Coupled salt and water flows in a groundwater basin

The postulates of irreversible thermodynamics and the law of conservation of mass were combined to yield two simultaneous partial differential equations describing the simultaneous transient-state flow of salt and water in fine-grained sediments. The resulting equations have been used to analyze the movements of groundwater and salt in a subterranean aquitard in the Oxnard, California, basin, a multiple aquifer system, which has been subjected to lateral seawater invasion of an upper aquifer. Chemico-osmotic coupling may induce a small chemico-osmotic consolidation of the aquitard (0.3 mm) over a period of about 25 years, but the aquitard should act as an effective pollution barrier to the movement of NaCl into a freshwater aquifer below. The ‘tightness’ of the aquitard to salt movement depends mainly on aquitard thickness, hydraulic permeability, and drawdown in overlying and underlying aquifers.