In many parts of the world, the most important reservoir of fresh water can be found below the ground surface in the form of groundwater. Aquifers tend to be depleted due to overpumping and the quality of the remaining groundwater tends to decline, due to waste releases, agricultural practices, mining operations, atmospheric deposition, and so forth.

Problems related to subsurface water resources are increasingly recognized by the wider public, the political process, water resources engineers and environmentalists, for their significance and complexity. These problems have accumulated over many years, mainly due to our inability to foresee the existence of subsurface transport pathways from various pollution sources and their long term impact on groundwater quality. Solutions to these problems are expensive and never simple, requiring carefully designed strategies for protection and restoration to be implemented, possibly over long periods of time. Achieving these goals requires first of all understanding of the physical, chemical and biological processes occurring at the aquifer scale. Such an understanding is reached by adopting state-of-the-art tools and developing new scientific knowledge pertinent to these complex issues. Rational decision-making related to water resources can only be achieved by first developing tools for realistic predictions of groundwater quality trends and fluctuations for any management scenario.