Remediation Technologies / Dual Phase Extraction (DPE)

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:

• Simultaneous abstraction of soil vapour and groundwater;
• Development of a cone of depression(and associated minor cone of ascension) and exposure of the capillary fringe (smear zone) to Vacuum Extraction;
• Mass transfer of VOCs from the liquid to the gaseous phase, particularly those with a high vapour pressure. In excess of 90% of the dissolved-phase VOCs is often air stripped (depending on the compounds) within the riser and pipe-work. In some cases, above ground treatment of the abstracted groundwater will not be necessary;
• Enhanced in-situ bio-degradation through oxygenation;
• Potentially significantly accelerated remediation of the soil and groundwater

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.