An integrated study of a Precambrian granite aquifer, Hvaler, Southeastern Norway
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- Artikler 
The Geological Survey of Norway (NGU) is performing an integrated study of the groundwater resources of the Precambrian Iddefjord Granite of Hvaler municipality in southeastern Norway. Linear fracture zones are identifiable from topographic maps, aerial photos, field inspection and geophysics. The two consistently most successful geophysical methods for identification of such zones have been total magnetic field and VLF measurements. However, investiga- tions in a newly constructed subsea road tunnel and test-pumping of boreholes on land indicate that a topographic or geophysical anomaly is no substantially transmissive fracture zone. The permeability of the Iddefjord granite appears rather low; a background value of around 10-9 m\/s has been calculated from test-pumping and from leakage into the Hvaler tunnel. The top 12 m or so of the granite appear to have an average permeability c.2-3 orders of magnitude higher The groundwater can be divided into 4 hydrochemical types, based on the degree of rock-water interaction and saltwater mixing. Saline groundwaters appear to be derived from fossil or current seawaters. Bicarbonate buffering, anion exchange and calcite\/fluorite satuaration appear to be important processes controlling pH, bicarbonate, fluoride and calcium concentrations.