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FOR DELFT NETNERwjDS 1T~ftT S — — — i.1 -c--~ 244 91CR -4 __1•” ~ —— - — -— - -----------t— —-~-~—--- —~ -— — - -~ --t~-,~~~-tf *4 - L -~~=~-rt:- - - —±fl- ~ _i~~__ ~ ~sW/’~’WW’/’t,Ç’~. PIT watex table direction - of flow •,~\ poli groundwater -- r’r-itiJLk— ~~--—- —-- ----~- ~~--- ~i~-- .~r‘~--~ H—~ USRAr?? - : . ~ ~. ‘!-‘4’ltMIJtJNf.\I.SFcr.i-,~.... l.&frtr u~cENrH~ ~~L_ Çfl47 e~~ W~TË~StWPIY AN~ ~ AT~M4{[RCJ 1 GROUND WATER CONTAMINATION BY PIT LATRINES Dar-es-salaarn (Manzese squatter area) case study by V.P. Mnyanga LIBRARY; INTERNATIONAL REFERENCE ~ENTRE F2R OOMMUNITY WATER ELJP~LY AND SAN~t.\ ~I~ ~ ~L4C) P.O. ~ 2509 AD The H~gue - - Ti~t.(0?Ü) 81~J11ext. 141/142 LO: 2(-P~-~~)G-~ ___ EXAMINATION COMMITTEE Prof. dr. ir. G.J.F.R. Alaerts (IHE), chairman Dr. Ir. C. van den Akker (RIVM) Dr. P. Kelderman (IHE) SUPERVISORS Prof. dr. Ir. G.J.F.R. Alaerts (IHE) Ms. H.E. Claringbould (IHE) Dr. P. Kelderman (IHE) M.Sc. Thesis Report E.E. 39 March, 1991 £aLs s mflAiCm Croundwater contamination from pit latrines is a potential health hazard especially in developing countries where shallow hand-dug welis are used to supplement conventional water supply (in cases of shortages). Analysis of the impact of groundwater contamination by pit latrines in Dar-es—salaam (Manzese squatter area) was carried out (chapter 5). Fluid and pollutant transport (chapter 2), microhial movement and survival in groundwater (chapter 3) as well as nutrient (nitrates) dynamics (chapter 4) were considered. Available data on the phenomenon were supplemented by the MFLOP model to obtain an insight into the nature of the problein. Results from the model shows that the groundwater in Manzese area is polluted by mostltly microorganisms with low die—off rates like faecal streptococci. However, validation of the model in the field situation is essential. 1 . N~DWGEM~N~ 1 wish to acknowledge with pleasure and sincere gratitude to the following individuals who have given help, advice, guidance, and inspiration during the course of this MSc.Thesis study:- Prof. Dr.Ir. G. Alaerts; Head of Environmental Engineering Department (IHE) and supervisor of this work, for his challenging discussions, generous help, stimulating and convincing advices, patient guidance, and constant encouragements and inspirations throughout the course of the study. Dr. P. Kelderman; Course leader of (WQM) Water Quality Management. and Miss. H. Claringbould; Mentor of low cost water supply, who served as my mentors for their immeasurable guidance, fruitful comments and discussions, motivation, constant encourageinents and valuable suggestions which made it possible for the work to be completed and on time. Dr. Ir. C. Van den Akker (from RIVM) for his kindness, cooperation, suggestions, amicable and valuable help, and guidance on how best the MFLOP software could be used and improved to suit the need and use for the study. Though 1 used to have brief contacts with him during his visits at the IHE as . a visiting lecturer, he was always ready to help even when given a short notice appointment. He did all this despite of his many pressing work in his office. Mr. S. Veenstra and Mr. J.C. Nonner for their stimulating comments, positive criticisms and suggestions. Mr. J. Rijnsburger (WASTE consultants) and Mr. G.J.G. Kok (Haskoning consultants) for their guidance and allowing me to use part of the data their firms collected from Dar—es-Salaam. 1 also wish to express my appreciation to the International Institute for Hydraulic and Environmental Engineering (I.H.E.), Delft, under the leadership of Director Prof. Ir. W.A. Segeren for its basic academic support, and to the Swedish International Development Agency (S.I.D.A.) for her financial support during my entire stay in the Netherlands (inciuding the eleven months of P.G. Diploma in Water Quality Management course). Lastly, though not least to my parents, whose prayers and blessings from a distance enabled me to complete the study successfully and to my family who missed my love during the period of study, for their understanding and patience. ii S . CONTENTS Page ABSTRACT i ACKNOWLEDGEMENTS ii TABLE OF CONTENTS iii LIST OF FIGURES Vi LIST OF TABLES Viii CHAPTER ONE 1.0 INTRODUCTION 1 1.1 Problem definition 1 1.2 Research objectives 2 1.3 Methodology 3 CHAPTER TWO 2.0 FLUID AND POLLUTANT TRANSPORT 5 2.1 Fluid transport 5 2.2 Pollutant transport processes 5 2.2.1 Concept 5 2.2.2 Advection (convection) 6 2.2.2 Dispersion and diffusion 