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Addis Ababa University School of Graduate Studies Faculty of Technology Chemical Engineering Department TWO DIMENSIONAL CONSERVATIVE CONTAMINANT TRANSPORT MODELING OF THE AKAKI WELLFIELD By Jemal Seid November-2009 Addis Ababa-Ethiopia Addis Ababa University School Of Graduate Studies Faculty of Technology Chemical Engineering Department TWO DIMENSIONAL CONSERVATIVE CONTAMINANT TRANSPORT MODELING OF THE AKAKI WELLFIELD By Jemal Seid Approved by Board of Examiners ___________________ _______________ _____________ Chairman, Department Signature Date Graduation Committee ___________________ _______________ _____________ Advisor Signature Date ___________________ _______________ _____________ Examiner Signature Date Declaration I, the under signed, declare that this thesis is my own work and that all sources of material used for the thesis have been dully acknowledged. ________________ _ _ _ _ _ _ _________ Jemal Seid Date This is to certify that the above declaration made by the candidate is correct to the best of my knowledge. ________________ _ _ _ _ _ _ _________ Advisor Date Two-Dimensional Conservative Contaminant Transport Modeling of the Akaki Wellfield By: Jemal Seid A Thesis Submitted to the School of Graduate Studies of Addis Ababa University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Environmental Engineering Nov, 2009 Acknowledgements I am deeply grateful to Addis Ababa Water & Sewerage Authority (AAWSA) staff members Ato Yirga Tadesse and Ato Zeleke Teferi who provided & helped me with the necessary information, data, as well as laboratory set up, with out which the accomplishment of this thesis work would be unsuccessful. Acknowledgements are also due to my advisor Ato Teshome Worku who arranged me in reaching the relevant institutions through official letters & guided me on how to proceed through out my work. I thank also the Chemical Engineering Department of faculty of technology for facilitating this process. Gratitude also goes to W/t Esete Berhanu who had taken part in writing the manuscripts of parts of this thesis work. Jemal S. Addis Ababa, Ethiopia. ii Abstract This thesis work focuses on non-reactive solute transport modeling of the akaki wellfield for two selected groundwater contaminants (chloride & fluoride) for the 25 operating boreholes administered by Addis Ababa Water & Sewerage Authority (AAWSA). The work is conducted based on laboratory analysis of groundwater samples from selected boreholes and based on historical data of the wellfield boreholes. The widespread use of chemical products, coupled with the disposal of large volumes of waste materials, poses the potential for widely distributed groundwater contamination. Because such contaminations can pose a serious threat to public health, prediction of the degree of contamination by appropriate numerical modeling tools is vital to aware the end user from possible risks. Mathematical models solved numerically are the subject of this thesis work focusing on conservative solute transport in the Akaki well field. Chloride & fluoride ions predictive modeling of the wellfield for the next ten years (2007-2017) is made first by calibrating the model input parameters using the available historical solute concentration data for selected boreholes at various periods. For calibration purpose, initial solute concentration was taken as 3 mg/l for chloride and 0.51 mg/l for fluoride and MATLAB simulation of chloride & fluoride ion concentration is done. The simulation results show that while chloride concentrations in the wellfield get increased; fluoride, however, is getting decreasing through out all of the boreholes in the wellfield. This is in agreement with the actual observed pattern of solute load of the wellfield revealing chloride is being introduced in to the wellfield by one or more mechanisms somewhere in the vicinity of the akaki river catchment (ARC) while fluoride is not. Keywords: aquifers, breakthrough curves, initial conditions, boundary conditions, calibration, prediction, conservative contaminant transport, hydraulic conductivity, porosity. iii Table of Contents Chapter Title Page Acknowledgements..………………………………………………………… ii Abstract……………..………………………………………………………. iii Table of Contents……..……………………………………………………...iv List of Tables…………..……………………….…………………………....vi List of Figures…………..……………………………………………….......vii Acronyms & Abbreviations…..………………………………………..…...viii 1. Introduction…..………..……………………………………………………..1 1.1 Background……..……………………………………………………………..3 1.2 Problem Statement..…………………………………………………………...5 1.3 Objective of the Study..……………………………………………………….7 1.3.1 General Objective………………………………………………………...7 1.3.2 Specific Objective………………………………………………………...8 1.4 Scope & Limitations of the Study…..