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Natural and anthropogenic influences on water quality: an example from rivers draining the Johannesburg Granite Dome

Jan-Marten Huizenga

MINI DISSERTATION

Submitted in the partial fulfilment of the requirements for the degree

MASTER OF SCIENCE

ENVIRONMENTAL MANAGEMENT

in the

FACULTY OF SCIENCE

at the

RAND AFRIKAANS UNIVERSITY

SUPERVISOR: PROF. J.T. HARMSE

JUNE 2004

ABSTRACT

The inorganic water chemistry (1979-1999) was evaluated of rivers between Johannesburg and the Hartbe espoort Dam (Limpopo/Olifants catchment, Gauteng), which drain dominantly the Johannesburg Granite Dome. These rivers include the Bloubank, Crocodile, Hennops, Jukskei, Little Jukskei, Magalies and Skeerpoort Rivers. The main purpose of this study is to id entify natural and anthropogenic factors that have influenced the river water chemistry for the period 1979-1999.

Water chemistry analyses of thirteen water monitoring sample sites were obtained from the CSIR (Environmentek): the “Water Quality on Disc, version 1.01. The following water quality parameters were evaluated: the pH and the concentrations of sodium (Na+), potassium + 2+ 2+ + 4+ - (K ), calcium (Ca ), magnesium (Mg ), ammonium (NH4 ), silica (Si ), fluoride (F ), 3- - orthophosphate (PO4 ), chloride (Cl ), total alkalinity (TAL, assumed to be bicarbonate: - 2- - HCO3 ), sulphate ( SO4 ), nitrate ( NO3 ) and the total dissolved solids (TDS).

Evaluation of the water chemistry usin g Stiff diagrams allowed a subdivision into three groups:

· Group 1: Crocodile River (north of the confluence with the Hennops River) and Jukskei River; · Group 2: Bloubank River and Crocodile River (between the confluences with the Bloubank River and Hennops River); · Group 3: Crocodile River (south of the confluence with the Bloubank River), Hennops River, Little Jukskei River, Magalies River and the Skeerpoort River.

The Crocodile River (south of the confluence with the Bloubank River ), Little Jukskei River , Magalies River and Skeerpoort River (Group 3) do not show any sign of water pollution. The inorganic water chemistry of these rivers is controlled by chemical weathering of the lithologies the rivers drain. The relatively high concentration of dissolved chemical species can be explained by the semi-arid climatic conditions in South Africa.

The other rivers do all show signs of inorganic water pollution. The pollution can be largely attributed to two factors, namely: (1) contamination with Central R and mine water affected by acid mine drainage in the 1980s and (2) urbanisation, in particular in the late 1990s.

Rivers contaminated with mine water include the Jukskei River and, to a lesser extend, the Crocodile River (north of the confluence with the Hennops River), and the Hennops River (Group 1). These rivers show the following chemical characteristics:

· Increase d levels of sulphate concentrations (e.g., up to 600 mg/l in the southern part of the Jukskei River) in the 1980s. · Low pH values (e.g., down to 3 pH units in the southern part of the Jukskei River), showing a correlation with high sulphate concentrations in the 1980s. ? High sodium and chloride concentrations in the 1980s, where the sodium concentration is significantly larger than the chloride concentration (e.g., Na+ > 200 mg/l; Cl- > 100 mg/l in the southern part of the Jukskei River) ? High fluoride concentrations (up to 3 mg/l in the southern part of the Jukskei River) in the 1980s. ? High phosphate concentrations (up to 2 mg/l in the southern part of the Jukskei River) in the 1980s.

Both the pH and sulphate concentrations increased and decreased, respectively and stabilised in the period between 1987 and 1989. pH and sulphate concentrations stabilised to alkaline conditions of 8+ and ~ 100 mg/l or less, respectively. Concentrations of sodium, chloride, phosphate and fluoride also decreased significantly after 1987.

The cause of the acid mine drainage can be either deep mining activities in the 1970s and/or reworking activities of the tailings in the Central Rand area in the early 1980s. The Central Rand area is situated in south of Johannesburg in the Orange/Vaal catchment area, in which the rivers drain towards the Vaal and Orange Rivers. This implies that mine water contamination must have occurred along northeast trending dykes, which acted as pathways for the mine water. The driving force for the mine water contamination is most likely the high water pressure built-up in the Central Rand mining area, which resulted from rising ground water after deep mining activities ceased in the 1970s.

Phosphate concentrations dropped significantly after 1987 and appear to be controlled by two factors: (1) The precipitation of calcite (i.e., phosphate sorbs to calcite while it precipitates). Calcite undersaturation caused by the low pH of the river water allowed high phosphate concentrations . (2) Implementation of the Special Phosphate Standard (1 mg/l) in 1985 for point sources. Fluoride concentrations were significantly lower after 1989 and might be related to an increase in pH. At a low pH, dissolution of apatite occurs, which releases fluoride. Furthermore , fluoride has a strong affinity for alumin ium, which is only present in acidic water.

Effects of urbanisation (i.e. waste disposal, septic effluent) are particularly characterised by increasing concentrations of sodium and chloride, which is observed in the Bloubank River and the Crocodile River (between the confluences with the Bloubank and Hennops Rivers) (Group 2). This effect, although expected, is less visible in the Jukskei River, which is probably due to the interference of the effects of mine water contamination.

ACKNOWLEDGEMENTS

I would like to thank the following people and organisations:

? Prof. J.T. Harmse for his valuable comments and suggestions during the preparation of this mini dissertation. ? The Department of Geography and Environmental Management at R.A.U., in particular Dr. J.M. Meeuwis, for giving an excellent course in Environmental Management. ? Prof. J.M. Barton (Department of Geology) for his suggestions regarding the water quality of the Jukskei River. ? The Department of Geology at R.A.U. for allowing me to carry out this study. ? The Rand Afrikaans University for financing this study. ? Last but not least, Michelle Lawton for her continuous support and “forcing” me to study again !

iii

TABLE OF CONTENTS

ABSTRACT i ACKNOWLEDGEMENTS iii LIST OF FIGURES vi LIST OF TABLES viii

1. Introduction

1.1. Fresh water in South Africa: the current status 1 1.2. Water quality in South Africa 2 1.3. Problem statement 3 1.3.1. Methodology 4 1.4. Organisation of this mini dissertation 5

2. Natural processes controlling water quality: chemical weathering 6

2.1. Introduction 6 2.2. Solubility of minerals 6 2.2.1. Correction of solubility calculations: the activity coefficient 8 2.2.2. Correction for solubility calculations: complexation 9 2.3. Software for equilibrium calculations 9 2.4. Chemical weathering of carbonates 10 2.5. Chemical weathering of silicates 10 2.6. Chemical characterisation of natural surface waters 14 2.6.1. General characterisation: Stiff diagram 14 2.6.2. Identification of water chemistry controlling mechanisms: Gibss diagram 15 2.6.3. Classification criteria for natural surface waters by Edmond & Stallard (1983, 1987) 16 2.6.4. River classification using mixing diagrams (Gaillardet et al., 1999) 17 2.7. Water Quality Index 17

3. An evaluation of the inorganic water chemistry (1979-1999) of rivers draining the Johannesburg Granite Dome 19

3.1. Introduction 19 3.1.1. Water quality data 19 3.2. Area description 20 iv

3.2.1. Geology 20 3.2.2. Mining activities 22 3.2.3 Agriculture 23 3.2.4. Population growth and urbanisation 23 3.3. Characterisation of water chemistry (1979-1999) 23 3.3.1. Group 1 25 3.3.2. Group 2 29 3.3.3. Group 3 31 3.4. Water Quality Index 34 3.4.1. Water quality objectives 34 3.4. 2. Water Quality Index for Group 1 sample sites 34 3.4. 3. Water Quality Index for Group 2 sample sites 35 3.4. 4. Water Quality Index for Group 3 sample sites 36

4. Discussion and conclusions 37

4. 1. Group 1 37 4.1.1. Phosphate concentrations 39 4.1.2. Fluoride concentrations 41 4. 2. Group 2 42 4. 3. Group 3 42 4.3.1. Sample sites A2H047Q01 and A2H051Q01 43 4.3.2. Sample sites A2H033Q01 and A2H034Q01 44 4.3.3. Sample site A2H013Q01 46 4.3.4. Sample site A2H014Q01 46 4.4. Conclusions 46 4.5. Outstanding questions and future research 47

References 49

APPENDIX I: Water chemistry of Group 1, 2 and 3 samples sites 53 APPENDIX II: Unit convers ions 67 APPENDIX III: Phreeqc-2 68 APPENDIX IV: Excel spreadsheet for water chemistry characterisation 72 APPENDIX V: Calculation of the Water Quality Index 73

LIST OF FIGURES

Figure 1: Relationship between climatic factors, weathering and water chemistry 2 Figure 2: Influence of natural and human factors on the natural water chemistry. 3 Figure 3: The process to set management objectives for development of water quality objectives. 4 - 2+ Figure 4: log10 [F ] versus log10[Ca ] diagram. 8 Figure 5: Relative abundances of chemical species in water as a result of mineral weathering. 12 Figure 6: Relation between surface runoff and total dissolved solids concentration for different lithologies. 13 Figure 7: Stiff diagram for average world river composition. 15 Figure 8: The variation of Na+/(Na+ + Ca2+) as a function of the total dissolved solids concentration. 16 + 2+ - Figure 9: Na -normalised diagram of Ca and HCO3 showing lithological endmembers. 17 Figure 10: Geological map of the Johannesburg Granite Dome and surroundings. 21 Figure 11: Aerial photograph from the Greater Johannesburg area. 22 Figure 12: Cation and anion variations for 1979/1980 and 1997/1999 24 Figure 13: Variation of total positive charge (S Z+) with time (Group 1). 25 Figure 14: pH and sulphate concentrations versus time ( Group 1). 26 Figure 15: Gibbs’ diagram (Group 1). 27 Figure 16: Sodium versus chloride concentration. 28 Figure 17: Mixing diagrams (Group 1) . 29 Figure 18: Gibbs’ diagram (Group 2). 30 Figure 19: Mixing diagrams (Group 2) . 31 Figure 20: Gibbs’ diagram (Group 3). 32 Figure 21: Mixing diagrams (Group 3) . 33 Figure 22: Water Quality Index for Group 1 sample sites. 35 Figure 23: Water Quality Index for Group 2 sample sites. 35 Figure 24: Water Quality Index for Group 3 sample sites. 36 Figure 25: Na+ versus Cl- for the Jukskei River. 38

Figure 26: The SIapatite dependency (dashed line) on the pH (a) and the variation (as indicated by the shaded line) of the phosphate concentration with the apatite saturation index (b). 39

Figure 27: The SIcalcite dependency (dashed line) on the pH (a) and the variation (as indicated by the shaded line) of the phosphate concentration with the calcite saturation index (b). 40 Figure 28: Variation of the activities of fluoride and calcium (Group 1). 41 Figure 29: Mg2+/(Mg2+ + Ca2+) versus K+/(K + + Na+ - Cl-) mole ratio’s. 44 Figure 30: Variation of magnesium, calcium and bicarbonate concentrations and pH with time (Group 3) . 45

Figure 31: Water chemistry for A2H012Q01 (Group 1). 54 Figure 32: Water chemistry for A2H023Q01 (Group 1). 55 Figure 33: Water chemistry for A2H040Q01 (Group 1). 56 Figure 34: Water chemistry for A2H042Q01 (Group 1). 57 Figure 35: Water chemistry for A2H044Q01 (Group 1). 58 Figure 36: Water chemistry for A2H045Q01 (Group 2). 59 Figure 37: Water chemistry for A2H049Q01 (Group 2). 60 Figure 38: Water chemistry for A2H013Q01 (Group 3). 61 Figure 39: Water chemistry for A2H014Q01 (Group 3). 62 Figure 40: Water chemistry for A2H033Q01 (Group 3). 63 Figure 41: Water chemistry for A2H034Q01 (Group 3). 64 Figure 42: Water chemistry for A2H047Q01 (Group 3). 65 Figure 43: Water chemistry for A2H051Q01 (Group 3). 66 Figure 44: Example of a worksheet used for recalculation of water chemistry data. 72

vii

LIST OF TABLES

Table 1: Water requirements by different sectors in South Africa. 1 Table 2: Solubility products of several mineral phases. 7 Table 3: PHREEQC equilibrium calculation of water with calcite/dolomite. 10 Table 4: Average lifetime of 1 mm sized crystals of different minerals. 11 Table 5: Relative chemical erosion rates for several lithologies. 13 Table 6: Average world river composition. 14 Table 7: Number of analyses for each sample site for each year. 20 Table 8: Correlation diagram for sample site A2H045Q01. 42 Table 9: Summary statistics for the Na+/( Na+ + Ca2+) (mg/l) ratio and TDS (mg/l) for sample sites A2H047Q01 and A2H051Q01. 43 2+ + - + Table 10: Summary statistics for Ca /Na and HCO3 /Na mole ratio’s for sample sites A2H047Q01 and A2H051Q01. 43 Table 11: Water chemistry results and PHREEQC calculations for magnesium, bicarbonate, calcium and pH for sample site A2H034Q01 45 Table 12: Important unit conversions. 67

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Chapter 1

Introduction

1.1. Fresh water in South Africa: the current status

Fresh water resources, including rivers, artificial lakes and groundwater, are under severe stress in South Africa. At present, South Africa is in a similar situation like countries in the Middle East and northern Africa (Miller, 2002): the fresh water resources are almost completely used and existing resources are suffering from a decreasing quality due to pollution (germs and chemicals) caused by urbanisation, industry, deforestation, mining, agriculture and energy use (e.g. Lusher & Ramsden, 2000). Considering the growth of the population and the required socio-economic development, it will be unlikely that water resources in South Africa are sustainable under the present conditions (Table 1) and it is expected that fresh water resources will be exhausted at the beginning of the next century (National Committee on Climate Change, 1998).

