PER 165
October 1988
A GEOHYDROLOGICAL APPRAISAL OF THE VAALPUTS RADIOACTIVE WASTE DISPOSAL FACILITY IN NAMAQUALAND, SOUTH AFRICA
by
Mannie Levin
ATOMIC ENERGY CORPORATION OF SOUTH AFRICA LIMITED PRETORIA THIS DOCUMENT MAY NOT BE COPIED IN ANY WAY WHATSOEVER PER-165
A GEOHYDROLOGICAL APPRAISAL OF THE VAALPUTS RADIOACTIVE
WASTE DISPOSAL FACILITY IN NAMAQUALAND. SOUTH AFRICA
by
MAMIE LEVIN
Thesis accepted for the PhD degree in the Faculty of Science, Department of Geohydrology at the University of the Orange Free State
1988
Promoter: Prof. J.F. Botha Co-promoter: Prof. J. Kirchner
DIVISION OF EARTH AND ENVIRONMENTAL TECHNOLOGY DEPARTMENT RESEARCH AND DEVELOPMENT ATOMIC ENERGY CORPORATION OF SOUTH AFRICA, LIMITED P 0 BOX 582, PRETOniA, 0001 OCTOBER 1988
ISBN 0 86960 862 2 CONTENTS Page
Samevatting (i) Abstract (iv) Acknowledgements (vii) List of Figures (viii) List of Tables (xix)
CHAPTER 1 INTRODUCTION 1
1.1 Purpose and Scope 2
CHAPTER 2 STUDY AREA 4
2.1 Site Location 4 2.2 Physiography 4 2.3 Population Distribution 7 2.4 Land Use 8 2.5 Vegetation 8 2.6 Climate 8
CHAPTER 3 GEOLOGY 9
3.1 Basement Geology 9 3.1.1 Namaqualand Hetamorphic Complex 9 3.1.1.1 Stratigraphy 9 3.1.1.2 Structural geology 10 3.1.2 Karoo Sequence 11 3.1.3 Kimberlite and related intrusives 11 3.2 Surficial Deposits 11 3.2.1 Dasdap Formation 13 3.2.2 Vaalputs Formation 14 3.2.3 Gordonia Formation 19
CHAPTER H SURFACE HYDROLOGY 21
4.1 Run-off 21 4.2 Evapotranspiration and Percolation 24 Page
CHAPTER 5 GEOHYDROLOGY OF THE UNSATURATED 3i ZONE
5.1 The Fundamental Law of Fluid Statics 32
5.2 Surface Tension and Capillary Rise 34 5.3 The Porous Continuum 36 5.4 Moisture Distribution in a Porous Medium 41 5.5 Total Soil Water Potential 43 5.6 Relationship Between Water Content 6 44 and the Matric Potential ¥ 5.7 Hydraulic Conductivity 46 5.8 Bulk Density 48 5.9 Soil Moisture 49 5.9.1 Water potential sensors 49 5.9.2 Neutron probe 51 5.10 Soil Moisture Studies at Vaalputs 53 5.10.1 Laboratory determination of moisture 53 content and retention curves 5.10.2 Field monitoring of moisture content 54 5.10.3 The hydraulic properties of the 63 various rock types 5.11 Natural Isotopes in the Soil Moisture 66 5.11.1 Environmental tritium 67 5.11.1.1 Method of sampling and 68 determination 5.11.1.2 Tritium results 70
5.11.2 Stable isotope 180 71 5.11 2.1 Method of sampling and 73 determination
5.11.2.2 180 results 73 5.12 Dispersivity 74 5.13 Distribution Coefficients 76 5.14 Soil Chemistry 79 íage
CHAPTER 6 GE0HYDR0L06Y OF THE SATURATED 84 ZONE
6.1 Mature of the Aquifers 86 6.2 Depth to the Piezometric Surface 18 6.3 Elevation of the Piezometric Surface 90 6.4 Transmissivity and Storage Characteristics 96 6.4.1 Test pumping 98 6.4.2 Packer tests 104 6.5 Conclusions 108
CHAPTER 7 HYDROGEOCHEMISTRY ;i3
7.1 Regional Hydrogeochemical Setting of the 113 Disposal Site 7.1.1 Water chemistry ">, » 7.1.1.1 pH and temperature IV 7.1.1.2 Salinity lit 7.1.1.3 Major elements 123 7.1.1.4 Trace elements 127 7.1.2 Natural isotopes in the ground waUer 131 7.2 Chemical Equilibrium of the Ground Water 137 7.3 Geochemical Processes 142 7.3.1 Precipitation reactions 146 7.3.2 Complex formation 154 7.3.3 Oxidation-reduction reactions 160 7.3.3.1 Redox reactions involving iron 161 7.3.3.2 Redox reactions involving 163 uranium 7.3.4 Ion exchange and adsorption 164 7.3.4.1 Ion exchange 164 7.3.4.2 Adsorption 168 7.3.5 Attenuation of radionuclide at the 1.6 Vaalputs disposal site. Page
CHAPTER 8 GROUND WATER MODELLING i?9
8.1 Site Specific Modelling 182 8.1.1 Description of the model 184 8.1.2 Discussion of results 192 8.1.2.1 The flow equation 192 8.1.2.2 The mass transport equation 192 8.1.3 Conclusions 192 8.2 Regional Modelling 193 8.2.1 Description of the model 194 8.2.2 Discussion of the results 196 8.2.2.1 The flow equation 196 8.2.2.2 The mass transport equation 197 8.2.3 Conclusions 205
CHAPTER 9 CONCLUSIONS 212
REFERENCES 218
APPENDIX A Water level data used in regional modelling. APPENDIX B Chloride concentrations used in regional modelling. APPENDIX C Chemical analyses of geological material at Vaalputs. - i -
SAMEVATTING
Die Vaalputs Nasionale Fasiliteit vir die Wegdoening van Radioaktiewe Afval is geleë op die Boesmanlandplato in die dorre westelike deel van die Republiek van Suid-Afrika. Die terrein is geplaas naby die aansluitingspunt van drie rivierkoirane en binne die van die Koarivier wat 'n fossieldreinering is.
Die geomorfologiese stabiliteit van die gebied word gereflekteer deur die sedimentêre akkumulasies van mid-tersiêre ouderdom (25 Ma) wat op die plato voorkom. Die todemgesteentes wat deel vorm van die Namakwalandse Metamorfe Kompleks bestaan hoofsaaklik uit granietgneis ingedring deur basiese noroto'iedintrusies. Die sedimentêre opeenvolging wat die wegdoenslote sal huisves, bestaan uit kleiagtige sedimente veryster en verkalk aan die bokant en bedek deur 'n dun lagie los rooi sand.
Al die parameters benodig vir numeriese grondwatermodellering is bekom en 'n metodologie ontwikkel om die voginhoud van die kleilaa wat die wegdosningsterrein onderlê, te moniteer. Die geohidrologiese geskiktheid van die huisvestingsmateriaal, blyk daaruit dat die versadigde hidrouliese geleiding gemiddeld 10~ m.s" bedrae.
Met behulp van natuurlike isotope is vasgestel dat reënwater nooit dieper as 3,5 m gedurende die af gel ope 50 jaar infiltreer het nie. Hierdie diepte is bevestig deur neutron,-^terleslngs na *n hoë reënval gedurende Desember 1985. Hierdie beperkte indringing kan teruggevoer word na die mineralogiese en chemiese samestelling van die sedimente. Die natriumryke karakter van die materiaal veroorsaak *n aansienlike afname in hidrouliese gel elding as gevolg van die dispersie deur die kollo'idale fraksie wanneer dit in kontak met reënwater kom. - ii -
Die diepte na die piesometriese vlak onder die terrein is gemiddeld 55 m. Grondwater is beperk tot beide vertikale en horisontale krake en verweerde nate. Pomp- en pakstuktoetse het aangedui dat strukture oor lang afstande verbind kan wees. Sulke strukture hou verband met die regionale tel.toniek van die gebied met strekkingsrigtings hoofsaaklik suid-oos na noord-wes en suid-wes na noord-oos. Roorgate weg van hierdie strukture, self op relatief kort afstande, is soms heeltemal droog. Hierdie afwesigheid van waterdraende strukture oor die hele gebied suggereer dat die strukture omtrent vertikaal is. Bo die watervlak toon alle boorgate 'n hoë transmissiwiteit vanweê tall? horisontale krake in hierdie sone soos gesien in die boorkern.
Die hoë transmissiwiteit van die waterdraende strukture onder die terrein en die plat piesometriese vlak word as voordelig beskou. In die geval van ernstige lekkasie van radionukliede wat die watervlak bereik, kan volgehoue uitpomp van grondwater, die piesometriese vlak laat daal om 'n kom-effek te skep. Difc sal verhoed dat kontaminasie privaatboorgate bereik.
Die relatief plat hidrouliese gradient in die rigting van die Koarivier dui op lae vloeispoed van die grondwater. Regionale hidrogeochemie bevestig dat regionale vloei vanaf die terrein na die Koadreinering, stadig en amper stagnant is. Hierdie observasie word ondersteun deur natuur±ike isotoopdata wat 'n konvensionele ouderdom van 10 000 jaar vir die grondwater onder die terrein, aandui.
Dit is verder aangedui dat die kwaliteit van die grondwater in verband gebring kan word met die wateroplosbare soute in die sedimente. Die grondwater is versadig ten opsigte van kalsiet en soms gips. Die water is verder in chemiese ewewig met kaoliniet en Na-montmorilloniet. - ill -
Die chemiese toestánde is gunstig vir die demping van enige radionuklied lekkasie. Cs word onomkeerbaar geadsorbeer deur 90 die illietkleifraksie. Sr word verwyder deur presipitasie as
SrS0A en SrC0_ in die grondvog en as SrCO, in die grondvater. 60 Co word volledig verwyder uit beide die grondvog en die 3+ grcidvater as CoCO,. Enige kobalt teenwoordig as Co word ook volledige neergeslaan as Co(OH),. Uraan toon lae Kd-waardes as gevolg van sy neiging om karbonaatkomplekse te vorm. 'n Mate van fiksering sal deur adsorpsie plaasvind en die moontlikheid bestaan dat dit lokaal kan presipiteer as karnotiet. Die beweeglikheid van uraan is egter nie 'n groot bekommernis nie aangesien dit slegs in spoor hoeveelhede in die afval teenwoordig sal wees.
Numeriese modellering voorspel dat in die onversadigde sone geen noemenswaardige beweging sal plaasvind onder heersende toestande nie. Deur 'n uiterste kontaminant soos chloried te gebruik is met regionale modellering aangetoon dat selfs onder katastrofiese toestande, die kontaminant nie buite die grense van die terrein sal versprei nie. Die finale gevolgtrekking is dus, dat in geval van 'n lekkasie die sisteem so stadig sal reageer dat voldoende tyd beskikbaar sal wees om die voorgestelde korrektiewe stappe te neem. Die terrein is dus geohidrologies geskik vir die wegdoening van laagaktiewe radioaktiewe afval. - iv -
ABSTRACT
The Vaalputs National Radioactive Waste Disposal Facility is located on the Bushmanland Plateau in the arid western part of the Republic of South Africa. The disposal site is situated close to the junction of three river bpsins and within that of the Koa River which is a fossil drainage.
The geomorphological stability of the area is reflected by the presence of sedimentary accumulations of mid-Tertiary age (25Ma) on the Plateau. The basement rocks, which form part of the Namaqualand Metamorphic Complex, consist mainly of granite-gneiss intruded by basic noritoid bodies. The sedimentary sequence, which will host the disposal trenches, consists of clayey sediments, ferruginized and calcretized at the top and covered with a thin veneer of loose red sand.
All the parameters necessary were obtained, and a methodology developed, to monitor the moisture content of the clay layers underlying the disposal site. The suitability of the host material, from a geohydrological point of view, is reflected by the low -8 —1 average saturated hydraulic conductivity of 10 m.s
Environmental isotope studies established that percolation only reached 3,5 m in depth during the past 50 years. This depth was confirmed by neutron meter measurements following a heavy rainfall event during December 1985. This restricted percolation may be traced back to the mineralogical and chemical composition of the sediments. The sodic character of the material causes a considerable decrease in hydraulic conductivity due to the dispersion of the colloidal fraction when in contact with rain water.
The depth to the plezometric surface below the site is, on average, 55 m. Ground water is confined to both vertical and horizontal fractures and weathered joints. Packer testing and pumping has - V - shown interconnection of structures over long distances. Such structures are related to the regional tectonics of the area with strike directions mainly from southeast to northwest and from southwest to northeast. Boreholes away from these structures, even at relatively short distances, are sometimes completely dry. Packer and test pumping have shown the permeability of the fractured rock and the relationship between the water-bearing structures. From this it could be concluded that the water-bearing structures must be nearly vertical. Above the water level all boreholes showed high permeability due to more horizontal fracturing in this zone.
The high transmissivity of water-bearing structures below the site and the flat piezometric surface are seen as advantageous. In the event of a serious leak and radionuclides reaching the ground water, sustained pumping may lower the piezometric surface creating a basin effect and preventing contamination from reaching private boreholes.
The relatively flat hydraulic gradient towards the Koa River indicates the slow movement of the ground water and regional hydrogeochemical studies have confirmed that regional flow away from the disposal site towards the Koa drainage is slow and nearly stagnant. This observation was also supported by environmental isotope data which suggests a conventional age of 10 000 years for the ground water underlying the site.
It was further shown that the quality of the underground water could be related to the water soluble salts in the sediments. The ground water is saturated with respect to calcite and, locally, gypsum. Furthermore, this water is in chemical equilibrium with kaolinite and Na-montmorillonite.
Thus, the geochemical environment is favourable for attenuating any 137 radionuclide leakage. Cs is irreversibly adsorbed by the 90 illite clay fraction. Sr is removed by precipitation as SrSO. and SrCO. irom the soil moisture and as SrCO. from the ground - vi - water. Co is completely removed from both the soil moisture and 3+ the ground water as CoCO,. Any cobalt, as Co , will be remo/ed completely by precipitating as Co(OH).. However, uranium showed low Kd-values as a result of its tendency to form carbonate complexes. Some fixing by adsorption will take place and the possibility exist that it may precipitate locally as carnotite. The mobility of uranium is, however, of no great concern as only trace quantities will be present in the waste.
Numerical modelling has predicted that in the unsaturated zone negligible movement of radionuclides will take place under present conditions. Using an extreme contaminant such as chloride, regional modelling has shown that, even under catastrophic conditions, the contamination will not spread beyond the boundaries of the site. The final conclusion is, therefore, that, in the event of a leakage, the geohydrological system will behave in such a slow way that ample time will be available to apply the suggested corrective steps. The site is, therefore, geohydrologically suitable for the disposal of low level radioactive waste. - vii -
ACKNOWLEDGEMENTS
The immense task of evaluating Vaalputs as a radioactive waste disposal site for the Republic of South Africa involved many scientists from a great variety of disciplines and their results have been used extensively throughout this thesis. It is not possible to list their names and those of their assistants, therefore, I would like to thank them for their entnusiasm and cooperation. However, I would like to mention the following people:
I would like to record my thanks and appreciation to the Atomic Energy Corporation of SA Ltd for the opportunity to undertake a project of this size and their permission to present it as a thesis. Dr P.D. Toens, Manager of the Department of Geotechnology, is thanked for his enthusiasm and support throughout the project. Dr B.B. Hambleton-Jones was a major driving force and without his many constructive suggestions this thesis would not have been complete. My promoter Prof. J.P. Botha for his confidence in me and willingness to help, as well as his contribution to this project and the thesis. Prof J. Kirchner for his critical evaluation and constructive advice.
All my colleagues for the team spirit and the willingness to co-operate and help with any aspect of the project. I would like to single out Miss L. Oliver for the excellent manner in which she handled the typing of the thesis. I am very grateful to Mrs S. Posnik and Mr L.C. Ainslie for editing the manuscript and making very helpful suggestions. The staff of the Institute for Ground Water Studies for their friendliness and help and I would especially like to thank Dr. G. van Tonder for devoting his valuable time in helping me model the regional geohydrology. Dr M.V. Fey, University of Natal, is thanked for assisting me in running the GEOCHEM program.
The inhabitants of Bushmanland and especially Awie and Elize Coetzee for their hospitability shown during visits. They make Bushmanland a nice place to work in.
Finally I would like to dedicate this thesis to my family for their patience, understanding and their unfailing support during this project. - viii - Page LIST OF FIGURES
Figure 2.1 Locality of Vaalputs.
Figure 2.2 Vaalputs and neighbouring farms.
Figure 2.3 Topography of Vaalputs and environs (McCarthy et_al., 1984).
Figure 3.1 General geology of the area around Vaalputs in folder
Figure 3.2 LANDSAT image of the palaeo-alluvial fans 13 which radiate eastwards from the Kamiesberge.
Figure 3.3 Locality and distribution of the Dasdap and 15 Vaalputs Form?Lions.
Figure 3.4 North-south geological cross-sections through 16 the disposal site (Jamieson, 1985).
Figure 3.5 East-west geological cross-sections through 17 the disposal site (Jamieson, 1985).
Figure 3.6 Trench wall geology. 19
Figure 4.1 Tertiary and quarternary sub-catchment 22 boundaries of the northwestern Cape (Pitman et al.. 1981).
Figure 4.2 Mean annual rainfall and potential evaporation 23 for the Orange and Buffels River Drainage Systems in Namaqualand (after Pitman et al.. 1981).
Figure 4.3 Topography of the disposal site and environs 30 at 1 m contour intervals (Hambleton-Jones, 1984a). - ix -
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Figure 5.1 Force diagram used in deriving the Fundamental 32 Equation of Fluid Statics.
Figure 5.2 The cohesive forces acting on a molecule inside 35 and on the surface of a liquid open to air. (Hillel, 1973)
Figure 5.3 Schematic representation of the pressure 36 difference across a curved fluid surface, Bear (1979).
Figure 5.4 Examples of voids in geological formations 37 (a) A well-sorted sediment (b) A poorly-sorted sediment (c) A well-sorted sediment with deposition of mineral matter (d) Rock rendered porous by fracturing, Bear (1979).
Figure 5.5 Schematic diagram of a cross-section showing the 38 normal three phases of a geological formation in the earth's upper crust.
Figure 5.6 Definition of the representative elementary 40 volume and the porosity e for a porous medium (Bear, 1979).
Figure 5.7 Schematic diagram illustrating the distribution 42 of water between the grains of a geological formation.
Figure 5.8 The distribution of pressure below and above 43 a free water surface.
Figure 5.9 Water retention curves from samples in 45 borehole AFW35S08 at 9,6 m and 14 to 14,8 m (Van der Watt, 1984, 1985). - X -
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Figure 5.10 Characteristic curves relating hydraulic 47 conductivity and moisture content to pressure head for a naturally occurring sand soil (Freeze and Cherry, 1979, p. 42).
Figure 5.11 Soil moisture and tritium profiles from four 55 auger boreholes.
Figure 5.12 Locality of boreholes in the vicinity of the 56 disposal site, used in Table 5.2 and 5.7 and in Fig. 5.11.
Figure 5.13 Water retention curves for the various rock 58 types underlying the disposal site. (Van der Watt, 1984, 1985, 1986).
Figure 5.14 Water retention curves for five samples from 59 the sandy gritty clay unit (after Van dev Watt, 1986).
Figure 5.15 Water retention curve for the average values 60 of the sandy gritty clay unit (Van der Watt, 1986).
Figure 5.16 Locality of the neutron meter access tubes on 62 the disposal site.
Figure 5.17 Determination of optimum count rate interval 64 for the 501DR neutron meter.
Figure 5.18 Soil moisture curve for neutron meter data 65 recorded on 85/12/13 at neutron tube site 4. - xi -
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Figure 5.19 During 1-4 December 1985 approximately 128 mm 67 of rain fell. The soil moisture measurements indicate the amounts and depths of infiltrating water at successive intervals.
Figure 5.20 The Van Genuchten approximation (-) and the 69 experimentally determined (+) soil moisture retention curve fcr the red clay at Vaalputs (Botha, 1986).
Figure 5.21 Correlation between moisture content by 72 weight, the volumetric moisture content and the geology as seen in auger borehole AW40S08.
18 Figure 5.22 0 profiles in samples from auger boreholes 75 AW40S08, AW30S03, AW25S13, AW35S03 (Verhagen, 1985).
Figure 5.23 Decrease of hydraulic conductivity as a result 83 of the salinity of the sandy gritty clay (Van der Watt, 1986).
Figure 6.1 Locality plan of area kriged with outline of 85 kriging contour area (Camisani-Calzolari, 1985).
Figure 6.2 Kriged results for the depth to the water 91 level. Regional geohydrological survey (Camisani- Calzolari, 1985).
Figure 6.3 Depth to the piezometric surface for Vaalputs 92 and surroundings.
Figure 6.4 Depth to the water level in the vicinity 93 of the disposal site in water-bearing monitoring boreholes. - xil -
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Figure 6.5 Kriged result3 for the elevation of piezo- 94 ne.iric surface. Regional geotaydrological survey (Camisanl-Calzolari, 1985).
Figure 6.6 Elevation of the piezometric surface for 95 Vaalputs and surroundings.
Figure 6.7 Elevation of the piezometric surface in the 96 vicinity of the disposal site as measured in the water-bearing monitoring boreholes.
Figure 6.8 Locality of the monitoring and other relevant 100 boreholes in the vicinity of the disposal site.
Figure 6.9 Generalized plan of the dry and water-bearing 100 zones in the vicinity of the disposal site.
Figure 6.10 Linear plots of water level drawdowns and 102 recoveries of observation boreholes during pumping tests on various boreholes. (Hodgson, 1984).
Figure 6.11 Drawdowns observed (+) and computed (-), from 103 a non-linear least squares fit of the Theis solution, in observation borehole GWB 9 (Botha, 1986).
Figure 6.12 Drawdowns observed (+) and computed (-), from 105 a non-linear least squares fit of the Theis solution, in observation borehole GWB 8 (Botha, 1986).
Figure 6.13 Correlation between transmissivity and fracture 110 density In a dry borehole. - xiii -
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Figure 6.14 Correlation between the transmissivity and 110 fracture density in a water-bearing borehole.
Figure 6.15 Average transaissivity in soae dry an< vater- 11' bearing boreholes to illustrate the l*oaogenous transaissivity above the water table (Hodgson, 1986).
Figure 7.1 Kriged results for the teaperature of the 115 ground water. Regional geohydrological survey (Camisani-Calzolari, 1985).
Figure 7.2 Kriged results for the conductivity of the 118 ground water. Regional geohydrological survey (Caaisani-Calzolari, 1985).
Figure 7.3 Interpretation of the diamond-shaped field. 119 (Johnson, 1975).
Figure 7.4 Piper plot of all the samples from the 121 Bushmanland Plateau taken during the geohydrological survey.
Figure 7.5 Density distribution for all samples taken 122 during the geohydrological survey, showing the geochemical character of the ground water.
Figure 7.6 Diagram to illustrate that the geochemical 125 character of the soil moisture approaches that of the ground water with increasing depth.
Figure 7.7 Kriged results for the chloride content of the 128 ground water. Regional geohydrological survey (Camisani-Calzolari, 1985). - xiv -
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Figure 7.8 Kriged results for the sulphate content of the 129 ground water. Regional geohydrological surrey (Camisani-Calzolari, 1985).
Figure 7.9 Kriged results for the bicarbonate content of 130 the ground waters. Regional geohydrological survey (after Camisani-Calzolari, 1985).
Figure 7.10 Anomalous values for the kriged variables Al, 132 Be, Ho, Cr, Co, As, Cu, B, Cd, Hi, U, Ti and Zn (Camisani-Calzolari, 1985).
Figure 7.11 Regional natural isotope sampling localities. 135
Figure 7.12 Activity diagram showing calcite saturation in 140 2+ 2- terms of log (Ca ) and log (CO* ).
Figure 7.13 Activity diagram showing gypsum saturation in 140 2+ 2- terms of log (Ca ) and log (SO ).
Figure 7.14 Activity diagram showing stability and satura- 141 tion of the various clay minerals at Vaalputs.
Figure 7.15 The solvability of Sr and Ca carbonate for an 150
open system (-log p-A, = 0,0316 kPa) as a 2+ function of pH and concentration (-log [He ] 2+ in molar). Sr (a) dots are plots for 2+ analysis from the soluble extract and Sr (b) crosses are plots after raising the levels of Sr to 5 mg.&~ (after Stumm and Horgan, 1970). - XV -
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Figure 7.16 Solubility of Sr and Ca carbonate for a closed 152 system in terms of pH and log concentration showing values for natural ground water from the disposal area at Vaalputs (after Stumm and Morgan, 1970).
Figure 7.17 Diagram showing fields of ferrous and ferric 162 hydroxides at 25*C and IOC kPa total pressure. Stability limits of water are also shown. Dashed line is the metastable boundary of Fe and Fe(OH). in water (after Garrels and Christ, 1965). Plots for pH and Eh for natural ground water from the disposal site c >e shown.
Figure 7.18 Depth-variation diagram showing sample interval, 168 calcium carbonate, cation exchange capacity and exchangeable cations for borehole WA0H0 at Vaalputs (Jakob, 1983).
Figure 7.19 Profiles showing the distribution of illite, 169 smectite and kaolinite in three boreholes at Vaalputs.
Figure 7.20 The activity of tracer quantities of cobalt 172 remaining in solution (i.e. not sorbed on the clay) plotted against the calcium concentration (molar) in the solution. The reference activity of cobalt at corresponding pH, but no calcium added, is also shown for comparison (Jakob, 1983). (A is the activity at start o and A is the activity at end of the experiment). - xvi -
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Figure 7.21 The distribution of cobalt in solution using 174 some bulk samples of boreholes W40N0 from Vaalputs. (A is the activity at start and A is the activity at the end of the experiment) (Jakob, 1983).
Figure 7.22 Uranium sorption on calcrete (0,5-1,0 and 174 2,5-3,2 m) (borehole V40H0) after 24 h equilibrium (Jakob, 1983).
Figure 7.23 Uranium sorption on clay (15,0-16,5 m), (bore- 175 hole V40H0) after 24 h equilibrium (Jakob, 1983).
Figure 8.1 Solution for a coupled system A -* B 182 (Princetovn University Water Resources Program, 1984).
Figure 8.2 Location of the waste disposal site showing 186 the section AA considered for modelling in the unsaturated zone (Botha, 1986).
Figure 8.3 Vertical cross-section AA showing the geolo- 188 gical formations as used in the unsaturated model (Botha, 1986).
Figure 8.4 The finite element mesh used in the simulation 189 of radioactive nass transport at Vaalputs (Botha, 1986).
Figure 8.5 The Dirichlet boundary values used along the 190 left (0-0) and right hand (A-A) sides of the finite element mesh in Fig. 8.4 for solving the flow equation (Botha, 1986). - xvii -
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Figure 8.6 The steady state water levels of the cross- 191 section AA in Fig. 8.3 simulated by FEMHATER (Botha, 1986).
Figure 8.7 The finite element mesh used in simulation 195 of the contaminant (Cl~) mass transport on a regional scale at Vaalputs.
Figure 8.8 Kriged values of the observed water levels 198 (mamsl) for the regional model.
Figure 8.9 Steady state solution for the simulation of 199 the kriged water levels (mamsl) in Fig. 8.8 using AQUAHOD.
Figure 8.10 Vector diagram showing the flow pattern for 200 the steady state conditions.
Figure 8.11 Simulation of the water levels after raising 201 the head by 20 m at nodes 218, 219, 239 and 240 under steady state conditions (Water levels in mamsl).
Figure 8.12 Vector diagram showing the flow pattern after 202 raising the head 20 m at nodes 218, 219, 239 and 240.
Figure 8.13 Vector diagram showing the flow pattern one 203 year after the head was raised 20 m at nodes 218, 219, 239 and 240.
Figure 8.14 Decline of the water level at node 218 204 with time. - xviii -
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Figure 8.15 Simulated kriged chloride concentration dis- 206 tribution for the regional model using AQUAuOD 2.
Figure 8.16 Simulated kriged chloride concentration distri- 207 bution after 10 years.
Figure 8.17 Simulated kriged chloride concentration distri- 208 bution after 100 years.
Figure 8.18 Sinulated kriged chloride concentration distri- 209 bution after raising the concentration at nodes 218, 219, 239 and 240 with 200 ppm Cl~ (subse quent to raising the head 20 m at these nodes).
Figure 8.19 The change in relative concentration with 210 distance using a dispersivity of 5 m and a linear velocity of 0,03 m.day- .
Figure 8.20 The change in relative concentration with 210 distance using a dispersivity of 100 m and a linear velocity of 0,03 «.day" . - xix -
P*ge
LIST OF TABLE:
Table 3.1 Stratigraphy of the Tertiary formations on the 12 Bushmanland Plateau.
Table 3.2 Generalized stratigraphy of the surficial 18 deposits in the experimental trenches.
Table 3.3 Results of particle size analyses of the different 20 sediments. (Percentage by weight collected on each sieve).
Table 4.1 Quarternary sub-catchment data (Pitman et al.. 1981). 24
Table 4.2 1976 Rainfall data for Pella (Redding and Hutson, 25 1983).
Table 4.3 Summary of soil water balance (per day) for the 27 second of a two-year simulation predicted by the Water Balance Model (Redding and Hutson, 1983).
Table 4.4 Cumulative evaporation, transpiration and perco- 29 lation (mm) predicted by the Water Flow Model for several values of potential evaporation (E ) and P potential transpiration (T ) (Redding and Hutson, 1983).
Table 5.1 Porosities for the different rock types from 40 Vaalputs (Van der Walt, 1984, 1985).
Table 5.2 Origin and bulk densities of various rock types 57 sampled for water retention curve determinations. (Van der Watt, 1984, 1985). - XX -
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Table 5.3 Averaged values of water retention for various rock 57 types, determined on individual core sections. 3 -3 (water content 6=m water.m soil) (Van der Watt, 1984,198J).
Table 5.4 Averaged values of water retention for the sandy 61 gritty clay, d»tc:nnined on individual core 3 -3 sections (water content 0 = m water.m soil) (Van der Watt, 1986).
Table 5.5 Comparison of water potentials using the filter- 61 paper method and moisture retention curves. Auger Hole AW20508.
Table 5.6 A typical data print-out of processed neutron meter 63 data for a field site. 3 -3 V = Volumetric moisture content (m moisture.m soil) W s Moisture content by weight (kg moisture.kg~ soil)
Table 5.7 Averaged values of the saturated hydraulic conduc- 68 tivity for the various rock types as determined by Van der Watt (1984, 1985,1986).
Table 5.8 Results for dispersivities measured in the labora- 77 tory, Stephenson (1985).
Table 5.9 Results for dispersivities measured in the field at 77 Vaalputs, Stephenson (1985). Mean values are quoted with the range in brackets.
Table 5.10 Average distribution coefficients (Kd) for the 81 various rock types (Meyer and Loots, 1984). - xxi -
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Table 5.11 Macro component water soluble salt analyses on soil 81 samples from auger borehole AW25S13 (Meyer, 1984).
Table 5.12 Results of chemical analyses on sediment samples 82 from the experimental trenches.
Table 6.1 Depth of water interception and pump tested yields. 99
Table 6.2 Results of pumping tests on boreholes at Vaalputs 107 (Hodgson, 1986).
Table 6.3 Dip of prominent joints and fractures observed by 109 the video recordings in borehole MON 4 (Hodgson, 1986).
Table 7.1 Chemical analyses of ground water from the 119 disposal site (mg.fi.- ).
Table 7.2 Regional isotope data. Analyses conducted by: 124 CSIR(+), Schonland Research Centre for Nuclear Science(*).
Table 7.3 Tritium data in ground water from Vaalputs and 134 surroundings (Verhagen, 1985).
Table 7.4 Isotope data obtained from samples taken during 137 test pumping (Verhagen, 1985).
Table 7.5 Chemical analyses of samples taken during test 138
pumping (mg.fi.- ).
Table 7.6 Isotopes of concern that will be present in the 143 radioactive waste received at Vaalputs. - xxii -
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Table 7.7 Chemical analysis of water-soluble extracts of the 145 various geological units from the disposal site, showing solids precipitating, as calculated by GEOCHEM. (All chemical species in mg.kg soil).
Table 7.8 Chemical analyses of natural ground water from 146 the disposal site at Vaalputs, shoving solids precipitating, as calculated by GEOCHEM. (All chemical species in mg.fi,- , except U in ug.fi.- ).
Table 7.9 Trace element and CaO content of calcretes from the 148 waste disposal trenches at Vaalputs. (Ca in X CaO, other elements in mg.kg- ).
Table 7.10 Trace element and CaO content of acid soluble 148 fraction of calcretes (same material as used in Table 7.9, Ca in % CaO, other elements in mg.kg- ).
