Soil vapor extraction (SVE) has become a common, effective method to remediate soils contaminated by volatile organic compounds (VOCs). The technology induces a soil gas flow through the vadose zone, which extracts VOCs into the soil gas being extracted. The Dual-Phase Vacuum Extraction (DVE) system uses a high vacuum source to extract both soil gas and ground water from the same extraction well. The creation of a two-phase flow in the extraction piping eliminates the need for a separate pumping system for ground-water recovery. The high vacuum can also induce a higher recovery of ground water than typical downhole pumping methods can provide.
An Air Force Base (AFB) site, located in the United States, previously used an underground storage tank to contain waste solvents, primarily methylene chloride and perchloroethylene, from paint stripping and application operations prior to disposal. Leakage from the tank system resulted in subsurface soils and ground water with elevated levels of these chlorinated solvents. The soils at the site consist of silty clays and clayey silts with low permeabilities. The DVE system was pilot-tested to evaluate performances for site remediation.
Two extraction wells were tested separately. The average soil gas extraction rate per well was 1.05 m3 per minute with radius of influence of 10.7 m. For ground water, the average recovery rate per well was 3 L/min with a radius of influence of 23.2 m. These radii influences were significantly higher than those estimated for traditional soil vapor extraction or ground-water removal technologies. Removal rates ranged from 11.4 kg/day for an area with high levels of VOCs to 2.3 kg/day for an area with lower levels of VOCs.