Environmental Engineering Reference
In-Depth Information
Figure 15.7b.
Flow parallel to contaminated zone (Cg = gas phase concentration) [JOH 90]
Figure 15.7c.
Flow below contaminated zone [JOH 90]
The vacuum extraction system operates under the principle that the organic
compounds contained in the petrol products can be evaporated at temperatures that
typically occur in the soil. The concept is largely based on Henry's law since
evaporation forms the base of the system. Petrol products in the unsaturated zone
exist in the vapor phase, in the dissolved phase (in interstitial water), in the liquid
phase or in the non-aqueous phase, and in the adsorbed phase. The system is thus
based on two mechanisms:
− fresh air injection in the unsaturated zone to evaporate the dissolved phase
(liquid) and hydrocarbons adsorbed with the vapor phase (mass transfer);
− displacement of the vapor via the winding shaft (suction phenomenon) occurs.
Thus the success of the technique depends on the volatility of the contaminant and
permeability of the ground to the air.