Table 7.11 Trace element and CaO content of the insoluble 149 fraction (after acid leaching). (Same samples as used in Table 7.10, Ca in X Table 7.12 Solubility products of some solids in water at 25°C. 149 (1) Matthess and Harvey (1982) and (2) Hem (1970). Table 7.13 Typical print-out showing the distribution of metal 153 and ligand species, as calculated by GEOCHEM. Table 7.14 Solids precipitating from soluble extracts of the 155 various geological units from the disposal site, as calculated by GEOCHEM, after raising the levels of Sr to 5 mg.fl." , Cs to 1 mg.fi.- and Co to 1 mg.fi. to simulate radionuclide leakage. (All chemical species in mg.kg' soil). - xxiii - Page Table 7.15 Solids precipitating from the natural ground water 156 from the disposal site, as calculated by GEOCHEN, after raising the levels of Sr to 5 ng.l~ , Cs to 1 mg.fi." and Co to 1 mg.fi" to simulate radionuclide leakage. (All chemical species mg.fi.- except U in jig.fi" ). Table 7.16 Percentage solids precipitating from the water 157 soluble extract, as calculated by GEOCHEN, after raising levels of Sr to 5 mg.fi." , Cs to 1 mg.fi" and Co to 1 mg.fi" . lable 7.17 Percentage solids precipitating from natural ground 157 water, as calculated by GEOCHEN, after raising the levels of Sr to 5 m.fi." , Cs to 1 mg.fi" and Co to 1 mg.fi" . Table 7.18 Typical output of metal complexes present in solu- 159 tion, at Vaalputs as calculated by GEOCHEN (concen tration of complexes expressed as - log [], where [] refers to a molar concentration). Table 7.19 Cation exchange capacities of various minerals 165 and colloids. Data from Carroll (1959) and Rosier and Lange (1972). Table 7.20 Geochemical enrichment factors (GEF) of uranium 171 for natural sorbents at pH's between 5 and 8,5 (Samama, 1984). Table 7.21 Experimental bulk partitioning coefficients (K^) 175 for cobalt and uranium in some samples of percussion borehole W40N0 from the waste disposal site at Vaalputs (Jakob, 1983). - xxiv - Page Table 8.1 The initial conditions used in the trench area 187 with the mass transport equation for the simula tion in the unsaturated zone (Botha, 1986). 137 Table 8.2 Concentrations of Cs at selected nodes as 193 predicted by the model for the unsaturated zone (Botha, 1986). Table 8.3 Changes in simulated chloride concentration at 197 nodes in a north-easterly direction from the disposal site. Table 8.4 Changes in simulated chloride concentration in 204 an easterly direction from the disposal site. - 1 - CHAPTER 1 INTRODUCTION ' Any nuclear power station during normal operation produces a certain amount of intermediate- and low-level radioactive wastes (ILLW) that cannot be disposed of by ordinary waste disposal methods. The intermediate-level radioactive waste consists mainly of resins, ventilation filters and evaporates while the low-level radioactive wastes comprises day-to-day contaminated garbage such as tissues, gloves, glassware, plastic containers, and clothing. The main radioactive isotopes to be found in these wastes include Co, 90 137 Sr and Cs with half-lives ranging from six to thirty years. These isotopes decay to a level similar to natural background radiation within about three hundred years. South Africa's first nuclear power station at Koeberg can produce as much as 2 000 drums of ILLW annually. Therefore, a specialist study group was formed in the late 1970's to report on radioactive waste management alternatives for commercial nuclear power in South Africa. On their recommendation a site-selection program was formulated which was divided into three phases, namely, a screening phase, a site suitability phase and a site and safety evaluation phase. Three areas in South Africa were identified by the screening phase as being suitable for the siting of a radioactive waste disposal/storage facility: (i) the central portion of the Richtersveld; (ii) the Kalahari, roughly north of Upington; (iii) an area in Namaqualand/Bushmanland. Regional geological and geohydrological surveys were undertaken in the above areas (Levin, 1980; Levin, 1982; Corner et al.. 1981; Hambleton-Jones and Levin, 1981). Based on these reports all three areas had potential sites but the distance from international - 2 - boundaries and Koeberg, played a decisive role during the final selection of the Vaalputs site in the Namaqualand/Bushmanland area. The bulk of the investigations recorded in this thesis were performed during the site suitability and evaluation phases, which initially involved regional and subsequently, detailed geological, geohydrological and related studies. From the beginning of 1986 field investigations decreased with the commencement of the safety assessment and conceptual modelling of the site according to acceptable international norms, culminating in a licence being obtained for the acceptance and disposal of ILLW. The method of disposal of ILLW at Vaalputs is by shallow land burial. The ILLW is placed in shallow trenches about 8 m deep, 20 m wide and 100 m long, then backfilled and covered with the material that has been excavated. This method of disposal is internationally accepted as safe and reliable and is practised in various countries. 1.1 Purpose and Scope The purpose of this study was to evaluate, from a geohydrological point of view, the safety and suitability of the Vaalputs National Radioactive Waste Disposal Site as a site for the disposal of ILLW in shallow trenches. The objective of the study was to: i) define the ground water system regionally as well as beneath the trenches; ii) monitor baseline conditions of soil moisture in the unsaturated zone and ground water in the saturated zone; iii) determine the geological and geohydrological parameters of the rock units which will host the waste, as well as to characterize the underlying granite; iv) predict the flow paths and time of travel of ground water from the disposal site to the nearest point of discharge, such as a - 3 - borehole; using the above parameters, in a numerical model: v) determine the extent of radionuclide migration from the disposal site. To achieve this, the scope of the study included: i) regional sampling of boreholes for chemical analyses and the monitoring of ground water levels; ii) drilling of boreholes and collecting cores to determine the geochemical and mineralogical characteristics, thickness, and hydrological properties of the overburden and underlying hard rock formations in and adjacent to the disposal site; iii) performing test pumping and packer-tests in boreholes drilled to study the geohydrological properties of the rock underlying the disposal site; iv) using numerical models to simulate ground water movement in the vicinity of the disposal site. - 4 - CHAPTER 2 STUDY AREA 2.1 Site Location The Vaalputs lational Radioactive Haste Disposal Facility is located in the northwestern Cape, 90 km southeast of Springbok (Fig. 2.1) between 30*05' and 30*10* south and 18*25* and 18*37' east, shown on the 1:50 000 topographic naps 3018BA Rorabees and 3018AB Rooifontein (Fig. 2.2) It falls within the District of •aaaqualand on adjoining portions of the farm Vaalputa (portion 1, Geelpan and portion 2, Garing) and Bokseputs (portion 1, Stofkloof) and is approximately 10 000 ha in extent. The Vaalputs repository (here after referred to as the disposal site) occupies approximately 100 ha on the portion Geelpan (Fig. 2.2). The disposal site has an area of 700 m x 900 m fenced in with a buffer zone of 200 m between the disposal area and the fence. 2.2 Physiography Physiographically, the study area is divided into two broad regions by the north-south escarpment which passes through the centre of the region (Fig. 2.3). To the west of this divide, the topography is rugged with the result that the drainage is largely controlled by geological structures. This area is known as Namaqualand. Bast of the divide lies the featureless Bushmanland Plateau at an elevation of about 1 000 m above mean sea level. The Vaalputs site straddles the escarpment with the larger part of the site on the Bushmanland Plateau. The watersheds separating three drainage ba3ins meet in the study area (McCarthy et al., 1984). The divides between the Koa River Basin in the northeast and the Buff els River Basin in the west, and between the latter and the Ollfants River Basin to the south and southwest are well-defined. The divide between the Koa and Oll£*nbB drainage basins, however, is ill defined and headward erosion by AIEXANOER BAY -30»S DURBAN 30»S-| INDIAN OCEAN ATLANTIC OCEAN CAPE PORT ELIZABETH TOWN 0 K)0 200 300 400 500 km 18*6 _i Figure 2.1 Locality of Vaalputa. 18 15 18° 30 18*45 30 18AB ROOIFONTEIN 3018BA NORABEES 00 30*00 OIK-NATJE PLELIEFONTEIN COMMUNAL RESERVE COURAGIC FONTEIN JO* 15 18" 15 18° 30 FARM BOUNDARIES lfi.5 / ROAOS 0 2 10 km SCALE Figure 2.2 Vaalputa and neighbouring faraa. - 7 - «••co- SPftfN6aOK -f-K'SC" »•» ktsmo BO'M' S ESCAUPME NT ^•05' ^*~ DRAINAGE LINES DISPOSAL SITE ^^«ATEHSMEO T 20 <£5l l-" <-E NAMAQUA ^GHii:, My SCALE Figure 2.3 Topography of Vaalputs and environs (McCarthy et al.f 1984). the Krom River (part of the Olifants drainage) is at present encroaching into the Koa drainage. Vaalputs is situated within the Koa River Basin which constitutes a fossil drainage system and therefore no active drainage occurs on the plateau in the vicinity of the disposal site. The area is characterized by low-amplitude fossil dunes which strike in a northeasterly direction. Small pans occur in the interdune areas, and, in some cases, in depressions on the dunes themselves. 2.3 Population Distribution The nearest population centres to Vaalputs are Kamieskroon, Garies, Springbok, O'Kiep and Nababeep which lie 60 km to 100 km from the site. Within a 60 km radius of Vaalputs minor settlements occur at Rooifontein, Leliefontein, Paulshoek and Kliprand. Only 102 people live within a 20 km radius of Vaalputs, 35 % of this community being migratory. - 8 - Farms on the Bushaanland Plateau receive both summer and winter rainfall and are grazed in summer months while winter is spent on farms in the escarpment area where winter rainfall is predominant. The population density surrounding Vaalputs is not expected to vary significantly over the next 50 years. 2.4 Land Use The main agricultural activity around Vaalputs is sheep farming. The carrying capacity during the drought, which lasted seven years, decreased from 1 sheep per 4 ha to 1 sheep per 9,5 ha. Sheep are raised for mutton as well as karakul pelts. 2.5 Vegetation The area is sparsely vegetated with shrubs, succilents, woody perennials and grasses typical of semi-desert areas. The area receives both winter and summer rainfall and the amount of plant species is therefore more than one would expect. Lloyd (1985) has identified some 160 vascula plants at Vaalputs including 12 grasses, 20 geophytes and nearly 40 succulents. Strong preferences are shown by the communities for soils with particular characteristics of salinity, calcareousness, acidity and sand depth. 2.6 Climate The climate is characterized by anticyclonic conditions throughout the year. The dominant wind direction is from the south to south west. Rainfall shows a bi-modal distribution with thunderstorms occurring during September to April whilst rainfall from May to August is associated with frontal weather systems. The Vaalputs site falls within the winter/summer rainfall transition zone. However, the disposal facility is located on the Bushmanland Plateau where summer rainfall appears to be predominant. The mean rainfall for the area is 74 mm per annum but during December 1985, 80 mm fell within 24 hours accumulating to 128 mm in 4 days. This is regarded as a 1 in 200 year event. Potential evaporation is high with a mean of 2 100 mm per annum (Redding and Hutson, 1983). Temperatures are extreme, often exceeding 40°C during a summer day and fall below 0°C during winter nights. - 9 - CHAPTER 3 6E0L06Y Rogers (1911) was the first to report on the general geology of the Bushmanland Plateau followed by Reuning (1930). Joubert (1971) mapped the area west of the Gamoep-Kliprand road while Albat (1984) mapped an area east of this road. Andersen et al.. (1983) reported on the geology of the Vaalputs site and environs. 3.1 Basement Geology The basement rocks of the Vaalputs area include the Namaqualand Hetamorphic Complex of Nokolian (Proterozoic) age, the Karoo Sequence of Late-Palaeozoic to Jurassic age, kimberlitic and related intrusions of Tertiary age (Fig. 3.1, Geological map in folder at the back). 3.1.1 Hamaqualand Metamorphic Complex 3.1.1.1 Stratigraphy The tectonic event that was responsible for the formation of the Namaqualand Metamorphic Complex has been dated at 1 050 Ma ago. During this event sedimentary and volcanic rocks were altered to metasediments and metavolcanics. These rocks are now grouped into pre-tectonic supracrustal rocks. The several intrusive rock types emplaced during the tectonic event have been grouped into syntectonic intrusive rocks. Pre-tectonic supracrustal rocks of the O'Kiep Group occur in the area as fine-grained biotite gneiss and contain irregular remnants of mafic material, pelites, amphibolites, pyroclastics and quartzites belonging to the Garies Subgroup (Fig. 3.1). Syntectonic intrusive rocks belonging to the Spektakel and Koperberg Suites respectively are the more important rocks of this type occurring in the study area. - 10 - The Spektakel Suite consists of an assemblage of distinctly ieucocratic, late tectonic granites of which only the Concordia type is present on Vaalputs where it is called the btofkloof Granite (Hambleton-Jones and Levin, 1981). The Stofkloof Granite is described by Andreoli et al.. (1986) and Hart and Andreoli (1985) as a composite suite of metamorphic crystalline rocks of granitic bulk composition ranging from granite sensu strictu to augengneiss and charnockite. The granite was emplaced as a sill-like mass and a lit-par-llt style of intrusion can be seen where it has intruded the underlying biotite gneisses. Several bodies of (charnockitic) noritoid and anorthosite belonging to the Koperberg Suite have been intersected during drilling in the area. It is important to note that these rocks were emplaced along "steep" structures. 3.1.1.2 Structural geology Several phases of folding (ductile deformation) and shearing and faulting (brittle deformation) can be recognised in the rocks of the Namaqualand Metamorphic Complex. Andersen et al.. (1983) compiled a structural map of the area u<*ing satellite images and aeromagnetic data to interpret the structure of the sand covered areas. Their map was updated by Andreoli et al., (1986) and is shown in Fig. 3.1 (inset 8). The area is entirely underlain by a flat-lying sheet of Norabees Granite which intruded during the late stage of the third phase of folding (F3) and early in the fourth phase of folding (F4). It has the appearance of being a large synform plunging at between 5 and 15 to the east. The dip is steepest on its northwestern flank where it dips at between 25 and 45° to the south-east. Elsewhere the dips range from 5 to 10°. Minor fluctuations in the dip of the granite fabric probably have been caused by F3 and F4 deformation (Andersen et al.f 1983). The majority of faults visible on aerial photographs and LANDSAT imagery have a north to northwest trend. The aeromagnetic survey revealed that, in addition to this dominant direction, secondary northwesterly, northeasterly and - 11 - easterly trends are present. The Garing linear (Fig. 3.1) is one of the najor structures recognised. Drilling of this structure revealed that, although it is water bearing in certain areas, it is probably annealed in other parts with no water present. 3.1.2 Karoo Sequence The Dwyka Tillite Formation is the only formation of the Karoo Sequence present in the region. Rocks of this formation outcrop over large areas east of Vaalputs. On the farm Santab Dwyka Tillite is preserved in a graben-like structure well below the surrounding granite outcrops (Fig 3.1, inset 8). Intrusion of dolerite sills or dykes in the vicinity caused induration of the tillite and, being more resistant to weathering, this tillite formed low ridges. On the Vaalputs site only one borehole in the extreme south-east corner of the farm intersected 8 metres of horizontally-bedded Dwyka Tillite. 3.1.3 Kimberlite and related intrusives Kimberlitic pipes, diatremes and melilite basalt sills of Tertiary age intruded into the basement rocks of the Namaqualand Metamorphic Complex. One such volcanic vent, known as a melnoite pipe, occurs on the Vaalputs site near the southern boundary with Bokseputs (Andersen and Muller, 1984). This pipe is filled with volcanoclastic sediments to a depth of more than 220 metres. The fault-related emplacement age of these volcanics range between late-Cretaceous (ca 65-70 Ma ago) to Oligocene (ca 35 Ma) (McCarthy et a!.. 1984). 3.2 Surficlal Deposits Using seismic refraction, Andersen and Roets (1983) outlined a large area on Vaalputs with a seismic velocity below 1 500 m.s~ (indication of rippability) down to a depth of ten metres. The seismic results were confirmed by an extensive percussion drilling program as veil as some pitting (Levin and Raubenheimer, 1983). Subsequently air-flush and auger drilling were used \.o obtain in situ uncontaminated samples (Jamieson, 1985). The lithostrati- - 12 - graphy of the Tertiary formations on the Bushmanland Plateau is shown in Table 3.1. Table 3.1: Stratigraphy of the Tertiary formations on the Bushmanland Plateau Formation Lithology Age (Ma) Origin Gordon!a Red sand 20-5 Aeolian dunes Calcrete and silcrete nodules. Ferruginised laminated sandy gritty clay. Fluvial Vaalputs Brown sandy gritty clay. 35 - 20 sheetvash Grey sandy gritty clay with intercalated pebble bands. Siliceous sandstone. Immature cross-bedded Dasdap arkosic grits. 38 - 20 Alluvial fan Conglomerate. Unconformity - Koalinised/silicified 65 surface Namaqualand Basement Metamorphic granitoids 1050 Complex 1 The geomorphology of the area and development of the surficial cover are described by McCarthy et al.. (1984) and Levin et al.f (1986). McCarthy et al.f (1984) pointed out that the surficial accumulations have been present on the Bushmanland Plateau since Miocene times (ca. 10 Ma), which reflects the remarkable geomorphological stability of the region in which Vaalputs is situated. - 13 - 3.2.1 Dasdap Formation The existence of a large alluvial fan on the southern part of the Bushmanland Plateau (Fig. 3.2) was first reported by Levin and Raubenheimer (1983). Drilling on the farm Platbakkies confirmed the development of thick surficial cover of Tertiary age on the basement. According to McCarthy et al.P (1984), the accumulation of fan material resulted from tectonic activity and uplift along the southwestern edge (Kamiesberge) of the Bushmanland Plateau. Figure 3.2 LAHDSAT image of the palaeo-alluvial fans which radiate eastwards from the Kamiesberge. The name Dasdap Formation was used by McCarthy et al.f (1984) for outcrops of conglomerate and sandstone exposed along the Dasdap drainage on the farms Banke and Burtonsputs. These sediments lie on a kaolinized and silicified surface of cretaceous age and consist of conglomerate, sandstone and cross-bedded arkosic grits. The major part of the conglomerate consists of small pebbles (5-20 mm) of blue quartz derived locally from quartz veins of that colour. Ferruginization of the upper portion of the formation and the subsequent break-up and formation of ferruginized nodules is observed, especially in the Kalkdraai area. Drilling on Platbakkies and Bokseputs revealed yellowish to white sandstone lying on the kaolinized surface. These sediments are correlated with the Dasdap Formation. Small exposures of silicified sandstone occur throughout the area in pans and deflation areas between the dunes. The extent of the formation is shown in Fig. 3.3. The gritty sandstone lying on a kaolinized basement floor has also been identified by drilling on Vaalputs. In the disposal area up to 10 metres of alluvium, consisting of weathered sandstone and granite gneiss boulders with the occasional well rounded quartz pebble set in a kaolinitic matrix, is found filling the deeper part of a palaeo-channel and is overlain by red sandy gritty clay. 3.2.2 Vaalputs Formation Further uplift along the southwestern edge of the Bushmanland Plateau caused incision into the kaolinized and silicified surface (McCarthy et al.. 1984). This incision, probably accompanied by a change in climatic condition from pluvial to more arid, has lead to the subsequent redeposition of reworked Dasdap sediments into the Vaalputs Fan (Fig. 3.3). Sediments of the Vaalputs Formation have accumulated in a channel-like depression called the Vaalputs Basin. The Vaalputs Formation overlies Dasdap sediments in the deeper part of the Vaalputs Basin but where these sediments are absent it lies directly on the kaolinized bedrock. The sedimentary units of the Vaalputs Formation, as determined from the borehole cores, are generally described as 0,5 - 1 metre of partially ferruginized aeolian sand; 1 to 5 metres of calcretized sandy gritty clay with some silcrete nodules; 15 to 20 metres of red to greyish fluvial gritty sandy clay and gravel with ferruginous nodules and blue quartz pebbles. A cross-section through the disposal site is shown in Figs. 3.4 and 3.5 (Jamieson, 1985). Mapping the walls of the experimental trenches, Levin (1985) recognized three periods of sandy gritty clay deposition, each followed by calcretization/silcretization (Fig. 3.6). Grey sandy gritty clay with large calcrete/silcrete nodules indicates humid - 15 - Figure 3.3 Locality and distribution of the Dasdap and Vaalpnts Formations. conditions while the overlying brown sandy gritty clay with small calcrete/silcrete nodules at the top points to a more arid environment. The laminated sandy gritty clay layer in the upper part is calcretized and ferruginized and covered with a sand veneer. Ferruginized nodules and blue quartz pebbles, very conspicious in the Dasdap Formation, occur concentrated in thin layers in the clay of the earliest period and scattered throughout the rest of the accumulations. The dominant process of sediment deposition was sheetwash. In total nine sedimentary units were identified by Levin (1985), as shown in Fig. 3.6 and Table 3.2. Apart from the 9 units, structures filled in with greenish or red sandy clay are present, increasing the inhomogeneity of the clay sequence. These structures vary in size and shape as shown in Fig. 3.6. Particle size analyses of the different sedimentary units are indicated in Table 3.3 showing that the clay content is lower for the Infill structures than for the main clay units. PSHI» WIS SOI» nnn W 35 WIS MS • *»S0S I MISS» «ISSISI »w)SN07 i nut WKNOO «usso) | tnnssoi i AWJSSH »FWHS"S -f- -t- rM7.ua-+-» I tan.-X « 4 1XI.0TS ttitm i tot} tit I rerj.r-t- » —*- ratiitm roniti tewior titans to'i'tr; iresmwi ttum» ten tn TSmVI a W32.5 PWS «FWB.5SU AFWHSSO] I AFWUSSOI «nS.ilS IKmC) ;01S ru UOmtl 12.17m W37.5 »n«r.ssi7.s »FtO75SI0 «rum sis i iwr* ....I,. riftlMl wtstt it*'//' Of urn Inn '•'.''/, • • • • v-H»i»-- • • • • • • tl.t. «IT PlU» tfCfWO Rod Swd tfwsissti Air flush Ctlcrttt borttiot» Iff C/4wfirtf mtusti Aug* borthot* wit no -5g3 hWft KioOnitic city Ptrcussion awê i tonhole lli:i Bêtic [ntrusirt et Html) Attuêl aft of 773 Wtêthtrtd Grtnitt projtctK/ bcrthott • • } Unwuthortd Gnmtt mto»x 1000* 0*fm Lm§ 1016,231 £l§Yêtian of borthotê Stilt 1*1 I /rums! I Figure 3.4 •orth-aouth geological eroM-aectlons through tha disposal alte (Jaarieaon, 1985). - 17 - «sssas WMS» «M#»5 ***mim warn »•*»* WMIM SO 5 "cwi »•».*» *vj*r «sis ww rvofiiivrrtm soe Wfc* »r*Mf **i*i^ wíJW temtn "«tin* srwmsv WVSV MSI** WSIW »J0fl* SJO tiff WJ*a» •CrlJi T9%JT mifêéê «fill» «rUH »r«» m,M vrrs»f w»*ï» »fffff fvtíiS't mrtStfJ Mtwtt.Wi ill wtm rtriTV tea £i»p tfr n** \*td Sort r^ om»» I Court» á*ii« • Nonunion toriMtt TMt M# V E53v] "*"f 'iotmiix cloy jJJ' unrnm l «f— t;;;:| í**« Mrvtiro ,H»II Actual nit of projectti i -*-^*V ji#I~ tormolt fomrto I zz^ \y//l mtHwrt ffrjmr» «MTMir ' ï'fl»f^0Í*/ I . •] umrotlhtrtt Ormito Bssm ^^~- i «• "X» 1 fQOfli» 0*11* imo 'O'SIV tlfilion ol tonltui 1 f momsl t Figure 3.5 laat-veat geological croaa-aectlona through the dlapoaal alte (Jaaleaon, 1985). Table 3.2: Generalized stratigraphy of the surficial deposits in the experimental trenches Unit Sedimentary Unit Thickness Age Origin (•) (Ma) 1 Windblown red sand 0,5 - 1,0 10-2 Aeolian dunes 2 Partly consolidated ferruginized sand 0,5 - 1,0 Aeolian dunes 3 Calcretlzed and silicified Pedogenesis under clay and sand 0,5 - 2,0 drying conditions A* Laminated ferruginized clay 1,0 - 3,0 5* Calcrete/silcrete nodules in brown clay matrix 0,0 - 2,0 6* Light brown clay 0,0 - 1,5 25 - 10 Fluviatile 7* Pebble layer 0,0 - 0,3 8* Large calcrete/silcrete (Vaalputs nodules in grey clay matrix 0,0 - 1,5 formation) 9* Grey clay 0,0 - 2,0 ., * Units 4 to 9 largely constitute the material which will host the radioactive waste. The clay content of 37 % compares well with that of Brynard (1983) who identified the clay minerals present. These consist on average of 46X montmorillonite, 32X illite and 21% kaolinlte. Brynard (1983) pointed out that, in general, the montmorillonite and kaolinite increase with depth while illite decreases. Calcite veins, though more concentrated in the upper layers, cut through the whole sequence. This indicates that movements resulting from collapse, compaction and shrinkage have already taken place and thus movement is less likely to occur in future. These calcite veins do penetrate deeper than 7 metres in places i.e. to the depth of the disposal trenches. - 19 - LEGENO SEDIMENTARY UNITS \~TZ-\ MINOSLONN RCO SANO FERRUGINIZCO SANO CALCRKTIZCO ANO SILICIFICO LAMINATCO CLAY &--T-J LAMINATCO FCRRU6IN1ZCO CLAY SMALL CALCRKTC SILCRCTC NODULES II IN 6REY CLAY MATRIX fN*«ula« S SOmml '.\ LIGHT SROHN CLAY PKBSLK LAYKR ISLUISH QUARTZ • KBSLKS*10m«nl LAR6C CALCRCTC SILCRETC NODULCS INCRCY CLAY MATRIX (NodulMlZOOmml 5m •1 6RCY CLAY Salt Vertical and Horizontal INFILL STRUCTURES RKO SANOY CLAY CRKCNISH SANOY CLAY STRUCTURES OR TUSULKS FILLED KITH RKO SANOY CLAY Figure 3.6 Trench vail geology. 3.2.3 Cordonls Formation Sand cover is ubiquitous over most of the Bushmanland Plateau where it overlies remnants of the Vaalputs and Oasdap Formations (Fig. 3.1). The topography gives the impression of hummocky longitudinal sand dunes (5 m high) orientated in a north-easterly direction. However, the sandcover is only between 0,5 and 2 metres - 20 - Table 3.3: Results of particle size analyses of the different sediaents. (Percentage by weight collected on each sieve). Sieve size «Greenish Light brown Grey clay *Red sandy Laminated Red (-a) sandy clay clay ferruginized sand clay clay 1,700 2,70 1,84 12,94 3,57 8,40 7,30 0,850 13,57 10,22 10,14 13,63 14,16 18,70 0,425 20,29 18,45 12,65 25,09 17,14 26,44 0,250 14,54 14,06 9,99 17,50 9,62 16,23 0,125 11,69 11,22 10,24 11,50 8,98 13,27 0,063 6,86 7,58 5,02 4,36 3,42 5,18 0,045 1,21 7,70 1,48 1,04 1,22 1,18 <0,045 29,13 35,91 37,54 23,30 37,06 11,69 * Infill structures thick and does not represent true dunes. McCarthy et al.f (1984) concluded that the coarse sand, low relief of the dunes, the presence of small pans and deflation surfaces on the dunes, all point to dunes in an advanced state of degradation. The sand cover has been tentatively correlated with the Gordonia Formation (SACS, 1980). - 21 - CHAPTER 4 SURFACE HYDROLOGY The disposal facility is located within the Koa River Basin which used to be part of the main course of the Orange River System until its headwaters were captured by the Olifants River from the south. Much of the Koa Valley is sand choked, with the main valley marked by a line of pans, the largest of which is Bosluis Pan. The cessation of the Koa River System is placed at mid-Miocene (20 Ma) by McCarthy et al., (1984). This is supported by the recent discovery of early mid-Miocene fossils at Bosluis Pan (Partridge, 1985). 4.1 Run-off In their appraisal of the total water resources of South Africa, Pitman et al., (1981) estimated the surface run-off for the Orange River Basin and Namaqualand. Of importance are their findings for the Tertiary sub-catchments of the Koa and Buffels Rivers in which the Vaalputs Site and environs are situated. The tertiary and quarternary sub-catchments, as defined by Pitman et al. (1981), are depicted in Fig. 4.1. Rainfall and evaporation contours, constructed by Pitman, are shown in Fig. 4.2 and indicate that the larger part of the Bushman land Plateau receives less than 150 mm per annum and the site itself under 100 mm rainfall per annum. This corresponds well with the average of 74 mm per annum calculated by Redding and Hutson (1983). Potential evaporation for the area seems to fall between 2 000 and 2 400 mm per annum. Annual potential evaporation could thus be as high as 30 times the average annual rainfall. A deterministic model was used by Pitman et al.. (1981) to predict Mean Annual Run-off (MAR) for the various sub-catchments. In order to draw a comparison between the sub-catchments of the region, MAR was converted to run-off per unit area per annum. - 22 - ^.riDifposalSitel..-,:/ r A. Fan ~'Ï:V 'ótó'^aj^»- Garits 18' INEFFECTIVE AREAS KEY Ineffective areas or enclosed „-- TERTIARY CATCHMENT • •* e drainage dasins Runoff from these i'ëáiV WARTERNARY SUB- areas does not reach the ocean <.™' CATCHMENT but may cause local streamflow or contribute to local pans marshes or vleis and possibly to the underground water Figure 4.1 Tertiary and quarternary sub-catch«ent boundaries of the northwestern Cape (Pltaan ££_ll>» 1981). - 23 - (m .km" .a" ). Compared to the 151 587 m .km" .a~ for the whole Orange River Basin, the total contribution from the Koa 3 -2 -1 River is estimated at only 550 m .km .a . The Buff els River, 15 km to the west of the site, has an estimated run-off of 3 -2 -1 6 123 m .km .a . Further subdivision of the tertiary sub-catchments into quarternary sub-catchments is indicated in Fig. 4.1, and their estimated virgin Mean Annual Run-offs (MAR) are shown in Table 4.1. In the Koa River MAR is restricted to the quarternary sub-catchments in the lower part of the valley where steeper slopes facilitate run-off. The upper part of the valley, in which the disposal site is located, is made up of ineffective drainage areas or enclosed basins. Run-off from these areas does not reach the major river system or the ocean, but may cause local streamflow or contribute to local pais, marshes or vleis and evaporate or percoxate to the ground water. The two quarternary Figure 4.2 Mean annual rainfall and potential evaporation for the Orange and Buffels River Drainage Systems in Ifaaaqualand (after Pitman ££_al., 1981). Table 4.1: Quarternary sub-catchment data (Pitman et al.f 1981) River Catchment Mean annual Virgin HAR number precipitation 106m3 (Fig. 4.1) D831 0* D832 0* 0841 0 Koa D842 0 D843 1 0844 2 D845 1 ooooooo o C846 ooooooo o 1 F311 240 13 F312 140 3 F313 90 1 Buffels F314 140 2 F315 185 5 F316 210 10 F317 180 2 ______*The disposal site is located on the boundary between these two catchments (Fig. 4.1) sub-catchments of the Buffels River, F312 and F313, adjoining the Vaalputs area (Fig. 4.1), contribute 8,3 X and 2,7 X respectively to the total MAR of the Buffels River (Table 4.1). This clearly illustrates the relatively low run-off from the disposal site and adjacent areas. 4.2 Evapotranspiration and Percolation Preliminary estimates of percolation, based on a few site observations and the limited rainfall records available in the Bushmanland area, were made by Hutson using two computer simulation models - a Water Balance Model and a Finite-difference or Water Flow Model (Redding and Hutson, 1983). Under the prevailing conditions of high evaporation rates and long dry periods, potential evapotranspiration far exceeds precipitation over a long period of time. However, percolation could occur during periods of high rainfall and these models assess the likelihood of deep percolation using a variety of combinations of transpiration and evaporation. - 25 - For a conservative assessment a high rainfall season from the general area was selected. The 1976 rainfall data for Pella (annual average, 77,1 mm), 160 km north-northeast of Vaalputs, were therefore used in the simulations (Table 4.2). These 1976 figures are much higher than the normal annual average for the Vaalputs area, which has an average of only 74 mm per annum (Redding and Hutson, 1983). Retentlvity of the soil was estimated using regression equations relating retentivity to the bulk density, silt and clay content of the soil at Vaalputs. Root distribution was estimated visually in an open trench, with the maximum depth of root penetration observed being about 400 mm. As a result of this a smooth distribution was used in the models. Table 4.2: 1976 rainfall data for Pella (Redding and Hutson, 1983) Date Rainfall (mm) 9/1 8,5 21/1 30,0 30/1 7,5 2/2 62,0 4/2 59,8 1/3 27,0 6/3 12,5 7/3 27,5 31/3 12,0 15/4 12,0 ,- The Water Balance Model operates on a daily basis with water added or removed in increments of 0,005 mm. All water is assumed to enter the profile, which is divided into 200 horizontal layers each representing 1 mm of water storage capacity, and is only removed from the soil by transpiration and evaporation, thus resembling tl?e - 26 - infiltration process in real soil. It is assumed that the initial water content of the profile is 0,2 mm per layer. Absorption by roots, which extend to a depth of 100 layers in this simulation, is in direct proportion to water content and decreases with increased depth. Therefore, the long dry periods between rainfall events result in the model not being very sensitive to transpiration rate. Evaporation from soils is rapid while the soil surface is vet but decreases after the surface layers have dried. At the end of the simulation the water allocated to layer 200 is assumed to represent percolation. However, the water retained between the root zone and layer 200 may (a) move upwards into the root zone or (b) move downwards, adding to percolation. Water in the root zone will eventually be lost to the atmosphere by evapotranspiration. Two successive years were simulated using the Water Balance Model, each having a rainfall pattern corresponding to the 1976 Fella data (Table 4.2). After year 1 an equilibrium was reached providing an estimate for the soil water content at the beginning of the next year. The results of modelling during the second yesr of the two-year simulation are shown in Table 4.3, using different combinations of potential evaporation and potential transpiration in the model. *.oss of water by transpiration greatly reduced percolation from 63 mm to 28 mm and from 112 mm to 35 mm. A lower evaporation rate also had a marked effect on percolation provided the transpiration stayed the same. An evaporation rate of 200 mm per day resulted in a percolation of 63 mm whereas a reduction of evaporation to 147 mm per day resulted in a percolation of 112 mm (Table 4.3). Storage change results when some of the water initially assumed present percolates or evaporates. Hutson (Redding and Hutaon, 1983) makes the point that, in reality, the probability of successive years of high rainfall is extremely low and a single year of high rainfall would lead to less percolation than shown in Table 4.3 as the soil profile would be drier at the start of the wet period. - 27 - Table 4.3: Summary of soil water balance (per day) for the second of a two-year «isolation predicted by the Water Balance Model (Bedding and Hutson, 1983). K = potential evaporation; T s potential transpiration; n = » constant E T n Rain Evaporation Transpiration Percolation Storage change mm.d nm.d~ mm nun 8 0 2,5 259 200 0 63 -4 8 4 2,5 259 98 134 28 -2 8 0 4 259 147 0 112 0 8 4 4 259 67 157 35 0 The Water Flow Model is a one-dimensional finite-difference model predicting flux density, water content and water potential distributions within a soil profile. All rainfall is assumed to infiltrate the soil at the maximum rate and evaporation is allowed from 06h00, increasing sinusoidally from zero to a specified potential rate at 12h00 and decreasing again to zero at 18h00. This specified potential rate was estimated from field measurements of the potential evaporation. A free draining profile is assumed to be air-dry at the start of the simulations, and transpiration is withdrawn from each soil segment in proportion to a specified root distribution, limited by decreasing water potentials. The results of this model depend largely on assumptions of root distribution, water retentivity and hydraulic conductivity. The time intervals by which the solution progresses are variable. Three simulations were done using this model (Table 4.4) and the following features of the data became evident: (i) Total evaporation is insensitive to potential evaporation (E ). which means that most evaporation is limited by soil P hydraulic conductivity. (ii) A percolation of only 17 mm was predicted in the absence of transpiration. - 28 - (ill) A transpiration rate (T ) as low as 4 mm.d~ was P sufficient to reduce percolation to 1,4 mm. (iv) All rain is assumed to enter the profile which was Initially air-dry. The balance of water left after provision is made for evaporation, transpiration and percolation is added to the profile. The profile water content increased respectively by 86, 85 and 32 mm above air-dry for the simulations in Table 4.4. This means that high rainfall years in succession could result in percolation to levels closer to those predicted by the water balance model as the initial profile contains moisture. Hutson (Redding and Hutson, 1983) notes that in the Water Flow Model a decrease in retentivity and/or an increase in hydraulic conductivity will increase percolation since water will move more rapidly to greater depths. In these simulations all rain was assumed to enter the soil. In practice surface sealing during rain storms could lead to runoff and the accumulation of water in surface depressions. Percolation at these points could be much higher than the average. The actual site, however, is situated on a dune crest (Fig. 4.3) devoid of any such collection areas. Ifo significant surface runoff takes place from the dunes because any rainfall rapidly infiltrates the unconsolidated sand cover. Run-off is more of a subsurface phenomenon where water percolating into the sand collects on the hard calcretized or ferruginized layer below the sand and moves laterally along this surface (Ruasel, 1984). This was also observed during the high rainfall event in the beginning of December 1985 when 128 mm fell within 4 days. No run-off was reported on the undisturbed dunes but the moisture content in the sand reached field capacity. It took at least two weeks of intense December evaporation (110 mm per day, Pitman et al. 1981) to dry the area to the extent that field vehicles could be used. Results of the percolation observations made subsequent to this high rsinfall event are discussed in the next chapter. TABU 4.4 cuaulatlva avaporatlon, tranaplratlon and percolation (as) pradietad by tha Uatar Plow Nodal for aavaral valuaa of potantlal avaporatlon (I ) and potantlal tranaplratlon (T ) (taddlnt and Hut«on, 1483) •p > 8. T • 0 1 1 Variable p («•.d" ) tp . 4, Tp - 0 (BB.d' ) tp • 4, Tp • * Cu» rain •vaporatlon Far-eolation •vaporatlon Pareolatlon •vaporatlon Tranaplratlon Percolation Day "• an an "" a» •B M - IS a.' 3.4 0.0 3.2 0.0 3.3 0.9 0.0 30 4*.8 27.7 0,0 23.2 0.0 23.1 4.9 0,0 45 1*9,2 «3.* 0,0 »3.4 0.0 58.1 11.7 0.0 to 1*9.2 »7.4 0.0 il.l 0.0 »0.4 14,3 0.0 75 23*. a 114,2 0.0 114,0 0.0 103,2 24.4 0,0 40 23*. a 118.9 0.5 118,7 1.0 105,8 34,3 0,0 105 248.9 132.7 2.* 131,4 3.* 118,1 41.4 0.0 120 2*1.0 144.2 4.* 144,8 5.9 130,8 44.3 0.0 135 2*1,0 148.3 *.3 14»,9 7.7 131,1 5*.4 0.1 ISO 2*1.0 149.8 7.7 148,4 9.2 131,2 •4,5 0.2 us 2*1.0 151.0 8.9 149,* 10.5 131.2 71.8 0.4 ISO 2*1.0 152.1 10,0 150,7 11.5 131,2 !••* 0,5 19S 2*1.0 153.0 10.8 151.« 12.4 131,2 82.* 0.* 210 2*1.0 153.9 11. t 1ÍÍ.4 13,2 131,2 •3.2 0.7 225 2*1.0 154,* 12.3 153,2 13.9 131,2 87,2 0.8 240 2*1,0 155,3 12.8 153,0 14.S 131.2 88,7 0.4 255 2*1.0 ISt.O 13.« 154,* 15,0 131,2 40,1 1.0 2)0 2*1.0 1S«,0 13.9 155.2 15,5 131,2 41,4 1.0 215 2*1.0 157.1 14,3 155,7 n.o 131,2 42.4 1.1 300 2*1.0 157,» 14.7 15*. 3 1*.4 131,2 43,3 1.2 315 2*1.0 158.2 15.1 15«, 8 U.7 131,2 «•.2 1.2 330 2*1.0 158.7 15.4 137.3 17,1 131,2 45.1 1.3 345 2*1.0 159.1 15.7 157.7 1'.* 131,2 •S.4 1.3 3*0 2*1.0 159.5 1*.0 158,2 17,7 131,2 4*.3 1.4 - 30 - LEGEND 1000 ELEVATION CONTOURS mamsl FENCES (1m INTERVALS) •INTERDUNE TROUGH 0 1.5 DUNE CREST fas •fe DISPOSAL SITE Sctle Figure 4.3 Topography of the disposal site and environs at 1 contour intervals. - 31 - CHAPTER 5 GEOHYDROLOGY OF THE UNSATURATED ZONE The unsaturated zone is defined as the strata between the land surface and the water table. It may also be defined as that part of the soil/rock column in which the void spaces between the soil/rock particles are not completely occupied by water. In this zone the water is held by capillary forces and the pressure is negative. This zone of negative pressures is called the "unsaturated zone**, "capillary zone" or "vadose zone". Of prime importance in any model used in simulating water movement and mass transport of radionuclides in the unsaturated zone, are three basic hydrogeological parameters along with geometrical and radionuclide decay parameters. The hydrogeological parameters are: i) the seepage velocity of the water carrying the radionuclides. This is dependent on the volumetric moisture, piezometric head, hydraulic conductivity and porosity. ii) The dispersion coefficients of the medium-solute interaction, and iii) the retardation coefficients of the medium and solute for each of the radionuclides. This is a measure of the capability of the porous medium to impede, by sorption (distribution coefficient) or exchange (soil chemistry), the movement of a particular radionuclide carried by fluid. The following parameters were thus studied in order to obtain input data for computer modelling of the unsaturated zone; hydraulic conductivity volumetric moisture content natural isotopes in the soil moisture dispersion coefficients - 32 - distribution coefficients soil chemistry. 5.1 The Fundamental Lav of Fluid Statics The physical and chemical properties of the water molecule make it possible to predict its behaviour in a porous medium such as soil. In order to do this it is necessary to look at the fundamental law controlling the water molecule's behaviour as a fluid. Soil moisture is never chemically pure but always contains some dissolved chemical species. Therefore, it can better be described as a fluid. The mere existence of a fluid implies that a pressure exists within the fluid. The study of fluid motion requires a knowledge of this pressure at any particular point within a fluid. The gravitational attraction of the earth is regarded as the most important force acting on a fluid in equilibrium with its surroundings. (p + dpldA /ogdAds {/ogdAdslsin 9 Figure 5.1 Force diagram used in deriving the Fundamental Equation of Fluid Statics. The pressure that exists within a fluid can be expressed by considering the elementary fluid volume shown in Fig. 5.1. Since the fluid is in equilibrium, the weight of the elementary fluid volume must be balanced by the difference of pressure across the volume. - 33 - The pressure p oust satisfy the equation: pdA-(p+ dp)dA-(pgsin6)dAds = 0 or after division by dAds dp/ds = -pgsinO (1) where p is the density and g the gravitational force. Two important pressure distributions are: Case 1 is the horizontal distribution (9 = 0) (dp/ds)/(e = o) = (dp/dx) = 0 (2) Case 2 the vertical distribution (6 = ^/2) (dp/ds)(9 =Tf/2) - (dp/dz) = - pg (3) From Equation (2) it follows that the pressure at any point on the sane horizontal plane in a fluid is the same provided the fluid is in equilibrium with gravity. Equation (3) indicates that in such a fluid there always exists a negative pressure gradient in the vertical direction. This is the Fundamental Theorem of Fluid Statics Using Equation (3), any pressure p at a height z can be calculated if a given pressure p an height z is known and density p is a constant or a known function of both pressure and height. P z I dp/pg * fdz <«) Po *o • z-z. - 34 - In subsurface flow, Equation (4) is used in the form P * = z0 + /dp/pg (5) Po where + is known as the piezoaetric head (or Hubert's potential) and the integral term on the right-hand side as the pressure head. If at p =0 and ZQ= Z, and the fluid is incompressible or the effect of pressure and density can be neglected, then Equation (5) simplifies to • = z + p/pg = z+h (6) 5.2 Surface Tension and Capillary Rise The molecules in liquid such as water are attracted to each other by cohesive forces. These large forces operating between molecules result in a very closely packed structure which resists forces tending to compress it. Within the liquid a molecule is attracted in all directions by equal cohesive forces, as shown in Fig. 5.2. At the interface of a liquid and a gas, however, an imbalance results as the liquid molecule at the interface experiences greater force into the liquid than the force attracting it into the gaseous phase (Fig. 5.2). The effect of this unbalanced force is that surface molecules are drawn inward into the liquid causing contraction of the surface. This phenomenon is called surface tension, denoted by the symbol o, and has the dimensions of force per unit length (Newton per metre). Surface tension is temperature dependant, decreasing almost linearly with rise in temperature (Hillel, 1973). This decrease is due to reduction in cohesive forces as the liquid expands and density decreases. This phenomenon is important ir the upper soil layers which are subject to temperature variation. Vapour preasure increases as result of the decrease in surface tension. - 35 - Air Liquid surface • . 