SITE INFORMATION AND CORRESPONDENCE_2008-2015

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Ms. Turkatte July 24, 2015 Page 4 probes were installed into and bottom in "an area of impact" as defined by SJCEHD. Attachment 2 includes a series of figures (Figure 11 through Figure 13) from the RI Report showing the pre-remediation condition in 1999. As noted in Table 1 of Attachment 1, six of the soil vapor monitoring probes were installed outside of the area of contamination as perimeter control points (SVMW-13, -14, -15, -17, -21 and SVMWE-003). The soil vapor monitoring probes located outside of the original area of contamination are also proposed to be abandoned by the pressure grout method as these areas would not have ever had contamination that would represent a threat to groundwater quality. Confirmation Data As part of the SVE system optimization activities, in addition to in-line SVE system monitoring with a photo ionization detector (PID), three rounds of confirmation soil vapor sample collection were conducted to evaluate the presence of residual Volatile Organic Compounds (VOCs) in the vadose zone. The confirmation soil vapor samples were collected both from SVE wells and from multiple depths in undisturbed soil. The SVE well samples were collected from the screen zones between 10 and 30 feet bgs and the undisturbed samples were collected from multiple depths between 5 and 20 feet bgs. The RWQCB prefers the collection of confirmation soil vapor samples from undisturbed soil as these samples best represent residual soil vapor concentration in the vadose zone at the Site. The first two rounds of soil-gas confirmation testing in 2010 and 2012 included sampling for PCE and its degradation products. Results from the first two events showed that only PCE required further evaluation because all other compounds were near or below their respective California Human Health Screening Levels (CHHSLs) and the laboratory detection limits. The 2010 and 2012 confirmation sampling results are shown on Attachment 3, Figure 4 and Attachment 3, Figure 5 shows the most recent 2013 soil vapor sampling results. The data show that the concentration of PCE in SVE wells -005, -014, -011, -034, -024, -027, -029 and -033 were non-detect or below the commercial CHHSL concentration in the final sampling event in May of 2012. The PCE results reported from samples collected from SVE-019 and -017 were slightly above the CHHSL in the May 2012 event. PCE concentrations reported from the multi- depth sample collection conducted in 2010 were all below the CHHSL; however, in the follow- up sample collection in May of 2012 samples collected from locations SG-1, SG-3 and SG-4 exceeded the CHHSL mostly in shallow(less than 10 feet bgs) samples. addendumtoabandonmentwp.doc engineers I scientists I innovators