Laserfiche WebLink
Ms. Turkatte <br /> July 24, 2015 <br /> Page 5 <br /> Additional pulsing activities were conducted between 2012 and 2013 primarily to address the <br /> SG-1 and SG-3/SG-4 areas. After additional pulsing, soil vapor samples were collected again at <br /> all of the former in-situ sample collection locations. As shown on Figure 5 in Attachment 3, the <br /> PCE results reported from five feet bgs samples collected in all seven locations were below the <br /> commercial CHHSL. <br /> Table 1 in Attachment 1 shows a well-by-well correlation between the confirmation samples <br /> collected and the SVE extraction and soil vapor monitoring probes proposed to be abandoned by <br /> the pressure grout method (column 12). In some cases, the well was sampled and in other cases <br /> the closest well or soil vapor sample collection point was used to demonstrate confirmation that <br /> the area is clean. <br /> PCE in Groundwater Results <br /> The soil cleanup at the site has also been demonstrated by significant decreases '' CE c✓ncc„A y mj <br /> i groundwater Vis. Attachment 4, Figure 49 shows initial PCE in A zone <br /> groundwater concentrations from 1999 and Attachment 4, Figure 9 shows the mostrecentPCE <br /> in groundwater concentrations from June of 2015. A comparison of the PCE in groundwater <br /> impacts in 1999 compared to PCE concentrations measured in June of 2015 show that PCE in <br /> groundwater have reduced significantly over time. Originally concentrations of PCE in <br /> groundwater exceeded 10,000 micrograms per liter (gg/L) and now the highest PCE in <br /> groundwater concentrations are below 100 µg/L only Yeportedyin wells on the east side of the <br /> site. The concentratipnsf PCE in groundwater monitoring wells directly below the former soil <br /> 4S •u+ <br /> source areas are all below the Maximum Contaminant (MCL) level (e.g. MW-006A, MW-007A <br /> or MW-109A). <br /> Risk-Based Screening Levels <br /> Additionally, concentrations of PCE in all locations from all three confirmation sampling events <br /> were below the site-specific risk-based screening levels developed in* Soil Closure Report <br /> (Geosyntec, 2012). The site-specific risk:based screening levels were developed to be used as <br /> screening values for VOCs at various depths bgs that are protective of commercial workers given <br /> Site-specific conditions. The Site-specific screening levels calculated in)hk Soil Closure Report <br /> are presented in Attachment 5, Table 4. A comparison of the most recent PCE sampling results <br /> to the Site-specific risk-based screening levels indicates that the PCE concentrations in the most <br /> addendumtoabandonmentwp.doc <br /> engineers I scientists I innovators <br />