Table 1: Water requirements by different sectors in South Africa (adapted from Basson, 1997). 1996 2030 Sector % use 1996 % use 2030 Vol.% increase 106 m3/year 10 6 m3/year Urban and domestic 2,171 10 6,936 23 220 Mining and industrial 1,598 8 3,380 11 112

Irrigation and 12,344 62 15,874 52 29 afforestation Environmental 3,932 20 4,225 14 8 TOTAL 20,045 100 30,415 100 52

The present demand for water has a severe impact on the environment (e.g. Weaver et al., 1999), namely:

· Reduced flow in rivers, many rivers have become seasonal; · Surface and groundwater pollution; · Loss of biodiversity.

Freshwater resources in South Africa are influenced by the following factors (Walmsley et al., 1999):

(1) Climatic conditions (Fig. 1). South Africa has an arid to semi-arid climate with a high variation in rainfall in time and space (e.g. Vogel, 2000). It is situated in a negative runoff zone, i.e. the annual evaporation exceeds by far the rainfall (Miller, 2002). Only 8.6% of the annual rainfall is available as surface water (Weaver et al., 1999). 1

(2) Population growth, particularly in the urban areas. Related to the population growth is the need for economic development and intensification of land use (i.e., irrigation). In 1996, ~12 million people did not have a fresh uncontaminated water supply and ~21 million people were without water borne sanitation.

Figure 1: Relationship between climatic factors, weathering and water chemistry (adapted from Plant et al., 2001).

1.2. Water quality in South Africa

Climatic conditions in South Africa results generally in high salinity surface waters (Fig. 1). In addition to the natural high salinity of surface waters, water pollution contributes significantly to the deterioration of the water quality (e.g. Lusher & Ramsden, 2000). Water pollution in South Africa is exemplified by the following:

· Fresh water pollution (measured in the form of Chemical Oxygen Demand) is estimated to be 4.74 tons per km3. South Africa occupies position 11 of a total of 69 countries (Nationmaster.com, 2003). · The average phosphorous concentration in natural waters, measured as orthophosphate, has been estimated at 0.73 mg per litre. South Africa is ranked nin th of a total of 141 countries (Nationmaster.com, 2003). · Salinisation, measured as total dissolved solids, averages around 1300 mS/cm. South Africa is at the 27th position of a total of 141 countries (Nationmaster.com, 2003). · The eutrophication of surface waters (Walmsley, 2003).

A de tailed overview of South Africa’s surface water quality status has been published by the Department of Water Affairs recently for the inorganic water quality (Hohls et al., 2002).

1.3. Problem statement

The chemistry of natural surface waters is influenced by natural and human factors (Fig. 2). The most important natural factor that controls the water chemistry is the bedrock geology through chemical weathering. Human factors include industrial, mining and agricultural activities , and urbanisation. These factors are interrelate d, for example, discharge of certain chemicals associated with human activities may influence the type and rate of chemical weathering of rocks and agricultural practices may change the vegetation and soil characteristics in a certa in area.

Figure 2: Influence of natural and human factors on the natural water chemistry.

In order to conduct an appropriate evaluation of the water chemistry, it is important to identify the contribution of the bedrock geology. This allow s decision makers to make a balanced evaluation of the causes of water pollution and to take subsequently mitigatory actions. It is evident that the water quality cannot improve beyond its equilibrium composition with the bedrock it drains and elevated concentration le vels of some chemical species may have a natural source, for example:

· Elevated fluoride concentrations in natural surface waters related to dissolution of the

mineral fluorite (CaF2) in rocks. · Low pH levels in natural surface waters related to presenc e of sulphide minerals in rocks. · Elevated levels of phosphate in natural surface waters related to dissolution of phosphate minerals ( e.g. apatite).

Van Veelen (2002) constructed a flow diagram for the process to management objectives for the development of water quality objectives (Fig. 3); this study focuses on the investigation of the current and past water quality status as defined by Van Veelen (2002) (Fig. 3), which is an essential part in setting management objectives for the development of water quality objectives. Note that Van Veelen (2002) only mentioned the investigation of the current water

quality. This study, however, will demonstrate that studying the past water quality status is essential as well.

Figure 3: T he process to set management objectives for development of water quality objectives. Modified after Van Veelen (2002).

In this study the river water chemistry of rivers north of Johannesburg that drain the Johannesburg Granite Dome are evaluated. The main purpose of this assessment is to investigate the changing river water chemistry in space and time in order to examine the role of the surface geology and anthropogenic factors on the water quality of the rivers and to identify the degree , change and cause of water pollution over time. Note that in this study only inorganic chemical species will be considered, i.e. biological parameters such as Escherichia Coli and faecal coliforms counts were not included.

1.3.1. Methodology

Chemical data (1979-1999) of sample sites located along the rivers draining the Johannesburg Granite Dome (i.e., the Bloubank, Crocodile, Hennops, Jukskei, Little Jukskei, Magalies and Skeerpoort Rivers) were evaluated using several geochemical techniques, which are explained in Chapter Two. Water quality data were commercially obtained from the CSIR (Environmentek): the “Water Quality on Disc, version 1.01”. The data are supplied by the Directorate of Hydrology and the Institute for Water Quality Studies (more details are available from the web site: http://dbn.csir.co.za/water/wqcd/).

1.4. Organisation of this mini dissertation

The first detailed section (Chapter Two) will provide the necessary background information on the natural processes that influence the water quality. The second detailed part of the thesis (Chapter Three) will discuss the river water chemistry of the specific rivers. A summary and discussion of the results , and general conclusions are presented in Chapter Four.

Chapter 2

Natural processes controlling water quality: chemical weathering

2.1. Introduction

This chapter will discuss the fundamental principles of how minerals and rocks contribute to the composition of natural waters. An overview will be given of how physical chemic al principles can be used to quantify dissolved species in natural waters as a result of mineral- water interaction. There are many excellent textbooks available that discuss these principles in great detail. For the purpose of writing this chapter, textbooks authored by Dominico & Schwartz (1990), Appelo & Postma (1993), Stumm & Morgan (1996) and White (2003) were used as main references.

2.2. Solubility of minerals

Minerals tend to dissolve in water. Dissolution (or chemical weathering) properties (i.e. , rate and tendency) of a particular mineral depend on the mineral composition and mineral structure. For example, the mineral calcite, CaCO3, dissolves more easily than the mineral quartz (SiO 2).

One can quantify the solubility property of a mineral wit h the solubility produc t. For example, the mineral fluorite (CaF2) dissolves in water according to the dissociation reaction:

2+ - CaF2 ® Ca + 2F (2.1)

For this reaction, the solubility product (K fluorite) is defined as:

2+ - 2 Kfluorite = [Ca ][F ] (2.2) where [Ca2+] and [F-] denote the concentration of Ca2+ and F- in solution (normally expressed -10.57 in mole per kg H2O or mole per litre). K fluorite has a value of 10 at 25°C. As 1 mole of 2+ - CaF2 dissociates into 1 mole of Ca and 2 moles of F , one can calculate the concentration of Ca2+ as follows. Assume that fluorite dissociates into x mol/kg of Ca 2+ and consequently 2x mol/kg of F-. Substitution of these values into Eq. (2.2) results in:

10 -10.57 = x (2 x) 2

where x is 1.9×10-4 mol/kg, i.e. [Ca2+] and [F-] are 1.9×10-4 and 3.8×10-4 mol/kg, respectively. From this calculation it can be seen that the smaller the solubility product of a mineral is, the more difficult it is to dissolve that particular mineral, i.e. the lower the ion concentrations are of which the solid is made of. Table 2 shows the solubility products of some mineral phases, illustrating that, for example, sulphide minerals are very difficult to dissolve whereas salt minerals such as halite and sylvite easily dissolve.

Table 2: Solubility products of several mineral phases (adapted from Dominico & Schwartz, 1990). Mineral compositions after Klein & Hurlbut (1999). Mineral phase Composition Solubility product (K) Halite NaCl 101.54 Sylvite KCl 100.98 -4.62 Gypsum CaSO4 10 -7.46 Magnesite MgCO3 10 -8.22 Aragonite CaCO3 10 -8.35 Calcite CaCO3 10 -10.7 Siderite FeCO3 10 -16.7 Dolomite (Ca,Mg)(CO3)2 10 -11.1 Brucite Mg(OH)2 10 -33.5 Gibbsite Al(OH)3 10 Pyrrhotite FeS 10-18.1 Sphalerite ZnS 10-23.9 Galena PbS 10-27.5 -4.00 Quartz SiO 2 10 -9.1 Montmorillonite (Na,Ca)(Al,Mg)6(Si4O10)3(OH)6 × nH2O 10 -9.4 Kaolinite Al2Si2O5(OH)4 10

The chemistry of natural waters can be characterised by indicating the Saturation Index (SI) for a number of mineral phases. The Saturation Index is a number, which indicates whether a solution is saturated, undersaturated or over saturated with respect to a particular mineral 2+ - 2+ phase. For example, if a solution has a certain concentration of Ca and F , [Ca ]sol and - [F ]sol , respectively, one can calculate the saturation state of the solution with respect to fluorite as follows:

2+ - 2 [Ca ]sol[F ]sol SI = log 10 (2.3) Kfluorite

The solution is saturated with respect to fluorite if SI is 0, undersaturated if SI < 0 and 2+ - 2 oversaturated if SI > 0. The product [Ca ]sol[F ]sol is defined as the Ionic Activity Product of fluorite, i.e. IAPfluorite.

The solubility product of limits the concentrations of the ions in solution, which can be illustrated with the example of fluorite (e.g. Appelo & Postma, 1993) . This can be graphically

- 2+ demonstrated in a log10 [F ] versus log10 [Ca ] diagram. Eq. (2.2) can be rewritten in a logarithmic format as follows:

2+ - log 10Kfluorite = log 10[Ca ] + 2log 10[ F ] = - 10.57

- 2+ which represents a straight line in a log10 [F ] versus log10[Ca ] diagram (Fig. 4). This figure illustrates that sufficient addition of Ca2+ (in the form of, for example, gypsum) to a fluorite undersaturated solution will result in a decrease of the fluoride (F -) concentration as soon as the solution becomes saturated with respect to fluorite , i.e. fluorite saturation is a limiting mechanism for the concentration of fluoride is solution (e.g. Appelo & Postma, 1993; Neal et al., 2003).

- 2+ Figure 4: log10 [F ] versus log10[Ca ] diagram showing the fields for fluo rite super saturation and undersaturation, separated from each other by the fluorite saturation curve (thick black line). Aqueous solutions should plot in the fluorite under saturation field or on the curve. Note that addition 2+ 2+ of Ca (i.e., as CaSO4) to a solution (grey square) will increase Ca until it reaches the saturation curve, further addition of Ca2+ will then result in fluorite precipitation and subsequent decrease of the fluoride concentration in solution (so called common ion effect). Figure adapted from Appelo & Postma (1993).

Solubility calculations are complicated by the fact that one should consider the reactive concentration for the cations and anions involved. The reactivity of a particular specie is influenced by (1) electrostatic shielding and (2) complex formation, which will be discussed in the next two sections.

2.2.1. Correction of solubility calculations: the activity coefficient

The above example of fluorite is an over simplification of the reality. One should take into account t hat anions and cations are shielded. For example, the Ca2+ cation is shielded by water molecules, which is a dipole. As a result, the concentration of Ca2+ is slightly lowered and its 8

reactivity is subsequently reduced. The reactive concentration, normally denoted as activity (a) is related the concentration multiplied with a correction factor for the shielding effect, which is called the activity coefficient (g), i.e.

ai = gi [i] (2.4)

where gi < 1. For solutions in which the concentration of the solutes is near 0, the activity coefficient approaches 1. The calculation of activity coefficients, using electrostatistical theory (e.g. Debije -Hückel theory), is discussed in detail in numerous physical chemistry textbooks (e.g. Atkins, 1998). A detailed explanation of the calculation of activity coefficients is beyond the scope of this thesis.

