Partial source treatment by in-situ technologies — a review of limits, advantages and challenges

Removal of contaminant sources or associated residual free phase pools often suffers from a combination of inefficiency, increased risk of contaminant spreading due to uncontrolled mobilization, and/or high treatment costs. The paper gives a brief overview of results from laboratory and field studies where chemical and biochemical in-situ source control actions are evaluated with respect to their efficiency on changes of source emission. The studies focused on the contaminant group of chlorinated ethenes. Chemical approaches aim to mobilize contaminant phases. By now these studies have been mainly executed in the laboratory and only few pilotscale field studies exist. The results indicate large emission rates at the beginning of the phase displacement but give less information on long-term emission rates. Biostimulation and bioaugmentation approaches revealed increased emission on short time scales and accumulation of cis- Dichloroethylene and Vinylchloride due to incomplete degradation of higher chlorinated solvents in the source zone. On long-term scales emission rates decreased and groundwater plumes were shrinking.