ARCHIVED REPORTS_2011 REVISED FEASABILITY STUDY

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measured at 260 ppbv (1397 pg/m3) SVE activities were discontinued in December 1999 with RWQCB approvals. 2 SVE DATA EVALUATION 2.1 Assessment of SVE System Mass Removal An estimated 880 pounds of VOCs (primarily TCE and chloroform) were extracted from the subsurface between 1988 until the discontinuation of SVE prior to 1994. Detailed records of mass removal rates are not available for the period after 1994. Nestle has conducted multiple soil vapor investigations and assessments (see Section 2.2) following the termination of active soil vapor extraction activities in December 1999. These investigations verified low levels of VOCs remain, although further active SVE was not recommended because of the low level of any remaining concentrations. 2.2 Sampling Following SVE Remedial Activities Following SVE remediation activities at the site, Nestle conducted two soil gas investigations to assess subsurface soil gas levels and determine if indoor air at the Site and nearby properties was threatened 6. Results of these soil vapor investigations in the area of the Site are shown in Figure A.3-3 and Table A.3-1. These investigations included the collection of the following samples: 2006 Soil Gas Sampling • A single soil gas sample at 5 feet below the ground surface (feet bgs) at each boring location from SG-2 to SG-10 (9 samples), • Four soil gas samples at 5, 10, 15 and 20 feet bgs from SG-1 2007-2008 Soil Gas Sampling • Three soil gas samples at 5, 10, and 15 feet bgs from SG-22, and • A soil gas sample and a duplicate sample at PSG-21 (initial sampling event), and three subsequent quarterly samples. Soil gas samples collected from borings SG-2 through SG-4 at 5 feet bgs showed TCE results of less than laboratory reporting limits of 11 micrograms per cubic meter (pg/m3), less than 11 pg/m3, and less than 13 pg/m3, respectively. Samples collected from boring SG-5 showed TCE contractions at 2.8 pg/m3. Based on the California Human Health Screening Levels (CHHSLs), TCE soil vapors pose no significant risk to building occupants. Additionally, the results define the horizontal extent of shallow soil gas impacts in the vicinity of these borings. The location for boring SG-22 was selected to delineate soil gas concentrations near boring SG-7 immediately west of the Site (Figure A.3-3). The TCE concentrations from SG-22 decreased with increasing depth (Table A.3-1). The deepest soil gas sample, collected at 18 feet bgs, did not contain concentrations of TCE or any VOCs above respective reporting limits. Although some TCE concentrations from SG-22 exceeded the commercial/industrial CHHSL, decreasing TCE concentrations were observed with increasing depth. This suggests the presence of TCE at this boring was related to a shallow, localized near surface release, not the upward movement of TCE vapors from deeper, impacted groundwater in this area west of the site.