Vulnerability of Groundwater in Tongatapu, Kingdom of Tonga Groundwater Vulnerability... 8.2 US Army

download Vulnerability of Groundwater in Tongatapu, Kingdom of Tonga Groundwater Vulnerability... 8.2 US Army

of 373

  • date post

    29-Sep-2020
  • Category

    Documents

  • view

    0
  • download

    0

Embed Size (px)

Transcript of Vulnerability of Groundwater in Tongatapu, Kingdom of Tonga Groundwater Vulnerability... 8.2 US Army

  • SOPAC/EU EDF 8 Reducing the Vulnerability of Pacific APC States

    Vulnerability of Groundwater in Tongatapu, Kingdom of Tonga

    Groundwater Evaluation and Monitoring Assessment

    Ian White, Tony Falkland and Tevita Fatai Australian National University

    Canberra, Australia June 2009

  • Tongatapu Groundwater Vulnerability, June 2009 page i

    Table of Contents Table of Contents i List of Tables viii List of Figures xi List of Annexes xviii List of Abbreviations and Units xviii Summary 1

    Introduction 1 Work carried out 1 Principle findings 2

    Recommendations 6 1 Introduction 12

    1.1 Vulnerability of Small Island States 12 1.2 SOPAC/EDF8 Study of Groundwater in Tongatapu 12 1.3 Vulnerability of groundwater in Tongatapu 16 1.4 Goal of this project 18 1.5 Project objectives 18

    2 Outline of the Project 19 2.1 Terms of Reference 19 2.2 Activities 19 2.3 Project team members 19 2.4 Objectives 19 2.5 Project Work Plan 19 2.6 Project outputs 20

    3 Water Monitoring, Institutional Issues and Demographics 21 3.1 Key monitoring data 21

    3.1.1 Rainfall, evaporation and SOI 21 3.1.2 Groundwater data 21 3.1.3 Pumping, consumption and leakage 21 3.1.4 Groundwater data checking, analysis and reporting 22

    3.2 Relevant agencies 22 3.3 Management and monitoring activities and responsibilities 22

    3.3.1 Geology Section, MLSNRE 22 3.3.2 Public Health Section of the Environmental Health Division, MoH 23 3.3.3 Tonga Water Board, TWB 23 3.3.4 Tonga Meteorological Service, TMS 23 3.3.5 Ministry of Agricultural, Food, Forestry and Fisheries, MAFFF 24 3.3.6 Waste Authority, WA 25 3.3.7 Ministry of Works, MoW 26 3.3.8 Environment Section MLSNRE 27 3.3.9 GIS Section MLSNRE 27 3.3.10 Ministry of Finance and Economic Planning, MFEP 27 3.3.11 Village Water Committees, VWCs 27 3.3.12 Village Women’s Groups 28 3.3.13 NGOs 28 3.3.14 Householders 28

    3.4 Institutional issues affecting the vulnerability of groundwater 29 3.4.1 Lack of protection of freshwater sources 29 3.4.2 Lack of a statutory basis for MLSNRE activities in water resources 29 3.4.3 Lack of national drinking water standards 29 3.4.4 Lack of coordination in the water sector 29 3.4.5 Lack of regular, routine reporting to Government 29

  • Tongatapu Groundwater Vulnerability, June 2009 page ii

    3.4.6 Lack of information on groundwater extraction 30 3.4.7 Lack of monitoring of private wells and bores 30 3.4.8 Lack of support for VWCs 30 3.4.9 Lack of controls on quarrying 30 3.4.10 Lack of a government-controlled drilling rig 30 3.4.11 Inadequate distribution of SMBs throughout Tongatapu 30 3.4.12 Lack of operational resources for monitoring groundwater 31 3.4.13 Lack of spatial information on the use of agricultural nutrients and fertilisers 31

    3.5 Demographics and the vulnerability of groundwater 31 3.6 Conclusions 35 3.7 Recommendations: Strategies for decreasing vulnerability 35

    4 Groundwater Sampling and Analysis 37 4.1 Outline 37 4.2 Groundwater measurements in village wells 37 4.3 Groundwater measurements in the TWB wellfield 38 4.4 Freshwater lens thickness in and around the TWB wellfield 39 4.5 Groundwater level and salinity logging at Mataki’eua well 117 39 4.6 Groundwater measurements around the TWMF 42 4.7 Testing wells for faecal indicator species 43 4.8 Testing wells for agricultural and industrial contaminants 46 4.9 Intensive water quality sampling by other agencies 48

    5 Properties of Groundwater in Village Wells 50 5.1 Outline 50 5.2 Summary of field measurements, August 2007 50 5.3 Previous field measurements 51 5.4 Trends in groundwater salinity 53 5.5 Rainfall and groundwater salinity 55 5.6 Water table elevations 57 5.7 Factors affecting water table elevation 58 5.8 Groundwater pH 61 5.9 Trends in groundwater pH 62 5.10 Groundwater temperature 63 5.11 Trends in groundwater temperature 64 5.12 Concluding comments and recommendations 65

    5.12.1 Spatial distribution and trends in EC 65 5.12.2 Water table elevation 65 5.12.3 Groundwater pH 66 5.12.4 Groundwater temperature 66 5.12.5 Unresolved questions 66 5.12.6 Recommendations on data collection, storage and analysis 67

