The Assessment of Groundwater Quality in Rural Communities: Two Case Studies from KwaZulu-Natal HeidiMichelle Sherman " , -,. j-':-.: ' f ' K "' ~ . ....-,....: ' ..... ~t::~ Submitted in partial fulfilment of the requirements for the degree of Masters of Science in the Department of Geology and Applied Geology University of Natal (Durban) 1998 • PREFACE This thesis documents the research done by the author, and is the author's own original work, unless specifically indicated to the contrary in the text. ii ABSTRACT The health and life expectancy of populations in developing countries is largely determined by the availability of good quality drinking water. Boreholes and springs generally provide water of better microbiological and physical quality than surface water sources, however,they may cause health and aesthetic problems due to chemical constituents dissolved out of the host rock. As part of a pilot study to assess the health-related quality of community water supplies, samples were taken from two Quaternary catchment areas in KwaZulu-Natal. The Umkomazi catchment area is located inland from Amanzimtoti, while the .Umfolozi catchment area is located north-east of Ulundi. The geology in these areas is significantly different. The Umkomazi area is predominantly underlain by basement rocks of the Natal Structural and Metamorphic Province, while the Umfolozi area is underlain by sedimentary rocks of the Karoo Supergroup. Geographical information systems (GIS) were used to examine the influence of lithology, rainfall and landuse activities on groundwater quality. Major ion analysis of groundwater samples from the Umkomazi area revealed a linear relationship between borehole and spring concentrations. Dwyka Tillite was found to produce water with the highest concentrations of major ions, while Karoo dolerite produced water with the lowest concentrations of major ions. Samples from basement rocks and Natal Group contained intermediate concentrations of major ions. In the Umfolozi area Karoo dolerite samples showed the lowest concentrations of major ions, while the Vryheid Formation and Dwyka Tillite produced the highest borehole and spring concentrations, respectively. High salinity levels in sedimentary rocks may be due to marine influence during deposition. Piper diagrams show relative enrichment of major cations and anions and Stiff diagrams showed characteristic patterns. Fluoride is associated with siliceous basement rocks and related to calcium concentrations through the solubility of calcium fluoride. The trace metals, manganese, iron and zinc were found to cause significant aesthetic problems and possibly health problems in sensitive individuals. These constituents are derived from weathering of bedrock and possibly from the corrosion of metal pipes. There is an inverse relationship between mean annual rainfall (MAR) and electrical conductivity (EC), except near the coast where windblown salinity increases with rainfall. Nitrate, ammonium and E. Coli contamination are linked to landuse activities such as occurrence of human and animal excreta near the water source and the proximity of pit latrines. It is recommended that rural communities be educated about the nature and importance of groundwater quality. 