Double cased screen

Air/water phase separation takes place in the DMF in order to avoid drying of the subsurface. By accurately positioning the DMF it is possible to obtain the necessary air-lift velocity to remove dense soil air charged with contaminants from the bottom of the well. Since contaminant concentrations often reach a maximum within the capillary zone, the Double-Cased Screen is normally placed within this area.
Due to laminar flow generated when extracting soil air via a DMF, this venting process can also be applied in less permeable soil using negative pressures between 40 and 80 millibars within the screened segment. In practice, the use of Double-Cased Screens as part of a Vacuum Vapor Extraction system results in a significant increase in the effectiveness and efficiency of the soil air ventilation process.

• system capable of seperating different phases (e.g. air/water/LNAPL)
• no clogging of screen due to special design of casing material (ca. 60% open filter space)
• SAV-system needs less total energy
• maximal utilization of the adsorptive capacity of activated carbon filter
• increase in the percentage removal of the pollutants from the subsoil
• inclusion of the capillary fringe in the remediation process
• larger radius of effectiveness
• fewer ventilation wells required
• conditioning of the withdrawn air is not required
• lower investment and operating costs
• reduction in the total remediation time
• minimum air-lift velocity for contaminated soil gas is attainable

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