2.2.2. Correction for solubility calculations: com plexation

In addition to the shielding effect, the reactivity concentration is also reduced by complexation, i.e., the formation of ion pairs. In the calculation example of fluorite in Section 2.2., it is, although not mentioned specifically, assumed that the only ions present in solution are Ca2+ and Cl-. However, this is again an over simplification of the reality and one should + + - also consider the existence of the following complexes: CaF , CaOH , HF and HF2 . The presence of these complexes reduces the reactive concentration of Ca2+ and F -.

Both, the calculation of activity coefficients and the formation of complexes can make the speciation calculation for natural waters rather complicated and as a result several software packages have been developed for these type of calculations.

2.3. Software for equilibrium calculations

There are a number of software packages available for equilibrium calculations . Most of these can be downloaded from the internet for free. The most widely used software package is PHREEQC-2 (version 2.7), which can be downloaded form the US Geological Survey website (http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/). PHREEQC can, amongst others, be used to calculate:

· The composition of natural waters that are in equilibrium with a certain mineral phases. · Speciation and saturation indexes.

Details of the program and user instructions are given by Parkhurst & Appelo (1999) . Appendix I II shows an example of how to use PHREEQC.

2.4. Chemical weathering of carbonates

Typical minerals that occur in carbonate rocks are calcite, CaCO3, and dolomite,

(Ca,Mg)(CO3)2. The solubility products of both minerals are listed in Table 2 and show that calcite is much more soluble (by a factor 108) than dolomite. The dissolution of calcite can be expressed by the following reaction (e.g. Appelo & Postma, 1993):

2+ - CaCO3 + CO2 + H2O ® Ca + 2HCO3 (2.5)

From this reaction it is clear that the amount of calcite that will be dissolved depends on the availability of CO2 in solution. Table 3 shows calculation results using PHREEQC for water in equilibrium with calcite and dolomite at different pressures for CO2 ( P ). CO 2

Table 3: PHREEQC equilibrium calculation of water with calcite/dolomite at different CO2 concentrations, corresponding to the natural variations (Appelo & Postma, 1993). Calcite Calcite Dolomite Dolomite Calcite & Calcite & dolomite dolomite P (atm.) -3.5 -1.5 -3.5 -1.5 -3.5 -1.5 CO 2 10 10 10 10 10 10 pH 8.3 7.0 8.4 7.1 8.4 7.1 Ca2+ (mg/ l) 20 100 12 62 14 71 Mg2+ (mg/ l) - - 7 37 6 32 Alkalinity (mg/ l) 60 293 73 360 73 374

Note that for rivers draining dolomite terrains, the mole ratio Ca2+ : Mg2+ should ideally be 1 : 1, which corresponds to a weight ratio of 1.6 : 1.

2.5. Chemical weathering of silicate s

Chemical weathering of rocks dominated by silicate minerals (Table 4) is much slower than chemical weathering of carbonate rocks and one may wonder whether it is really worthwhile to investigate the effect of silicate weathering on the composition of natural surface waters. However, silicate weathering is still responsible for about 50% of the total dissolved load in the rivers on Earth (e.g. Appelo & Post ma, 1993).

Table 4: Average lifetime of 1 mm sized crystals of different minerals (pH = 5, 25°C) (adapted from Lasaga, 1984). Mineral compositions after Klein & Hurlbut (1999). Mineral Composition Lifetime (years)

Quartz SiO 2 34,000,000

Muscovite KAl3Si3O10(OH)2 2,700,000

Forsterite (olivine) Mg2SiO4 600,000

K-Feldspar KAlSi3O8 520,000

Albite (Na-feldspar) NaAlSi3O8 80,000

Enstatite (orthopyroxene) Mg2Si2O6 8,800

Diopside (clinopyroxene) CaMgSi2O6 6,800

Nepheline (feldspathoid) NaAlSiO 4 211

Anorthite (Ca-feldspar) CaAl2Si2O8 112

One can use as rule of thumb that mineral phases formed at high pressure and temperature are more susceptible to chemical weathering compared to minerals formed at lower pressure and temperature. For example, minerals such as olivine, pyroxene and Ca-feldspar, which are formed in the typical mantle rocks such as basalts (i.e., Drakensberg) or gabbro (i.e., Bushveld Complex) dissociate much quicker than mineral phases (i.e., quartz, K-feldspar) occurring in continental crust rocks such as granites.

Chemical weathering reactions of silicate mineral phases involves partial dissolution (i.e., incongruent dissolution) and the formation of an insoluble secondary mineral phase, i.e.

reactant phase ® weathering residue + dissolved ions

Typical secondary mineral phases produced during chemical weathering are insoluble (i.e., low solubility product, see Table 2) aluminium-rich clay mineral phases such as kaolinite, montmorillonite, gibbsite, and iron-oxides (see Table 2 for mineral compositions).

Incongruent dissolution reactions have the following general characteristics (e.g. Appelo & Postma, 1993; Bluth & Kump, 1994; Bowser & Jones, 2002):

· Involvement of water and/or hydrogen proton (H +) as a reactant.

· Hydrogen protons are normally supplied by carbonic acid (H2CO3), which is the product + of the reaction between H2O and CO2. (i.e., H2O + CO2 ® H2CO3, H2CO3 ® H + - HCO3 ). · Immobility of iron and aluminium. These elements stay behind in an insoluble residue. - 2+ + + · Release of HCO3 and cations such as Ca , K and Na (Fig . 5).

· A part of the silica gets dissolved in the form of H4SiO 4 (i.e., precipitation of SiO2 normally does not occur). Silica is solely derived from mineral phases such as Ca-rich feldspars, olivine, pyroxene, amphibole and biotite, but not quartz or K-feldspar. The

silica concentration in natural waters is a good indicator of the extend of silicate weathering as its source is only chemical weathering. · The most common residue formed is kaolinite.

An example of typical ncongruenti dissolution reaction is the formation of kaolinite from albite or anorthite, respectively:

+ - 2NaAlSi3O8 + 2CO2 + 11H2O ® Al2Si2O5(OH)4 + 2Na + 4H4SiO4 + 2 HCO3 (2. 6)

2+ - CaAl2Si2O8 + 2CO2 + 3H2O ® Al2Si2O5(OH)4 + Ca + 2HCO3 (2. 7)

Figure 5 shows relative abundances of chemical species liberated during chemical weathering of several rock-forming minerals.

Figure 5: Relative abundances of chemical species in water as a result of mineral weathering resulting in kaolinite as an end product (adapted from Garrels & Mackenzie, 1971).

Meybeck (1987) determined the relative rate of chemical weathering for a number of different lithologies normalised to granite (Table 5). It is these relative erosion rates that control the river chemistry. For example, crystalline surface rocks (igneous and metamorphic rocks) occupy 34% of the global surface and contribute 12% of the dissolved load of the rivers whereas evaporates only occupy only 1.3% of the global surface but contribute 17% to the dissolved load (Meybeck, 1987).

Table 5: Relative chemical erosion rates for several lithologies (Meybeck, 1987). Rock type/lithology Erosion rate relative to granite Granite 1.0 Gneis/schist 1.0 Gabbro 1.3 Sandstone 1.3 Volcanic rocks 1.5 Shale 2.5 Marble, amphibolite 5.0 Carbonate rocks 12 Gypsum 40 Rock salt 80

Figure 6 illustrates the variation in total dissolved solids for different lithologies as a function of the annual runoff. It shows that with an increasing runoff, rivers draining lithologies such as granite, schist’s and gneisses will show a decrease in their total dissolved solids concentrations due to dilution. On the other hand, the total dissolved solid concentration in rivers draining limestone and volcanic rocks will only show a slight decrease, which implies that mineral dissolution is increasing with increasing runoff.

Figure 6: Relation between surface runoff and total dissolved solids concentration for different lithologies (adapted from Walling, 1980).

Based on weathering characteristics of different lithologies, a number of diagrams have been developed that can be used to characterise and classify natural surface waters according to their bedrock geology, which will be discussed in the next section.

2.6. Chemical characterisation of natural surface waters

2.6.1. General characterisation: Stiff diagrams

A Stiff diagram shows the patterns of anions and cations in water (Stiff, 1951; Appelo & Postma, 1993). The Stiff diagram is constructed from the recalculation of the cation/anion concentrations (normally given in mg/l) into millie quivalents per litre (see Appendix II). These diagrams allow a quick visual inspection of the water chemistry by looking at the shape of the diagram (illustrating the concentrations of the different species relative to each other) and the width of the diagram (illustrating the absolute concentrations). The diagram is in particular powerful in comparing the water chemistry of different river systems or the variation of a single river system in time and space.

Table 6: Average world river composition (Meybeck, 1985), recalculated into mmol/l and meq/l. Normal range in unpolluted fresh water and potential sources are also indicated (Appelo & Postma, 1993). World river composition Species Normal range (mg/l) Source mg/l mmol/l meq/l Feldspar, rock-salt, Na+ 8.5 0.37 0.37 2 – 46 zeolite, atmosphere K+ 1.5 0.04 0.04 0. 5 – 8 Feldspar, mica Carbonate, gypsum, Ca2+ 15.0 0.37 0.75 2 – 200 feldspar, pyroxene, amphibole Dolomite, serpentine, Mg2+ 3.9 0.16 0.32 1 – 50 pyroxene, amphibole, olivine, mica + 0.02 0.00 0.00 - - NH4

SiO 2 10.4 0.17 0.69 1 – 60 Silicate minerals F- - - - - Fluorite

3- Organic matter, phosphate PO 0.01 0.00 0.00 0 – 2 4 minerals (apatite) Cl- 10.5 0.30 0.30 2 – 70 Rock salt, atmosphere Carbonate minerals, HCO - 53 0.87 0.87 0 – 300 3 organic matter Atmosphere, gypsum, SO2- 12.3 0.13 0.26 1 – 500 4 sulphide minerals

2 - Atmosphere, organic NO 0.1 0.00 0.00 0.1 – 2 3 matter

Figure 7 shows a stiff diagram for an average world river composition (Table 6). An Excel spreadsheet was developed for the calculation of Stiff diagrams and a number of other chemical parameters (Appendix IV1).

Figure 7: Stiff diagram for average world river composition constructed from data in Table 6.

2.6.2. Identification of water chemistry controlling mechanisms: Gibbs ’ diagram

Gibss (1970) used Na+/(Na+ + Ca2+) (mg/l) versus the total dissolved solids (mg/l) diagram in order to distinguish different mechanisms that control the chemistry of natural surface waters, namely (1) atmospheric precipitation; (2) dissolved salts derived from rocks and (3) evaporation crystallisation process (Fig. 8). Rivers should plot in the boomerang shaped shaded area in the diagram. The shape is explained by the following factors (e.g. Day et al., 1998): (1) Rocks containing dominantly Na+ and K+ are less soluble producing only small quantities of TDS, (2) Rock dominated rivers show high concentrations of Ca2+, Mg2+ and - + - HCO3 . Evaporation dominated rivers show high concentrations of Na and Cl and low concentrations of Ca2+ due to calcite precipitation.

1 The Excel spreadsheet is available on request. Please e-mail the author at [email protected]. 15

Figure 8: Variation of the weight ratio Na+/(Na+ + Ca2+) as a function of the total dissolved solids (mg/l) in order to characterise the three principle mechanisms that control water chemis try. Any river composition should plot in the boomerang shaped shaded area. White dot indicates the average world river composition (Table 6). See text for further explanation. Figure modified from Gibbs (1970).

A further more detailed characterisation of rock dominated river compositions can be done by using classification criteria by Stallard & Edmond (1983, 1987).

2.6.3. Classification criteria for natural surface waters by Stallard & Edmond (1983, 1987)

Stallard & Edmond published two articles in 1983 and 1987 on the aqueous geochemistry of the Amazon river system in which they, amongst others, investigated the influence of the surface geology and the chemical weathering processes on the river chemistry. In these publications they proposed classification criteria for rivers, which have been reviewed by White (2003).

Stallard & Edmond (1983) used the total cation charge, denoted as SZ+, for their river classification. The total cation charge is expressed in milliequivalent or microequivalent per litre (meq/l or meq/l, respectively, see also Appendix II). Stallard & Edmond (1983) defined the following four principal river groupings:

· SZ+ < 200 meq/l. These rivers drain heavily weathered terrains, showing relatively high concentration levels of iron and aluminium, and a low pH. · 200 < SZ+ < 450 meq/l. These rivers drain siliceous terrains. · 450 < S Z+ < 3000 meq/l. Rivers draining carbonate and minor evaporate rocks result in a high total cation charge . · SZ+ > 3000 meq/l. These rivers are also characterised by a Na : Cl and (Ca + Mg) : - 2- ( HCO3 + SO 4 ) meq ratio’s of 1 : 1, which is caused by draining of carbonate and evaporate rocks.

