Model Studies Of Groundwater Quality And Formation Characteristics In Phreatic Aquifers

ABSTRACT

Model studies of groundwater quality and formation characteristics in phreatic aquifer were carried out in Rivers State the study area. The research was to find a better solution of pollution transport in groundwater, considering the effect of geologic parameters such as heavy metals, micronutrients, porosity, permeability, and void ratio. The source of pollution was through indiscriminate dumping of biological wastes and wastes from soakaway, regenerating the wastes in most parts of the study area. This research was carried out through an experiment performed for E.coli transport, including some other parameters that influence microbial growth, inhibition and variation for fast migration within a short period of time. These parameters are heavy metals, micronutrients, permeability, porosity, and void ratio. Velocity of solute transport (E.coli) was determined through column experiment in each soil sample for all the locations. Empirical model was applied through experimental results plotted, generating a polynomial equation. The expressions from polynomial were applied to verify the results for E.coli, micronutrients, heavy metals, degree of porosity, permeability and void ratio. The physiochemical parameter from the study carried out found that the growth of E.coli under environmental conditions favoured it. The research was able to produce the level of physiochemical parameter influencing E.coli concentration in groundwater. The presence of E.coli depends on the availability of nutrients as well as favourable conditions in terms of physiochemical parameter. More so, the concentration increased with depth in micronutrient. The study confirmed that the higher the depth of water, the lower the population of E.coli in some locations based on the decrease in substrate utilization; while in some areas, it varies. The study explained that the rapid growth on the population of E.coli is experienced when the pH value is acidic than alkaline. The study carried out was able to express the stabilization of groundwater quality by inhibiting the presence of metallic element in some locations; while in few locations in the study area, it was discovered that the presence of  E.coli in different aquifers have lower percentage and become less harmful to the quality of groundwater for human utilization. The level of porosity were investigated on the migration of E.coli influenced by porosity from one aquifer to the other, the results were calibrated and verified generating a model that can be applied to predict the rate at which E.coli transport within a short period of time. The variation of micropores i.e. void ratio from different soil depositions were determined, calibrated and verified. The results can be applied to predict the variations in the micropores and hydraulic conductivity within the soil structure, as it influences the variation in the migration of E.coli in phreatic aquifers. The rate of liquid flow within the soil profile (stratum) i.e. through the rate of permeability, is imperative because it has contributed to the rate of distribution of E.coli, as well as effectiveness in terms of stability in the region by reducing the migration and transport at different strata, this was investigated in the study. The results on the level of flow and the influence on the permeability were determined in the study areas. The permeability results were verified to predict the rate of velocity of water like that of solute at different soil formations, this results verified can be applied to predict the velocity of ground water influencing the rate of transport at different strata, the verified model result can be applied to predict the time at which the microbes can transport to groundwater aquifers in all the study areas. The soil compositions influenced by E.coli concentration as well as the rates of migration were investigated, the soil profile that contains high concentration known to be gravel and coarse were determined. Finally, the developed model from experimental results should be applied by thorough assessment of the area, to determine the type of concept to be applied in assessment of ground water quality in the study location through design of boreholes.

 

 

 

 

 

TABLE OF CONTENTS

 

CHAPTER 1: INTRODUCTION

1.1       Background of the study                                                                             1

1.2       Transport influence and Geologic History of Rivers State                   6

1.3       Statement of Problem                                                                                  10

1.4       Objectives of the Study                                                                               11

1.5       Scope of the Study                                                                                       13

CHAPTER 2: LITERATURE REVIEW                                                                       

2.1       Darcy’s Law                                                                                                  15

2.1.2   Transport Processes                                                                                     15

2.1.3   Molecular Diffusion                                                                                                17

2.1.4   Mechanical Dispersion                                                                               18

2.1.5   Advective Dispersive Equation (ADE)                                                    19

2.1.6   Degradation                                                                                                  19

2.2       Determining Straining of Escherichia coli from Breakthrough Curve            21

2.2.1   Pore size Density Function                                                                         29

2.2.2   Bacteria Transport Model                                                                           30

2.2.3   Determining the Van Genuehten Parameters                                           32

2.2.4   Tracer Breakthrough                                                                                   33

2.2.5   E.coli Breakthrough                                                                                     33

2.2.6   Volume available for Straining                                                                  36

2.2.7   Indicator Organisms                                                                                                43

