NATO/CCMS Pilot Study Evaluation of Demonstrated and ... - CLU-IN

NATO/CCMS Pilot Project on Contaminated Land and Groundwater (Phase III) January 2001
c) Soil air extraction
The efficiency and the design of the soil air extraction strongly depend on the soil characteristics, as these
have an important effect on the movement and transportation of soil air (gas). The most important
determining soil characteristics are: soil structure, stratigraphy, porosity, grain size, water level, residual
contamination, and presence of macro pores.
The air permeability of the soil represents the effect of these different soil characteristics. The air
permeability indicates to what extent fumes can float through a porous environment.
Air permeability and airflow velocity are linearly dependent. The higher the air permeability and the
airflow velocity, the greater the chances of an effective soil air extraction.
Taking into account that the loamy/clayey unsaturated zone at the van Oss site is heterogeneously built,
the air transportation throughout the soil is prevented and the airflow velocity is relatively small. A
solution to break this heterogeneity was to mix this oil with structure-enhancing additives till the depth of
0.5 m above ground water level. This also enlarged the porosity of the soil, which was favourable for air
transportation.
In order to get a large zone of influence, the placement of horizontal injection and withdrawal drains was
chosen. Placement of drains was performed in layers, the soil mixed with structure-enhancing additives
being completed (Figure 2)
The withdrawn air was purified in an air treatment establishment, consisting of following units:
- Air/water separator and air filter
This separator and filter eliminates soil damp (water) and fine particles that may damage the mechanical
equipment, and might disrupt further air treatment. The water discerned needs to be collected and, if
contaminated, purified.
- Vacuum pump
The vacuum pump causes the suction in the underground. The compression heat in the pump causes a
temperature increase and a corresponding decrease of the relative humidity of the airflow when leaving
the blower.
- Air cleaning unit
The pumped up air was treated by means of biofiltration and active carbon filtration.
- Measure devices
By measuring the different parameters the air treatment and soil air extraction could constantly be
monitored and adjusted.
The above mentioned decontamination concept has a double advantage:
- It avoids transportation of considerable volumes of contaminated soil (approx. 12.000 tons with a
concentration higher than 1000mgkg DM) to an adapted dumping-ground;
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