# An Assessment of the Impact of Gypsum Deposit Development on Changes in the Radiation Environment
## 3 Results and Discussions  
### Water  
The obtained results of determining the activities of uranium isotopes and uranium concentration in water are presented in Table 1. The results of the study of the chemical composition of water according to the data [8] are shown in Table S2. The maximum total alpha activity of uranium isotopes, 0.202 \(\pm\) 0.030 Bq L\({}^{-1}\), was recorded in quarry waters (sample W-11) (Table 1). It is higher than the maximum permissible concentration (MAC) for drinking water [38]: 0.2 Bq L\({}^{-1}\). The alpha activity of water in the quarry water settling pond (Table 1) and in the lower reaches of the Chuga River (Figure 3a) (samples W-12 and W-4) was at the level of 0.05-0.06 Bq L\({}^{-1}\). The activity of 0.04 Bq L\({}^{-1}\) was established in the groundwater of the spring (Table 1) (sample W-9) and in the lower reaches of the Pozera River (Figure 3a) (sample W-13). The minimum total alpha activity of uranium isotopes of 0.4-11 mBq L\({}^{-1}\) was recorded in three lakes and in the upper reaches of the Pozera River (samples W-5, W-3, W-1 and W-7). In the middle reaches of the Pozera River, the upper reaches of the Chuga River and two lakes, the activity concentration of uranium isotopes was 16-28 mBq L\({}^{-1}\) (samples W-14, W-6, W-8, W-10 and W-2). Elevated \({}^{234}\)U/\({}^{238}\)U activity ratios of 1.3-1.8 were prevalent in the river (samples W-14, W-2, W-4 and W-8) (Figure 3b) and lake (samples W-3, W-5 and W-10) waters (Table 1). Decreased uranium isotope ratios of 1.0-1.2 were characteristic of spring groundwater and quarry waters (samples W-9, W-11 and W-12). They were also found in two river (Figure 3b) (W-1 and W-13) and two lake (Table 1) (W-6 and W-7) water samples. The range of uranium precipitation from infiltration waters can be constructed by using the equations Eh\({}_{\text{max}}\) = 0.40-0.06 pH and Eh\({}_{\text{min}}\) = 0.40-0.08 pH, obtained by comparing the data of detailed hydrogeochemical sampling and analysis with the theoretically expected equilibria. The intervals of the onset of uranium precipitation are expected at the following extreme pH values: at pH 6.5 Eh from +20 to \(-\)150 mV and at pH 8.5 Eh from \(-\)90 to \(-\)200 mV [39]. According to Table S2 and Figure 4a, almost all analyzed samples were above these ranges. The only exceptions were samples W-1 and W-5 with minimum Eh values of \(-\)40 and \(-\)52 mV, pH values of 6.59 and 7.01 and, accordingly, minimum uranium concentrations of 0.02 and 0.25 \(\upmu\)g L\({}^{-1}\). There is no clear correlation between the uranium concentration and Eh; however, if we exclude the samples least affected by hydrochemical processes with Ca-HCO\({}_{3}\)-SO\({}_{4}\) composition with minimum TDS values at the level of 0.1 g L\({}^{-1}\) and leave only samples with Ca-SO\({}_{4}\) composition with TDS values of 0.5-2.3 g L\({}^{-1}\), then there is a linear correlation with the determination coefficient R\({}^{2}\) = 0.57 (Figure S1). Figure 3: Distribution of uranium isotopes activity (**a**) and \({}^{234}\)U/\({}^{238}\)U ratio in the direction of rivers flow (south–north) (**b**). The isotopic composition of uranium in water reflects the balance between (i) the \(\alpha\)-recoil effect with the transition of nonequilibrium \({}^{234}\)U into water from rocks [40; 41; 42; 43; 44] and (ii) the rate of rock dissolution with the transition of both isotopes into water in an equilibrium ratio. The lower the rate of rock dissolution, the less equilibrium uranium will pass into water. This was well demonstrated by [PERSON] et al. (1982) [45] by using a granite massif as an example. The intense fracturing of insoluble rocks contributed to the creation of very high \({}^{234}\)U/\({}^{238}\)U ratios in water due to the alpha-recoil effect. Therefore, the lower the \({}^{234}\)U/\({}^{238}\)U ratio in water, the higher the rate of rock dissolution.