GERHARD BARMEN on the COMBINATION of ISOTOPE HYDROGEOLOGY with REGIONAL FLOW and TRANSPORT MODELLING an Application to the Groundwater System of Southwestern Sweden
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GERHARD BARMEN ON THE COMBINATION OF ISOTOPE HYDROGEOLOGY WITH REGIONAL FLOW AND TRANSPORT MODELLING An Application to the Groundwater System of Southwestern Sweden Department of Engineering Geology Lund Institute of Technology Lund University DEPARTMENT OF ENGINEERING GEOLOGY LUND INSTITUTE OF TECHNOLOGY LUND UNIVERSITY ON THE COMBINATION OF ISOTOPE HYDROGEOLOGY WITH REGIONAL FLOW AND TRANSPORT MODELLING AN APPLICATION TO THE GROUNDWATER SYSTEM OF SOUTHWESTERN SWEDEN GERHARD ALEXANDER BARMEN THESIS 1992 THIS SERIES IS PUBLISHED BY Department of Engineering Geology Lund Institute of Technology P.O. Box 118 S-221 00 Lund The LUTVDG/TVTG series comprises 1000-series • Dissertations 3000-series - Research reports 5000-series - GrarV, t ton theses 7000-series - C •• n s and symposia reports • Tv /. eports 811992 Gerhard Barmen Printed in Swed * .it Reprocentralen, v und University, Lund ISRNLUTVDG 'VTG--1006--SE ISBN 91-628-058/ « Due of issue April 23, 1992 CODEN: iSR-ft LUTVDG/TVTG- -10 0 6 -,-&£ Authors) Sponsoring oipnintion Gerhard Barmen Title and subtitle ON THE COMBINATION OF ISOTOPE HYDROGEOLOGY WITH REGIONAL FLOW AND TRANSPORT MODELLING An application to the groundwater system of southwestern Sweden Abstnct Many different methods and tools can be used when trying to improve the information basis on which decisions are made for maintaining a quantitatively and qualitatively safe, long-term use of groundwater resources. In this thesis, classical hydrogeological examinations, hydrochemical investigations, environmental isotope studies, computerized groundwater flow modelling and radioisotope transport modelling have been applied to the large system of reservoirs in the sedimentary deposits of southwestern Scania, Sweden. The results obtained are first presented separately and subsequently the measured and calculated radioisotope contents are compared. There are onlv few reports available at present on such a combination of methods. The stable isotopes ZH, I8O and '3 C and the radioactive 3H and 14C have been measured and the results obtained can improve the estimations of the periods of recharge and the average circulation times of the groundwater reservoirs studied. A groundwater flow model based on finite difference techniques and a continuum approach has been modified by data from traditional hydrogeological studies. A calibration against piezometric records has been made for 1970, assuming steady-state conditions, and also for the transient evolution from 1840 to 1988. The same computer code, NEWSAM, has been used to simulate steady-state and transient isotope transport in the area studied, taking into account advective transport with radioactive decay. The interacting groundwater reservoirs studied have been represented by a three-dimensional system of grids in the numerical model. A major merit of this combination of isotope hydrogeology and regional flow and transport modelling is that the isotope transport simulations help to demonstrate where zones particularly vulnerable to pollution are situated. These locations are chiefly the result of the hydrogeological characteristics traditionally examined, but they are revealed by means of the transport model. Subsequent, more detailed investigations can then be t'ocussed primarily on these vulnerable zones. High contents of radioisotopes in the main aquifer of southwestern Scania may indicate that groundwatcr withdrawals have stimulated recharge from shallow aquifers am! surface waters and that the risk of pollution has increased. There are also several difficulties concerning the detailed, quantitative interpretations of the results, and these difficulties must be (he focus of future work. Even if the aquifer system studied here can be classified as unusually homogeneous and well-defined, the number of isotope measurements is small compared to the extension of the system. Furthermore, the calculated concentrations are similar over large areas. Therefore, it is at present not possible to calibrate the isotope transport model by measured isotope concentrations in order to verify or reject the results of the underlying groundwater flow model. Keywords Groundwater, environmental, isotopes, flow, transport, numerical modelling, regional scale, Alnar(> valley Classification system and/or index terms (if any) Supplementary bibliographical information Lan*ua|e English ISSN and key titie ISBN 91-628-0587-8 Recipient's notes Number of pages 201 **• SEK 200:- Security da&dfication Distribution by (name and address) Dept Engineering Geology, Lund University, Box 118, s-221 00 LUND, Sweden I, the undersigned, being the copyright owner of the abstract of the