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URS s • <br />Mr. Robert McClellon <br />July 28, 2006 <br />Page 4 <br />oxygen concentration in all probes ranged from 0% to 19.6%. The carbon dioxide concentration in all <br />probes ranged from 0.8% to 25.1 %. The results for each probe and each extraction well are summarized <br />in Table 2. <br />CONCLUSIONS AND RECOMMENDATIONS <br />Four VOC constituents (acetone at 12 gg/L [MW -2]; carbon disulfide at 0.8H gg/L [MW -2]; <br />cis-1,2-dichloroethene at 0.66J gg/L [MW -2]; and chloroform at 1.7 gg/L [MW -3]) were detected in the <br />groundwater samples collected on June 19, 2006. When these values are compared to the most <br />conservative established levels (i.e., primary MCLS, CSALDW, or TOT) identified above, all of the <br />detected constituents were less than these levels, ranging from approximately one order of magnitude to <br />more than three orders of magnitude less that the established level. Although the results of the <br />groundwater sampling were less than the established values, we recommend that groundwater samples be <br />collected for three consecutive quarters to confirm these contaminants remain at concentration less than <br />these regulatory values. If the results confirm that the contaminants and their concentrations remain less <br />than the regulatory values during this period, we recommend that additional groundwater sampling be <br />discontinued. <br />Methane was measured above 5.0% in VW -4, VW -5S, VW -5D, VW -6S, VW -6D, EW -1, and EW -2. <br />Based on the most recent quarterly results, the extent of the methane plume appears to be characterized <br />along the northern boundary of the site. We recommend that a passive soil vapor extraction trench be <br />installed to control methane from leaving the site. A work plan to install the passive soil vapor extraction <br />trench was transmitted to SJCEHS and the San Joaquin Valley Air Pollution Control District on July 7, <br />2006 for approval. Following approval of this work plan from your agency and the SJVAPCD, we plan to <br />initiate the field activities to install the trench. If you have any questions, please give me a call at (916) <br />679-2081. <br />Very truly yours, <br />URS <br />Jay G. Kamine <br />Senior Civil Engineer <br />JGK/gng <br />Enclosures: Table 1 — Groundwater Analytical Results Summary <br />Table 2 — Field Measurement Results Summary <br />Figure 1 — Site Plan <br />Attachment 1 — Boring Logs <br />Attachment 2 — Well Development Logs <br />Attachment 3 — Monitoring Well Sampling Logs <br />Attachment 4 — Analytical Report <br />Judy McCampbell (RadioShack) <br />K:\Wprocess\25532\WoridEnterprise\Quarterly Rpt\2Q06\CovLtrRpt.doc <br />