1111 11 ^^n+m 111111 I^WTTTTT : TnfmnwfT ^gSSigHx;: Liquid Figure 5.2 The cohesive forces acting on a molecule inside and on the surface of a li Hillel (1973) states that soluble substances also influence surface tension. Electrolytes cause an increase while other soluble substances, such as detergents, reduce surface tension. To investigate the magnitude of the surface tension, the double-curved surface element with surface tension a and radii r^ and r. subtending the angles d+ and d9 is considered, as shown in Figure 5.3. In order to remain in equilibrium the external forces, p and p., on this element must be balanced by the surface forces. Expressed mathematically, this implies that EF = 0. By using Figure 5.3, this equation can be expressed in terms of its cartesian components as IFX » o^dS-o^dd * 0 iFy • orid^-or^d^ • 0. (Pi-Po)*» • 2oTid^Bin(de/2) + 20T2d9sin(dv/2) • 0 - 36 - PidA Figure 5.3 Schematic representation of the pressure difference across a curved fluid surface (Bear, 1979). or, since sin (6) = 6 for small values of 6 and dA = r.dvr.d0 (Pi-po)rjd^r2d0 + 2orid$(d9/2> + 2ar2d6(d$/2) = 0 Division by r.d$r d9 yields the well known Laplace equation Po-Pi • <* From a physical point of view Equation (7) implied that if the curvature is positive, aa in Fig. 5.3, then the outward pressure is larger than the inward pressure, as is the case at the interface between water and air. This explains why water rises in a capillary tube placed in a bowl of water. The pressure difference is Pc = P0- Pj (8) 5.3 The Porous Continuum The porous medium normally consists of closely packed solid grains with voids in between them. Water, or any other fluid, can only be - 37 - stored in these voids within the medium's matrix. Although many Instances are known where these voids are isolated from adjacent voids, reference to voids in this discussion will refer to those which are interconnected continuously by interstices to the domain of flow. The ability of a medium to transmit a fluid depends on the volume of voids. This parameter is therefore of prime importance to the study of fluid motion through a porous medium. In Fig. 5.4 some examples are shown of voids found in geological material. The geological media at Vaalputs, hosting the disposal trenches can be described as varying between the following types. (i) poorly sorted sedimentary material (ii) poorly sorted with deposition of mineral matter (Calcium carbonate and iron oxides) (iii) material mentioned under (ii) rendered porous by fracturing. (a) (b) Figure 5.4 Examples of voids in geological formations (a) A well-sorted sediment (b) A poorly-sorted sediment (c) A well-sorted sediment with deposition of mineral matter (d) Bock rendered porous by fracturing (Bear, 1979). Any method to define a measure of the volume of voids uniquely, should consider the three main components of the media namely, water, air and solid matrix. The volume of any portion of porous medium can be defined by - 38 - V = V + V + V (9) w s a where V = volume of water V = volume of solid s V = volume of air a A cross section through such a piece of porous material is shown in Fig. 5.5. ep = (AVPw + AVPa)/AVp Solid matrix Q Air Q Water Figure 5.5 Schematic diagram of a cross-section showing the normal three phases of a geological formation in the earth's upper crust. The porosity, defined by e = (Vw + Va)/V (10) seems to be a good measure for the volume of voids. To be meaningful, however, the volume V must be specified in some manner. Consider V , the volume element centered around P in Fig. 5.5. For large values of V" the ratio P c =(V + V )/V p v pw pa' p - 39 - will re&tin constant or change gradually if V Is decreased uniforally, depending on the homogeneity of the material. As shown in Fig. 5.6 V can attain a value of 1 or V -0 depending on P P the element being so small that it only includes a solid grain or a void. The volume V used in Equation 9 must be selt ;ted such that Vmin < » V < - Vmax where the terms V . and V are fixed in Fig. 5.6. In this min max way porosity is meaningful and a unique quantity. The value of V defined in this way is known as the representative elementary volume (REV). Porosities for the different rock types encountered at the disposal site are Indicated in Table 5.1. The volume of fluid contained in the voids of a porous medium is closely related to the porosity. The conventional way of expressing this quantity is by either one of two variables: (i) the moisture content defined by 9 = Vw/V (11) where V is volume of water and V is total volume. Dimensions of 9 are (L3.L~3) (ii) the water saturation defined by Sw - 6/e (12) From Equations (11) and (12) it follows that at saturation point of a porous medium, 0 » e and S • 1 Hence, 0 < = 9 < * e and 0 < • S„ < • 1 - 40 - Domain of porous medium Q. > Inhomogeneous medium > / > Homogeneous medium vmin vmax Volume Vp Figure 5.6 Definition of the representative elementary volume and the porosity e for a porous medium (Bear, 1979). Table 5.1 : Porosi :ies for the different rock types from Vaalputs (Van der iStt, 1984, 1985) ROCK TYPE BOREHOLE DEPTH (m) POROSITY Sand Surface 0,35 Ferruginous sand AFW42.5S10 0,5-1,26 0,30 Calcrete AFW40S05 0,5-2,0 0,23 Sand" Gritty Clay AFW35S08 9,6 0,37 AFW35S08 14-14-8 0,42 AFW42.5S13 8,48-9,48 0,45 AFW37.5S05 8,3-9,3 0,40 Weathered Granite AFW32,5S03 16,5-16,98 0,36 The density is another parameter necessary for the study of soil moisture flow in the unsaturated zone. The density is vital in the case of soil-moisture monitoring with the neutron meter. Referring to the three volumetric components Vg, Vy and Va in Equation 9 and the respective mass fractions M , Mw and it is clear fl v - V that three densities can be defined aa follows: - 41 - (I) Density of solids pg= Ms/Va (II) Dry bulk density pb = Ms/V (ill) Wet bulk density Oy = M/V where N = N + M + M denotes the total mass of porous W S A. material. The bulk density is related to the volumetric moisture content, 9, through the mathematical expression: © - (em/Pw)/Pb where 3 -3 6 volumetric moisture content (m water.m soil) 6 mass moisture content (kg water, kg" soil) m _3 soil bulk density (kg.m ) Pb _3 density of water (kg.m ). 5.4 Moisture Distribution in a Porous Medium Surface tension forces are the dominant forces which hold water in the soil. Just as the meniscus in the capillary tube is formed, menisci extending from grain to grain across each pore channel are formed (Fig. 5.7). The radius of curvature on each meniscus reflects the surface tension on that individual, microscopic air-water interface (Freeze and Cherry, 1979, p39). In addition to this, capillary water filling voids, an adsorbed thin film of water, only a few molecular layers thick, covers the solid grains as shown in Fig. 5.7. The main forces binding this film of water to the solid matrix are the adhesive forces. These forces are strong and the film of water can in many cases, only be removed by external energy. The surface area of a particle is Inversely proportional to its volume. Therefore, fine-grained material will expose a larger surface area to voids than coarse-grained porous medium. This explains why fine-grained clayey formations contain large volumes of water, but are unable to release it. - 42 - Adsorbed water Figure 5.7 Schematic diagraa illustrating the distribution of water between the grains of a geological formation. In the unsaturated zone the presence of curved menisci formed between the adsorbed water and soil grains, implies that this interstitial water must obey Laplace's Equation (7) for capillary pressure. Hence it is shown as capillary water in Fig. 5.7. Taking atmospheric pressure as a reference pressure, conventionally zero at the water/air interface, Laplace's Equation (7) reduces to -Pw - o (l/r2 + 1/r!) (13) In order to avoid using a negative pressure to describe the pressure experienced by the capillary water, a positive quantity, capillary pressure, was introduced. This is defined by t = "Pw <") The term matric pressure or matric potential is used nowadays, which is much more descriptive. The introduction of a negative pressure was advantageous as it allows the consideration of the entire moisture profile in the field in terms of a simple continuous pressure extending from the saturated into the unsaturated region below and above the water table as shown in Fig. 5.8. - 43 - -P. Subatmospheric Negative pressure pressure \ +p Superatmospheric Positive ^l ^ pressure pressure Figure 5.8 The distribution of pressure belov and above a free water surface. 5.5 Total Soil Water Potential Jones et al.f (1982) defines soil water potential as the amount of work needed to remove a unit volume or mass of water from a given location in the soil profile to a reference pool of free water. This definition of soil water potential as potential energy has its fundamentals in physical mechanics. However, it may also be explained through the thermodynamic concepts of free energy (Hillel, 1973; Jones, fit al-, 1982). Taking both fluid mechanics and thermodynamics into account the total soil-water matric potential, f, can be divided into three major components: (i) Matrix potential (tm) (11) Osmotic potential (* ) (ill) Gravitational potential (* ) The matrix potential f , as discussed In section 5.4, results from capillary and adsorptive forces due to the soil matrix. These forces attract and bind water in the soil and lower its potential energy below that of bulk water (Hillel, 1973). The thermodynamic properties of soil water are affected by the presence of solutes in the water which lower its potential energy. As stated previously, solutes lower the vapour pressure of soil water. This phenomenon, called osmosis, is important whenever a membrane diffusion barrier is present which transmits the water more - 44 - readily than the dissolved salts. The osmotic potential f is important in the interaction between plant roots and soil and is restricted to the upper soil zone. The gravitational potential q> is due to the soil water's position in the earth gravitational field relative to some chosen reference position such as the water table. The total soil water potential is equal to the sum of these three components. T Tm To Tg The soil water potential can be expressed in three forms: (i) Energy per unit mass, y = hg (joule.kg" ) where g is the acceleration due to gravity. (ii) Energy per unit volume or pressure y = hp g (kPa) where p is the density of the water. (iii) Energy per unit weight, * = h is the height of a column of water equal to the pressure head. The term, hydraulic head, is preferred. The hydraulic head is, in fact, the total pressure head and includes both the gravitational head and the matric head. 5.6 Relationship Between Water Content 6 and the Matric Potential «|> The only instrument that measures the matric potential or suction directly is the tensiometer. Jones e_t al., (1982) and Piaget (1975) give detailed descriptions of this apparatus. All other instruments infer soil water potential from measuring electrical resistance, temperature, or relative humidity. Soil water potential may also be obtained indirectly through its relationship to the volumetric moisture content. At a low volumetric moisture content a stronger suction will result because surface tension forces increase as water content decreases (i.e. become more negative). As the volumetric moisture content - 45 - 3000 — 1000— W35 S08 (9.6) SANDY GRITTY CLAY 300— VV35 S08 ÍU-U.8) WHITE CLAY c 100— o o. o Q. •C« 30-h 10— 3 — X 0,1 0,2 0,5 Volumetric moisture content 9 (m 3 water, m'3 soil) Figure 5.9 Water retention cunrea fro» aaaplea in borehole AFV35S08 at 9,6 • and 14 to 14,8 • (Van der Watt, 1984, 1985). increases, the surface forces decrease and suction is reduced (i.e. become less negative). This relationship between 0 and f varies from soil to soil depending on its texture (i.e. percentage sand, silt and clay) but also on bulk density and temperature. The curve constructed by plotting volumetric water content versus water potential is called the soil water retention curve. In Fig. 5.9 curves are shown for the loose sand and clay from the Vaalputs disposal site. These curves were obtained while drying the sample (which was saturated at the start) and are referred to as soil-moisture retention or desorption curves. A sorption curve may also be obtained through measurement while wetting the soil. The relationship between 0 and t is hysteretic: meaning that a different curve is obtained on drying than on wetting. The two curves shown in Fig. 5.10 bound the family of curves possible and form what is known as the hysteresis loop. The arrows show the direction of measurement and the internal lines, called scanning lines, show the course that 0 and f would follow if the soil were only partially wetted, then dried or vice versa. 5.7 Hydraulic Conductivity The seepage velocity, which is denoted by V, is defined as the average velocity of water in a porous medium. In terms of other hydrogeological characteristics, the seepage velocity is expressed by Darcy's Law: Vu * -(l/0)K(9)v> (15) for the unsaturated zone where V * seepage velocity (m.s~ ) 3-3 0 » volumetric moisture content (m water.m soil) K(8) • hydraulic conductivity in the unsaturated zone (m.s ) Vf • gradient of the soil moisture potential. The gradient of the soil moisture potential may be approximated as the difference at two locations divided by the distance between them and Equation (15) becomes - 47 - Unsaturated M*-Satu rated — Saturated moisture content 30 = porosity of soil n=30% 20 |i o » <-> >» «I 10 t:- o £ -400 -300 -200 -100 0 100 (a) Saturated ^ I hydraulic 0 03* conductivity «0=0.026 cm/mm o o IS » m . min~l ) : conductivit y 0 01|- (0 t- •o tí >> X J9X -400 -300 -200 -100 100 Pressure head, ^( cm of water) (b) Figure 5.10 Characteriatic curvea relating hydraulic conductivity and aoiature content to preaaure head for a naturally occurring aand aoil (Freeze and Cherry, 1979, p. 42). - 48 - Vu = -(l/eWBXt! - *2)/^ (16) Jones et al.f (1982) states that in order to describe flow it is necessary to know the gravitational potential and the matric potential. The gravitational potential is calculated from the position in the soil column and need not be measured. Under saturated conditions Equation (16) may be written as q = - (l/e)Ksat The hydraulic conductivity is, therefore, a function of the moisture content of the soil, K = f(6), where the moisture content is, as stated earlier, a function of the water potential. It is thus possible to express K as a function of the water potential K = f(f). K is obtained when the matric potential is zero, S&w which will be the case below the water table. Above the water table values are much lower. 5.8 Bulk Density As stated previously in section 5.3 the water content and bulk density are related by the equation 18 ev * (Pb/Pw>Om < > where p is density of water and p. the bulk density. The normal procedure for soil moisture measurement is to dry a sample in an oven at 106 C for 24 hours. The sample is then re-weighed to determine the mass of solids. The moisture content by mass is expressed as a percentage 8. - 49 - 8 = (mass of water x 100)/(mass of solids) (19) The moisture content in soil retention curves is expressed on a volumetric basis, 6 6 » (volume of water x 100)/(volume of soil) (20) Bulk density of the soil is defined as the mass of the solids divided by the total volume of soil. p = (mass of soil)/(total volume of soil) (21) 5.9 Soil Moisture Redistribution of soil moisture in the field may be monitored directly by changes in moisture content or indirectly from measurement of the water potential. The most suitable method for monitoring moisture content is with the neutron probe, while water potential may be measured with a water potential sensor. 5.9.1 Water potential sensors There are four types of water potential sensors available, as discussed by Jones e_£_ftl.» (1982) and Everett et al.f (1984). (i) The tensiometer is the only instrument that measures water potential directly. The limitation of this instrument is the range which is limited to the 0 to -100 kPa scale (Piaget, 1975). It is also not possible to take measurements at great depths as the range is greatly reduced e.g. to -50 kPa at 0,3 cm (Jones, et al.r 1982). (ii) Soil psychrometers are instruments that infer water potential from a measurement of the relative humidity of the soil atmosphere. This measurement is based on the relationship between the sum of the matric and osmotic potentials, and the relative humidity of the soil air: - 50 - tm + to =(ÏT/M)0n(Rh) (22) where t - soil water matric potential (J.kg~ ) t * soil water osmotic potential (J.kg ) K = universal gas constant (J.mole- .°K~ ) T = Kelvin temperature ( K) H = molecular weight of water (kg.mole- ) Rh = relative humidity x 0,01 For water at 25°C, RT/M = 1.37 x 103 J.kg"1: • + • = 1.37 x 105 En (Rh) m o The limitation of this instrument is the lack of accuracy at high water potentials (>-100kPa). They are therefore unreliable in wet soils. They only function at depth where large temperature gradients are eliminated (Jones et al.f 1982). Kearl (1982) successfully used the thermocouple psychrometers in his studies on the LLW site at the Nevada Test Site. • According to Kearl (1982) the psychrometer is effective for water potential measurements in the range -100 kPa to approximately -6500 kPa. Above -100 kPa Kearl (1982) used tensiometers which function well in the range 0 to -80 kPa. (iii) A third method of water potential measurement is with heat dissipation sensors (Jones et al.f 1982). After equilibrium between soil and a porous matrix is reached, the water content of the matrix is determined by measuring the heat dissipation characteristics of the matrix. The temperature at the centre of the matrix is monitored before and after heating. The temperature difference is a function of the thermal diffusivity, and- therefore the water content of the matrix. This method is limited to water potentials <-100 kPa and good contact between soil and sensor is necessary. (iv) One of the most widely used methods of measuring soil moisture is by means of electrical resistance. Since the introduction of gypsum blocks in 1940, the method has been improved (Bouyoucos and Hick, 1947; Bouyoucos, 1949) and new materials have been introduced (Perrier and Harsh, 1958; Bourget et_al., 1958). Introduction of modern electronics circuitry has helped to eliminate problems and increase resolution (Goltz et al.. 1981). The sensor is commonly made of gypsum, nylon or fibreglass. The relationship between the electrical resistance and water potential of the matrix is determined. In the nylon and fibreglass blocks the soil moisture provides the conductive medium. In the gypsum block, the moisture is always 2+ saturated with respect to gypsum and thereby providing Ca 2- and SO. ions. Increase in moisture is determined 4 primarily by the water content of the gypsum block. The nylon and fibreglass blocks operate in the range from saturation to approximately -100 kPa while the gypsum block's response is quite linear over the matrix potential range from -30 kPa to -1500 kPa or lower which makes it an ideal monitoring device for arid soils if contact between the block and the soil can be assured. Although no direct water potential measurements have been taken at Vaalputs, the installation of gypsum blocks during waste disposal is planned. The blocks are easy to use and may be placed at the soil/waste interface, below a waste container or any place and depth without the limitations of the other methods discussed. Monitoring of the wick-effect (gravel layer below a soil layer) can also be performed using the gypsum block method. 5.9.2 Heutron probe The technique of moisture measurement, using thermalized neutrons is well studied and several authors have reported on the theoretical - 52 - and experimental considerations for the design and calibration of the neutron meter (Botha, 1963; Olgaard, 1965; Kashi and Koskinen, 1966; Olgaard and Haahr, 1967; Couchat, 1983 and Everett et al.f 1984). The neutron meter normally consists of a probe housing a * americium-241/beryllium neutron source and a boron tri-fluoride (BF,) detector. Fast neutrons are emitted by the neutron source into the surrounding soil to be measured. Neutrons richochet strongly from large atoms and it requires several hundred collisions with these large atoms to slow down a neutron to a thermal level. However, if they collide with hydrogen atoms neutrons are dramatically slowed down as a neutron has the same mass as the hydrogen atom. Loss of energy on collision in this case is great and after only 20 collisions is the fast neutron thermalized. The boron tri-fluoride (BF.) detector is responsive to weak, thermal neutrons and gives a direct indication of the extent of thermalization and therefore hydrogen present. In addition to the above publications several methods for calibration have been published by, inter aliaf Harais and Smit (1960); Karsten et al.f (1975), and Nakayama and Reginato (1982). Measurements by the neutron meter are affected by variations in the bulk density of a soil. This limitation and the procedure to correct for it is reported by Karsten and Haasbroek (1973), Wilson (1982) and Botha (1986). The influence of density on neutron meter measurements is facilitated by an instrument that detects both neutrons and gamma rays (density) with the same probe. In addition to the neutron 137 source the probe contains a gamma source (usually Cs) and a gamma detector. The instrument is so designed that the geometry of the spheres of detection are coincident and therefore the same sample is measured for both moisture and density. The effect of elements other than hydrogen on the determination of moisture content by the neutron method have also been noted by Botha (1963), Burn (1966) and Baubenheimer and Riemand (1985). Other - 53 - sources of error in the calibration, such as probe positioning, electronics and site heterogeneity, are discussed by Sinclair and Williams (1979). 5.10 Soil Moisture Studies at Vaalputs At Vaalputs the unsaturated zone below the trench area is between 50 and 60 • thick, consisting of surficial material of between 15 and 30 m in thickness, while weathered and fractured granite and associated rocks constitute the remaining strata down to the water table. Cr)ss-sections through the disposal site area are shown In Fig. 3.4 and 3.5. Samples for parameter determination were obtained by large diameter auger drilling, air-flush core-drilling, pitting and trenching. For parameter determination the unsaturated zone is divided into loose red sand, sandy gritty clay, white kaolinitic clay, waathered granite and fractured granite. The packer tests (section 6.4.2) provided information about the fractured granite above the water table. Packer testing of 25 holes indicated, without exception, that this zone if much more permeable than was previously envisaged. Subsequent diamond drilling showed that flow predominantly takes place through fractures, although some flow through the weathered granite matrix is also possible. Where the same section was tested twice on the same day, a slight decrease in the transmissivity was noviced. This is ascribed to the swelling of clay minerals after injection of water during the first test. 5.10.1 Laboratory determination of moisture content and retention curves Baseline neasurements of the soil moisture content (percentage by weight) were done on samples obtained from 16 auger bor-.holes drilled on the Vaalputs site. Profiles, varying between 10 and 20 m In depth, were fairly uniform in moisture content, which ranged from 6 to 20 % by weight. Four of these profiles are shown in Fig. 5.11 and the locality of relevant boreholes in Fig. 5.12. - 54 - The purpose of the soil moisture studies was to determine the soil moisture potential which is related to the hydraulic conductivity. Russel (1984) used a field method at Vaalputs to determine coisture potentials in auger and air-flush borehole samples. A pre-weighted (oven-dry) Whatman No 42 filter paper is inserted between two pieces of sample (Hamblin, 1981). This can be done in situ or with core samples. The filter paper is re-weighed after a certain time and knowing the moisture content of the sample a value for the water potential is read from a calibration curve. In this way Russel (1984) was able to distinguish between very dry, < -1000 kPa, and wetter, > -1000 kPa. He concluded that a fairly uniform -1000 kPa potential exists down to the bedrock at Vaalputs. Van dcr Watt (1984, 1985, 1986) used the laboratory method to determine soil moisture retention curves for the whole spectrum of rock types present on Vaalputs. Air-flush core samples were used and moist are retention was measured at soil moisture metric potential valuer, of 0, -3, -10, -30, -100, -300 and -1 800 kPa. The retention curves for the various rock types are shown in Fig. 5.13, 5.14 and 5.15 and the results tabled in Table 5.2, 5.3 and 5.4. The retention curves in Fig. 5.14, 5.15 and the corresponding results in Table 5.4 refer specifically to samples of the clay which will host the radioactive waste. Using Van der Watt's retention curves, Russel's water potentials were evaluated in auger borehole AW20S08. This comparison is give.i in Table 5.5 from which it is clear that hardly any correlation exists. The fllterpaper method is therefore not considered useful in determining water potential. Bulk densities were determined for the same material en which water retention curves were constructed. Tne values for the various rock types are given in Table 5.2. The densities are normal for compacted soils and slightly parked said. Sock typ?7 such as ferruginized 6ai»d and calcrete soaetin,?* gave atypical values because of heterogeneity. Values for the;je rock types rt.ned from 1600 kg.nf3 to 2000 kg.m"3. 5.10.2 Field monitoring of moisture content A Campbell Pacific Nuclear (CPN) 501DR neutron meter was used for field monitoring of moisture movement in the unsaturated zone. The AW30 S08 2 <. 6 8 10 12 H. 16 18 20 MOISTURE I wt Vol 0 1 23(.S6789 10TU W30 NOO TT ------« 6 8 10 12 H. 16 18 20 MOISTUR[(wt%) I I SAND CALCRETE NODULAR CALCRETE M aAY MATRIX AW25 S13 /W*5 S03 2 4 6 8 10 12 11.16 18 20 MOISTURE (wt'/.t 2 U 6 8 10 12 It, 16 18 20 MOISTURE !***/•) SANOY GRITTY aAY 23(.S6789 10TU 01231.S6789 10TU 0 1 »• . + •-.• #• — •••+ . » » I •»• • » SMALL PEBBLES IWmml M aAY MATRIX WHITE CLAY WEATHERED GRANITE MOISTURE Iwl %l TRITIUM ITU) Figure 5.11 Soil Moisture and tritium profiles fro» four auger boreholes. - 56 - 501DR was fully calibrated for moisture and density as described by Raubenheimer and Niemand (1985) and density corrected by Botha (1986). For soil moisture monitoring of the disposal site ten aluminium access tubes (50 mm wide) were installed to a depth of 9 metres. The positions of the access tubes at the disposal site are shown in Fig. 5.16. Measurements were taken at 0,5 m Intervals down each access tube. Clamps on the lowering cable ensure that the same position is read each time the probe is lowered. A counting time of 32 seconds is used as this is the shortest counting time with good counting statistics, as illustrated in Fig. 5.17. The CPN instrument is equipped with a microprosessor and field readings are stored in the memory until the data are dumped onto a IBM PC at the office. Various programmes have been written to process the data and a typical program output is presented in Table 5.6 and Fig. 5.18. AW25S03 W30N00 o AW30S03 100 200 300 4)0 500 m I I I I nl SCALE AW25S1J i e s c N o * Agg#r drilling • Air fluid c«r» drilling O Pfrcuition drilling AFWM,SS10 VAALPUTS Figure 5.12 Locality of boreholes in the vicinity of the disposal site, used in Table 5.2 and 5.7 and in Fig. 5.11. - 57 - Table 5.2: Origin and bulk densities of various rock types sampled for vater retention curve determinations. (Van der Watt 1984, 1985) Sedimentary Unit Borehole No Intersection Bulk density (m) kg.m"3 Red sand - - 1 672 Ferruginised sand AFW42,5S10 0,5 - 1,26 1 963 Calcrete AFW40,S05 0,5 - 2,0 1 644 Sandy gritty clay AFW37.5S05 9,3 - 9,3 2 063 White kaolinitic clay AFW35S08 14 - 14,8 1 590 Weathered granite, transported AFW35S13 20,0 - 20,5 2 081 Weathered granite, in situ AFW32.5S03 16,5 - 16,98 2 039 Table 5.3: Averaged values of vater retention for various rock types determined on individual core sections, (vater content 9 = m3 vater.sf3 soil) (Van der Watt, 1984, 1985). Matrix Red rerrugi- Calcrata Sandy gritty Whita Waatherad Weathared potential •and nleed clay kaolinitic granite in a granita ir (kPa) «and clay clay matrix aitu 0 0,355 0,299 0,231 0,401 0,430 0,238 0,364 -3 0,208 0,242 0,203 0,358 0,422 0,231 0,313 -10 0,124 0,185 0,187 0,316 0,300 0,194 0,280 -30 0,076 0,198 0,190 0,321 0,418 0,172 0,265 -100 0,058 0,173 0,205 0,285 0,327 0,133 0,214 -300 0,040 0,141 0,132 0,272 0,232 0,125 0,212 -1800 0,035 0,123 0,144 0,172 0,114 0,183 - 58 - LEGEND Red sand Ferruginized sand Calcrete and ferruginized sand Sandy ghtty clay White kaolinitic ctay Weathered granite and sediments Weathered granite 3000 1000 2 300 - ¥ 100 - e -a. 0,16 0.24 0,32 0,40 0,48 (volumetric moisture content m* water. m"3soil) Figure 5.13 Water retention curves for the various rock types underlying the disposal site. (Van der Watt, 1984, 1985, 1986). - 59 - Data in Tool» *.• 20/7 9/13 £ c o a. E 0.20 0.10 0 1.0 6 volumetric moisture content lmJ wittr. «f3 toil ) Figure 5.14 Water retention currea for fire saaplea fro» the sandy gritty clay unit (after Van der Watt, 1986). $ volumetric moisture content (m3 wêttr. m"í toil) Figure 5.15 Water retention curve for the average values of the sandy gritty clay unit (Van der Watt, 1986). - 61 - . Table 5.4: Averaged values of vater retention for the sandy gritty clay, determined on individual core sections, (vater content 6v - m3 vater. •T3 soil) (Van der Watt, 1986) Sample No Matrix- potential 9/13 9/15 9/16 20/6 20/7 Average for 9/13-20/7 (kPa) e e e e e e -1.5 0,387 0,452 0,457 0,424 0,386 0,421 -5,0 0,358 0,416 0,372 0,383 0,386 0,383 -30 0,283 0,307 0,270 0,312 0,293 0,293 -300 0,254 0,294 0,242 0,249 0,270 0,261 -1800 0,244 0,240 0,222 0,224 0,242 0,234 Bulk density 2 019 2 050 2 261 I 178 2 151 2 142 kg.t. m -3 Table 5.5: Comparison of vater potentials using the filterpaper method and moisture retention curves. Auger bore hole AW20S08 Depth Geology t filter y retention em* m Cm) field lab. paper curve (kPa) (kPa) 1,7 - 2,3 Calcrete 8,37 9,19 -1000 - 500 4,3 - 4,8 Gritty 18,81 13,72 -10OO - 30 sandy clay 6,*- 7,6 Greenish clay 13,58 13,64 -1000 - 30 7,6 - 8,8 Gritty sandy 21,79 18,72 - 100 - 3,5 clay 8,8 - 11,3 Weathered 9,86 7,95 - 500 -1800 granite - 62 - Monitoring started in March 1985 when it was decided to monitor only once a month as very little rain had fallen and negligible moisture movement was expected. During the first four days of December 1985, however, 128 mm of rain were recorded on the site. The figures for 1 to 4 December 1985 were 87 mm, 24 mm, 1 mm and 16 mm respectively. Immediately following this event, daily monitoring was carried out until changes stabilized, after which monitoring was done at longer intervals. After three months monthly readings were commenced. The movement of soil moisture recorded after the high rainfall event is illustrated in Fig. 5.19. The background values are the average values recorded during the nine months preceeding the rainfall. It is clear that peak infiltration occurred within the first three days after the rainfall. Return to pre-event levels was slow but, after seven months it was almost back to normal. The most important observation is that soil moisture movement apparently did not penetrate deeper than 3,5 m. This agrees with the results of the natural isotopes studies of soil moisture movement (section 5.11). i 'SITE 3 1 l j ! «SITE I. SITE 2 m I I I 0 E H Q • Niutron prob* acctss tubti SITE 1 K I SITE» i SITE s n 0 100 200 300 W>0 500, SCALE SITE US ISITEÍ SITES M • SITE 7 VAALPUTS Figure 5.16 Locality of the neutron meter access tubes on the disposal site. - 63 - The gradual decrease in soil moisture after an initial increase is largely due to upward movement by evaporation and evapotranspira- tion, but the slow addition of moisture to the underground supply cannot be excluded. 5.10.3 The hydraulic properties of the various rock types As stated previously (section 5.7) flow in the unsaturated zone can be studied by using Darcy's law: q = -K(9)Vf (23) where 4 = Darcy flux (m.s~ ) -1, K (9) = Unsaturated hydraulic conductivity (m.s ) = gradient of the water potential (m.m~ ) Table 5.6: A typical data print-out of processed neutron meter data for a field site. 3 -3 V = Volumetric moisture content (m moisture.m soil) W = Moisture content by weight (kg moisture.kg- soil) BOREHOLE SITE 4 85/12/13 DEPTH WET DENSITY WET DENSITY V MOISTURE W MOISTURE -3 -3 m kcf.m kg.m 0.5 1920.9 1817.2 10.3785 5.7114 1.0 2255.7 2021.4 23.4311 11.5916 1.5 2084.4 1738.1 34.6242 19.9204 2.0 2213.0 1911.1 30.1893 15.7964 2.5 2181.1 1902.8 27.8325 14.6270 3.0 2228.8 1981.4 24.7413 12.4868 3.5 1904.1 1678.9 22.5143 13.4098 4.0 2099.1 1930.2 16.8904 8.7508 4.5 1939.4 1752.7 18.6539 10.6431 5.0 2010.9 1826.0 18.4912 10.1267 5.5 2017.3 1844.9 17.2444 9.3471 6.0 2057.5 1899.3 15.8168 8.3276 6.5 2034.9 1888.5 14.6370 7.7504 7.0 2013.8 1844.2 16.9516 9.1916 7.5 2234.9 2071.8 16.3122 7.8735 8.0 2179.7 1996.6 18.3078 9.1693 8.5 2148.2 1993.1 15.5077 7.7807 - 64 - J 16 32 64 COUNT TIME (Sec) MOISTURE 32 COUNT TIME (Sec) DENSITY Figure 5.17 Determination of optimal count rate interval for the 501DB neutron aeter. - 65 - M/W/1 O—O Oltl far IS/12/11 » VOIUHE PERCENTAGE MOISTURE • ' WATER, a'1 SOU Figure 5.18 Soil aoiature curre for neutron meter data recorded on 85/12/13 at neutron tube aite 4. - 66 - The unsaturated hydraulic conductivity is essential in predicting the hydraulic properties of the unsaturated soils. The determination of this parameter is, however, time consuming. Spatial variability further complicates the estimation of reliable values for this parameter. The problem is overcome by the use of more readily available moisture retention curves and an obtained value for the saturated hydraulic conductivity. The method by Campbell (1974) is one of several that have been proposed for calculating unsaturated hydraulic conductivities of porous media from moisture retention functions. Botha (1986) used the more sophisticated mathematical approximation of Van Genuchten and Nielsen (1985) to predict the unsaturated hydraulic conductivity Fig. 5.20. Saturated hydraulic conductivities of the various rock types have been determined by Van der Watt (1984 and 1985, 1986). Averaged values of the saturated hydraulic conductivities for the various rock types are shown in Table 5.7. 5.11 Natural Isotopes in the Soil Moisture In addition to hydrogen (H) of mass 1(H), small amounts of its 2 stable isotope deuterium ( H or D) and the radioisotope tritium 3 ( H or T) occur naturally. On the other hand oxygen of mass 16 ( 0) and small amounts of its stable isotopes 0 and 0 also occur naturally. Together these isotopes combine to form 18 different water molecules and 12 ion species. The rare isotopes D, 17 18 T, 0 and 0 occur in greatest abundance in combination with the common isotopes hi and 160, as HD(160), HT(160), 17 18 H2( 0), and K*2( 0) (Matthess and Harvey, 1982, p. 3). The abundance of the above isotopes is particularly suited for studying the movement of soil moisture. This is especially true in arid and semi-arid environments, where changes in the hydrological system are subtle and difficult to detect by direct observation. The most suitable environmental isotope to use as a natural tracer is tritium, especially in conjunction with the stable oxygen Isotope, 0. - 67 - "—"—* Pre-rain average ' ' " u 85/12/07 \ „ . j Post ——— 86/01/06 ) { r.in • • • 86/05/07 ] 0 " ' 86/06/25/ 5 15 25 VOLUME % MOISTURE ( m3 moisture, m"3 soil) Figure 5.19 During 1-4 December 1985 approximately 12S mm of rain fell. The soil moisture measurements indicate the amounts and depths of infiltrating water at successive intervals. 5.11.1 Environmental tritium Tritium (T) concentration in soil water in the unsaturated zone has been used to estimate local recharge by several investigators (Verhagen ejL_4l., 1978; Allison and Hughes, 1983; Allison ££_&!., 1984 and Sonntag £i_gl., 1984). Tritium abundance is measured in tritium units (TU) and 1 IU T/-«H• - 33"'H/XH1" «--10 • Tritium is present in precipitation as result of: (i) Natural production by cosmic-ray interaction with the atmosphere. This source contributes about 5 Tritium units to rain water from the inland regions of Southern Africa. Table 5.7: Averaged values of the saturated hydraulic conductivity for the various rock types as determined by Van der Watt (1984, 1985, 1986) Rock types Borehole Bulk density Saturated hydraulic (kg.m-3) conductivity (n.s"1) Ferruginized AFW42S10 29,0 x 10~8 sand AFW37.5S03 1 975 Sandy gritty AFW35S05 7,59 x 10"8 clay AFW35S08 2 230 Weathered 1,96 x 10"8 granite in AFW35S08 2 159 clay matrix Kaolinitlc clay AFW32,5S13 1 683 6,0 x lO"8 Weathered granite AFW32.5S03 2 128 7,95 x 10~8 (il) Nuclear fallout. The natural level of 5 TO prior to 1955 increased to a maximum 60 TU in rain water measured during 1963/64 in Southern Africa. It has decreased to the present level of about 9 TU (Verhagen and Levin, 1986). Tritium is a radioactive isotope of hydrogen and therefore decays. It has a half-life of 12,4 years which means that tritium levels in pre-bomb (pre-1955) rain water have declined to a maximum of about 1 TU at present and will be negligible in 50 years time. Rainvater is therefore labelled with this natural tracer, which can be followed over a period of several decades. In a homogeneous, unsaturated zone identification of the downward moving tritium peak allows for a semi-quantative interpretation of the percolation rate. 5.11.1.1 Method of sampling and determination As pointed out by Allison ££_al., (1984), sampling from consolidated or cemented materials may be a problem. Drilling methods, such as ' coxing or percussion, involves either air or water M a coolant which render the samples useless. It was therefore decided to use a - 69 - .20 .24 .28 .32 .36 .40 Volumetric moisture content 5.20 The Van Cenuchten approximation (-) and the ezperiaentally determined (+) «oil aoiatnre retention cnrre for the red clay at Vaalpota (Botha, 1986). - 70 - large diameter (900 mm) bucket auger, which also had the advantage that a large sample was available for rapid packing and preserving. Two litre preserve jars, carefully prepared beforehand, were used for sampling. Care was taken to ensure that only jars under vacuum up to the point of sampling were used.. For tritium analysis, water was extracted quantitatively from the soil by vacuum distillation and treated as described by Verhagen (1985). The accuracy of tritium measurements is of the order of about 1 X, and the limit of detection is 0,2 TU. The usual yield of water was 99 X and therefore the ratio of weight of water collected to the original weight of moist material is taken as the true percentage by weight of moisture in the sample. The pre-sampling jar preparation and post-sampling treatment and final measurements were performed in the laboratories of the Schonland Beaearch Centre for Nuclear Sciences. 5.11.1.2 Tritium results Samples from five auger profiles have been quantitatively distilled and tritium levels in the resulting water were established. The results have previously been reported by Levin and Verhagen (1985), Verhagen (1985) and Verhagen and Levin (1986). As some of the initial values were seemingly anomalous, instrumentation and procedures were re-checked to eliminate any errors. The weight percentage moisture and the measured tritium concentration for the individual profiles are graphically displayed against depth in Fig. 5.11. At about 1 m depth a tritium peak ranging from 6 :o 10 TU is found which is comparable with present-day rain in the area, which contains 9,9 ± 1,0 TU (Verhagen, 1985). Similar profiles were observed for the first few metres of all the auger holes. The stratlgraphic column for each profile is also displayed against depth and, although some variation in moisture content was observed with depth, there is a good degree of correlation with the geology. - 71 - This is especially true if the volumetric water content is calculated, using the density previously determined for the various rock units. This correlation is illustrated for auger hole AW40S08 in Fig. 5.21. Below one metre depth there is a decrease in tritium to almost zero between 3 and 4 metres. The only values of significance below this depth was found in auger hole AW30S08 and borehole W30R00 where 4,5 TO were detected. The initial drop in tritium concentrations is interpreted as defining the depth to which rain water has been able to percolate over the last few decades. Percolation at the site down to 3,5 m was confirmed by neutron meter observations after the high rainfall event in December 1985, as discussed in section 5.10.2 and shown in Fig. 5.19. According to Verhagen (1985) the negligible tritium values observed in most profiles just below the initial peak suggests relatively tightly held water within the clay material which is not easily exchanged with more mobile infiltrating rain water. In comparison with the homogeneous surficial sands, the underlying unsaturated zone is highly heterogeneous and clay-bound and is much less susceptible to piston-like flow. However, the possible displacement of the tritium peak downwards by the recent high rainfall event needs to be investigated. The possible rapid movement of water to greater depths than 3 to 4 m, aa seen in auger hole AW30S08 (Fig. 5.11), can be ascribed to movement along preferential pathways in the unsaturated zone. Napping of the experimental trench walls (Levin, 1985) has shown features such as desiccation cracks, collapse structure», rootholes, cracks and ant holes which could provide conduits for water movement to deeper levels. 5.11.2 Stable isotope 180 The isotopic ratio 180/160 is of special interest to the hydroïogist. This ratio is expressed as delta units (6) which - 72 - V. MOISTURE "5 2 6 10 It 18 22 26 30 34, Red sand taitrtt* Red togrtv sandy 9m ff clay F» natfutn and Quartithc ptosis* Red *a s/ty o/tefl sandy a. au 13 Whi*t kMliMTlC o 15- cia, < ? 