High-performance purging with portable MPE unit

Multi-phase extraction of free product where conventional purging falls short

Manual or bailer purging is slow and inefficient when free product (LNAPL) has accumulated in the piezometer: it recovers little product per visit and barely induces flow from around the screen. At SOILUTIONS we use our portable high-vacuum unit – the same one we use for SVE efficiency tests – to carry out high-performance purging by multi-phase extraction (MPE), combining free product extraction and drawdown of the piezometric level in a single unit.

Methodology

• Vacuum extraction: a single probe applies vacuum to the piezometer, simultaneously extracting free product, water and air from inside the screen and its immediate surroundings.
• Induced drawdown: the vacuum depresses the water level around the point, mobilising product adhering to the borehole walls and the nearby ground that a bailer never reaches.
• High yield per visit: a greater volume of free product is recovered in each intervention than with passive purging, reducing the number of visits needed to deplete the free product thickness.
• Portable unit: being van-mounted, it is deployed directly over the piezometer without civil works or heavy machinery, allowing several points in a network to be treated on the same day.

Scope

Applicable to investigation and monitoring piezometers with measurable free product, as a complement or alternative to periodic manual purging, and can be combined with our own SVE efficiency tests at the same point.

Why it is necessary

A piezometer with untreated free product is an active source of contamination and a point that counts against any monitoring file. High-performance purging speeds up product recovery, reduces the number of campaigns needed and provides flow rate and extracted volume data that are useful for sizing a future active recovery phase.