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Former Beacon Station No. 12474 March l8,2002 Stockton California Problem Assessment Report/Corrective Action Plan 4 resource and sensitive receptors beyond the current plume boundaries. Post-remediation monitoring would demonstrate plume stability and progression of natural attenuation prior to closure. 10.1 Recommended Corrective Action The recommended corrective action includes installation and operation of soil vapor extraction and air sparging systems. Soil vapors would be extracted from vapor wells VW- 1, VW-2, VW-3, VW-7 and intermittently from VW-4, VW-5 and VW-6. Compressed air would be introduced to air sparge well AS-1, and monitoring wells MW-2 and MW-12. On the basis of an evaluation of the remedial effectiveness, an additional air sparge well may be installed east of monitoring well MW-10. Soil vapor extraction and air sparging may be adequate to remediate soil and groundwater to levels which will not threaten beneficial use of the groundwater resource and allow for natural attenuation to proceed with measurable results. Groundwater extraction has been demonstrated as a feasible alternative in that the • calculated radius of influence would be sufficient to capture impacted groundwater. However, the necessity of a groundwater extraction system should be considered only after evaluation of the effects of soil vapor extraction and air sparging systems on the soil and groundwater environments. 10.2 Description of Proposed Remedial Installations Horizon proposes the installation of soil vapor extraction and air sparge remediation systems consisting of the following elements: • Soil vapor conveyance piping in trenches from vapor extraction wells VW-1 through VW-7 to a remediation compound located behind the station building (Figure 9); • A process control manifold for the vapor extraction piping; 474PARCAP3-02.doc 21 Project No. 1474.23 HORIZON ENVIRONMENTAL INC.