Modeling of Arsenic Transport in Groundwater Using Modflow
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MODELING OF ARSENIC TRANSPORT IN GROUNDWATER USING MODFLOW A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF MASTER OF ENGINEERING IN ENVIRONMENTAL ENGINEERING SUBMITTED BY PHURAILATPAM SUPRIYA (Roll No. 3451) UNDER THE ESTEEMED GUIDANCE OF Prof. S.K. SINGH DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING DELHI COLLEGE OF ENGINEERING UNIVERSITY OF DELHI JUNE, 2005 Department of Civil & Environmental Engineering Delhi College of Engineering, Delhi-42 CERTIFICATE This is to certify that the project report entitled “MODELING OF ARSENIC TRANSPORT IN GROUNDWATER USING MODFLOW” being submitted by PHURAILATPAM SUPRIYA (Roll No. 3451) is a bonafide record of her own work carried under my guidance and supervision in partial fulfillment for the award of the degree of Master of Engineering in Environmental Engineering from Delhi College of Engineering, Delhi. Prof. S.K. Singh Professor Deptt. Of Civil & Environmental Engineering Delhi College of Engineering, Delhi i ACKNOWLEDGEMENTS Any accomplishment requires the efforts of many people and this work is no exception. I appreciate the contribution and support, which various individuals have provided for the successful completion of this study. It may not be possible to mention all by name but the following were singled out for their exceptional help. It is with immense pleasure that I acknowledge my gratitude to Prof. S.K. Singh, Professor, Delhi College of Engineering, Delhi, for his scholastic guidance and sagacious suggestions throughout this study. His immense generosity and affection bestowed on me goes beyond his formal obligations as guide. It is with immense affection that I acknowledge my gratitude to Dr. D.K.Singh, Water Technology Centre, Indian Agricultural Research Institute (IARI), Delhi for his perpetual encouragement, generous help and inspiring guidance throughout this study. I would like to express my sincere thanks to Dr. P. B. Sharma, Principal, Delhi College of Engineering, Delhi for allowing me to perform this study. I would like to acknowledge the Central Groundwater Board (CGWB), Kolkatta for making the data available without which this work would have been impossible. I would like to thank Mr. Soumyajit Mukherjee, Research Scholar, IIT Roorkee for his kind help that eventually led to this dissertation. The moral support and love given by my friends Shraddha Singhai, Payal Singla, Shweta Sharma, and Sunita Verma help me stood when were times difficult. It would be gross mistake on my part, if I forget the love and blessings of my grandmother, my parents, my brothers and my sisters that I could not have raised to this height in my life. Dated: (Phurailatpam Supriya) ii ABSTRACT Arsenic contamination in the groundwater is increasing at an alarming level with time and more areas are becoming contaminated. At least 28 million people currently drink water containing more than 50 µ g/l of arsenic and many more consume water with > 10 µ g/l of arsenic. Evidence of chronic arsenic toxicity is accumulating and includes melanosis , hyperkeratosis of palm and sole, gangrene and skin cancer. A MODFLOW based three-dimensional model has been simulated to understand the