The classic studies of Badon Ghyben [see 1 of “References” at end of paper] and Alexander Herzoerg [2].that defined the basic principles governing the relation between salt water and fresh water in water‐bearing sands are now fairly well known. They showed that fresh water floats on the heavier salt Water and that, under static conditions, the ratio between the head of the fresh water above mean sea‐level and the depth of the contact between fresh and salt water below mean sea‐level, is determined by the relative specific gravities of the two waters. Other studies have shown that under ordinary conditions there is little mixing between the fresh and salt waters, so that the zone of contact is narrow. Instances have been observed in which the chloride‐content of the water has ranged from a few parts to several thousand parts per million within a few feet. It would seem, therefore, that the basic conditions under which fresh and salt water occur together in water‐bearing sands are somewhat similar to those in the tidal estuaries of streams. The principal differences are caused by the frictional resistance of the sand which prevents rapid movements of both fluids and probably retards their mixing.
