ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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Soil gas samples collected from well PSG-21 in December 2007, March 2008, June 2008, and August 2008 were below the residential CHHSL for TCE during all four sampling events (Table A.3-1). The TCE concentrations varied from 15 lag/m3 to 35 Pg/M3 during this period, remaining below the TCE CHHSL throughout any seasonal variations. Well PSG-21 lies between the Site and the adjacent property to the west, thus it is located such that COCs volatilizing from groundwater beneath the site would likely be detected in the well if such a process were occurring. Based on the lower soil vapor concentrations observed at PSG-21, the much higher TCE soil vapor concentrations at SG-22 and SG-7 were deemed unrelated to migration of TCE from the Site and could be related to an isolated off-site source (Figure A.3-3). TCE concentrations in shallow soil gas samples from borings within vacant properties near the Site (SG-1, SG-9 and SG-10) did not exceed the commercial/industrial CHHSLs for shallow soil gas (Table A.3-1). SG-1 was located near the M-6 groundwater monitoring well cluster and SG-9 and SG-10 were located nearest to former vapor extraction wells VE-9 through VE-12. Because the property is currently zoned for industrial use, commercial/industrial CHHSLs were applied and TCE concentrations in this area were below thresholds of concern for risks to human health. 3 CONCLUSIONS Nestle installed the Site SVE system to remove VOCs within in the vadose zone beneath the former decaffeination facility and nearby areas. The system was effective and the vadose zone in the area of the Site has been remediated to the extent feasible using SVE. Following the termination of SVE activities in December 1999, the following conclusions regarding the effectiveness of SVE have been established: 1. The SVE system(s) have successfully removed VOC vapors from the vadose zone beneath the Site. Over 880 pounds of VOCs were removed from the vadose zone based upon a review of mass removal rates. 2. Post-remediation investigations and soil vapor sampling in 2006 through 2008 in the area of the Site confirm the lack of soil vapor impacts in shallow soil gas samples, above levels of concern with regard to indoor air exposure levels for commercial/industrial property. 3. Since the successful completion of SVE activities and post-remediation sampling, active remediation has been focused on extraction and treatment of impacted groundwater to target the remaining VOCs beneath the Site. SVE would not be effective as a groundwater treatment technology for the Site because VOCs below the water table would have to move by diffusion to the water table interface and then volatilize before being removed by SVE. These are very slow processes and therefore SVE is not recommended to address VOCs in groundwater.