Dual-phase extraction is an established technique for the simultaneous extraction of contaminated groundwater and soil vapour. More commonly used in silty or clayey soils, where a higher vacuum is required, the technique obviates the need for submersible pumps. High vacuum soil vapour extraction improves the feasibility of soil vapour extraction in lower permeability soils. The deeper vacuum increases the radius of influence and the mass transfer of volatile contaminants. The technique offers the following advantages over other conventional remediation techniques:
It is frequently believed that dual-phase or multi-phase extraction is limited by depth. This is because a vacuum can inherently not exceed -1 bar (equivalent of circa 10m). In other words, a vacuum cannot lift the water-table in a well by more than 10 metres. However, Dual/multi-phase extraction can in fact remove liquids from depths far exceeding 10 metres by air entrainment of the liquids.