    6 Measurements at the TWB Mataki’eua/Tongamai Wellfield 68 6.1 Outline 68 6.2 Groundwater salinity, July-August 2007 68 6.3 Groundwater salinity profiles across Mataki’eua/Tongamai 70 6.4 Relationship between pH and salinity 71 6.5 Groundwater level and salinity logging at Mataki’eua well 117 72 6.6 Water table drawdown due to pumping 75 6.7 Estimation of aquifer horizontal hydraulic conductivity 77 6.8 Trends in groundwater salinity 77 6.9 Trends in groundwater salinity of Mataki’eua well 106 78 6.10 Rainfall and groundwater salinity 80 6.11 Rainfall and groundwater salinity in Mataki’eua well 106 82 6.12 Comparison of groundwater salinity at Mataki’eua/Tongamai and village wells 83

  • Tongatapu Groundwater Vulnerability, June 2009 page iii

    6.13 Impact of pumping on groundwater salinity 85 6.14 Impact of pumping on groundwater salinity of Mataki’eua well 106 87 6.15 Estimated impacts of increased pumping 88 6.16 Concluding comments and recommendations 89

    6.16.1 Spatial distribution of salinity 89 6.16.2 Thickness of the freshwater lens 90 6.16.3 Groundwater pH 90 6.16.4 Groundwater elevation and pump drawdown 90 6.16.5 Temporal trends in groundwater salinity 90 6.16.6 Unresolved questions 91 6.16.7 Recommendations on data collection, storage and analysis 91

    7 Measurements at the Tapuhia Waste Management Facility 93 7.1 Salinity distribution in groundwater around the TWMF 93 7.2 Relationship between pH and salinity 94 7.3 Approximate salinity profile of groundwater at the TWMF 95 7.4 Water table elevation and recharge to hydraulic conductivity ratio 95 7.5 Direction of groundwater flow at Tapuhia 96 7.6 Faecal indicators of contamination at the TWMF 97 7.7 Past intensive water quality sampling at the TWMF 98

    7.7.1 Field and laboratory EC and pH 98 7.7.2 Major cations and anions 98 7.7.3 Relation between bicarbonate concentration and field pH 101

    7.8 Chemical contaminants 103 7.9 Nutrients 104 7.10 Conclusions and recommendations 106

    7.10.1 Conclusions 106 7.10.2 Recommendations 107

    8 Intensive Groundwater Testing in Tongatapu 108 8.1 Faecal indicators in groundwater samples 108 8.2 US Army survey of water quality, July 2007 110 8.3 Comparison with previous measurements of faecal indicators 111 8.4 Intensive chemical sampling of 10 selected wells 111

    8.4.1 Field measurements of EC and pH 111 8.4.2 Comparison of field and laboratory measurements of EC and pH 112 8.4.3 Relation between TDS and EC 114 8.4.4 Major cations and anions 114 8.4.5 Relation between bicarbonate concentration and pH 115 8.4.6 Relation between EC and chloride concentration 116 8.4.7 Relation between EC and concentrations of other major ions 117 8.4.8 Ion ratios of groundwater samples 119 8.4.9 Ion ratios of “end members” 119 8.4.10 Estimation of all major ions from field measured EC 121

    8.5 Comparison with previous measurements of major ions 122 8.5.1 Trends in the chloride concentration of groundwater, 1965 – 2007 122 8.5.2 Comparison with previous major ion analyses 126

    8.6 Pesticides, hydrocarbons and aromatics in sampled wells 129 8.7 Trace elements in sampled wells 129 8.8 Nutrients 131 8.9 Faecal Indicators in the 10 selected wells 133 8.10 Comparison with previous tests in Fanga’uta Lagoon 133

    8.10.1 Trace elements 133 8.10.2 Pesticides 133 8.10.3 Nutrients 134 8.10.4 Faecal coliforms 136 8.10.5 Relation to rainfall and groundwater discharge into the Lagoon 136

  • Tongatapu Groundwater Vulnerability, June 2009 page iv

    8.11 Comparison with previous groundwater analyses in Tongatapu 136 8.11.1 Trace metals 136 8.11.2 Pesticides 137 8.11.3 Imports of agricultural chemicals 138 8.11.4 Organics and petroleum products 139 8.11.5 Nutrients 139 8.11.6 Trends in groundwater nutrient concentrations 141

    8.12 Fertiliser use in Tongatapu 142 8.13 Domestic inputs of nutrients to groundwater 143 8.14 Concluding comments 146

    8.14.1 Faecal indicators 146 8.14.2 Ph, EC and major ions 147 8.14.3 Salinity trends 147 8.14.4 Pesticides, aromatics and hydrocarbons 148 8.14.5 Trace elements 148 8.14.6 Nutrients 149 8.14.7 Trend in nutrients 149

    8.15 Unresolved issues 149 8.16 Recommendations 150

    9 Groundwater Recharge 151 9.1 Overview 151 9.2 Empirical relationship between rainfall and recharge 151 9.3 Estimating recharge from the water balance 152 9.4 Description of the recharge model 153 9.5 Results of analyses 154 9.6 Discussion of results 158 9.7 Conclusions, unsolved issues and recommendations 161

    9.7.1 Conclusions 161 9.7.2 Unresolved issues 162 9.7.3 Recommendations 162

    10 Sustainable Groundwater Pumping in Tongatapu 163 10.1 Overview of groundwater yield 163 10.2 Preliminary estimates per unit area 163 10.3 Impact of droughts on freshwater thickness 163 10.4 Impacts of pumping on freshwater thickness 164 10.5 Estimate of sustainable yield for whole of Tongatapu 165 10.6 Comparison with current groundwater extraction 166 10.7 Area of influence of Mataki’eua/Tongamai pumping 168 10.8 Future wellfields for Tongatapu 169 10.9 Conclusions and recommendations 170

    10.9.1 Unresolved Issues 170 10.9.2 Recommendations 171

    11 Droughts 172 11.1 Overview 172 11.2 Rainfall variation in Tongatapu and ENSO events 172 11.3 Defining drought 173

    11.3.1 Meteorological or climatological dro