Groundwater constitutes an important component of many water resource
systems, supplying water for domestic use, for industry, and for
agriculture. Management of a groundwater system, an aquifer, or a system
of aquifers, means making such decisions as to the total quantity of
water to be withdrawn annually, the location of wells for pumping and
for artificial recharge and their rates, and control conditions at
aquifer boundaries. Not less important are decisions related to
groundwater qUality. In fact, the quantity and quality problems cannot
be separated. In many parts of the world, with the increased withdrawal
of ground- water, often beyond permissible limits, the quality of
groundwater has been continuously deteriorating, causing much concern to
both suppliers and users. In recent years, in addition to general
groundwater quality aspects, public attention has been focused on
groundwater contamination by hazardous industrial wastes, by leachate
from landfills, by oil spills, and by agricultural activities such as
the use of fertilizers, pesticides, and herbicides, and by radioactive
waste in repositories located in deep geological formations, to mention
some of the most acute contamination sources. In all these cases,
management means making decisions to achieve goals without violating
specified constraints. In order to enable the planner, or the decision
maker, to compare alternative modes of action and to ensure that the
constraints are not violated, a tool is needed that will provide
information about the response of the system (the aquifer) to various
alternatives.