Abstract
The literature of groundwater hydrology deals almost exclusively with through-flow aquifers, i.e. bodies of permeable rocks that contain water in all their voids, and have active recharge, appreciable through-flow and adequate discharge. The present paper augments this picture by addressing groundwater systems with the likely occurrence of stagnant aquifers, i.e. bodies of permeable rocks that contain water in all their voids, but are sealed off from recharge and discharge, and thus have no water through-flow. A phenomenological approach, based on first principles of physics, geology, hydrology and chemistry, is applied in the present account because groundwater is a concealed fluid that can not be traced directly. Hydraulically isolated pressurized (artesian) aquifers are identified in continental rocks of the Hazeva Formation, Miocene, in the Hazeva area, within the Rift Valley. The different aquifers are defined by the properties of waters ascending in artesian wells, e.g. concentration of major ions, 14C-based water ages, isotopic composition, and hydraulic heads. The different pressurized aquifers are interpreted as hydraulically isolated stagnant aquifers because: (1) the continental host rocks reveal a high degree of facies changes, and permeable rocks occur in lenses of limited extension, alternating with impermeable rocks, (2) the present climate is extremely arid and no effective recharge is observed, (3) the groundwaters analyzed in the region contain no measurable tritium, and 14C ages range from 1000 to more than 25 000 years, and (4) the hydrogen and oxygen isotopes indicate recharge occurred under different paleo-climates. According to the conceptual model suggested, the currently stagnant aquifers are fossil through-flow aquifers that have each been cut off from recharge by overlying impermeable sediments and their discharge stopped by burial beneath the active base of drainage. The artesian pressure is attributed to compaction by overlying rocks.
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