The Geohydrology Science Working Group is working together to identify potential geohydrologic studies (and associated societal benefits) that may be performed in an underground laboratory or observatory. The term "laboratory" implies a place that scientific experiments and studies may be performed, while "observatory" implies that processes that change through time will be observed. The Geohydrology Working group is working from the premise that a formal Geohydrologic Observatory and Laboratory will provide tangible scientific opportunities not available by other means, and that significant societal benefits may result. Fundamental geohydrologic issues may be investigated, including, for example, groundwater storage capacity and its controls, natural gas storage capacity and its controls, and groundwater and contaminant flow and transport processes, among many others. The Geohydrologic Observatory and Laboratory will offer a site to conduct large-scale, multidisciplinary studies as a community, as opposed to single investigators. Integral to scientific goals are proposed programs to foster education and training for future generations of scientists and teachers from K-12 to visiting researchers, focusing on those groups that have remained underrepresented throughout the 20th century.