17 Brown yellow ctay (Ftrrua>nous> Waftttred gramf» •™M| • % Hontuft 0« mast ba»i* •>---• % Honturt ofl volumetric bens Figure 5.21 Correlation between moisture content by veight, the volumetric moisture content and the geology as seen in auger borehole AW40S08. are per mille (parts per thousand or %o) differences relative to an arbitrary standard known as Standard Mean Ocean Water (SNOW): 6X0 (R-R.tandard)/Ratandard x * 00° 18 16 B tne where S and stan(»ard •*• isotope ratios 0/ 0, of the sample and the standard, respectively. The accuracy of measurement 18 is usually better than ± 0,2 X for 6 0 (Freeze and Cherry, 1979, p. 137). The various isotopic forms of water have slightly different vapour pressures and freezing points. These two 10 properties give rise to different 0 concentrations in water in various parts of the hydrological cycle, by the process of isotopic fractionation. During evaporation from the oceans, the water vapour 18 produced is depleted in 0, relative to ocean water. Upon 18 condensation, the rain or snow that forms, has higher 0 concentrations than the remaining water vapour. - 73 - 18 Using the local 0-label in areas of low recharge, semi quantitative information on recharge rates for that locality may be obtained. 5.11.2.1 Method of sampling and determination 18 0 measurements were performed on the same bulk samples of water distilled from the individual soil samples as were used for tritium analysis, but these measurements were carried out before isotopic enrichment (Verhagen, 1985). Isotope fractionation, as a result of distillation, was slight as water yields from individual distillations were at least 99 %. This indicated that insignificant losses were experienced and therefore ensured negligible 18 fractionation. The 0 isotope content was determined by mass spectrometry in which CO, is used as the standard gas for the 18 0 isotope. 5.11.2.2 180 results 18 The 6 0 results for a number of soil profiles were determined by Verhagen, (1985) and some of them are shown in Fig. 5.22. These profiles display a similar pattern to those observed in the tritium 18 data. The more positive 6 0 values near surface 18 corresponding to higher TU values. Lower down 6 0 values drop to lower (more negative) values at about 2 to 3 m. The deep values are more uniform but distinctly lower than at the top. In contrast to the tritium values, which showed slow-moving, 18 tightly-bound moisture, the S 0 show great variations from profile to profile, spanning a range of nearly 3 Xo (where %o denotes per 1000 and is read "per mil"). The values in the unsaturated zone of the profiles differ substantially from those measured in the saturated zone (section 7.1.2). The more enriched values in the shallower sections point to a greater degree of evaporation before or during infiltration. Lover down the profile the values lie closer to the expected values for local rain water. The relative isotopic uniformity, according to Verhagen (1985), suggests that It was derived from more sustained rainfall than is the case at present. The variability between profiles at different sites results from site-specific control of infiltration such as local topography, rock types, present and moisture profile before infiltration. Similar variability is displayed in the saturated zone. 5.12 DispersiTity The term dispersion refers to the movement, with respect to the fluid, of a contaminant carried by the fluid through a porous medium. This is a nonsteady, irreversible process in which two basic transport phenomena are involved, convection, which is the transport of the contaminant due to the moving water and molecular diffusion, which is the movement of the contaminant due to concentration gradients, also called spreading (Freeze and Cherry, 1979). Molecular diffusion is depenuant on the internal kinetic energy of the fluid, which is zero only at 0°K. This implies that diffusion takes place whether the liquid is at rest or in motion (Botha, 1986). At slow flow rates molecular diffusion provides the major component of dispersion, but this will decrease as concentration gradients become flatter. Molecular diffusion is also referred to as self-diffusion or ionic diffusion. The diffusion flux refers to the mass of diffusing substance transported through a given cross section per unit time, and is proportional to the concentration gradient (Freeze k Cherry, 1979, p. 113). This is known as Pick's first lav and is expressed as: F - - D (dCdx). (24) -2 -1 where F • mass flux (kg.m .s ) 2 -1 0 > diffusion coefficient (m .s ) C * solute concentration (g.H~ ) and (dCdx) the concentration gradient, which is a negative quantity in the direction of diffusion. However, there are also the convective components of dispersion that are caused entirely by the motion of the fluid. This is known as - 75 - 6"0(%} 3 -2 -1 0 +1 •3 -2 -1 0 -4 -i -2 -Í -J -2 -1 0 I I I 1 1- +—I—f—r- -I—\-r\—h i—»—I—h 2- 4- ki70-|- T4- AVV40 S08 AW30 S03 AW25 S13 AW35 S03 • » i i i_ i i i i_ Figure 5.22 0 profilea in samples from auger boreholes AV40SOS, AW30S03, AW25S13, AW35S03 (Verhagen, 1985). mechanical dispersion or hydraulic dispersion. Freeze and Cherry (1979, p. 75) discuss the three causes of this dispersion. The first is the different flow velocities of molecules across individual pore channels due to the drag exerted on the fluid by the pore surface. The aecond ia cauaed by the difference in pore aize along the flow paths of the fluid. The third is the dispersive process which is related to the branching, interfingering and tortuoaity of the pore channels. The solute can spread in two directions, namely, in the direction of bulk flow, which is known aa longitudinal dispersion and perpendicular to the flow which ia called transverse or lateral diaperaion. Longitudinal ia normally greater than latsral dlapersion (Freeze and Cherry, 1979, p. 76). According to Botha (1986) mechanical dlapersion can be expressed in terms of a dispersive flux which alao satiafies Fick'a law. - 76 - Stephenson (1985) and Stephenson and De Jesus (1985) estimated the dispersivity of the unsaturated clays at Vaalputs. After some initial trial tests in the laboratory and the field, a final set of teats was conducted at Vaalputs. These final tests involved the injection of a pulse of Scandium-46 ( Sc) into an injection hole which was then monitored in adjacent objervation be «holes. The Sc EDTA-complex is not adsorbed on the clay and its gamma-radiation spectrum is not interfered with by natural radiation. The laboratory results are reported in Table 5.8 and the field results in Table 5.9. The differences between the two sets of results are not unexpected because of the small sample size and absolute controlled conditions in the laboratory compared to the field. The differences between horizontal and vertical values are due to the horizontally bedded nature of the sediments resulting in higher horizontal than vertical dispersion. 5.13 Distribution Coefficients The term, sorption, has been used to describe the phenomenon whereby species are removed from the liquid phase and held onto the solid phase. The distribution coefficient (K.) is a measure of the interaction between a particular dissolved ion or molecule, the porous medium and the fluid. Hatthess and Harvey (1982) define the Kd of a radionuclide as a measure of the partitioning of ion species between the solution and the solid adsorbing phase. During subsurface flow the radionuclide in the liquid phase will move with the transporting solution, but the radionuclide adsorbed onto the solid phase will remain stationary. It is assumed that adsorption takes place at a rate such that the solute is in equilibrium with the adsorbent. This can be expressed for some substance C as: amount of C in solid phase a amount of C in liquid ohase (25) mass of «olid volume of solute Table 5.8 Results for disperaÍYÍtie» aeaaured in the laboratory, Stephenson (1985) Sample Depth Direction Dispersion coef. Dispersivity Ho (m) of flow (m2.*"1) (m) 1. Brown sandy W35S08 5,5 horizontal D s 1,3 z 10"5 5.0 gritty clay 5,5 vertical D » 1,3 x 10"8 0,65 2. Brown sandy WAOS08 7,0 horizontal D = 4,1 x 10~6 1,78 gritty clay 7,0 vertical D * 2,3 x 10"6 0,85 3. White clay W35S08 11,5 horizontal D = 4,6 x 10"7 1,15 11,5 vertical D = 6,2 X 10"8 0,62 Table 5.9 Results for diapersivities •easured in the field at Vaalputs, Stephenson (1985). Mean values are quoted with the range in brackets. Dispersivities Lithology Saturated/ Vertical flow Horizontal flow unsaturated (m) (m) Brown sandy unsaturated 0,5 (0,4 - 0,8) 0,02 (0,01 - 0,1) gritty clay saturated 1,0 White clay unsaturated 0,1 (0,4 - 0,6) 0,05 (0,03 - 0,15) saturated 0,2 0,1 amount of C in liquid phase (26) • Kd volume of solute The proportionality coefficient K., in Equation 26 is known as the distribution coefficient (Staley £t__al., 1979, Botha, 1986). In the unsaturated zone the distribution coefficient is related to - 78 - the volumetric moisture content ft, because the volume of solute is equal to the product of the volume of solid phase and the volumetric moisture content 8, amount of C in solid phase volume of solid a amount of C in liquid phase mass of solid amount of C in solid phase /a/ x (27) amount of C in liquid phase where p * density of the solid phase if p s kg.m-3 then the dimensions of K In the saturated zone the volume solute per unit saturated material equals the product of the volume of solid phase and the porosity c. The relationship between the distribution coeffient in the saturated zone, Kds, and the distribution coefficient, K. , in the unsaturated zone is given by: KdU * (9/e)Kd8 Only the hydrogeological aspects of sorption are covered in this section in M far they are applicable to the modelling of the unsaturated zone. The geochemical aspects of sorption are dealt with in section 7.3.4. Neyer and Loots (1984) determined distribution coefficients (K.-values) for the radionuclides 137Cs, 60Co, 90Sr 238 and U in material from the different geological layers at Vaalputs. In order not to increase the surface area of the soil by grinding and hammering, samples were obtained by using auger drilling, and, during preparation, the material was powdered by hand and passed through a 1 mm sieve. The so-called batch agitation-suspension method described by Ryan et al. (1969) was used for the determination. According to Meyer and Loots (1984) this method tends to overestimate the Kd-values as the method maximizes the surface area of the soil and the adsorption reaction is carried out to completion in the batch test - 79 - which ia seldom the case in the natural environment. The values in Table 5.10 must be seen as an upper limit for the K.-values. The a K.-value of a soil-water system is particularly sensitive to the chemistry of the water. Therefore, ground water from boreholes on the disposal site was used during the K.-determinations in the laboratory to simulate rain water that has percolated into the clay. The laboratory measurement of K.-valuea on disturbed samples is fairly easy. In situ measurements in the field, on the other hand, are complicated. The K.-value3 strongly depend on variables such aa mineralogy, particle size, chemistry of the solute and chemical nature of the radioactive species. K.-valusa for use in ground water modelling muat, therefore, be selected with care. 5.14 Soil Chemistry The sandy gritty clay, in which the final disposal trenches are to be located, may be described aa a sequence of palaeosoils formed under arid conditions of low rainfall and high evaporation. The main characteristics of this type of soil are the poor removal of leached soluble salta and the subsequent accumulation of calcium carbonate in the B-hcrizon. Only the influence of the soil chemistry on the hydraulic properties of these soils is discussed here while the geochemical aspects are dealt with in section 7. The water soluble salta in the rock units of the sedimentary profile, were determined by Meyer (1984), with typical reaults shown in Table 5.11. This waa done in order to determine the solute composition necessary for laboratory determination of K.-valuea for the different rock units at the diapoaal aite. The brown sandy gritty clay unit will hoat the radioactive waate to a depth of 8 m. Soil parameter analyses were done on the sand and various clay unite within the brown aandy gritty clay unite to evaluate the suitability of the material from a soil chemical point of view. The samples were taken from the clays exposed in the side walls of the experimental trenchea (Levin, 1985) and the analyaia was undertaken by the Soil and Irrigation Research Institute (Table 5.12). The reaction - + 2+ CaX + 2 Ha » Ka2X + Ca where Ha.X represents the ionic species N»+ on an exchange site of soil colloids and is responsible for variations in the Exchangeable Sodium Percentage (ESP) in soils, which is defined as; Exchangeable Sodiua -1 ESP » (mcq.lOO g Soil) x 100 Cation Exchange Capacity (meq.100 g_1 Soil) where, exchangeable sodium is that sodium which is held by adsorption and the cation exchange capacity is the sum total of the exchangeable cations that the soil can adsorb; both being expressed in meq (milli-equivalents). Sodic soils are defined as soils with ESP values greater than 15 % and are unique in their hydraulic properties because of their potential to retard the downward movement of water when irrigated with pure water eg. rain (Kautsky, 1983). In agriculture, sodic soils are undesirable partly because irrigation waters are chemically prevented from infiltrating into the root zones. This is due to the colloidal fraction which becomes dispersed or deflocculated when in contact with pure water. The brown sandy gritty clays present in and around the disposal site (Table 5.12) are considered sodic soils and are therefore favourable for the inhibition of downward moisture movement. In most soils, the cation exchange capacity (CEC) beara a direct relationship to the clay content. Ratios found at Vaalputs indicate the presence of structured mixed clays, like kaolinite - montmorillonlte, which is indeed what Brynard (1983) found. The relatively high ESP values and CBC/clay ratios obtained on the Vaalputs sediments make them a very favourable medium for radioactive waste disposal. Hydraulic conductivities determined on core samples by Van der Watt (1986) showed a decrease in hydraulic conductivity with time. In Fig. 5.23 a decrease in hydraulic conductivity and a resultant decrease in electric conductivity of the effluent during the - 81 - Table 5.10 Average distribution coefficients (K.) for d tbe various rock types (Meyer and Loots, 1984) K. values a 238 0 137Cs 60Co 90Sr Rock Types Loose red sand 2.5 485 1 528 9.1 Calcretized sand 2,5 589 2 295 8,4 Brown sandy gritty clay 6,8 341 1 076 7,1 White clay 1,4 220 1 524 8,3 Weathered granite 3,0 261 578 5,5 Table 5.11 Haerocoaponent water soluble salt analyses on soil samples from auger borehole AW25S13, (Meyer. 1984). Depth in metres: 0-0,7 0,7-2,4 2,4-5,6 5.6-9,0 9,0-lC,2 Type of soil: LRS CS+BSGC BS6C BS6C WC pH (Sat. paste) 8,5 8,5 8,4 8,3 7,8 Anions CO. 120 170 70 60 0 mg.kg HC03 620 560 520 500 460 soil SO4. 200 190 180 110 210 CI 200 220 480 720 880 F 10 9 22 20 21 Cations Ra 440 380 580 680 800 mg.kg"1 K 36 58 44 54 50 soil Ca 48 54 36 38 41 Mg 19 18 18 18 21 LRS » Loose red sand CS * Calcretized sand BS6C » Brown sandy gritty clay WC » White clay - 82 - Table 5.12 Results of chemical analyses on sediment samples from the experimental trenches. Depth zone 0-0,5 m 2,0 to 8,0 m Rock unit Sand Brown sandy Red sandy Greenish gritty clay clay sandy clay Sand X 86,7 47,2 67,7 75,5 Silt X 3,7 16,4 6,6 7,9 Clay X 9,6 36,4 25,7 16,6 pH (Sat. paste) 6,0 7,0 7,2 7,3 Conductivity mS/m 17 870 1190 780 Extractable Ca meq X 1,17 9,92 7,90 3,95 Extractable Hg meq X 0,28 8,68 2,15 3,34 Extractable K meq X 0,30 1,70 1,09 0,65 Extractable Ra meq X trace 7,16 7,26 2,97 Cation exchange Capacity (CEC) 3,07 25,21 1,98 9,95 Ca/Hg ratio 4/1 1/1 4/1 1/1 Inferred ESP X 1 19 43 20 CEC/clay ratio 0,31 0,69 0,50 0,59 determination of hydraulic conductivity is shown. This phenomenon is explained by the dispersion or dissolution of soluble salts taking place when water is passed through the clay causing a decrease in hydraulic conductivity. - 83 - lu 600"g ÍU "1 (No Hydraulic conductivity of sample :1 Electrical conductivity of fceffluent NO 120 HO MO MO 200 TOTAL VOLUME OF CFRUCNT (m(J Figure S.23 Decrease of hydraulic conductivity as a result of the salinity of the sandy gritty clay (Van der Watt, 1986). - 84 - CHAPTER 6 GE0HYDR0L06Y OF THE SATURATED ZONE Leaching of radionuclides fro* the trenches could lead to eventual contamination of the ground water supplies. The characterization of the saturated zone, which is defined as the area below the water table, is therefore a fundamental requirement of disposal site assessment. Freeze and Cherry (1979, p44) summarized the main differences between the unsaturated zone and the saturated zone, of which the following are the most important: (i) The saturated zone occurs below and the unsaturated zone above the water table. (ii) All pore spaces in the saturated zone are filled with water and therefore the volumetric moisture content 6 equals the porosity c. This is not the case in the unsaturated zone where pore spaces are only partially filled. (Ill) Below the water table the pressure is greater than atmospheric pressure. (iv) The hydraulic head is measured with a piezometer as opposed to a tensiometer in the unsaturated zone. (v) In the saturated zone, the hydraulic conductivity is constant and does not depend, as in the unsaturated zone, on the pressure head. Studies of the saturated zone at Vaalputs included measure.v«nt of water levels, sampling for and conducting chemical analyses, dating of ground water, as well as performing pumping and injection tests. Initially a regional geohydrological survey was conducted over an 2 area of 29 300 km , talcing approximately one water sample per Figure 6.1 Locality plan of area kriged with outline of kriglng contour area (Caaiaani-Calsolari, 19«5). - 86 - 35 km (Fig. 6.1). Later, an area of 5 940 km , was surveyed in more detail by monitoring every available borehole and increasing 2 the density to about one sample per 30 km . This area, with Vaalputs near its centre, is covered by the following maps in the 1:50 000 series; 2918CD, 2918DC, 2918DD, 3018AB, 3018BA, 3018BB, 3018AD, 3018BC and 3018BD (Levin, 1983a). Finally, investigations were concentrated on the radioactive waste disposal site itself. 6.1 Mature of the Aquifers Aquifers may be classified as uncosflned or confined, depending upon the presence of a piezometric surface or a water table. In the absence of overlying impermeable state, the upper surface of the zone of saturation is the water table, or phreatic surface. More precisely, this is defined as the surface at which pore water pressure equals atmospheric pressure and is revealed by the level at which water stands in a well penetrating the aquifer (Todd, 1959). Two main aquifer types are observed, namely unconfined and confined. A third aquifer type is called a leaky aquifer and is associated with confined aquifers. An «confined aquifer is one in which the water table serves as the upper surface of the zone of saturation. It is also known as a free, phreatic or non-artesian aquifer. The water table undulates and changes in slope, depending upon areas of recharge and discharge, pumpage from wells and permeability of the strata. Rises and falls in the water table correspond to changes in the volume of water in storage within an aquifer. Confined aquifers, also known as artesian or pressure aquifers, occur where ground water is confined under a pressure greater than atmospheric by overlying, relatively impermeable strata. In wells penetrating such an aquifer, the water level will rise above the bottom of the confining bed to the piezometric surface. Rises and falls of water in cased wells penetrating confined aquifers result primarily from changes in pressure rather than changes in storage volumes. Hence confined aquifers have only small changes in storage and serve mainly as conduits for conveying water from recharge areas to location* of natural or artificial discharge. - 87 - The confining strata causing, per definition, confined aquifers is never completely impermeable. Slow inflow takes place from this less permeable rock into the adjacent confined aquifer. Such an aquifer is called a leaky aquifer. Aquifers comprise nonindurated sedimentary deposits, fracture zones in dense rocks, porous sandstone beds, solution channels in limestone and many other rock types. It is therefore important to define the hydrological properties of the more important rock types in the area. Each rock type has its own primary and secondary hydrological properties, which can be described as follows: (i) Primary or syngenetic hydrological properties of rocks are inherent characteristics such as crystal cavities, porosities, permeabilities, etc. These properties are restricted to rocks unaltered by secondary processes, agents or forces such as weathering, folding and jointing. (ii) Secondary or epigenetic hydrological properties are those formed by events subsequent to the formation of the rock, such as faulting, weathering, folding and jointing. These are the more important hydrological properties of most crystalline and metamorphic rocks as they control the occurrence, storage and movement of ground water. During the regional survey aquifers were found to be contained within three distinct classes of rock, namely sedimentary, volcanic and fractured crystalline rocks. Aquifers in sedimentary rocks sre those in rocks of the Dwyka Tillite Formation of the Karoo Sequence to the east of Vaalputs and the shallow river gravels in the escarpment area. In sediments of the Karoo Sequence, water movement is along bedding planes, cleavages, joints or fsult plsnes. These waterbodies constitute aquifers of the confined type. In the river valleys ground water is contained in the sand and gravel, filling depressions in the river beds. Because of low rainfall and small volumes, these are not important sources of ground water. - 88 - Aquifers In volcanic rocks are restricted to the zone of kinberlltic and basaltic lntnisives along the escarpment and towards the north of Vaalputs. They do not solely represent aquifers in volcanic rock as water not only occurs in fractured volcanic rock but also in sediments or breccias filling the craters. Due to confining clay layers in the sediments these aquifers constitute confined aquifers. One such aquifer was drilled into on the southern boundary of Vaalputs. The most Important aquifer in the area is located in the fractured crystalline rocks» which also underlie the disposal site. In contrast to the Intrinsic and syngenetic permeability of sands, gravels and clays, the permeability of fractured rocks is epigenetic and of tectonic origin which include pressure relesse due to unloading of overburden. Hear the land surfsce the fractures tend to be larger or more pronounced than at deeper level, and it is generally accepted that the fractures tend to decrease in opening size and number with depth. Water is confined to fractures, weathered joints and to contacts with basic lntrusives and therefore constitute confined aquifers (Levin, 1983a). These basic intruslves are associated with features such as "steep" structures and megabrecclas that transect the entire area (Lombaard and Schreuder, 1978). However, none of these features have been identified in the immediate vicinity of the disposal site. 6.2 Depth to the Piezometrlc Surface As mentioned previously, wster struck in the fractured crystalline rocks is confined. It will therefore rise in the borehole to the plezometrlc surface. For example, water was struck in borehole WW 4 at 105 s and the water level rose to 56 m, which was the hydrostatic pressure level of the water in the aquifer at that locality and time. The depth to the free wster tsble defines the thickness and distribution of the unsaturated zone and is dependent on topography and climate. The depth to the water table is in general deeper under hills and less under low lying areas. The depth to the water - 89 - level is an indication of the minimum depth that water interception could be expected. The water level is dynamic and is influenced by recharge, withdrawal, run-off, the earth's tides, seismic events and any changes in atmospheric pressure (Davis and De Viest, 1967; Freeze and Cherry, 1979). Water-level recorders installed at Vaalputs showed diurnal changes in the order of 20 mm per cy< e. This and all the other fluctuations, pumping excluded, are not regarded important at Vaalputs considering a piezometric level of 55 m below surface. 2 A regional survey was carried out covering an area of 29 300 km by Levin (1983a). During this survey water levels were measured and collar heights estimated from 1:50 000 toposheets. Camisanl-Calzolari (1985) geostatistically analysed the data using the kriging technique. Data from 584 boreholes spread over the area shown in Fig. 6.1, were used in the exercise. The kriged results for the depth to the water level are shown in Fig. 6.2. For the larger part of the area the water level is 36 m deep below the surface, with the deepest values in the northern part of the sand-filled Koa River drainage. Deeper levels normally correspond to areas of thicker surfici«l cover, such as the area south of Vaalputs where water levels of up to 100 m were recorded. The disposal site is situated on the edge of an area of deeper ground water which extends south of Vaalputs (Fig. 6.3). Within the disposal site, Fig. 6.4, the piezometric surface lies between 50 and 60 m below surface. This implies that any direct recharge of ground water in and around the disposal site will have to penetrate 15 to 30 m of surficisl material, then 2 to 3 m of weathered granite and 20 to 30 m of fractured granite before reaching the water table. Botha (1986) has shown that the saturated fractured granite may be regarded *B a porous zone. However, it is blanketed by an impervious clay layer, reducing any large scale recharge and minimizing ground water circulation. The deep piezometric level could therefore be seen as a favourable parameter for isolating radioactive waste at Vaalputs. - 90 - 6.3 Elevation of the Piezometric Surface The piezonetric surface of a confined aquifer is an imaginary surface coinciding with the hydrostatic pressure level of the vater in the aquifer. Boreholes generally have to psnetrate this surface in order to intersect water-bearing strata. It is possible to find large areas or blocks of little/or unfrastured rock where this surface is absent. At Vaalputs several boreholes drilled up to 150 • were dry and today they contain no more than a metre of seepsge vater. In practical terms the piezometric surface is therefore discontinuous or Interrupted in the impermeable or unfractured localities. The topography of the regional piezometric surface, with reference to a datum level, such as ses level, resembles the surface topography of the area. The direction of flow can be inferred from piezometric level contour maps. The contour lines are called equipotential lines and the direction of flow is perpendicular to these lines. The use of contour maps of elevation of the piezometric surface is important in estimating the rate and direction of ground water movement. The distance between contour lines is a measure of the gradient of the water level and an Indication of the flow velocity. Widely spaced contours may mean highly . transmissive rock and relatively slower ground water velocity. Steep or narrowly spaced contours are associated with rocks of lower transmissivity. The higher hydraulic gradient suggests a higher flow velocity. A contour map of the kriged piezometric level values by Camisani-Calzolari (1985) is shown in Fig. 6.5. The widely spaced contours on the Bushmanland Plateau and in the Koa Valley would suggest slow-moving or even stagnant ground water. In the Buffels and Olifants drainage areas steeper gradients are an indication of higher rate of movement. Ground vater flow is mainly the result of differences in topographic elevation according to Bredehoeft ejt__ai.» (1982). It is thus - 91 - m ABOVE 116 106 - 116 96 - 106 86 - 96 76 - 86 66 - 76 56 - 66 46 - 56 36 - 46 26 - 36 16 - 26 6-16 BELOW 6 UNDEFINED AREA KILOMETRES Figure 6.2 Kriged results for the depth to the water leyel. Regional geohydrological survey (Camisani- Calzolari, 1985). - 92 - 30°05'- — 30° 05' 30°10'H —30°1om0 ' 30°15'- 30°15' 18° 30* 18°35' LEGEND • BOREHOLE LOCALITY ^70^ DEPTH OF THE PIEZOMETRIC SURFACE ( 10m CONTOUR INTERVAL) _^EOGE OF THE PLATEAU o i i: 3it 5 km Figure 6.3 Depth to the piezoaetric lerel for Vaalputa and aurroundinga. - 93 - MON 17 • S1O0 M0NI3 ,,GWS3 451.00 - L E G E N 0 * M0N 57.00 54,15 "1 i + Percussion borehole ' <| 5J.45 0^52.57 • Depth fo *he piezome*ric ievet (m) GWBl • 5 2. «5 MON;^ 54.90 | i MON3 — 5S. 30 \\ "••"'"•54.45 ! MONlï 0 100 200 300 400 500 i I • 5«.« i SCALE MONl^i 54.7. 0 MON 6 56, W MONO • MONK 56.70 57,20 PBHiS$59,0» // VAALPUTS G"»'*5M0 Figure 6.4 Depth to the water level in the vicinity of the disposal site in water-bearing monitoring boreholes. possible to determine the direction of water flow from the disposal area by using flow-lines perpendicular to the contours. In this way it is shown that ground water flows east to north-east towards the Koa Valley. The nearest point of discharge from the disposal site is Bosluispan in the Koa Valley, a distance of approximately 50 km. Discharge occurs in the form of evaporation in the salt pans as no surface flow takes place in this drainage system. The piezometric surface around Vaalputs is illustrated in Fig. 6.6 and it can be seen that the disposal site is located well east of the watershed in an area with relatively flat gradients. The subdued topography of the piezometric surface at the disposal site itself is well illustrated by the detailed plan in Fig. 6.7. No attempt was made to contour the piezometric level as it is clear that the surface is relatively flat with a slight gradient to the east or north-east. - 94 - h <-H 8 8 2 8 0 rt e> i* (* IW o samawoiDi Tu> 0) U J>=> i-l O 3 4) (0 00 41 M r-t (0 33ttOkl*4OO>COI>-«0tt-*C'3 13 (U c 00 •rol eoeoooneowr-cvir-CMr-cvii'- •H ao H « * PÍ a I I I I I I I I I I I 9 2 3 60 •H I* - 95 - 30°05'- 30°05' 30°10' - —30°10' 980 990, 30oic'° 15 . •30°15' 18<> 30' 18*35' LEGEND • BOREHOLE LOCALITY 98(K WATER ELEVATION CONTOUR (10m INTERVAL) y o 1 2 3 u s ^^ WATERSHED ^Ë^&Ë^SÍS^ ^^ km Figure 6.6 Elevation of the piezoaetric aurfaee for Vaalputs and surroundings. HON 17 • GWB3 KS.40 HON 12 nwti * „ • 5Í.ÏS L E G E N 3 MONi^nvss WON 10 + Percjssion borehole CWB<. I »55.73 • tlivi'ion of pitzomttric Itvtl (numsll 955 Í57.H HCN2 mso M0N3Í «1»SS.tO It GWBS TON 15 • 0 MO 200 300 U)0 500 m •S4.7* • *5*.30 SCALE M0N4. •55.00' l_ _MON_6_. HON 13 »5*50 M0N1I. I I V* ^ I • •5 ».70 PBH16 • W7.2» VAAIPUTS GWB1 • »54.10 Figure 6.7 Elevation of the piezoaetric surface in the vicinity of the disposal site as aeasured in the water-bearing Bonitoring boreholes. The flat piezometric surface underlying the disposal site must be seen as a valuable asset to the facility. In the event of serious leakage of radionuclides from the trenches into the ground water, large scale pumping of the ground water underneath the site, will lower the piezometric level and create a local basin effect. In this way contamination can be confined to a small area and spreading to the environment reduced. 6.4 Transmisslvity and Storage Characteristics Ground water flow in fractured rocks is different from that in homogeneous porous granular media. The nature of fracturing can change over short distances as fracture systems resulting from different tectonic events (faulting, folding and shearing) may display different hydrological characteristics. - 97 - Fracture systems are made up of fractures or fracture zones occurring as closely-spaced highly interconnected discrete fractures, shear zones and joint sets. The most important properties controlling flow through fracture systems is fracture orientation, spacing, opening, length, fracture interconnection and the stress field. Fracture flow may also be influenced by material such as clay, calcite etc. partly filling the fractures. According to Gale (1982) the blocks of rock between fractures in granite have -8 —1 a hydraulic conductivity of less than 10 m.s and therefore significant flow can occur only through the fracture system. In contrast to fracture zones the openings in shear zones may be filled by mylonite or other minerals depending on their ages and their stress history. Shear zones may be up to tens of metres wide and extend for kilometres. The rock material in shear zones is normally brecclated and deformed. Due ?o the ingress of water and oxygen, parts of a shear zone may be highly weathered and clayey, reducing permeability in that part of the shear. This is the case at Vaalputs where several boreholes drilled into a shear zone only produced moist clay but no water. However, a borehole drilled into the unweathered brecciated part of the shear produced 23 000 litres per hour. Orientation of fractures in outcrops usually reflects what may be expected below surface, but if no outcrop occurs in the area of investigation several techniques can be used to determine structure orientation such as orientated core drilling, down-the-hole calliper or video recording. Hallik et al.f (1983) used the radial vertical sounding (VES) method in India to outline the predominant directions of fractures in granitic rock obscured by surficial cover. Test pumping and packer testing have become well established methods of evaluating fracture flow in granites at radioactive waste disposal sites, as reported by Strips in Sweden (Witherspoon et al.. 1981), BRGM in France (Bertrand et al.f 1981), Whiteshell in England (Davidson, 1981) and Cornwall (Bourke ejL_ftl., 1981; Bourke et al.. 1982 and Heath and Durranee, 1985) and Climax, Nevada Test Site in the USA (ISherwood et al.. 1982). At Vaalputs boreholes drilled for monitoring purposes were also subjected to pumping and packer testing in order to obtain information about the transmissivity and storage characteristics of the granitic basement. 6.4.1 Test pumping During the initial stages of the investigations boreholes 6WB 1 to GWB 9 plus PBH 16 were drilled to investigate the granitic aquifer underlying the area (Levin and Jamieson 1986). Of these only GWB 2 and GWB 6 did not yield any water. Boreholes GWB 7, GWB 8 and GWB 9 were observation boreholes to GWB 5, GWB 3 and PBH 16 respectively. The positions of these boreholes are shown in Fig. 6.8 and the test results in Table 6.1. Subsequent to the selection of the final disposal site 19 boreholes, HON 1 to 19, were drilled for monitoring purposes at selected positions around and in the vicinity of the disposal site as shown in Fig. 6.8 (Levin and Jamieson, 1986). Of these boreholes only 7 yielded significant quantities of water while the rest were dry. These boreholes were drilled to a depth of 100 m, but in HON 2 drilling was terminated at 96 m because of the hydrostatic pressure and H0H 14, 15, 16, 18 and 19 were drilled to 150 m without intersecting any ground water. Based on the test results, shown in Table 6.1, the distribution of ground water in the disposal area is restricted to a east-northeast striking zone as indicated in Fig. 6.9. The direction of strike of this zone fits into the regional structural pattern as interpreted by Andersen (1988). Interpretation of the detailed magnetic and resistivity surveys covering the disposal area indicates that the watp.r-bearing zone occurs at the intersection of a number of linear structures. The higher yielding boreholes are located on these inferred linear structures or near possible intersections. Test pumping was performed on eight of the highest yielding boreholes. While pump testing boreholes, all boreholes in the immediate vicinity were monitored for drawdown using continuous chart recorders. These pump tests were carried out by the Institute for Ground Water Studies and reported by Hodgson (1984, 1986). - 99 - Table 6.1: Depth of water interception and pop tested yields Borehole Ho. Final depth Water interception Yield • • l.h"1 PBH 16 100 73 2 400 GVB 3 100 55 14 000 GWB 5 78 66 14 000 KOH 2 105 98 and 105 10 400 HON 4 100 65,8 and 82 10 400 HON 10 102 93 8 750 MOlf 11 100 81 6 700 HOH 12 96 88 and 93,5 18 000 The drawdown curves for the observation boreholes GWB 7, GWB 8 and GWB 9, test pumping during 1984 are shown in Fig. 6.10. These plots are on a linear scale for better comparison of the curves. Hodgson (1984) points out that the aquifer intersected by GWB 3 and GWB 5 does not conform to porous flow while that intersected by PBH 16 does conform. He concluded that the steep drawdown curves for GWB 7 and GWB 8 are due to dewatering as result of a decrease in the permeability characteristics of the aquifer. This decrease in permeability is an inherent characteristic of some fractured aquifers with limited or restricted interconnection between fractures. This conclusion was confirmed by the very slow recovery of the water level after pumping had ceased. Test pumping PBH 16, located on a possible fault, showed a response typical of a homogeneous and isotropic medium. Botha (1986) used the data from the observation borehole GWB 9 to prove that the flow during this test pumping satisfied the Theis equation (Fig. 6.11) and that flow in the aquifer may be regarded as porous flow. Results from the other boreholes test pumped (GWB 3 and GWB 5) were also subjected to this test and the only exception was borehole - 100 - •nOHi» líSEKO • won;» • HON IT «ON 11^ OOHSA •*5»rti WW) NO r- + n[ • Agger 8or.--.-lis «CK :<( •HON 10 *!*"ti **'»*•» •GW84 • »0N "4 W JO Sib A* 25 STj • «CN2 • j|M0N4 4 ay» 2« . «HON J NOR a 4 ewes • «3N1Í ncN?)> o no loo no UM soon >. ..«iSPi. • NON-J GWI PSHTS#* " • GWB1 Figure 6.8 Locality of the monitoring and other relevant boreholes in the vicinity of the disposal site. CD riï'f'ii Cry ion» • w»t»rb*aring 6or»nol# 500 1000 m S Ory Dorrhoit Stil» Figure 6.9 Generalized plan of the dry and vater-bearing zones in the vicinity of the disposal site. - 101 - GWB 3 which deTÍated only slightly fro» the water-level response predicted by the Theis solution. Botha (1986) reasoned that this deviation is the result of a pumping rate that was too high but emphasized the fact that the difference in the two curves in Figs. 6.11 and 6.12 demonstrates the presence of inhomogeneites in the granitic aquifer. During the latter part of 1985 fire of the newly drilled Monitoring boreholes were test pumped and reported by Hodgson (1986). HOH 11 reacted similarly to PBH 16 while the others were significantly dewatered during the pumping tests, as CUB 3. The concepts of transmissivity T and storativity S were exclusively developed for analysing well hydraulics in confined aquifers. The transmissivity of the aquifer determines the ability of the aquifer to transmit water through its entire thickness. Storativity is dimensionless and Freeze and Cherry (1979, p60) define it for a saturated confined aquifer as the volume of water that an aquifer releases from storage per unit surface area of aquifer per unit decline in the component of hydraulic head normal to the surface. Tranamissivity T for a confined aquifer of thickness b is defined as T s Kb where K » the saturated hydraulic conductivity (m.s~ ) b = confined aquifer thickness (m) It follows that if K has dimensions m.s~ then the dimensions of T 2 -1 is m .s in the SI metric units. The storativity or storage coefficient Ss is defined (Freeze and Cherry, 1979, p59) as S * S/b / /OBSERVATION HOLE GWB9 PUMPING AT PBH16 «^S»E w.r -l - z 2 -1 -2 PUMPING RECOVERY -3 X 28B0 5760 8640 11520 TIME IN MINUTES Figure 6.10 Llnoar plota of vatar laval drawdowns and recorarlea during pumping taats on various boraholaa. .125 0.000 I I > > | I I I I | *• »• I > \JB** * » • I > • -.125 § i -.250 -.375 -. 500> -1.6 -1.2 -.8 -.4 0.0 .4 log(t) (t in d) Figure 6.11 Drawdowns observed <+) sad computed (-), fro» a non-linear leaat aquarea fit of the Thela solution, la borehole GHB 9 (Botha, 19S6). - 104 - «here S * pg(* • e 0 ) * Specific storage (m~ ) p = fluid density kg.sT -2 g 3 acceleration doe to gravity m.s « * aquifer compressibility m .H c » porosity /3 » fluid compressibility m2.*-1 The storage capacity of fractured rock is generally very saall. Because of limitations on continuity of fractures and difficulty of movement of water through constrictions, the transmitting capacity is not easy to predict. However, using the data obtained during the pumping tests, reliable values for T and 5 nay be calculated. These values sre presented in Table 6.2 for the eight boreholes test pumped. According to Freeze and Cherry (1979, p60) the range for S -2 —4 values is between 0,5 x 10 and 0,5 z 10 in confined aquifers while T valuea for fractured rock and a confined aquifer thickness of 100 n would both be in the order of 0,1 to 100 • 2 .day -1 . Hodgson (1986) reported local and regional values for the transaissivity and the storage coefficient (Table 6.2). The local value concerns the immediate surroundings of the borehole sites, whereas the regional value includes the furthest responding observation borehole ± 500 m away. 6.4.2 Packer tests Inflatable double packers were used, st a constant spacing of 5 netres between packera. The results were reported by Hodgson (1984, 1986) who pointed out that injection pressures were limited to s maximum of 800 kPs because of the deep water level in the area (50-60m). This wss done to ensure that the presaure did not open joints or fracture rock. Hodgson (1984, 1986) reported the results of packer tested sections, above and below the piezometric level, as transmiasivities 2 -1 -1 (a .day ) and not permeabilities (m.s ). The resson for using trrnsmissivities even in the dry part of the borehole, is the fractured nature of the m- rial packer tested. A packer spacing of -1.00 -.50 0.00 log(t) (t in d) Figure 6.12 Drawdowns observed (+) and coaputed (-), fro» a non-linear least squares fit of the Thela solution. In borehole GHB 8 (Botha. 