111 TABLE OF CONTENTS 1. INTRODUCTION 1 1.1 NATURE OF PROJECT .. .. ..•....... ........~ 1 1.2 ACKNOWLEDGEMENT OF COLLABORATING ORGANISATIONS 3 2. DATA ACQUISITION AND ANALYSIS 5 2.1 SAMPLING DESIGN 5 2.2 SAMPLING METHODS 5 2.3 LABELLING METHODS 7 2.4 POSITIONING METHODS 10 2.5 SAMPLEANALVSIS 10 2.6 GEOGRAPHIC INFOMATION SYSTEMS (GIS) 11 3. DESCRIPTION OF STUDY AREAS 14 3.1 LOCATION AND DEMOGRAPHIC FRAMEWORK 14 3.2 LITHOSTRATIGRAPHV , 19 3.2.1 Umkomazi Study Area 22 3.2.2 Umfolozi Study Area ~ 26 3.3 GEOLOGICAL STRUCTURE 28 3.3.1 Umkomazi Study Area 28 3.3.2 Umfolozi Study Area 29 3.4 HVDROGEOLOGV.. ..... ...... ...... ... .. .......... ... .. .. ..... ................ .. ... .............. ... ..•... 30 3.5 SOILS 35 3.5. 1 Umkomazi Study Area 35 3.5.2 Umfolozi Study Area 35 3.6 VEGETATION AND AGRICULTURE 36 4. WATER QUALITY PARAMETERS 38 4.1 MICROBIOLOGICAL QUALITY 38 4.2 PHVSICAL QUALITY 38 4.3 CHEMICAL QUALITY 39 4.3.1 Major ions 39 4.3.2 Minor ions 41 4.3.3 Trace Metals 43 4.4 WATER QUALITY STANDARDS 44 5. PREVIOUS HYDROCHEMICAL STUDIES ~ 47 5.1 BASEMENT ROCKS 48 5.2 NATAL GROUP SANDSTONE 51 5.3 DWYKA FORMATION 52 5.4 ECCA GROUP 55 5.5 KAROO DOLERITE 58 6. INFLUENCE OF LITHOLOGY ON GROUNDWATER QUALITy 61 6.1 COMPARISON OF BOREHOLE AND SPRING WATER 61 6.1.1 Umkomazi Area 63 6.1.2 Umfolozi Area 65 6.2 MAJOR IONS 67 IV 6.2.1 Piper Diagrams: Relative Abundance 67 6.2.2 StiffDiagrams: Characteristic Patterns 78 6.2.3 Milliequivalent Scatter Diagrams: Trend Analysis 90 6.2.4 Statistical Analysis ~ 92 6.3 MINOR IONS 101 6.4 TRACE METALS 107 7. INFLUENCE OF RAINFALL ON GROUNDWATER QUALITY 117 8. INFLUENCE OF LAND USEACTIVITIES ON GROUNDWATER QUALlTY123 9. CONCLUSIONS 130 Acknowledgements 134 References 135 Appendices 139 Appendix 1: Sample Form Appendix 2: Standards Appendix 3: Data Appendix 4: Landuse Activities v = LIST OF FIGURES FIGURE 3.1 LOCATION OF THE UMKOMAZI AND UMFOLOZI STUDY AREAS 15 FIGURE 3.2 POPULATION AND EMPLOYMENT STATISTICS OF THE UMKOMAZI AREA 17 FIGURE 3.3 POPULATION AND EMPLOYMENT STATISTICS OF THE UMFOLOZI AREA 18 FIGURE 3.4 GEOLOGICAL MAP OF THE UMKOMAZI AREA 20 FIGURE 3.5 GEOLOGICAL MAP OF THE UMFOLOZl AREA 21 FIGURE 4.1 THE RELATIONSHIP BETWEEN ELECTRICAL CONDUCTIVITY (EC) AND TOTAL DISSOLVED SALTS (TDS) IN THE TWO STUDY AREAS 39 FIGURE 6.1 RELATIONSHIP BETWEEN CHEMICAL CONCENTRATIONS AND LITHOLOGY. 62 FIGURE 6.2 MEDIAN BOREHOLE CONCENTRATIONS ARE GREATER THAN MEDIAN SPRING CONCENTRATIONS BY A FACTOR OF APPROXIMATELY 1.85 63 FIGURE 6.3 AVERAGE FLUORIDE CONCENTRATIONS ARE APPROXIMATELY 10 TIMES HIGHER IN BOREHOLES THAN IN SPRINGS 64 FIGURE 6.4 MEDIAN BOREHOLE AND SPRING CONCENTRATIONS AREAPPARENTLY UNRELATED FOR ANTHROPOGENIC POLLUTANTS AND TRACE METALS 65 FIGURE 6.5 PLOT OF UMFOLOZI BOREHOLE AND SPRING ELECTRICAL CONDUCTIVITY (EC) : 66 FIGURE 6.6 PIPER DIAGRAM, BASEMENT ROCKS 71 FIGURE 6.7 PIPER DIAGRAM, NATAL GROUP SANDSTONE 72 FIGURE 6.8 PIPER DIAGRAM, DWYKA TILLlTE. 