Reactive Henry problem: effect of calcite dissolution on seawater intrusion

Abstract

Freshwater stored in a coastal aquifer is extensively extracted through pumping wells due to high water demand in coastal area (touristic, industrial, and public use). To enhance freshwater security and to avoid contamination of water reserves, seawater intrusion becomes a topic of great interest for hydrogeologists. During the last few decades, hydrogeologists have provided a deeper understanding of the prediction, processes, investigative tools, and management of such systems. The majority of the studies quantifies these hydrogeological systems using traditional density-dependent flow and transport models and does not consider the effect of the chemical reactions. Interdependence of density-dependent flow and chemical reactions and their effects on the porosity and permeability is the most important key toward a reliable modeling of these complex systems. Seawater intrusion can increase by the solid matrix dissolution processes in the saltwater–freshwater mixing zone in the case of a coastal carbonate aquifer. The dissolution of such rocks can easily induce a development of porosity and permeability as a result of the mixing processes. The increase of permeability would enhance further seawater flux to the freshwater side. In this work, a relatively complete modeling scheme is presented to quantify and predict this risk. The modeling of such a problem requires a set of highly nonlinearly coupled equations. In this regard, GEODENS code used in this work can solve these equations by a finite element procedure; it can handle density-dependent flow, transport, and geochemical reactions in porous media. Its main purpose is to represent the physicochemical processes in the subsurface system. The code is used to simulate the effect of calcite dissolution during seawater intrusion in a coastal carbonate homogeneous aquifer.