2.2.8   Morphology and Surface Characteristics of E.coli Taxonomy             46

2.3       E.coli in Water                                                                                              48

2.3.1   Hydrophilic Bacterial Cell Wall                                                                50

2.3.2   The Surface Charge of E.coli                                                                     52

2.3.3   Non-uniform Surface charge Distribution                                               53

2.3.4   General Bacteria Transport Model                                                                        55

2.3.5   Simplifying the rate expression for fractional surface coverage

(Eqn. 2.36) for E.coli Transport                                                                 60

2.3.6   Blocking                                                                                                        61

2.3.7   The Attachment Rate Coefficient                                                              62

2.3.8   The Single Collector Contact Efficiency (h₀)                                          64

2.3.9   The Straining Rate Coefficient                                                                  65

2.4       Relative Importance of the Bacteria Transport Mechanisms                68

2.4.1   The Filter Coefficient (β)                                                                            69

2.4.2   Factors Affecting the Contact Efficiencies                                              70

2.3.3   Effect of Grain Size Uniformity of Sediment                                          71

2.4.4   Factors Affecting the Collision Efficiency                                              72

2.4.5   Effect of Ionic Strength                                                                               75

2.4.6   Effect of Lipopolysaccharides Composition in the outer Membrane  76

2.4.7   Effect of Geochemical Heterogeneity                                                      77

2.4.8   Effect of Grain Surface Roughness                                                           79

2.4.9   Evidence of Bimodal Efficiencies                                                             79

2.4.10 Filter Coefficients and Collision Efficiencies from Field

and Laboratory Experiments                                                                      82

2.5       Kinetic Desorption or Detachment                                                           85

2.5.1   Factors Affecting Inactivation                                                                   86

2.5.2   Effect of protozoa and antagonists                                                                       87

2.5.3   Other effects on the die-off rate coefficient                                            88

2.6       Measuring and Modeling Straining of Escherichia coli in

Saturated Porous Media                                                                  96

2.6.1   Theory                                                                                                           99

2.6.3   Model Fitting and Numerical Modeling Tools                                        101

2.6.4   Electrokinetic Characterization of E.coli, Cell Size

and Stability of the E.coli Suspension                                                      103

2.6.5   Nature and Occurrence of Straining, Attachment and Detachment     104

2.6.6   Model Fitting                                                                                                107

2.7       Sensitivity of the Model Results to Parameter Values                           109

2.7.1   Comparing Modelled and Measured Values                                           110

2.7.2   Effect of Transport Distance                                                                      112

2.7.3   The fitting parameter B and the mass balance of strained bacteria     134

2.8       Transport of E. coli in Columns of Geochemically Heterogeneous     Sediment                                                                                                        120

2.8.1   Porosity of the column sediments                                                             125

2.8.2   Column experiment method                                                                       126

2.8.3   The result conditions during the experiments                                        127

Fig 2.18:

2.8.4 The breakthrough curves                                                                              127

2.8.5   Sticking efficiency                                                                                       128

2.8.6   Effects of Lag and Maximum Growth in Contaminant

Transport and Biodegradation Modeling                                                 132

Source: Taylor & Francis, 2007).

2.8.7   Description of kinetics                                                                                133

2.9       Modeling Solute Transport in Porous Media                                           140

2.10    Virus Transport from Septic Tank Systems near Seasonally

Inundated Areas through Shallow Aquifers                                             151

2.11    Factors Affecting Microbial Survival in Groundwater                          160

2.12    Studies on Viruses                                                                                      164

2.12.1 Studies on Viruses and Bacteria                                                               171

2.12.2  Studies on Bacteria and Cryptosporidium                                              174

2.13    Comparison of Escherichia coli and Campylobacter Jejuni

Transport in Saturated Porous Media                                                       178

2.14    Survival of Water Quality Indicator Microorganisms in the

Groundwater Environment Temperature and Total

Dissolved Solids Effects                                                                             189

