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Mr. Cervantes 16 October 2012 Page 2 but requested that additional soil gas samples be collected after a year to confirm that there was no significant rebound. In May of 2012, Arcadis collected an additional round of soil gas samples from temporary soil probes and from SVE wells. Analytical results from the soil gas probes indicated that concentrations of PCE had rebounded slightly (to a maximum of 5 times the California Human Health Screening Level [CHHSLs]), while PCE concentrations in the SVE wells showed a slight reduction from the previous round of sampling. The results of the additional sample collection were presented in a July 13, 2012 Soil Closure Report, which also included Site-specific risk based cleanup goals for vapor intrusion and a request for closure of the soil source area at the Site. The Trust met with the CVRWQCB on September 4 and 28, 2012 to discuss the request for soil closure. During these meetings,the CVRWQCB expressed their concern with the number of soil vapor sampling locations with PCE concentrations above the commercial CHHSL. The CVRWQCB also noted that the SVE system, though operated for more than 10 years, was never optimized to address high concentration PCE source areas. Therefore, the CVRWQCB requested that source area focused pulsing and testing of the SVE system, followed by an additional round of confirmation samples be completed to ensure that the SVE system has achieved its maximum effectiveness. This Work Plan includes a detailed description of the activities requested by the CVRWQCB during the September 28, 2012 meeting. Work Plan Objective The objective of this Work Plan is to present the scope of work necessary to meet the data objectives presented herein. In general the data objectives are: 1) assess whether the SVE system has been optimized in areas where the PCE concentration remains above the commercial CHHSL and 2) determine whether on-Site soil remediation is complete. A Soil Closure Report will be prepared based on the results of the field testing and data evaluation activities outlined below. SVE System Optimization Testing SVE system optimization testing will include short-term, focused vapor extraction from SVE wells in areas where PCE concentrations remain above CHHSLs. Based on May 2012 soil-gas sampling results (Figure 2), concentrations of PCE reported in three temporary soil gas sampling points (SG-1 at 3,000 micrograms per meter cubed [pg/m31; SG-3 at 1,500 µg/m3; and SG-4 at 1,100 l g/m3) and two soil vapor extraction wells (SVE-17 at 1,300 gg/m3 and SVE-19 at 950 20121000-SVE optimization and Confirmation Testing engineers I scientists I innovators