SITE INFORMATION AND CORRESPONDENCE

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5. SVE SYSTEM OPERATIONS TERMINATION The SVE system operation will terminate once soil vapor concentrations have reached asymptotic stabilization or soil gas cleanup goals have been achieved at the end of the 12- month rebound assessment period. If after 12 months of repeated shutdown/startup cycles, the VOC concentrations from any monitoring well or extraction well still exceed the soil gas cleanup goals, the operator can proceed with closure. Depth discrete soil gas and soil sampling will be conducted as part of closure activities. If rebound has continued to occur or soil gas cleanup levels are exceeded, depth discrete samples will be evaluated to determine whether the continuing source of the concentrations is the unsaturated zone or groundwater. It is anticipated that soil vapor concentrations may result in continued rebound effects due to fluctuations of the water table and/or volatilization of VOCs from the capillary zone above the water table. Fine-grained materials located in close proximity to the water table are likely to contain VOCs that have risen into the capillary fringe due to cohesive and adhesive forces. Also, soil in close proximity to the water table may contain VOCs due to previously higher groundwater elevations. Remediation of elevated soil gas and/or soil VOC concentrations close to the water table are beyond the intent of, and also the technically and economically practicable limit of, the soil source control program. VOCs in the capillary fringe are best addressed through the groundwater cleanup program. Closure with residual VOCs in soil may entail a risk assessment to determine whether groundwater quality could be affected by the remaining VOCs. Closure with residual VOCs may also include other restrictions. Clean closure of a site will proceed if soil gas cleanup goals are achieved. Clean closure requires completion of a closure report as further described below. A risk assessment will not be required for clean closure. The following actions will be taken to fulfill the SVE closure requirement: (1) Depth- discrete soil gas confirmation sampling will be conducted to determine whether the depth- specific cleanup goals for soil gas have been achieved and to assess the residual VOC soil concentrations; (2) This depth discrete soil gas sampling will be conducted within 60 days after termination of the SVE system; and (3) A closure/post remediation report will be prepared and submitted to DTSC staff. The report will be submitted within ninety (90) days following completion of depth-discrete sampling and will include at a minimum the following information: a. System optimization efforts conducted to maximize the SVE system performance; b. Monitoring data and quality control/quality assurance data collected from the extraction wells and monitoring wells; c. Depth-discrete soil gas confirmation results at each site; d. An estimate of the total VOC mass in the vadose zone before and after the operation of a full-scale SVE system (based on soil gas sampling results); and e. An analysis based on monitoring data generated throughout the full-scale SVE operation, including the pulsed mode period. The analysis will include discussions of 1 ) VOC concentration vs. time, 2) cumulative extracted VOC mass vs. time; and (3) 9