Formatted Title
Novel Composite Materials for the In Situ Remediation of Aged Chlorinated Contaminant Plumes
Background/Objectives
The aim of the German research project CONTASORB was the development and field testing of novel composite materials for the in situ decontamination of groundwater contaminated with halogenated organic substances. The focus of the project was laid on the improved long-term stability of known in situ reagents such as Carbo-Iron® and on a trap and treat approach: the coupling of local accumulation of the pollutants by adsorption to suitable sorbents and subsequently the oxidation of these adsorbed pollutants (TrapOx®). One remediation goal was the successful in situ removal of even aged contaminant plumes, in which cis-DCE and VC occur as dominant metabolites.
Approach/Activities
For the corrosion-inhibited Fe(0)-activated carbon-composite Carbo-Iron®, a long-term laboratory test under strongly corrosive conditions showed that only 25% of the iron was consumed within 160 days. At the same time, the product has a high dechlorination rate for TCE and PCE. For cis-DCE and VC, the adsorption of the chlorinated contaminants on Trap-Ox®-zeolites was demonstrated first, followed by the degradation of the adsorbed compounds by a heterogeneous Fenton-like reaction after exposure of the pollutant-laden zeolites to H2O2.
The corrosion-stabilized Carbo-Iron® and the Trap-Ox®-zeolites were field tested in a pilot test at a PCE/TCE-contaminated site in northern Germany. The local, fine-scale hydrodynamics were explored in high resolution using an extensive Intrasense® program. The highest levels of pollution measured at this location were around 31,000 μg/L PCE, values above 10,000 μg/L were still present up to depths of 4.5 m. The aged plume contained high proportions of cis-DCE and VC. Using permanent injection points and direct push injections, two spatially separate injection transects were created to inject the reactive materials into the subsurface across the main downstream direction of the groundwater. The effects of the pilot test were verified by an innovative monitoring program based on CSIA and qPCR analyses as well as hydrogeological investigations in addition to the determination of pollutant concentration, transformation products and hydrogeochemical parameters.
Results/Lessons Learned
The high effectiveness of the newly developed in situ decontamination materials - corrosion-resistant Carbo-Iron® and Trap-Ox®-zeolites - was demonstrated by almost complete reduction in pollutants in the field. The desired reduction in PCE and TCE concentrations downstream of the injection zone was achieved; for cis-DCE, a decrease of about 75% was observed. An increased reduction was also observed for VC. This means that an integrated, effective and complete in situ system is now available for the treatment of aged chlorinated contaminant plumes.