movement of water and arsenic in the study area situated in the Yamuna Sub-basin, West Bengal. Microbial reduction of iron oxyhydroxide (FeOOH) and release of its sorbed arsenic load to solution is an important mechanism by which arsenic enters groundwater. Arsenic pollution does not arise from oxidation of sedimentary sulphides nor from ion- exchange with phosphorus derived from fertilizer (or other sources). MODFLOW was run for the study area and the movement of water in the study area was simulated. It was seen that the variation of hydraulic heads was more in clay than in sand layer. Arsenic was assumed to be injected continously at a well 12005m away from both the western and northern side of the Yamuna Sub-basin in the block of Chakdah, Nadia district at a depth of 25m from the ground level. Simulation was performed for the movement of arsenic for every 1 year for a stretch of 20 years. The spatial and temporal distribution of arsenic was studied through contours maps for 1, 5, 10, 15, and 20 years. The concentration of arsenic vs time graph was also drawn. It was seen that arsenic was spreading more in the sand layer than in the clay layer, affecting more and more places near the study area. iii TABLE OF CONTENTS CERTIFICATE i ACKNOWLEDGEMENTS ii ABSTRACT iii TABLE OF CONTENTS iv LIST OF FIGURES viii LIST OF TABLES x CHAPTER 1 INTRODUCTION 1 1.1 GROUNDWATER 1 1.2 GROUNDWATER CONTAMINATION 1 1.3 GROUNDWATER REMEDIATION 2 1.4 GROUNWATER MODELING 3 1.5 ARSENIC CONTAMINATION OF GROUNDWATER 3 1.6 OBJECTIVES OF THE STUDY 4 CHAPTER 2 LITERATURE REVIEW 5 2.1 GROUNDWATER CONTAMINATION 5 2.2 ARSENIC CONTAMINATION OF GROUNDWATER 6 2.2.1 Arsenic- General Information 6 2.2.2 Arsenic Contamination of Groundwater in India 7 2.2.3 Arsenic Contamination of Groundwater in West Bengal 8 2.2.4 Harmful Effects of Arsenic 9 2.2.5 Determing Exposure to Arsenic 10 2.2.6 Theories of Arsenic Mobilization 10 (1) Pyrite Oxidation and Irrigation Drawdown 11 (2) Competitive Exchange with Fertilizer-Phosphate 12 (3) Reduction of FeOOH 13 2.2.7 REMOVING ARSENIC FROM WATER 15 2.3 APPLICATIONS OF MODFLOW 15 iv CHAPTER 3 MECHANISMS AFFECTING THE SOLUTE TRANSPORT IN GROUNDWATER 18 3.1 DARCY’S LAW 18 3.2 TRANSPORT MECHANISMS 18 3.2.1 Advection 18 3.2.2 Diffusion 20 3.2.3 Dispersion 21 3.2.4 Linear or Non-linear Sorption 24 3.2.5 Biodegradation 25 CHAPTER 4 MODELING OF GROUNDWATER CONTAMINATION 27 4.1 INTRODUCTION TO GROUNDWATER MODELING 27 4.2 USE OF GROUNDWATER MODELS 28 4.3 DEVELOPING A GROUNDWATER MODEL 28 4.4 TYPES OF ERROR 30 4.4.1 Computational Error 30 4.4.2 Calibration Error 31 4.5 DRAWBACKS AND USEFULNESS OF THE MODELING 31 4.6 APPLYING NUMERICAL MODELS TO FIELD SITES 31 CHAPTER 5 PROCESSING MODFLOW FOR WINDOWS (PMWIN) 32 5.1 INTRODUCTION 32 5.2 PACKAGES UNDER PMWIN 32 5.2.1 MODFLOW 32 5.2.2 PMPATH 32 5.2.3 MT3D 33 5.2.4 MT3DMS 33 5.2.5 MOC3D 33 5.2.6 PEST and UCODE 33 5.3 MODFLOW 34 5.3.1 Grid 35 5.3.2 Layer Type 38 5.3.3 Boundary Condition 38 (1) IBOUND (MODFLOW) 38 v (2) ICBUND (MT3D) 39 5.3.4 Layer Top and Bottom 39 5.3.5 Time 39 5.3.6 Initial Hydraulic Heads 39 5.3.7 Horizontal Hydraulic Conductivity and Transmissivity 40 5.3.8 Vertical Hydraulic Conductivity and Leakance 40 5.3.9 Storage Terms 40 5.3.10 Effective Porosity 40 5.3.11 MODFLOW Packages 41 (1) Density