2.6.4. River classification using mixing diagrams (Gaillardet et al., 1999).

Gaillardet et al. (1999) used water quality data of 60 rivers for the construction of Na+ 2+ + - + normalised diagrams. The mole ratio Ca /Na versus the mole ratio HCO3 /Na diagram allows the classification of rivers according to their end member lithology through which they drain (Fig. 9). The diagram also allows distinguishing polluted from non-polluted rivers.

Figure 9: Na+-normalised diagram of Ca2+ and - HCO 3 showing the lithological endmembers for silicates, carbonates and evaporates. Non-polluted rivers should plot in between these end members. The dark grey area shows the plotting area for some European polluted rivers. Polluted rivers - + generally plot at low HCO 3 /Na values. White dot: average world river composition (Table 6). Figure modified from Gaillardet et al., (1998).

2.7. Water Quality Index

The Water Quality Index is a parameter to summarise the water quality data relative to a defined set of objectives. The index can be used to compare sample sites and to identify

changes. In this study, the Water Quality Index developed by the Canadian Council of Ministers of the Environment (CCME) (2001a, b) was used. The index (abbreviated as CCMEWQ1 ) is based on the (1) number of variables whose objectives are not met, (2) the frequency with which the objectives are not met and (3) the amount by which the objectives are not met. The CCMEWQ1 can vary between 0 (poor water quality) and 100 (excellent water quality). A detailed description of the calculation method is given in Appendix V.

The calculation of the Water Quality Index requires that an appropriate set of objectives is defined for a number of relevant water quality parameters. The Department of Water Affairs and Forestry (1996a-e) has published a set of water quality guides that define these objectives for different user groups (e.g. recreational, agricultural, etc.). The objectives used in this study will be given in Chapter Three, Section 3.4.1.

Chapter 3

An evaluation of the inorganic water chemistry (1979-1999) of rivers draining the Johannesburg Granite Dome

3.1. Introduction

In this chapter, the water quality of the rivers draining the Johannesburg Granite Dome situated between the Hartbeespoort Dam and Johannesburg will be evaluated and discussed. These rivers include the Bloubank, Crocodile, Hennops, Jukskei, Little Jukskei, Magalies and Skeerpoort River (Fig. 10). The main reasons for the selection of this area are the following:

(1) The area is characterised by relatively simple bedrock geology (granidioritic gneisses and migmatites and minor (ultra)mafic and sedimentary lithologies). (2) Some of these rivers have been severely polluted whereas others are relatively clean. The comparison between these rivers allows distinguishing the influence of natural and anthropogenic factors on the river water quality. (3) The presence of a large number of water quality monitoring stations for which an extensive water quality data set is available from the Department of Water Affairs and Forestry for the years 1979 until 1999.

3.1.1. Water quality data

As mentioned previously in Section 1.3.1., water quality data were commercially obtained from the CSIR (Environmentek): the “Water Quality on Disc, version 1.01”. This CD contains water quality data for 2000 sample sites in South Africa. Water samples are collected as part of the national water quality monitoring programme and are chemically analysed at the Institute for Water Quality Studies. In this study, thirteen samples sites in the area of interest were selected for detailed analyses (Fig. 10). Sample sites and the numbers of analyses used are indicated in Table 7.

Water quality data used in this study include the pH and the concentrations of major elements (all in mg per litre, i.e. mg/l): sodium (Na+), potassium (K +), calcium (Ca2+), magnesium 2+ + 4+ - 3- - (Mg ), ammonium ( NH4 ), silica (Si ), fluoride (F ), orthophosphate ( PO4 ), chloride (Cl ), - 2- - total alkalinity (TAL, assumed to be bicarbonate: HCO3 ), sulphate ( SO4 ), nitrate (NO3 ) and the total dissolved solids (TDS).

Table 7: Number of analyses for each sample site for each year. The samples sites are subdivided into three groups based on their water chemistry (see Section 3.3). GROUP 1 GROUP 2 GROUP 3

A2H012 A2H023 A2H040 A2H042 A2H044 A2H045 A2H049 A2H013 A2H014 A2H033 A2H034 A2H047 A2H051 1979 12 17 17 17 15 14 11 4 5 No data 2 16 15 1980 246 44 46 49 47 47 47 37 43 10 6 46 46 1981 12 17 16 48 49 15 16 43 41 9 33 18 17 1982 246 9 11 41 38 10 11 12 43 7 43 10 10 1983 322 13 13 45 49 13 14 43 47 2 43 13 9 1984 80 12 12 48 48 12 8 48 51 4 51 9 8 1985 41 11 14 52 53 15 7 53 52 5 53 9 6 1986 51 13 13 52 53 12 10 52 52 4 50 10 9 1987 53 14 12 51 49 14 13 52 51 2 52 13 13 1988 52 14 13 51 52 13 12 62 51 3 49 12 12 1989 52 13 13 52 52 13 13 57 52 4 50 13 13 1990 210 15 13 49 46 13 14 52 47 3 50 14 14 1991 397 16 16 31 32 17 14 51 31 4 40 14 14 1992 362 36 38 43 46 36 12 52 45 4 40 12 11 1993 384 51 28 53 52 51 23 52 52 4 67 13 13 1994 91 55 52 51 54 52 51 52 51 3 60 12 12 1995 54 51 51 52 51 52 52 53 52 4 52 11 20 1996 54 56 50 54 53 51 53 53 53 4 53 13 47 1997 52 53 41 42 50 49 50 51 50 3 49 12 48 1998 52 49 No data No data 49 48 48 49 52 4 49 13 49 1999 51 39 No data No data 38 37 38 35 37 1 39 10 39 TOTAL 2699 599 469 881 976 584 517 963 958 84 931 293 425

3. 2. Area description

3.2.1. Geology

An in depth description of the geology of the Johannesburg Granite Dome, including a detailed geological map, is given by Anhaeusser (1973). The geology is largely dominated by granitoid gneisses and migmatites of Archean age (~3200 Ma) (Anhaeusser, 1999) (Fig. 10). The Johannesburg Granite Dome (Fig. 10) can easily be recognised on the aerial photograph (Fig. 11). The granite intruded into (ultra)mafic greenstone remnants , including dunites, harzburgites, pyroxenites and metagabbro’s (e.g. Anhaeusser, 1973, 1999) . Immediately north of the Johannesburg Granite Dome, dolomites, quartzites (i.e., Magaliesberg) and shales of the Transvaal Supe rgroup occur and the most northern part of the area shown in Figure 10 comprises rocks belonging to the Bushveld Igneous Complex (i.e., granites, gabbro’s and felsites). South of the Johannesburg Granite Dome, the geology is dominated by rocks from the Witwatersrand Supergroup (shale, quartzite and conglomerate) and the Ventersdorp. + + 2+ 2+ - Chemical weathering of these rocks release ions such as Na , K , Ca , Mg and HCO 3 as a result of incongruent dissolution of rock-forming minerals such as feldspar, mica, amphibole and pyroxene (see Chapter Two).

Figure 10: Geological map of the Johannesburg Granite Dome and surroundings. Map compiled from the Geological Map of South Africa. 21

Figure 11: Aerial photograph from the Greater Johannesburg area taken from the space shuttle Columbia (December 1990) facing north at an altitude of 360 km. Note the rectangle shaped light-coloured mine dumps south of the Johannesburg Granite Dome. White circle: confluence of the Crocodile and Hennops Rivers. Source: NASA, http://eol.jsc.nasa.gov/.

3.2.2. Mining activities

Mining operations in the area are restricted to sand and stone quarries. Deep mining activities have not taken place in the study area. Gold mining operations were concentrated south of Johannesburg (Central Rand area, including Roodepoort, south Johannesburg, Germiston and Boksburg, see Fig. 10), located in the Olifants/Vaal primary catchment area. Most gold mining operations ended in the 1970s. The only active mines in the 1980s included East Rand Proprietary Mines and Durban Roodepoort Deep (Werdmüller, 1986). Reworking of the slimes for further gold extraction started in the early 1980s as a result of improved technology (allowing profitable recovery of ~0.8 ppm gold-bearing slimes) and the high gold price (~US$ 600 per ounce) (Scott, 1995).

3.2.3. Agriculture

Agricultural activities mainly occur in the less dense ly populated northern part of the area, near the confluence of the Jukskei and the Crocodile R iver.

3.2.4. Population growth and urbanisation

In South Africa, the general population growth is about 2% (Van der Merwe & Van der Merwe, 2000) and the average annual urban population growth is 3.7% (Lemon, 2000). This has resulted in fast growing residential areas north of Johannesburg including Alexandra, Sandton and Midrand. It has also led to numerous informal settlements without sufficient service provision, in particular in the vicinity of Ale xandra.

3.3. Characterisation of water chemistry (1979-1999)

In this section, the river water chemistry characteristics and the variation over time will be described. No corrections for atmospheric input were made. Water quality data were evaluated as f ollows:

(1) Construction of Stiff diagrams for 1979 and 1999 (for some sample sites these years may differ, depending on the availability of data, see Table 7) illustrating the variation of the + + 2+ 2+ + - - 2- - major cations (Na + K , Ca , Mg , NH4 ) and anions (Cl , HCO 3 , SO 4 , NO3 ) with time. The use of Stiff diagrams allow s a quick visual comparison of water chemistry in space and time. 2- (2) Construction of variation diagrams of several chemical species (SO4 , total dissolved - 3- 4+ solids, pH, F , PO4 , Si ) with time. Annual median values were used to determine changes in the water chemistry with time. 2- (3) pH versus SO4 variation diagrams. (4) The use of several geochemical discrimination diagrams as discussed in the previous chapter. (5) Calculation of the Water Quality Index for each sample site.

Figure 12: Cation and anion variations for 1979/1980 (dashed line) and 1997/1999 (solid line enclosing the shaded area) for each sample site. The sample sites have been categorised into three groups based on the shape of the Stiff diagrams. Cation and anion milliequivalent values were calculated from annual median concentration values.

Based on the shape of the Stiff diagrams, three groups of sample sites can be distinguished each representing a typical water chemistry (Fig. 12):

· Group 1: sample sites A2H012Q01, A2H023Q01, A2H040Q01, A2H042Q01 and A2H044Q01. These sample sites are located along the Jukskei River and the Crocodile River (north of the confluence with the Hennops River). · Group 2: sample sites A2H045Q01 and A2H049Q01. These samples sites are located at the Crocodile River (between the confluences with the Bloubank and the Hennops Rivers) and the Bloubank River. · Group 3: sample sites A2H013Q01, A2H014Q01, A2H033Q01, A2H034Q01, A2H047Q01 and A2H051Q01. These samples sites are located at the Magalies River, the Hennops River, the Skeerpoort River, the Crocodile River (south of the confluence with the Bloubank River) and the Little Jukskei River.

3.3.1. Group 1

Figures 31-35 (Appendix I, pp. 54-58) summarise the variation of the water chemistry with time for the individual sample sites. The water chemistry for this group is characterised by the following:

- · High sulphate and nitrate, and low total alkalinity ( HCO3 ) concentrations in 1979/1980, changing to low sulphate and high total alkalinity concentrations in 1997/1999. These relations give the Stiff diagrams (Figs. 12, 31-35a) for sample sites belonging to Group 1 its characteristic shape.

Figure 13: Variation of total positive charge (SZ+) with time for sample sites belonging to Group 1. The total positive charge for each year is calculated from the annual median cation values.

· A generally high total positive cation charge (SZ+). The total positive cation charge shows a decreasing te ndency with time (Fig. 13). Downstream sample sites display lower S Z+ values (Fig. 13). ? Low pH values in the early 1980s (down to below 3 in the southern part of the Jukskei River) (Fig. 14, 31-35d). · Decreasing sulphate and total dissolved solids concentrations , and increasing pH values with time (Figs. 14, 31-35b, c, d). · A negative correlation between pH and sulphate concentration from 1979 until 1987- 1989, after which the pH stabilises around 8+ and the sulphate concentration stabilises to concentrations < 200 mg/l (Figs. 31-35e). This feature becomes even clearer when all analyses were used (Fig. 14).

Figure 14: pH (open squares) and sulphate concentrations (black squares) versus time for the period 1979-1997 (sample sites A2H040Q01 and A2H042Q01) and 1979-1999 (sample sites A2H012Q01, A2H023Q01, A2H044Q01) . Both the pH and the sulphate concentrations stabilise between 1987 and 1989.

· Fluoride concentrations show elevated concentrations in the early 1980s (~2-3 mg/l for samples sites A2H040Q01 and A2H042Q01, ~ 1-2 mg/l for the other sites) and shows a

slight decrease (~1-2 mg/l for samples sites A2H040Q01 and A2H042Q01, ~ 0.5 mg/l for the other sites) from 1989 onwards (Figs. 31-35f); · Phosphate concentrations show elevated levels in the early 1980s (~2 mg/l) and decrease to levels < 0.5 mg/l from 1987 onwards (Figs. 31-35g). · Relatively high nitrate concentrations in the early 1980s (Figs. 31-35a). · Generally, cation and anion concentrations decrease whereas pH and the total alkalinity increase downstream the Jukskei River to the north.

