ABSTRACT
Atolls commonly consist of a ring of small carbonate islets surrounding a shallow seawater lagoon. Under favorable geologic and recharge conditions small quantities of fresh groundwater may be contained within the larger islets. Usually fresh groundwater occurs as a thin, lens-shaped body separated from the underlying seawater by a layer of mixed water called the transition zone (Figure 1). As described by Under wood et al. (1992) and Griggs and Peterson (1993), the size and shape of a fresh groundwater lens within an atoll island are controlled primarily by the geologic frame work and hydrodynamic processes resulting when a two-phase fluid system (fresh water and saltwater) is subjected to a combination of recharge, discharge, and tidally driven stresses.