7 2.2.3 Random-walk method 15 2.2.4 Sorption 17 2.2.5 The effect of immobile water 19 CHAPTER THREE 3.0 MICROBIAL MOVEMENT AND SURVIVAL IN GROUNDWATER 20 3.1 Introduction 20 3.2 Factors affecting pathogen survival 20 3.2.1 Survival in soils 20 3.2.2 Survival in groundwater 21 3.3 Die—off computations 22 111 3.4 Factors affecting pathogen movenent 25 3.4.1 Pore clogging process 26 3.4.2 Straining filtration 29 3.4.3 Sorptive filtration 30 3.5 Field Investigation of pollutant movement 31 3.5.1 Bacteria in the saturated zone 31 3.5.2 Bacteria in the unsaturated zone 31 3.4.3 Movement of viruses 32 CHAPTER FOUR 4.0 NITRATE AS CONTAMINANT 33 4.1 Introduction 33 4.1.1 Nitrification 33 4.1.2 Denitrification 34 4.2 Movement of nitrate within groundwater 34 4.3 Field investigations 35 4.4 Severity of nitrate contamination in groundwater 38 CHAPTER FIVE 5.0 DATA INFLUENCING GROUNDWATER CONTAMINATION IN DAR-ES-SALAAM 40 5.1 Introduction 40 5.2 Physical data 41 5.2.1 Location and topography 41 5.2.2 Climate 43 5.2.3 Soils 44 5.3 Social data 44 5.3.1 City population 45 5.3.2 Dar—es—salaam administration 45 5.3.3 Ward population 45 5.3.4 Housing 46 5.3.5 Water supply 47 iv 5.4 Sanitation in Dar-es--salaam 49 5.4.1 General 49 5.4.2 Pit latrine construction 50 5.4.3 Pit latrine use 53 5.4.4 Cleaning and waste disposal 54 5.4.5 Filling of pits 55 5.4.6 Excreta generation per capita 56 5.4.7 Ernptying of pit latrine in Dar—es--salaam 57 5.4.8 Problems experienced with existing pit latrine 62 5.4.9 Sullage disposal 62 5.4.lOCare of the shallow welis 63 5.4.llflomestic wastewater generation per capita 64 5.5 Conciuding remarks 65 CHAPTER SIX 6.0 “MFLOP version 2.0e’ AS A PREDICTIVE MODEL 67 6.1 Introduction 67 6.2 Background of the FLOP model 67 6.3 Assumptions in the model 70 6.4 Use of the model for Dar-es-salaam (Manzese) case study 70 6.4.1 Sensitivity of the model 70 6.4.2 Manzese model 79 CHAPTER SEVEN 7.0 CONCLUSION AND RECOMMENDATIONS 88 References Appendices v . LIST OF FIGURES Page 2.1 Movement of groundwater pollution 6 2.2 Dispersion process at a microscopic scale 7 2.3 The effect os scale on hydrodynamic dispersion processes 8 2.4 Spreading of a definite fluid portion due to dispersion 10 2.5 Field measured values of longitudinal dispersivity as a function of scale length for saturated porous media 11 2.6 Longitudinal dispersivity Vs. scale length for saturated porous media 12 2.7 Longitudinal dispersivity Vs. scale length for unsaturated porous media — 13 • 2.8 Comparison between plug flow and dispersion flow 14 2.9 Two individual random paths (12 steps each) starting from a point-like particle source 17 3.1 First—order degradation (plug flow) 23 3.1 Location of the clogging layer (mat) from a pit latrine 26 3.2 Development of the clogging layer and its permeability changes 28 3.3 X—section of an absorption field in plain field loamy sand with typical bacterial counts locations 29 4.1 Hydrogeological section of study area showing build—up of nitrates in soil around a pit latrine 37 4.2 Nitrogen transformation in a pit latrine 38 5.1 Map of Tanzania showing location of Dar-es-salaam city 41 5.2 Effluent river 42 5.3 Influent river 42 5.4 Section of a pit latrine 51 5.5 VIP latrine 52 5.6 Digging method 58 5.7 Flushing method 58 5.8 On—site disposal 60 5.9 Disposal in transfer stations 61 6.1 Flow from eight (8) infiltration weils to an extraction well 69 vi 6.2 Welis arrangement in the sensitivity test 71 6.3 Plan of a six bedroomed house found in Manzese 72 6.4 Flow time ~‘ariationswith aquifer porosity 73 6.5 Flow time variations with aquifer thickness 74 6.6 Flow time variatioris with distance between weils 75 6.7 Flow time variations with extraction well discharge 76 6.8 Flow time variations with regional velocities 77 6.9 Groundwater velocity variations with regional slopes 78 6.10 Data input file for Manzese model 80 6.11 Breakthrough curve for case No.1 83 6.12 Streamlines showing the Manzese model 84 6.13 Breakthrough curve for case No.2 85 . vii LIST OF TABLES Page 1) for viruses and 3.1 Die-of f rate constants (day bacteria in groundwater 24 3.2 Half—time (time of 50% reduction) of various bacteria cultures in well water, at 9—12°C 25 5.1 Population projection for Dar—es-salaam city 45 5.2 Water—borne diseases caused by faecal pathogens 47 5.3 Domestic wastewater generation per capita in Dar—es-salaam 64 5.4 Predicted distribution loads of Dar—es—salaam 64 6.1 Regional groundwater velocity calculations 81 6.2 Manzese model output resuits 82 viii .