APPLICATION OF FLUID ELECTRICAL CONDUCTIVITY LOGGING FOR FRACTURED ROCK AQUIFER CHARACTERISATION AT THE UNIVERSITY OF THE WESTERN CAPE’S FRANSCHHOEK AND RAWSONVILLE RESEARCH SITES Dissertation submitted to the University of the Western Cape in the Fulfilment of the degree of Master of Science By CANDICE LASHER Department of Earth Sciences Faculty of Natural Sciences, University of the Western Cape Supervisor DR. JACOBUS MARTINUS NEL Co-supervisor PROFESSOR OKKE BATELAAN November 2011 Cape Town, South Africa DECLARATION I declare that “APPLICATION OF FLUID ELECTRICAL CONDUCTIVITY LOGGING FOR FRACTURED ROCK AQUIFER CHARACTERISATION AT THE UNIVERSITY OF THE WESTERN CAPE’S FRANSCHHOEK AND RAWSONVILLE RESEARCH SITES” is my own work, that it has not been submitted for any degree or examination in any other university, and that all the sources I have used or quoted have been indicated and acknowledge by complete references. Full name: Candice Lasher Date: November. 2011 Signed i ABSTRACT Application of Fluid Electrical Conductivity Logging for Fractured Rock Aquifer Characterisation at the University of the Western Cape’s Franschhoek and Rawsonville Research Sites. Candice Lasher MSc Thesis Department of Earth Sciences University of the Western Cape, South Africa Keywords: Aquifer protection and management, borehole logging, fractures, groundwater flow, hydraulic properties, transmissivity, transmissive fractures. Characterisation of fractured rock aquifers is important when dealing with groundwater protection and management. Fractures are often good conduits for water and contaminants, leading to high flow velocities and the fast spread of contaminants in these aquifers. A cost effective methodology is required for the characterisation of the role of individual fractures contributing to flow to boreholes in fractured rock aquifers. Literature shows that some of the conventional methods used to characterise hydraulic properties in fractured rock aquifers are expensive, complicated, time consuming and are associated with some disadvantages such as over-or under- estimations of flow rates. ii This thesis evaluates the use of Fluid Electrical Conductivity (FEC) logging in fractured rock aquifers. This FEC data are compared to various traditional methods used to determine aquifer hydraulic properties applied at the Franschhoek and Rawsonville research sites. Both these sites were drilled into the fractured rock Table Mountain Group (TMG) Aquifer, forming one of the major aquifers in South Africa. Methods applied in this thesis to characterise the aquifer includes geological mapping, drilling and geophysics (borehole and surface) to determine significant geological characteristics and borehole construction. Constant Discharge (CD) tests were used to determine total borehole yield while Fluid Electric Conductivity (FEC) logging was used to quantify the contribution of individual fractures with depth. Comparisons of the scale and dimension of the information obtained from the different methods were evaluated for their benefit and usefulness. FEC logging proved to be beneficial as the data obtained is both qualitative and quantitative. The application of the FEC method in the Table Mountain Group fracture rock aquifer was tested in relation to more frequently methods such as drilling, surface and borehole geophysics and CD test. FEC logging proved to be fast, cost effective and practical in deep boreholes. FEC logging worked well as a supplementary method to CD tests. These two methods are complimentary to each other and should be used in combination to gain as much information and knowledge about fractured rock aquifers as possible. iii ACKNOWLEDGEMENTS This thesis would not have been possible without the assistance of many individuals and institutions. I would like to acknowledge my debt of gratitude and wish to record my sincere thanks to the following: • My supervisor, Dr. Jacobus Martinus Nel from Earth Sciences Department, University of the Western Cape for his assistance. • My Co-promoter, Prof. Okke Batelaan from Department of Hydrology and Hydraulic Engineering, Vrije Universiteit Brussel, and the Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Belgium. • This project was supported and funded by VLIR. • Eskom, Kelley Reynolds, for sponsoring me during an international conference. • Christine Doughty for her assistance with FEC analysis and The Lawrence Berkeley Lab who provided me with the BORE II simulation software. • The Department of Water Affairs, Nico de Meillon for conducting borehole geophysics at both research sites. • Martin de Klerk of Cape Geophysics for performing surface geophysics at the Franschhoek research site. • The Earth Science students at UWC are thanked for their friendship, support and assistance during my studies. • Mr Shamiel Davids, for his undivided assistance during the field work component of this thesis. iv Special thanks to my family and friends for their assistance, support, patience and understanding during the study and research, but most importantly, God, for empowering me with the knowledge! v ABBREVIATIONS AND ACRONYMS l/s litres per second S/cm microSiemens per centimeter AFEC ambient fluid electrical conductivity BRM1 Berg River Monitoring 1 °C Degrees Celsius CD Constant Discharge CPS counts per second EC electrical conductivity FEC Fluid electrical conductivity FFEC flowing fluid electrical conductivity g/cc gram per cubic centimetre IGS Institute for Groundwater Studies km kilometers m2/d metres squared per day m metres mbc metres below collar mbgl meters below ground level mm millimetres mm/a millimetres per annum mS/cm milliSiemens per centimeter vi mV milliVolts SP self potential TMG Table Mountain Group UWC University of the Western Cape VLIR Vlaamse Interuniversitaire Raad (Flemish Interuniversity Council) WGS84 Since the 1st January 1999, the official co-ordinate system for South Africa is based on the World Geodetic System 1984 ellipsoid, commonly known as WGS84, with the ITRF91 (epoch 1994.0) co-ordinates of the Hartebeesthoek Radio Astronomy Telescope used as the origin of this system. This new system is known as the Hartebeesthoek94 Datum. WRC Water Research Commissions YSI Yellow Springs Incorporated vii TABLE OF CONTENTS DECLARATION ....................................................................................................................................... I ABSTRACT .............................................................................................................................................. II ACKNOWLEDGEMENTS .................................................................................................................... IV ABBREVIATIONS AND ACRONYMS ............................................................................................... VI LIST OF FIGURES................................................................................................................................. XI LIST OF TABLES................................................................................................................................. XII LIST OF PLATES ................................................................................................................................XIII CHAPTER 1 GENERAL INTRODUCTION 1.1 INTRODUCTION......................................................................................................................... 1 1.2 SELECTION OF STUDY AREA ................................................................................................. 2 1.3 AIMS AND OBJECTIVES ........................................................................................................... 3 1.4 APPROACH ................................................................................................................................. 4 1.4.1 Desktop study ....................................................................................................................... 4 1.4.2 Field methods performed during research study ................................................................. 4 1.4.3 Data interpretation .............................................................................................................. 5 1.5 STUCTURE OF THE THESIS ..................................................................................................... 5 CHAPTER 2 2 LITERATURE REVIEW 2.1 THE ROLE OF FRACTURES IN FRACTURED ROCK AQUIFERS ......................................... 7 2.2 INFORMATION REQUIRED WHEN CHARACTERISING A FRACTURED ROCK AQUIFER ..................................................................................................................................... 7 2.3 METHODS TO DELINEATE FRACTURES AND TRANSMISSIVE ZONES .......................... 8 2.3.1 Geological mapping and cross-sections .............................................................................. 9 2.3.2 Drilling .............................................................................................................................. 10 2.3.3 Surface geophysics ............................................................................................................ 10 2.3.4 Borehole geophysics and caliper logging. ......................................................................... 11 2.3.5 Constant Discharge (CD) tests .......................................................................................... 15 2.3.6 Fluid Electrical Conductivity logging ..............................................................................