Kvaliteten av grunnvann. Meddelelse fra Vannboringsarkivet nr. 5.
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Quality of ground water: The quality of ground-water from drilled wells in Norway is little known. The ground water mainly occurs in fractures. Open fracture-systems, with rapid circulation of ground-water, may easily lead to contamination. Analyses of water from drilled wells in rocks, are carried out at Statens Inst. for Folkehelse. The results of these analyses are given to the Geological Survey. Results of analyses: pH, total hardness, dissolved iron (Fe) and manganese (Mn) are shown in the diagram, Fig. 4. The pH-values show little variation. Water from the Cambro-Silurian shales and limestones has the highest hardness. The high contents of iron in these rocks, especially in black shales, are due to pyrite and pyrrhotite. The manganese in some of the wells in Permian plutonic rocks comes from mangnese-mineralisation in fractures. Ingress of saltwater may occur in wells near the coast. The conditions vary from place to place, depending on the rock-type, dip of beds and fractures. In fig. 6 the wells A, B and C obtained fresh water close to the sea, while the well D gave salt water after a short period of pumping. Salt water also occurs occasionally in wells within an area which was covered by the sea after the Quarternary glaciation (fig. 7). Here the salt originates from marine clays and sometimes from rock-fractures with poor circulation.