In-situ techniques are mainly used where the ground water is contaminated, the excavation of soil is impractical or uneconomic and can be widely applied to treat a range of contaminants.
Non Aqueous Phase Liquid (NAPL) Recovery is where light non-aqueous contaminants such as Petrol & Kerosene which are less dense than water, accumulate at the top of an aquifer and dense non-aqueous contaminants such as Creosote, Coal Tars, Polychlorinated Biphenyls and Chlorinated solvents sink until they are stopped by an impermeable layer. The sustainable removal of these separate phase liquids is often required until a residual, immobile fraction remains. Recovery can be carried out as a standalone process or a part of a multi treatment application.Pump and Treat process plant utilise a number of methods for the removal of contaminated groundwater. Following its extraction, the groundwater can be treated in a variety of ways which are tailored to suit the requirements of the specific site and contaminants.
Chemical Oxidation is a technique that we have used to reduce dissolved concentrations of contaminants, where there is low risk of rebound from residual sources. The technique involves injection of chemical oxidants and often a chemical activator into the ground to chemically destroy the contaminants of concern.
Multi-phase Extraction or the ‘bio-slurping’ technique removes groundwater oils and volatile contaminants from ground water and soil by inserting an adjustable length of tube into a well. This is then connected to a vacuum pump, which ‘sucks up’ the contaminants along with groundwater, this in turn creating a vacuum induced negative pressure zone resulting in a flow to the well. Once the water level is reduced, the tube begins to draw in and extract the vapours. This removal of vapours promotes air movement through the unsaturated zone, increasing oxygen content and enhancing biological activity.
Soil Vapour Extraction is for the removal of organic pollution from the soil area between the surface and the groundwater by creating a localised vacuum via wells drilled into the ground, similar to the above technique, extracting the air and vapour which is then treated at the surface. It is very useful for highly volatile contaminants such as petrol.
Permeable Reactive Barriers (PRBs) do not treat the source of contamination but run from the surface of the ground down to an impermeable underground layer, to trap groundwater against it. This can then be filtered through controlled areas in the barrier at a set rate to clean out any contaminants.
A full investigation is made of the site, tests are carried out and detailed groundwater modelling used to identify if the barrier is the most efficient and effective method of treatment in the time required.
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