Directed Soil Air Circulation systems (SAC) are employed for the remediation of soils contaminated with volatile hydrocarbons by enhancing the IEG Vacuum Vapor Extraction (IEG-VVE) technique. In addition, they can be used to inject gas into the soil for the stimulation of biological or chemical degradation.

Two screens built into the borehole are separated into an upper and a lower section, each of which is connected to an aboveground blower. This allows for the withdrawal of air from either segment individually or from both simultaneously. The extracted air is re-infiltrated into the soil after passing through a suitable treatment unit (i.e. IEG GAC-Sorb Granular Activated Carbon filter). Horizontal and vertical flow circulation cells are generated in the soil surrounding the extraction well. The circulation direction is reversible and can be adjusted according to the contaminant distribution in the soil.

The SAC-VVE system, in contrast to conventional soil venting methods, is capable of generating a directed circulation through the centre of the contamination. No fresh air is added to the circulation system. Air passing through the blower is heated, thereby enhancing desorption of contaminants adsorbed onto soil particles. This leads to a more effective remediation of the site.

In order to stimulate the biological degradation of contaminants nutrients, in either liquid or gaseous form, can be introduced into the circulation cell. Chemical conversion of toxic substances into harmless and/or immobile material can be achieved insitu by introducing, for example, strongly reactive gases into the soil. If only biodegradable substances are to be removed from the subsoil, a SAC-VVE system (without an above-ground extraction unit) consisting of an axial ventilator in the screened well can be implemented. If the capillary fringe is to be remediated along with the unsaturated zone, it is possible to create a circulation cell directly around the well rinsing the capillary fringe.

This is achieved by a combination of of SAC-VVE and Coaxial Groundwater Circulation-Sparge (CGS-Sparge).

Advantages

• The IEG SAC-VVE system can be operated in clay and silt with a low hydraulic conductivity
• The system needs less energy and less maintenance
• Maximum utilisation of the adsorptive capacity of the IEG GAC-Sorb Granular Activated Carbon filter
• Increase in the percentage removal of pollutants from the subsoil
• Inclusion of the often highly-contaminated capillary fringe zone in the remediation process
• Larger effective radius of treatment
• Lower number of ventilation wells required for the remediation of a specific area
• Reduction in the total remediation time
• Circular flow can be achieved by extracting from the lower or upper point and reinjecting into upper or lower point