Hydrogeology of Grand Cayman, British West Indies: a karstic dolostone aquifer

Abstract

On Grand Cayman, freshwater bodies present in the Bluff Formation are typically small and occur as thin lenses floating on top of dense saline water. Evaluation of the water resource potential of these freshwater lenses is difficult because of their variable hydrological conditions, complex paleohydrogeology and aquifer heterogeneity. Secondary porosity created by preferential dissolution of aragonitic fossil components is common. Open fissures and joints developed under tectonic stress and karst development associated with sea-level fluctuations are, however, the two most important causes of porosity and permeability in the aquifers on Grand Cayman. Fracture and karst porosity control the lens occurrence by: (1) acting as avenues for the intrusion of seawater or upward migration of saline water; (2) acting as recharge focal points; (3) enhancing hydrodynamic dispersion; (4) defining lens geometry; (5) facilitating carbonate dissolution along joints and fissures. A clear understanding of the hydrological and geological conditions is important in developing small lenses in a setting similar to that on Grand Cayman. This pragmatic approach can help identify the optimum location of the well field and avoid areas particularly susceptible to saline water intrusion.