## 3 Results and Discussion
### Full-scale intervention  
The results obtained during the experiment supported a definitive design choice for the full-scale intervention, determined the remediation of the identified contamination areas, and allowed achievement of the objectives and closure of the project. The following graphs illustrate the results of post-treatment monitoring of some piezometers installed in the four intervention areas for a period of two years. The first series of graphs refer to the pilot test area. The graphs show a reduction in chlorinated solvents detected after full-scale intervention in shallow aquifer below the threshold limits (CSC) established by Italian law (Figure 10). The tendency of CAH concentrations showed a reduction to nondetectable levels within only a few weeks from application. The evolution of the concentrations of chlorinated solvents measured in some piezometers that intercepted the intermediate aquifer in intervention areas 2 and 3 are shown in Figure 11 (see Figure 8 for identifica  
Figure 10: Concentrations of (**a**) 1,2 dichloroethene (1,2-DCE) and (**b**) 1,2-dichloropropane detected in a piezometer installed in the pilot test area. The post-intervention scenario shows a clear improvement in the state of water contamination. The concentrations detected across the piezometric network after the full-scale intervention are clearly below the remediation objectives. The parent compounds (PCE and TCE) and daughter compound (DCE) [29; 30] exhibited reductions of one order of magnitude within the first month. With regard to the concentration detected in the shallow aquifer in the last area of intervention (area 4, see Figure 8), a sequential increase of DCE and vinyl chloride was observed in subsequent monitoring data (Figure 12). Figure 11: Concentration trend of chlorinated solvents measured in the intervention (**a**,**b**) area 2 and (**c**,**d**) area 3. The last intervention area is located upstream of the railway station from a hydrogeological point of view. The increment of PCE and TCE concentration in the post-excavation phases shows that chlorinated solvents entered from areas outside the site. The injection of reagents reduced the concentration of compounds with higher numbers of chlorine atoms. The increase of DCE and VC after the injection indicates that solvent degradation proceeded without limitation despite the significant reduction of parent compounds in the aqueous phase [29; 30]. Under anaerobic conditions, accumulation of cis-DCE or vinyl chloride (VC) is often observed at CAH contaminated sites [60]. Hydrogen atoms replace chlorine atoms one after the other, resulting in the typical dechlorination sequence from PCE via TCE, cis-DCE, and VC, down to ethane. The rate of reductive dechlorination decreases with the decreasing number of chloroatoms, causing an accumulation of cis-DCE or VC [60]. Compounds with a higher degree of chlorination, such as PCE and TCE, were detected at lower concentrations, presenting intense biological dechlorizing activity after the injections. Previous studies underlined that unanswered questions remain regarding the effectiveness of activated carbon-based amendments, given the lack of both field data and evidence of a biodegradation process [10]. The results obtained in the last intervention area (Figure 12) clearly highlight the occurrence and persistence of biodegradation. A combined injection of PlumeStop(tm) and HRC(tm) into groundwater represents an innovative remediation operation, the first of its kind to be realized on a large scale in European territory. Intervention monitoring played a fundamental role in validating the performance of the implemented remediation strategy. The reduction of CAH concentration below CSC limits is evidence of the effectiveness of the adopted remediation technology for abatement of chlorinated solvents, through the combined action of contaminant absorption and biodegradation processes.