2.14.1 Biomass Structures in Porous Media                                                       196

2.14.2 Microbial Attachment/Detachment Processes in Porous Media         199

2.14.3 Modeling Biological Reactions in Porous Media                                  212

2.14.4 Heterogeneity, Transport, and Scaling Issues                                         215

2.15    Solute Transport Models                                                                           222

2.15.1 Deterministic-functional models                                                               223

2.15.2 Stochastic-mechanistic models                                                                 223

2.15.3 Stochastic-functional models                                                                    225

2.15.4 Deterministic-mechanistic models                                                                        226

2.15.5 Solute Transport Models for Multi-Layered Porous Media                  228

2.15.6 Solution of Governing Equations for Transport Models                       231

2.15.7 Parameter Estimation                                                                                  236

2.15.8 Modeling of Solute Dispersion                                                                 236

2.15.9 Models for Solute Dispersion at various Scales                                     238

2.15.10 Deficiency of Previous Researchers                                                       244

CHAPTER 3: METHODOLOGY

3.0       Theoretical Background                                                                             248

3.1       Experimental Method                                                                                  250

3.2       Permeability Test                                                                                         250

3.3       Physiochemical Analysis of Heavy Metals and Micro Elements         252

3.4       Column Experiments                                                                                   252

3.4. 1 Experiment set up                                                                                        252

3.5       Bacteriological Testing of Water                                                               253

3.5.1   Choice of Technique                                                                                   253

CHAPTER 4: RESULTS AND DISCUSSION

4.0       Data Analysis                                                                                               256

4.1       Concentration of Micronutrients versus Depths at Different

Locations                                                                                                       259

4.2       Concentration of Heavy Metals versus Depth at different Locations  270

4.3       Concentration Result of Micronutrients at Upland Location               296

4.4       Concentration of Column Experiment at Different Depths                   314

4.5       Concentrations of Heavy Metal, and Micronutrients at Different

depths in Coastal Locations                                                                       331

4.6       Concentration Micronutrients at different Depths and Locations       335

4.7       Concentrations of E.coli at different Depths and Locations                 339

4.8       Model Verification for Permeability, Porosity and Void Ratio

Experimental Result                                                                                                343

4.9       Calculated and Measured Values of Porosity at Different

Depths and locations                                                                                   364

 

4.10    Calculated and measured Model Values for Void ratio at

Different Depths and Locations                                                                386

4.11    Determined Coefficient of Permeability Result and Discussion          407

4.12    Verified model result for E.coli, micronutrient and heavy metals       424

4.12.1 Model Result from Column Experiment (E. coli)                                   424

4.12.2 Calculated and Measured Values of E. coli transport                           434

4.12.3   Calculated and Measured Values for Heavy at Different depths       454

4.13    Calculated and Measured values Micronutrients at different

depths and Locations                                                                                  474

4.14    Velocity of Micro organism (E.coli) transport from Column

Experiment at Different Locations                                                                        494

CHAPTER 5: CONCLUSION AND RECOMMENDATIONS

5.1       Conclusion                                                                                                    513

5.2       Recommendations                                                                                       524

5.3       Further study                                                                                                            525

References                                                                                                                526

Appendices

 

CHAPTER ONE

INTRODUCTION

1.1     Background of the Study

Throughout history, the quality and quantity of drinking water has been the major concern and the most vital issue in human welfare on earth today. The quality and quantity of water valuable to human have disappeared because of water shortage resulting from changes in climate. Even temperature, fluctuation, and limited precipitation caused problems. Devastating drought in Africa in 1980 resulted in catastrophic crop failure and more so; water is the most abundant liquid on earth. It covers three quarters of the earth, and settlement hinges on the availability of water. In man, three quarters of the fluid in him are made up of water. A man can live about a month without food, but he will die in a week without water, hence experts claim that declining supplies of fresh water will be a source of increasing tension in coming years. Worldwide, more than one billion people do not have access to clean water. About thirty percent of groundwater consist of fresh water, most of which are inaccessible, unusable or may be obtainable at great expense of energy. Only three-tenth of one percent of total fresh water can be truly considered as renewable. The water from rainfall seeping into the soil to nourish plant and tree growth and lakes, flow into the ocean and evaporating into the atmosphere in a natural hydrological cycle that will produce more rain. In 2004, there were still at least one billion people across the world, which do not have access to safe drinking water. Many of these people live in rural areas and are among the poorest and more vulnerable to be found anywhere in the world.

