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improper flow balancing or blower design, water table upwelling, or unexpected stratigraphy <br /> Consider replacing wells, adding wells, rebalancing the air flows in the system, controlling <br /> groundwater levels, or resizing the blower <br /> h) Is there evidence that contaminant vapors have escaped containment by the SVE system? <br /> This may be due to inadequate flow from certain wells to create proper capture zones, prolonged <br /> system shutdown, preferred airflow pathways, or other outside sources of contaminants <br /> Consider increasing the extraction rates from selected wells or the entire system, adding wells in <br /> selected areas, reducing downtime, or augmenting SVE with other source removal alternatives <br /> i) If the SVE and off-gas treatment systems are located outside, are there provisions to drain <br /> water lines and sump(s) when the unit is shut down`s Inspect the aboveground systems for proper <br /> insulation and /or heat tracing to prevent rupture of lines due to formation of ice during <br /> operation <br /> 8) Alternatives for Possible Cost Savings <br /> The contaminant compounds remaining in the vadose soils and/or their concentrations may have <br /> changed sufficiently that other alternatives are more cost effective Consider the following <br /> a) Has the system reached its cleanup objectives? Determine if the SVE operation is still <br /> necessary, or have the concentrations decreased so that the operation can be terminated? Can the <br /> off-gas treatment system be taken off line due to decreased levels of contaminants in the vapor <br /> stream? <br /> b) If the cleanup objectives have not yet been met, can the system be turned off and natural <br /> attenuation be allowed to achieve the cleanup objective while remaining protective of human <br /> health and the environment? (Refer to Air Force protocols for evaluating natural attenuation) <br /> c) Can individual wells be removed from the system? Can the above-ground system operate <br /> efficiently at a reduced flow rate? Evaluate the cost savings by reducing the number of wells (In <br /> some cases, the capacity gained by removing non-productive wells may allow higher airflow <br /> rates through more contaminated parts of the site However, the blowers may need to be <br /> adjusted or replaced with different sized units to accommodate changes in airflow/vacuum <br /> requirements) <br /> 06/07/99 <br /> Page 7 of 8 <br />