## 3 Results and Discussion
### Radioactivity Parameters of Drinking Water in the Studied Area
By considering only the gross alpha and beta activities, along with the locality, the model was still significant (pseudo-F = 2.1, \(p=0.012\)), but the explained variation was lower, namely, 32.7% (17.3% adjusted). The localities were scattered in the ordination space (Figure 5). Figure 4: The t-value biplots for the radioactivity parameters (radon-222, gross alpha and beta activities) of surface water (Surf) in relation to deep water Deep (**a**) and subsurface water SSurf (**b**). The pink circle delimits the ordination space for significant positive response to the considered variable, while the blue circle marks the negative response. Figure 5: The biplot of redundancy analysis (RDA) relating the gross alpha and beta activity parameters to the localities and the surface (Surf) and groundwater (Ground) sources. The names of localities are written in full. The first two constrained axes are illustrated, but the second axis is not significant. The first ordination axis, which was the only significant one (pseudo-F = 2, \(p\) = 0.012), was given by the opposition between Surf and Ground water sources, with gross alpha and beta activities increasing in localities with Ground water sources. The radioactivity level of Sibiu and other large towns (Cisnadie, Avrig) using Surf water was lowest, while some smaller localities (Aciliu, Tilisca, Sacel) using Ground water, with the exception of Tilisca, showed the highest radioactivity level (Figure 5). Tilisca, which uses Surf water, is close to Aciliu, and the geology of the site may explain the particular radioactivity of this source. In the underground of the Tilisca locality, [PERSON] [60] mentioned the presence of gneiss rocks, exploited as a valuable resource for the construction industry [61]. [PERSON] et al. [46] observed that due to its properties (density, durability, and water absorption capacity), this rock stores many natural radionuclides, including \({}^{226}\)Ra [61; 62], which contributes significantly to the gross alpha activity [63], and \({}^{40}\)K [61], which plays an important role in the gross beta activity [63], also showing a significant positive correlation with \({}^{222}\)Rn abundance [61]. Other rocks described as being associated with high radon levels, especially in groundwater, are granite [62; 64; 65], shale, and phyllite [64]. Thus, the presence of such rock types could contribute to the unexpected high levels of water gross alpha and beta activities from the three localities. Furthermore, in the case of wells, [PERSON] and [PERSON] [66] explained that the way these are used and the type of technical plant of groundwater extraction can influence the amount of radon in the water. Regarding the Aciliu locality, [PERSON] [67] mentioned the frequency of landslides in the Aciliu-Apoldu area, a fact that can be associated with the reduction in surface and underground water quality [68], but also with higher amounts of radionuclides [69; 70]. Although the locality of Sacel is known for its industrial limestone [60], the presence of this mineral cannot explain the higher radioactivity of the water, as it is usually associated with a lower quantity of radionuclides [71], but the activities related to its extraction and industrial use [72] could support the increase of the gross alpha and beta activities. According to the national report, in 2021 the radioactivity parameters of drinking water in Romania were situated below the allowable values. Compared to the national level, Sibiu County belongs to the areas with the lowest values of gross alpha and beta activities [73]. The maximal value of Rn-222 in the sample from Paltinis (43.3 Bq/L) could be explained by the geology (crystalline schist) of the study site--Cindrel Mountains in the Southern Carpathians. Regarding the radioactivity of groundwater, similar results were reported in the Galati region of Romania, the highest gross alpha and beta activities being found in samples collected from drilled wells [74].