Quicker Soil and Ground Water Clean Up Remediation of Impacted Sites by Dual-phase Extraction

Historical operations of industrial and above-ground activities have led to releases of contaminants into underlying soils and groundwater. Several in-situ technologies for the cleanup of soils and groundwater at sites impacted by petroleum hydrocarbons or chlorinated solvents are available, including, but not limited to, high-vacuum dual-phase extraction (DPE), soil vapor extraction combined with groundwater pumping or air-sparging, soil excavation and offsite disposal followed by groundwater pumping or in-situ groundwater treatment, and thermal injection or electrical resistance heating. Many technologies treat impacted soils or groundwater, but not both.

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High-vacuum DPE systems are desirable where fast clean-ups at the source area where leakage occurred (such as leaking underground storage tanks) are needed. High-vacuum DPE systems are suitable for sites where contamination is present in both the soils (vadose) and groundwater (saturated) zones, and where the soils are lower in permeability which require a higher vacuum. DPE systems are energy-intensive, but are particularly effective for source removal, addressing contaminants at the soil/water interface (capillary fringe) and in lower-permeability and heterogeneous zones. During DPE, the groundwater table is depressed, creating a cone of depression that exposes the soils at the capillary fringe to vapor extraction. Contaminants stuck at the capillary fringe are thus removed, paving the way for groundwater to be remediated. Mobile DPE systems are typically used where it is not practical to employ a fixed-based system (i.e, offsite wells where significant dissolved-phase contaminants are present).

During DPE, vapors and liquids are extracted from DPE wells installed in contaminated soils and groundwater, using a high-vacuum liquid-ring pump. Vapors are treated by activated carbon adsorption or by thermal/catalytic oxidation and are discharged under a site-specific or various-location permit issued by the local Air Quality Management District. Extracted liquids are typically treated with activated carbon adsorption and then are discharged to the storm drain under an NPDES permit or to the sanitary sewer, or collected in an onsite water storage tank.

Use of DPE systems are ideal at underground storage tank sites where releases of gasoline fuels has occurred. DPE systems are particularly effective in the removal of free product floating on the groundwater. In California, many sites where DPE was employed have received regulatory closure under the State Water Resources Control Board’s Low-Threat Underground Storage Tank Case Closure Policy. DPE is also very useful in removing chlorinated solvent compounds at dry cleaning, aerospace, and other industrial or manufacturing facilities where spills or leaks due to site operations have occurred.  

For questions, please contact Steve Ridenour (steve.ridenour@altaenviron.com) or Mike Cassidy (mike.cassidy@altaenviron.com). We can also be reached by phone at 888-608-3010.