The remediation of a chlorinated hydrocarbons (CHC) contaminated aquifer always contains a risk, because of the possibility of uncontrolled downwards mobilization of the CHC into deeper parts of the aquifer. This scenario would be even more harmful to the environment. The application of well known remediation techniques for CHC as e. g. pump-and-treat is not useful because of its extremely long duration caused by the low solubility of CHC.
The topic of the present study was the investigation of a new hydraulically controlled and site-directed in-situ remediation technique for CHC. This new technology is a combination of the techniques of alcohol flushing and the groundwater circulation well (GCW). The combination of these two is highly promising concerning the controlled mobilisation and the site-directed remediation. The circulation flow field of the GCW is used for the hydraulic control of the flow regime and for the effective and site-directed regulation of the mass transport. The alcohol flushing uses the favourable chemical and physical properties of the alcohol to make the organic contaminant more soluble.
The work presented aims at determining the hydraulic boundaries, which allow the hydraulically controlled regulated water-alcohol-circulation (WAC), limited to two dimensions for the selective CHC-remediation, with the help of a GCW. For this purpose for the GCW an injection and extraction unit was developed, each of which consisted of different chambers.
For the hydraulically controlled WAC a theory was evolved based mathematically on a potential approximation of the flow problem with buoyancy effects caused by the simultaneous flow of water and alcohol. As the central results of this theory:
- a stability-diagram specified over ratios of dimensionless Gravitational-Numbers was established. The Gravitational-Number physically describes the ratio of friction to gravitational force and in consideration of density differences the ratio of friction to buoyancy force.
- the derivation of required pressure differences, which occur at the dividing plates between the different sections of the GCW injection filter control of the WAC.
In the stability-diagram, stable and instable regions could be identified for a buoyancy pressure influenced layer caused by a special injection of the alcohol. In several two dimensional experiments with confined homogenous aquifer conditions the stability-diagram as well as the hydraulically controlled WAC on the basis of the relevant pressure differences could be established.
Two remediation experiments with the CHC Perchlorethylene (PCE) as artificial contaminant demonstrated conclusively the complete remediation of a sand lens.