Ground Remediation Systems Ltd

Where hydraulic control is required and/or a cone of depression is required to mobilise LNAPL towards the well and where hydraulic conductivity/permeability is relatively low it is frequently more practical and cost effective to abstract both groundwater and LNAPL together and to separate the LNAPL above ground using an oil/water separator.

A principal advantage of total fluids abstraction is that relatively small diameter wells such as 4"/100mm can be used instead of the generally 8"/200mm id wells required for a dual-pump arrangement of a submersible pump and skimmer pump within the same borehole.

A range of different total fluids abstraction technologies can be employed including:

1. Submersible, top filling pneumatic controllerless displacement pumps;
2. Self priming surface mounted centrifugal pumps;
3. Pneumatic or electric diaphragm pumps;
4. High Vacuum, Multi-Phase Extraction

1. Pneumatic controllerless pumps can operate at substantial depths but have a limited abstraction rate of typically up to 1 to 2m3/hr. These pumps are tried and tested, reliable and robust and extremely simple to install and operate. Bottom filling pneumatic pumps can also be used for DNAPL recovery
2. The self priming surface mounted centrifugal pumps are limited by a maximum suction lift of 6 to 7 metres and can emulsify some LNAPLS in the water, however, compared to the Pneumatic Controllerless pumps they are more cost effective.
3. Diaphragm pumps are also limited by the maximum suction lift of 6 to 7 metres and are require a higher maintenance level. Conversely these pumps work well connected to an automated manifold switching from 1, 2, 3 or 4 wells in sequence for example. They tend not to cause emulsifications.
4. High vacuum multi-phase extraction is an extremely versatile approach and, contrary to popular opinion, can operate at substantial depths well in excess of the 9 or 10 bar that a straight vacuum can achieve. Multi-phase extraction is also especially suitable for DNAPL recovery.