Package 41 (2) Drain Package 41 (3) Evapotranspiration Package 41 (4) General Head Boundary Package 41 (5) Horizontal Flow Barrier Package 41 (6) Interbed Storage Package 42 (7) Recharge Package 42 (8) Reservoir Package 42 (9) River Package 42 (10) Streamflow Routing Package 42 (11) Time-Variant Specified-Head Package 43 (12) Well Package 43 (13) Block-Centered Flow 2 Package 43 5.3.12 Model Run 43 5.4 MATHEMATICAL MODEL OF MODFLOW 44 5.5 MT3D 45 5.5.1 Initial Concentration 47 5.5.2 Advection Package 47 5.5.3 Dispersion Package 47 5.5.4 Chemical Reaction Package 47 5.5.5 Sink & Source Concentration Package 47 5.6 MATHEMATICAL MODELING OF MT3D 48 CHAPTER 6 MATERIALS AND METHODS 49 6.1 THE STUDY AREA 49 vi 6.2 HYDROLOGY OF THE STUDY AREA 51 6.2.1 Surface Water Hydrology 51 6.2.2 Groundwater Hydrology 52 6.3 LITHO LOGS AND ARSENIC LEVELS OF THE STUDY AREA 52 6.4 GROUNDWATER FLOW MODELING USING MODFLOW & SOLUTE TRANSPORT MODELLING USING MT3D 54 CHAPTER 7 RESULTS AND DISCUSSION 59 7.1 VARIATION OF HYDRAULIC HEADS 59 7.1.1 Variation of Hydraulic Heads in the Clay Layer (1st Layer) 59 7.1.2 Variation of Hydraulic Heads in the Sand Layer (2nd Layer) 60 7.2 DISTRIBUTION OF ARSENIC IN THE STUDY AREA 60 7.2.1 Distribution of Arsenic in the Clay Layer (1st Layer) 60 7.2.2 Distribution of Arsenic in the Sand Layer (2nd layer) 62 CONCLUSION 93 RECOMMENDATIONS 95 APPLICATIONS OF THE STUDY 97 FUTURE SCOPE OF WORK 98 RERERENCES 99 APPENDIX-I 105 APPENDIX-II 106 APPENDIX-III 109 vii LIST OF FIGURES Figure Page Figure Name No. No. 1.1 A schematic aquifer (After Florida Geological Survey) 2 2.1 Groundwater contamination through various processes 6 3.1 Breakthrough curves showing effects of dispersion and retardation 21 3.2 Longitudinal dispersion and Transverse dispersion 22 3.3 Effect of Dispersion (after Kinzelbach, 1992) 23 Diagram showing Block Centered Grid System (after McDonald 5.1 36 and Harbaugh, 1988) Spacial discretization of an aquifer system (after McDonald and 5.2 37 Harbaugh, 1988) 5.3 Schematic structure of the ground water modeling component 45 6.1 Map showing the blocks under the study area 50 6.2 Custom grid of the model 55 7.1 Variation of hydraulic head in the clay layer (1st layer) 75 7.2 Variation of hydraulic head in the sand layer (2nd layer) 76 Contour map showing distribution of arsenic in the clay layer (1st 7.3 77 layer) after 1 year Contour map showing distribution of arsenic in the sand layer (2nd 7.4 78 layer) after 1 year Contour map showing distribution of arsenic in the clay layer (1st 7.5 79 layer) after 5 years Contour map showing distribution of arsenic in the sand layer (2nd 7.6 80 layer) after 5 years Contour map showing distribution of arsenic in the clay layer (1st 7.7 81 layer) after 10 years Contour map showing distribution of arsenic in the sand layer (2nd 7.8 82 layer) after 10 years Contour map showing distribution of arsenic in the clay layer (1st 7.9 83 layer) after 15 years viii Contour map showing distribution of arsenic in the sand layer (2nd 7.10 84 layer) after 15 years Contour map showing distribution of arsenic in the clay layer (1st 7.11 85 layer) after 20 years Contour map showing distribution of arsenic in the sand layer (2nd 7.12 86 layer) after 20 years 7.13 Concentration of arsenic in borehole no.