## 4 Results and Discussion
### Hydrochemical Surveys and Water Quality  
The most relevant physicochemical parameter indicators of the main inorganic contamination processes, caused by ICCE in the groundwater from the topmost layers of the Aveiro Quaternary aquifer system (i.e., the unconfined aquifer), are shown in Table 2. As observed, mean and median values for the analysed parameters were considerable higher in the 2007 sampling campaign than in the others. The exception was pH, which exhibited a slight decrease in the 2007 campaign. It should be noted that the 2007 campaign also showed the highest data variation for several parameters such as pH (4.4-10.1), electrical conductivity (EC; 50-26,800 uS cm\({}^{-1}\)), Cl (8-14,840 mg L\({}^{-1}\)), Na (6.1-10,600 mg L\({}^{-1}\)), and Fe (10-167,000 uS cm\({}^{-1}\)). Sulphate was the exception, showing an increase over the study period, with a maximum value (3037 mg L\({}^{-1}\)) in the 2016 campaign (Table 2). In general, the first campaign (1989) showed the lowest mean electrical conductivity value (574 uS cm\({}^{-1}\)), as well as the lowest concentration of the analysed ions (Cl\({}^{-}\) 89.65 mg L\({}^{-1}\); SO\({}_{4}\)2\({}^{-}\) 82.53 mg L\({}^{-1}\); and Na\({}^{+}\) 56.0 mg L\({}^{-1}\)). However, for Fe the highest mean value (9922.6 uS L\({}^{-1}\)) was recorded in the 2007 campaign. For the 1989 and 2016 campaigns, the mean and median pH values were almost the same (Table 2). As expected, the EC and concentration variations of the analysed parameters were positively correlated, while pH values were inversely correlated. In addition, the temporal evolution of these parameters was in accordance with that obtained in the geophysical \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Parameter** & \
\begin{tabular}{c} **Campaign** \\ **Year** \\ \end{tabular} & **Unit** & **Minimum** & **Mean** & **Median** & **Maximum** &
\begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} & **Samples** \\ \hline \multirow{3}{*}{**EC**} & 1989 & & 143 & 574 & 470 & 1785 & 350 & 60 \\  & 2007 & \(\mu\)S cm\({}^{-1}\) & 50 & 3849 & 1102 & 26,800 & 5812 & 34 \\  & 2016 & & 102 & 1687 & 613 & 13230 & 3087 & 32 \\ \hline \multirow{3}{*}{**pH**} & 1989 & & 3.8 & 6.0 & 6.2 & 7.3 & 0.69 & 60 \\  & 2007 & & 4.4 & 5.5 & 5.3 & 10.1 & 1.04 & 34 \\  & 2016 & & 3.5 & 6.0 & 6.3 & 7.8 & 0.97 & 32 \\ \hline \multirow{3}{*}{**CI**} & 1989 & & 17 & 89.65 & 67.5 & 237 & 59.88 & 60 \\  & 2007 & mg L\({}^{-1}\) & 8 & 1268.28 & 183.0 & 14,840 & 2735.06 & 34 \\  & 2016 & & 17 & 387.44 & 72.6 & 2903 & 851.20 & 32 \\ \hline \multirow{3}{*}{**SO\({}_{4}\)**} & 1989 & & 10 & 82.53 & 69.0 & 297 & 56.20 & 60 \\  & 2007 & mg L\({}^{-1}\) & 15 & 364.07 & 147.0 & 2130 & 507.06 & 34 \\  & 2016 & & 13 & 232.88 & 60.5 & 3037 & 567.26 & 32 \\ \hline \multirow{3}{*}{**Na**} & 1989 & & 8.0 & 56.0 & 46.0 & 145 & 38.4 & 60 \\  & 2007 & mg L\({}^{-1}\) & 6.1 & 920.5 & 146.5 & 10,600.0 & 1984.7 & 34 \\  & 2016 & & 13.9 & 288.5 & 72.0 & 2366.8 & 615.3 & 32 \\ \hline \multirow{3}{*}{**Fe**} & 1989 & & 65.0 & 592.6 & 162.5 & 11,000.0 & 1609.9 & 60 \\  & 2007 & \(\mu\)S L\({}^{-1}\) & 10.0 & 9922.6 & 960.0 & 167,000.0 & 29,047.8 & 34 \\ \cline{1-1}  & 2016 & & 3.6 & 144.3 & 21.0 & 1458.9 & 343.3 & 32 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: For the selected periods (1989, 2007, and 2016), summary of statistics for analytical data and groundwater samples in the study area. surveys, which showed a substantial increase in the spread of contamination in the period of 2001-2006, and a general attenuation of electrical conductivity from then onwards.