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Dual Phase Vacuum Extraction

In this process extraction wells are installed below the water table into saturated ground. A strong vacuum is then applied through the wells.

DPVE relies on the application of strong vacuums and high flows in the subsurface to entrain and recover total fluids and vapours. It’s most common application is for the recovery of mobile LNAPL contamination and/or grossly impacted groundwater and vapours within the saturated zone in and around the smear zone. The combination of vacuum forces and abstraction make this technique more effective than ‘Pump and Treat’. However due consideration of its effectiveness needs to be considered in less permeable geology, where targeting viscous LNAPL or at sites impacted with DNAPL’s.

Churngold offers two different DPVE approaches. The first uses high vacuum pumps, which are connected to specially designed lances installed close to the water table within vertical wells installed across the impacted zone. The strong vacuum forces and high flow generated at the lance tip, in simplest terms, suck up groundwater and/or LNAPL, pushing them through the lance to an above ground treatment plant. The vacuum also acts to create a pressure gradient that draws surrounding contamination, particularly LNAPL, towards the extraction point.

The second method uses a ‘two pump’ system, a high vacuum pump linked to a series of down-well pumps. The high vacuum and high flow generated by the vacuum pump act as already described, drawing contamination into the extraction point, where the down-well pumps continually recover it.

The above ground treatment plant design is similar to that described in the ‘Pump and Treat’ Section. However additional separation plant is required to separate recovered vapours and total fluids. It is also recommended that additional process control be used to maintain safe operation, including the use of meters to detect potentially explosive atmospheres within the system. If the risk of explosive atmospheres is of concern Churngold has built and operated a number of appropriately rated ATEX systems.