Multi-Phase Extraction

The Process

Multi-phase extraction (MPE), also known as dual-phase, two-phase, or vacuum-enhanced extraction, is an innovative soil and groundwater remediation process that combines the benefits of soil vapor extraction (SVE) with those of groundwater pump-and-treat. During MPE extraction, high vacuums are applied to sealed extraction wells that are screened within the vertical zone of interest. Liquid and gaseous phases of contaminants are removed from the well through a single conduit for ex situ treatment and disposal. Alternatively, some variations of MPE use an additional in-well pump for removal of liquid phases.

The Hardware

MPE systems typically use a liquid-ring pump (LRP) to produce vacuums as high as 28" Hg whereas the rotary blowers used on soil vapor extraction (SVE) systems produce a vacuum of about half that amount. The high vacuum produced by the LRP, which is routed to extraction wells via piping, effectively pulls contaminants within the saturated and unsaturated zones of the aquifer towards the well for collection. MPE is especially effective in clay when compared to conventional SVE.

The high vacuum produced by the LRP also effects better removal of heavier petroleum constituents (higher molecular weight) as the lower relative atmospheric pressure reduces the temperature at which these compounds volatilize. Once in vapor form, these heavier contaminants are much more readily removed from the subsurface.

Drop-tubes, also known as stingers or straws, are typically used in the wells to place the point of extraction below the ambient groundwater surface to create a cone of depression around the well. Floating contaminants are drawn into the cone of depression, and the well, by gravity and advection. Drop tubes also allow water to be raised from depths exceeding 30 ft. below grade.

Contaminant removal is initiated in the drop-tubes within the well as contaminants present within the water that is entrained within the extracted air stream volatilize. Further treatment occurs within the air-water and oil-water separators and the air stripper within the MPE trailer.

The Results

Application of MPE results in faster cleanup times at comparable costs when compared to conventional methods of remediation. All required equipment can usually be housed in one 16 ft. trailer. After treatment within the MPE trailer, extracted water is usually clean enough for reintroduction to the subsurface.

EEI has successfully applied MPE technology at over 20 sites. Petroleum compounds are most frequently targeted but MPE has also been demonstrated for removal of chlorinated compounds such as TCE.