1986). - 106 - 5 m was selected and transmissivities were calculated over this thickness. Permeability is equal to the transmissivity measured over 1 m thickness. In order to report the packer tests results as permeabilities would require subdividing the transmissivity values by 5. Should the transmissivity over a 5 m interval result from only one fracture, then the permeabilities obtained by subdivision for the other four 1 m intervals, would be meaningless and incorrect. The packer tests at Vaalputs were carried out to investigate the permeability distribution of the fractured rock both in the unsaturated and the saturated zones. Packer tests had to start below the base of the casing which sealed off the overburden and weathered zone. Packer testing was performed on the water-bearing GWB boreholes and all the MON boreholes. Additional information on the nature and frequency of fracturing of the granites was obtained from a video survey of selected boreholes, and the drilling of four diamond core drillholes, one next to a dry borehole and the other three next to water-bearing boreholes. Diamond drillhole DDH 1 was vertical and drilled next to HON 14 which was dry down to 150 m. DDH 3 and DDH 4 were 30 inclined boreholes at right angles to each other, and drilled to intersect the water-bearing structures in HON 4. Borehole DDH 5 was drilled at another 30° incline at HON 11 to intersect the water-bearing structure observed in this water borehole. The results of the packer tests for a dry borehole and a water-bearing borehole are shown in Figs. 6.13 and 6.14 respectively. Also shown in these figures is the fracture density pattern recorded in the adjacent diamond drillholes. In the dry borehole HON 14 (Fig. 6.13) there is a fair correlation between fracture density and flow measured over 5 m intervals, especially above the piezometric level. However, the transmissivity is significant throughout the borehole and does not depend on the number of fractures per tested section. In the water-bearing borehole HON 11 (Fig. 6.14) there seems to be less correlation - 107 - Table 6.2: Result* of pumping tests on boreholes at Vaalputs (Hodgson, 1986) Borehole Number Transmissivity Storage m^.day-l Coefficient GWB 3 30 1 x 10"A 6WB 5 25 9 x 10-5 PBH 16 26 6 x 10-5 HON 2 (Local) 13 No observation MON 2 (Regional) 4,1 hole HON 4 (Local) 37 8 x 10-5 HON 4 (Regional) 3,2 3 x 10"5 HON 10 (Local) 8 1 x 10-5 HON 10 (Regional) 1,3 3 x 10~6 HON 11 (Local) 2,7 4 x 10"6 HON 11 (Regional) 12 3 x 10-5 HON 12 (Local) 45 7 x 10-5 HON 12 (Regional) 3,3 6 x 10"6 between the three parameters except at the point of water interception. It must be concluded that it is not the number of fractures per tested section that is important but rather their interconnection with other major fractures that determine the ability of the rock type to transmit water. Hodgson (1984) is also of the opinion that the main flow occurs through fractures, although some flow through the weathered granite matrix is also pobiible. The nature of the transmissive zone above the water level was revealed by a down-the-hole video recording and joints and fractures in the water-bearing percussion boreholes (Table 6.3). The majority o of these structures are horizontal or dipping at less than 45 . Freeze and Cherry (1979, pl60) refer to LeGrand (1949) who attributed the occurrence of near-horizontal fractures in granite, parallel to ground surface, to stress release caused by erosion of overburden. According to him the frequency and aperture of this type of fracture decreases rapidly with depth, and at Vaalputs horizontal fractures are virtually absent by the time the piezometric surface is reached between 51 and 58 m deep (Table 6.3). Below the water level the water-bearing features are usually single open fractures as seen in the diamond core and the video recording. In borehole HON 4 water was struck at 65-66 m and 82,1 m. The fracture at 66,5 m is horizontal while that at 82 m is almost vertical. The TV-survey showed that the fracture producing the high yield in MON 12 is a single fracture while that in HON 11, producing only one third that of MON 12, is a broken zone. Although the results for PBH 16 showed a highly permeable water-bearing structure this borehole tested only 2 700 litres per hour. Zero transmissivities were rare as shown in Fig. 6.15, even in the dry boreholes, and only in HON 18 was a significant impermeable zone recorded. Hodgson (1984) noted a decrease in transmissivities in the unsaturated zone when the same borehole was tested twice on the same day. This he ascribed to the swelling of clay minerals in the fractures or weathered zones after the first injection test. He further noticed a tendency for the transmissivity to decrease with depth even below the water level. This confirms the findings of Gale (1982) who analysed a large amount of transmissivity data recorded in fractured crystalline rocks. A geological investigation of the drill core shows that, although the rock formation is crystalline, both fine and coarse grained granitic phases are present, which have also been intruded by basic rocks. A large percentage of the joints and fractures parallel the foliation. However, the water-bearing structures are not associated with a particular rock type or contact between different rock types. Water-bearing features, therefore, seem to have formed during the various periods of tectonism recorded in the area (Andreoli el fil., 1986). As stated previously (6.4.1) the water-bearing zone at Vaalputs is associated with the intersection of faults and shear zones as shown in inset 8 of Fig. 3.1 6.5 Conclusions Taking cognizance of all the geohydrological results obtained thus far from investigations in the saturated zone, the following conclusions can be drawn: - 109 - Table 6.3: Dip off proainent joints and ffractures observed by the video recordings in borehole HOH 4 (Hodgson, 1986). Depth of joint Dip of joint (m) (degrees) 24,4 80 25,7 0 29,1 0 31,0 40 51,2 0 52,1 0 54,9 80 Water level 66,5 0 81,4 80 82,1 80 83,2 80 84,0 80 84,2 80 87,3 60 88,8 60 90,0 60 92,2 30 92,6 80 (i) The distribution of ground water in the disposal area is restricted to a north-east striking water-bearing zone. The direction of strike of this zone fits into the regional structural pattern and the geological and geophysical information indicate that this zone occurs at the intersection of a number of linear structures. (ii) The fact that zones exist in completely dry boreholes with similar transmissivity to that in water-bearing boreholes, 00H1 HON 11 0DH5 Fracture density Transmissivity Fracture density fractures. 15m r1 DDH5 m2. day"' fractures ,(5m)"' 00H1 Water -4 -3 -2 -1 -0 Flow at 100 k PQ m3.day_1 (Log scale) I'Xyl Transmissivity IZ'h'A Granite -* -3 -2 -1 -0 Flow at 100 k Pa r^^ Flow Egg} Overburden in», day-» (Log scale) jtV*H Transmissivity Granite Overburden Figure 6.13 Correlation between transaissÍTÍty Figure 6.14 Correlation between transaissÍTÍty and fracture density in a dry and fracture density in a water bearing borehole. - Ill - is an indication that these "dry" ireas are isolated from the "wet" areas with insignificant interlinking fractures. This again suggests that the majority of the water-bearing structures must be sub-vertical because horizontal structures would convey water into large areas and would hare resulted in a higher success rate of water interception. (iii) There is a definite decrease in transmissivity with depth, the unsaturated zone below the overburden being far more transmissive than the saturated zone below the piezometric level, or for dry boreholes at greater depth. (iv) Test pumping in the water-bearing zone of the disposal site has shown that some of the water-bearing structures are linked over long distances. In one instance response in the water level was evident 500 m away, within two hours after pumping commenced. Botha (1986) has shown that flow within these structures conforms to porous flow. (v) The general geohydrological behaviour of the aquifer underlying the disposal site can be regarded as very favourable for a radioactive waste disposal site for the following reasons: Firstly, in spite of the high transmissivity of the unsaturated zone below the overburden, the depth of the piezometric level (55 m) would give migrating radionuclides a long residence time before reaching the saturated zone. This is important in the case of radioactive waste which will decay and be harmless on reaching the piezometric level. Even if it reaches the depth of the piezometric level it may not encounter a water-bearing structure, but an isolated "dry" zone where only extremely slow seepage takes place. Secondly, the piezometric surface underlying the disposal site is relatively flat, suggesting a slow rate of movement, towards the fossilized Koa Valley about 50 km away, which is the nearest point - 112 - TRAMSMISSIVITY a2, day'1 LOG SCALE WATER BEARING DRY Figure 6.15 Average transaissivity in some dry and water-bearing boreholes to illustrate the homngenous) traoaaisaivity above the water table (Hodgson, 1986). of discharge. Discharge through the process of evaporation is extremely slow. Boreholes in the direction of movement are sparse and water use is low. It is therefore highly unlikely that the radionuclides would overcome all the geological and geohydrological barriers to reach the Vaalputs site boundary within the statutory prescribed 300 years. Thirdly, in the improbable event of radionuclides reaching the saturated zone, corrective action can easily be instituted. Heavy continuous pumping would lower the piezometric level and cause a basin effect with ground water moving toward» and not away from the disposal area. The interconnection of structure» over long distances within the water-bearing zone, would make it possible to effectively clear the aquifer of pollutant. - 113 - CHAPTER 7 HYDROGEOCHEMISTRY It is known that the chemical composition of ground water is the direct result of physio-chemical changes undergone by rain water percolating down to and movement in the saturated zone. The concentration of various ionic species present depends on factors such as climate, quantity of water, soil thickness, vegetation, the rate of movement of the water or contact-time with the rock and the mineral assemblage of the rock type. It would therefore be appropriate to consider the hydrogeochemistry of the unsaturated and saturated zones as well as the geochemistry of the relevant aquifers. It is also important to consider the setting of the Vaalputs disposal site within the existing chemical concentration gradients and use natural occurring isotopes to investigate the time it has taken for these gradients to develop. A discussion of chemical concentration gradients in this chapter is followed by a site-related discussion of the geochemical processes encountered in the unsaturated and saturated zones. It is this geochemical make-up of the ground water at the site that would control the migration of radionuclides in the event of a leakage. A monitoring program has been established as a timely detection system for any spread of contamination, and to guarantee the integrity of the site. 7.1 Regional Hydrogeochemical Setting of the Disposal Site The regional water sampling program that ran concurrently with the water level survey (Chapter 6) formed part of the site suitability investigations recommended by Corner and Scott (1980). Sampling was done in accordance with the procedures prescribed by Levin (1983b). During the 1983 survey approximately 850 samples were taken. Samples were analysed nor brth major ion and trace elements. Major ions included Ma*, K*. Ca2+, Mg2* and Si, P", Cl", 2- S0. , MO., while trace elements Included Al, As, B, Be, Cd, Co, Cr, Cu, Fe, Ita, Ho, Hi, Ti, U, V and Zn. In addition, pB, 2- - Eh, CO. , HCO , conductivity and temperature were measured on site. The initial interpretation of the results was reported by Levin (1983a). As a result of the smaller area considered by the kriging method (Fig. 6.1) the number of samples were reduced to about 584 which were then geoatatistically treated by Camisani-Calzolarl (1985). The main objective of the geostatistical investigation was to scrutinize the data for the presence of any economic minerals which would render the site unsuitable. 7.1.1 Vater chemistry 7.1.1.1 pH and temperature The pH of the ground water varied between 6,5 and 8,4 with a mean of 7,06 which falls well within the range for natural ground vater as indicated by Baas Becking et al.r (1960). These pH-values are in agreement with those obtained by Bond (1946, p.33) for the granite gneiss ground water from this area, which ranged between 7,0 and 7,9. pH-determinations were carried out on site in order to reduce the effects of CO.-loss and aeration, as discussed by Garrels and Christ (1965, p. 129-131). They stated that if the time delay between the taking of the sample and analysis is such that equilibration with the atmosphere takes place, an incorrect (too high) pH may result. The temperature range of the ground vater at which the pH valuea were read, vas between 18°C to 26°C. Contours shoving the thermal gradients, ss measured in the ground vater, are depicted in Fig. 7.1. There is a component of ground water flow induced by the presence of a thermal gradient from higher to lover temp areas (Freeze and Cherry, 1979, p.508). As seen in Fig. 7.1, the thermal pattern in the vicinity of Vaalputs is fairly complicated and probably distorts the normal flov associated vith the hydraulic gradient. The reason fotf the higher temperature values in the eastern part of Fig. 7.1 is difficult to explain but could be due to - 115 - as 225' 215' 205 195 18»- 17* 1*5 IS5-I 145 ABOVE 23.9 GO Eg 135 23.4 - 23.9 02 22.9 - 23.4 22.3 - 22.9 5S us 21.8 - 22.3 o 21.2 - 21.B pJ|05 20.7 - 21.2 20.1 - 20.7 95 19.6 - 20.1 (15 19.0 - 10.6 18.5 - 1S.0 75 17.9 - 18.5 BELOW 17.9 «5 UNDEFINED AREA 65 45- 35- 25 15' »• 1» 2» 35 4» 55 115 7» fl» 9» 10» 115 125 13» 14» 165 IS» 175 IBS 19» 205 2 KILOMETRES Figure 7.1 Krlged result» for the temperature of the ground vater. Regional geohydrological survey (Caaisani- Calzolari, 1985). - 116 - dolerite intrusives or radioactive decay as uranium content in the ground water of that area is anomalously high (Camisani-Calzolari, 1985). The lower temperatures observed in the Koa Valley nay be ascribed to cooling by evaporation. 7.1.1.2 Salinity The movement and salinity distribution of ground water is controlled by hydraulic, thermal and chemical gradients. The chemical composition of the ground water will change as long as disequilibrium exists between the water and the rock with which it is in contact. Chebotarev (1955) has shown that the salinity of ground water varies with change in hydraulic gradient, depth of occurrence and the distance from the recharge area. The moat significant changes in salinity take place in the zone of active ion exchange and the least soluble salts precipitate first followed by the more soluble salts. Chebotarev (1955) also suggested the following sequence for the increase of total salinity from recharge to the discharge areas. HCO"-HCOr+cr-Cl"+HCO>cr+SOÍ~-Cl" 3 3 3 4 This sequence, applicable to arid zones, can be regarded as correct for the vertical as well as the horizontal aquifers. Johnson (1975) pointed out that one should find Ca/MgHCO water at the recharge area changing, through base exchange, to a NaHCO. character and then on to Chebotarev's (1955) sequence. He further suggested that, with the increase in total dissolved solids (TDS) and HaCl saturation, the less soluble carbonates are precipitated at what he termed the calcrete line. Beyond this line he envisaged 2- - only halite and gypsum deposits. The SO. + CI character is only maintained if the hydraulic gradient remains measurable. The sulphate is lost if the gradient becomes zero and the water becomes a brine. Schoeller (1959) stated that mineral concentration by dissolution cannot go beyond a certain stage because of the tendency of water to reach a physio-chemical equilibrium with the rock with which it is in contact. This tendency, however, is changed by evaporation, and concentration and precipitation may continue to a point of total crystallisation. - 117 - A quick and easy indirect field Method to determine the salinity of ground water is by way of its electrical conductivity. According to Hatthess and Harvey (1982, p.71), a direct relationship exists between concentration and conductivity. They suggest that an estimate of the TDS of fresh water in mg.i~ be obtained by multiplying the conductivity of the water, in mS.m~ , by the factor 0,65. The contribution of the carbonate and sulphate ions towards the electrical conductivity of the water is much less than that of chloride. Therefore, calcium carbonate and calcium sulphate water have a lower conductivity than a sodium chloride water with the same TDS (Hatthess and Harvey, 1982, p.72). The mean electrical conductivity of the ground waters sampled is 477,2 mS.m~ or a mean TDS of 3 100 ag.i~ . A contour map of the kriged values is presented in Fig. 7.2. At the disposal site electrical conductivities range between 350 and 550 mS.m~ (Table 7.1). Higher values to the north and northwest of Vaalputs correspond with the Koa Siver drainage which is regarded as a discharge area by Levin (1983a). There is a steady increase in conductivity and, therefore, TDS from Vaalputs towards the Koa Valley, corresponding with the low hydraulic gradient (Fig. 6.5). Considering Vaalputs and vicinity as an area of recharge, the change in water quality conforms to the chemical sequence, as suggested by Chebotarev (1955) and Johnson (1975) with increased sulphate and chloride concentration being observed towards the discharge point (Bosluis Pan in the Koa Valley), where the sulphate eventually precipitates as gypsum, leaving a sodium chloride brine. The electrical conductivity and TDS do not conform to the individual ion concentrations or chemical composition of the ground water regime. Various graphical methods to interpret hydrochemical data have been developed and the technique developed by Piper (1944) ia particularly useful as it gives an, indication ot the chemical character of the ground water, regardless of concentration. The use of this technique is also discussed by Johnson (1975), Van der Linde and Hodgson (1977) and Levin (1980). Using Fig. 7.4, Johnson (1975) explained the diamond-shaped field further: jj mho/cm ABOVE 8949 8347 - 8949 7748 - 8347 7143 - 7745 6541 - 7143 5939 - 6541 5338 - 5939 4736 - 5338 4134 - 4736 3532 - 4134 2930 - 3532 2329 - 2930 BELOW 2329 UNDEFINED AREA 1» ZS 3S 4» 59 89 7S 8S »ft 10» II» 125 136 lift 10 1BÍ. iSTzflJ KILOMETRES Figure 7.2 Krlged results for the conductivity of the ground water in unho.ca(louho.csi=lmS.sf ). Regional geohydro- logical survey (Caaisani-Calzolari, 1985). - 119 - Table 7.1 : Chemical analyses of ground water fro» the disposal site (mg.i ) BOREHOLE NO MOH 2 NONA MOB 10 MOIf 11 HON 12 GWB 7 GWB 3 PH 7,5 7,5 7,1 7,3 6,9 7,3 7,3 Cond.mS.m~ 475 350 500 500 550 400 500 HCO" 405 410 367 354 343 412 355 275 369 372 169 183 < 338 408 CI" 1442 1313 1550 1638 1688 1000 1360 Na+ 1022 768 1023 1023 1055 720 830 K+ 21,5 16,9 20,6 22,9 23,1 18 23 C.2+ 98,8 44,6 103,8 129,3 135,9 40 74 Mg2+ 68,8 43,2 66,6 91,1 94,4 59 90 Si 12,7 11,5 11.9 10,6 12,0 11,3 11,6 Figure 7.3 Interpretation of the diamond-shaped field. (Johnson, 1975). (i) Sodium chloride brines will almost always be plot in the vicinity of point A. (ii) Calcium chloride brines, although rare in hydrology, usualy plot at point B. (ill) Water contaainated with gypsum plots in the region C. (iv) Recent recharge waters plot in the region D. (v) Sea water plots at point E. (vi) Recent dolomitic waters plot in the region F. The bulk of the Bushmanland ground waters plot in the upper half of the diamond-shaped field (Fig. 7.4). According to Johnson (197S) the top half of the diamond-shaped diagram represents static and other unusual waters, high in Hg/CaCl and Ca/MgSO.. He stated that the chloride character of the ground water becomes evident as the gradient flattens, or the transmissivity decreases and therefore, as the regime becomes stagnant. Tredoux (1987) queries Johnson as he found that, in the dynamic unconfined Atlantis aquifer, the ground water also plots in the upper half. In contrast to the Atlantis aquifer the gradient on the Bushmanland Plateau is rather flat and it would therefore represent the regime originally proposed by Johnson. The lower half of the diamond-shaped field contains ground water normally found in a dynamic basin environment, and those commonly encountered in geohydrology. Tredoux (1987) found that in the case of the Auob Sandstone aquifer his data agrees well with the criteria defined by Johnson (1975). The few samples falling within the lower half of Fig. 7.4 are samples from aquifers such as gravels or shallow ground water associated with dolerite sills and dykes in the Dwylca Tillite Formation, and does not represent the main ground water regime. The use of the diamond shaped field was further modified slightly to interpret the large number of samples from the Bushmanland Plateau. The diamond-shaped field was divided into equal areas with each area constituting 0,125 X of the total. Plotting of all the samples collected during the regional survey produced the density diagram shown in Fig. 7.5. The following conclusions regarding the chemical character of the ground water may be drawn from diagrams Fig. 7.4 and Fig. 7.5; - 121 - Figure 7.4 Piper plot of all the samples from the B'jshmanland Plateau taken during the geohydrologieal surrey. (i) The sodium chloride/sulphate dominated character of the ground water is obvious from the concentration of samples + + around 60 X (Na + K ) and about 90 % (S04~ + Cl") in the diamond-shaped field. In the cation field Hg2+ dominates Ca slightly whereas, in the anion 2- field, Cl" is the dominating ion with S04 higher than HC0~ + CO2". (ii) All the samples plot away from the character of sea water (point E on Fig. 7.3) showing ground water which has higher Ca2+/Mg2+ and HC0~ percentages than sea water. Sifliplts ptr 0125% of total irti Figure 7.5 Density distribution for all samples taken during the geohydrological surrey, showing the geocheaical character of the ground vater. (lii) Almost all the samples plot in Johnson's (1975) static and discoordinated regimes which make up the top half of the diamond-shaped field (Fig. 7.3). This confirms a static stagnant regime as interpreted from the hydraulic and chemical gradients. 2- - (iv) The absence of a stronger (CO. + HCO.) component in the chemical character is remarkable. The two samples marked N (Reelsput) and Z (Zwartrand) in Fig 7.5, falling in the dynamic regime, represent samples taken in the Dwyka Tillite Formation. These sampling points are more than 100 km apart and possibly represent perched aquifers on dolerite sills at shallow depth. Dating has shown the sample at Z (Zwartrand) to be recent recharge vater (Table 7.2). The fact that it does not plot at point D, as Johnson suggested, is due to the arid and saline character of the soil as will be discussed later (see section 7.2). - 123 - 7.1.1.3 Major elements Electrical conductivity, IDS or salinity, and chemical character are all aspects dealing with the combined chemical constituents of ground water. However, it is useful to investigate the concentration and distribution of the individual ionic species. For this purpose it is only necessary to consider the anions as the 2+ 2+ + + values of the cations Ca , Mg , Ha and K are dependent on those of the anions and base exchanges. Chloride Once chloride enters ground water it cannot easily be removed as it does not enter into redox reactions, or forms salts with low solubility, and is not readily sorbed on mineral surfaces. If chloride enters the ground water which occurs only through rainfall, then the circulation of ground water could simply be analysed by its chloride content. However, there are some complicating factors, e.g. the chloride contribution from rocks, which should be kept in mind (Hem, 1970). The water-soluble salts in the various units of the sedimentary profile at the disposal site, were determined by Meyer (1984) and typical results for such a profile are shown in Table 5.11. There is a definite increase in chloride, and associated sodium concentration, with depth. Plotting of these results on the conventional Piper diagram (Fig. 7.6) illustrates the increase in chloride concentration from sample 1 to 5, in the lower righthand triangle, while the change in chemical character with depth is shown in the diamond-shaped field (samples 1 to 5). It is possible to visualize the evolution of the underlying ground water (sample 6) from rain water percolating down through the profile, collecting salts, to eventually attain a chemical character close to that in the saturated zone. Once added to the underground storage it will equilibrate and acquire the eLemictl character of the ground water. Table 7.2: Regional laotope data. Analyaaa eonduetad by: CSIR(+) and Schönland Research Cantra for Nuclear Scienca(*) 14 18 FARM NAME BOREHOLE CONDUCTIVITY HC03 "c c (i) AGE TRITIUM « o NO (tnS.nT ) (mg.l-1) (%0 PDB) (years) (TU + 1) (%o SHOW) Boesmanplaat 417+ 8 500 313 - 2.3 26,6 + 0,4 9 300 0,6 + 1,2 Vaalputs 519+ 2 250 328 - 8,8 27,1 + 0,5 9 200 1.4 - 4,4 Vaalputs 519* - 8.6 37,5 + 0,5 6 570 - 4,3 Norabees 505+ 4 750 229 - 9,9 62,8 + 0,7 2 440 0 - 3,0 Norabées 505* - 9,6 57,9 + 0,6 3 090 - 2,8 Lepel 501+ 7 250 288 -U»1 45,5 + 0,6 6 200 0.4 i,l Skianelkop 502+ 8 000 207 - 8,8 44,4 + 0.6 5 220 0,5 - 3,6 Bitterputs 451+ 14 000 176 - 4,8 72,9 + 0,7 1 240 0 - 1,8 Zuurwater 465+ 10 000 211 - 4,4 65,6 + 0,7 2 090 0 - 3,7 Lekkerdrink 559+ 9 000 202 - 6,8 39,1 + 0,5 6 240 0 - 2,3 Sarep"" 492+ 5 500 270 - 7,9 82,1 + 0,6 280 0 - 3,3 Zwartrand 487+ 800 344 -10,6 110,9 + 1,2 20 11,6 - 4,9 Platbakkies 323* - 8,6 16,0 + 0,4 14 700 - 5,0 Platbakkles 001* -11,2 63,9 + 0,7 2 300 - 5,0 Goubees 504* - 8,8 43,2 + 0,5 5 430 - 2,7 Rondegat 520* -10,2 16,5 + 0.4 13 200 - 5.3 Santab 524* - 7,5 75.8 + 0,8 920 - 2,8 LEGENQ (See table 5.11 ) Figure 7.6 Dlagraa to illustrate that the geochealcal character oï the aoll «oiature approaches.; vliat of: the ground vater with Increaalng depth. - 126 - The presence of high chloride concentrations in the soils at Vaalputs is not surprising because low precipitation and high evaporation prevent salts from being flushed out of the soils, and allov them to accumulate in the profile. Frontal air masses carry salt, derived from sea spray, far inland during the winter months and Brikson (1958) estimated that the Kalahari may receive as much as 2 kg .ha' .a~ . The Bushmanland Plateau, being much closer to the coast, may expect more than double this figure. The mean chloride content of the samples taken during the survey was 1 505 mg.i~ , which is quite common for ground water from arid regions (Davis and De Viest, 1967, p. 110). Contours of the kriged chloride for the survey area are shown in Fig. 7.7. The distribution pattern is identical to that of the electrical conductivity because of the direct relationship between the two parameters. The highest concentrations coincide with the salt pans in the Koa Valley where salts are being concentrated by evaporation. Flow of ground water is so slow and anisotropic that no flow may take place in certain areas (Schoeller, 1959, p. 67). The high chloride values in these areas may, therefore, be used as an indication of the degree of stagnation, contact time with the rock, the distance travelled and the degree of evaporation (Schoeller, 1959, p. 68). The chloride chemistry of the region is important in illustrating the suitability of the Vaalputs site for the disposal of radioactive waste. The relatively flat hydraulic gradients (Fig. 6.5), a steep increase in the chemical gradient (Fig. 7.2), and an cross-directed thermal gradient (Fig. 7.1) can only result in very slow movement or stagnant conditions. This is confirmed by the chloride distribution shown in Fig. 7.7. Sulphate The mean sulphate content for all the survey samples is 379 mg.t . Using Piper's method of calculation, this represents only 15 % of the anions, compared to 78 X for the mean chloride value. However, the contour map of the kriged sulphate values (Fig. 7.8) shows great similarity with that of the kriged - 127 - chloride contours. Similarly, the highest concentrations are centered over the discharge area at Bosluis Pan in the Koa Valley. On the disposal site values in the ground water vary between 169 and 408 mg.f. (Table 7.1). Bicarbonate The distribution contours for the bicarbonate ion are more complex than those of the other ions. This is illustrated in Fig. 7.9 which shows a trend at right angles across the Koa Valley. Lower values in the Koa Valley are to be expected as all bicarbonate and carbonate would have been eliminated at the calcrete line (Johnson, 1975), whereafter only chloride and sulphate remain in solution. Higher concentrations of bicarbonate are present in the Karoo Supergroup rocks outcropping to the east and southeast of Vaalputs. As previously indicated in Fig. 7.4, no samples show bicarbonate percentages characteristic of recharge areas, as suggested by Johnson (1975). The mean bicarbonate value is 250 mg.i" while values at the disposal site range between 343 to 412 mg.ft" . 7.1.1.4 Trace elements With the development of sophisticated analytical techniques, such as Inductively Coupled Plasma (I.C.P.), it is possible to measure natural concentrations of some elements which are present in ground water only in trace amounts. Sampling of these elements is complicated by their diverse chemical behaviour (Klopper, 1977: Marchant, 1978) and the method selected is that described by Levin (1983b). The main objective of sampling trace elements was to establish the presence of potential mineral deposits in the Vaalputs area. This is a well-known method of exploration, especially for metals such as mercury, silver and bismuth (Levinson, (1974); Davis and De Wiest, (1967) p. Ill and 115) or associated base metals. rag/1 ABOVE 3304 3041 - 3304 2778 - 3041 2515 - 2778 2252 - 2515 1989 - 2252 1726 - 1989 1463 - 1726 1200 - 1463 937 - 1200 674 - 937 411 - 674 BELOW 411 UNDEFINED AREA 15 ::i 35 45 5» «ft 75 85 95 III* IIS 13ft 133 145 15ft 185 175 185 KILOMETRES Figure 7.7 Kriged results for the chloride content of the ground water. Regional geohydrological survey (Caaisani- Calzolarl, 1985). - 129 - mg/1 ABOVE 804 739 - 804 674 - 739 609 - 674 544 - 609 479 - 544 414 - 479 349 - 414 284 - 349 219 - 284 154 - 219 89 - 154 BELOW 89 UNDEFINED AREA LO ZD .15 15 55 G9 TO (18 »ft 105 115 IÏ5 135 US IOS 165 175 180 185 205 21 KILOMETRES Figure 7.8 Kriged results for the sulphate content of the ground water. Regional geohydrological survey. (Camisani- Calzolari, 1985). - 130 - mg/1 ABOVE 311 293 - 311 275 - 293 257 - 275 239 - 257 221 - 239 203 - 221 185 - 203 167 - 185 149 - 167 131 - 149 113 - 131 BELOW 113 UNDEFINED AREA 15 Z5 35 45 55 05 75 85 »5 105 115 125 135 145 15» 185 175 186 195 205 KILOMETRES Figure 7.9 Kriged results for the bicarbonate content of the ground waters. Regional geohydrological survey (Camisani-Calzolari, 1985). - 131 - Data for each trace element were kriged and anomalous areas plotted (Camisani-Calzolari, 1985). A metallogenic zone striking north-east, to the north of Vaalputs was revealed (Fig. 7.10) corresponding closely with some of the known base metal deposits and occurrences of the north-western Cape. In the immediate vicinity of Vaalputs, however, no anomalies were found and it was concluded that no obvious major mineral occurrence underlies the site, which is supported by the results of airborne magnetic and IRFUT-surveys over the area (Holtz, 1983; Torrens, 1982). It is important to note that the trace element concentrations are not merely a function of the concentration of salts (IDS) in the ground water. The direction of strike of the metallogenic zone (Fig. 7.10) is at right angles to that of the conductivity (Fig. 7.2) suggesting different concentration mechanisms for the major and trace elements. The direction in Fig. 7.10 correlates well with that of the bicarbonate distribution (Fig. 7.9). This correlation may be the result of the complex chemistry of some trace elements which are eliminated by processes such as co-precipitation or adsorption while others stay in solution as complexes at pH values of between 6,5 and 8,0. 7.1.2 Hatural Isotopes In the ground wster The use of natural isotopes in elucidating percolation in the unsaturated zone has already been discussed in section 5.11 and, therefore, their presence in the saturated zone only will be dealt with here. Measurement of stable and radioactive natural isotopes in ground water can be useful for resolving cases of ground-water mixing and the direction of reactions in more complex ground-water situations (Talma, 1981; Hook, 1980). The presence of tritium in the ground water in amounts similsr to that in present day rain water from the area, would be an indication of rapid and active percolation taking place. Low but measurable tritium in the ground water points to longer residence times, for ground water in the unsaturated zone before final addition to the - 132 - ( SWA/ 1 \NAHIBIA k l\ '•*-- > 1 / • \*-* •. VI' * *" v \7s)2 . SPRINGBOK HETAILOGENIC PROVINCE Figure 7.10 AnoBuloua values for the kriged variables Al, Be, Ho, Cr, Co, As, Cu, B, Cd, Hi, O, Ti and Zn (Canisani-Calzolari, 1985). - 133 - underground storage. The absence of tritium in the ground water means no addition to the storage during the last SO years (Verhagen, 1985). Fractionation of the stable isotopes provides a means of characterizing different ground-water bodies, and assists in the interpretation of migratory patterns. These fractionation processes in the atmosphere prior to and during rain, result in concentration 18 changes in the isotopic ratios. Careful interpretation of the 0 levels in the ground water enables the unravelling of the recharge history at the sampling locality. 14 C, with a half-life of 5 730 years, can be used for age 14 determination up to 50 000 years. Dating with C is based on the theoretical decrease in isotope concentration with time, from an initial value, C , to a concentration C at the time of sampling. ° 14 C represents the C content of recent material and is called modern carbon (mc). A value of between 50 X mc and 100 X mc may be regarded as recently recharged ground water. If tritium is present the ages of mixtures of younger and older water may be misleading and care must be exercised in the interpretation of results. In the absence of tritium, however, ground water with 14 C values below 50 X mc may be considered older than 5 730 years. Based on the initial results of the regional ground water survey, samples were taken for C, 0 and H analysis in collaboration with the CSIS and later the Schonland Research Centre. The results are summarized in Table 7.2. In a follow-up sampling program tritium concentrations were measured in ground water in the vicinity of Vaalputs (Table 7.3). A further series of samples were taken for C, H and 0 analysis during pumping tests conducted at newly drilled monitoring boreholes at the disposal site. These data are presented in Table 7.4. The localities of the sample sites (Tables 7.2 and 7.3) on the 14 Bushmanland plateau ait ah-.vn in Figure 7.12. C results for the initisl sampling program range from 16,5 X mc to 109 X mc, with the - 134 - highest value accompanied by a tritium value of 11,6 TU. Some of 14 the lov C values are associated with measurable tritium, suggesting some admixtures of recently recharged ground water. During the follow-up survey, tritium was determined with greater resolution (Verhagen, 1985) confirming previous results. The results of the regional survey of environmental isotopes in the ground vater underline the complex ground water rer'me displayed by the distribution of its major chemical constituents. Verhagen (1985) is of the opinion that regional flow considerations are of secondary importance in establishing the chemical composition of the 18 ground water. This fact is borne out by the 0 values (Table 7.2) which demonstrate that local rather than regional conditions, play a more important role during the chemical evolution of the ground water. Table 7.3: Tritium data in ground vater from Vaalputs and the surrounding area (Verhagen, 19g5) Borehole Ho. Farm Name Tritium Sain water 9,9 ± 1,0 W80R10 Vaalputs 0,3 ± 0,2 413 Riembreek 2,0 ± 0,3; 1,8 ± 0,3 409 Vaalputa 0,1 ± 0,3 411 Vaalputs 0,6 ± 0,3 505 Iforabees 0,0 ± 0,2 516 Vaalputs 1,6 ± 0,3 518 Goratees 0,0 ± 0,2 519 Vaalputs 1,2 ± 0,3 520 Rondegat 0,0 ± 0,3 The site-dependence is also demonstrated by the C and H data and no regional trends are seen. The role played by local physiographic conditions is clearly illustrated at Zvartrand 14 (Fig. 7.11) where the higheat C percentage and associated tritium values were found. Rapid percolation, facilitated by the presence of a dolorite intrusive, resulted in present-day ground water with low TOS. - 135 - f UTTER PUTS> 651 559 LCKKER DRINK fZUURWATER GOUBEEF-T •504 BOESHANPLAATi 41*7 •519 VAALPUTS NORABEES Í505 fcÓT 5161 VRIEHBREEKI LEPCL •501 ^ANTAB^ RONDEGAT 524 - 7 502 " ^ " 492. 30*15" 520. ZVÍARTRAMO^rSARAIP PLAT 4AKK1ES SKIHHElKOPl •001 & 10 30 km 0 20 i Scale Figure 7.11 Regional natural isotope aaapllng localities. - 136 - Verhagen (1985) stated that no "fossil" ground water is present in the area and the ages up to 14 700 years merely suggest a slow moving hydrological system. This is especially true in areas, such as the disposal site, where direct percolation is hampered by thick surflcial accumulations consisting of low-permeability clay-rich sediment*. Slow recharge, accompanied by an even slower moving ground water regime, results in conventional ages of 10 000 years being measured ac the disposal site. Theoretically, water quality should improve during long term pumping towards that present in the recharge area Johnson (1975). This may hold true for homogeneous permeable sedimentary aquifers but not for a fractured aquifer under thick sedimentary cover. Pumping in this case only results in yielding a mixture of older and younger water from the fractures. Slight changes in chemistry are due only to a change in proportions of these mixtures during pumping. During the pumping tests of the monitoring boreholes (Hodgson, 1986) a decision was made to sample both for chemistry and environmental isotopes at the beginning and the end of each pump test. The results of these analyses are shown in Table 7.4 for the isotopes and Table 7.5 for the chemistry, while the localities of the boreholes are shown in Fig. 6.8. Only in GWB 5 and HON 11 were 14 significant rises in C found, suggesting an increase in the 14 recent component with time. The increase in C was not accompanied by an increase in tritium and it is therefore not easy to explain this behaviour with present knowledge. The reason for the variation within the conductivity measurements during pumping (Table 7.5) is unknown at present. The regional tritium results show significant local rainfall infiltration. However, at Vaalputs the effectively zero tritium indicates no significant contribution to the ground water from recent precipitation. He further noticed that the small but definite differences in 6 180 values of the individual boreholes suggest significantly different recharge conditions even over the limited area of the site. - 137 - Table 7.4: Isotope data obtained from samples taken during test pumping (Verhagen, 1985) Borehole Pump test 3H (T.ff.) 14C (pmc) 6180(Xo) GWB 3 begin 0,3 ± 0,2 - -4,8 GWB 3 end 0,4 ± 0,3 24,0 ± 0,5 -4,9 GWB 5 begin 0,2 ± 0,2 29,8 ± 0,5 -5,5 GWB 5 end 0,0 ± 0,2 32,7 ± 0,7 -5,4 PBH 16 begin 0,2 ± 0,2 19,4 ± 0,5 -5,6 PBH 16 end 0,1 ± 0,2 18,0 ± 0,6 -5,7 GWB 1 begin 0,3 ± 0,3 - -5,7 GWB 1 end 0,2 ± 0,2 21,8 ± 0,5 -5,7 MOW 2 begin C,4 ± 0,4 19,9 ± 0,5 -3,8 HON 2 end 0,0 ± 0,2 21,0 ± 0,9 -3,9 MON 4 begin 0,1 ± 0,2 26,6 ± 0,5 -4,2 MON 4 end 0,2 ± 0,7 23,9 ± 1,0 -4,2 MON 10 begin 0,1 ± 0,9 19,2 ± 0,7 -3,9 MON 10 end 1,9 ± 0,3 19,7 ± 0,6 -3,6 MON 11 begin 0,8 ± 0,3 18,7 ± 0,7 -3,5 MON 11 end 0,3 ± 0,3 54,4 ± 0,6 -3,5 MON 12 begin 0,4 ± 0,3 20,8 ± 0,8 -3,4 MON 12 end 0,0 ± 0,3 20,8 ± 0,4 -3,4 7.2 Chemical Equilibrium of the Ground Water There is general consensus among investigators in hydrogeochemistry that the chemical composition of ground water is largely determined by reactions and processes taking place while rain water percolates through the unsaturated zone, and comes in contact with mineral surfaces (Hem, 1963; Hem, 1970, p. 45; Jacks, 1973; Schoeller, 1959, p. 54; Bricker and Garrels, 1967). Hem (1963) summed it up as follows: "The chemical composition of ground water is certainly strongly influenced by things that happened to the water before it entered - 138 - Table 7.5: Chemical analyses of samples taken during test pumping (ag.ftT ). Borehole HON :_ HOR 4 NOR 10 NOR 11 MON 12 Pump teat begin end begin end begin end begin end begin end pH 7.3 7,5 7,0 7,5 7,1 7,1 7,6 7,3 6,9 6,9 Cond 550 475 400 350 600 500 550 500 475 550 (mS.«_1) HCO~ 400 405 399 410 359 367 354 354 348 343 334 338 277 275 372 369 376 372 386 408 < cr 1 446 1 442 1 320 1 313 1 547 1 550 1 625 1 638 1 674 1 688 R.+ 1 023 1 022 771 768 1 023 1 023 1 023 1 023 1 055 1 055 K+ 21,3 21,5 17,5 16,9 20,8 20,6 23,2 22,9 22,8 23,1 C.2+ 95,2 98,8 44,2 44,6 102,6 103,8 117,3 129,3 129,3 135,9 ««2* 67,7 68,8 43,3 43,2 73,3 66,6 89,9 »1.1 87,7 94,4 the ground-water reservoir. Once it has arrived in an aquifer, however, the water is subject to a fairly stable set of conditions. Ground water moves slowly and is therefore in contact with a large surface area of solid-phase rock minerals for considerable periods of time. Temperature or pressure changes may occur in ground-water reservoirs, and organic matter and bacterial activity may influence ground-water composition. On the whole, however, the conditions within a ground-water reservoir favour the establishment of chemical equilibria in the reversible chemical reactions that may occur among the solutes contained in the water and the solids in the aquifer." All the major chemical constituents, except chloride and to a lesser extent sodium ions, participate in these reversible chemical reactions. Using stability diagrams it is possible to establish the degree of equilibrium attained between the liquid and solid phase. These stability diagrams show mineral equilibria relationships for various minerals predicted from thermodynamic considerations (Garrels and Christ, 1965). Stability diagrams have found wide application in hydrogeochemistry in predicting which mineral species are stable and present in normal ground water (Hambleton-Jones, 1976; Jacks, 1973; Ramesan, 1982; Tredoux, 1981). - 139 - It must be pointed out that these diagrams only apply under ideal conditions where all phases are stoichiometric and activities are equivalent to concentrations. Ground waters, particularly those of the Bushmanland Plateau, are certainly not ideal solutions and caution must be exercised in the interpretation of these diagrams. The most important mineral equilibria relationships in natural ground water are that of calcite, gypsum and the silica minerals. The calculation of the activity-concentration relationship applied here is dealt with by Garrels and Christ (1965, p. 20-71) and Stumm 2+ 2- and Morgan (1970). Plotting the Ca and CO activities calculated for some of the ground waters from the disposal site (Table 7.1) revealed that the water is saturated with respect to calcite (Fig. 7.12). This is supported by the presence of calcite veins in the clayey formations of the unsaturated zone (Levin, 1985) and in fracture fillings below the water table (unpublished core logs). 2+ 2— In three cases the activities of Ca and SO. plot in the undersaturated field of the gypsum activity diagram (Fig. 7.13) but two analyses plot on the boundary within the saturated gypsum field. The presence of abundant gypsum crystals was noticed at the disposal site only in the auger borehole AW35S08 (Fig. 5.12) at 6,1 m (Jamieson, 1985) and not in any of the numerous other boreholes drilled in and around the disposal area. However, the erratic distribution of gypsum in the superficial sediments could reflect the sporadic saturation of gypsum in ground water from the disposal site. Chemical reactions, such as the alteration of feldspar to clay minerals during weathering, are partially Irreversible reactions (Stumm and Morgan, 1970). Equilibrium relations for the reactions between common rock-forming minerals and aqueous solutions are known and available in the literature (Helgeson et al.. 1969; Stumm and Morgan, 1970; Garrels and Christ, 1965; Freeze and Cherry, 1979). According to Freeze and Cherry (1979, p. 277) it is quite common for ground water to plot in the kaolinite fields of stability diagrams, such as those in Fig. 7.14, while only a small percentage - 140 - Saturated V*/, £'/- -4 ^. C*.. O -5 Undersaturated -6 -7 1 ' • • ' ' ' •L- 1 -1 • • ' ' I • J -S -3 -2 Log (Ca2*) Figure 7.12 Activity diagraa showing calcite saturation in terms of log (Ca2+) and log (CO*-). Saturated -2 - o Undersafurated -5 -1—I 1 L_l 1 1—I—i 1 I -I. I 1 1 1—I—I 1—1—i .A. .4 ' I I—J I I I 1 I i k • ' If -5 -U -3 -2 Log (Ca2*) Figure 7.13 Activity diagraa showing gypsum saturation in terms of log (Ca2+) and log (SoJ~). - 141 - LT *i i "-i S—"HI H—' ' T ^i —r1- t 10 '00 1 10 100 1 10 100 SiOj mg/l Si02 mg/i SiO: mg/l Figure 7.14 Activity diagram shoving stability and saturation of the various clay minerals at Vaalputs. plot in the montmorillonite field and hardly any plot in the other fields. The conditions for water to achieve equilibrium with respect to feldspar minerals are long contact time with the solid phase and sluggish flow conditions. It has already been pointed out that such conditions do exist in the disposal area. The SiO. values (Table 7.1) were plotted on the stability diagrams after Freeze and Cherry (1979, p. 272). On the log + + (!fa )/(H ) against log Si(0H)4 diagram (Fig. 7.14) the values plot well within the Na-montmorillonite field. On the log 2+ + (Ca )/(H ) against log Si(0H)4 diagram all values plot in the + + kaolinite field. On the log (K )/(H ) against log Si(0H)4 diagram, values plot in the microcline and kaolinite fields but close to the kaolinite-microcline boundary. In all cases the samples plot well within the solubility limits of amorphous silica as water may well be in equilibrium with more than one mineral phase (Freeze and Cherry, 1979, p. 273) and normal for most ground waters (Garrels and Christ, 1965, p. 361). Brynard (1983) showed that the clay minerals present in the surficial sediments constitute mainly kaolinite, illite and montmorillonite (smectite) which confirm the stability of these - 142 - minerals in the geochemical environment at the disposal site. As shown in Fig. 7.14 the sodium silicate minerals in solution are in equilibrium with montmorillonite, while the potassium silicate minerals fall on the boundary between potassium feldspar and kaolinite. 