Since the earlier editions of this book in 1959 and 1980, the groundwater resource field has made tremendous strides in awareness of the environment, concerns and competition for water supplies, contamination of groundwater, and enhanced regulation of water resources. This new edition includes the many new developments that have occurred in the groundwater field. Chief among these is the role of computers, not only for organizing data and solving problems, but also in managing groundwater resources on a basin-wide basis for known or anticipated inputs and outputs.  Special focus is placed on modern groundwater modeling methods, including a detailed description of MODFLOW. Junior or senior level, or graduate level