A3.10.6.5 Containment Options
Containment technologies are used to contain the pollutant, therefore eliminating the source.
Low Permeability Cut-Off Walls
Low permeability cut-off walls or diversions are installed below ground. They are used to contain, capture, or redirect groundwater flow in the vicinity of a contaminated site. The types of barriers are soil-bentonite slurry walls, cement-bentonite slurry walls, grouted barriers, and sheet piling cut-offs.
A slurry wall is the most common and least costly technique. The walls are constructed in a vertical trench. Soil bentonite and cement bentonite are amongst the types of materials used to backfill the slurry trench. Grouting occurs when a particular fluid is injected into a soil mass to reduce water flow and strengthen the formation. Sheet piling cut-offs use wood, steel, or precast concrete.
Barrier technologies may be used in advance of other remedial activities. The use of cut-off walls to contain groundwater contamination close to the source, for example, can reduce drastically the pump-and-treat groundwater cleanup time by cutting pumping needs by as much as 90%.
Capping Systems
Impermeable membranes and clay materials can be used to physically contain contaminated materials.
Sub surface Drainage
Subsurface drains refer to any type of buried conduit used to convey and collect aqueous discharges by gravity flow. The discharge collection is performed by a sump, which is installed as part of the system. Treatment would be with carbon adsorption and air stripping.
Groundwater Pumping
Groundwater pumping is used to manage the groundwater to contain or remove a plume, or to adjust groundwater levels to prevent the formation of a plume.
Pump-and-treat systems are widely used in site remediation and are effective for containing contaminant plumes and removing contaminant mass. The methods use one or more extraction wells.
The groundwater removed during pumping is treated at the surface and discharged. The discharge may occur either to a point where it does not supply any recharge to the aquifer, or to a point in the aquifer itself where it does not influence the velocity field around the pumping wells or enhances natural biodegradation.