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

NATO/CCMS Pilot Project on Contaminated Land and Groundwater (Phase III) January 2002
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The withdrawn air was purified in an air treatment establishment, consisting of following units: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;
• It relocates the problem of the desired quality from a problem of volume to a problem of time. The
final quality of the soil is function of the time period in which the system is applied.
The complete decontamination setting is represented in Figure 2.
4. RESULTS AND EVALUATION
The bioremediation of the unsaturated zone was started in October 1995, after the hot spots had been
excavated and the remaining soil had been mixed with compost and wood flakes. After two months a first
analysis campaign was executed. The results have been visually represented in Figure 3. Further analysis
campaigns were executed after 5 and after 10 months. These results have been represented in Figure 4 and
Figure 5. Based on the visual representation of the horizontal spread of the contamination in the different
figures it has become clear that the bioremediation technique is successful.
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