The international community has set up ambitious millennium development goals, to reduce by half the number of people without clean water by 2015. In this context the need for sustainable development and management of groundwater cannot be overstated. Across large swathes of Africa, South America, and Asia, groundwater provides the realistic water supply option for meeting dispersed rural demand. Alternative water resources can be unreliable and expensive to develop, surface water (if available) is prone to contamination and often seasonal, and rainwater harvesting can be expensive and requires good rainfall throughout the year. Groundwater, however, can be found in most environments, if you look hard enough with the appropriate expertise. Groundwater is the portion of the earth water cycle that flows underground. Groundwater originates from the precipitation that percolates into the ground. Percolation is the flow of water through soil and porous/fracture rock. The water table separates the saturated, or aquifer zone from the unsaturated or vadose zone, where the water does not fill all the voids or space in the soil or rock.  The general trend is for water in the unsaturated zone to move down water until it reaches the water table.         On the other hand, water in the saturated zone moves primarily along horizontal hydraulic gradients, from high to lower elevation, the ocean is the natural sink for groundwater flows.

Groundwater does not recycle readily. Rate of groundwater turnover vary from days to years, and from centuries to millennia, depending on aquifer location, type, depth, properties, and connectivity. The average time for the renewal of groundwater is 1,400years. Shorter renewal times tend to be associated with shallow groundwater, while longer renewal times are associated with deep groundwater.

Groundwater flow occurs under conditions that are usually classified as being either confined or unconfined. Confined groundwater flow is vertically constructed by the local geology and characterized by having positive fluid pressure throughout the domain. Conversely, unconfined flow occurs where there is a transition flow, positive fluid pressures in the saturated part of the domain, across an interface called the phreatic surface where the fluid pressure is atmospheric, into the unsaturated zone where fluid pressures are negative due to capillary forces. Because there is an open continuum, between surface processes, both natural (e.g. recharge) and artificial (e.g. waste disposal), and subsurface flow processes under unconfined conditions, then it is imperative that unconfined flow processes can be quantified to aid in the understanding and management of stresses upon the resource.               Figure 1.1 shows a schematic diagram of an unconfined aquifer and associated features such as the phreatic surface and recharge processes.

L

H

Surface water

Unconfined aquifer

Surface water

Region where horizontal flow modeling is valid

Region where horizontal flowmodeling is invalid

Region where horizontal flowmodeling is invalid

Recharge

 

 

 

 

 

 

 

 

Figure 1.1: Unconfined groundwater flow and associated processes at the regional scale.

 

This explains predominance of unconfined beds being recharged by high rain intensities. This increases the groundwater aquifers under the influence of deltaic aquifer as expressed in the figure. Technique of Seepage-face boundaries occur at the interface between an unconfined aquifer and a surface water body. The formation of seepage-face boundaries is caused by vertical flow components, which can dominate at the groundwater-surface interface and therefore cannot be detected through the use of models that invoke horizontal flow strategies.

Over the past decade, this recognition is in part, a response to the realization of how the ubiquitous nature of horizontal flow modeling has stifled the understanding of the complicated three-dimensional flow patterns in several studies in some regions. In a recent survey of hydrological research, experts identified coupled groundwater and surface water problems (under the umbrella of salt-water intrusion problems), as one of the five, groundwater related societal problems that are presently unresolved and cannot be reliably resolved using current scientific knowledge. Further, the importance of understanding unconfined flow and groundwater-surface water interaction has been highlighted, as an important point of interdisciplinary research. For example, previous expert presented a review, which linked a poor understanding of subsurface flow at the groundwater-surface water interface to a lack of understanding of water quality changes and nutrient cycling in the vicinity of the groundwater-surface water interface.

Therefore, given that a lack of understanding of unconfined groundwater flow simulation at the groundwater-surface water interface has been established, most previous studies  has presented  a largely theoretical development of various numerical modeling strategies able to simulate unconfined groundwater flow where vertical processes on solute transport and seepage-face formation were necessary. The model development is used to investigate several specific research objectives.

