Grunnvann i Vestfold. Meddelelse fra Vannboringsarkivet nr. 11.
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Drilling for water has become very common in the county of Vestfold since World War II. The water is mostly restricted to fractures, joints, fissures and solution openings in the rocks. The main rock-types found in Vestfold are: Cambro-Silurian sediments (limestone, sandstone and shale), Permian lavas and plutonic rocks. Wells drilled in the lavas usually yield considerable amount of water (up to 40.000 l\/h), and several large waterworks utilize water from such wells. The Cambro-Silurain sediments usually give sufficient water for small waterworks. The plutonic rocks are very massive, therefore, the possibilities for obtaining water from these rocks are more doubtful. Some places Quaternary alluvial deposits offer favourable conditions for well construction. Some analyses of water from drilled wells in Vestfold are shown in Tab. 1. Common types of springs in Vestfold are shown in figs. 8-11. Ingress of salt water may occur in wells near the coast. The conditions vary from place to place depending on the rock-types, dip of the beds, and fractures. Salt water also occurs occasionally in wells and springs within the area which was covered by the sea after the Quaternary glaciation (fig. 6). Here the salt originates from marine clays and from rock fractures with poor circulation.