…………………………………………8 1.5 Significance of the Study……………..……………………………………….9 2. Literature Review…………………………………………...………….…..10 2.1 Groundwater and Aquifers………………………………..…………………10 2.2 Groundwater Flow…………………………………………..………………13 2.3 Sources of Groundwater Pollution…………………………..………………16 2.4 Contaminant Transport Processes in Groundwater…………..……………...25 2.5 Background on Akaki Well Field……………………………..……………..31 2.6 Groundwater Pollution Monitoring Parameters: Focus on Pollutants…….....37 3. Materials & Methods…………………..…………………………………....43 3.1 Research Materials…………………………………..……………………….43 3.2 Modeling Features……………………………………..…………………….43 3.2.1 Numerical Solution Technique Scheme of the Selected Model………...45 iv 3.2.2 Model Domain, Grids and Boundary Conditions……………….………52 3.2.3 Input Parameters to the Model & Calibration Data………………….….55 3.3 Data Analysis: Conservative Transport Modeling of Akaki Well Field.……64 3.3.1 Calibration & Sensitivity Analysis of Parameters………………………65 3.3.2 Model Prediction and Validation……………………………………….70 4. Results and Discussions...…………………………………………………..79 4.1 Chloride Ion Simulation Results……….…………………………………….79 4.2 Fluoride Ion Simulation Results………….………………………………….87 5. Conclusions & Suggestions…….....…….………………………………….93 5.1 Conclusions...………………………………………………………………...93 5.2 Suggestions……..……………………………………………………………95 References…………...……………………………………………………….96 Appendices Appendix A-1: Program for Fluoride Ion Calibration Model………………..99 Appendix A-2: Program for Validated Fluoride Ion Prediction ……………103 Appendix B-1: Water Quality Monitoring Data for Borehole BH06……….109 Appendix B-2: Water Quality Monitoring Data for Borehole BH07……….111 Appendix B-3: Water Quality Monitoring Data for Borehole BH22……….112 Appendix B-4: Water Quality Monitoring Data for Borehole EP04………..114 Appendix B-5: Water Quality Monitoring Data for Borehole EP08………..115 Appendix C-1: Hydraulic Gradient Data of AWF & Selected Sites………..117 Appendix C-2: Aquifer Lithology Data for Selected Wellfield Sites……….123 Appendix C-3: Transmissivity Data for Selected Wellfield Sites…………..128 v List of Tables Table 1.1: Towns & Cities in Ethiopia Supplied from Groundwater…………………......1 Table 1.2: Bacterial Population of the Wellfield………………..………………………...7 Table 2.1: The Order of Magnitude of the Permeability of Natural Soils……………….14 Table 2.2: Potential Groundwater Contamination Sources………………………………19 Table 3.1: Discretization Scheme of the Wellfield………………………………………55 Table 3.2: Water Level Data for the 25 Boreholes in the Akaki Well Field…………….56 Table 3.3: Transmissivity Data for Selected Boreholes of the Akaki Well Field……….57 Table 3.4: Aquifer Lithology Data for the 25 Boreholes in the Akaki Well Field……....58 Table 3.5: Average Hydraulic Conductivity of the Aquifers in the Well Field………….60 Table 3.6: Average Hydraulic Gradient of the Wellfield………………………………..61 Table 3.7: Summary of Initial Input Parameters to the Calibration Model……………...62 Table 3.8: Major Anions Concentrations for Borehole 06………………………………63 Table 3.9: Major Anions Concentrations for Borehole 07………………………………63 Table 3.10: Major Anions Concentrations for Borehole 22……………………………..64 Table 3.11: Major Anions Concentrations for Borehole EP 08…………………………64 Table 3.12: Calibrated Input Parameters to the Predictive Model………………………70 Table 3.13: Major Anions Concentrations at Selected Boreholes for July 2009 ………..71 Table 3.14: Major Anionic Concentrations at Selected Boreholes for October 2008…...78 Table 4.1: Comparison of Observed and Computed Chloride Concentrations………….79 Table 4.2: Spatial Chloride Concentration Distribution at the End of June 2017……….80 Table 4.3: Comparison of Observed and Computed Fluoride Concentrations…………..87 Table 4.4: Spatial Fluoride Concentration Distribution at the End of June 2017………..88 vi List of Figures Fig 1.1: Location of Akaki Well Field…………………………………………………….4 Fig 1.2: Akaki Well Field Site...…………………………………………………………..5 Fig 1.3: Chemically Polluted Little Akaki River …………………………………………6 Fig 1.4: Organic Pollution in Kebena River………..……………………………………..6 Fig 2.1: Schematic representation of contaminant plumes possibly associated with various types of waste disposal...………………………………………………………...17 Fig. 2.3: Longitudinal and Transverse Spreading due to Mechanical Dispersion...……..29 Fig 3.1: Modeling Protocol Flow Diagram………………………………………………45 Fig 3.2: Finite difference grid of Akaki wellfield with 9 x 7 node system ……………..47 Fig 3.3: Model Area of the Akaki Well field……………………………………………54 Fig 4.1: Chloride concentration Surface Plot of the Wellfield at the End of June 2017...81 Fig 4.2 Chloride Breakthrough Curve for Borehole BH07………………………………82 Fig 4.3 Chloride Breakthrough Curve for Borehole BH10………………………………83 Fig 4.4 Chloride Breakthrough Curve for Borehole BH16………………………………83

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