The unsaturated zone is the medium through which pollutants move from the soil surface to groundwater. Polluting substances are subjected to complex physical, chemical and biological transformations while moving through the unsaturated zone and their displacement depends on the transport properties of the water-air­ porous medium system. Pollution caused by human activities, agriculture, and industry, has brought about a growing interest in the role of the unsaturated zone in groundwater pollution. Due to the complexity and the multidisciplinary nature of the subject, it is being investigated by specialists from various scientific disciplines, such as soil physicists, chemists, biologists, and environmental engineers. This state of affairs has motivated the initiative taken by the Water Quality Commissions of IUPAC (the International Union of Pure and Applied Chemistry) and IAHS (the International Association of Hydrological Sciences) to convene an international workshop, which was organized and hosted by the Institute of Soils and Water of the Agricultural Research Organization in Bet­ Dagan, Israel in March 1983. The lecturers at the workshop were an invited group of specialists who are engaged in studying the many facets of the unsaturated zone, and the present book is a selection of their presentations. Each chapter of the book relates to a different aspect of the unsaturated zone.

Inhalt

A. Modeling of Pollutants Transport.- Introductory Comments.- 1. Tracing Parcels of Water and Solutes in Unsaturated Zones.- 1.1 Introduction.- 1.2 Convective Transport by Simple Flows.- 1.2.1 Movement of Water in Unsaturated Soils.- 1.2.2 Movement of Solutes in Unsaturated Soils.- 1.2.3 Detailed Analysis of Constant Flux Absorption.- 1.2.4 Relative Speeds of Wetting and Solute Fronts.- 1.2.5 Drainage to a Deep Water Table.- 1.3 Convective Transport by Complex Flows.- 1.3.1 Structured Media.- 1.3.2 Secondary Flows Induced by Density Variations.- 1.3.3 Unstable Wetting Fronts.- 1.4 Conclusions.- References.- 2. Solute Transport in Soil at Field Scale.- 2.1 Introduction.- 2.2 Basic Concepts of Stochastic Modeling.- 2.3 Succinct Review of Previous Work.- 2.4 Conclusions and Outline of Future Investigations.- References.- 3. Migration of Organic Fluids Immiscible with Water in the Unsaturated Zone.- 3.1 Introduction.- 3.2 Multiphase Flow.- 3.3 Physical Characteristics.- 3.4 The Migration of the Immiscible Phase.- 3.5 Migration of Dissolved Components.- 3.6 The Migration of Gas Components.- 3.7 Microbial Degradation.- 3.8 Migration in Fissured Media.- 3.9 Conditions in the Unsaturated (Porous) Zone.- 3.10 Measures After Spills of Organic Liquids.- 3.11 Practical Investigations.- 3.12 Cooperative Research.- 3.13 Conclusions.- References.- B. Behavior of Inorganic Chemicals.- Introductory Comments.- 4. Pollution of the Unsaturated Zone with Nitrate.- 4.1 Introduction.- 4.2 Nitrate as a Pollutant.- 4.3 Sources.- 4.4 Behavior.- 4.5 Movement.- 4.6 Possible Solutions.- References.- 5. Behavior of Phosphates in the Unsaturated Zone.- 5.1 Introduction.- 5.2 Equilibrium Models Based on Adsorption Isotherms.- 5.3 Solubility Equilibrium.- 5.4 The Kinetic Approach.- 5.5 Conclusions.- References.- 6. Unsaturated Zone Pollution by Heavy Metals.- 6.1 Introduction.- 6.2 Abundance.- 6.3 Contamination of Groundwater by Heavy Metals.- 6.4 Solubility.- 6.5 Complexation.- 6.6 Colloidal Solutions of Heavy Metals.- 6.7 Precipitation and Coprecipitation.- 6.8 Adsorption and Ion Exchange.- 6.9 Radioactive Decay.- 6.10 Biochemical Processes.- 6.11 Gas Exchange.- 6.12 Filtration.- References.- 7. Effect of Acid Rain on Soil and Groundwater in Sweden.- 7.1 Introduction.- 7.2 Acidification of Precipitation and Surface Water.- 7.2.1 Precipitation.- 7.2.2 Surface Water.- 7.3 Acidification of Soil and Groundwater.- 7.3.1 Terrestrial Water Flow, Especially in Moraine Terrain.- 7.3.2 Acidification Processes.- 7.3.3 Processes in Podzols.- 7.3.4 Sulfate Behavior in Soils.