The process of Enhanced Reductive Dechlorination (ERD) for the biological degradation of chlorinated compounds, is now a widely used and proven in situ remediation approach. Nevertheless, ERD is often used only as a ‘polishing step’ of the plume, rather than a stand-alone primary remediation technology.
In our experience, the potential of ERD is much more powerful than a final stage to address residual dissolved phase contamination. In many cases, it is the only viable remediation option available when site conditions are difficult, as was the case at this an active industrial site located at an airport in the Southwest of France.
After a successful pilot test, full-scale application using a single injection of REGENESIS’ controlled-release electron donor 3-D Microemulsion (3DMe) into 70 injection points. ‘Top-down’ direct-push injections were used to provide a targeted vertical distribution of the electron donor.
The injection work was carried out in 3 weeks total, spread over 2 campaigns:
In the downgradient plume area, an excellent reduction of the parent compound TCE can be observed: for example the areas around Pz3, PzA and well Pz10 shown in the graphs below. The graphs show the sequential formation and degradation of the daughter products DCE and VC, which then decrease showing that full reductive dechlorination is occurring.
In the Source Area, rapid degradation can be observed in the first months after the pilot test, followed by a slight fluctuation of concentrations at lower level until the full scale application was completed.Following the full scale injection, TCE is rapidly reduced and maintained at a low concentrations. The daughter product DCE can be observed increasing and following the degradation of TCE in the mobile porosity. The DCE concentration presently remains slightly elevated, but not increasing.
As full ERD is occurring, this suggests an in flux of parent compound that is being rapidly degraded (TCE breaks down more quickly than cis-1,2DCE). It is thought that this is occurring through back-diffusion of residual dissolved phase contamination in the over-lying clay (immobile porosity). Due to the longevity of the treatment provided by the 3DMe (4-5 years), the residual mass diffusing out of the immobile porosity will continue to be treated until it is completely depleted