“…The water chemical composition and especially environmental isotope signatures of δD, δ 18 O, 87 Sr/ 86 Sr, 3 He/ 4 He, and 40 Ar/ 36 Ar in the thermal groundwater convey valuable information about the hydrochemical evolution of the groundwater system, water-rock interaction and groundwater recharge conditions, which can be used in the context of sustainable groundwater resource management [5][6][7][8][9][10][11][12][13][14]. In particular, the study and combination of these isotopic chemical parameters on groundwater in other important aquifer systems within deep sedimentary basins, such as the Parisian Basin, e.g., [15][16][17], Pannonian Basin, e.g., [8,18], or Baltic Artesian Basin, e.g., [19], led to the successful distinction between younger meteorically recharged and very old, partly highly saline fossil formation waters.…”