7.3 Geochemical Processes The fate of any radionuclide migrating out of the containers at Vaalputs must be seen against the possible chemical reactions in which such a nuclide may participate on its migration path. This slow-down, stopping or fixation of the radionuclide by chemical reaction is suitably termed retardation and forms part of the retardation or reduction factor in the numerical modelling of the migration of radionuclides. The radionuclides present in Koeberg waswastt e and of concern at Vaalputs include Co, Sr, Cs, 137, Cs. These isotopes, their source and half-lives are shown in Table 7.6. Moore et al.f (1987) indicate that 95 X of the activity received from Koeberg is contained in resins immobilized in cement. If it can be shown that these wastes can be safely disposed of at Vaalputs, then the site will have been demonstrated to be safe, since the other waste will not be more hazardous than the resins. Moore e_£ si., (1987) further stated that the refined radioactive 234 waste from Pelindaba will only include trace quantities of U, 235 238 231 U, U and Pa. The activity of these wastes is so low that it does not come within the definition of "radioactive material," which is defined as: "any substance which consists of or contains any radioactive nuclide whether natural or artificial, and whose specific activity exceeds 0,002 microcurie per gram of chemical element and which has a total activity greater than 0,1 microcurie"; (Government Gazette, 1980). Chemical processes involved are restricted by available chemical constituents in the mineral assemblages, soil moisture and, below the water table, the ground water chemistry. Chemical analyses of the sedimentary profile and granite are available from work by Brynard (1988). Analyses for some boreholes in the disposal area showing values for elements of concern are shown in Appendix C. - 143 - Table 7.6 : Isotopes of concern that vill be present in the radioactive waste received at Vaalputs. SOURCE ISOTOPE HALF-LIFE (a) Corrosion products 60Co 5,3 Fission 90Sr 28,1 products 134Cs 2,3 137Cs 30,2 234 Refined u 2,47 x 105 Uranium 235U 7,10 X 108 238U 4,51 X 109 231P. 3,56 X 104 One can assume that the composition of the soil moisture will closely resemble that of the water-soluble constituents, determined after equilibrium is reached. Analyses of water-soluble constituents from the various rock types underlying the disposal site were selected from the report by Meyer (1984) and are shown in Table 7.7. The elements Sr, Cs, Co, V and U were not included in Meyer's report and were therefore determined in a similar manner on the same samples at a later stage. Chemical analyses of ground water from the water-bearing monitoring boreholes around the disposal site are indicated in Table 7.8. Of prime importance to the study of radionuclide migration are those chemical processes and reactions involving the isotopes of concern. The more important chemical processes that will be considered are the following: (i) Precipitation reactionr (ii) Complex formation - 144 - (ill) Redox reactions (iv) Ion exchange reactions (v) Adsorption Various computer programs have been developed to assist in the study of these chemical processes by calculating the equilibrium speciation of the chemical elements in a soil solution based on chemical thermodynamics. The only such program in operation in the Republic of South Africa is GEOCHEM. This program, written by Sposito and Hattigod (1979), was applied for its capability to predic which solids will precipitate and which complexes will form, given the chemical composition of soil moisture extract or natural ground water. The program was run at the Computer Centre for Hydrological Sciences, University of Natal in Pietermaritzburg, using the soluble extract and natural ground water data from Vaalputs as tabulated in Tables 7.7 and 7.8. For the soluble extracts, an open system with respect to CO, was assumed and therefore the normal partial CO. -3 5 pressure of 0,0316 kPa (10 ' bar) was assumed. In the case of the natural ground water the system was regarded closed with respect to CO, and no partial pressure was applied. GEOCHEM was first run to simulate natural conditions and thereafter the concentrations of the relevant elements were increased as follows Sr from about 1 to 5 mg.2~ , Cs from zero to 1 mg.i~ , Co from <0,1 to 1 mg.Jt" , in order to simulate leakage of radionuclides. In this way elements absent or present in negligible amounts in the natural solutions are present in sufficient quantity to participate in the chemical reaction. Table 7.7: Chaadcal «nalyaaa of water-aoluble extracts of the various geological unit» fro* tha disposal sit (Mayer. 1984). showing solids precipitating, as calculated by GBOCHKM. (All chemical species in •«-*K soil) Saaple No 1 2 3 4 5 6 7 8 9 10 Rock Type Calcrete Calcrete Calcrete Calcrete Clay Clay Kaollnile Kaolinite Weathered Weathered clay clay granite granite Depth (•) 0.5-1.1 0.9-1,5 2.0-2,4 2.5-3,5 5.3-6.2 7,6 8.2 9,0-10,2 12,2-12,8 12,8 13,7 13,7 14,2 Borehole AU30S08 AU30N02 AU25S13 AW2SS13 AU30S08 AU25SI3 AU2SS13 AU35S03 AU3SS03 AW35S03 pH 7.7 8.0 8.5 8.4 7.5 8,3 7.8 7.2 7.1 7.1 co3 0 40 170 70 0 60 0 0 0 0 HC03 550 580 560 520 4 70 500 460 3 70 320 300 760 240 190 180 560 110 210 240 260 360 S04 Cl 520 820 220 480 460 720 880 780 960 /60 Na 760 780 380 580 600 680 800 640 740 620 K 44 66 58 44 58 54 50 41 38 40 ca 64 66 54 36 48 38 41 39 52 55 Kg 17 17 18 18 17 18 21 24 33 35 Sr 0.9 0.7 0.7 0.7 0.3 0.9 0.4 0,2 0,6 0.5 CS <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 Co <5 <5 <5 <5 <5 <5 <5 <5 <5 Solids CaC03 CaC03 precipitating 1 - 146 - Table 7.8: Chemical analyses of natural ground vater fro* the disposal site at Vaalputs, shoving solids precipitating, as calculated by GEOCHEH. (All cheaical species in ag.l~ , except 0 in ug.l~ ). BOREHOLE NO MOW 2 HON 4 HON 10 HON 11 HON 12 GWB 7 GWB 3 Eh (v) +0,081 +0,046 +0,109 +0,069 +0,156 +0,007 +0,034 PH 7,5 7,5 7,1 7,3 6,9 7,3 7,3 Cond(mS.m~ ) 475 350 500 500 550 400 500 HC03 405 410 367 354 343 412 355 372 183 so4 338 275 369 408 169 CI 1 442 1 313 1 550 1 638 1 688 1 000 1 360 Na 1 022 768 1 023 1 023 1 055 720 830 K 21,5 16,5 20,6 22,9 23,1 18 23 Ca 98,8 44,6 103,8 129,3 135,9 40 74 Mg 68,8 43,2 66,6 91,1 94,4 59 90 Sr 1,0 0,9 1.1 1,1 1.3 1,1 1,2 Cs 0,0 0,0 0,0 0,0 0,0 0,0 0,0 Co <0,1 <0,1 <0,1 <0,1 <0,1 <0,1 <0,1 V <0,01 <0,01 <0,01 <0,01 <0,01 <0,01 <0,01 U 112 97 50 50 117 120 116 Solids CaC03 precipitates in all cases precipitating SrS04 precipitates in all cases 7.3.1 Precipitation reactions Soil moisture percolating through subsurface material picks up soluble salts. The vater may become saturated vith respect to one of the sslts in solution. Due to slight changes in physio-chemical conditions the solubility limit can ultimately be exceeded. Generally this only applies to the sparingly soluble subreanccs such as the sulphates of Ca and Sr and the carbonates of Ca, Sr and Co. - 147 - Strontium is chemically similar to calcium and has the ability to occupy structural positions in minerals normally occupied by calcium (Day 1963, p. 173). For example Bricker and Garrels (1967) noted that aragonite always has a higher Sr content than calcit- on precipitation because of the ease with which the relatively large Sr++ ion substitutes into the aragonite structure. The occurrence of strontium enrichment in limestone was also noted by Hem (1970). Brynard (1988) investigated the composition of calcrete present in the disposal trenches at Vaalputs. He dissolved various calcrete samples in diluted nitric acid. Analyses were done on the original sample, the insoluble residue and the leachate. Analytical results are shown in Tables 7.9, 7.10 and 7.11, from which the following conclusions can be drawn: (i) A large percentage of the strontium dissolved with the CaCO, and was present as SrCO. in a co-precipitate. (ii) Strontium and barium, enriched in the insoluble residue, are likely to be present as SrSO. and BaSO.. Both these salts are insoluble in an acid medium, SrSO. slightly less than BaSO.. They both form co-precipitates with calcium salts and Brynard (1988) found a good correlation between the distribution of these elements in the sedimentary rocks of Vaalputs. (ill) Geochemical conditions during the formation of the calcretes were favourable for the co-precipitation of strontium with calcium and barium. These precipitates are still stable today, thousands of years since their formation. The solubility limits of SrSO. (celestite) and SrCO, (strontisnite) are not reached in most ground wsters (Hatthess snd Harvey, 1982, p. 259; Hem, 1970, p. 195). Davis & De Wiest (1967 p. 114) are of the opinion that the concentration of strontium in some ground water is limited by the low solubility of strontium sulphate (celestite). Solubility products of some solids in water at 25°C are shown in Tsble 7.12. The order of decreasing solubility is CaSO., SrS04, CaCOj and SrCOj. Table 7.9: Trace element and CaO content of calcretes from the waste disposal trenches at Vaalputs. (CaO in X CaO, other elements in mg.kf~ ). SAMPLE HO CaO Sr Cu Zr Y Ba 1 51,23 201,4 10,6 23,3 103,8 15990,5 2 52,17 124,2 6,0 18,6 88,5 123,2 3 49,85 128,9 6,3 34,4 82,7 5189,6 4 50,20 97,1 7,6 48,1 103,3 1538,4 5 49,61 164,4 9,3 59,7 101,7 2110,6 6 45,9'> 125,6 7,4 89,2 149,4 122,0 7 43,81 142,1 8,6 95,2 109,9 334,1 8 44,11 148,0 8,2 113,7 171,2 3610,1 9 41,00 111,7 8,0 67,8 52,6 137,8 15 46,30 164,8 8,2 50,7 126,0 10465,7 Table 7.10: Trace element and CaO content of acid soluble fraction of calcretes (same material as used In Table 7.9, Ca in X CaO, other elements mg.kg" ). SAMPLE NO CaO Sr Cu Zr Y Ba 1 52,80 93,76 2,28 1,05 2,10 106,38 2 46,43 95,11 1,98 0,93 2,78 12,70 3 54,23 78,04 2,08 0,96 2,24 166,19 4 55,80 83,09 2,42 0,48 6,28 40,10 5 54,33 105,13 2,67 1,03 3,49 49,08 6 48,89 111,97 2,56 0,85 2,05 10,77 7 52,79 127,33 2,29 0,98 2,13 31,10 8 59,68 122,55 2,57 1,10 2,20 180,61 9 49,26 110,33 3,29 0,94 2,35 22,30 15 54,03 108,79 2,28 1,58 2,11 243,23 - 149 - Table 7.11: Trace element and CaO content of the insoluble fraction (after acid leaching). (Same samples as used in Table 7.10, Ca in X CaO, other elements mg.kg"1) Sample no CaO Sr Cu Zr Y Ba 1 4,27 503,7 27,0 130,1 933,0 48427,8 2 7,10 120,0 13,0 372,0 935,0 10170,4 3 7,84 85,0 15,0 169,0 696,0 3155,1 4 5,26 100,0 11,0 303,0 825,0 5165,9 5 3,60 46,4 11,8 267,8 592,0 685,6 6 2,02 39,7 9,8 389,5 886,9 433,8 7 2,31 45,6 10,2 389,7 545,0 353,4 8 6,38 104,4 5,2 330,7 584,7 12444,1 9 1,95 36,6 9,5 208,1 169,4 318,3 15 2,45 346,3 22,7 187,0 434,4 54921,3 Table 7.12 : Solubility products of some solids in vater at 25°C. (1) Mattfcess and Harvey (1982) and (2) Hem (1970) SOLID SOLUBILITY PRODUCT SOURCE 9 CaC03 4,82 x 10" (1) CaSO. 6,1 x 10"5 4 (1) 1,6 x 10"9 (1) SrC03 2,b x 10"7 x'D SrS04 2,11 x 10"" (1) FeC03 CoCO, <2,11 x 10"" (2) - 150 - -1 Insoluble -2 „ -3 ex Sr2*(b) x *x * o X w Sr2-(a) / oi -6 -7 Soluble -8 - J i I 8 12 PH Figure 7.15 The solubility of Sr and C» carbonate for an open system (-log p = 0,0316 kPa) as a function of rC0rn9 2 pH and concentration (-log We2+] in molar). Sr2+ (a) dots are plots for analyses from the soluble extract and Sr".2'+ (b) crosses are plots after raising the levels of Sr to 5 «g.f (after Stums) and Morgan, 1970). Strontium saturation of the soil moisture (soluble extract) and the natural ground water from the disposal site at Vaalputs, were studied using the computer program GEOCHEM. The data used and the results for the two simulations are shown in Tables 7.7 and 7.8. A typical print-out showing the distribution of metal and ligand species, as calculated by GEOCHEM, is shown in Table 7.13. In the case of the soil moisture simulation, which was considered open to the atmosphere, only CaC03 precipitated from two samples with ?H 8,5 and pH 8,4 (Table 7.7). Garrels & Christ (1965, p. 83) - 151 - noted that a system containing CaCO. in water, in equilibrium with the atmosphere, has a pH of 8,4, which explains the precipitation of CaCO. in those two samples. Plotting the strontium concentrations on the CaCO. and SrCO. stability diagram, Fig. 7.15, by Stumm and Morgan (1970, p. 181) for a system open to CO., it can be seen that strontium values fall within the soluble field and no precipitate can be expected. The natural ground water system was considered closed to the atmosphere and, as shown in Table 7.8, CaCO. and SrSO, precipitated in all seven cases considered. This confirmed the CaCO. saturation found previously and shown in Fig. 7.12. The reason for strontium not precipitating as SrCO. was investigated by plotting the calcium and strontium values of Vaalputs ground water (Table 7.8) on the stability diagram by Stuom and Morgan (1970, p. 179) for a closed system in terms of pH and log concentration. As shown in Fig. 7.16 the strontium concentrations are too low and all values lie within the soluble field. The analytical values for cobalt and cesium were below the detection limits for both the soluble extract and the natural ground water and could, therefore, not be considered by GEOCHEM. Similarly, Uranium did not produce any precipitate probably due to there being insignificant vanadium present to form carnotite. During the radionuclide leakage simulation cobalt and cesium concentrations were raised to 1 mg.il- while that of strontium was increased to 5 mg.it- . It was further assumed that all other conditions stay the same and GEOCHEM was run again. The results for the soil moisture simulation are shown in Table 7.14. As in the previous simulations CaCO. precipitated only from samples 3 and 4. Strontium precipitated as SrSO. from sample number 1 and »» SrCO. from the three samples with pH values above 8,0. Plotting these strontium values on the stability diagram (Fig. 7.15) shows that only three values fall within the insoluble SrCO. field. - 152 - 2 - VS. Ca2* Insoluble •k - 01 x *v _Ca2* Sr2* U -6 z o o Soluble -8 - -10- ....i Í . i . i.i i i 10 12 PH Figure 7.16 Solubility of Sr and Ca carbonate for a closed syatesi in terms of pB and log concentration shoving values for natural ground water froa the disposal area at Vaalputs (after Stuna and Morgan, 1970). - 153 - Table 7.13 Typical print-ovt ahoving the diatributlon. of aetal and ligand apeciea, aa calculated by GBOCHEM. PRIMARY DISTRIBUTIONS OF METALS AND LIGANDS K SOLIB POM.WÍTH Cójí/ ÏÍÏ5 PERCE HOB 4 MG m ?£'/ %-zwm §8SBB 8i$ c£4 ', U Mi SR MobTHWIffg 8:8111® '46 PER?ÍSÍ K iSu9i 9^:i II i£4 ? l:J III? NA •M mm Í8ÍKIB ffl h mm C02+ IN SOLID FORM WITH C03-/ 99.9 PERCENT CS ÍMDTBWW* 9!:8 lii» U02 BOUND WITH C03-/ 100.0 PERCENT C03- IS A_FREE_LIGAND/ 0.2 .PERCH a$Braf f j km: PERCENT 2+/ PERCENT 2' PERC: S04 LID ¥op W$TH Sg „/, Ll PERCENT S «A '/ MHE CL WWW7 % - 154 - From GEOCHEM calculations cobalt precipitated from all the samples as CoCO,. However, the bulk of the cobalt received from Koeberg will be fixed to resins. It is therefore reasonable to assume 2+ cobalt vill only be present as Co . When GEOCHEM was run with 3+ cobalt as Co the cobalt precipitated completely as the hydroxide Co(OH).. The solubility of CoCO. is less than that of siderite and this, according to Hem (1970) and Everett et al.f (1984), may be an important factor in limiting the cobalt concentrations in solution with high carbonate concentration. The GEOCHEM simulation using the increased Sr, Co and Cs concentrations in the natural ground water again produced SrSO. and CaCO. from all samples as well as the complete precipitation of cobalt as CoCO. (Table 7.15). 3+ In the unlikely event of cobalt being present as Co , all the cobalt will precipitate as Co(OH),. It is important to note that at Vaalputs between 96,7 and 99,6 X of all cobalt will precipitate from the extracted solutions (Table 7.16), and 99,9 X of all cobalt will precipitate from the natural ground water (Table 7.17). Calculations further indicate that between 16,1 and 59,7 X of all strontium may precipitate under favourable conditions from the soil moisture (Table 7.16). In the case of the natural ground water between 82,9 and 93,8 X of all atrontium will precipitate. 7.3.2 Complex formation The term "complex ion" is used to describe all ions other than monoatomic regardless of the nature of the forces binding the atoms together (Carrels and Christ, 1965). The formation of complexes in solution greatly depends on its concentration. Vfhen highly diluted little complexing can be expected but complex formation is favoured by increasing the concentration. The mobility of metal ions in solution is markedly influenced by complex formation as a result of the charge change during complexing. A positively charged cation normally participating in cation exchange, becomes negatively charged and mobile on Table 7.14: Sollda precipitating fro* soluble extracts of the various geological units fro» the disposal alta. aa calculated by GBOCHBH, after ralatns the levela of Sr to Sag.l , Ca to lag.*. and Co to ls».l~ to tiaulate radionuclide leakage. (All chemical species in «ft kl~ soil) Saaoj>le .««- 1 2 3 4 5 6 J 8 9 10 Rock Vyrie Calcrete Calcrete Calcrete Calcrete Clay Clay Kaolinlte Kaolinite Weathered Weathered clay clay granite granite Depth iaO 0.5-1.1 0,9-1.' 2,0-2,4 2.5 3.5 5.3-6.2 7.6 8.2 9,0-10,2 12,2-12,8 12,8 13,7 13,7-14.2 Borehole AU30S08 AU30N0^ AU25S13 AU25S13 AU30S08 AW25S13 AW25S13 AW35S03 AW35S03 AU35S03 PM 7.7 8.0 8.5 8.4 7.5 8.3 '.8 ».2 7.1 7.1 co3 0 40 170 70 0 60 0 0 0 0 HCO 550 580 560 520 470 500 460 370 320 300 *°4 760 240 190 150 560 110 210 240 260 360 Cl 520 820 220 480 460 720 880 780 960 760 Ha 760 780 380 580 600 680 800 640 740 620 K 44 66 58 44 58 54 50 4) 38 40 Ca 64 66 54 36 48 38 41 39 52 55 1% 17 17 18 18 17 18 21 24 33 35 Sr 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5,0 5,0 0.5 Cs 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Co 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 V 3 10 18 18 2 4 2 0,03 0,03 0,11 u 0.08 0,10 0.2 <0,01 <0,01 <0,01 0,05 1.0 1.0 1.0 Solids CaC03 CaC03 SrC03 precipitating SrS04 SrC03 SrC03 CoCO CoCO CoC03 CoCO CoCO CoCO CoC03 CoCO CoC03 CaCO - 156 - complexing. Neutral ion pairs in solution are also considered complex iona by the computer program GEOCHEH. Complex formation in extracted soil solutions and natural ground waters from the Vaalputs waste disposal repository, were computer-simulated with GEOCKEM. The program partitions each metal present into free ionic, hydrolyzed, and inorganic complex forms based on thermodynamic considerations appropriate to the system. Table 7.18 is a typical output of metal complexes as calculated by GEOCHEM, present in extracted solutions and natural ground-water at Vaalputs. Table 7.15: Solids precipitating from the natural ground water, as calculated by GBOCHEM, after raising the levels of Sr to 5mg.i , Cs to lag.*' and Co to lmg.i to simulate radionuclide leakage. (All chemical species mg.t~ except U in ug.g~ ). BOREHOLE NO HON 2 MOW 4 HON 10 HON 11 HON 12 GWB 7 GWB 3 PH 7,5 7,5 7.1 7,3 6,9 7,3 7,3 Cond.mS.n~ 475 350 500 500 550 400 500 HC03 405 410 367 354 343 412 355 S0 338 275 372 169 4 369 408 183 Cl 1442 1313 1550 1638 1688 1000 1360 Ha 1022 768 1023 1023 1055 720 830 K 21,5 16,9 20,6 22,9 23,1 18 23 Ca 98,8 44,6 103,8 129,3 135,9 40 74 Hg 68,8 43,2 66,6 91,1 94,4 59 90 Sr 5,0 5,0 5,0 5,0 5,0 5,0 5,0 Ca 1,0 1,0 1,0 1,0 1,0 1,0 1,0 Co 1,0 1,0 1,0 1,0 1,0 1,0 1,0 V <0,01 <0,01 <0,01 <0,01 <0,01 <0,01 <0,01 U 112 97 50 50 117 120 116 Solids CaC03 Precipitates in all cases precipitating SrS04 Precipitates in all cases CoC03 Precipitates in all cases - 157 - Table 7.16: Percentage solids precipitating from the water soluble extract, as calculated by GEOCHEM, after raising lerels of Sr to 5ag. I"1, Ca to 1««.I"1 and Co to lag.I-1. SAMPLE 1 2 3 4 5 6 7 8 9 10 X Sr as SrCO. 59,7 37,9 16,1 X Sr as SrSO. 0,6 X Co as CoCO. 99,1 99,4 99,6 99,6 98,8 99,6 96,7 97,7 96,9 96,7 Table 7.17: Percentage solids precipitating from natural ground vater, as calculated by GEOCHEM, after raising lerels of Sr to Sag. ft-1, Cs to lag.t and Co to lag.ft"1. BOREHOLE HO MOH 2 MOM 4 MOW 10 MOW 11 MOH 12 GWB 7 GWB 3 X Sr as SrSO. 92,3 90,1 93,0 93,2 93,8 82,9 85,1 4 X Co as CoCO. 99,9 99,9 99,9 99,9 99,8 99,9 99,9 - 158 - In order to explain the table the cobalt complexes must be considered. Carbonate, sulphate, chloride and hydroxy1 complexes are indicated. The concentration of a particular complex is followed by three digits denoting the "stoichiometric index" which indicates the number of metal atoms, the nvmber of ligand or complexing ion, and the number of H or 0H~, respectively, in the complex. The third digit is positive if H is present and is negative if OH" is present in the complex. Three cobalt carbonate complexes can form as follows: CoCO., CoHCO. and Co(CO.) ~. The most stable complex form is CoCO. and, as Table 7.13 indicates, 99,9 X of the cobalt precipitates as CoCO.. In the case of strontium the charged complexes that form are SrHCO*, SrCl+ and SrOH+, indicating that these complexes may participate in cation exchange reactions, if stable. In Table 7.17, 92,3 X of all strontium metal precipitates as SrSO. 2- and minor amounts are complexed with SO. and CI . Cesium forms only one complex with chloride, CsCl . However, in 2+ Table 7.13, 98 X of all cesium is free as Cs with only 2 X bondeled to Cl~ in solution. Similar to strontium the positive osCosCll + ccomple x may participate in ion cation exchange reactions if stable. The presence of uranium in ground water originates from the more soluble uranyl ion U0t+, a» shown by the Eh-pH and solubility studies published by Garrels and Christ (1965, p. 254-256). It forms complexes with carbonate, sulphate, chloride and hydroxyl ions. Table 7.13 shows 100 X bonding of uranium to the carbonate ion and, therefore, carbonate must form the most stable complexes. Boyle (1984) found that, although uranium may form complexes with carbonate, phosphate, sulphate, silicate, fluoride and chloride, the only stable complexes predominating above pH 7,0 are the di- and tricarbonate complexes shown in the following equations: HC0~ z »+ + C03~ - 159 - Table 7.18: Typical output of aetal complexes present in solution, at Vaalputa as calculated by GBOCHEH (concentration of coaplexes expressed as - log [], «here [] refers to a •olar concentration). CONCENTRATIONS OF COMPLEXES CA C03- 6.22 0 5.43 1 1 1 CA S04 4.75 0 CA CL 4.91 0 CA OH 9.13 -1 MG C03- 5.36 0 4.38 1 1 1 MG S04 3.70 0 MG CL 3.85 0 MG OH 7.17 -1 20.11 4 0 -4 SR C03- 8.59 0 7.60 1 1 1 SR S04 6.52 0 SR CL 6.48 0 SR OH 11.49 -1 K C03- 7.67 0 5.97 1 1 1 11.33 2 1 K S04 5.31 0 11.91 1 1 1 8.17 2 1 K CL 5.15 0 X OH 10.37 -1 NA C03- 6.07 0 3.77 1 1 1 8.93 2 1 NA S04 3.20 0 9.90 1 1 1 4.36 2 1 NA CL 3.05 0 NA OH 8.17 -1 C02+ C03- 8.72 0 8.43 1 1 1 11.77 1 2 C02+ S04 9.45 0 C02+ CL 10.71 0 C02+ OH 11.03 -1 12.72 1 0 -2 17.82 1 0 CS CL 6.81 0 U02 C03- 8.00 0 6.34 1 3 0 U02 S04 14.48 0 15.47 1 2 0 U02 CL 15.04 0 U02 OH 12.25 -1 H C03- 2.41 0 1 1 3.61 0 1 2 H S04 8.35 0 1 1 26.25 0 1 2 H CL 17.39 0 1 1 + - U0^ + 2C0*~ + 2H20 J U02 2+ 2 4- UO + 3C0 l - U0- C0 ) 2 3 Z 2< 3 3 Hambleton-Jones and Smit (1984) have shown that the stabilities of these complexes are pH and bicarbonate dependent. Carlisle (1980) and Mann and Deutscher (1978) argued that precipitation of calcrete 2- (CaCO.) under arid conditions depletes the CO. ion concentration and thereby destabilizes the uranyl complexes. In the presence of pentavalent vanadium and potassium the uranyl ion will precipitate aa carnotite (K,(U0 )2V_0 .3H-0). Vaalputs falls within an area favourable for the development of surficial uranium occurrences (Hambleton-Jones, 1984) and carnotite mineralization was observed on a number of farms in the area, and towards the Koa Valley (unpublished exploration reports). The presence of carnotite was noted at the base of the surficial deposits in percussion borehole W20N0 at the disposal site (Jamieson, 1985). However, using the method described by Hambleton-Jones and Smit (1984), carnotite solubility index calculations were done for both the extracted soil solutions and the natural ground water from Vaalputs. Only negative values, varying between - 0,78 and - 4,46, were found, indicating that these solutions are undersaturated with respect to carnotite and therefore carnotite will not precipitate. 7.3.3 Oxidation-reduction reactions Oxidation-reductions reactions involve only those elements or species which can take part in electron transfer. In natural waters, therefore, the«e reactions have the greatest relevance to the hydrogeochemistry of iron and related transition metals and to possible biochemical reactions involving carbon, nitrogen, oxygen and sulphur cycles. These relatively rapid and reversible reactions can be described theoretically using equilibrium methods (Garrels and Christ, 1965). The presence or absence of free oxygen essentially determines whether oxidizing or reducing conditions will prevail. Oxygen is normally available to reasonable depths as a result of percolating water carrying dissolved oxygen and also diffusion and flow dispersion (Matthess and Harvey, 1982, p. 107). - 161 - The redox potential of a solution is a convenient parameter to describe the relative intensity of oxidizing or reducing conditions during field investigations. The symbol, Eh, is used to denote the oxidation-reduction potential which is positive for oxidizing and negative for reducing conditions. Eh measurements are very sensitive to changes in dissolved oxygen and should preferably be measured In situ. This is seldom the case and only under exceptional conditions are such measurements stable and reproducible (Garrels and Christ, 1965, p. 136-138). Langmuir (1971, p. 599) suggested that Eh measurements should be considered primarily as a "descriptive tool". Stuns and Morgan (1970, p. 318) calculated equilibrium constants for the possible redox reactions in ground water and listed them in order of decreasing oxidizing potential at pH 7. From this list mainly iron and, to a lesser extent, manganese are important to this study. Both these elements originate from the dissolution of ferromagnesium minerals such as biotite. 7.3.3.1 Redox reactions involving iron The following types of equilibrium ere important in iron chemistry (Hem, 1963): (i) hydrolysis, with or without oxidation or. reduction, for example 2 Fe3+ • H20 j FeOH + + H+ (ii) solution and precipitation reactions involving anions other than 0H~, such as 2 FeC03 + H+ ; Fe + + HC03 (iii) redox equlibris, such as 2+ Fe(0H)3 + 3H+ + e j Fe + 3H20 •10 •»» \$ •*» «0.1 •V. -%, . • 04 v*\ OLí •>v v "x. • 0.4 X *h to '02 rv.^s ^ x 00 xN?° ^S. -0.2 -04 "•*>>. \. v »vv>v - ^^ ^ -0.Í ••*ío^ \ v \ O.B *V>X , %* -i.a _i_ i i ii i 6 • 10 12 14 pH Figure 7.17 Diagram shoving; fields of ferrous and ferric hydroxides at 25*C and 100 kPa total pressure. Stability limits of vater are also show. Dashed line is the aetastsble boundary of Fe and Fe(0B)2 in vater (after Carrels and Christ, 1965). Plots for pB and Eh for natural ground vater from the disposal site are shown. The Eh and pH data from the monitoring boreholes at Vaalputs (Fig. 7.17) (Table 7.8) were plotted on the iron hydroxides stability diagram (Garrels and Christ, 1965). All values fall within the stable ferric hydroxide field as expected from the positive Eh (+0,007 to +156) and neutral pH (6,9-7,5) values. This suggests that condition- are favourable for precipitation of ferric hydroxide from the ground water. The presence of abundant oxidized - 163 - iron minerals in the material hosting the disposal trenches and the favourable conditions for further precipitation are important to radionuclide containment for two reasons: (i) surface adsorption; and (ii) co-precipitation. Surface adsorption is the more important of the two and will be discussed later. Co-precipitation of uranium with amorphous ferric hydroxide is known in the natural geochemical environment (Samama, 1984). According to Samama, co-precipitation of iron and uranium hydroxides have been investigated in the laboratory by Sharkov and Yakoleva (1971). They have shown that these co-precipitates attached themselves to basic mineral species such as clays, feldspars, and carbonates. Brynard (1988) analysed a ferruginous nodule from the Dasdap Formation consisting of quartz and opaline ferruginized material. si0 The sample analysed about 30 X total iron, 60 X 7» with all the other elements in low quantities. The sample contained 75 ppm U, no Th or Zr and metals such as Zn, Hi, Co, Cr, all in relatively high proportions, suggesting co-precipitation of all these elements with iron. 7.3.3.2 Redox reactions involving uranium Uranium, as previously stated, is present in ground water as soluble 6+ 2+ uranyl (U ) complexes, such as the U0- carbonate complex. In a highly reducing environment these uranyl complexes are absent and the solubility of U for pH between 2 and 7 is less than 0,01 mg.ft' (Speer ££ al., 1981). They pointed out that reducing U to U + will form a virtually insoluble uranous compound effectively retarding the mobility of the uranium (nuclide" . However, it is doubtful if reduction of uranium is possible \zAar the natural oxidizing conations presently existing at Vaalputs. - 164 - 7.3.4 Iota exchange and adsorption Ion exchange and adsorption are the most important chemical processes because they can change the chemical character of a whole aquifer. Tredoux (1981) reviewed the work done on ion exchange and mentioned that as early as 1850 scientists noticed the base exchange properties of aquifers. Since then numerous investigators reported on the influence of these surface reactions on water quality in aquifers, among them Benick (1924), Foster (1950), Schoeller (1959) and Tredoux vx981). From the literature it is clear that two different types of surface reactions, ion exchange and adsorption, are possible. As both may occur at the same time, it is not easy to distinguish between them. The main difference between the two reactions can be attributed to the difference of the bonding forcea between the adsorbed ion and the adsorbent. Although all intermediate degrees of attraction may occur there are two extreme forms(Matthess and Harvey, 1982, p. 87, Schoeller, 1959). Firstly, the physical or Van der Waal's forces, in which the attraction between adsorbent and adsorbate is weak and, secondly, chemical adsorption (also called chemisorption or specific adsorption) with a strong valency bond. Hatthese and Harvey (1982) pointed out that reactions involving the valency bond may not only bind on the surface but actually fix ions into the crystal lattice of the adsorbent. Everett si ftl>> (1984) stated that the difference between ion exchange and adaorptlon lies in the fixation of the ion adsorbed. In the caae of ion exchange, the ion retains its mobility, but with adsorption the bond is so tight that the ion may be regarded as fixed. Chang and Page (1979) investigated the mechanism of adsorption and concluded that the covalent bond appears to be more important. Based on this exchangeability of the ion, the following discussion will deal with ion exchange and adsorption separately. 7.3.4.1 Ion exchange It is well known that iaany rock forming minerals and their weathering products are capable of exchanging cations and, in some - 165 - Table 7.19: Cation exchange capacities of Tarious minerals and colloids. Data from Carroll (1959) and Rosier and Lance (1972). Mineral Cation exchange capacity (meq.lOOg-1) at pH 7 Kaolinite 3-15 Hontmorillonie 50 - 150 Hontronite 75 - 80 Illite 10 - 70 Vermiculite 100 - 150 Chlorite 10 - 40 Glauconite 11 - 20 Humic Acids 100 - 500 Organic matter up to 300 cases, anions at their surfaces. These reactions are pH dependent and, under natural ground water conditions, anion exchange is not regarded important. This study concerns itself with the fate of cationic radionuclides and therefore only cationic exchange will be discussed. The cation exchange capacities of the various minerals shown in Table 7.19 were compiled by Edmunds (1977) from the data of Carroll (1959) and Bosler and Lange (1972). There are essentially three different ways in which cation exchange can take place (Tredoux, 1981; Hatthess and Harvey, 1982): (i) By occupying vacant cation positions on the edge of clay crystal lattices, for example the kaolinite and halloysite minerals. In the case of vermiculite and montmorillonlte this mode of exchange accounts onl/ for 20 % of the exchange capacity. The number of vacancies, and therefore the exchange capacity, increases with decreasing grain size. magnesium. Exchanges in this case take place on the basal cleavages planes and there is extensive fixation on these surfaces (Schoeller, 1959). Exchange in this way is responsible for 80 X of the exchange capacity of vermiculite and aontaorillonite. This exchange nay contribute to the capacities of Minerals with imperfect crystal structures such as illite, chlorite, halloysite etc., where fixation of cations takes place mainly on the outer surfaces. Grain size is not important in this case. (iil) By substitution of hydrogen and hydroxyl ions on the edge of all clay mineral particles. This is most important in minerals such as kaolinite and halloysite having an hydroxyl sheet on one side of the basal cleavage planes. Hydroxyl interlayers are important in montmorillonite and vermiculite. Hatthess and Harvey (1982, p. 91) noted that, for ions with the same valence, the bonding affinity of the exchanging ion increases with the atomic number while it decreases with decreasing ionic size. This implies a decrease with increasing hydrated radius. The ion with the smaller hydrated radius will therefore tend to displace the ion with the larger hydrated radius. This is expressed by the affinity series (Edmunds, 1977; Freeze and Cherry, 1979, p. 133): Cs+ > 8b+ > K+ >Na+ >Li+ stronger •*-•-» weaker B.2+> Sr2+>Ca2+ >Mg2+ Schoeller (1959, p. 61) called this affinity "the power of fixation," and arranged the Ï mo- and divalent cations in order of decreasing power of fixation: fH> f R1» f Ba> f Sr > f Ca> fMg> fK> flia> fLi - 167 - Some exchangers may have higher exchange capacity for selected ions. The selective uptake of up to 13 Z Cs by zeolites is an example (Matthess and Harvey, 1982, p. 91). In general the exchange is quickest in minerals in which the exchange takes plare predominantly on crystal edges (e.g. kaolinite) and slower with montmorillonite, vermiculite and attapulgite, because of the time it takes for the exchanging ion to diffuse into the exchanger (Matthess and Harvey, 1982, p. 92). The sum of the individual exchangeable bases of a soil sample is equal to the cation exchange capacity of the soil. The cation exchange capacity is expressed as milliequivalents per 100 g of sample (meq.lOOg- sample). Normally the exchangeable cations in a soil sample are replaced by either ammonium acetate or sodium acetate and the amounts of ammonium or sodium ions adsorbed are determined. Using drill samples from borehole W40N0 (locality shown in Fig. 6.8) Jakob (1983) measured the cation exchange capacity (CEC) utilizing 2+ strontium (Sr ) as the exchangeable cation. His results are shown in Fig. 7.18, where he expressed the CEC as meq per 100 gram sample. Based on these results Jakob (1983) did some experiments to determine partitioning coefficients of uranium and tracer quantities of cobalt. As it is impossible to distinguish between cation exchange and sorption, this will be discussed later. Cation exchange capacities of various minerals and colloids are shown in Table 7.19 as determined by various investigators. The main clays present at Vaalputs, as determined by Brynard (1988) are montmorillonite (smectite), illite and kaolinite. The distribution of these clays in three boreholes from the disposal site is shown in Fig. 7.19. The main trends are that smectite increases with depth, and illite decreases, while kaolinite contributes to the balance. As smectite (montmorillonite) has the larger CEC values, according to Table 7.19, it is beneficial to have this clay in the lower strata to act as a fixer horizon for radionuclides. - 168 - 7.3.4.2 Adsorption According to Everett ££ aJL., (19F4, p. 132) the main points regarding the adsorption of trace metals are: (i) Sorption occurs at the surface of amorphous iron and manganese hydroxides and oxides and aluminium minerals. (ii) Soil properties, such as grain size, do not influence adsorption characteristics. (iii) Other cations do not influence sorption reactions. SAMPLE EXCHANGEABLE CATIOPS DEPTH INTERVAL CATION EXCHANGE (nwq.toog'1) (m) DESCRIPTION M * C» CO) CAPACITY meq.wog-') K Na Mo O 10 20 JO 0 10 20 JO 010 O 10 0 10 20 0 20 40 'Y LOOSE RED SAND± ÏÏ |-i ' '_ p, | f Lio CALCRETE + SILCRETE 111 S> NDV :: CLAY CALC. 8ILCRETE GRITTY/FINE- GRAINEO CLAY WHITE SANDSTONE + CLAV 144 100 WHITE CLAY 101 111 :CUY BAND I n\ GRANITE 211 22 J 220 Figure 7.18 Depth-variation diagram shoving sample interval, calcium carbonate, cation exchange capacity and exchangeable cations for borehole W40HO at Vaalputs (Jakob. 1983). - 169 - BOREHOLE W30 SIO Wtathrrtil Bastmtnt frtslt Bast mint 75 0 T> 0 ''5 0 Ti Smectite Illtte Kaolinite Silt* Clay ( BOREHOLE W40 NO tírd Sana Wtathtrtd Bastmtnt Frtsh Baitmint Smectite [Kite Kaolimte Silt and clay (<45>j(ii) Vol % BOREHOLE W40 SIO Whitt cur Wnrhtrra Bsstmtnt frith Bêtimint Smectite [Kite Kaolimte Silt «Clay voi % (<45r> Figure 7.19 Profilea ahoving the distribution of llllte, eaectlte and kaoliaite in three horeh£& a at Vaalputa (after Brynard, 1988). (iv) Even trace elements which normally form anions (complexes) are adsorbed. Hem (1970, p. 126) pointed out that the oxides and hydroxides of manganese in rocks and soils are those in which the oxidation states of manganese are Mn , Mn and Hn These have the tendency to adsorb other metallic cations very strongly and as result of this they frequently contain significant impurities. Samama (1984) discussed the concentration of uranium in lateritic geochemical terrains where the main concentrating factor is thought to be finely divided amorphous iron hydroxide (Table 7.20). At pH between 6 and 7 the best enrichment occurs, but it is not easy to distinguish between true sorption and precipitation on the finely divided species. Rozkhova et al.f (1958) studied the inclusions of uranium in hydrogoethite which could not be detected mineralogically. They have used the process of electrodialysis to prove that the uranium is not part of the mineral but is held by a bond with a "sorptional character". A further example of sorption by iron and manganese hydroxides and oxides is that of cobalt mentioned by Hem (1970, p. 201). He suggested that this could be the reason for the low concentration of cobalt in natural waters. According to Matthess and Harvey (1982, p. 91) the bonding of 90 Sr during surface adsorption in soils depends on the effect of hydrated iron and aluminium oxides. The iron content of the geological formations at Vaalputs is relatively high varying from 0,55 to 19,95 X Fe.0, but is normally of the order of 2 to 5 X Fe2°3* Manganese values are of the order of 0,01 X MnO but values of 0,15 X MnO were recorded in the weathered granite. These values are ohown for various boreholes and the various geological strata at the disposal site in Appendix C. The presence of iron oxides and manganese oxide is ubiquitous in the sediments at the dispoaal site and' ?