L. Niel Plummer is Scientist Emeritus with the U.S. Geological Survey, National Research Program, Reston, VA. He holds B.A. (1967) and M.S. (1969) degrees in geology from the University of Kentucky, and Ph.D. (1972) in Geochemistry/Geology from Northwestern University, Evanston, Illinois. He was Assistant Professor of Geological Sciences at the State University of New York at Buffalo, NY from 1972-1974. He joined the National Research Program of the USGS full time in 1974 as Research Hydrologist. He was appointed Senior Research Scientist with the USGS in 1992, and retired in 2012, remaining active as Scientist Emeritus. He is internationally recognized for his research in aqueous geochemistry, thermodynamics and kinetics of carbonate mineral reactions, geochemistry and hydrogeology of groundwater systems, geochemical modeling, hydrochemical studies of regional aquifers, and groundwater-dating studies. He has been a consultant to the Isotope Hydrology Section of the International Atomic Energy Agency (IAEA), Vienna, Austria. His research over the past 44+ years has encompassed aspects of kinetics and thermodynamics of carbonate mineral-water systems, modeling of chemical and isotopic evolution of groundwater, hydrochemical studies of groundwater systems, and groundwater dating on the anthropogenic, radiocarbon, and million-year timescales. He has authored or co-authored 175 research papers, book chapters, USGS reports and other documents in peer-reviewed scientific literature. His publication on calcite dissolution kinetics, American Journal of Science, 1978, currently has more than 900 citations (Google Scholar), and a paper on the solubility of calcite, aragonite and vaterite published in Geochimica et Cosmochimica Acta in 1982 has more than 1100 citations. He was co-creator of several geochemical modeling computer codes that have been widely applied to interpret geochemical processes in groundwater systems, such as NETPATH, with more than 600 citations. In 1992 he was co-pioneer of a technique of groundwater dating using chlorofluorocarbons, a study that has been widely cited. His most recent research has focused on applications of multiple environmental tracers in groundwater dating in karst and fractured rock, assessment of susceptibility of water-supply wells to anthropogenic inputs, a hydrochemical study of the Middle Rio Grande Basin, NM, studies of the occurrence of perchlorate in paleo groundwater, groundwater dating on the million-year timescale, and theoretical developments in radiocarbon dating of dissolved inorganic carbon in groundwater systems. Among other awards, he is recipient of the Meritorious (1987) and Distinguished Service (1996) Awards from the US Department of Interior, and the O.E. Meinzer Award (1993) from the Hydrogeology Division of the Geological Society of America.