## 3 Materials and Methods
### Chemical, Physical, and Geotechnical Characterization of Contaminated Soil
The decree sets two different limits: one for the contamination threshold concentration in soil, subsoil, and groundwater for sites intended for public green spaces, private use, and residential areas (indicated by letter a in the table), and another for sites designated for commercial and industrial use (indicated by letter b in the table). For SOIL1, the values of arsenic and hexavalent chromium are below the threshold limits, for both designated purposes, indicating relatively low contamination. However, soil samples SOIL3, SOIL4, SOIL5, and SOIL6 show concerning levels of arsenic and hexavalent chromium, with values exceeding the established limits, indicating significant contamination. These results highlight the need for remediation and monitoring interventions to mitigate environmental and health risks. In particular, arsenic intake can cause gastrointestinal issues, severe skin damage, and lung cancer. Its mechanism of action is typical of metals, as it binds to sulfur-containing enzymes, inhibiting their proper function. Since arsenic forms stable covalent bonds with carbon, it undergoes partial methylation in the liver, reducing its toxicity. In this methylated form, it can no longer bind to enzymes and is excreted through urine. Instead, chromium is known to be associated with sensitizing effects, such as allergic contact dermatitis. The evaluation of the leachability of the samples was carried out using the following methods, in accordance with the UNI EN 12457-2 standard [60]:  
* The pH-dependent leaching test, which determines the mobilization of elements as a function of pH. * A percolation leaching test, which simulates the behavior of percolation. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Contaminant** & **Unit** & **SOIL1** & **SOIL2** & **SOIL3** & **SOIL4** & **SOIL5** & **SOIL6** & **a** & **b** \\ \hline Arsenic & mg/kg dry & 2.2 & 67 & 55 & 58.6 & 69.4 & 68.3 & 20 & 50 \\ Hexavalent chromium & mg/kg dry & 0.5 & 0.5 & 16.7 & 25.3 & 28.9 & 28.4 & 2 & 15 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Contaminant quantities above limit in soil analysis. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Parameter** & **SOIL 1** & **SOIL 2** & **SOIL 3** & **SOIL 4** & **SOIL 5** & **SOIL 6** \\ \hline Uniformity & 55.5 & 52.6 & 29.4 & 17.4 & 23.5 & 47.3 \\ coefficient of & 2.68 & 2.10 & 0.4 & 0.53 & 0.53 & 3.1 \\ curvature (\(C_{c}\)) & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Uniformity coefficient and coefficient of curvature of the analyzed soil. * A dynamic leaching test for monolithic materials or materials that behave like monoliths in their application. This method addresses the surface phenomena relevant to these materials. To quantify the potential release of chloride, sulfate, and heavy metals (HMs) from the stabilized aggregates, the leaching tests were performed with a single-washing step of 24 h and a liquid-to-solid ratio of 10. After the tests, the aggregates were separated from the leaching solution and dried at 105 \({}^{\circ}\)C for weight determination to assess any mass loss. To ensure the reliability of the results and compliance with internationally standardized methods, the leaching tests followed recognized industry protocols. Specifically, methods outlined by APAT CNR IRSA were followed for parameters such as nitrates, chlorides, and chemical oxygen demand (COD). The same APAT CNR IRSA procedure was adopted for the analysis of fluorides, sulfates, and zinc. For the determination of metals and metalloids like barium, copper, zinc, arsenic, and cadmium, the international method UNI EN ISO 17294-2:2016 [61] was applied. Cyanides were analyzed following EPA methods 9010C and 9213, widely recognized in environmental studies. Asbestos analysis was carried out according to the Italian Ministerial Decree (M.D. 06/09/94), ensuring adherence to national regulations.