/ill certainly play a role in immobilizing radionuclide leakage. - 171 - Table 7.20: Geocheaical enrichment factors (GEF) of uranium for natural sorbents at pB's between 5 and 8,5 (Samama, 1984) Mineral Sorbents GEF 6 6 X-ray amorphous Fe (0H)3 1.1 x 10 - 2.7 x 10 fine-grained goethite 4 x 103 4 6 "amorphous" Ti(0H)4 8 x 10 - 10 humic acids and peat 103 - 104 phosphorites 15 oontmorillonitc 6 kaolinite 2 Norse (1986) gave an overview of the surface chemistry of calcium carbonate minerals in natural waters. He referred to Kornicker 2+ eJL_al. (1985) who studied the adsorption of Co on carbonate 2+ mineral surfaces. They found that Co had a much higher affinity 2+ 2+ for calcite compared to aragonite because Ca and Hg compete 2+ with Co for adsorption sites. They concluded that adsorption is 2+ influenced by factors such as the carbonate mineralogy, the Co concentration, and the composition of the solution. Jakob (1983) studied the effect of calcium on the sorption of tracer quantities of cobalt. He showed that the sorption of cobalt decreases with increasing amounts of calcium (Fig. 7.20). A reference experiment shows that «hen no calcium is added the sorption at the same pH will be higher for calcium above 0,5 M. The pH dependence of cobalt sorption was deuc' .trated by Jakob (1983) in Fig. 7.21 for the various geological sediments at - 172 - MjCaH Figure 7.20 The actirity of tracer quantities of cobalt regaining in solution (I.e. not sorbed on the clay) plotted against the calcium concentration (molar) in the solution. The reference activity of cobalt at corresponding pH, but no calcium added, is also shown for coapariaon (Jakob, 1983). (A is the activity at start and A is the activity at end of the experiment). Vaalputa. However, aa cobalt precipitates as Co(OH), in the neutral range, aome of the observed aUaorption may be due to precipitation. Similar pH dependence atudiea ahoved that, in the neutral range, pH 6 to 8, uranium ia better adaorbed on calcrete above pH 7 than below, as illuatrated in Fig; 7.22. Uranium aorption on clay indicated that the beat aorptipn occurs around pH 5,5 to 6,0, aa shown in Fig. 7.23. - 173 - The partitioning coefficient (K.) values for cobalt and uranium, as determined by Jakob (1983), are shown in Table 7.21 for the various geological strata. This compares well with tha- obtained by Meyer and Loots (1984) indicated in Table 5.10, except that Jakob shows uranium can vary locally within the white clay. It must be pointed out that these K. values were determined under laboratory conditions which cannot be applied as such under field conditions. However, the trends observed may be envisaged in the field although their magnitude may be different. These values are averaged out for the various geological units but the geological environment at Vaalputs is inhomofeneous and large differences would be expected with small changes in locality. Cesium is very effectively retarded by adsorption onto clay minerals, especially illite (Olsen si al.» 1986). The very slow migration of Cs reported from all the waste disposal sites is a result of the affinity of this element for selective and irreversible adsorption onto illite. Only the competition of other cations present in solution may affect the adsorption of Cs, but not the pH or Fe- and Hn-hydroxides. The presence of soluble organic complexes of Ca also has little effect on its migration (Olsen £jL-Al., 1986). The relatively high K. values for Cs at Vaalputs, as compared to Sr and U (Table 5.10), may be ascribed to the presence of illite. The clay and silt material (<45|an) constitute up to 39 X of the brown clay and it is this material that will play a major role in the retardation of radionuclides. The mean volumetric composition of the clay is 46 X smectite (montmorillonite), 32 X illite and 21 X kaolinite (Brynard, 1983). Davis and De Wiest (1967, p. 144) report that, below the cribs at 137 Hanford waste disposal site, Cs was the least mobile as result of the strong sorption onto clay surfaces. ^T74 - i» —.M^~ 101 Ao m solution A A CALCAREOUS SILCRETE •—• KAOLINITE *—"GRITTY CLAY 10-a HCI 6M 3M 1M 10» -+- +4 pH Figure 7.21 The distribution of cobalt in solution using somt bulk saaples of boreholes W40MO from Vaalpota. (AQ is the activity at start and A ia the activity at the end of the experiment) (Jakob, 1983). %U SORBEO /»9 U SORBEO .g~1 SAMPLE pH Flcure 7.22 Uraniw sorption on calcrete (0,5-1,0 and 2,5-i,/- •) (borehole W40H0) after 24 h equilibria (Jakob, 1983). - 175 - Table 7.21: Experimental bulk partitioning, coefficienta (K.) a for cobalt and nraniiai in aoae saaplea of percussion borebole W40KO froa the vas«:e disposal site at Vaalpnta (Jakob, 1983). SAMPLE DEPTH (n) K. for Co K for U PH a d Calcrete/Silcrete 1,0 - 2,3 8,4 1738 Calcareous Silcrete 8,0 - 8,8 8,4 1200 Gritty Clay 8,8 - 12,8 8,1 1400 14,4 - 20,0 7,9 2358 White Clay 15,0 - 16,5 8,3 1.3 15,0 - 16,5 5,5 35 20 °/o U HgU S0RBED M S0RBED .g-1 10 SAMPLE Figure 7.23 Uraniua sorption on clay (15,0-16,5 •) (borehole W4OM0) after 24 h equilibria* (Jakob, 1983). - 176 - 7.3.5 Attenuation of radionuclides at the Vaalputs disposal site It is useful to look at the total attenuation of radionuclides that can be expected at Vaalputa taking all the above-mentioned processes into account. In the context of this study the radionuclides 60Co, 90Sr, 134Cs, 137Cs and the U-lsotopes are the only isotopes of consequence that will be disposed of at Vaalputs. Due to their long half-lives they remain radioactive during the life of the repository (± 60 years) and after its closure. Of these, Cs will be the most abundant radionuclide. (i) 60Co 2+ It is expected that cobalt will only be present as Co at the Vaalputs site. As such it will precipitate completely from the soil moisture or the natural ground water as CoCO.. In the unlikely event of cobalt being present as Co +, it will precipitate completely as the insoluble Co(OH).. A further barrier to the migration of Co are its strong sorption properties. It may adsorp onto iron and manganese oxides or the clays. High K. values are indicated for sorption of Co in all the geological units present at Vaalput'i. It Is therefore concluded that Co will effectively be fixed below the trenches in the case of a leakage. (ii> 134C. and 137Cs Cesium does not participate in any of the precipitation reactions. However, Cs and Cs do not seems to present problems st other radioactive waste disposal sites due to their affinity for selective and irreversible adsorption onto illite. The occurrence of illite and other clays at Vaalputs and JC. values found for cesium Indicate that cesium should be effectively removed from the soil moisture. The migration of Cs and Cs should therefore present no problems and should be retarded effectively at Vaalputs *n case of leakage. - 177 - (iii) 90Sr Strontium is reported to be among the most mobile radionuclides present at Hanford and Savannah River (Davis and De Wiest, 1967, p. 144), Haxey Flats (Parker and Grant, 1975) and Oak Ridge (Parker and Grant, 1975, Olaen ejfc_ll., 1986). At Oak Ridge the reason for 90 the mobility of Sr was thought to be complex formation, although 90 it is commonly known that Sr does not easily form complexes and Is transported in the uncomplexed form. At Vaalputs it has been demonstrated that strontium, depending on the pH of the soil moisture, should locally precipitate as SrSO. 4 or as SrCO. as up to 60 X of strontium precipitated in the calcretlzed clay as SrCO.. Any strontium leaking from the soil moisture into the ground water will also be precipitated as SrCO-. In the ground water environment at Vaalputs more than 85 X othereforf the e strontiudeminismh oncise removethe ground da s wateSrCO.r i.s reachedStrontiu. mTh elevel relativels willy low K. values reported for strontium are therefor» of only minor concern at Vaalputs. (lv) Uranium Due to complexing of the uranyl ion as the triscarbonate complex, uranium seems to be the most mobile Isotope at Vaalputs. It is important to note from theoretical (Garrels and Christ, 1965) and practical considerations (Olsen et al.. 1986) that the stability of complexes is sensitive to relatively small changes in chemical controls (pH, Eh etc.). One would therefore expect that soluble (complexed) ions may precipitate at the interface of a geochemical boundary. The reported low K. values are due to complexing and the pH dependence of sorption. The pH of 5,5 to 6 where maximum sorption of uranium occurs is not expected at Vaalputs. However, uranium does exhibit sorption which varies locally within the heterogeneous geological environment, as shown by Jakob (1983). Chemica* analysis showed natural concentrations could be as high as 100 mg.kg~ in certain localities (Appendix C). The presence of the insoluble carnotite mineral has also been observed at Vaalputs, though calculations shoved that the soil moisture and ground water is in general undersaturated with respect to this mineral. - 179 - CHAPTER 8 GROUND WATER HODELLING The long-term integrity and containment of a low-level radioactive waste disposal site is the ultimate licensing requirement, of main concern is the infiltration and uptake of radionuclides by ground water, leading to the eventual contamination of underground water supplies. Measurement and prediction of ground water contaminant transport Involves an understanding of both tha ground water hydrology and chemical transport mechanisms. Prediction of tha behaviour of contaminant transport may be achieved through mathematical simulations. A large number of mathematical simulations, so-called models, are available today and the choice of the correct model requires an intimate knowledge of the geohydrological characteristics of the specific site. Two basic types of mathematical models exist: analytical models using analytical mathematical (algebraic) methods to solve empirical equations and numerical models used to simulate complex heterogeneous aquifers of Irregular shape often encountered In the field and which use numerical methods to solve the complex equations. There are two approaches to numerical simulations: those that Involve a finite-difference formulation, and those that involve a finite-element formulation. Tha differences between the two formulations are explained by Freeze and Cherry (1979, p. 18) by means of a two-dimensional, horizontal, confined aquifer of constant thickness discretlzed Into a finite number of blocks, each having a noda In the centre which defines tha hydraulic properties for the entire block. Tha fundamental difference between the two formulations lies in the nature of this nodal grid (mash). Tha finita element method Is superior in that it allows the design of an irregular mash that can be hand-tailored to any specific application. The number of nodes Is lass than raqulrad for the finite-difference simulation. Further advantages of the finite-eleaent approach are in the way it treats boundary conditions and in the simulation of anisotropic media. This approach was therefore the obvious choice for simulating the complex containment/transport conditions at Vaalputa. The consenration of mass is the basic principle used by most mathematical models to predict the fate of contaminants. Haas balance or material balance for a contaminant in a given locality is expressed by mathematical equations. The equation may be written in words as the rate of the rate of transport the rate of trans change of mass of mass into and out formation of mass at location x of location x at location x In order to demonstrate the construction of a simple mathematical model, Princeton University Water Resources Program (1984, p. 18) used radioactive decay as an example of transformation of mass. Their explanation is to a certain extent reproduced here. For a first order decaying substance the half-life can be shown to be t 1/2 P. 6?3 The half-life is therefore a function of the decay rate \.. The smaller the value of X. the larger the half-life and the longer the contamination problem. When substance A decays, it produces an end-product B that is also of co icern. This can be expressed a« A - B If the equation expressing the rate of decsy of A is written as - 181 - then the equation expressing the rate of production of B is written as ÍL »+y.x..A At X where y is called a yield coefficient and expresses the mass of B produced per mass of A decayed. If for each unit of A that has decayed, one unit of B is produced, then y - 1 and the equation is simply » +X,.A At l The solution is B » Bo + y.Ao - y.A().exp(-X1.At) or B - Bo + y.Ao.(l - ^(-X^t)). If B is also characterized by a first order decay rate, K , then » + y.X-.A - X,.B, At l z 2 and the aolution ia yX.A B * exp(-X..At) - exp (-X,.At) + B0exp(-X,.At) XA - A X 2 l It is notable that the solution equation becomes complex rather rapidly *a the system complexity incresses from one first order decaying substance to two, as shown in Fig. 8.1. If this change of mass takes place in a liquid such as ground water then the balance equation may be written as - 182 - the rate of change rate of mass the rate of mass of mass of species A flow of species flov of species A in a volume with A into the volume out of the volume time net rate at which species A is decaying in the volume. Direct analytical solutions for these complex equations are not possible and more sophisticated numerical mathematical techniques are necessary. Host modern textbooks on ground water, such as Freeze and Cherry (1979), give an introduction to this subject while the fundamental mathematical concepts are discussed by Botha and Finder (1983). A discussion of the mathematical principles of numerical ground water modelling is beyond the scope of this thesis and only the practical application of such models to the Vaalputs scenario is presented. MASS Ao Bo 0 TIME Figure S.l Solution for a coupled system. A - B (Princeton university Vater Besources Frogxsu, 1984). 8.1 Sits Specific Modelling As in other highly specialized fields, it was clesr from the onset of this project that the Atomic Energy Corporation (AEC) lacked - 183 - expertise in the field of geohydrological modelling. The Institute for Ground Water Studies (IGS) at the University of the Orange Free State was therefore contracted to carry out these studies. The choice of model dictated the geohydrological parameters that had to be determined. These parameters, the basic theory and method of determination have already been discussed in Chapter 5. The most important of them are: (1) the expected influx of water into the system (ii) the dispersion coefficients (iii) the hydraulic velocities (lv) the K.-values for the various isotopes expected to be present in the waste. To complete the set of input parameters, the Department of Nuclear Waste Technology at the AEC supplied an inventory of the actual activities predicted to be in the trenches after closure of the site. The parametric data were not available immediately as methodologies for their determination had to be devised. Furthermore the chosen model required data collected over a long period to monitor fluctuations (if any) that would have to be taken into consideration for verification. Therefore, the preliminary finite-element model reported on by Botha and Cogho (1983) made use of generic data. Although the results were encouraging the exercise proved that a model can only be realistic once it is calibrated against actual field data. This cslibration would be complete once the model could mimic past ground water conditions and then attempt to predict future behaviour. The modelling of contaminant behaviour is commonly used with confidence on s regionsl scale in the saturated zone. It is, however, less common in the unsaturated zone, but as Botha (1986) - 184 - pointed out, the theory is applicable to the unsaturated zone provided that it can be treated as a porous aediua. The unsaturated zona at the Vaalputs site consists, as previously described, of a sediaentary package overlying fractured rock. Although fractured rock is not generally considered porous, Botha (1986) showed that the saturated zone at Vaalputs behaves like a porous aediua (See section 6). The flow of subsurface water in the zone satisfies the aost primitive cfc racteristics of flow in a porous aediua - Darcy's law. Using the one-dimensional aodel originally developed by Aikens et alt (1979), Botha and Cogho (1984) simulated mass transport, using some of the field data that became available at that time. These included, dlspersivlty values (Stephenson, 1984), percolation (Hutson and Bedding, 1983) and K.-values (Meyer and Loots, 1984). Two conclusions considered important were reached by this aodel. The first was the doalnant effect that the dispersion coefficient had on the activity present at the discharge point. The 137 seconc was that the model indicated that the isotopes Cs and 90 Sr would form the bulk of the activity at the discharge point and therefore only these two needed to be considered. The authors stressed that these results only represented the best estimates available at that time and verification thereof was necessary using a more detailed model coupled with more representative data. Sufficient data became available at the beginning of 1985 to use the more sophisticated finite-element numerical aodel initially selected for the Vaalputs sites by Botha (1985). The aodel still needed refinement and Botha pointed out that the model has to be calibrated and verified with more site-specific data. After the computer code had been changed and refined, Botha (1986) concluded that the results obtained would be acceptable as representative of the actual situation at Vaalputs. 8.1.1 Description of the model The model is only concerned with possible movement of radioactive nuclides from the trench bottom downwards to the natural water - 185 - table. Movement of contamination was investigated, using a 1 500 m long cross-section AA across the repository as shown in Fig. 8.2. This left sufficient overlap to include an area outside the disposal site. The interpolated geological profile for this cross-section is shown in Fig. 8.3. The piezometric level, as previously discussed, is relatively flat and was fixed at 52,5 m below surface for this profile or 960 mamsl. The model used by Botha (1985, i.986) is based on the computer codes FEWWATRR and FEMWASTE (Teh and Ward, 1980, 1981) developed at the Oak Ridge National Laboratory. These codes use -he Galerkin finite element technique (Botha and Pinder, 1983) to solve the basic flow equation in combination with the mass transport equation. The finite element mesh ultimately selected by Botha (1986) is shown in Figure 8.4. Site specific data were available for the following parameters: saturated hydraulic conductivity, porosity and moisture retention curves (Van der Watt, 1984, 1985 and 1986), K. values (Neyer and Loots, 1984) and dispersivities (Stephenson, 1985). Van Genuchten's approximation (Van Genuchten and Nielson, 1985) was adopted by Botha (1986) for Van der Watt's moisture retention curves. It soon became clear that the volumetric moisture contents determined in the field with the neutron meter were too low and therefore not compatible with the values of the moisture retention curve obtained from Van Genuchten's approximation. The investigation of mass • transport across the cross-section AA was therefore restricted to steady-state conditions in order to avoid using any initial conditions in the light of the uncertain moisture values. The boundary conditions for the flow equation, up to a depth of 8,5 m, were derived from the volumetric moisture content data observed in the field. In view of the difficulties experienced with the available data it was decided to use the average moisture values, based on the original neutron meter calibration curve and adjusted for the dry density. Representative values for the deeper lsyers were obtained by interpolation from the value at 8,5 m to the - 186 - 34400 34100 e 35 200 o o o I X 3SM0 34000 42 no Y- Coordinate Figure 8.2 Location of the vaste disposal site shoving the section AA considered for modelling in the unsaturated zone (after Botha, 1986). level of the piezometrlc surface. Fig. 3.5 represents the soil head values used aa boundary conditions along the sides of the cross-section. The boundary conditions at the top part of the profile were kept at the fixed head distribution derived from the adjusted moisture values, while the boundary at the bottom part of profile was assumed to be impermeable. Since the area in vhich the repository is situated has not been used previously for the storage or dumping of radioactive materials, it is natural to assume an initial value of zero concentration for the mass transport equation. The boundary conditions used with the mass transport equation were restricted to the following: The radioactive concentration in the repository (nodes 446, 434, 433, 447, 435, 423 and 406 to 411 in Fig. 8.4) was allowed to vary according to the number of containers - 187 - present at a specific time. The data shown in Table 8.1 indicate the total amount of radioactivity that will leach from the containers if no credit is taken for the shielding effect of the containers themselves. On the rest of the surface (nodes 453 to 464, Fig. 8.4) the concentration was fixed at zero. The boundary conditions on the other three sides were taken to be time-dependent Neumann boundary conditions, i.e. a variable flux which depends on the concentration present at a specific node and time. This was done in order to account for leakage from the system. Table 8.1: The initial conditions used in the trench area with the mass transport equation for the simulation in the unsaturated zone (Botha, 1986). 12 Concentration (10 Bq) after Node 12 y 24 y 36 y 48 y 60 y 69 y 72 y 446 0,0 0,0 4.184E7 4.921E0 4,921E0 4.939E5 4.869E2 434 0,0 2.638E1 4,184E7 4,921E0 4.921E0 4,939E5 4,869E2 422 1,043E4 2,638E1 4.184E7 4,921E0 4.921E0 4,939E5 4,869E2 406 1,043E4 2,638E1 4,184E7 4,921E0 4,921E0 4,939E5 4,869E2 407 1,043E4 2,638E1 4,184E7 4.921E0 4,921E0 4,939E5 4,869E2 408 1,043E4 2,638E1 4,184E7 4.921E0 4,921E0 4,939E5 4.869E2 409 0,0 2,638E1 4.184E7 4,921E0 4.921E0 4,939E5 4,869E2 410 0,0 0,0 4,184E7 4,921E0 4,921E0 4,939E5 4,869E2 411 0,0 0,0 0,0 4,921E0 4,921E0 4,939E5 4,869E2 423 0,0 0,0 0,0 4,921E0 4,921E0 4,939E5 4,869E2 435 0,0 0,0 0,0 0,0 4,921E0 4,939E5 4.869E2 447 0,0 0,0 0,0 0,0 4.921E0 4,939E5 4,869E2 This form of specifying the boundary conditions has the advantage that one can change the results easily by multiplication with a suitable scale factor. 0 300 600 900 1200 1 Distance (m) **• gg Granite f\] Weathered granite ||| White clay [\] Red clay IH Calcrete • Sand Figure 8.3 Vertical croaa-section AA shoving the geological formations BB used in the unsaturated oodel (Botha, 1986). ö» ÏSt- ÉSL l?47 Jits fe!Z_ o E «I i£L HL. 1ZJ- o ss| ISI »51. m. 113 •o *»l 121. ia- Ü_ ii. #- !•_ it I» 11 15 x distance in m.lO"2 Figure 8.4 The finite eleaent mesh used in the simulation of radioactive mass transport at Vaalputs (Botha, 1986). - 190 - 1025 1000 f Pressure head (m) Figure 8.5 The Dirlchlet boundary valuea need along the left (0-0) and right hand (A-A) aidea of the finite eleaent aeah in Fig. 8.4 for aolring the flow equation (Botha, 1986). -i ï * i 1 * i i ïi rt ti rt rt * x values m.10"2 Figure 8.6 The steady state water levels of the cross-section AA in Fig. 8.3 simulated by FEMWATER (after Botha, 1986). - 192 - 8.1.2 Discussion of the results The model is not yet calibrated and therefore care must be exercised in interpreting the results. Botha (1986) pointed out that no attempt was made to conduct a sensitivity analysis on the model. Very preliminary numerical experiments, however, indicated that the moisture capacity is the most sensitive parameter in the model. 8.1.2.1 The flow equation Botha (1986) incorporated the full saturated domain from the piezometric level downwards into the model. As can be seen in Fig. 8.6 a boundary effect occurs at the water level near the edge of the trench. To remove this would require much more detailed information on the distribution of moisture in that area. -8 —1 Flow velocities of the the order of 10 m.s are restricted to the area below the piezometric level. Velocities decrease upward from about 10~ m.s~ near the piezometric level to approximately 10~ m.s ut the surface indicating very restricted movement of any ontaminant. 8.1.2.2 The mass transport equation 137 90 The work of Cogho (1984) suggested that Cs and Sr may cause problems in the environment. However, Botha (1986) restricted the 137 model to Cs, due to the problems experienced with the moisture values. As suggested by the low water velocities, the movement of 137 Cs was very restricted. The only meaningful movement was close to the trench area. The results at the relevant nodes are presented in Table 8.2. 8.1.3 Conclusions The mass fluxes obtained with this model are so small that they can be neglected for all practical purposes, except near the boundary of the trench. Botha (1986) argued that if the present results can be accepted as representative of the actual situation at Vaalputs, then - 193 - one should not expect any probleas even if the waste were dumped there without any containers. Caution should, however, be taken as the boundary conditions used for the flow equation are somewhat superficial. Botha is of the opinion that there is no reason to believe that «ore site-related data, very intense rains excluded, would alter the predictions of the present model to such an extent that any leakage from the proposed repository would cause serious environmental hazards. Table 8.2: Concentrations of Cs at selected nodes as predicted by the model for the unsaturated zone (Botha, 1986) Concentrations (HBq) after Hode 12 y 24 y 36 y 48 y 60 y 69 y 72 y 313 0,000 0,001 0,147 0,278 0,411 0,507 0,538 372 0,279 1,237 2,665 4,800 6,955 8,529 9,055 374 3,650 16,165 34,864 63,033 91,257 111,752 118,267 375 3,472 15,428 33,227 59,948 87,265 107,154 113,S75 376 2,555 14,443 32,233 58,887 86,022 105,905 112,425 378 0,000 0,008 6,207 34,089 62,427 82,559 89,079 379 0,000 0,000 0,000 19,184 45,140 63,652 69,627 402 0,248 1,099 2,358 4,223 6,083 7,348 7,760 404 3,108 13,741 29,516 53,090 76,669 92,888 98,196 413 0,000 0,000 0,000 20,823 48,932 69,069 75,571 8.2 Regional Modelling The regional modelling is concerned exclusively with the possible movement of contaminant outside the disposal area and even outside the Vaalputs site boundaries. The area considered measured 2 approximately 72 x 62 km or about 4 750 km , centred on the Vaalputs site and includes major parts ->f the nine adjacent 1:50 000 scale topo-cadastral sheets, callei the Norabees Block. - 194 - 8.2.1 Description of the model The reason for constructing this model was to get some insight into the possible behaviour of the regional hydrologic system, subject to given initial and boundary values. The model used in obtaining the results discussed below, is based on the iterative solution of the coupled flow and mass transport equations developed for the saturated zone. The model used for this investigation is based on the computer codes AQUAMOD 1 and AQUAMOD 2 developed by Van Tonder and Cogho (1987) at the Institute for Ground water Studies in Bloemfontein. The codes use the Galerkin finite element technique (Botha and Pinder, 1983) for the simulation of saturated ground water flow and pollution. The finite element mesh constructed for this investigation is shown in Fig. 8.7. Chemistry and water level data for the model were available from the regional survey by Levin (1983a) as well as all the relevant data gathered on the Vaalputs site, especially reports by Hodgson (1984 and 1986). Where parameters were not available, such as porosity and dispersion, generic values were used. Steady state solutions were obtained using prescribed boundary conditions. These steady state solutions were then used as initial conditions for the time-dependent simulations. Only Dirichlet boundary conditions were used in modelling the system. The Dirichlet boundary condition is a prescribed condition, in other words the water level and/or element concentration has to be prescribed on certain boundaries. In simulating the steady state solution and the time-dependant flow, this type of boundary condition was used on all boundaries. However, in simulating the time-dependant pollution these boundary conditions were applied to the following nodes (Fig. 8.7): 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 22, 43, 64, 85, 106, 127, 148, 169. This step was necce8sary for the convergence of the numerical solution. The whole area modelled is underlain by fractured granitic rock and the following assumptions had to be made as to some of the parameters: - 195 - atoooo-4 3SOOOO-I 360OW-* Y-COORDINATE Figure 8.7 The finite element aesh used in simulation of the contaatinant (Cl~) mass transport on a regional scale at Vaalputs. (i) Transaissivity values used were within the limits of those reported by Hodgson (1986). (ii) A ratio of 5:1 was used for longitudinal to transverse dispersivity. (ill) The porosity was kept constant at 0,01. (iv) An arbitrary value of 26 metres was chosen for the thickness of the aquifer. (v) For the mass transport only chloride concentration was used to simulate pollutant transport in the ground water. 8.2.2 Discussion of the results The kriged water level data, chloride concentrations and the co-ordinates for each node are presented in Appendix A and B respectively. 8.2.2.1 The flow equation A contour nap of the kriged water level values in metres above mean sea level (maasl) used is shown in Figure 8.8, while the steady state solutions are indicated in Fig. 8.9. A vector diagram of the simulated flow is presented in Fig. 8.10 showing that the main flow is from the higher area in the southwest, spreading to the west, east and northeast away from the watershed. In order to simulate a catastrophic event such as a rise in the water level at Vaalputa, the water levels at nodes 218, 219, 239 and 240 were raised by 20 metres. The resultant head contours are shown in Fig. 8.11 indicating that the 990 m contour now includes the Vaalputs site, dramatically changing the flow vector diagram, Fig. 8.12. However, one year after this event the flow vector pattern is back to normal, if one compares Fig. 8.10 and 8.13. To further illustrate this the decline of the raised head at node 218 against time is shown in Fig. 8.14. - 197 - 8.2.2.2 The mass transport eqaatlon A contour nap of the kriged chloride concentrations used is shown in Fig. a. 15. Simulation for 10 years did not show any significant change in the contours on this scale (Pig. 8.16). Snail changes in concentration at various nodes can be seen in Table S.3 and 8.4. However, definite changes in the contour pattern take place after a 100 year simulation as shown in Fig. 8.17. Table 8.3: Changes la simulated chloride concentration at nodes in a northeasterly direction from the disposal site. lode Initial value After 10 years After 100 years _1 _1 mg.t cr mg.i_1Cl~ ng.t cr 240 1235 1227 1178 262 1307 1290 1162 284 1460 1451 1328 306 1581 1575 1521 328 1721 1688 1592 350 1979 1959 1823 372 2132 2113 1991 394 2300 2287 2179 416 2462 2435 2281 The catastrophic event simulated previously was extended by increasing the chloride concentration by 200 mg.ft' at the same nodes (218, 219, 239 and 240), where the head was raised by 20 m. This would simulate a cataatrophic release of the pollutant under these conditions. The chloride contoura in Fig. 8.18 show the concentration on the Vaalputs site that reaulted from thia. The regional pattern had not changed and the flow pattern waa back to normal after about one year. The fate of the pollutant will therefore be exactly »8 simulated previously for the 10 and 100 year period notwithstanding the increase in concentration or rise in head. - 198 - -310000 - -320000 - -330000 - -340000 - i x -350000 - -360000 -40000 -30000 Y - COORDINATE Figure 8.S Kriged values of the observed vater levels (sassl) for the regional aodel. - 199 - -310000 - -320000 - -330000 - -340000 - i -350000 - -360000 -60000 -50000 -40000 -30000 -20000 -10000 Y - COORDINATE Figure s.o Steady state solution for the siaolation of the krlged vater lerels (•aasl) in Fig. S.t using AQUAHOD. - 200 - 310000- 320000- 330000- < z 5 350000- 360000- "» -* * •* -* A 1 —I -60000 -50000 -(.0000 -30000 -20000 -10000 r- C00R0INATE Figure 8.10 Vector diagraa shoving the flow pattern for the steady state conditions. - 201 - -310000 - -320000 - -330000 - I o s -340000 o I X -350000 - -360000 -60000 -50000 -40000 -30000 -20000 •10000 Y - COORDINATE Figure 8.11 Simulation of the water levels after raising the head by 20 • at nodes 218f 219, 239 and 240 under steady state conditions (water levels in mamsl). « * * ^ «•••.,.,,»».,-" ^ ^ 310000- « < < < • t t - , » + , A > ' 320000- * * * 330000- •••:-:KLf^:::: ::•••' • • - : • •*»•»•»* ^ , " k AT E z a » A V • **-*•*•»-» •»»* 340000- >,,*.»••-» -» ^ > <* COO S " * * » v *-^^*^- 350000- 360000- 1 | / 7 » I I ! 1 1 I 1 -60000 -50000 -40000 -30000 -20000 -10000 0 r- t 0 ORDINATE Figure 8.12 Vector diagran shoving the flow pattern after raising the head 20 0 at nodes 218, 219, 239 and 240. - 203 - -310000- -320000- -330000- a o -340000- -350000- -360000 - -60000 -50000 -40000 -3000O -20000 -10000 Y - COORDINATE Figure 8.13 Vector diagram shoving the flow pattern one year after the head was raised 20 m at nodes 218, 219, 239 and 240. - 204 - Table 8.4: Changes in simulated chloride concentration at nodes in an easterly direction from the disposal site. Node Initial value After 10 years After 100 years _1 mg.l_1Cl~ mg.%~lClL~ mg.i cr 240 1235 1227 1178 241 1300 1298 1246 242 1300 1292 1269 243 1490 1460 1346 244 1700 1675 1475 245 1773 1768 1658 246 1798 1788 1721 247 1910 1895 1812 248 1981 1966 1864 WATER LEVEL CHANGE WITH TIME WtfER LEVEL, (m) 200 300 TIME (Days) Figure 8.14 Decline of the water level at node 218 with time. The theory behind the advection-dispersion model for the prediction of contaminant migration in the saturated zone, is discussed by Freeze and Cherry (1979 p. 389) and Gillham and Cherry (1982). The model is based on the one dimensional form of the advection-dispersion equation. - 205 - D.(32C/812)-V. (9C/9Jl)=8C/3t where ft = a curvilinear coordinate direction taken along the flow line. V = the average linear ground water velocity. D- = coefficient of hydrodynamic dispersion in the longitudinal direction (ie. along t*:a flow path). C = solute concentration. The one dimensional spreading out of the concentration from the disposal site was simulated choosing a fixed linear velocity of 0,03 m.day" and dispersivities of 5 m and 100 m. Continuous supply of a nonreactive contaminant at the disposal site is assumed. The effects of adsorption, ion exchange, chemical reaction or radioactive decay are not considered. This exercise would therefore present a worst case scenario as any of the aforementioned effects will retard the spreading of contaminant and therefore enhance the suitability of the site for disposal. Fig. 8.19 shows a concentration profile for the conditions using a dispersivity of 5 m and linear velocity of 0,03 m.day- while Fig. 8.20 shows the profile using a dispersivity of 100 m and a linear velocity of 0,03 m.day- . In both cases 2 000 m is reached in a 100 year period but the curve shapes illustrate the concentration differences at various distances after the same time interval. 8.2.3 Conclusions Modelling over such a large area is complex and some generalizations and assumptions have to be made. Considerably more field data on the geology and hydrological parameters would be required to make more realistic simulations. More "possible event" scenarios may be investigated such as mimicking time dependent leaching from the site. - 206 - -310000 - -320000 - -330000 - I o 8 -340000 - u I X -350000 - -360000 -60000 -50000 -40000 -30000 -20000 -10000 Y - COORDINATE Figure 8.15 Simulated krlged chloride concentration (ng.iT ) distribution for the regional aodel using AQUAM0D 2. - 207 - -310000 H -320000 -\ -330000 ï a 8 -340000 H o I X -350000 4 -360000 -f -60000 -50000 -40000 -30000 -20000 -10000 Y - COORDINATE .-1, Figure 8.16 Simulated kriged chloride concentration («g.l ) dis tribution after 10 years.) - 208 - -310000 - -320000 - -330000 - I S -340000 - I x -350000 - -360000 -60000 -50000 -40000 -30000 -20000 -10000 Y - COORDINATE i-l. Figure 8.17 Simulated kriged chloride concentration (mg.l ) distribution after 100 years. - 209 - -310000 - -320000 - -330000 - 1 o K 8 -340000 - u I X -350000 - -360000 - -60000 -50000 -40000 -30000 -20000 -10000 Y - COORDINATE »-l. Figure 8.18 Simulated kriged chloride concentration (ng.i ) dis tribution after raising the concentration at nodes 218, 219, 239 and 2A0 with 200 mg.iT Cl~ (subsequent to raising the head 20 • at these nodes). DtSPERSIVITY 5m C/Co too fat» * * 075 050 0.25 • 000 1000 75O0 2O0O DISTANCE (m) —— 1 Yteer —•— 10 \feera -*- 100 Ybers Figure 8.19 The change in relative concentration with distance using a disperaiTity of 5 • and a linear Telocity of 0,03 a.day- 1 DISPERSIVITY 100m 0.75 050 0.25 0.00 0 500 1000 1500 2000 DISTANCE(m) — 1 Year -+- 10 >ears -*- 100 Years Figure 8.20 The change in relatiTC concentration with distance using a dispersiTlty of 100 • and a linear Telocity of 0,03 n.day- 1 - 211 - Using a contaainant such chloride as a pollutant is an extrene case because of its very high Mobility. Cationic radionuclides will behave differently, talcing adsorption, cation exchange and radioactive decay into account. This exercise, however, illustrates that the Vaalputs site could, even under catastrophic conditions be considered a suitable site. The slow Movement and migration of any contamination would provide enough time to implement corrective steps to counteract the spreading of pollutants. - 212 - CHAPTER 9 CONCLUSIONS The Vaalputs disposal site is located on the western edge of the relatively flat Bushraanland Plateau at an altitude of 1 000 metres above mean sea level. The disposal site is situated close to the triple junction of the Koa, the Buff els and Olifants Basins and is located within the fossil Koa Basin which means that no active drainage occurs on the plateau in the immediate vicinity of the disposal site. The area can be described as arid with an average annual rainfall of 74 mm. There is no surface run-off from the disposal site as rainfall immediately percolates into the sand, collects on the underlying calcrete surface and drains away to lower lying areas. Some of subsurface run-off collects in small pans in the interdune troughs. Regionally the disposal site is located within the Koa Drainage Basin with a flat hydraulic gradient suggesting slow ground water movement to the east and northeast. It is separated from the Buffels Drainage Basin to the west by a prominent watershed and to the south from the Olifants Drainage Basin by an ill-defined watershed. The long-term geomorphological stability of the area is reflected by the sedimentary accumulations of mid-Tertiary age (25 Ma). Very little geomorphological change can be expected over the next 300 years apart from redistribution of sand by sheet erosion, affecting only the top few centimetres. The basement rock consists of the fairly homogeneous Stofkloof Granite intruded by basic bodies of the Koperberg Suite. These rocks are overlain by a sedimentary cover of up to 30 m thick. The - 213 - sequence consists of 10 to 15 m of kaolinite/illite/smectite clays partly developed in situ and partly sedimentary; 15 - 20 m of fluvial red/brown to greyish clayey grit, which will host the disposal trenches; 1 to 5 m of calcretized clay with some silcrete nodules; and 0,5 to 1 m of loose and partially ferruginized aeolian sand at the top. In the unsaturated zone parameters necessary for numerical modelling were successfully obtained and a methodology established to monitor the moisture content of the geological units underlying the disposal site. Moisture retention curves determined for the various geological units below the trenches allowed the expression of the hydraulic conductivity in terms of the volumetric moisture content and the hydraulic head adopting Van Genuchten's approximation. The —8 low saturated hydraulic conductivities, averaged at 10 m.s~ ,show the eminent suitability of these formations as a host medium for waste disposal. Environmental isotope studies proved valuable in establishing the 18 nature and depth of percolation. 0 isotope profiles indicated the localized nature of infiltration while tritium showed that percolation during the last 50 years only reached 3,5 m depth. This was confirmed by neutron meter measurements subsequent to the rainfall event of 120 ma measured over four days in December 1985. Field measurements of the saturated dispersivity showed values ranging from 0,2 to 1,0 m in the vertical direction and 0,02 to 0,1 m in the horizontal direction. The clays in and around the disposal site have a sodic character and dispersion or deflocculation of the colloidal fraction takes place when in contact with pure or rain water. This was effectively demonstrated in the laboratory by the decrease in hydraulic conductivity when water is passed through the material. This property, which is a direct result of the high water soluble component of the material, enhances the suitability of the host medium for the disposal of radioactive waste. The depth to the piezometric level below the site is on the average 55 m. Ground water is confined to fractures, weathered joints and further afield to contacts between granitic rock and basic intrusives. The confined nature of the aquifer is demonstrated by the intersection of the ground water at depths below 55 m which then rise to the hydrostatic pressure level. The piezometric surface below the site is flat falling by approximately a meter along the diagonal of the site (± 1,5 km) to the northeast. The flat nature of this surface is seen as an advantage because in the case of severe leakage of radionuclides from the trenches into the ground water, large scale pumping of the ground water underneath the site will lower the piezometric level and create a local basin effect. In this way flow of ground water away from the site is Immobilized or even reversed and the spread of radionuclides to the surrounding boreholes prevented. Test pumping gave yields of up to 18 6001.h~ in the monitoring boreholes which is considered high for this area. Draw down curves in observation boreholes during pumping suggest interconnection of structures over long distances (500 m). This observation, however, could not be generalized as boreholes with similar permeability a short distance away were completely dry. The water-bearing structures are related to the tectonic history of the area. Packer testing suggested higher transmissivity in the fractured unsaturated zone above the piezometric surface than below. There is, as expected, a good correlation between fracture density and transmissivities. Similar transmissivities in water-bearing and dry boreholes at short distances suggest that the majority of the water bearing zones must be vertical because horizontal structures will convey water over larger areas. Storage factors in the order of 10~ are acceptable for a fractured unconfined aquifer but transmissivities tend to be high as they range from 1,3 to 45 2 -1 m ,d . The high transmissivities could be advantageous during possible dewatering operations in the event of leakage. - 215 - Regional chemical concentration gradients show an increase from the disposal site towards the Koa Drainage. The higher salinities towards the Koa Drainage are an indication of stagnation which confirms the slow movement suggested by the hydraulic 14 gradients. C isotope studies confirmed long turnover times with the older component dominating in the disposal site area where a conventional age of 10 000 years was obtained. No tritium was detected in these waters suggesting no addition of more recent 18 water. 0 isotopes showed more localised as opposed to a regional origin for the ground water. It was further shown that the quality of the underground water below the site could be the result of an evolutionary process, as the quality of soil moisture, reasoned from the soluble salts present, shows a progressive increase in salinity with depth, approaching the quality of the ground water. This build up of salinity is surely a result of cyclic evaporation in the upper layer being carried down and implies long residence times and slow movement of the ground water supported by the low hydraulic conductivities. The geochemistry of the ground water below the site proved to be saturated with respect to calcite and locally saturated with respect to gypsum. This water is further in chemical equilibrium with the day minerals kaolinite, smectite and illite.. The low iron and manganese is a result of the oxidizing environment and the presence of these elements is ubiquitous in the overlying lithologies attesting to their removal from the soil moisture. Taking cognisance of the geochemistry and mineralogy of the various lithologies and the chemistry of the ground water, the retardation potential of the various lithologies were evaluated. Distribution coefficients for the various radionuclides were determined for each 137 lithology. Satisfactory values were obtained for Ca and Co, however those of Sr and U were low. It has been demonstrated that Co will be totally removed from either the soil moisture or the ground water as CoCO.. In the event of Co being present, that will precipitate completely as Co(OK).. Cobalt also has strong sorption properties which could play a role should complete precipitation not occur. Cesium ( Cs and Cs) as experienced elsewhere in the world should present no problems as it is effectively and irreversibly adsorped onto illite which is present throughout the sedimentary sequence at Vaalputs. 90 Chemical precipitation will also remove Sr partially from the soil moisture as SrSO. or SrCO, and almost completely from the ground water as SrCO.. Any strontium not precipitated in the soil moisture and reaching the ground water, will largely precipitate, with strontium levels diminishing. Uranium presents a problem as it does not adsorb readily due to complex formation. Low K. values are experienced which may vary within the heterogeneous geological environment and some uranium will therefore be removed by adsorption. The presence of the stable carnotite mineral and relatively high uranium content in some of the sediments, does indicate that favourable localities exist where uranium may precipitate in this form. Geochemical calculations have shown that the soil moisture and ground water is undersaturated with respect to this mineral. Uranium is however of no great concern at Vaalputs as only trace quantities of its isotopes will be present in the waste from Pelindaba. This waste will only represent a fraction of the total waste disposed of at Vaalputs. Prediction of the behaviour of contaminant transport may be achieved through mathematical simulations and was performed for both the unsaturated and the saturated zone. It was shown that the mass fluxes obtained with modelling are so small that they can be neglected for all practical purposes. However, since the boundary conditions were somewhat superficial care must be taken in interpreting the results. It was further concluded' that more - 217 - site-related data would not alter this prediction to such an extent that any leakage within the trenches would cause a serious environmental hazard. On a regional scale, making general assumptions for dispersivity, porosity and the thickness of the aquifer, it was found that should contamination reach the ground water, no serious migration could be expected. Using chloride, which is a conservative tracer as a worst case scenario it was demonstrated that no dramatic migration takes place. Even increasing the hydraulic head at the disposal site by 20 m did not result in any significant movement. The increased head dissipated within one year to normal levels. Using a tracer, such as chloride, as a pollutant is an extreme case and cationic radionuclides will behave differently, taking adsorption, cation exchange and radioactive decay into account. The calculations, however, illustrate that even under catastrophic conditions the system will behave in such a way that enough time for corrective steps will be available. 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NODE X-COORO Y-COORO WATERLEVEL (m) 1 -6SS24 8 -35 6129 2 1050 C 2 -62660 3 -35 7326 3 1037 5 3 -59833 4 -35 6523 4 1043 8 4 -56968 6 -35 9720 5 1043 8 5 -54109 3 -36 0917 6 1043 8 6 -51184 6 -36 2114 7 1050 0 7 -48366 3 -38 6932 4 1050 0 8 -45548 1 -37 2049 8 1037 5 9 -42729 8 -37 1768 3 1000 0 10 -39911 6 -37 1868 0 987. 