# An Assessment of the Impact of Gypsum Deposit Development on Changes in the Radiation Environment
## 3 Results and Discussions
### Water
This pattern can explain the lower values of the uranium isotope activity ratio in quarry waters, since the crushing of rocks during mineral extraction occurs most intensively and contributes to their increased dissolution. The uranium isotope ratio is virtually independent of Eh in the oxidizing environment of the aquifer [46; 47] (Figure 4b). The graphs in Figure 4c-f indicate a correlation of uranium concentrations with TDS, calcium, sulfate ion and strontium (R\({}^{2}\) = 0.50, 0.48, 0.46 and 0.36, respectively). The correlation of calcium and sulfate ion with TDS is in turn explained by their content in the chemical composition of water at the levels of 90 and 80 mg-eq %, respectively. Strontium is approximately uniformly distributed in gypsum and passes into water synchronously with calcium and sulfate ion. The maximum uranium concentration (7.34 \(\pm\) 1.10 ug L\({}^{-1}\)) was found in the quarry waters sampled in August 2024. These waters were also characterized by the maximum  
Figure 4: Dependence of uranium concentration in natural waters on Eh (**a**), TDS (**c**), calcium (**d**), sulfate ion (**e**) and strontium (**f**), and dependence of \({}^{234}\)U/\({}^{238}\)U on Eh (**b**). The anomalous value of uranium concentration in quarry waters (7.34 \(\mu\)g L\({}^{-1}\)) was not taken into account when constructing the graphs. TDS value of 2.6 g L\({}^{-1}\) (see Table S2). In the spring groundwater, in the quarry water settling basin and in the Chuga River (samples W-9, W-12 and W-4), the TDS values were 0.3 g L\({}^{-1}\) lower. These waters also had the highest uranium concentrations (1.35-1.96 \(\upmu\)g L\({}^{-1}\)). All these waters had a calcium sulfate composition and were formed by dissolving gypsum to complete saturation [48]. A distinctive feature of the quarry waters is their enrichment with 0.3 g L\({}^{-1}\) in Na\({}_{2}\)SO\({}_{4}\) and NaCl salts, apparently of anthropogenic origin (see Table S2). In fresh groundwater circulating in sulfate and carbonate rocks of the North Dvina cartesian basin (Mezen syneclise), uranium concentrations above 2 \(\upmu\)g L\({}^{-1}\) have not been detected [49]. Average concentrations of 6.6 \(\upmu\)g L\({}^{-1}\) with maximum concentrations of up to 18.5 \(\upmu\)g L\({}^{-1}\) have been established in the aquifer complex of the Padunskaya suite of the Verdian, composed of red-colored ferruginous siltstones and sandstones [50]. Therefore, the most likely source of high uranium contents in quarry waters may be overburden rocks, represented by reddish-brown moraine loans with gravel and pebbles of igneous rocks carried out during the last glacial period from the Baltic (Fennoscandian) shield. They are stored in dumps (see Figure 1) and are subject to weathering with the removal of soluble compounds, including uranium sorbed by iron hydroxides and organic matter (see Section 3.3.1). Peatlands, widespread in the study area, can also be enriched in uranium. Even the so-called bog uranium ores are known and are found in areas with a humid climate due to the transfer of uranium by soil and groundwater and sedimentation on natural organogenic reducing barriers [51; 52]. In January and February 2025, the uranium concentrations in quarry waters consistently decreased to 5.52 \(\pm\) 0.82 and 5.30 \(\pm\) 0.80 \(\upmu\)g L\({}^{-1}\), while the ratio of uranium isotope activities increased slightly (samples W-11-1 and W-11-2 in Table 1). This indicates a decrease in the intensity of overburden dissolution processes in winter. Minimum uranium concentrations (0.02-0.25 \(\upmu\)g L\({}^{-1}\)) were observed in two lakes and in the upper reaches of the Pozera River (samples W-3, W-5 and W-1). In these reservoirs, groundwater recharge was minimal or absent altogether (total mineralization of 0.1-0.8 g L\({}^{-1}\)). In the remaining water samples, a variable ratio of groundwater and atmospheric components was observed, and accordingly, uranium concentrations had intermediate values.