STAGNANT AQUIFER CONCEPT .2. SMALL-SCALE ARTESIAN SYSTEMS - HAZEVA, DEAD-SEA RIFT-VALLEY, ISRAEL

The literature of groundwater hydrology deals almost exclusively with through-flow aquifers, i.e. bodies of permeable rocks that contain wat er in all their voids, and have active recharge, appreciable through-f low 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 th eir voids, but are sealed off from recharge and discharge, and thus ha ve 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 aq uifers are defined by the properties of waters ascending in artesian w ells, e.g. concentration of major ions, C-14-based water ages, isotopi c 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 t he region contain no measurable tritium, and C-14 ages range from 1000 to more than 25 000 years, and (4) the hydrogen and oxygen isotopes i ndicate recharge occurred under different paleo-climates. According to the conceptual model suggested, the currently stagnant aquifers are f ossil through-flow aquifers that have each been cut off from recharge by overlying impermeable sediments and their discharge stopped by buri al beneath the active base of drainage. The artesian pressure is attri buted to compaction by overlying rocks. The Hazeva trapped pressurized groundwater systems are of special interest as they are (1) young, i. e. 1000 to more than 25 000 years old, (2) shallow, i.e. 50-250 m deep , and (3) small - the aerial extension of individual groundwater traps being in the range of 10 to 10(2) km(2). The identification of stagna nt pressurized groundwater systems warrants special attention because establishment of their existence opens new economic applications, poss ibly surpassing the importance of the traditional exploitation of self -flowing groundwater. The potential value stems from the basic propert ies of entrapment: (1) the isolation from any recharge and contact wit h the surface makes such systems immune to contamination, thus providi ng ideal water reservoirs for emergencies caused by pollution accident s, including nuclear disasters, and (2) the lack of discharge makes de pressurized (exploited) stagnant groundwater systems potential reposit ory sites for toxic and nuclear wastes, freed from the danger of uncon trollable hydrofracturing.