Criteria for recognition of the sea water in ground‐waters

In semiarid regions near the seacoast excessive pumping of wells is liable to cause salt‐water intrusion either from the ocean itself or from relatively impervious marine sedimentary rocks surrounding the aquifer which yields ground‐water. Since the ground‐waters of semiarid regions commonly have a relatively high and variable concentration of dissolved salts, a slight increase in concentration, such as is found by measuring resistivity [see 8 of “References” at and of paper[, may not alone be sufficient to prove the presence of sea water. On the other hand, since ground‐waters usually differ widely from sea water in composition, it might be thought that changes in the proportions of different chemical components of well‐waters in the direction if sea water could be used to detect the beginnings of admixture. Actually, however, the observed changes in composition of well‐waters may be quite different from those that would occur on simple mixing with a small portion of sea water owing to the modifications which sea water itself may undergo as it passes through the ground or through marine and estuarine sediments. The absence of those proportional changes which would result from a direct mixture of sea water and ground‐water cannot be taken as a warrant for disregarding other signs of salt‐water encroachment.