Various processes within the unsaturated zone affect ground-water availability and portability, as well as concentrations of water vapor and trace gases in the atmosphere. The rate at which precipitation or applied irrigation water infiltrates, its redistribution following infiltration, and the partitioning of the redistributed soil moisture between ground-water recharge and evapotranspiration affect the rate at which the ground-water reservoir is replenished and the degree to which ground water might be contaminated by chemical applications, spills, or disposal. Consequently, knowledge of and methods to quantitatively measure and predict these processes are needed to determine the impact of such societal practices as irrigation development [...]
Summary
Various processes within the unsaturated zone affect ground-water availability and portability, as well as concentrations of water vapor and trace gases in the atmosphere. The rate at which precipitation or applied irrigation water infiltrates, its redistribution following infiltration, and the partitioning of the redistributed soil moisture between ground-water recharge and evapotranspiration affect the rate at which the ground-water reservoir is replenished and the degree to which ground water might be contaminated by chemical applications, spills, or disposal. Consequently, knowledge of and methods to quantitatively measure and predict these processes are needed to determine the impact of such societal practices as irrigation development for agriculture, the use of agricultural chemicals, and the disposal of radioactive and/or hazardous waste in the unsaturated zone on both the availability and potability of ground water. Processes governing transport in the unsaturated zone gas phase are also important in determining the potential for ground- water contamination by volatile compounds, the rate at which water is returned from soil moisture to the atmosphere as vapor, and the fate of other "greenhouse gases", such as carbon dioxide, methane, and chlorofluorocarbons (CFCs). An understanding and quantification of these processes is needed both to assess the hazards of ground-water pollution and to better predict the impact of global change on future climate.
