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This has resulted in an increased emphasis on environmental tracer methods, partly because tracers are directly relevant to predicting the movement of dissolved contaminants and partly because the time scales for flow in arid vadose zones are often so slow that information from short-term physical monitoring may be difficult to extrapolate to the longer scale appropriate for solute transport. Figure 1 Cumulative water volume as a function of cumulative chloride mass (both per unit area) for three boreholes in the Pasco Basin, Washington. One frequently used tracer in this situation is also one of the simplest—chloride. They are studied mainly for the information they give about the ground water flow regime rather than the nature of the chemical activity in the ground water system. Such tracers have assumed new prominence in the past decade as a result of the refocusing of attention in applied ground water hydrology from questions of ground water supply, which are somewhat independent of the details of the flow path, to questions of ground water contamination, for which understanding the flow path and the nature of solute transport along it are central.
One major trend in vadose zone hydrology has been a new interest in the behavior of water in arid-region vadose zones, mostly as a result of the need to predict contaminant transport at waste disposal sites.
How can the scientific research establishment promote the transfer of basic research results into applications?
Many recent writers on this topic have attempted to generalize answers to these questions.
Although a shallow upper zone of arid-region soils is typically hydraulically active, response time in deep desert vadose zones is on the scale of 10 years (Phillips, 1994; Murphy et al., 1996).
Even the basics of water flow in arid-region vadose zones are still incompletely understood.