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Ms. Turkatte <br /> July 24, 2015 <br /> Page 6 <br /> recent confirmation samples are at least one order of magnitude lower than the Site-specific <br /> screening levels. <br /> Soil Screening for Groundwater Protection <br /> To assist in setting a target remedial concentration for PCE in soil vapor for use in developing <br /> the soil vapor remediation plan, an analytical model was used to calculate the concentration of <br /> PCE in soil vapor that can remain on site without resulting in groundwater quality impacts above <br /> the MCL of 5 µg/L for PCE in groundwater. Analytical modeling was performed using the soil <br /> screening analytical equations from U.S. Environmental Protection Agency (U.S. EPA) Soil <br /> Screening Guidance (U.S. EPA, 1996). These equations represent the processes of partitioning <br /> PCE from soil vapor to soil moisture, the downward movement of PCE within leachate, and the <br /> mixing of leachate with groundwater. <br /> Based on these modeling efforts and assumed groundwater quality goals, a target remedial <br /> concentration of 150 µg/l, for PCE in soil vapor was estimated to be protective of groundwater <br /> quality. All concentrations of soil vapor measured during the confirmation sample collection <br /> events are well below the target remedial concentration protective of groundwater. <br /> Summary <br /> In summary and per the SJCEHD criteria and supported by the data and analysis attached, <br /> Geosyntec is proposing to abandon the SVE and soil vapor monitoring probes by the pressure <br /> grout method. A summary of the data supporting this proposal are listed below: <br /> 1) The SVE wells and soil vapor monitoring probes are installed to a maximum depth of 30 <br /> feet bgs, have screen intervals between approximately 10 and 30 feet bgs and a radius <br /> influence of approximately 80 feet. The depth and distribution of the SVE system was <br /> designed to thoroughly overlap the area of VOC impact in the subsurface. <br /> 2) The SVE system operated for over 10 years followed by a 3-year optimization period. <br /> This extended period of operation better assures sufficient removal of VOCs from the <br /> vadose zone at the Site. <br /> 3) Consistent with the SJCEHD criteria, all of the SVE wells and the majority of the soil <br /> vapor monitoring probes were installed in an"area of contamination" as shown by the RI <br /> addendumtoabandonmentwp.doc <br /> engineers I scientists I innovators <br />