All sample sites plot close to each other in the Gibbs ’ diagram (Fig. 15). Two trends are apparent; a decrease in the TDS concentration downstream and a decrease in the Na+/(Na+ + Ca2+) ratio and TDS concentration for each individual sample site from the late 1980s to the early 1990s .

Figure 15: Gibbs’ diagram (Gibbs, 1970) illustrating the plotting area for sample sites belonging to Group 1. Annual median values were used. See Chapter Two for an explanation of the diagram.

The decrease in the Na+/(Na+ + Ca2+) ratio can be attributed to a decrease in the sodium concentration with time (Fig. 16).

Group 1 sample sites are furthermore characterised by high sodium and chloride concentrations, subsequently decreasing with time (grey arrow in Fig. 16). Figure 16 also shows that the Cl-/Na+ (mg/l) ratio is increasing with time.

Figure 16: Sodium versus chloride concentrations for the period 1979-1997 (sample sites A2H040Q01 and A2H042Q01) and 1979-1999 (sample sites A2H012Q01, A2H023Q01, A2H044Q01). Grey arrow indicates change with t ime illustrating a steady decrease in sodium and chloride concentrations from 1979 until 1999.

The sample sites show similar trends in the Gaillardet et al. (1998) mixing diagram (Fig. 17). 2+ + - + Each sample site shows an increasing Ca /Na mole ratio and increasing HCO3 /Na mole ratio from the early 1980s to the late 1990s caused by decreasing sodium (Fig. 16) and increasing bicarbonate concentrations (Figs. 31-35a).

Figure 17: Mixing diagrams (after Gaillardet et al., 1999) for Group 1 sample sites . T he grey 2+ + - + arrow illustrates increasing Ca /Na and HCO3 /Na mole ratio’s with time. Annual median concentration values were used for construction. The area indicated with the dashed line indicates the area of sample site A2H047Q01, which is assumed to be the least polluted sample site for the Johannesburg Granite Dome (see Section 3.3.3.).

3.3.2. Group 2

Figures 36 and 37 (Appendix I, pp. 59-60) summarise the variation of the water chemistry with time for the individual sample sites. The water chemistry for this group is characterised by the following (Figs. 36 and 37):

· Low sodium and chloride concentrations relative to magnesium and calcium. Magnesium and calcium concentrations are similar. The water chemistry shows hardly any change over time (Figs. 36 and 37a), with the exception of sodium, potassium, and chloride , which show a slight increase. The total positive cation charge (SZ+) varies between 6000 and 7200 meq/l. · Sulphate concentrations show small variations and are below 100 mg/l (Figs. 36 and 37b). · Slightly increasing total dissolved solids concentrations and pH values with time (Figs. 36 and 37b, c, d). The pH stabilises around 8+ after 1988. · No correlation between pH and sulphate concentrations between 1979-1999 (Figs. 36 and 37e. · Low fluoride concentrations (< 0.4 mg/l) (Figs. 36 and 37f); · Low phosphate concentrations (< 0.2 mg/l) (Fig s. 36 and 37g).

Both sample sites plot close to each other in the Gibbs’ diagram (Fig. 18).

Figure 18: Gibbs’ diagram (Gibbs, 1970) illustrating the plotting area for sample sites belonging to Group 2. Annual median values were used. See Chapter Two for an explanation of the diagram.

Figure 19: Mixing diagrams (after Gaillardet et al., 1999) for Group 2 sample sites . The grey 2+ + - + arrow illustrates increasing Ca /Na and HCO3 /Na mole ratio’s with time. Annual median concentration values were used for construction. The area indicated with the dashed line indicates the area of sample site A2H047Q01, which is assumed to be the least polluted sample site for the Johannesburg Granite Dome.

In the mixing diagrams (Fig. 19) both samples show a similar trend: an decreasing Ca2+/Na+ - + mole ratio and a decreasing HCO3 /Na mole ratio from the early 1980s to the late 1990s + 2+ - caused by increasing Na concentrations. The high Ca and HCO3 concentrations can be explained by the fact that the Bloubank River drains dolomite.

3.3.3. Group 3

Figures 38-43 (Appendix I, pp. 61-66) summarise the variation of the water chemistry with time for the individual sample sites. The water chemistry for this group shows the following characteristics:

- · High total alkalinity ( HCO3 ) and low sulphate, sodium and chloride concentrations for the entire time period. These relations give the Stiff diagrams (Figs. 12, 38-43a) its characteristic shape for this group. The total positive cation charge (SZ+) varies between 4000 and 5500 meq/l. Exceptions are samples sites A2H014Q01 and A2H051Q01 with values of 7000-8000 meq/l and 2500-3000 meq/l, respectively. · Generally, the water chemistry shows a minor change over time (Fig. 38-43a), with the exception of sample site A2H014Q01; · Slightly increasing total dissolved solids concentrations and pH values with time (Figs. 38-43b, c, d). The pH stabilises around 8+ after 1988. · No correlation between pH and sulphate concentrations between 1979 and 1999 (Figs. 38- 43e). · Low fluoride concentrations (< 0.4 mg/l) (Figs. 38-43f). 31

· Low phosphate concentrations (< 0.1 mg/l) with the exception of sample site A2H014Q01 (~1-2 mg/l) (Figs. 38-43g).

Figure 20: Gibbs’ diagram (Gibbs, 1970) illustrating the plotting area for sample sites belonging to Group 3. Annual median values were used. See Chapter Two for an explanation of the diagram.

The sample sites plot at similar TDS concentrations but different Na+/(Na+ + Ca2+) ratios in the Gibbs’ diagram (Fig. 20).

The mixing diagrams (Fig. 21) show that the chemistry of all samples (with the exception of A2H014Q01) can be explained by chemical weathering of silicate and carbonate rocks .

Figure 21: Mixing diagrams (after Gaillardet et al., 1999) for Group 3 sample sites. Annual median concentration values were used for construction. The area indicated with the dashed line indicates the area of sample site A2H047Q01, which is assumed to be the least polluted sample site in the Johannesburg Granite Dome.

3.4. Water Quality Index

3.4.1. Water quality objectives

Van Veelen (2002) defined water quality objectives for the Jukskei River Catchment based on the different user groups and activities. Table 7 shows these objectives for the Jukskei River Catchment.

Table 7: Management water quality objectives for Jukskei River Catchment area (Van Veelen, 2002). Objectives indicated with an asterisk were not given by Van Veelen (2002) and defined in this study . See text for further explanation. Water Quality Parameter Objective pH 6.5 – 8.4 Chloride 15 mg/l Fluoride 1.0 mg/l Nitrate + nitrite 6 mg/ l Phosphate 0.05 mg/ l * Sodium 100 mg/l Sulphate 200 mg/l Total dissolved solids* 500 mg/l

The reference level of sodium was not defined by Van Veelen (2002) and is set at 100 mg/l using domestic water guidelines (Department of Water Affairs and Forestry, 1996a). The reference level of total dissolved solids is determined from Figure 6 (Chapter One), assuming a minimum runoff in a granitic terrane, and set at 500 mg/l. For each sample site, all available water analyses were used to calculate the Water Quality Index using an Excel spreadsheet program developed by the Canadian Council of Ministers of the Environment (2001a, b) (Appendix V).

3.4.2. Water Quality Index for Group 1 sample sites

The water quality of Group 1 sample sites was poor in the early 1980s , changing to marginal in the late 1990s (Fig. 22). The water quality for sample sites downstream the Jukskei River is slightly better compared to samples sites upstream. All chemical parameters contribute more or less equally to the poor water quality in the 1980s whereas in the 1990s the water quality is lowered by high concentrations of phosphate, nitrate , chloride , fluoride and total dissolved solids.

Figure 22: Water Quality Index for Group 1 sample sites for the years 1979-1997. (A2H040Q01 and A2H042Q01) and 1979-1999 (A2H023Q01, A2H044Q01 and A2H012Q01). Water quality objectives are indicated with the grey shaded and white area.

3.4.3. Water Quality Index for Group 2 sample sites

The water quality of Group 2 sample sites is fair to good and shows a more or less constant pattern for the entire period of 1979-1999 (Fig. 23). Chemical parameters that in particular contribute to the lowering of the water quality include the chloride and phosphate concentrations.

Figure 23: Water Quality Index for Group 2 sample sites for the years 1979-1999. Water quality objectives are indicated with the grey shaded and white area.

3.4. 4. Water Quality Index for Group 3 sample sites

The water quality of the sample sites belonging to Group 3 is generally good (Fig. 24). The only exception is sample site A2H014Q01, which has a fair water quality. The water quality did not significantly change for the period 1979-1999. Chemical parameters that do have effect on the water qualit y status include the pH (too high), chloride and phosphate concentrations. For sample site A2H014Q01, it includes chloride, phosphate, nitrate and total dissolved solids concentrations.

Figure 24: Water Quality Index for Group 3 sample sites for the years 1979-1999. Water quality objectives are indicated with the grey shaded and white area.

Chapter 4

Discussion and conclusions

4. 1. Group 1

Group 1 sample sites are situated along the Jukskei River and the Crocodile River. The se samples sites have a poor to marginal water quality and the Jukskei River is the most polluted river in the area. The water quality has only improved from poor to marginal for the period 1979 to 1999. The most important chemical characteristics for this group include : (1) The high sulphate concentrations and low pH values in the early 1980s and the negative correlation between pH and sulphate concentrations between 1979 and 1987-1989. After 1987-1989 sulphate concentrations stabilise to variable levels different for each sample site and the pH stabilises to a constant level around 8+ for all sample sites. Other chemical characteristics include high concentrations in the early 1980s of chloride, fluoride, sodium and phosphate .

The Group 1 Stiff diagrams (Fig. 12, Chapter Three) illustrate that the relationship between the cations and anions is the same for all sample sites whereas the absolute concentrations are decreasing downstream to the north. This can be explained by simple dilution and implies that the main source of pollution must be situated in the south.

The high sulphate concentrations associated with low pH values are typical characteristics for acid mine drainage (e.g. Banks et al., 1997; Bell, 1998). The reactions involved in acid mine drainage are given below (e.g. Banks et al., 1997; Nordstrom & Alpers, 1999). Pyrite (FeS 2), which is the main sulphide mineral phase in the Witwatersrand ore (e.g. Robb & Robb, 1998) , oxidises in presence of water to produce sulphate and hydrogen protons according to the reaction:

2+ 2- + 2FeS2 + 2H2O + 7O 2 ® 2Fe + 4 SO 4 + 4H (4.1)

The produced ferrous iron subsequently oxidises to ferric iron:

2+ + 3+ 4Fe + 4H + O2 ® 4Fe + 2H2O (4.2) where the ferric iron triggers the following reactions:

3+ 2+ 2- + FeS2 + 14Fe + 8H 2O ® 15Fe + 2 SO4 + 16H (4.3)

3+ + 2Fe + 3H2O ® 2Fe(OH)3 + 3H (4.4) 37

These reactions can either take place underground or in tailing dumps (e.g., Scott, 1995; Bell, 1998; Naicker et al., 2003), in particular during erosion or reworking when they are exposed to air (Venter, 1995; Bell, 1998). Considering the fact that the origin of the pollution must be in the south of the area, the most likely sources are gold mining activities in the Central Rand or East Rand areas.

Figure 25 shows the chloride and sodium concentration trend for the Jukskei River and the average sodium and chloride concentrations of the mine water from the Central Rand (Scott, 1995) and the Cl-/Na+ (mg/l) ratio for mine water from the East Rand (Scott, 1995). Mine water from the East Rand shows generally higher values for sodium and chloride (> 200 mg/l) and a higher Cl-/Na+ (mg/l) ratio than mine water from the Central Rand. The diagram illustrates that the high sodium and chloride concentrations in the Jukskei River can be explained with mine water contamination from the Central Rand area and demonstrates that mine water contamination from the East Rand mining area is highly unlikely as it is characterised by Cl-/Na+ mass ratio of 1.1 (Scott, 1995) that does not correspond with Cl-/Na+ mass ratio of 0.54 (Scott, 1995) that is observed in the Jukskei River at high concentrations of sodium and chloride (Fig. 25).

Figure 25: Na+ versus Cl- for the Jukskei River (grey arrow, see Fig. 16, Chapter Three), Central Rand mine water (grey circle) (Scott, 1995), East Rand mine water (dashed arrow) (Scott, 1995) and the Little Jukskei River (ellipse). The Jukskei River shows a trend with time from mine water values to values comparable to those of the Little Jukskei River, indicating improving water quality.

Due to the lack of water quality data before 1979, it cannot be determined whether the poor water quality existed already before 1979. The cause of the acid mine drainage can, therefore, be either deep mining activities in the 1970s and/or reworking activities of the tailings in the Central Rand area in the early 1980s , which took place mainly as a result of improved technology and a high gold price (Scott, 1995).

