ABSTRACT
Groundwater makes up more than a quarter of all available freshwater in the world, and it is also one of the purest forms of water on Earth. Despite these, groundwater was one of the least-exploited natural resources until just a few decades ago, as its access was (and still is, to some extent) more difficult and expensive when compared to surface water resources. However, a combination of factors, including explosion in population, dwindling surface water resources per capita, and developments in technology, has changed this situation in recent times. The last few decades have witnessed a significant exploitation of groundwater resources around the world, both in the developed world and in the developing world, including in the United States, Europe, and Asia (e.g., Konikow and Kendy, 2005). Indeed, in many parts of the world, groundwater is the only viable source of water of safe quality, such as the quality required for drinking and household use. With the relative ease in withdrawal of large quantities of water from depths of even hundreds of meters, groundwater has also become the only or primary source of water for irrigation in many countries. While there are already increasing concerns about the recent and current levels of exploitation of groundwater, the situation will likely become even worse in the future, due both to our continued increase in water demands and to the anticipated negative impacts of climate change on our water resources. As a result, there is a clear and urgent need to improve our understanding and modeling of groundwater flow and transport phenomena.
