In English, French & German. 5,422 terms deal with the geology of groundwater within the framework of the hydrologic cycle, geohydrology, contaminant hydrology, computer application to groundwater and subsurface pollution problems, environmental implications of groundwater use, regulatory aspects of groundwater protection, wellhead protection programs, interaction of groundwater systems with biogeochemical cycles, geochemistry of natural waters and contaminant chemistry, and water resources management.