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concentrations in soil. The primary criteria for determining whether technically and <br /> economically practicable cleanup has been achieved will be the system stabilization <br /> criteria. The system stabilization criteria, together with soil gas cleanup goals will be <br /> evaluated during a 12-month period rebound assessment following an initial determination <br /> of stabilization. One or possibly both of the two criteria will be used to determine whether <br /> each site has achieved technically practicable and economical soil cleanup. These two <br /> criteria are further discussed below: <br /> Primary Cleanup Criterion <br /> a. System stabilization (asymptote) criteria: <br /> After the SVE system has reached an asymptote (as defined in Section 4.3 above), the <br /> operator will shutdown the SVE system and begin rebound testing as described below. <br /> Rebound will be indicated if static VOC vapor concentrations measured at the extraction <br /> well(s) or monitoring wells exceed two hundred percent (200%) of the vapor concentrations <br /> measured at the end of the final stabilization period (stabilized asymptotic VOC <br /> concentrations measured at the extraction well). If it is determined that rebound has <br /> occurred and the rebound is above cleanup goals, the SVE system will be turned back on. <br /> This on and off(startup/shutdown) and monitoring for rebound cycles will continue for 12 <br /> months. <br /> If, after the twelve months repeated shutdown/startup cycles, the VOC concentrations from <br /> any monitoring well or extraction well still exceed the soil gas cleanup goals, the operator <br /> will proceed with operations termination as discussed in Section 5. <br /> Secondary Cleanup Criterion <br /> b. Soil gas cleanup goals: <br /> The SVE operation will continue until it reaches an asymptote. Once the SVE reaches its <br /> asymptote, the operator will shut down the SVE units and begin rebound and soil gas <br /> cleanup level testing as described below. If the rebound is less than the cleanup goals, <br /> the SVE units can remain idle, and monitoring will continue during the 12-month rebound <br /> assessment period. Soil gas cleanup goals are further discussed in Section 4.6. <br /> If the VOC concentrations in all monitoring and extraction wells are below cleanup goals <br /> at the end of the 12-month period, the operator proceeds to a clean closure. Closure <br /> reporting procedures are discussed further below. <br /> 4.5 VOC Concentration Rebound and SVE System Restart <br /> VOC concentration rebound may be the result of one or more factors, including: (1) <br /> preferential vapor transport through relatively permeable soil and subsequent re- <br /> 6 <br />