## 3 Results and Discussion
### Design of Remediation Strategy and Implementation of Pilot Test  
The design of the remediation strategy should consider the specificity of the contaminated site, which can be summarized as follows:  
1. A relatively large area is affected by a low concentration of contaminants. 2. Small masses of chlorinated solvents have to be treated. 3. There is thin and slow groundwater circulation in the shallow aquifer. 4. There are channelized coarse-grained sediments that can act as drains for fluids to be injected into the aquifer. We considered the technological approaches suitable for a situation of widespread contamination with the presence of well-identified higher contamination spots. The potentially applicable technologies fall within the range of in situ interventions, both physical-chemical and biological. The applicability of technologies such as monitored natural attenuation (MNA) and enhanced natural attenuation (ENA) [57] was experimentally verified. Experimentation (not shown here) showed that natural attenuation phenomena do not allow a significant reduction of contaminants in the groundwater. However, the experiments revealed the possibility to accelerate the reductive dechlorination biological process by adding an electron donor [30]. Based on the results, biological reductive dechlorination was recognized as a potential approach for site remediation, but the extremely low chlorinated aliphatic hydrocarbon (CAH) concentration and consequent kinetic limitation made it unfeasible for the site. The possibility of using a dispersed colloidal activated carbon (PlumeStop(tm), Regenesis, San Clemente, CA, USA) was investigated as a site-specific remediation approach [10]. The micrometric carbon is marked by a proprietary surface-charge modification to enable dispersion and can be easily injected into a contaminated aquifer. It creates an in situ adsorption zone that can potentially reduce CAH concentration quickly. Furthermore, it raises the kinetics of the biological reduction by locally increasing the bioavailable CAH concentration at the carbon surface [11]. The technology was co-injected with an electron donor (HRC(tm), Regenesis, San Clemente, CA, USA) to stimulate indigenous bacteria to degrade the chlorinated compounds [12]. The intervention consists of creating an injection front corresponding to some contaminated piezometers. Based on contamination evolution, different areas for the application of PlumeStop(tm) and HRC(tm) were selected (Figure 8). For each area, the characteristics of the aquifers to be treated and the quantities of product to be injected were identified. A multiple injection system was developed for the generation of reactive  
Figure 8: Identification of the pilot test and other intervention areas. zones [10]. Fixed stations allowed the injection of reagents at high pressure, repeated over time and at different depths along the vertical, to use selective dosing corresponding to the most contaminated zones. The treatment stations were customized depending on the type of contamination, the geological sequence, and permeability characteristics. Injections were performed at regular depth intervals, starting from the deeper portions and gradually moving toward the shallower ones, to affect the more permeable layers of the intermediate aquifer (\"isolated\" by an impermeable septum) first, and then the less permeable shallow aquifer. High-pressure injections traced the product's rise along with fractures and preferential flow pathways. Thus, low-pressure injections were performed to facilitate good distribution of the product into the more permeable layers. The multiple injection system was customized depending on local characteristics. For this reason, the pilot test area was investigated in detail. The ERT survey and soil and groundwater sampling confirmed satisfactory dispersion of PlumeStop(tm) during pilot testing. The investigations carried out with Geoprobe penetrometers verified effective diffusion of the product in the shallow aquifer.