Environmental tracers in groundwater as tools to study hydrological questions in arid regions [Elektronische Ressource] / presented by Hany el-Gamal

Hany El-Gamal

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2005
• Nombre de lectures: 82
• Langue: Deutsch
• Poids de l'ouvrage: 3 Mo

Extrait

Dissertation
submitted to the
Combined Faculties of the Natural Sciences and for Mathematics
of the Ruperto-Carola University of Heidelberg, Germany
for the degree of
Doctor of Natural Sciences



































presented by
Master-Physicist: Hany El-Gamal
born in: El-Menoufia, Egypt
Oral examination: 08.06.2005
Environmental tracers in groundwater as tools to
study hydrological questions in arid regions

































Referees: Prof. Dr. Werner Aeschbach-Hertig
Prof. Dr. Kurt Roth Zusammenfassung

In der vorliegenden Arbeit werden Umwelttracer wie Edelgase, stabile Isotope,
Tritium und SF verwendet um hydrologische Fragen in ariden Regionen zu studieren. 6
Theoretische Modelle und numerische Methoden zur Behandlung des Phänomens von
Luftüberschüssen in Grundwasser werden diskutiert. Das Potential dieser Ansätze zur
Beschreibung des Phänomens der Entgasung, das in einigen Grundwasserleitern
gefunden wird, wird ausgelotet. Diese Arbeit enthält zwei bedeutende Anwendungen
von Umwelttracern um Grundwasser in Gebieten mit sehr aridem Klima zu studieren.
Das Hauptziel dieser Studien war, den Ursprung und das Alter des Grundwassers an
solchen Standorten zu bestimmen. Die erste Studie untersucht Aquifere welche neu
entwickelte "reclamation areas" südwestlich des Nildeltas in Ägypten mit Wasser
versorgen. In diesem Gebiet wird das Grundwasser hauptsächlich aus dem Nil
erneuert, wenn auch mit einer niedrigen Rate. Die meisten Proben wurden vor der
Fertigstellung des Assuan Staudamms im Jahre 1969 infiltriert und haben Alter > 50
a, nur wenige in der Nähe des Oberflächenwassers gelegene Brunnen liefern jüngeres
Wasser. Die zweite Studie untersucht Quellen, welche Oasen in den Bergen des
nördlichen Oman versorgen. Das Wasser dieser Quellen wird durch Niederschlag auf
Zeitskalen von Jahren bis höchstens wenige Dekaden erneuert. Die meisten Proben
haben junge Alter im Bereich von 2-10 a.

Abstract

Environmental tracers such as noble gases, stable isotopes, tritium, and SF are used 6
in this work to study hydrological questions in arid regions. Theoretical models and
numerical methods to treat the excess air phenomenon in groundwater are discussed.
The potential of these approaches to describe the phenomenon of degassing, which is
found in some aquifers, is explored. This work contains two major applications of
environmental tracers to study groundwater in areas with very arid climate. The main
goal of these studies was to determine the origin and age of groundwater in such
locations. The first study investigates aquifers supplying water to new reclamation
areas southwest of the Nile Delta in Egypt. In this area, the groundwater is mainly
recharged from the Nile River, albeit at a low rate. Most of the samples were
recharged before the completion of the Aswan High Dam in 1969 and have ages > 50
yr, only few wells located near to the surface water yield younger water. The second
study investigates springs supplying oases in the mountains of Northern Oman. These
springs are recharged by precipitation on time scales of years to at most a few
decades. Most of the samples have young ages ranging between 2-10 yr.

Contents
Contents ........................................................................................................................I
1 Introduction...............................................................................................................1
1.1 Outline..................................................................................................................1
1.2 Groundwater ........................................................................................................3
1.3 Groundwater as a source of freshwater resources................................................4
2 Noble gases in groundwater hydrology...................................................................6
2.1 Sources of noble gases.........................................................................................8
2.2 Noble gas solubilities10
2.3 Excess air ...........................................................................................................13
2.4 Calculation of noble gas temperature and excess air.........................................18
3 32.5 Dating groundwater with the H- He method....................................................20
3 Models to describe excess air and degassing in groundwater.............................25
3.1 Unfractionated excess air model........................................................................25
3.2 Partial re-equilibration and diffusive degassing models....................................26
3.3 Closed-system equilibration model....................................................................28
3.3.1 General derivation of the CE-model equation ............................................28
3.3.2 The original formulation of the CE-model equation...................................33
3.3.3 Interpretation of the CE-model and its parameters.....................................35
3.4 Ledo-Paniselian aquifer (Belgium) as a field example of degassing.................39
3.4.1 Study area....................................................................................................39
3.4.2 Evaluation of the noble gas data by inverse modeling ...............................42
3.4.3 Correction of the He concentration in the Ledo-Paniselian aquifer ...........46
3.4.3.1 Case 1: Early degassing (at the time of infiltration) ............................46
3.4.3.2 Case 2: Late degassing (at the time of sampling) ................................47
3.4.3.3 Comparison of radiogenic He values...................................................48
3.5 Other examples of degassing .............................................................................49
4 Groundwater dating by sulfur hexafluoride and CFCs ......................................53
4.1 Properties of sulfur hexafluoride .......................................................................53
4.2 The solubility of SF in water ............................................................................54 6
4.3 Atmospheric history of SF ................................................................................58 6
4.4 Sampling, extraction, and measurement of SF samples ...................................59 6
4.5 Dating young groundwater by SF .....................................................................63 6
4.6 Dating groundwater by chlorofluorocarbons (CFCs) ........................................67
5 A multi-tracer study of groundwater in reclamation areas south-west of the
Nile Delta, Egypt ........................................................................................................72
5.1 Introduction........................................................................................................72
5.2 Study area...........................................................................................................72
5.2.1 Geomorphological features.........................................................................73
5.2.2 Groundwater system ...................................................................................74
5.2.2.1 The Recent aquifer...............................................................................74
5.2.2.2 The Pleistocene ....................................................................................76
5.2.2.3 The Pliocene aquifer ............................................................................79
5.2.2.4 The Miocene aquifer79
5.2.2.5 The Oligocene aquifer..........................................................................80
5.2.3 Geochemistry and water quality .................................................................81
5.3 Methods..............................................................................................................86
5.3.1 Tritium ........................................................................................................86
5.3.2 Stable isotopes ............................................................................................86
I
5.3.3 Noble gases .................................................................................................86
5.4 Results and discussion .......................................................................................87
5.4.1 Stable isotopes ............................................................................................87
5.4.2 Noble gases90
3 35.4.3 H- He and SF groundwater ages ..............................................................95 6
5.5 Summary and conclusions .................................................................................99
6 Environmental tracer study of groundwate