## 4 Results and Discussion
### Geophysical Survey
#### 4.1.2 Temporal Variation of Conductivity in the Area  
Considering that seasonal changes in the geophysical data are not significant for the EM34 geometry used, the spatial variations of electrical conductivity for the area in the vicinity of ICCE were compared for 2001, 2006, and 2016 (Figure 4) regardless of the period of the year the measurements were taken. As observed, for all the periods considered, the highest conductivity values were found near the ICCE with an overall gentle decrease as the distance from this site increases. In general, these values distribution over the area replicate the main groundwater flow paths (i.e., E-W and E-SW). Figure 3: **(A)** Location of profiles 1 and 2 (map coordinates: UTM; WGS84—29N zone); **(B)** Seasonal variation of electrical conductivity in profiles 1 and 2 in the dry (September) and wet (February) season of 2016 (HF—horizontal fields; VF—vertical fields). Figure 4: Electrical conductivity maps from 2001, 2006, and 2016 obtained through electromagnetic (EM34) methods. (HF—horizontal fields on the left; VF—vertical fields on the right). Map coordinates: UTM; WGS84—29N zone. In addition, data measured with vertical coils (referring to shallower investigation depths, corresponding to the unsaturated and saturated zones of the unconfined aquifer) and data obtained with horizontal coils (reaching deeper depths of the unconfined and semi-confined aquifers) showed similar locations for the main electrical conductivity hotspots (Figure 4). Thus, the most important hotspots were located: (a) in the vicinity of the mud dam (Figure 4, area A), at first to the southwest (maps representing 2001 data), and then to the west and south; (b) the region to the east of the Veiros pond (Figure 4, area B on the maps from 2006 and 2016), whose anomaly later extends to the east, towards the anomaly of the mud dam generating a large contaminated area; (c) anomalies located near the ditches that carried effluents away from the ICCE, (Figure 4, area C on the bottom maps); and (d) a linear anomaly to the south, located over the expected position of an old buried pipe also used to carry effluents away from the ICCE (Figure 4, area D on the maps representing data from 2016). Another important feature on the maps of Figure 4 is the low intensity anomaly just to the west of the sealed landfill. This anomaly is very weak in the earlier maps, but increases in intensity in the central maps (Figure 4, area E on the 2006 maps). Afterwards, this anomaly showed an evident decrease, both in intensity and spatially, proving the efficiency of the remediation works. The differences in the hotspots for vertical coils (Figure 4; maps on the left) and horizontal coils (Figure 4; maps on the right), mostly refer to the intensity values. The horizontal fields showed lower conductivity values due to the greater relative representation that the non-saturated zone has at the depths reached by the vertical coils. Notwithstanding, both HF and VF maps showed that the unconfined and the semi-confined aquifers were impacted, which was particularly evident in the measurements for 2006 and 2016, and clearly revealed the extension and evolution of the contamination plume, providing a general qualitative image of the impacts near the ICCE. From 2006 onwards, data revealed remarkably high conductivity values just to the east of the Veiros pond, which were not observed in 2001, and thus must correspond to some event that subsequently occurred. As several remediation actions took place and industrial processes altered over time, it is necessary to investigate the effects, if any, of these measures in the contamination process of the area. The information provided by the maps in Figure 4 is qualitative and reveals contaminated areas, hotspots, and their general geographic extension. However, it is difficult to extract quantitative information concerning contamination spread. Therefore, further data analysis is required if detailed information on preferential paths, velocities, and contamination spread are to be obtained.