> attenuation, and will provide protection of current beneficial uses of the groundwater <br /> 474PARCAP3-02.doc 20 <br /> HORIZON ENVIRONMENTAL INC. <br /> Project No. 1474.23 <br />