## 4 Results and Discussion  
### Composition of the Pond Water  
The pond water composition is stable in all analyzed samples, and it is characterized by a slightly alkaline or alkaline pH values, oxidizing conditions, and a relatively low total dissolved solids (TDS) concentration level of 0.5 g L\({}^{-1}\). The waters are of sulfate-Ca type, which is typical for mine tailings. The concentrations of the observed elements in most cases do not exceed the MPCfp levels [42] (Table 1). The main toxic elements are As and Sb, and the concentrations are relatively stable. In particular, the contents of As and Sb exceed MPCfp by an average of 22 and 180 times, respectively. Concentrations of Al, Cu, Zn, and Mo are at or slightly higher than MPCfp. The most excess over the concentrations of a background reservoir (\(\mathrm{I_{conc}W}>5\)) was determined for Sb, As, Cd, Se, Cr, Ca, and \(\mathrm{SO_{4}}^{2-}\), which indicates contrasting conditions in terms of water composition in Komsomsolsk pond and Chany Lake. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **KP (n = 6)** & **CL (n = 10)** & **MPCfp** & **I\({}_{\text{conc}W}\)** & & **KP (n = 6)** & **CL (n = 10)** & **MPCfp** & **I\({}_{\text{conc}W}\)** \\ \hline pH & 8.14 & 7.16 & & & Al & 47 & 47 & 40 & 1.2 \\ Eh & 406 & 458 & & & Mn & 130 & 23 & 50 & **5.7** \\ S & 590 & 168 & & & Cu & 2.8 & 1.8 & 5 & 1.6 \\ \(\mathrm{SO_{4}}^{2-}\) & 270 & 12 & 100 & 23 & Zn & 53 & 14 & 50 & 3.8 \\ \(\mathrm{HCO_{3}}^{-}\) & 35 & 38 & & 0.92 & Pb & 1.1 & 0.44 & 6 & 2.5 \\ Cl\({}^{-}\) & 6.6 & 5.6 & 300 & 1.2 & Cd & 3.7 & 0.056 & 5 & 66 \\ \(\mathrm{F^{-}}\) & 2.2 & 1.4 & 0.75 & 1.6 & Se & 1.7 & 0.05 & 2 & 33 \\ \(\mathrm{NO_{3}}^{-}\) & 12 & 5.6 & 40 & 4.6 & Ba & 56 & 28 & 740 & 2.0 \\ \(\mathrm{Ca^{2+}}\) & 85 & 16 & 180 & 5.4 & Sr & 310 & 78 & 400 & 4.0 \\ \(\mathrm{Mg^{2+}}\) & 17 & 3.7 & 40 & 4.6 & Cr & 0.88 & 0.05 & 20 & 18 \\ \(\mathrm{Na^{2+}}\) & 18 & 6.1 & & 2.9 & Co & 0.38 & 0.37 & 10 & 1.0 \\ \(\mathrm{K^{+}}\) & 3.0 & 2.0 & 50 & 1.5 & Ni & 1.5 & 0.68 & 10 & 2.2 \\ \(\mathrm{SiO_{2}}\) & 2.8 & 8.5 & 10 & 0.32 & P & 66 & 120 & 60 & 0.55 \\ Fe & 0.36 & 0.26 & 0.05 & 1.4 & Ti & 5.3 & 2.1 & 60 & 2.5 \\ As & 0.22 & 0.0057 & 0.01 & 39 & Rb & 2.3 & 0.92 & 100 & 2.5 \\ Sb & 0.90 & 0.0026 & 0.005 & 350 & Mo & 1.8 & 0.45 & 1 & 4.0 \\ \hline \hline \end{tabular} Note: KP—Komsomsolsk pond; CL—Chany Lake; n is sample quantity.  
\end{table} 
Table 1: Composition of water in Komsomsolsk pond and Chany Lake, Eh in mV, electroconductivity S in \(\mathrm{\mu S/cm}\), \(\mathrm{SO_{4}}^{2-}\)–Sb in mg/L, Al–Mo in \(\mathrm{\mu S/L}\). Komsomsomsolk pond currently exists due to the replenishment of water with seasonal precipitation--rain and snow waters. The plant was stopped in 1999, and pulp effluents from ore processing have not been received into it since that time. A substantial reduction in metal and metalloid concentrations in the pond water would be expected. However, the water composition with high concentrations of many elements, the main ones being arsenic and antimony, has remained stable for over 20 years [40; 43; 44]. In 2017, geophysical surveys of internal zonality of the Komsomsomsk tailings using electrical resistivity tomography (ERT) were carried out [40]. The infiltration of highly mineralized acidic waters at a depth of 20 m and contamination of drinking water in the Komsomsomsk settlement were detected. One of the ERT profiles crossed the tailings pond, capturing surface water area of the pond (Figure 2). The geoelectric structure of the section indicates the transition of highly conductive zones (the pond: blue and cyan layers) to underlying diorites with low conductivity (yellow and red layers). Low-resistance zones (<60 Ohm\(\cdot\)m) beneath the water/solid boundary extend to a depth of \(\sim\)10 m, spreading along the coastal zone of the pond at a \(\sim\) of 25 m from the water. We interpret such zones as some flooded areas with a constant interaction of the material of the tailings and pore waters within. [PERSON] et al.