The Central Rand area, however, is situated in south of Johannesburg in the Orange/Vaal catchment area, in which the rivers drain towards the Vaal and Orange Rivers. Furthermore, it is noticeable that the Little Jukskei River is not contaminated at all. This implies that mine water contamination must have occurred along northeast trending structures. Dykes in the Central Rand area trend in a northeast direction (McCarthy et al., 1990) and it is likely that these structures acted as pathways for the mine water due to the high water pressure build up as a result of rising groundwater after deep mining operations ceased in the 1970s (Harmse, personal communication, 2004). If this is indeed the case, it implies that mine water contamination still had some noticeable effect on the water chemistry in the Crocodile River (sample site A2H012Q01, see Fig. 10), about 75 km north of the Central Rand area illustrating the poor buffer quality of the granitoid terrane, which the Jukskei River drains .

The mixing diagrams (Fig. 22, Chapter Three) demonstrate a strong sensitivity for acid mine 2+ + - + drainage, i.e. low Ca /Na and HCO 3 /Na mole ratio’s and an increase of both ratio’s with improving water quality conditions.

4.1.1. Phosphate concentrations

Phosphate concentrations are in particular high during the period 1980-1987 and appear to correlate with low pH values, suggesting that the pH may control the phosphate concentration levels. Another factor that should be kept in mind, however, is that the Special Phosphate Standard (1 mg/l) for point sources has been implemented in 1985. If that is the case, the correlation between an increase in pH and a decrease in phosphate concentration might also be purely coincidental.

Figure 26: a. T he SIapatite dependency (dashed line) on the pH (black diamonds). Phosphate concentrations (open squares) tend to be lower at higher pH. SIapatite (25°C) was calculated using the program PHREEQC (Parkhurst & Appelo, 1999). Annual median concentration values were used for Group 1 sample sites situated along the Jukskei River (A2H040Q01, A2H042Q01, A2H023Q01 and A2H044Q01). Grey area: field of apatite saturation. b. Diagram showing the variation (as indicated by the shaded line) of the phosphate concentration with the apatite saturation index. Grey area: field of apatite saturation. See text for further explanation. 39

In order to test the pH control on the phosphate concentration, a diagram was constructed to illustrate the relationship between pH, phosphate concentrations and the saturation index of hydroxyapatite, SIapatite (Ca5(PO4)3(OH)) (Fig. 26) and calcite, SIcalcite (Fig. 27).

Apatite was chosen because it has been suggested that apatite saturation may be a limiting factor to the phosphate concentration in natural waters (Appelo & Postma, 1993). Calcite has been selected as an alternative mineral which may decrease the phosphate concentration when it precipitates. A number of studies have demonstrated that phosphate may sorb to the calcite and subsequently incorporated into the crystal lattice (e.g. House, 2003, and references therein).

Figure 26a shows that SIapatite strongly depends on the pH (the correlation coefficient r is

0.95). Figure 26b shows, however, that the apatite saturation (SIapatite = 0 at pH = 7.1) does not correlate significantly with low phosphate concentrations. Apatite saturation has, therefore, hardly any influence on the phosphate concentration. It appears that the surface water occurs in a state of apatite oversaturation without apatite precipitation.

Figure 27a shows, similar to Figure 26a, a strong correlation between the calcite saturation index and pH (correlation coefficient r is 0.99). Figure 27b shows, contrary to Figure 26b, that the calcite saturation (SIcalcite = 0 at pH = 7.8) does seem to separate two fields of low and high phosphate concentrations corresponding to calcite oversaturation and undersaturation, respectively.

Figure 27: a. T he SIcalcite dependency (dashed line) on the pH (black diamonds). Phosphate concentrations (open squares) tend to be lower at higher pH. SIcalcite (25°C) was calculated using the program PHREEQC (Parkhurst & Appelo, 1999). Annual median concentration values were used for Group 1 sample sites situated along the Jukskei River (A2H040Q01, A2H042Q01, A2H023Q01 and A2H044Q01). Grey area: field of calcite saturation. b. Diagram showing the variation of the phosphate concentration (as indicated by the shaded line) with the calcite saturation index. Grey area: field of calcite saturation. See text for further explanation.

This implies that precipitation of calcite does control the phosphate concentration in the Jukskei River. The source of phosphate can be either natural (i.e. the mineral apatite) or anthropogenic, i.e. fertiliser use for agricultural purposes, urban runoff and sewage.

In conclusion, lower phosphate concentrations in the Jukskei River are probably caused by higher pH values resulting in calcite precipitation and a lower phosphate input from point sources as a result of the implementation of the Special Phosphate Standard in 1985.

4.1.2. Fluoride concentrations

Fluoride concentrations show a similar pattern as the phosphate concentrations; high fluoride concentrations from 1980 until 1989, after which a significant drop can be observed. Figure 28 illustrates that the river water is generally undersaturated with respect to the mineral fluorite, except for the highest observed concentrations of calcium and fluoride, which are close to fluorite saturation. Figure 28 also demonstrates the significant correlation between fluoride and calcium. The correlation between calcium and fluoride (correlation coefficient r is 0.62) (Fig. 28) suggests a common source for both, e.g. the minerals fluorite (e.g. Saxena & Ahmed, 2001, 2003) or apatite in which (OH)- has partially been replaced by F -.

Figure 28: Variation of the act ivities of fluoride and calcium. Fluorite (CaF 2) saturation (grey line) acts as a limiting fluoride concentration mechanism. Fluoride and calcium activities were calculated using PHREEQC (Parkhurst & Appelo, 1999). Annual median concentration values were used for Group 1 sample sites situated at the Jukskei River. See text for further explanation.

Fluorite and apatite are both common accessory minerals in granitic rocks. It is difficult to establish exactly which controlling factors are involved in the concentration of fluoride as there are too many parameters involved. However, the correlation of high fluoride concentration levels with low pH suggests that the pH has some influence, i.e.:

· The strong affinity of fluoride for aluminium (e.g. Bell et al., 2001). Elevated concentration levels of aluminium results from a low pH (causing dissolution of Al-rich minerals such as kaolinite) allow ing high fluoride levels as the fluorite saturation cannot be reached under these circumstances (e.g. Nordstrom & Alpers, 1999) . Central Rand mine water with a pH of 2.8 contains about 90 mg/l aluminium. · Preferential dissolution of the mineral apatite, which may contain some fluoride, at low pH.

4.2. Group 2

Group 2 sample sites have a fair water quality and show still some signs of acid mine drainage, reflected in the slight lower pH values in the early 1980s (between 7 and 7.5) before stabilising around 8. The most significant change in the water chemistry is the increase in sodium and chloride concentrations from 1979 to 1999. The sodium increase is clearly demonstrated in the mixing diagrams (Fig. 19, Chapter Three). Possible anthropogenic sources for sodium and chloride are difficult to determine (Panno et al., 2002). The significant correlation (Table 8) between species such as bicarbonate, calcium, chloride, magnesium and ammonium suggest waste dumps and/or septic effluent as a potential source (Panno et al., 2002).

Table 8: Correlation diagram for sample site A2H045Q01 (n = 587 ).

2+ 2+ + + - - - 4+ 2 - - + 3- pH TDS Ca Mg K Na HCO3 Cl F Si SO4 NO3 NH4 PO4 pH 1.00 TDS 0.32 1.00 Ca2+ 0.19 0.81 1.00 Mg2+ 0.12 0.77 0.92 1.00 K+ 0.37 0.16 -0.07 -0.22 1.00 Na + 0.46 0.65 0.42 0.32 0.60 1.00

- HCO3 0.34 0.80 0.69 0.69 0.03 0.57 1.00 Cl - 0.48 0.66 0.62 0.50 0.44 0.65 0.50 1.00 F- -0.03 0.27 0.23 0.19 0.25 0.33 0.15 0.14 1.00 Si 4+ -0.19 -0.22 -0.22 -0.21 -0.01 -0.20 -0.21 -0.18 -0.10 1.00 2 - SO4 0.13 0.72 0.79 0.77 0.10 0.51 0.49 0.51 0.42 -0.25 1.00

- NO3 0.07 0.08 0.05 -0.01 0.32 0.12 0.00 0.18 0.21 0.03 0.09 1.00

+ NH4 0.01 0.16 0.06 0.04 -0.05 0.01 0.00 0.04 0.02 -0.12 0.04 -0.03 1.00

3- PO4 -0.13 -0.04 -0.11 -0.12 0.28 0.16 -0.12 0.06 0.19 0.09 0.02 0.13 -0.03 1.00

4.3. Group 3

This group of samples does not show any significant change in water chemistry from 1979 to 1999. The water quality is good and these samples sites are the least affected by pollution in

the entire area (with the exception of sample site A2H014Q01). These rivers are characterised by a relatively high total positive cation charge, which would classify them, according to Stallard & Edmond (1983), as river draining dominantly carbonate and evaporate rocks. Obviously, this is not the case and the relatively high positive cation charge can most probably be explained by climatic conditions of a high temperature and low rainfall (Fig. 1, Chapter One ) (e.g. Plant et al., 2001; Oliva et al., 2003).

4.3.1. Sample sites A2H047Q01 and A2H051Q01

The rivers that drain the granite terrane (sample sites A2H047Q01 and A2H051Q01) have a similar chemistry (compare Stiff diagrams in Fig. 12, Chapter Three), although the absolute concentrations is higher for sample site A2H047Q01. The water chemistry of these sample sites is largely dominated by chemical weathering of the rocks and can be used as a reference standard for rivers draining the Johannesburg Granite Dome.

Both sample sites have a similar range for the Na+/(Na+ + Ca2+) ratio (mg/l) in the Gibbs’ diagram whereas the TDS concentration (mg/l) is slightly higher for sample site A2H047Q01 (see Fig. 18, Chapter Thr ee and Table 9). These values, in particular the Na+/(Na+ + Ca2+) ratio, are representative for unpolluted rivers that drain the Johannesburg Granite Dome.

Table 9: Summary statistics for the Na+/( Na+ + Ca2+) (mg/ l) ratio and TDS (mg/ l) for sample sites A2H047Q01 and A2H051Q01. A2H047Q01 A2H051Q01

Na+/( Na+ + Ca2+) TDS Na+/( Na+ + Ca2+) TDS Mean 0.33 284 0.33 155 Median 0.33 261 0.33 154 Standard 0.05 58 0.05 47 deviation Minimum 0.21 74 0.18 55 Maximum 0.50 458 0.70 528 Count 290 42 2

2+ + - + Table 10: Summary statistics for Ca /Na and HCO3 /Na mole ratio’s for sample sites A2H047Q01 and A2H051Q01. A2H047Q01 A2H051Q01

2+ + - + 2+ + - + Ca /Na HCO 3 /Na Ca /Na HCO 3 /Na Mean 1.19 2.57 1.17 3.32 Median 1.15 2.52 1.15 3.22

Standard 0.25 0.51 0.24 0.87 deviation Minimum 0.58 1.51 0.25 0.31 Maximum 2.13 4.64 2.58 7.53 Count 291 425

In the mixing diagrams both sample sites have similar median values for the Ca2+/Na+ and - + HCO3 /Na mole ratio’s (Table 10), which can be considered as ideal values for unpolluted rivers that drain the Johannesburg Granite Dome. The slight offset to the carbonate endmember can be explained by preferential weathering of calcite that occurs in the granite, either disseminated or in veins (White et al., 1999).

The water analyses are plotted in a Mg2+/(Mg2+ + Ca2+) versus K +/(K+ + Na+ - Cl-) mole ratio diagram, which can be used to identify the bedrock types (Fig. 29) (Stallard & Edmond, 1983) and illustrate that the water composition is dominated by chemical weathering of granitoids. Sample sites A2H040Q01 and A2H044 Q01 are plotted as well, showing that these samples sites have a tendency to lower Mg2+/(Mg2+ + Ca2+) and K +/(K+ + Na+ - Cl-) mole ratio’s (Fig. 29).

Figure 29: Mg2+/(Mg2+ + Ca2+) versus K+/(K+ + Na+ - Cl-) mole ratio’s for samples sites A2H051Q01, A2H047Q01, A2H040Q01 and A2H044Q01 (black diamonds) with predicted ratio’s for several granitoids (grey squares) (Stallard & Edmond, 1983).

4.3.2. Sample site s A2H033Q01 and A2H034Q01

The water chemistry at sample sites A2H033Q01 and A2H034Q01 show clear signatures of the dolomite weathering, in particular in the mixing diagrams (Fig. 21, Chapter Three) in which they both plot in between the silicate and the carbonate endmember. The samples plot

in the Gibbs’ diagram at low Na+/(Na+ + Ca2+) ratio’s as a result of the relatively high Ca2+ concentrations due to preferential carbonate weathering. Figure 30 shows the concentration variation of magnesium, bicarbonate, calcium and the pH for sample site A2H034Q01 with time. Table 11 gives the average values for these chemical species and the PHREEQC calculation results for a dolomite -calcite carbonate rock for several values of P , clearly CO 2 illustrating that weathering of carbonate rocks can explain the water chemistry to a large extend.

Figure 30: Variation of magnesium, calcium and bicarbonate concentrations and pH with time for sample site A2H034Q01. Mean and Median values for the chemical parameters are given in Table 11.

