A fundamental knowledge of processes that control groundwater composition is required for informed management of water quality. The Voronka groundwater body in northeastern Estonia represents a good example of a complicated, overexploited groundwater system where conceptual understanding of baseline quality and governing hydrogeochemical processes can support sustainable aquifer management. A conceptual understanding or conceptual model is a simplified representation or a working understanding of the real hydrogeological system and its processes. The baseline chemical composition of the Voronka groundwater body was formed during the last glaciations, when glacial meltwater intruded into water-bearing rocks. Two main processes that can change Voronka groundwater body quality at the present day are: (1) seawater intrusion and (2) water exchange between buried valleys and formation’s groundwater. Future monitoring and management should focus on changes in the natural composition of groundwater caused by abstraction. The HCO3–/Cl– value is the best parameter to describe the fluctuations in natural background chemistry in the Voronka groundwater body and to assess significant trends induced by abstraction. In case of the discovered trends, a suite of isotope methods, especially 14C, 3H, δ2H, δ18O and δ13C, can be used to detect whether the intrusion of seawater or exchange of water with buried valleys is taking place.
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