- 7.3.5 Behavior of Soil Solutions as Affected by Soil Acidification.- 7.3.6 Acidification of Soil.- 7.3.7 Acid Groundwater.- 7.3.8 Changes of the Chemistry of Groundwater.- 7.4 Modeling the Acidification.- References.- 8. Heavy Metal Pollution of Natural Surface Soils Due to Long-Distance Atmospheric Transport.- 8.1 Introduction.- 8.2 Atmospheric Pollution in Norway.- 8.3 Heavy Metals in Norwegian Surface Soils.- 8.4 Conclusions.- References.- C. Behavior of Organic Compounds.- Introductory Comments.- 9. Chemical Nature and Reactivities of Soil Organic Polymers.- 9.1 Introduction.- 9.2 The Genesis of Humus Materials.- 9.2.1 Humification by Biological Processes.- 9.2.2 Humification by Chemical Processes.- 9.3 Structures of Humus Substances.- 9.3.1 Extraction and Fractionation of Humus Substances.- 9.3.2 Structural Information from Degradative Procedures.- 9.3.3 Structural Information from Nondegradative Procedures.- 9.3.4 Sizes and Shapes of Humus Substances.- 9.4 Practical Applications of Information from Structural Studies of Humus Substances.- References.- 10. Behavior of Pesticides in the Unsaturated Zone. Adsorption and Transport Phenomena.- 10.1 Introduction.- 10.2 Adsorption.- 10.2.1 General Considerations.- 10.2.2 Some Published Experimental Results.- 10.3 Transport Phenomena.- 10.3.1 Transport with Flow of the Soil Solution.- 10.3.2 Molecular Diffusion.- 10.4 Conclusion.- References.- 11. Nonbiological Degradation of Pesticides in the Unsaturated Zone.- 11.1 Introduction.- 11.2 Properties of the Solid-Liquid Interface Affecting Pesticide Degradation.- 11.3 Importance of Surface-Catalyzed Degradation Processes in the Unsaturated Zone.- 11.4 Factors Affecting Surface-Induced Pesticide Degradation.- 11.5 Conclusion.- References.- 12. The Effect of Solid Organic Components of Sewage on Some Properties of the Unsaturated Zones.- 12.1 Introduction.- 12.2 Composition of Organic Solid Components of Sewage.- 12.3 Physical Effects of Organic Solids.- 12.3.1 Waste Waters.- 12.3.2 Sewage Sludges.- 12.4 Chemical Effects of Organic Solids.- 12.4.1 Enrichment by Chemicals.- 12.4.2 Changes in pH and Total Salt Content.- 12.4.3 Effect on the Exchange Complex and Dissolution-Precipitation Processes.- References.- D. Biological Processes.- Introductory Comments.- 13. Biochemical Processes in Unsaturated Zones.- 13.1 Introduction.- 13.2 Substrates for Microbial Growth.- 13.3 Microbial Metabolites in Relation to Plant Growth.- 13.4 Microbial Effects on Soil Structure.- 13.5 Nutrient Cycles.- 13.6 Pollutant/Microorganism Interactions.- 13.7 Conclusion.- References.- 14. Pathogenic Bacteria and Viruses in the Unsaturated Zone.- 14.1 Introduction.- 14.2 Persistence of Bacteria and Viruses.- 14.3 Transport Processes.- 14.4 Filtration Processes.- References.- E. Unsaturated Zone and Groundwater: Pollution Sources.- Introductory Comments.- 15. Agricultural Pollutants and Groundwater Quality.- 15.1 Introduction.- 15.2 Application Rates.- 15.3 Movement to Groundwater.- 15.3.1 Water Movement.- 15.3.2 Adsorption and Degradation.- 15.4 Results.- 15.4.1 Nitrates.- 15.4.2 Pesticides.- 15.5 Case Study.- References.- 16. Nitrogen Presence in Groundwater as Affected by the Unsaturated Zone.- 16.1 Introduction.- 16.2 Geohydrological and Historical Background of the Coastal Plain Aquifer.- 16.3 Nitrogen in the Coastal Plain Aquifer.- 16.4 Nitrogen Sources.- 16.4.1 Exhaustive Sources.- 16.4.2 Continuous Sources.- 16.5 Nitrogen Stored in the Unsaturated Zone.- 16.6 Processes Modifying Nitrogen Storage in the Unsaturated Zone.- 16.7 The Unsaturated-Saturated Interface.- 16.8 Nitrogen in Groundwater.- References.- 17. Prevention of Groundwater Pollution on a National Scale: Israel as a Case Study.- 17.1 Introduction.- 17.2 Wastes and Potential Pollutants.- 17.2.1 Physical Background.- 17.2.2 The Potential Pollutant Load.- 17.3 Plans and Trends in Land Disposal.- 17.3.1 Agricultural Wastes.- 17.3.2 Wastewater Treatment.- 17.3.3 Solid Waste Disposal.- 1…