Throughout the world increasing demands for safe drinking water and requirements to maintain healthy ecosystems are leading policy makers to ask complex social and scientific questions about how to assess and manage our water resources. This challenge becomes particularly difficult as policy and management objectives require scientific assessments of the potential for ground-water resources to become contaminated from anthropogenic, as well as natural sources of contamination. Assessments of the vulnerability of ground water to contamination range in scope and complexity from simple, qualitative, and relatively inexpensive approaches to rigorous, quantitative, and costly assessments. Tradeoffs must be carefully considered among the competing influences of the cost of an assessment, the scientific defensibility, and the amount of acceptable uncertainty in meeting the objectives of the water-resource decision maker.
Ground water occurs almost everywhere beneath the land surface. The widespread occurrence of potable ground water and the natural processes that tend to provide barriers to some types of contamination are some of the reasons why ground water is used as a source of water supply by about one-half the population of the world, including almost all of the population that is served by domestic water-supply systems (Alley and others, 1999).
The ground-water-flow system, as defined in this report, includes effects of geologic deposits, interactions with surface waters, pumping, and other stresses on movement of water controlling advective transport of contaminants. Understanding the ground-water-flow system enables scientists to determine the potentially important factors controlling the intrinsic susceptibility of a ground-water resource. For this report, a ground-water resource is considered to be any aquifer or portion of an aquifer (including a well or wells) regardless of whether it is presently used a source of public water supply. In this way, the actual or potential source water for a public supply and(or) a public-supply well is included in the definition of a ground-water resource, as is any ground water that is not presently used by humans.
Read more:Assessing groundwater