Geophysical surveys using vertical electrical sounding for groundwater exploration in the Baikal region

The purpose of this study is to assess the feasibility of groundwater exploration for economic, drinking and technical purposes using geophysical methods in the Baikal region. The investigations are carried out under complex hydrogeological conditions due to the peculiarities of the geological and tectonic structure of the Baikal Rift Zone. The region is characterized by a sharp lateral and vertical variability in the distribution of fractured zones in rocks of various genesis and lithological composition, limited distribution of aquifers, the prevalence of seasonal frost and permafrost, the presence of thermal waters confined to water-bearing fault zones. To achieve this goal, the vertical electrical sounding (VES) method was employed. This method has proven e]ective for identifying objects with contrasting electrical resistivity at di]erent depths. In the study area, the low resistivity (5–30 Ohm•m) of hard rocks, in the absence of water-saturated clay deposits, can be attributed to fractured zones saturated with high-temperature mineralized solutions (20 °C and above). For water-saturated rocks containing cold groundwater with lower mineralization than hydrothermal solutions (less than 1 g/L), the range of resistivity can vary from 90 to 190 Ohm.m. Studies were conducted at three sites located in the Republic of Buryatia and in the Irkutsk Region. As a result of the geophysical surveys, locations of fresh groundwater were identified at all studied sites, and evidence of a potential hidden geothermal reservoir was found at the Bezymyannaya Bay site. At two of the sites, drilling confirmed the reliability of the data obtained from the VES surveys. The sharp contrast in resistivity between dry and water-saturated rocks makes it possible to use geophysical methods for groundwater exploration, despite the diverse geological and tectonic conditions of the Baikal region.