 

 

1.2     Transport Influence and Geologic History of Rivers State

Rivers State is part of the Niger Delta, which is at the Southern end of Nigeria bordering Atlantic ocean and extends from about Longitude 3’9⁰E and Latitude 4’30-5⁰ 20N. Rivers State is part of the Niger Delta Environment that developed from the moto delta in the Northern part Basin during the companion transgression and ended with the Paleocene transgression. Rivers State formation is generated from the Niger Delta modern formation during the Eocene. It has three major depositions also just like every other part of the Deltaic Environment. Marine mixed and continental generally observed in the Deltaic Environment. The three major formations are Benin, Agbada and Akata formation; it was estimated that one million cubic meter of sand are carried towards mahin every year. While that of the Niger Benue are deposited on top of the Delta.

Since the study focuses on the Benin formation i.e. groundwater disintegrating to sombrero that transit at the Ahoada River, the geologic history of Rivers State are predominated by the deposited formation.  The stratigraphy of the study area (Rivers State) are deposited by locustrine, Alluvial and fluvovia including off lap sediments, The locustrine deposit in the study area is heterogeneous predominant while alluvial and fluvovia deposits are homogenous predominant. Its coastal area on the study is where off lap sediments including tidal channels of 60ft and 800ft deep.

More so, the fluvovia has marine deposits that include clay upward changing to laminated clay silt and fine sand. The fluviomarine character gradually becomes more pronounced, the sand thickens, and the grain size increase and plant remains become more prominent. While the fluviotile deposits are best followed from inland to the coast, the sediments are characteristically finer upward and the width thickness ration is of order of 400-800 far the point bars, thus distinguishing them from tidal channel deposits.

This implies that there will be variations on the stratigraphy in the study area and will definitely influence the transport base these conditions. The deposited formation were confirmed to be the highest yield formation from a phreatic aquifer deposited, in every part of Rivers State, predominantly 90% of sand stone and 5% of sand stone and sedimentary deposited, it also has a predominant of montmonorite clay mineral including some other locations of deposited some hazardous chemical from manmade activities and natural origin. Its water table base on the study has an average of 7.5m water table. But in most coastal environment, it has an average of 1.5m water table.

The study also confirms that a good aquiferous zone has an average of 30-36m in the upland area while in the coastal area is 12-15metres. Porosity of the soil was confirmed to be very high which makes the focus of the study imperative for pollution transport, as abstraction of groundwater of good quality is complex due to its high level of variation in depth of formation for quality water. More so, some deposited physiochemical parameters are also confirmed to be deposited on some part of Rivers state, the deposition has the man made activities influence including the natural origin.

More so, in general, aquifer passage reduces pathogenic microorganism concentration and numerous successes have been reported in cases like artificial recharge schemes or riverbank filtration project, where microorganisms were completely removed. In Rivers State this is a serious problem; over sixty percent of the water abstracted from the ground is polluted water, because of inadequate implementation of design and application of standard in other to prevent these pollution threats of human life. However, studies in the USA have shown that up to half of all US drinking water well tested had evidence of fecal contamination and an estimated 750,000 to 5.9 million illnesses and 1400-9400 deaths per year may result from contaminated groundwater.

World Health Organization reports that in Africa around 80% of the population in the largest cities (in Asia around 55% have on site sanitation, such as septic tanks, pour-flush, VIP latrines or samples pits and experts say in developing countries in Asia, South American and African for an estimated one billion persons living in urban area, the main source of drinking water is groundwater.

Certainly, E. coli is one of the major bacterial that play major role in all the subject areas associated with the environment e.g. soil, air, and water. Many water borne diseases are caused by pathogenic bacteria, and it is the major task of water treatment.

Bacteria like E. coli, which normally lives in the intestine of warm blooded animals and are excreted with faces, are used as indicator bacteria. If present in water sample, they indicate that a contamination of water has taken place, and thus the potential presence of pathogenic exists. E. coli is the parameter tested, as an indicator of the presence of fecal bacteria and perhaps virus which pose a significant risk to human health. The most common health problem arising from the presence of fecal bacteria in groundwater is diarrhea, but typhoid fever, infectious hepatitis and gastrointestinal infections can also occur. Although E. coli bacterial are an excellent indicator of pollution, they can come from different sources e.g. septic tank effluence, farmyard waste, and landfill sites.