Table 11: Water chemistry results for magnesium, bicarbonate, calcium and pH (sample site A2H034Q01) together with PHREEQC equilibrium calculations assuming a calcite-dolomite carbonate rock for different values of P reflecting the common range in natural surface water CO 2 (Appelo & Postma, 1993). 2+ - 2+ Mg (mg/l) HCO3 (mg/l) Ca (mg/l) pH Mean 21 154 31 8.1

A2H034Q01 Median 22 157 32 8.2 Standard 1.9 15 3.4 0.4 deviation PHREEQC ( P = 10-1.5) CO 2 32 360 71 7.1 PHREEQC ( P = 10-2.5) CO 2 14 163 31 7.7 PHREEQC ( P = 10-3.5) CO 2 6 73 14 8.4

4.3. 3. Sample site A2H013Q01

The water quality at sample site A2H013Q01 reflects weathering of dominantly silicate and carbonate rocks (Fig. 21, Chapter Three). In the Gibbs’ diagram (Fig. 20, Chapter Three), it plots in between the sample sites A2H033Q01/A2H034Q01 and A2H047Q01/A2H051Q01, confirming the mixed signature of silicate and carbonate rocks. Noticeable is the relative high magnesium concentration compared to calcium, suggesting weathering of Mg-rich minerals such as amphibole (e.g. Fig. 5, Chapter Two).

4.3. 4. Sample site A2H014Q01

This sample site is clearly different from the others in the group. It does show a significant change in water chemistry over time. Similar to Group 2, it shows some signs of mine water contamination as is reflected in the lower pH values in the early 1980s (between 7 and 8) (Fig. 38, Appendix I). Phosphate concentrations are also high, correlating with lower pH values (Fig. 38, Appendix I) as is the case for Group 1. The decreasing tendency of calcium, magnesium and bicarbonate concentrations with time (Fig. 38, Appendix I) is probably related with the change in pH from around 7 to 8. At a relatively low pH, a higher rate of chemical weathering of the dolomite, which the Hennops River drains (Fig. 10, Chapter Three), is expected (e.g. Appelo & Postma, 1993).

4.4. Conclusions

The conclusions of this study include the following:

(1) The Jukskei River is the most polluted river in the Johannesburg Granite Dome , followed by the Hennops, the Bloubank and the Crocodile River s. The Little Jukskei, the Magalies and the Skeerpoort River s do not show any form of inorganic water pollution. (2) Water pollution of the Jukskei River in the early 1980s can be largely attrib ute d to mine water contamination from the Central Rand area, resulting in low pH, high sulphate, high sodium, high chloride and high nitrate concentrations. The effect of mine water contamination can be traced up to the Crocodile River , 75 km north of the Central Rand area and illustrates the poor buffering capacity of the granitoid terrane. (3) Phosphate and fluoride concentration levels in the Jukskei River show some correlation with pH and implies that these concentrations are high as a result of surface waters undersaturated in fluorite and calcite (i.e. no limiting factor is present for phosphate and fluoride concentrations). It also shows that the phosphate input into the presently eutrophic Hartbeespoort Dam was in particular high in the 1980s. Potential sources for these chemical species can be either natural (i.e. mineral phases apatite and fluoride) or agricultural activities (i.e. use of fertiliser).

(4) The overall pH stabilised from 1987-1989 onwards and is similar (~8+) for all rivers draining the Johannesburg Granite Dome. This is a typical equilibrium pH associated with weathering of fresh granitoid rocks producing relatively large amounts of bicarbonate (e.g. White et al., 1999). (5) The Bloubank River and Crocodile River (between the confluence with the Jukskei and Bloubank Rivers) show some signs of acid mine drainage, which is reflected in the lower pH values in the early 1980s . Sodium and chloride show a systematic increase in both rivers , which is related to septic effluent and waste disposal as a result of population growth in the area. This effect, although expected, is less visible in the Jukskei River which is probably due to the interference of the large effects of acid mine drainage on the water chemistry. (6) The Hennops River also shows some indication of mine water contamination as is illustrated by the lower pH values in the early 1980s. As a result of the low pH, the river shows higher concentrations of calcium, magnesium and bicarbonate due to higher rate of dissolution of the dolomitic bedrock. (7) The Little Jukskei, Magalies and Skeerpoort Rivers, which do not show any signs of pollution do still have a relatively high concentration of dissolved chemical species, most probably associated with semi-arid climatic conditions. The ir water chemistry reflects weathering of silicate and/or carbonate rocks. The water chemistry of these rivers can be used as a reference for polluted rivers in the area. (8) Geochemical discrimination diagrams can be very helpful in the evaluation of the inorganic water chemistry of natural surface waters in order to distinguish natural and anthropogenic contributions . It does require, however, a large number of analyses over a number of years in order to identify trends.

4.5. Outstanding questions and future research

This study has focussed on the inorganic water quality of rivers draining the Johannesburg Granite Dome. The results of this study have raised a number of new questions, which are all beyond the scope of this study and, therefore, requirin g more detailed studies. The se questions include the following:

? How did the mine water contamination effect the concentration of metals in the Jukskei River such as aluminium, iron, manganese and uranium. These metals have been identified in ground and surface water s in the Witwatersrand mining areas (e.g. Naicker et al., 2003; Winde & Van der Walt, 2004). Did high concentrations of these metals result in precipitation of certain minerals and if so, under what conditions will these minerals dissolve and release those metals? ? At present, the eutrophication of the Hartbeespoort Dam is a “hot” environmental issue. Questions about this matter were even raised in the National Assembly in June 2003 (National Assembly, 2003). This study has shown that the largest contributor of phosphate

to the Hartbeespoort Dam is the Jukskei River, in particular in the 1980s. One may, therefore, wonder whether the present eutrophication of the Hartbeespoort Dam is associated with steady phosphate increase in the sediments of the Hartbeespoort Dam over the years or with the present phosphate input. ? What is or are the reason(s) for the steady recovery of the Jukskei River after 1987? Is this due to different mining practices as a result of stricter environmental legislation or is there a natural control, i.e. less pyrite became available for acid mine drainage as it was consumed.

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Van Veelen, M. 2002: Development of principles and procedures for the establishment of water quality objectives for aquatic systems and their application on the Jukskei River system, Gauteng. Unpublished Ph.D. thesis Rand Afrikaans University, Johannesburg, South Africa. Venter A.J.A. 1995: Assessment of the effect of gold-mine effluent on the natural aquatic environment. Unpublished Ph.D. thesis Rand Afrikaans University, Johannesburg, South Africa. Vogel, C. 2000: Climate and climatic change: causes and consequences. In Fox, R. & K. Rowntree. (eds.): The Geography of South Africa in a Changing World. Oxford University Press, 284-303. Walling, D.E. 1980: Water in the catchment ecosystem. In Gower, A.M. (ed.): Water Quality in the Catchment Ecosystems. New York: Wiley, 1-48. Walmsley, R.D. 2003: Project 1: Phase 1. Development of a Strategy to Control Eutrophication in South Africa. A Review and Discussion Document. Water Quality Management Series. Department of Water Affair and Forestry. http://www.dwaf.gov.za. Walmsley, R.D., J.J. Walmsley & M. Silberbauer. 1999: Freshwater Systems and Resources. National State of the Environment – South Africa. Department of Environmental Affairs and Tourism. http://www.environment.gov.za/. Weaver, A., W. Le Roux & R. Pretorius. (eds.). 1999: State of the Environment in South Africa 1999 – an overview. http://www.ngo.grida.no/soesa/. Werdmüller, V.W. 1986: The Central Rand. In Antrobus, E.S.A. (ed.): Witwatersrand Gold – 100 years. Geological Society of South Africa, 7-47. White, A.F., T.D. Bullen, D.V. Vivit, M.S. Schulz & D.W. Clow. 1999: The role of disseminated calcite in the chemical weathering of granitoid rocks. Geochimica Cosmochimica Acta, 63, 1939-1953. White, W.M. 2003: Geochemistry. http://www.geo.cornell.edu/geology/classes/geo455/ Chapters.HTML. Winde, F. & I.J. Van der Walt. 2004: The significance of groundwater-stream interactions and fluctuating stream chemistry on waterborne uranium contamination of streams – a case study from a gold mining site in South Africa. Journal of Hydrology, 287, 178-196.

APPENDIX I

Water chemistry of Group 1, 2and 3 sample sites

In this appendix, the water chemistry of the individual sample sites for each group is characterised using the following:

? Stiff diagrams for 1979 and 1997/1999 (a). ? Time (years) versus sulphate concentration (mg/l) (b). ? Time (years) versus TDS concentration (mg/l) (c). ? Time (years) versus pH (d). ? Sulphate concentration (mg/l) versus pH using annual median values (e). The grey arrow illustrates the trend with time. The numbers indicate the year. ? Time (years) versus fluoride concentration (mg/l) (f). ? Time (years) versus phosphate concentration (mg/l) (g).

Annual median (50%), 25%, 75%, minimum and maximum values (Fig. 31b) were used for diagrams b, c, f and g.

Figure 31: Water chemistry for A2H012Q01.

Figure 32: Water chemistry for A2H023Q01.

Figure 33: Water chemistry for A2H040Q01.

Figure 34: Water chemistry for A2H042Q01.

Figure 35: Water chemistry for A2H044Q01. 58

Figure 36: Water chemistry for A2H045Q01.

Figure 37: Water chemistry for A2H049Q01.

Figure 38: Water chemistry for A2H013Q01.

Figure 39: Water chemistry for A2H014Q01.

Figure 40: Water chemistry for A2H033Q01.

Figure 41: Water chemistry for A2H034Q01.

Figure 42: Water chemistry for A2H047Q01.

Figure 43: Water chemistry for A2H051Q01.

APPENDIX II

Unit conversions

Water quality data, such as supplied by the Department of Water Affairs and Forestry are expressed in milligrams per litre sample (mg/l) for the anions and cations in solution. However, speciation calculations are indicated in number of moles per kg water (mol/kg

H2O), the molality. The molality is identical to the concentration (i.e., moles per litre: mol/l) if it is assumed that the density of the solution is 1 kg/litre.

In order to convert milligrams per litre to moles per litre, one should divide by the molar mass (M) of the specific specie (e.g. Appelo & Postma, 1993):

1 mg / l 1 mmol / l = M and for the calculation of milliequivalents per litre:

1 meq / l = charge of ion ´ 1 mmol / l

For unit conversion, the following relationships were used (e.g. Appelo & Postma, 1993:

Table 11: Important unit conversions. Units Conversion relation

Concentration to molality 1 mol/l » 1 mol/kg H2O Milligrams per litre to parts per million 1 mg/l = 1 ppm Concentration in moles per litre to millimoles per litre 1 mol/l = 1000 mmol/l Concentration in moles per litre to micromoles per litre 1 mol/l = 106 mmol/l Concentration in millimoles per litre to micromoles per litre 1 mmol/l = 1000 mmol/l

APPENDIX III

Phreeqc – 2

PHREEQC is a computer program for hydrochemical calculations developed by Parkhurst & Appelo (1999). The program has many options but is in this thesis used for the calculation of speciation and saturation indexes (SI). Below follows an example of a speciation and SI calculation for an average world river composition (data from Meybeck, 1985, see also Table 6 in Chapter Two).

The input file is as follows: # # SOLUTION: AVERAGE WORLD RIVER COMPOSITION units mg/kgw temp 20.0 Na 8.5 K 1.5 Ca 15.0 Mg 3.9 Amm 0.02 Si 10.4 F 0.0 P 0.0 Cl 10.5 Alkalinity 53.0 as HCO3 S(6) 12.3 N(5) 0.1 END which results in the following output file:

------Reading data base. ------

SOLUTION_MASTER_SPECIES SOLUTION_SPECIES PHASES EXCHANGE_MASTER_SPECIES EXCHANGE_SPECIES SURFACE_MASTER_SPECIES SURFACE_SPECIES RATES END ------Reading input data for simulation 1. ------

SOLUTION: AVERAGE WORLD RIVER COMPOSITION units mg/kgw temp 20.0 Na 8.5 K 1.5 Ca 15.0 68

Mg 3.9 Amm 0.02 Si 10.4 F 0.0 P 0.003 Cl 10.5 Alkalinity 53.0 as HCO3 S(6) 12.3 N(5) 0.1 END ------Beginning of initial solution calculations. ------

Initial solution: AVERAGE WORLD RIVER COMPOSITION.

