Biorisanamento in situ di sorgenti storiche da DNAPL. Pozzi a ricircolazione per la ottimale distribuzione di donatori di elettroni e mobilizzazione di contaminanti da zone a bassa permeabilità

In this paper, an example, on a full scale and on the Italian territory, of the design and management of an in situ bioremediation intervention and the mobilization of chlorinated solvents, in a historically contaminated industrial site characterized by a complex hydrogeological conformation is reported. In particular, the presence of historical accumulations of chlorinated substances in layers with very limited permeability, with consequent slow back diffusion phenomena, has been addressed with the use of groundwater circulation wells, IEG-GCW®, which allow the mobilization and external treatment of contaminants retained in portions of the aquifer that cannot be attacked with traditional pumping systems. Furthermore, the occurrence of reductive dechlorination phenomena limited by the electron donor deficiency was addressed by using recirculation as a system for their continuous distribution, generated by the fermentation of a biodegradable polymer (PHA). The aim of the work is also to underline the relevance of a 3D hydrogeochemical model for the representation and understanding of the contamination dynamics and decontamination mechanisms in a highly contaminated industrial site. A multi-phase approach was followed allowing the management and release of data during the various phases of remediation, from the characterization of the site, through the conduct of a pilot test, up to full-scale remediation, thus allowing to monitor, analyze and manipulate the information in 4D space-time. Multi-source and multi-temporal scenarios reveal the impact of current hydraulic dynamics and describe the decontamination mechanisms in relation to the interventions implemented over time, quantifying the overall performance of the strategies adopted in terms of reducing the concentrations of contaminants present in groundwater. The results illustrate the effectiveness of the recirculation system in the progressive reduction of the mass of contaminants in the secondary sources identified, both by mobilization of contaminants and by enhancement of the in situ biological reductive dechlorination processes. It also confirms the usefulness in the management of interventions and in the representation of the results of the integrated georeferenced model.