The published data about the elimination of bacteria and viruses in groundwater has been compiled by experts who show that in different investigations, 99.9 percent elimination of E.coli occurred after 16 to 120 days with a mean of 35 days for polio-hepatitis and entero-viruses. The natural environment, in particular the soil and subsoil is effective in moving bacteria and viruses by prediction filtration and absorption. There are two high-risk situations: Where permeable sand and gravel with shallow water are present and where fracture rock, particularly limestone is present close to the ground surface. The slow pace of the migration is where there are deposition of clay, which hinders the migration of the microbes, although preferential flow path, such as crack in the clay like mineral, can allow rapid movement, and by passing of the subsoil.

1.3     Statement of Problem  

Rivers State, the study area of this dissertation being an industrialized state                                                  has high increase of population generating waste at a very high rate; precisely E.coli is part of this waste generation. It becomes imperative that such issue under study should be addressed with thorough research and some better solution to prevent the spread of diseases emanating from E.coli through groundwater contaminant should be generated.

The area under study has very high porosity based on hydrogeological studies, thus facilitating the transport of micro organisms especially E.coli. This usually leads to a high level of groundwater contamination leading to the breakdown of public health. Public health is a serious concern, because health is wealth. The behaviour of man’s activities has also attributed to the condition of pollution generated from our environment. Therefore, it is imperative that the cause of these problems emanating from manmade activity should be thoroughly examined in other to find better solution to prevent these problems and increase the health status of the citizens, as it is part of our economic development.

1.4     Objectives of the Study

Public health is an area of great concern due to the pollution level emanating from E. coli, through the transport source in the study area, since health is wealth, it should be thoroughly examined in other to see how the transport disperse to the aquiferous zone. A previous study was carried out on construction materials, abstraction of groundwater, and the way pollution is generated through the application of construction methods, precisely in Rivers State. These were as a result of application of substandard materials in design criteria and construction method. But the area of transport of        E. coli was not carried out because it was above the scope of the study. Based on the limited scope, it becomes necessary that further studies should be carried out to cover a large part of the Rivers State environment; by analytically selecting the most affected locations for the study, the most affected areas can be used as a determinant for every part of Rivers state environment.

The serious effect of these pollution transports from E.coli, how it affect human is a serious disaster to human body. In this context, E.coli multiplies within the human digestive tract, producing a potent toxin that damages cells of the intestine lining. These lesions permit blood to rise to the bloody diarrhea, which generally develops within several days, eating contaminated food is one of the characteristic symptoms of infection from these pathogens.

Water pollution is also caused by the presence of undesirable and hazardous materials, beyond certain limits. Based on these unhealthy elements from    E. coli, the objective of this research will focus on the following:

1. To investigate the transport of coli through homogenous porous aquifers with respect to depth of aquifer and initial concentration.
2. To investigate the transport of coli through homogeneous and heterogeneous porous aquifer with respect to depth of aquifer and level of concentration.
3. To evaluate the relative importance of E. coli transport, which include their process and occurrence in natural environment
4. To determine the coefficient of permeability of selected aquifer in several locations in study of four years (i.e. from 2004-2010) from the well-log history.
5. To critically analyze the geological history and its influence on the transport of coli in the study area.
6. To generate model that will generate better solution based on the geological formation in the study area.
7. To calibrate and verify the experimental result from E.coli concentration and other influence on transport which include heavy metals, micronutrients, porosity, permeability and void ratio.
8. To determine the velocity of solute transport (coli) from each soil sample to ground water Aquifer.
9. To make necessary recommendations to stakeholders.

1.5     Scope of the Study

The scope of this study covers some selected locations in  Rivers State, these selected locations are based on the critical analysis survey of most area concentrations of easy level of transport, based on its level of porosity and geological formation, including its topography, this  ascertain all levels of transport in the study area.

The result from these selected locations from the study area will generate a general determinant level or model of pollution prevention and transport level to aquiferous zones in every part of Rivers State.

 

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