Possible Areas of Application
The directed soil air circular flow system (BLK) is employed for the remediation of soil contaminated with volatile hydrocarbons. In addition, it can be used to inject gas into the soil for the stimulation of biological or chemical degradation.
System Components
The BLK process consists of a specially adapted vapor extraction well, an above-ground mounted vacuum blower, and a waste air decontamination system, for example disposable filters or regenerative activated carbon filters.
Description of Method
The screens built into the borehole are separated into an upper and a lower section, each of which is connected to the above-ground blower. This allows for the withdrawal of air from either segment individually or from both simultaneously. The air extracted, after passing through a suitable remediation unit (i.e. activated carbon filter), is re-infiltrated into the soil. Horizontal and vertical flow circulations 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.
BLK, in contrast to conventional venting methods, is capable of generating a directed circulation through the center 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.
For stimulating the biological degradation of contaminants, nutrients, in liquid or gas form, can be introduced into the circulation. Chemical conversion of toxic substances into harmless and/or immobile material can be achieved in situ by introducing, for example, strongly reactive gases into the soil.
If only biodegradable substances are to be removed from the subsoil, a BLK system (without an above-ground extraction unit) consisting of an axial ventilator in the screened well can be implemented.
If the capillary fringe should be remediated along with the unsaturated (vadose) zone, it is possible to create a circulation directly around the well rinsing the capillary fringe. This is achieved by a combination of BLK and groundwater ventilation (KGB).
The following advantages can be specified
- The temperature increase in the subsurface causes an increase of the diffusion constant of the contaminants which leads to a faster desorption
- The rise of the temperature also leads to the formation of azeotropic vapor-soil gas mixtures
- Biological degradation processes are further stimulated by maintaining a constant temperature and moisture level in the subsurface
- Adjustment of the circulation pattern according to the contamination to clean up areas with higher contamination levels first
The soil air circular flow system (BLK) is a process patented by IEG Industrie Engineering GmbH, D-72770 Reutlingen, Germany.
