Sources and geochemistry of groundwater in fractures

Principal investigator: Mats Åström, Linnaeus University

Long-term monitoring of groundwater in deep underground fractures in the crystalline bedrock of the Äspö Hard Rock Laboratory and, also, of surface-drilled boreholes in the nearby Laxemar area has revealed that this groundwater has multiple sources. These sources include: glacial-melt water; water from the Littorina Sea (ca. 7500-4000 BP); water from the Baltic Sea; modern meteoric water; and, a very old, deep-lying, saline water source.

With increasing depth there is, in general, an increase in salinity and sulphate concentrations but a decrease in bicarbonate and organic-matter concentrations. A characteristic feature of this groundwater is elevated concentration of Cs, particularly in waters of marine origin. Also, this groundwater typically has low concentrations of rare earth elements but a high variability in their fractionation patterns. Increased understanding of the sources and geochemical development of groundwater in bedrock fractures is crucial for understanding, and ensuring the long-term protection of, regolith groundwater and surface water bodies.

Sampling of groundwater in a fracture in the Äspö Hard Rock Laboratory.  Photo: Tobias Berger.
Sampling of groundwater in a fracture in the Äspö Hard Rock Laboratory.
Photo: Tobias Berger.