above-mentioned dissertation, hereby grant to all reference sources permission to publish and disseminate the abstnct of the above-mentioned dissertation. Pat, ON THE COMBINATION OF ISOTOPE HYDROGEOLOGY WITH REGIONAL FLOW AND TRANSPORT MODELLING AN APPLICATION TO THE GROUNDWATER SYSTEM OF SOUTHWESTERN SWEDEN AV GERHARD ALEXANDER BARMEN AKADEMISK AVHANDLING som för avläggande av teknisk doktorsexamen vid tekniska fakulteten vid Lunds universitet kommer att offentligen försvaras vid sektionen för väg- och vattenbyggnad, John Ericssons väg 1, hörsal V:A, tisdagen den 19 maj 1992, kl 13.15. Abraxas abrasax Thesis antithesis synthesis that becomes thesis again Meaningless. Unreal. Meaningless. And in the quiet night the spiders spin their webs and the crickets fiddle In autumn Gunnar Ekelöf PREFACE AND ACKNOWLEDGEMENTS The ideas for this work were generally indicated already when I began my postgraduate studies at the Department of Engineering Geology, Lund Institute of Technology, in 1983. However, for me the real start of this study occurred in October 1986, when I met my supervisor, Professor Leif Bjelm, near the Jardin de Luxembourg in Paris, and he enthusiastically proposed a thesis treating the groundwater reservoirs of southwestern Scania by a combination of isotopic investigations and numerical flow and transport modelling. At that time my interest in these methods had developed after a very inspiring year as visiting student at the Laboratory of Quantitative Hydrology and Hydrogeology, Paris School of Mines, Fontainebleau, and at the Laboratory of Isotopic Hydrology and Geochemistry, Paris University XI, Orsay. In practice, though not formally, this thesis has been carried out as a joint project of these three research establishments. I would like to express my sincere appreciation to Professor Leif Bjelm, Professor Ghislain de Marsily and Professor Jean-Charles Fontes for their generosity with their expert knowledge, benevolent guidance, support and never-ending encouragement throughout this work. It has been quite a tough task to try to span over several scientific disciplines and to work at three institutes at the same time. Nevertheless, the personal adventures and sensations have been greater than the feelings of despair. For instance, I should not want to have missed the first experience of sitting at a mass spectrometer in Orsay and the result from the analysis of a tiny quantity of gas seemed to reflect the isotopic composition of the groundwater I had sampled in Scania. I am very grateful to Annick Filly and Marc Massault for their skilled guidance in the techniques of isotope analysis and for having patience with my first stumbling steps in the laboratory. Another pleasant memory is the occasion when the first results of transport simulations could be examined after one night's work on the minicomputer. Calculations of isotope values in almost 10000 meshes and for more than 100 years had stopped all other activities but the figures seemed to be reasonable! I am greatly indebted to Emmanuel Ledoux for his generous help and guidance with the numerical model, often late into the evening and at weekends. It has also been a stimulating experience to search for historical and detailed information in libraries and archives about the methods involved in this thesis and about the groundwater geology of southwestern Scania. For instance, the early investigations undertaken for the water-works of the town of Malmö a century ago are a delight for the reader and the climatic records of Tycho Brahe give a valuable historical perspective. Particular recognition is due to the Alnarp committee and its members, who via Bo Leander, VBB-VIAK, made their piezometric and hydrochemical records available to me. Another important source of information has been the Well Archives of the Swedish Geological Survey and I would especially like to thank Ove Gustafsson and Mats Påhlsson at the branch office in Lund for helping me to find valuable data. OUe Andersson, VBB-VIAK, made the former archives of VIAK available to me, which is gratefully acknowledged. I would also like to thank the personnel at the water-works and at the municipalities of southwestern Scania, who provided assistance both when I was collecting groundwater IV samples and when I was searching for useful hydrogeological records. The increase in the water consumption and in the waste production during the past century often set off exciting reflections and discussions during these visits. A handful of owners of private wells have given similar services, for which I am very thankful. Most of the hydrochemical analyses of the water samples were carried out in the laboratory of the Department of Water and Environmental Engineering, Lund Institute of Technology. It was a great pleasure to work together with Mona Hamrin and Ylva Persson and I am indebted to them for this assistance.