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S <br /> Environmental <br /> Mr.Marcus Pierce Resources <br /> 3 January 2006 <br /> Page 3 Management <br /> PID measurements taken between July and November 2002 indicated a <br /> declining VOC vapor in soil trend; however, little correlation with vapor <br /> sample analytical results was shown. Therefore, the PID measurements <br /> were not used further in the evaluation. <br /> The result of the analyses of vapor samples collected at the site indicated <br /> that the majority of the contaminant mass in the soil is located southwest <br /> of the Engine House. Samples collected following system shutdown <br /> indicated that the highest residual VOCs in soil were located at DPEX-01, <br /> VMP-02-9', and DPEX-05. However, total VOC concentrations in <br /> VMP-02-9' and DPEX-05 had declined 97 and 98 percent, respectively, <br /> from pre-remediation values. <br /> A comparison of the results from the August 2002 sample, collected <br /> 1 month after system shutdown, and the November 2002 samples <br /> showed that VOC concentrations in soil rebounded in DPEX-01, <br /> DPEX-02, DPEX-03, and VMP-02-9'. The VOC analyte with the highest <br /> concentration at each of these locations was vinyl chloride. VOC <br /> concentrations from the other 11 sample points declined between August <br /> and November 2002. <br /> Ground water monitoring has indicated a significant improvement in <br /> ground water quality since monitoring began in 1992. A comparison <br /> between VOC detections in March and November 2002 indicated that, <br /> despite shutdown of the dual-phase portion of the system in July 2002, <br /> VOC concentrations continued to decline. <br /> REBOUND EVALUATION ADDENDUM <br /> Based on review of the 2003 Evaluation, the RWQCB has requested <br /> additional work to assess current concentrations of residual VOCs in the <br /> source area. The additional work will include collection of vapor <br /> samples in Summa canisters at the following 15 points: DPEX-01 thru <br /> -08,SVE-01 thru -03,VMP-01-9', VMP-02-9',VMP-03-9', and VMP-04-9'. <br /> These vapor data will be compared to the vapor data collected <br /> previously on site (presented in the 2003 Evaluation). In addition, the <br /> ground water monitoring data collected in March 2006 will be compared <br /> to the data collected prior to shutting the system down (March 2002). <br /> The Rebound and Remediation Effectiveness Evaluation Addendum will <br />