73 FIGURE 6.9 PIPER' DIAGRAM, VRYHEID SANDSTONE 74 FIGURE 6.10 PIPER DIAGRAM, KAROO DOLERITE 75 FIGURE 6.11 PIPER DIAGRAM, UMKOMAZI SAMPLES 76 FIGURE 6.12 PIPER DIAGRAM, UMFOLOZI SAMPLES 77 FIGURE 6.13 STIFF DIAGRAM, UMKOMAZI BOREHOLES AND SPRINGS (BASEMENT) 81 FIGURE 6.14 STIFF DIAGRAM, UMKOMAZI BOREHOLES AND SPRINGS (NATAL GROUP) 82 FIGURE 6.15 STIFF DIAGRAM, UMKOMAZI BOREHOLES AND SPRINGS (DWYKA, DOLERITE, QUATERNARY) 83 FIGURE 6.16 STIFF DIAGRAM, UMFOLOZI BOREHOLES (DWYKA TILLlTE) 84 FIGURE 6.17 STIFF DIAGRAM, UMFOLOZI BOREHOLES (VRYHEID FORMATION) 85 FIGURE 6.18 STIFF DIAGRAM, UMFOLOZI SPRINGS (VRYHEID FORMATION) 86 FIGURE 6.19 STIFF DIAGRAM, UMFOLOZI RETICULATED SYSTEMS (VRYHEID AND DWYKA) 87 FIGURE 6.20 STIFF DIAGRAM, UMFOLOZI BOREHOLES (DOLERITE) 88 FIGURE 6.21 STIFF DIAGRAM, UMFOLOZI SPRINGS (DOLERITE) 89 FIGURE 6.22 BICARBONATE SPECIES VERSUS CHLORIDE. UMKOMAZI SPRINGS HAVE A LOWER TAL TO CHLOR IDE RATIO 90 FIGURE 6.23 THE ENRICHMENT OF SODIUM PLUS POTASSIUM COMPARED TO THE ENRICHMENT OF MAGNESIUM PLUS CALCIUM 92 FIGURE 6.24 RELATIONSHIP BETWEEN MEDIAN CONCENTRATIONS OF MAJOR IONS AND LITHOLOGY IN THE UMKOMAZI AREA 95 FIGURE 6.25 INVERSE LINEAR RELATIONSHIP BETWEEN BOREHOLEAND SPRING CONCENTRATIONS OF POTASSiUM 96 FIGURE 6.26 RELATIONSHIP BETWEEN MEDIAN CONCENTRATIONS OF MAJOR IONS AND LITHOLOGY IN THE UMFOLOZI AREA 98 FIGURE 6.27 TDS CONCENTRATIONS OVERLAIN ON THE UMKOMAZI GEOLOGY MAP.. 99 VI FIGURE 6.28 TDS CONCENTRATIONS OVERLAIN ON THE UMFOLOZI GEOLOGY MAP. 100 FIGURE 6.29 UMKOMAZI FLUORIDE CONCENTRATIONS GROUPED BY LITHOLOGY 101 FIGURE 6.30 UMFOLOZI FLUORIDE CONCENTRATIONS GROUPED BY LITHOLOGY 102 FIGURE 6.31 VARIATION IN CONCENTRATIONS OF CALCIUM AND FLUORIDE•..... ........ 103 FIGURE 6.32 UMKOMAZI TRACE METAL CONCENTRATIONS SEPARATED BY LITHOLOGY AND SOURCE TYPE. 11 0 FIGURE 6.33 UMFOLOZI TRACE METAL CONCENTRATIONS SEPARATED BY LITHOLOGY AND SOURCE TYPE 111 FIGURE 6.34 PROCESSES BY WHICH IRON ENTERS DRINKING WATER (AFTER TAYLORAND HOWARD, 1994) 112 FIGURE 6.35 IRON CONCENTRATIONS OVERLAIN ON THE UMKOMAZI GEOLOGY MAP. 114 FIGURE 6 .36 IRON CONCENTRATIONS OVERLAIN ON THE UMFOLOZI GEOLOGY MAP. 115 FIGURE 6.37 RETICULATED SYSTEMS AND BOREHOLES SHOW SIMILAR TRACE METAL CONCENTRATIONS 116 FIGURE 7.1 KwAZuLU-NATAL MEAN ANNUAL RAINFALL (MAR) 118 FIGURE 7.2 RELATIONSHIP BETWEEN MAR ON EC IN THE UMKOMAZIAREA 119 FIGURE 7.3 RELATIONSHIP BETWEEN MAR ON EC IN THE UMFOLOZI AREA 120 FIGURE 7.4 UMFOLOZI SAMPLES SHOW AN INVERSE RELATIONSHIP BETWEEN EC AND MAR, WHEREAS UMKOMAZI SAMPLES SHOW A POSITIVE LINEAR RELATIONSHIP. SPRINGS HAVE LOWER EC THAN BOREHOLES 121 FIGURE 8.1 E. COLI (PER 100ML) COMPARED TO NITRATE (MG/L) 123 FIGURE 8.2 COMPARISON BETWEEN DISTANCE TO NEAREST PIT LATRINE AND E. COLI COUNT 127 FIGURE 8.3 COMPARISON BETWEEN DISTANCE TO NEAREST PIT LATRINE AND NITRATE CONCENTRATION 128 vu LIST OF TABLES TABLE 3.1 SIMPLIFIED STRATIGRAPHIC COLUMN 19 TABLE 3.2 STATISTICS OF REPORTED BOREHOLE YIELDS (AFTER DRENNAN MAUD AND PARTNERS, 1995 B) 34 TABLE 3.3 MAJOR SOIL GROUPS (AFTER DAVIES LYNN AND PARTNERS, 1995 A) 35 TABLE 3.4 NATURAL VEGETATION OF NORTHERN NATAL (AFTER DRENNAN MAUD AND PARTNERS, 1995 A, AND VAN WYK, 1963) 36 TABLE 4.1 DEPARTMENT OF WATER AFFAIRS AND FORESTRY CLASSIFICATION, UNIT OF MEASUREMENT IS MG I L UNLESS OTHERWISE STATED. (AFTER KEMPSTER ET AL, 1996) 44 TABLE 5.1 SUMMARY OF PREVIOUS HYDROCHEMICAL