Groundwater is one of the most important resources in the world. In many
areas, water supplies for industrial, domestic, and agricultural uses
are de- pendent on groundwater. As an "open" system, groundwater may
exchange mass and energy with its neighboring systems (soil, air, and
surface water) through adsorption, ion-exchange, infiltration,
evaporation, inflow, outflow, and other exchange forms. Consequently,
both the quantity and quality of groundwater may vary with environmental
changes and human activities. Due to population growth, and industrial
and agricultural development, more and more groundwater is extracted,
especially in arid areas. If the groundwater management problem is not
seriously considered, over- extraction may lead to groundwater mining,
salt water intrusion, and land subsidence. In fact, the quality of
groundwater is gradually deteriorating throughout the world. The problem
of groundwater pollution has appeared, not only in developed countries,
but also in developing countries. Ground- water pollution is a serious
environmental problem that may damage human health, destroy the
ecosystem, and cause water shortage.