Hydrogeology is the study of groundwater – it is sometimes referred to as geohydrology or groundwater hydrology.
A hydrogeologic study or investigation is a study of the subsurface hydrologic and geologic conditions in an area or location. Data are collected about the type and thickness of geologic materials, the occurrence of ground water, how it flows in pore spaces and/or fractures, the quality of the ground water, and what can be expected at wells.