Simultaneous pumping of fresh and salt water from a coastal aquifer

Abstract

When fresh water is pumped from an aquifer which is open to a recharging salt-water body, care must be taken to avoid the encroachment of salt water into the well. A measure which sometimes may be taken when there is also a demand for filtered salt water is to supplement the fresh-water well by a salt-water well, located between the fresh-water well and the coast, and to pump both wells at comparable rates. This paper analyzes the idealized case where the aquifer is confined, thin, homogeneous and isotropic, semi-infinite in areal extent, and bounded on one side by a straight recharge boundary; it is furthermore assumed that the nonpumping piezometric surface of the aquifer has a steady, uniform slope towards the boundary. As a result of the analysis a relation is established between the distances from each of the wells to the boundary, the ratio between the pumping rates of the two wells, and the maximum pumping rate at which no salt water is induced into the fresh-water well; this relation can be used in the selection of the optimum location of the pair of wells.