5 1 1 -37093 4 -37 2007 7 956 3 12 -35234 1 -37 2127. 3 950. 0 13 -31443 1 -37 2149 1 937 5 14 -27653 2 -37 2067. 9 931 .3 15 -23862 3 -37 1986 6 918 8 16 -20072 4 -37 1905 3 906. 3 17 -16281 4 -37 1824 1 900 0 18 -12491 7 -37 1721 .2 900. 0 19 -10029 7 -37 1721 2 893 8 20 -7568 8 -37 1702 0 887. 5 21 -5108 0 -37 1601 1 875 0 22 -66070 9 -35 5400 0 1025. 0 23 -63157 2 -35 6503 4 1037 5 24 -60204 7 -35 7505. 1 1043. 8 25 -57228 .5 -35 8570 4 1043 8 26 -54238 1 -35 9794 0 1043 6 27 -51257 .8 -36 1641 2 1050 0 28 -48291 9 -36 4064 0 1043 8 29 -45346 2 -36 6229 9 1043 8 30 -42406 2 -36 7557 8 1000 0 31 -39472 .0 -36 8003 2 968 8 32 -36617 5 -36 8269 7 962 5 33 -33580 .6 -36 8421 6 950 .0 34 -30297 8 -36 8483 4 931 3 35 -26661 . 7 -36 8477 .0 931 3 36 -22907 0 -36 8438 5 916 8 37 -19067 .6 -36 8418 9 906 .3 38 -15169 2 -36 8505 4 900 0 39 -12152 .4 -36 9279 4 900 .0 40 -8626 3 -36 8609 9 893 8 41 -6033 7 -36 8S63 4 881 .3 42 -5027 7 -36 9001 4 881 3 43 -66663 .6 -35 5044 .6 1000 .0 44 -63697 2 -35 5667 .5 1031 3 45 -60602 .8 -35 8431 . 1 1037 .5 46 -57489 9 -35 7297 .9 1043 .8 47 -54381 2 -35 8373 .8 1043 .8 46 -51285 2 -35 9715 . 7 1043 .6 49 -48206 .2 -36 1217 . 7 1043 .6 50 -45140 6 -36 2910 .8 1037 .5 51 -42080 .8 -36 3636 .6 1018 .8 52 -39020 3 -36 4273 .8 1000 .0 53 -35916 . 7 -36 4621 a 975 .0 54 -3271 1 .5 -36 4814 . 3 962 .5 1 - NOOE X-COORD Y-COOHO WATERLEVEL (m) 55 -29330. 9 -364899. 6 937. 5 56 -25767. 1 -364910. 3 931 .3 57 -22032. 4 -364880. 9 925. 0 58 -18139 . 5 -364860. 9 912. 5 59 -14076. 3 -364949. 5 900. 0 60 -9072. 4 -365084. 3 900. 0 61 -7239. 4 -365054. 0 900. 0 62 -4422. 3 -365353. 3 667. 5 63 -247. 4 -366341. 8 875. 0 64 -67582. 2 -354399. 2 * 975. 0 65 -64288. 3 -354799. 2 1031 .3 66 -61008. 2 -3S5257. 7 1037. 5 67 -57748. 0 -355847. 4 1037. 5 68 -54507. 8 -356604. 4 1037. 5 69 -51294 . 1 -357519. 3 1037. 5 70 -48104. 2 -35851 1 .4 1037. 5 71 -44930 .0 -359449. 6 1037. 5 72 -41759 . 1 -360217. 7 1012. 5 73 -38571 .7 -360766 . 1 993. 8 74 -35338 .6 -3611 15. 3 961 .3 75 -32021 .6 -361310. 6 962 5 76 -28588 5 -361392. 2 943. 8 77 -25018 .6 -361387.. 7 931 .3 76 -21299.. 6 -361322. 9 925. 0 79 -17397 .9 -361231 2 925.. 0 80 -13165 8 -361 139.. 7 900. 0 81 -8446 .0 -361076 . 4 900 0 82 -6116 4 -361035. 8 900. 0 83 -3045 2 -361029.. 8 881 .3 84 957 .6 -360527 .7 875.. 0 85 -68494 .7 -353787 .5 950 .0 86 -64850 6 -353852 .0 1006. 3 87 -61407 3 -353953 . 7 1031 .3 88 -57981 .4 -354212 .9 1031 .3 89 -54605 .5 -354647 .5 1031 .3 90 -51277 . 1 -355220 .5 1025 .0 91 -47985 3 -355863 .2 1031 .3 92 -44715 .0 -356494 5 1031 .3 93 -41448 .7 -357042 .6 1000 .0 94 -38166 .0 -357465 .6 1000 .0 95 -34843 .5 -357753 .6 981 .3 96 -31457 .0 -357916 .9 962 .5 97 -27985 .9 -357970 .8 943 .8 98 -24415 .0 -357927 .9 937 .5 99 -20729 .8 -357797 .2 925 .0 100 -16896 .8 -357587 . 1 925 .0 101 -12843 . 1 -35731 1 .9 906 .3 102 -8454 .0 -357016 .5 900 .0 103 -5721 .0 -356960 .5 893 .8 104 -2530 .9 -356712 .0 875 .0 105 957 .6 -356253 . 1 875 .0 106 -68802 .6 -353346 .9 925 .0 107 -65460 . 4 -352810 .3 962 .5 108 -61761 3 -352461 8 1000 .0 109 -58160 . 1 -352388 .6 1000 .0 - 2 - NODE X-COORD Y-COORO WATERLEVEl 1 10 -54653.. 1 -352542 2 1000. 0 111 -51222 . 7 -352845 3 1000 .0 112 -47844. 3 -353230. 5 1000 0 113 -44494 .9 -353635. 0 993 .8 114 -41 153, 3 -354005. 9 993. 8 115 -37799.. 4 -354306. 5 987. 5 116 -34413. 9 -354517. 2 981 .3 117 -30979 9 -354630. 7 966. 8 118 -27484. 6 -354644. 8 950. 0 119 -23921 .8 -354555. 6 950 0 120 -20291.. 4 -354352. 3 931 .3 121 -16597.. 1 -354012. 7 925. 0 122 -12849. 4 -353528. 7 906. 3 123 -8937 .9 -352902. 8 900. 0 124 -5788.. 8 -353023. 2 887. 5 125 -2448 . 4 -352887. 7 875. 0 126 957. 6 -351978. 5 875. 0 127 -70371 .8 -352949. 4 900. 0 128 -65982.. 7 -351 474. 6 937. 5 129 -62011 .9 -350656.. 7 950. 0 130 -58236 3 -350345. 6 962. 5 131 -54624 .2 -350288. 3 943 .8 132 -51117. 2 -350388. 8 981 .3 133 -47674 .9 -350581.. 6 993.. 8 134 -44267 3 -350815. 3 993. 8 135 -40870 .5 -351046 .2 987 .5 136 -37464 .9 -351241 .9 987.. 5 137 -34034 . 4 -351379 .3 981 3 138 -30566.. 2 -351443.. 1 962.. 5 139 -27053 . 4 -351 420 .0 950 0 140 -23497.. 9 -351293 .8 950 .0 141 -19916 .2 -351037 .9 937 .5 142 -16356 .9 -350606 . 1 925.. 0 143 -12893 .0 -349880 .5 906 .3 144 -9816 .5 -348912 5 900 .0 145 -5945 .9 -349338 . 1 887 .5 146 -2456 .0 -349455 .6 875 .0 147 940 .2 -349380 .6 875 .0 148 -71117 3 -351868 .8 875 0 149 -66310 .3 -349229 .2 887 .5 150 -62025 .6 -348473 .9 900 0 151 -58158 .6 -348069 . 4 900 .0 152 -54495 .2 -347884 . 1 912 .5 153 -50950 .3 -347842 .5 968 .8 154 -47473. 0 -347695 .5 1000. 0 155 -44029 .9 -348001 .6 987 .5 156 -40597 3 -348125 .5 981 3 157 -37156 . 7 -348238 .0 981 .3 156 -33694 . 1 -348316 .2 961 3 159 -30199 . 7 -346341 .3 956 .3 160 -26669 3 -348295 . 1 950 .0 161 -23107 .9 -348155 .6 950 .0 162 -19538 .2 -347889 .6 031 .3 163 -16018 .6 -347437 .6 918 .8 164 -12751 .0 -346709 .9 900 .0 - 3 NODE X-COORO Y-COORO WATERIEVEL (m) 165 -9816. 5 -344933. 4 900. 0 166 -5929. 0 -346160. 6 693. 8 167 -2373. 8 -346408. 7 681 .3 16« 940. 2 -346447 . 4 875. 0 169 -71364. 4 -345989. 7 650. 0 170 -65687. 8 -346448. 3 875. 0 171 -61721 . 1 -345972. 5 881. 3 172 -57896. 6 -345594. 7 861 .3 173 -54257. 9 -345339. 9 925. 0 174 -50720. 8 -345203. 6 981. 3 175 -47239. 4 -345158. 1 993. 8 176 -43783. 9 -346172. 6 987. 5 177 -40333. 2 -345218. 3 975. 0 178 -36871. 7 -345270. 1 975. 0 179 -33387. 5 -345306. 7 962. 5 160 -29872. 0 -345309. 5 950. 0 181 -26321 . 0 -345260. 3 950. 0 182 -22736 .6 -345137. 3 943. 6 183 -19130. 8 -344910. 6 925. 0 184 -15540.. 7 -344538. 0 912. 5 185 -12022. 0 -343928. 3 900. 0 186 -9543 .9 -343443 2 900. 0 187 -5325 7 -343412. 5 900. 0 188 -2154 0 -343541 .0 893. 8 189 940. 2 -343514. 3 881 .3 190 -68546 .8 -343066.. 2 850 .0 191 -64903 9 -343620. 9 850. 0 192 -61 1 12 6 -343366. 3 875 .0 193 -57473 4 -342977. 4 912. 5 194 -53927 9 -342673 9 962 .5 195 -50440. 3 -342473. 6 993. 6 196 -46982 .5 -342361 .5 987 .5 197 -43534 5 -342313. 7 981 3 198 -40081 . 1 -342306 .5 975 .0 199 -36610 .6 -342318.. 4 975 .0 200 -33113 3 -342331 .2 956 .3 201 -29581 .6 -342329 .0 943 .8 202 -26009 .3 -342296 . 7 943 .8 203 -22391 .9 -342217 .9 937 .5 204 -18724 . 1 -342072 .8 931 .3 205 -14988 .7 -341635 .9 906 .3 206 -11152 . 4 -341519 . 0 900 .0 207 -6364 .0 -341009 .5 900 .0 208 -4574 .5 -3409S6 .8 900 .0 209 -1849 .9 -340796 .5 900 .0 210 940 .2 -340561 . 1 893 .8 21 1 -66538 .3 -342059 . 3 850 .0 212 -63691 .2 -341341 .5 856 .3 213 -60368 . 7 -340724 . 2 900 .0 214 -56956 . 4 -340251 .0 943 .8 215 -53544 .0 -339897 .0 987 .5 216 -50132 .3 -339654 .0 1000 .0 217 -46717 . 4 -339500 .9 993 .8 218 -43291 . 4 -339415 . 4 967 5 219 -39847 .0 -339376 .6 981 3 - 4 - NOOE X-COORO Y-COOflO KVATERLEVEL Cm) 220 -36376. 9 -339366. 7 981 .3 221 -32874. 2 -339371 .1 956. 3 222 -29332. 2 -339373. 1 943. 8 223 -25743. 0 -339378.. 2 937. 5 224 -22096. 4 -339363. 1 937. 5 225 -18373. 7 -339324. 3 931 .3 226 -14533. 7 -3392S5. 4 906. 3 227 -10432.. 4 -339139. 1 900. 0 228 -5793. 4 -339002. 6 900. 0 229 -3956.. 6 -338567. 5 900. 0 230 -1608. 5 -338121. 3 900. 0 231 940. 2 -337648. 0 900. 0 232 -65686. 4 -341055. 0 850. 0 233 -62724.. 7 -338873. 7 868. 8 234 -59648. 4 -337967. 7 925. 0 235 -56437 1 -337394. 8 962. 5 236 -53155. 2 -337007. 2 975. 0 237 -49827 . 4 -336744. 3 993 8 238 -46463. 4 -336573. 6 1000. 0 239 -43067.. 1 -336471 .4 967. 5 240 -39638. 6 -336418. 9 975. 0 241 -36175.. 7 -336401 .7 975. 0 242 -32674. 4 -336409. 2 956. 3 243 -29129. 2 -336434.. 7 943. 8 244 -25532. 2 -336475. 1 937. 5 245 -21871 .2 -336531 . 4 931 .3 246 -18125. 7 -336608. 5 925. 0 247 -14257. 9 -336709 8 900 0 248 -10214. 8 -336833. 9 900. 0 249 -6154 .2 -336947 . 1 900 .0 250 -3816 3 -336214 0 900 .0 251 -1491 .6 -335461 .9 900 .0 252 940. 2 -334714. 8 900.. 0 253 -64834 5 -337060 . 4 850 .0 254 -61994.. 6 -335843. 0 900 .0 255 -59035 .8 -334939 .0 925 .0 256 -55976 .9 -334374 . 4 956 3 257 -52809 0 -333997 . 7 962 .5 258 -49556.. 8 -333744 . 7 967 .5 259 -46240 .8 -333579 .5 1000 .0 260 -42874. 3 -333479. 0 987 .5 261 -39464 .0 -333427 3 975 .0 262 -36012 2 -333413 . 4 975 .0 263 -32517 .9 -333430 .8 943 .8 264 -28977.. 1 -333477 .5 943 .8 265 -25383 .0 -333557 .3 937 .5 266 -21725 5 -333680 2 925 .0 267 -17990 .2 -333864 8 925 .0 268 -14157 3 -334138 .8 900 .0 269 -10235 .5 -334513 .8 900 .0 270 -6154 .2 -334964 .3 900 .0 271 -3885 5 -333853 . 7 900 .0 272 -1486 .5 -332793 . 9 900 .0 273 940 .2 - 3 3 1 7 8 1. 7 900 .0 274 -64149 .6 -332972 .6 850 .0 - 5 NODE X-COORO V-COORD WATERIEVEL Cm) 275 -61319. 8 -332242. 0 900.0 27« -58557. 6 -331633. 5 925.0 277 -55627. 3 -331 163. 0 950.0 27» -52544. 4 -330872. 0 962 5 279 -49347. 3 -330660. 9 981 3 280 -46066. 9 -330522. 6 975.0 281 -42723. T -330439. 4 975.0 282 -39329. 7 -330399. 3 975.0 283 -35890. 5 -330395. 3 975.0 284 -32407. 1 -330424. 6 950.0 285 -28877. 2 -330489. 7 943.8 286 -25295. 6 -330599. 1 937 .5 287 -21655. 7 -330770. 6 931 .3 288 -17950. 4 -331035. 0 925.0 289 -14177. 7 -331443. 8 900.0 290 -10306. 1 -332101. 1 900.0 291 -6462. 1 -332971. 9 900.0 292 -3976. 0 -331424. 0 900.0 293 -1542. 8 -330052. 8 900.0 294 940. 2 -326848. 6 900.0 295 -62910. 5 -328858. 5 850.0 296 -60801. 3 -328490. 2 893.8 297 -58274. 3 -328139. 0 918.8 298 -55430. 6 -327857. 9 937.5 299 -52390. 2 -327650. 9 956.3 300 -49217 2 -327507. 0 962.5 301 -45952. 7 -327412. 7 968.8 302 -42622.. 0 -327358., 1 975.0 303 -39239. 3 -327336. 6 975.0 304 -35811 .9 -327345.. 4 968.8 305 -32341 .9 -327384;. 9 950.0 306 -28828 . 1 -327460 .2 950.0 307 -25266 5 -327583 .0 937.5 308 -21652 .0 -327774 .3 925.0 309 -17982 . 1 -328070 .5 925.0 310 -14263 .0 -328537 . 4 906.3 31 1 -10536 . 7 -329269 .2 900.0 312 -6462 . 1 -330949 .8 900.0 313 -4201 .0 -328629 .2 900.0 314 -1613 .9 -327176 . 1 900.0 315 940 .2 -325915 . 4 900.0 316 -62161 .9 -324825 .0 856.3 317 -60767 .6 -324688 .0 875.0 318 -58269 .5 -324563 .2 912.5 319 -55420 .5 -324454 .0 937.5 320 -52361 .0 -324367 .6 950.0 321 -49173 . 4 -324304 .8 956.3 322 -45901 .6 -324264 .3 962.5 323 -42570 .0 -324244 .6 975.0 324 -39192 . 1 -324245 .0 975.0 325 -35774 .6 -324266 .2 956.3 326 -32319 . 7 -324311 .2 950.0 327 -28826 . 4 -324386 .3 950.0 328 -25290 . 7 -324503 . 1 937.5 320 -21706 .6 -324681 .0 925.0 - 6 - totocxtotototofattototototototototototototototototototoutfdtotototototoutotototototacatotototototototototototo «•«••NNNNNNNNNN«««(IIC)OI«OI«aiU V>«OiO 3 NODE X-COORD V-COORO WATERLEVEL (m) 385 -46020. 0 -314770. 0 S50. 0 38« -42633. 4 -314641 . 7 3 50.0 387 -39243. 1 -314893. 4 950. 0 388 -35846. 1 -314932. 1 950. 0 389 -32442. 2 -314961. 8 9 50 0 390 -29032. 1 -314983 8 9 4; s 391 -25616. 5 -314997. 2 925 .0 392 -22192. 6 -314998. 2 925. 0 393 -18746. 2 -314960. 0 925. 0 394 -15228. 3 -314934. 3 912. 5 395 -11442. 5 -314853. 6 900. 0 396 -6889. 6 -314754. 5 900. 0 397 -4869. 7 -314576. 8 900. 0 398 -2088. 1 -314388. 7 900. 0 399 940. 2 -314162. 8 i»00. 0 400 -70217 . 9 -308624. 4 850. 0 401 -64477. 7 -310065. 7 893. 8 402 -60292. 4 -310666. 6 916. 8 403 -56534. 1 -31 1067. 8 937. 5 404 -52974 5 -311337. 0 943 8 405 -49506. 0 -311519. 9 950. 0 400 -46085 8 -311644 4 950. w 407 -42683 7 -311729 2 950. 0 408 -39269 6 -31 1786 5 950 0 409 -35898 9 -311823 2 950 0 410 -32511 2 -311842 0 950 0 411 -29130 2 -311841 8 937 5 412 -25762 4 -31 1816 5 925 .0 413 -22417 0 -311753 9 925 0 414 -19103 9 -311633 9 925 .0 415 -15828 1 -31 1426 1 906 3 416 -1261 1 0 -311115 6 900 .0 417 -9056 2 -310700 1 900 0 418 -5948 9 -310955 1 900 .0 419 -2489 3 -311128 0 900 0 420 940 .2 -31 1249 . 7 900 .0 421 -69729 7 -306641 6 856 .3 422 -64629 .6 -307018 .7 887 .5 423 -60414 .7 -307572 .6 912 .5 424 -56636 .9 -307965 .7 931 .3 425 -53054 .3 -308239 .6 937 .5 426 -49568 .9 -308427 .9 950 .0 427 -46135 .4 -308556 3 950 .0 428 -42728 .0 -308642 .8 950 .0 429 -39334 .2 -308698 .9 950 .0 430 -35949 .6 -308730 8 950 .0 431 -3*574 .9 -308740 .0 943 .8 432 -29216 .0 -308723 .0 3 31 .3 433 -2588» .3 -Í08670 .3 !<2 5 .0 434 -22608 4 -308563 . 7 925 0 435 -19419 T -308371 8 9. s .0 436 -16390 .a -306043 .5 90S 437 -13682 .3 -307476 . 1 90 C V 438 -12370 . 4 -306738 . 4 900 ?+ 439 -6945 .5 -307409 .7 900 /* - 8 - NODE X-COORO Y-COORD WATERIEVEL 440 -2882. 6 -3 07944.6 900.0 441 940. 2 -3 08316.5 900.0 442 -67739. 9 -3 03763.0 850.0 443 -63948.. 6 -3 04179.6 875.0 444 -60216. 1 -3 04635.6 887.5 445 -58579 7 -3 04981.2 912.5 446 -53045. 7 -3 05224.7 931.3 447 -49584.. 1- 3 05393.0 943.8 446 -46163. 2 -3 05508.0 950.0 449 -42761.. 1 -3 05585.1 950.0 450 -39371. 0 -3 05634.0 950.0 451 -35992 .0 -3 05659.6 950.0 452 -32625.. 1 -3 05662.2 943.8 453 -29276 . 1 -3 05637.2 931.3 454 -25962.. 1 -3 06573.9 931.3 455 -22718 .0 -3 05452.1 931.3 456 -19598. 1 -3 05236.9 925.0 457 -16693 . 7 -3 04864.2 906.3 458 -14189. 3 -3 04223.2 900.0 459 -12318.. 8 -3 02697.6 900.0 460 -7409. 0 -3 04220.0 900.0 461 -3088 . 7 -3 04894.1 900.0 462 940. 2 -3 05383.4 900.0 APPENDIX B Chloride concentration used in regional modelling. W» * (•» H» -» O N • Ul «U N •• ooaN*ui»uN-o«oi'iaui»uK>^o« dN«UI«>UM-'0« N« tfl « U M ' I I I I I I I I I I • I I i i i i i < i • i • i i i i i i i i i i i i i i i i i i • i i i i i i i t I | !_._._. W»0INOi k*«*UU(ilM«OOOOOCtlN»WOtOlllin«*U»UNN Ni»giOMMuukNio-'NOiaaN»ioooia«io»«Aiovi^uiuiONaaaiNNioMON. 56 -25767. 10000 •364910.30000 1807.53700 S -22032. 40000 364880.90000 1963.65500 S -18139. 50000 •364860.90000 1996.33200 5 -14076. 30000 364949.50000 2050.30000 6 -9072. 40000 -365084.30000 2082.41400 6 -7239. 40000 •365054.00000 2086.43700 6 -4422. 30000 •365353.30000 2090.09100 -247. 40000 •366341.80000 2100.30000 -67582. 20000 -354399.20000 1163.01500 -64286. 30000 -354799.20000 1184.54800 -61008. 20000 -355257.70000 1235.21000 -57748. 00000 -355647.40000 1300.30000 -54507. 80000 -356604.40000 1333. 76000 -51294. 10000 -357519.30000 1331 .40500 -48104. 20000 -358511.40000 1373.97300 -44930. 00000 -359449.60000 1407.41900 -41759. 10000 -360217.70000 1350.30000 -38571. 70000 -360766.10000 1514.45700 -35338. 60000 -361115.30000 1607.82300 -32021. 60000 -361310.60000 1739. 34000 -28588. 50000 -361392.20000 1778.91100 -25018. 60000 -361387.70000 1900.30000 -21299. 60000 -361322.90000 1960.65300 -17397. 90000 -361231.20000 1990.67500 -13165. 80000 -361139.70000 2048.70700 -8446. 00000 -361076.40000 2100.30000 -6116. 40000 -361035.80000 2082.89100 -3045. 20000 -361029.80000 2068.97100 957. 60000 -360527.70000 2054.29600 -68494. 70000 -353787.50000 1146.04300 -64850. 60000 -353852.00000 1180.32800 -61407. 30000 -353953.70000 1222. 17300 -57981. 40000 -354212.90000 1294 .29800 -54605. 50000 -354647.50000 1324 .55000 -51277. 10000 -355220.50000 1319.64200 -47985. 30000 -355863.20000 1314. 16500 -44715. 00000 -356494.50000 1321 .57600 -41448. 70000 -357042.60000 1354.42300 -36168. 00000 -357465.60000 1423 . 15900 -34843. 50000 -357753.60000 1527.46500 -31457 00000 -357916.90000 1650.00000 -27985. 90000 -357970.80000 1757.01600 -24415 00000 -357927.90000 1799. 71700 9 -20729. 80000 •357797.20000 1904. 12700 10 -16896. 80000 •357587.10000 1990.30000 10 -12843 10000 -357311.90000 2039 . 11800 102 -8454 00000 -357016.50000 2048.32400 10 -5721 00000 -356960.50000 2042.27600 10 -2530 90000 -356712.00000 . 25.33900 10 957 60000 -356253.10000 2000.30000 10 -68802 60000 -353346.90000 1 137.97909 10 -65460 40000 -352810.30000 1174 .00200 10 -*1781 30000 -352461.80000 1200.30000 10 -58160 . 10000 -352368.60000 1 184 .84200 110 -64653 10000 -352542.20000 1278.72100 - 2 - NODE Y-COORD X-COORD CHLORIDE CON (mg/littr) 111 -51222. 70000 -352845. 30000 1300. 30000 1 12 -47844. 30000 -353230. 50000 13 10. 31500 1 13 -44494. 90000 -353635. 00000 1313. 98800 1 14 -41 153. 30000 -354005. 90000 1344 .5100 0 115 -37799. 40000 -354306. 50000 1367. 39700 116 -34413. 90000 -354517. 20000 1485. 66000 117 -30979. 90000 -354630. 70000 1599. 76300 116 -27484. 80000 -354644. 80000 1752. 97000 119 -23921. 80000 -354555. 60000 1841 . 87700 120 -20291. 40000 -354352 .3000 0 1873. 98200 121 -16597. 10000 -354012. 70000 1946. 53500 122 -12849. 40000 -353528. 70000 2023. 60000 123 -8937. 90000 -352902 .8000 0 2025. 29500 124 -5788. 80000 -353023 .2000 0 2022. 85900 125 -2448. 40000 -352867. 70000 2019. 69200 126 957 60000 -351978 50000 2017. 44900 127 -70371. 80000 -352949. 40000 1100. 30000 128 -65982 . 70000 -351474 .60000 1 167.5990 0 129 -62011. 90000 -350656 .70000 1151. 93800 130 -58236 .30000 -350345 .60000 1 139. 46600 131 -54624..2000 0 -350288. 30000 1 186.1690 0 132 -51 117 .20000 -350388 .80000 1 193.5090 0 133 -47674..9000 0 -350581 ..8000 0 1253. 69900 134 -44267 .30000 -350815 .30000 1290..4850 0 135 -40870..5000 0 -351046 .20000 1300. 30000 136 -37464 .90000 -351241 .90000 14 19..0600 0 137 -34034..4000 0 -351379 .30000 1450. 30000 138 -30566 .20000 -351443 . 10000 1575..5540 0 139 -27053.. 40000 -351420 .00000 1649. 25000 140 -23497 .90000 -351293 .80000 1750 .30000 141 -19916. 20000 -351037 .90000 1842.. 15700 142 -16356 .90000 -350606 . 10000 1904 .21900 143 -12893. 00000 -349880 .50000 1930 .66900 144 -9816 .50000 -348912 .50000 1998 .36700 145 -5945 90000 -349338 . 10000 2000 .30000 146 -2456 .00000 -349455 .60000 2000 .30000 147 940. 20000 -349380 .60000 2000 .30000 148 -71 117 .30000 -351868 .80000 1 124 .92900 149 -66310 .30000 -349229 .20000 1 164 .33000 ISO -62025 .60000 -348473 .90000 978 .86120 151 -58158 .60000 -348069 .40000 1064 .85600 152 -54495 .20000 -347884 .10000 1066 .35300 153 -50950 .30000 -347842 .50000 1 132 .16600 154 -47473 .00000 -347895 .50000 1229 .88200 155 -44029 .90000 -348001 .60000 1237 .40100 156 -40597 .30000 -348125 .50000 1318 .67600 157 -37158 .70000 -348238 .00000 1344 . 75400- 158 -33694 . 10000 -348318 .20000 1375 .85100 159 -30199 . 70000 -348341 .30000 1586 .97900 160 -26669 .30000 -348295 . 10000 1645 .46300 161 -23107 .90000 -348155 .60000 1739 .98300 162 -19538 .20000 -347889 .60000 1804 .56700 163 • - 1 3 0 1.6000 8 0 -34;«37 .60000 • 190* .73100 164 -12751 .00000 -346709 .90000 1997 .77200 165 -9816 .50000 -344933 .40000 2024 . 22700 - 3 - NODE Y-COORO X-COORO CHLORIDE CON (mg/lit«r) IBS -5929. 00000 -346180. 60000 2017. 82900 167 -2373. 80000 -346408. 70000 2021 . 47200 168 940. 20000 -346447. 40000 2000. 30000 169 -71364. 40000 -345989. 70000 940. 33900 170 -65887. 80000 -346448 .3000 0 924 .5153 0 171 -61721 . 10000 -345972. 50000 91 1 .7298 0 172 -57896. 60)00 -345594. 70000 930. 30000 173 -54257 90000 -345339. 90000 1064 22600 174 -50720. 80000 -345203. 60000 1 104.1800 0 175 -47239 40000 -345158. 10000 1 188.1300 0 176 -43783. 90000 -345172. 60000 1224. 06400 177 -40333 20000 -345218. 30000 1300 16700 178 -36871 . 70000 -345270. 10000 1321 12500 179 -33387 50000 -345306. 70000 1343 27900 180 -29872 00000 -345309. 50000 1501 .2360 0 181 -26321 00000 -345260. 30000 1651 3O60O 182 -22736. 60000 -345137. 30000 1667. 85500 183 -19130. 80000 -344910. 60000 1755 49400 184 -15540. 70000 -344538. 00000 1861 .5470 0 185 -12022 00000 -343928 . 30000 2028. 44200 186 -9543 90000 -343443 . 20000 2026. 0O20O 187 -5325 70000 -343412 50000 2022 1 1500 188 -2154 00000 -343541. 00000 2027. 44900 189 940 20000 -343514 30000 2030 38500 190 -68546 80000 -343065. 20000 743 6S900 191 -64903 90000 -343620 90000 7\ 1 66680 192 -611 12 60000 -343366. 30000 791 06450 193 -57473 40000 -342977 40000 930 73680 194 -53927 90000 -342673 90000 1034 31 100 195 -50440 30000 -342473 60000 1 100 3O00O 196 -46982 50000 -342361 50000 1 123 56900 197 -43534 50000 -342313 7O00O 1 168 04500 198 -40081 10000 -342306 50000 1250 30000 199 -36610 60000 -342316 40000 1253 36900 200 -331 13 30000 -342331 20000 1322 26500 201 -29581 .60000 -342329 .00000 1482 . 71000 202 -26009 .30000 -342296 70000 1598 79100 203 -22391 .90000 -342217 .90000 1753 .38800 204 -18724 .10000 -342072 .80000 1758 19900 205 -14988 .70000 -341835 .90000 1963 .34000 206 -11152 .40000 -341519 .00000 1985 .32700 207 -6364 .00000 -341009 .50000 2000 .30000 208 -4574 .50000 -340986 .80000 2040 . 1 4300 209 -1849 .90000 -340796 .50000 2058 .75800 210 940 .20000 -340581 . 10000 2064 .60700 21 1 -66538 .30000 -342059 .30000 661 . 13640 212 -63691 .20000 -341341 .50000 701 .96940 213 -60368 .70000 -340724 .20000 781 .26790 214 -56958 .40000 -340251 .00000 910 . 46400 215 -53544 .00000 -339897 .00000 1006 .55200 216 -50132 .30000 -339654 .00000 1039 .97200 217 -46717 .40000 -339500 .90000 1115 .21200 216 -43291 .40OO0 -339415 .40000 1181 . W80G 219 -39847 .00000 -339376 .60000 1247 . 18400 220 -36375 .90000 -339366 .70000 1255 .57800 Z o o m ii i i i i i i i • i i i i i i i i i i i i • i i i i i i i i i i i i i i i i i i i i OkO> I I |—_— N>»s>IOCdCdCd**»tf»«*lWC»0» I I I •'-•••MMMUUU**»UlOlUlAOI I I I -> - - N M M U — jk U«O»N.»giaM»()Ma0NIIIIO-<« — Id -< d AO*a- a«Ml»U>K>lkUMOlO-'CMOuaaOttOiaUlNOIUK)OI I I I I I I I I I I I I I I I I I I I t I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I CdCdCdCdCdCdCdCdldCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdCdldCdCdCdCdCdCdldCdCdCd Cd Cd Cd Cd Cd (d Cd Cd Cd Id Id Cd Cd Cd X N>K>->Mu»»kUuwuuuu(ubuu»«o rororor>>-> — -> — -»-•-.-•___*_. o ts>tOI\>H>-«_-.-»-.-.-.-»-»-« X Aa-'O-'OttAttNNAUUN-' o o a» -« -* -«• 000-'0<0^4-4-4*CdCdK>->00 3 NOOE Y-COORD X-COORO CHLORI0E CON (mg/litar) 276 -58557. 60000 -331633 . 50000 639. 84610 277 -55627. 30000 -331 183 .oooo o 600 . 30000 278 -52544. 40000 -330672. ooooo 820 .3022 0 270 -49347. 30000 -330660. 90000 936 . 43270 280 -46066. 90000 -330522. 60000 1050 . 30000 281 -42723. 70000 -330439. 40000 1085 .8880 0 262 -39329. 70000 -330399. 30000 1224. 79300 283 -35690. 50000 -330395. 30000 1338. 10400 284 -32407. 10000 -330424 . 60000 1460. OOOOO 28S -28877. 20000 -330489. 70000 1481 . 52200 288 -25295. 60000 -330599. 10000 1712. 92200 287 -21655. 70000 -330770. 5O00O 1850. 30000 288 -17950. 40000 -331035. OOOOO 1878. 09400 289 -14177. 70000 -331443. 80000 1873. 33400 290 -10306. 10000 -332101 . 10000 1958. 63300 291 -6462. 10000 -332971 . 90000 2064. 71200 292 -3976. ooooo -331424. OOOOO 2000. 30000 293 -1542. 80000 -330052. 80000 2108. 75900 294 940. 20000 -328848. 60000 2155. 82100 295 -62910..5000 0 -328858. 50000 610. 66460 296 -60801. 30000 -328490. 20000 616. 81560 297 -58274 30000 -328139. OOOOO 634 32470 298 -55430. 60000 -327857. 90000 726. 78180 299 -52390. 20000 -327650. 90000 768. 39120 300 -49217. 20000 -327507. OOOOO 941 .5610 0 301 -45952..7000 0 -327412..7000 0 1042. 10700 302 -42622. 00000 -327358. 10000 1066. 53400 303 -39239..3000 0 -327336..6000 0 1234 53900 304 -35811 . 90000 -327345. 40000 1448. 96400 305 -32341 ..9000 0 -327364. 90000 1563 .61500 306 -28828. 10000 -327460. 20000 1581. 79800 307 -25266 .50000 •327583. OOOOO 1705 . 74300 308 -21652. 00000 -327774 30000 1941 . 47700 309 -17982 . 10000 -328070 .50000 1971 .52600 310 -14263. ooooo -328537..4000 0 1974 01 100 311 -10536 .70000 -329269 .20000 1995 .67100 312 -6462. 10000 -330949..6000 0 2055 97800 313 -4201 .00000 -328629 .20000 2115 .90600 314 -1613..9000 0 -327176 . 10000 2187 .65300 315 940 .20000 -325915 .400OO 2215 .26600 316 -62161 .90000 -324825 .OOOOO 550 .30000 317 -60767 .60000 -324688 .00000 618 .81550 316 -58269 .50000 -324563 .20000 653 .54610 319 -55420 .50000 -324454 .00000 750 .30000 320 -52361 .00000 -324367 .60000 663 .94310 321 -49173 .40000 -324304 .80000 950 .30000 322 -45901 .60000 -324264 .30000 1095 .01700 323 -42570 .00000 -324244 .60000 1 161 .91200 324 -39192 .10000 -324245 .00000 1511 .72100 325 -35774 .60000 -324266 .20000 1592 .90400 326 -32319 .70000 -32431 1 .20000 1600 .00000 327 -28826 .40000 -324386 .30000 1624 .80800 328 -25290 .70000 -324503 . 10000 721 .88300 329 -21706 .60000 -324681 . OOOOO 1994 .77200 330 -18066 .30000 -324952 . 50000 2012 .40700 6 - NOOE Y-COORO X-COORD CHLORIDE CON (mg/1i tar) 331 •14383. 20000 •325369. 70000 2000. 30000 332 -10699. 80000 -326037. 30000 2101 . 07300 333 -7539. 40000 •326902. 50000 2100. 30000 334 -4335. 40000 -325432. 80000 2186. 22800 335 -1676. 20000 •324123. 60000 2350. 30000 336 940. 20000 •322982. 30000 2402. 70500 337 63860. 80000 320777. 20000 599. 42050 33» 61272. 40000 •320863. 30000 628. 54790 339 58590. 10000 -320967. 40000 714. 70750 340 •55599. 10000 -321025. 70000 621 .1 1640 341 •52449. 40000 •321060. 10000 882. 34570 342 •49207..9000 0 -321080. 30000 901 .1973 0 343 45906. 80000 •321095. 40000 1 141 .5480 0 344 -42562.. 40000 •321 1 1 1 .5000 0 1388. 85900 345 -39183. 20000 •321 133. 20000 1575. 20600 346 -35773..5000 0 -321 164. 30000 1672. 48300 347 -32334..9000 0 -321209. 10000 1669. 56600 348 -28866.. 10000 -321273. 30000 1720. 00000 349 -25363..0000 0 -321366. 00000 1883. 59200 350 •21817.. 10000 -321500. 60000 1979. 26600 351 -18213..00000 -321698. 20000 2100. 30000 352 -14529.. 10000 -321988. 30000 2096. 61200 353 •10773..7000 0 -322384. 10000 2200. 30000 354 -7111..3000 0 •322877. 10000 2203. 45200 356 -4356..6000 0 -321869. 80000 2243. 03700 356 -1720..90000 -320934. 30000 2532.. 13000 357 940..2000 0 -320049. 10000 2649..5840 0 358 -65052..8000 0 -316743..3000 0 500..3000 0 359 -62310..0000 0 •317097..2000 0 683..7435 0 360 -59166..4000 0 •317405..1000 0 800..3000 0 361 -55915..4000 0 -317623..0000 0 91 1 .8226. 0 362 -52620..2000 0 -317765..6000 0 930..3000 0 363 •49297..9000 0 -317860..0000 0 1065..9660 0 364 -45953..3000 0 -317924..9000 0 1326..2860 0 365 -42588..2000 0 •317972..8000 0 1460..3000 0 366 -39203..8000 0 -318012..3000 0 1550.. 18100 367 -35800..8000 0 -318049..3000 0 1632..8000 0 368 -32379..3000 0 -318088..4000 0 1689..3280 0 369 -28938..8000 0 -318133..6000 0 1754..6960 0 370 -25476..1000 0 -318189.. 10000 1913..3130 0 371 -21982..6000 0 -318260..5000 0 1972..4220 0 -18436. 372 .20000 -318354..8000 0 2132 .40200 -14780. 373 .90000 -318478..2000 0 2210 .35200 -10877 374 .90000 -318632 .20000 2373 .15100 375 -6268 .00000 -318787 .40CO0 2456 .89700 376 -4391 .50000 -318232 .20000 2605 .85500 377 -1826 .00000 -317668 .70000 2620 .64700 378 940 .20000 -317118 .00000 2700 .30000 379 -67160 .50000 -312648 .60000 642 .96470 380 -63561 .60000 -313400 .40000 727 .69350 361 -69615 .60000 -313952 .20000 826 .86020 382 -56266 .80000 -314291 .80000 959 .91130 383 -52815 .80000- -314516 .50000 1069 .57700 384 -49409 .40000 -314667 .30000 1 \77 .81600 385 -46020 .00000 -314770 .00000 1333 .74200 7 - OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OO00o0000000000OO0OO0O00OO0O0OO0OOOO0»«OOOOOOOOOOOOOOOOO o^o«io>nonotf>o • •C4©OI««»-l*»-©»©f<»©©íM*>l«r<©»«-'» ooooooooooooooooooooooooooooooooooooooooooooooooooo©©oo ooooooooooooooooooooooooooooooooooooooooooooooo©oooo©o© OO00O0©0OOOOOO0©OOOO0©O0OOOOOO©0000000O000000000000©000 ©OOOooooooooooooooooooo©oooooooooooooooooo©o©ooooo©©o©o s*»B(0(VNOfl«lfleK(0»NBBO(»»WK)NO«l«l(M»'-<0'-'-OK»MOMOOinOOieOO( •inN"n^«o ai<» > K«0iO'ivn«ift»sB0>O' Nn*i 44 1 940 20000 -306 316.50000 3150.45100 442 -67739 90000 -303 763.00000 649. 1 1990 443 -63948 60000 -304 179.60000 950.30000 444 -60216 10000 -304 635.60000 974. 1 1230 445 -56579 70000 -304 981 .20000 1 142.51600 446 -53045 70000 -305 224 . 70000 1288.09500 447 -49584 10000 -305 393.00000 1334.67600 448 -46163 20000 -305 508.00090 1450.30000 449 -42761 10000 -305 585.10000 1428.51700 450 -39371 00000 -305 634.00000 1564.77800 451 -35992 00000 -305 659.60000 1696.26600 452 -32625 10000 -305 662.20000 1839.09100 453 -29276 10000 -305 637.20000 1968.39800 454 -25962 10000 -305 573.90000 2000.30000 455 -22718 00000 -305 452.10000 2194.41000 456 -19596 10000 -305 236.90000 2287.39200 457 -16693 70000 -304 864.20000 2437.64000 458 -14189 30000 -304 223.20000 2600.30000 459 -12318 80000 -302 697.60000 2635.01700 460 -7409 00000 -304 220.00000 2981.22100 461 -3086 700O0 -304 894.10000 3147.92900 462 940 20000 -305 383.40000 3300.30000 APPENDIX C CHEMTCAL ANALYSTS OF SOME Ef.RMRMTS RELEVANT TO THTS THESIS FOR VARTOUS BOREHOLFS TM THE DTSPOSAL AREA AT VAALPUTS. arpandls C otamUal inaljraia of torn «lawti ralovant to thla thaala for «arloua boraholaa la tha «lafoaal •raa at Vaalputa. CaO, *a203. MnO and E2C ara raaortad In parcontata irttlla Sr, Ca, Co. U and V ara raportad in ««.ki'1. •10 Sam BOREHOLE Wa C WnO tt30 Sr C< CO tc.o 2 3 W20M0 0,41 1.27 0.J1 1.28 31,0 0.79 4.0 1.0 56.0 W30«o 5,25 1.82 0,01 1.01 79.0 1.10 6.0 1.0 79.0 W30S10 0.17 2,2 0.01 1.53 38.0 2.08 3,0 1.0 76.0 U40H0 3,97 2,08 0,05 1.79 85,0 1.43 6,0 *,0 39.0 U40S10 2>: 3.39 0,06 1,92 96.0 0.00 7,0 1.0 88.0 \ .— CALCUT* BOREHOU tCaO Wa20j MnO UCjO Sr Ca Co W2080 5.8-7,5 2.2-3.5 0.01 1.6-2 0 75-104 1.75-2.43 8-11 1.0 117-209 W30B0 10,07 3.84 0.01 1.55 107,0 1.10 Í.0 1.0 131 W30S10 10.51 3.31 0.01 1.75 115,0 0,0 4.0 1.0 88 W40M 9.9-11.5 2.0-1.3 0,03-0,04 1.*« 137,0-169,0 1,44-1.54 4.0-5 0 5,0-6 .0 50-105 V40S10 11,65 2,84 0,04 1.64 144,0 2.25 1.0 1.0 97 no SAMDT GRITTY CLAY BOREHOLE %Ca0 Wa203 «mo «2o sr Co W20M 0,73-12.51 1.59-17.64 0,01-0,03 0,76-5,47 61.0-93,0 0.0-2,61 4.0-19,0 l.o 86-215 W30H0 0,61- 3,82 2.67-4,78 0,01-0,03 1,86-2.86 54,0-98,0 7,48-2.72 10.0-19,0 l.C-21,0 54-133 W30S10 u.36-11,14 2.5-4,13 0,01-0,03 0.87-2.18 40,0-81,0 0-2,22 1,0-14,0 1.0 64-13C (MOW) 0,54- 4,35 1,96-5,70 0.03-0.05 0.08-1.62 74,0-191,0 1.43-9.50 3,0-29,0 3.0-9,0 51-116 W43S10 2.82 3,8 0.06 1.36 72,0 1.90 3.5 1.0 93. WHITE KAOLHITXC CLAY BOREHOLE XCaO Va203 MnO «20 Sr Ca Co W20H0 0,55-12.51 1.73-17,64 0,01-0.03 0,76-5,47 76,0-368,0 O.C-2,61 7.0-59,0 1.0 86-215 U30R0 10,19 2,64 0.01 0,81 93,0 1.69 10,0 1.0 62,0 U30S10 1,06-4,81 0,55-3,20 0,01 0.31-4.99 44,0-85,0 0,54-2,39 5,0-19,0 1,0-3,0 29,0-51,0 «4080 1.74-U.9B 0,99-5,65 0,02-0,04 0,72-2,05 162-558 1.31-6,27 9,0-30,0 3,0-100,0 2,0-48,0 W40S1C 1,08-11.07 1,66-14,34 0,01-0,30 1,16-4,31 99,0-499,0 1,65-3,51 3,0-76,0 1,0-9,0 59,0-147,0 MtArHBRED CRABIT1 BOREHOLE XCaO Va203 MnO W20 Sr Ca Co W20K0 2.77- 5 16 2,9-12 73 0,12- 0 03 0,98-3 SO 303-383 0,0-2,61 4,0-49.0 1.0 86-213 W30R0 0.94 3,59 0,01 «.70 W30S10 0.93 6,42 0,01 3,85 76.0 1.67 13,0 3,0 39.0 U40R0 3.47 19,95 0.15 0,67 236.0 3.28 43,0 9,0 196 H40S10 6.49 3.34 0,08 1.30 • 79,0 1,39 8,0 1,0 94 rUSH CRAiITt BOREHOLE «CaO Va203 MnO tt20 Sr Ca Co W2080 W30M0 WOS'.O 1,03 4,44 0.01 1,56 72,0 1,62 4,0 1,0 63.0 W40M0 3,71 16,99 0,07 2,43 181,0-197,0 1,50-3,76 18,0-82,0 7,0-26,0 77-1209 W40S10 5,60 1,66 0,06 1.S5 753,0 0,82 '. ,0 1,0 46,0 W40N00 MAJOR~ELEMENTS X Si02 Ti02 A1203 Fe203 MnO K&O CaO Na20 K20 RED SAND 1 81.20 .56 5.67 2.08 .05 1.27 3.97 .43 1.79 CALCRKTK 2 65.55 .39 5.37 1.95 .04 2.57 11.51 47 1.43 3 65.34 .35 6.52 2.26 .03 3.51 9.87 .55 1.46 RED C.UCC 4 71.02 .45 7.26 2. 69 .04 3. 52 3.45 .57 1.52 5 58.82 .36 6.10 2 23 .04 2. 27 14.46 .39 1.22 6 74.79 .60 9.79 3. 52 .05 1 34 1.96 .40 1.51 7 70.92 .68 12.65 4. 36 .04 0 82 1.84 .42 1.47 8 68.24 .76 15.56 4..5 6 .04 0 54 1.13 .39 1.62 9 81.30 .55 65 3..0 2 .04 1. 33 1.12 .42 1.32 10 81.75 .51 79 2..5 0 .05 2. 32 1.17 .44 1.07 11 72.99 .38 40 1 .9. 6 .04 1. 81 8.52 .43 .88 12 64.31 .38 17 2..2 8 03 4. 35 10.85 .33 .80 13 77.64 .48 11 4..6 7 .03 2. 38 1.77 .46 .87 14 60.49 .24 16.07 5..7 0 .03 2. 14 4.77 .65 .95 WHITE CLAY 15 59.69 .24 18.14 3..7 5 .03 2. 35 4.51 .96 1.08 16 58.81 .20 17.11 3 .61 .03 2. 16 5.58 .80 .94 17 69.59 .11 14.43 1 .95 .02 1. 83 3.54 1.06 .72 18 54.28 .13 18.75 1 .94 .02 2. 31 7.90 2.54 .90 19 57.73 .10 23.32 1 .67 .03 1. 52 6.00 2.47 1.03 20 58.08 .07 23.93 1 .51 .02 1. 08 6.18 2.99 1.04 21 56.72 .07 23.59 3 .39 .03 0. 84 5.42 2.85 1.08 22 57.09 .10 22.60 4 .22 .03 1. 44 5.47 2.57 1.16 23 58.31 .08 23.50 1 .89 .02 1. 25 5.81 3.06 .98 24 64.26 .08 20.59 .99 .02 0. 00 1.74 7.05 2.05 25 52.37 .29 11.88 .65 .04 1. 35 11.98 2.19 .76 WEATHERED BASEMENT 26 56.09 1.51 11.79 19.95 .15 0.91 3.47 2.21 .67 27 25.60 3.38 6.90 50.38* .26 2.02 1.36 0.91 .32 FRESH BASEMENT 28 66.32 .74 10.55 16.99 .07 0.15 3.71 2.06 2.43 *FerruRinized zone W40N00 30°00'S- INSET 1: LOCALITY MAP OF VAALPUTS IN SOUTHERN AFRICA .Pretoria PELINDABA* Johannesburg Ludentz <* 30°15'S- • Upioftoo \ .Springbok • VAALPirre 'Durban \KOEBERG East London Cape Towné- s Port Elizabeth 3O°30'S-- GOURIQUA SECTION 2 GEOLOGICAL MAP O Comi INSET 2: GEOLOGICAL DATA SOURCES 18°30'E 30" 00 S 30°00'S AIRB INSET 3: U ENRICH! 30°15'S 30° 15' S 30° 30' S — -(-300 30' S 18°30'E 18°45'E P. Joubert, 1971, Precambnan Research Unit, University ol Cape Town, 10 H.M Albat, 1984, Precambnan Research Ur it. University ol Cape Town, 33 N J B Andersen, 1982-1986. unpublished mapping N.J.B. Andersen, E Raubenheimer; M Levin, 1983, Atomic Energy Corporation, unpublished internal report |with map) MAG Andreoli, 1986. urpublishec mapping Spri I8?30' 101 .* • ti. SECTION 3 ATOMIC ENERGY CORPORATION C P OF THE VAALPUTS NATIONAL NORTHWESTERN CAPE, Compiled by M.A.G. Andreoli, N.J.B. Andersen, E Department of Geotechnology, Atomic Energy Corj 10 12 1:25 000 AIRBORNE RADIOMETRIC SURVEY SPECTRAL INSET 3: URANIUM CHANNEL ANOMALIES AND THORIUM- INSET 4: RESIDUAL FIELD IND ENRICHED ZONE (B-C5, C7) IN WEATHERED BASEMENT SURFACE GEOLOi Springbok 1O0km n"rt,T„",M ... .* II __ . » ^^ ip J SECTION T HON OF SOUTH AFRICA, LIMITED SAL RADIOACTIVE WASTE DISP ^PE, SOUTH AFRICA ben, E. Raubenheimer, N. Niemand and M. Levin irgy Corporation of South Africa Ltd, Pelindaba 2 3 4 5 km I I I I km 1:25 000 SPECTRAL FILTERING OF PORTION OF THE AEROMAGNETIC SURVEY UAL FIELD INDICATING NEAR INSET 5: LOW-PASS FILTERING (0,001 CYCLES/SAMPLE INTEI [RFACE GEOLOGY INDICATING MAGNETIC ANOMALIES IN THE BASEMEN SECTION 5 [SPOSAL FACILITY, INSET 6: FOLIATI evin PLE INTERVAL) BASEMENT EXPLANATION AEROMAGNETIC SURVEY: Area flown bv Aircraft Operatin Ranges: Inset 4,+ 140 (red) to - RADIOMETRIC SURVEY: Area flown by A.O.C.; compilati INSET 7: TOTAL FIELD AEROMAGNETIC SURVEY Y +60 +55 +35 +30 be SECTION 6 INSET 6: FOLIATION + LINEATION MEASUREMENTS TRUE t^\C NORTH Dots - Lineations Contours - Foliation Poles ^PLANATION OF GEOPHYSICAL INSETS Aircraft Operating Co. (A.O.C.); compilation by Geoterrex Ltd. Datum: 28 000 nanotesla 4,+ 140 (red) to - 147 (blue); Inset 5, + 970 (red) to + 230 (blue); Inset 7 + 770 (red) to + 240 (blue) A.O.C.; compilation by Geodass S.A. Range from < 20 counts/s (green) to > 120 counts/s (blank). ETIC SURVEY INSET 8: REGIONAL GEOLOGICAL SETTING OF THE RADWASTE DISPOSAL TERRAIN +35 +30 +25 Y +60 +25 I I I \ V ,•-, SECTION 7 30°05' V/ V: /A / SECTION 8 Sprinj !8°30' 100 \ > »• • • •• Q \ #r,»«p^,. Q..A•;'••.•;• i'ái^K. * «r it».'». c-^jr^ri^'. i -X .. ^ / T« \ .."..••..•• #.".. »•«- »- >• * „ *»» rtMfc -' " '* * :v>.^^^;>^r;^^:^r \° ^ -. ../7 ,...... ,, ,...... •A(/yyy//>^W-^^' w- f ^:\ « -- - kO.'.>. • • • v.*. .sa '•; • • • -*I\f i \ ^ •• • l- •••.••..••..v..••..••.."..••..••I-..••.."..•..'•.."!."..••!. ,-. X_'' ,-, ./.. Springbok SECTION 9 100 km *v....v.^o\\;x:-.;;.^^W^V'A r..-.,V..A\A-, ..-'-:' >**•• .« ./ "'<-' \ -«7 ,-.x ,-,,,U.-.^ ...... 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L ! 1 -' •' y^ /- i;'\ '1^^ \ í i ^^Sk- I- -' / J—/ ^^ii" v i ,'iiA • -' £• ••'••- :: \ •• •!••;'',•• .••..'rVf* '.•*..•• 'TCSÍ" •• •• •• • Al ' ' » -' ^. .. I '-/:• o\ / \ '' " "Í '•• "'. --' V-'t'"' I \ X ' V •' ^. / ' /,< , f~. I .. . .', \ i. .. - -• --' './,•'•-»•-- •- *" •• "\/'NÍ. " " •' " " ?•-' Tk H '"^ 'm s ' ' " •' •• •-' •• .y ;-.---i.w - > ; •• •• • \i .• •• /•r • •• • - \_i* •• "i •• •• \< > ^-^x»• i ... ./ / -/ í—'-'1- ...Op •r• —!l ff\\ )\ -^* ^7f— « • • • yW*^ • • • • 9 • • V'* • » • tfj(/ • * x * • • ***** • • v-e . T-o H\if'\ • • V ' ,A''°.-*\' "»• •,/•/• • ••/•• • 1«• • "•!' 90• •• -.•. •.•. •A#r,*• .\ • ,.•* 'i ]^• •• i ! •••• •••• «»\ •••• •••'• r •' •• *••• * *.• •..\.« * \« •' ;! •« •• •••• • • •• • •• • •* pN^vf,\. • • *« • • ¥•' /'*/'Í t' Lr^ V ^"0 \J \ / y * / T^V' k ''' \ ' /' '' í ^!»'' r;.\ .. uT;-,. \.. •• °.. •>. .V, ••/ •• JT •• •/ «^-N «A »': •• A .'"' ' •• •• .'. •' •• *v' x. T i;Wi-'*-V7^rH^V s^-K^A; •• -\ • \ •••• v> • ••-. t ; N \ ,/TM'.; .J .. ,\/ ./ . iv^f "..'..?»f •>.•:'•* •! /'•• «V " .,..*... ..\ / • •• •• ... V • .? t # L 4 •\t » * I* * ** lp •* • •_, •' K". • / •/VNT'M •• •• ••'. •• y •* •* *'* *" A •• •• •* ••/\ !••!•• "• ••'-•• •' -»' •• 5 .„. .A ,/ 2i l.\ ••/I'*' '*. .' Yv V *• •• •• •• ••' .«/•• .-' L' '• V' ".;'*T .»•,-.'" '| TK> •••-•, '• •• •• / •• H/ *i " •••*« ' ]'•„••*//•• V /*'\ ••"..«•'••••"./ • ,-• • • •• X' >. ••'.. 'A. >• • •• ••.' .'•• •!• •• • SECTION 11 •*• . X-V 'W' •HT' • \ WLOt* 1 .\ X .«.' .*?£#% - 0 5 10 20 SCALE E4S km SECTION 12 RY COLUMN INTRUSIVE COLUMN Lithology Li^il brown j— FT " Intermediate Ddrk brown »t ti Tk liaNowsand cover F^TTQ fc=t Itsione. sanHston ? : Td:"'**£ bceslPMtbaKk'Pii) - - i Oliv n« melilile basall. kimbBflite and fi?lai«ri £ • ':•'$'•';•• diairettiBS |3567 Ma) SECTION 13 »x rv. t « V-v r * * •./".• ^ • --/; •' •• ; '. \_. -; •r ~ . /• V. . > \ '.' s H; i/ i *. "k\° r/, -.•:/ " A 30°10'- 339 OOO X 1040 1030 1020 1010 ^ /•::'•'-::•'•::'•'•:::•::::'.::;::"" Ï ,'••..".."..-...... " "/!.:.:.-.."J">:.-..:.-,.-:. *,.;T*1'. 4 ;••;• " " /.."..••.."..••..••..••..••..".."..•\'.".. T .. .# SECTION 14 Kiipr'afl d / í ; * 65 km / / - :"::••::"•::"%:"::"•""::"::"«••»••:'•'•".' / '' 18°30' ..••,-.,-..K^,l^ .. x.X.V. .. \ . X ', x . 11 V». •» , / .• __«^ _*• . I *\ X •;-*: N / vv\ / / -' \ ,; / yy X I /y . \ ! .**..X..'V.' "ïv"..".."*y ..'*.." w • * •• •• •• •• • • •• • *\ «•--/.-• • • .*• • _^ • ^kjkx * • 1 •_• • • /v* 4A ^ x V X •'' ' ••' TQ v^ ~'"'nc .'" X/ • .••' \ \ / S\ 7 X •..'•..••..•-..• Srjt^«'i;"..v/ •• ./" •>?-,' •• •• •• J.Tk'i 1'.'\.",{'KS',-'L/?»' ••/-"•"•'"*> •Al'/ ?••• «•• v' "-AN-A" ''• ,-' ",-•• •• •,< r» > .•• -»• •..;'*T A/ ""! •• >*• ••/ *• **/•*/ •• '• t'. ,<-' é . • •> _a_l »J »— • • ,m • • • • • - - - - — "* *• - - -v ^.J—^—~r~ _ . i_ _ £-. ^^ », ._ », m 9 * • \ • ^•::-;>v\::::,:::::^;::-::-/| .."..".."..••..•:.••..••.*. ---.'' ; -' ; • TJ \ \T-Q ,-—' 1 T.*".."*.."X-*."-VÍ'.** .K"'.-*':'*/S*-*#.**yf"ï •* •v*-."V» •• *P r' '•• •• •• •• •• •• •• '»4 * 'jJJJ,-^ "* •"•*"" • * •• •• •• •• _Vl /' y .- ^ i í' ^ ;•-/ s //../...\ .\ Í .. i s.x ^J¥** ^."•".<\'"A-\"ss-~-^ ,;."..' .. J" •7t:»:xT>*i^_i|^v: < .\. \ '-' •' ,'A'-í. r\i X •• •! »• •• •• ,-*•' «'.*". i /'T'v''.. ••..•'.'.--;í\-. .••,,-•„>•-.'. •V.Btxr««p ::::.::.S::::ftp,::::::v:::::>::::::::^,::.;;!.-::>o;; . ^..-..-'"..^..-^y .-Í-- •• ••• •• f^..-..-..-^.-..-^^ ... •• •-..., /J \ ..'. ;'.. V • •• »• •• ••'• ""• " t4> ".."..'~ -L- .-*.'*• '* •' /••••//••••••"••"••"•1 SECTION 15 Dia },!?X:M Calcrete > < Suboutcrops below Tk and T-Q, shallow sand cover on the left oc SECTION 17 I- VAALPUTS Sandy and gritty clay White kaolimtic clay (Vaalputsl, siltstone, sandstone, Td DASDAP and conglomerate, silicihed in places (Platbakkies) LATE - Silicifted. kaolmitized basement gneiss anc granitoids CRETACEOUS JURASSIC TO LATE- KAROO SEQUENCE PALAEOZOIC OWYKA Diamictite and unconsolidated boulders 3 x ui -i Q. 2 Rocks of undetermined magmatic and or h o metamorphic origin u u z a. z c ~1 Intr usive relationship* Geological contacts definite, approximate, and r.on|fiClural Structure form lines ^*~~~'^. Suboutcrops Vaaiputs Fm ~"~.^•~"'~^. Dasriap Fm ^*" ^^0*' DwylrDwvba FFmm i Strike and dip of foliation, t-anrling subhoo/ontal y/' foliation tvc^- <.'.*' ~2-*~ Tk and cover 7T-0 fc=fc SECTION 18 pi t. sandstone, Td latbakkies) OO CO I mbj o o Olivine-melilite basalt, kimberhte and related » ••• «o' Í eo 1 »o _ diatremes (35-67 Ma] •nd granitoids »:T-C: :-:•:- f Basalt and dolente (undifferentiated) iEWi Pegmatite and giant quartz veins (syn- to late - f tectonic) Enderbite, anorthosite and nonte [* 1 100 Ma] KOPERBERG f SUITE Charnockite. charno-enderbite and undifferentiated ^ pyroxene-gneiss «iHN KLIPRAND Id magmat"; artdor hrgh-ji-ade W ,& a) Charnockite interbanded/gradational 10 ortho- CHARNOCKITE gneiss SUITE .am Ma / Leucogranite. alaskite l~ garnet and foliated in SPEKTAKEL places); b) intrusive dykes SUITE " 'i^" "*"* Vaalputs fine to meotum grained granite gneiss Stofkloof megacrystic Ir garnet) granite 9neiss. SYNTECTONIC c) undeformed relic GRANITE SUITE Riembreek streaky augen gneiss HOOGOOR Mho Quartrofeldspathic pink gneiss SUITE LITTLE NAMAQUALAND Nababeep-type biotite augen gneiss SUITE Mph Granite gneiss and charnockite Undifferentiated Stream Fault, oftsti vedynd inferred with biock on downthrow «& Abandoned prospect side Fracture Windmill Wrenc i lauli. arrows indicate relalivB lateral Boreholes water-hearing, dry displacement Mam mad Maior thrust fobserved anri i',i*rred) with daggers in upper sheet Secondary road and track Ouct-le shear /one. mylonite Homestead SECTION 19 T-' l-J \ \ ', 30°10'— + 339 OX 1040 1030 1020 1010 1000 metres a.a.s.1. 990 980 970 960 S\ -.... ° ^-%,%'•• * 950 Mr \ 940 WW -*•.• • í -V \ .. »••"« V ..'• . .. y- • - \ í:::::::::::: —r.-.rt- /.--..••..-•..••/->..• r- •<::•• ^Í: / i« KHpfiaiid " "'::••::••:: 65 km .. ../ "/...„-...... • 18°30' SECTION 20 £xn^y ^v: ? . .,>4v .-'.••..•-..••.-..•>>• i >5ocv>-"í'--'""-t"T , , „r\.--..--..--..' , /-'.."..f-.>;v"*"*""*'?"""-'^-»":/.'--i.'J" ''-'' 'Vvv". •..••..••..V • ••i.y-v^ .. .. , ^', •• •• í.. .r--^.. #,«'-..--..»..-../•./•..*"..•••• jv' í"^\^.r--..--..--:.y::-- "..".."' ^^*^^t-^j * •" •* ** /•* •* ** -'' V„%#-** \ ** ** 1* ** •• •• •*' •'*. 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V-..-V-.--•..•••••-..••.-:->-••--**--•••'•'••""••*••'-"- ..••\'*\'.~..••.-;;. :"«*.."..••./•„••„••}..••..•;' ^ h-./- • •- •-. i ••..*• L— ^i-y v... ^:-.•|..u^_^_^ f •• ^..^ 7p>;-..-..-,. ••••• ..•]'..-.. : ^•::-::-:>::-::-J^í-::"i-..-.í, >./%/?::::-::-o^v-..--."v"..--..-% •::V-;:^::::::::::::::::::"f::^::;:^--::--v >•^.•'í":f•^:>:::^:^/f::•^:••::••:>::>::••::•C^::::::^: : :: ; : ^:-V« ::"" ::-:K:--:. ::"::-% ^T^/^.^^/^^::::}./^:••::-•::••:>•::••:^f:: ^^ .,".V'..'/ Tk :.".\'..".."A\" •• •• •• -' /•• •• *' ** ••»-•» ".•-..-. .. .'•-.•//••• / •• i •• •• * ;.••..-..•• ••' ' '•• ••..•' *--*• ••-•••..••-.••-?•.•-.•• •••••-•••::•• v.#•-•••••••••-••• ••.:-•' DISPOSl í-.-'-l'.'//^^ MM?W?2^0Ziï$^^ -**iZ.V-v.v.v.v.W!v.^i>- Stcy\oH 1* EXPLANATORY NOTES TO THIS MAP ARE INCLUDED IN THE PROCEEDINGS VOLUME TO TÉ[ "!—rr MT'.'.A W ;:••:*.^/:-::pf-.::..::.^::::::>;^::--::-\-::--::--::•"•V- -N^^vy^^^^^ ~ ^ j£^N**vfe •Av•'^.•^.•i^^•0ï^^/^"v•ff^O^/^.•^.•^/^.;:.\>.r..*^.••.>:v•-.. .-> ^:Í:::;^C& V\VQ v f -^* -/"") t ctíV^:::^^:^,^: ; JNJ :\:-;P;; ." . • •'0 V?'.* **..... 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V'» TO / j' • •[ • • • • \• • \ T» / / / 4 • • • • fJ • • • • • • , j. :-v ,,< .Ifí \,. i mm T;JQ .. t. • . /7 •'.--.• •-"'• •• •' •• * • "\ v-X* iJ í • '(\,>-^-- ••.. *..••..•".."..T "X ,• ".."..".."%•" •• ,-'•• "^^ >.:• *• T-OT-*. » , A :.Í.-f:.••••••• ••/ ••/•..ra-.-/ ../ •• •• ••/•• •>v «\{"v"» , T \ / / ••• 8* •• ,i -'/// •• •••• • •••..••.•• •• •• •• "fo\\'-'- •• • " "; ••••.."..•• •' •••••..••,'.% -f- 18°35' 1040 1030 DISPOSAL SITE 1020 1010 Ty 1000 metres a.m.s.l. 990 1 980 II ' 970 960 F950 SCcrioN 22 940 )LUME TO THE RADWASTE '86 CONFERENCE, 8 - 12th SEPTEMBER 1986, CAPE WWN_ x a. z z 0 < 2 < Q Quaruo-feldspsihc gneiss, feldspunic quartzitc 0 h UJ O o Magnetile-quartzite and iron formation 0 2 O'OKIEP 2 Q GARIES SUBGROUP S o Z — Biotite-magnetite qneiss, fine grained; migmaiitic in < * places -j %fi z Aluminous bioiite gneiss ~ cordiente, sillimanite. < ~ game! and spinel 0 < I I MM* intrusion oreccia of granitoids ,n pi.ragneiss m * MM* < • « z ^ Intrusive i£lationships Ur Geological contacts; definite; approximate; and Fa conjectural sic Fr Structure form lines W dii ^,.—-""'" Suboutcrops: Vaalputs Fm •""'.^•-»'*" "2, Dasdap Fm. «*• -—^*" DwykDwvka FmFm . i Strike and dip of foliation/banding, subhorizontal 3°>/ ' foliation , Lineations: plunge; subhorizontal Zo Steep structure 3kf Syncline Anticline Pi SCCTI0N 11 Leucogranite. alaskite {± garnet and foliated in SPEKTAKEL places), b) intrusive dykes SUITE (spathic quarizite i Vaalputs fine to medium grained granite gneiss i tttion Stofkloof megacrystic (± garnet) granite gneiss, SYIMTECTONIC c) undeformed relic GRANITE SUITE ined; mtgmatitic in Riembreek streaky augen gneiss Rente, siilimamte, Quartzo-feldspathic pink gneiss HOOGOOR Í SUITE • • », LITTLE NAMAQUALAND |neiss • » * » i Nababeep-type biotite augen gneiss SUITE » H * ~ } Granite gneiss and charnockite Undifferentiated Stream Fault, observed and inferred with block on downthrow & Abandoned prospect side Fracture t Windmill Wrenci fault, arrows indicate relative lateral Boreholes: water-bearing; dry displacement Main road Major thrust (observed and inferr-ad) with daggers in upper sheet Secondary road and track Ductile shear zone, mylonite I Homestead | Building, construction Zone o* cataclastic rocks 1022,3 Trigonometric beacon Silicifiod quartz breccias ' ••—.._, ,' Security fence \S\ Overturned sequence Property boundary S€CT\OH 24 Final draughting and colour separations by A.J.H. van Wyk RWD 3/B/36