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Doctorat
Israel
Flow and transport processes is an extremely saline aquifers, example from the Dead Sea area
Titre : Flow and transport processes is an extremely saline aquifers, example from the Dead Sea area
Auteur : Magal, Einat
Université de soutenance : Ben-Gurion University of the Negev
Grade : Doctor of Philosophy (PhD) 2010
Résumé partiel
Understanding groundwater flow is essential for proper management of groundwater
resources and monitoring its quality and quantity. Tracing the migration of a tracer
that has been injected artificially into the aquifer is a powerful tool for achievement of
direct estimate of groundwater flow and transport processes. Since most of the
experience in the world comes from groundwater of relatively low salinities, the goals
of this work were to quantify directly the flow and transport processes in highly saline
hydrogeological environments and specifically at the Dead Sea shore. The importance
of real time quantification of these processes is due to the continuous drop of the Dead
Sea level that has significant impact on the adjacent hydrological systems. The wide
range of groundwater salinities at the Dead Sea coast requires the tracers that are
conservative in such system. Therefore, the first goal was the assessment of the
sorption properties of fluorescent dyes in highly saline groundwater. The suitable
tracers were chosen to be used as conservative tracers at the other parts of the work.
The flow properties of the groundwater were directly assessed in a field experiment in
Fashkha springs and the transport of colloids was evaluated using colloid size tracers
in laboratory experiments with solutions with wide range of salinities including that of
the Dead Sea brines.
The capability of five fluorescent dyes to serve as conservative tracers in highly saline
groundwater was evaluated by a series of batch experiments on pure minerals and
natural sediments. Dye sorption was tested in four different salinities (from fresh
rainwater to Dead Sea water) on the pure minerals : calcilte, dolomite, quartz,
bentonite and kaolinite and on four natural sediments taken from boreholes drilled
along the Dead Sea shore. It was found that the dyes Sulfo-Rhodamine B and Eosin
are strongly adsorbed on pure minerals and sediments and therefore cannot be used as
conservative tracers in saline groundwater. Uranine and Pyranine sorption is increased
at higher salinities, therefore they can be used as tracers in moderately saline
groundwater only. Na Naphthionate was found to be the best tracer for fresh and
saline water, with minimal sorption in all cases. Sorption of the dyes on four natural
sediments was measured and values were found to be in accord with those of previous
sorption on pure minerals. Sorption on natural sediments was also estimated based on
the mineral composition of the sediment and the known sorption on the pure minerals.
The estimated sorption values were usually 25% lower than those of the sorption
directly measured. Nevertheless, sorption on pure minerals can be used as a first
approximation for sorption on natural sediments.
The impact of sediment to solution ratio was tested for Uranine as a model dye. The
distribution coefficient (Kd) of Uranine in highly saline Dead Sea water was found to
be dependent on the sediment to solution ratio (mass/volume), where low ratios
resulted in higher values of Kd. Also, higher Kd values were calculated for fine grain
size due to higher sorption capacity on larger surface areas. The difference in Kd,
however, is not directly related to the specific surface size of the grains and should be
examined separately.
Mots Clés : Aquifers — Dead Sea (Israel and Jordan). — Groundwater flow — Dead Sea (Israel and Jordan). — Hydrogeology. — Radioactive tracers in hydrogeology — Saline waters
Page publiée le 10 janvier 2012, mise à jour le 21 novembre 2018