Hydrogeochemical provenance and evolution in Ganhai Well’s groundwater, Eastern Tibetan Plateau

The Ganhai Well (27.48°N, 101.46°E), an earthquake monitoring well since September 1980, is situated in the earthquake-prone of the eastern Tibetan Plateau, China. Despite years of monitoring, the hydrogeochemical origins and evolution of groundwater in the well remain unclear. Based on a weekly water sampling in 2022, the hydrochemical characteristics of the Ganhai Well were extrapolated. (1) The groundwater’s ions are derived from evaporite (45.2%-48.0%) and silicate rocks (36.4%-40.9%), followed by carbonate rocks (12.2%-15.4%), and negligible anthropogenic inputs (less than 1%). In the Ganhai Well, calcite tends to precipitate and crystallise, whereas dolomite maintains equilibrium with the solution. (2) It is a significant observation that the groundwater within the Ganhai Well is deep-seated, confined soda water (HCO₃·Cl-Na type), characterised by minor temporal fluctuations in its ionic concentrations and high stability. This hydrogeochemical profile establishes it as an extremely valuable and sustainable water resource, offering considerable support for regional ecological preservation and economic development.