------Solution composition------

Elements Molality Moles

Alkalinity 8.686e-04 8.686e-04 Amm 1.111e-06 1.111e-06 Ca 3.743e-04 3.743e-04 Cl 2.962e-04 2.962e-04 K 3.836e-05 3.836e-05 Mg 1.604e-04 1.604e-04 N(5) 7.139e-06 7.139e-06 Na 3.697e-04 3.697e-04 P 9.686e-08 9.686e-08 S(6) 1.280e-04 1.280e-04 Si 1.731e-04 1.731e-04

------Description of solution------

pH = 7.000 pe = 4.000 Activity of water = 1.000 Ionic strength = 2.074e-03 Mass of water (kg) = 1.000e+00 Total carbon (mol/kg) = 1.066e-03 Total CO2 (mol/kg) = 1.066e-03 Temperature (deg C) = 20.000 Electrical balance (eq) = 5.047e-05 Percent error, 100*(Cat-|An|)/(Cat+|An|) = 1.76 Iterations = 6 Total H = 1.110140e+02 Total O = 5.551044e+01

------Distribution of species------

Log Log Log Species Molality Activity Molality Activity Gamma

H+ 1.048e-07 1.000e-07 -6.980 -7.000 -0.020 OH- 7.139e-08 6.789e-08 -7.146 -7.168 -0.022 H2O 5.551e+01 1.000e+00 1.744 -0.000 0.000 Amm 1.111e-06 AmmH+ 1.105e-06 1.050e-06 -5.957 -5.979 -0.022 Amm 4.102e-09 4.104e-09 -8.387 -8.387 0.000 AmmHSO4- 1.397e-09 1.328e-09 -8.855 -8.877 -0.022 C(4) 1.066e-03 69

HCO3- 8.626e-04 8.214e-04 -3.064 -3.085 -0.021 CO2 1.978e-04 1.979e-04 -3.704 -3.704 0.000 CaHCO3+ 3.036e-06 2.891e-06 -5.518 -5.539 -0.021 MgHCO3+ 1.276e-06 1.214e-06 -5.894 -5.916 -0.022 CO3-2 4.208e-07 3.459e-07 -6.376 -6.461 -0.085 NaHCO3 1.623e-07 1.624e-07 -6.790 -6.790 0.000 CaCO3 1.592e-07 1.593e-07 -6.798 -6.798 0.000 MgCO3 3.935e-08 3.937e-08 -7.405 -7.405 0.000 NaCO3- 1.842e-09 1.752e-09 -8.735 -8.756 -0.022 Ca 3.743e-04 Ca+2 3.654e-04 3.003e-04 -3.437 -3.522 -0.085 CaSO4 5.608e-06 5.611e-06 -5.251 -5.251 0.000 CaHCO3+ 3.036e-06 2.891e-06 -5.518 -5.539 -0.021 CaCO3 1.592e-07 1.593e-07 -6.798 -6.798 0.000 CaHPO4 4.496e-09 4.498e-09 -8.347 -8.347 0.000 CaOH+ 5.238e-10 4.983e-10 -9.281 -9.302 -0.022 CaH2PO4+ 3.646e-10 3.468e-10 -9.438 -9.460 -0.022 CaPO4- 1.016e-10 9.668e-11 -9.993 -10.015 -0.022 Cl 2.962e-04 Cl- 2.962e-04 2.816e-04 -3.528 -3.550 -0.022 H(0) 1.432e-25 H2 7.162e-26 7.166e-26 -25.145 -25.145 0.000 K 3.836e-05 K+ 3.834e-05 3.646e-05 -4.416 -4.438 -0.022 KSO4- 2.497e-08 2.376e-08 -7.603 -7.624 -0.022 KHPO4- 2.245e-12 2.135e-12 -11.649 -11.671 -0.022 KOH 1.263e-12 1.264e-12 -11.898 -11.898 0.000 Mg 1.604e-04 Mg+2 1.565e-04 1.288e-04 -3.806 -3.890 -0.085 MgSO4 2.600e-06 2.601e-06 -5.585 -5.585 0.000 MgHCO3+ 1.276e-06 1.214e-06 -5.894 -5.916 -0.022 MgCO3 3.935e-08 3.937e-08 -7.405 -7.405 0.000 MgOH+ 3.105e-09 2.954e-09 -8.508 -8.530 -0.022 MgHPO4 2.607e-09 2.608e-09 -8.584 -8.584 0.000 MgH2PO4+ 1.991e-10 1.894e-10 -9.701 -9.723 -0.022 MgPO4- 5.880e-11 5.594e-11 -10.231 -10.252 -0.022 N(5) 7.139e-06 NO3- 7.139e-06 6.787e-06 -5.146 -5.168 -0.022 Na 3.697e-04 Na+ 3.694e-04 3.515e-04 -3.433 -3.454 -0.022 NaSO4- 1.761e-07 1.675e-07 -6.754 -6.776 -0.022 NaHCO3 1.623e-07 1.624e-07 -6.790 -6.790 0.000 NaCO3- 1.842e-09 1.752e-09 -8.735 -8.756 -0.022 NaOH 2.321e-11 2.322e-11 -10.634 -10.634 0.000 NaHPO4- 2.164e-11 2.059e-11 -10.665 -10.686 -0.022 O(0) 0.000e+00 O2 0.000e+00 0.000e+00 -43.765 -43.765 0.000 P 9.686e-08 H2PO4- 5.232e-08 4.978e-08 -7.281 -7.303 -0.022 HPO4-2 3.669e-08 3.004e-08 -7.435 -7.522 -0.087 CaHPO4 4.496e-09 4.498e-09 -8.347 -8.347 0.000 MgHPO4 2.607e-09 2.608e-09 -8.584 -8.584 0.000 CaH2PO4+ 3.646e-10 3.468e-10 -9.438 -9.460 -0.022 MgH2PO4+ 1.991e-10 1.894e-10 -9.701 -9.723 -0.022 CaPO4- 1.016e-10 9.668e-11 -9.993 -10.015 -0.022 MgPO4- 5.880e-11 5.594e-11 -10.231 -10.252 -0.022 NaHPO4- 2.164e-11 2.059e-11 -10.665 -10.686 -0.022 KHPO4- 2.245e-12 2.135e-12 -11.649 -11.671 -0.022 PO4-3 1.918e-13 1.223e-13 -12.717 -12.912 -0.195 S(6) 1.280e-04 SO4-2 1.196e-04 9.820e-05 -3.922 -4.008 -0.086 70

CaSO4 5.608e-06 5.611e-06 -5.251 -5.251 0.000 MgSO4 2.600e-06 2.601e-06 -5.585 -5.585 0.000 NaSO4- 1.761e-07 1.675e-07 -6.754 -6.776 -0.022 KSO4- 2.497e-08 2.376e-08 -7.603 -7.624 -0.022 AmmHSO4- 1.397e-09 1.328e-09 -8.855 -8.877 -0.022 HSO4- 9.020e-10 8.580e-10 -9.045 -9.066 -0.022 Si 1.731e-04 H4SiO4 1.729e-04 1.729e-04 -3.762 -3.762 0.000 H3SiO4- 2.240e-07 2.131e-07 -6.650 -6.671 -0.022 H2SiO4-2 1.265e-13 1.036e-13 -12.898 -12.984 -0.087

------Saturation indices------

Phase SI log IAP log KT

Amm(g) -10.29 1.02 11.31 Amm Anhydrite -3.19 -7.53 -4.34 CaSO4 Aragonite -1.68 -9.98 -8.31 CaCO3 Calcite -1.53 -9.98 -8.45 CaCO3 Chalcedony -0.15 -3.76 -3.61 SiO2 Chrysotile -10.03 22.81 32.83 Mg3Si2O5(OH)4 CO2(g) -2.30 -20.46 -18.16 CO2 Dolomite -3.36 -20.33 -16.97 CaMg(CO3)2 Gypsum -2.95 -7.53 -4.58 CaSO4:2H2O H2(g) -21.95 -22.00 -0.05 H2 H2O(g) -1.64 -0.00 1.64 H2O Hydroxyapatite -9.21 -49.35 -40.14 Ca5(PO4)3OH O2(g) -40.91 44.00 84.91 O2 Quartz 0.27 -3.76 -4.04 SiO2 Sepiolite -6.96 8.93 15.89 Mg2Si3O7.5OH:3H2O Sepiolite(d) -9.73 8.93 18.66 Mg2Si3O7.5OH:3H2O SiO2(a) -1.01 -3.76 -2.75 SiO2 Talc -6.70 15.28 21.98 Mg3Si4O10(OH)2

------End of simulation. ------

------Reading input data for simulation 2. ------

------End of run. ------

No memory leaks

APPENDIX IV

Excel spreadsheet for water chemistry characterisation

An Excel spreadsheet was developed for the recalculation of water chemistry data that are given in mg/l to mmol/l and meq/l. The spreadsheet also constructs a Stiff diagram and calculates several parameters that are required for classification. The spreadsheet is available from the author (e-mail: [email protected]).

Water chemistry characterisation

Sample locality number: A2H081Q01 Locality description: Crocodile River at Hartbeespoortdam Date / Year: 1987

INPUT DATA OUTPUT RESULTS

Cations (mg/l) Cations RESULTS STIFF DIAGRAM Estimation (maximum) log activities and SI mmol/l meq/l Na 49.4 2.15 2.15 Cations (meq/l) (without correction for complexation and activities) K 8.9 0.23 0.23 + + 2+ + 2 Ca 42.7 1.06 2.13 K + Na -2.38 -0.5 log [Ca /(H ) ] 11.6 2+ + + Mg 16.8 0.69 1.38 Ca -2.13 -1.5 log [Na /(H )] 4.6 2+ 2+ + 2 11.4 NH 4 0.0 0.00 0.00 Mg -1.38 -3 log [Mg /(H ) ] + SiO2 (NH4) 0.00 -4.5 0.17 0.70 Si 4.9 SI fluorite -1.2 Antions (meq/l) Anions (mg/l) Anions - mmol/l meq/l (NO3) 0.04 -4.5 2- F 0.7 0.04 0.04 (SO4) 1.86 -3 - PO4 0.3 0.00 0.01 (HCO3) 1.72 -1.5 - Cl 50.6 1.43 1.43 Cl 1.43 -0.5

HCO3 105.1 1.72 1.72

SO4 89.5 0.93 1.86 PARAMETERS FOR CLASSIFICATION NO 3 2.6 0.04 0.04 River classification based on weathering (Stallard & Edmond, 1983) TDS (mg/l) 402.5 Charge meq/l SZ+ ( meq/l) 6588 + + pH 7.3 SZ 6.59 SiO2 / SZ 0.03 - Flow rate SZ 5.10 D (%) 13 River classification (Gibbs, 1970) Na+ / (Na+ + Ca+) (mg/l) 0.54 TDS 403

Cation source identification (Stallard & Edmond, 1983) (Na + K) / Cl 1.5

(Ca + Mg) / (HCO 3 + SO4) 1.0

(Ca + Mg) / HCO 3 2.0

Rock type and weathering classification (Stallard & Edmond, 1983) Si 0.03

HCO3 0.33

(Cl + SO 4) 0.63

Weathering reactions (Stallard & Edmond, 1987) Na - Cl 0.64 Si 0.16 K 0.20

Identification siliceous lithologies (Stallard & Edmond, 1983) Mg / (Mg + Ca) 0.39 K / (Na + K - Cl) 0.24

Figure 44: Example of a worksheet used for recalculation of water chemistry data.

APPENDIX V

Calculation of the Water Quality Index

The Water Quality Index used in this study has been developed by the Canadia n Council of Ministers of the Environment (CCME) (2001a, b). The CCME Water Quality Index (version 1.0) (CCMEWQI) is defined as follows:

æ F 2 + F 2 + F 2 ö CCMEWQI º 100 - ç 1 2 3 ÷ (A1) ç 1.732 ÷ è ø where:

F1 represents the percentage of variables that depart from their objectives, relative to the total number of variables measured:

æ number of failed variables ö ç ÷ F1 = ç ÷ ´100 (A2) è total number of variables ø

F2 represents the percentage of failed individual tests:

æ number of failed tests ö F2 = ç ÷´100 (A3) è total number of tests ø

F3 is a function that scales the normalized sum of the excursions from objectives (nse) to yield a range between 0 and 100.

æ nse ö ç ÷ F3 = ç ÷ ´100 (A4) è 0.01 nse + 0.01 ø

The collective amount by which individual tests are out of compliance is calculated by summing the departures of individual tests from their objectives and dividing by the total number of tests. The nse variable is, expressed as:

n å departurei nse = i=1 (A5) total number of tests

For the cases in which the test value must not exceed or fall below the objective:

æ failed test ö departure = ç i ÷ - 1 (A6) i ç ÷ è objective j ø

The value of CCMEWQI varies between 0 and 100, indicating the following:

· Poor water quality: CCMEWQ1 value between 0 and 44; water quality is almost always threatened. · Marginal water quality: CCMEWQ1 value be tween 45 and 64; water quality is frequently threatened. · Fair water quality: CCMEWQ1 value between 65 and 79; water quality is usually protected but occasionally threatened · Good water quality: CCMEWQ1 value between 80 and 94; water quality is protected with only a minor degree of threat. · Excellent water quality: CCMEWQ1 value between 95 and 100; complete absence of any threat.

An Excel spreadsheet for the calculation of the CCMEWQ1 can be downloaded from the website http://www.ccme.ca.