TRITIUM/3He AGE DATING OF GROUNDWATER OF THE CONTINENTAL UNITED STATES

Between 1996 and 2010, the Lamont-Doherty Earth Observatory Noble Gas Laboratory has dated approximately 2,000 groundwater samples using the tritium/³He age method. The samples are drawn mainly from the continental United States, many of them as part of water quality studies under the auspices of the U.S. Geological Survey.

Taken as a whole, the data measured in the Lamont-Doherty Earth Observatory Noble Gas Laboratory represent a broad survey of continental waters, and bracket a wide range of hydrogeological settings, geochemical conditions and climatic zones. Hydrological settings range from unconfined/confined aquifers to fractured-rock aquifers and even more uncommon settings such as geothermal waters. The set of samples cover zones of humid subtropical climate in the southeastern U.S. to areas of semiarid steppe climate or even desert climate in the mid-western U.S.

The measurements also expose an interesting range of methodological issues related to very different sampling sites, sample integrity, laboratory procedure, and analytic techniques that can be used to investigate the performance of the methodology.

Our presentation will explore these issues, and will present summary results on the ranges of a set of variables (including tracer age, terrigenic helium contributions, pre-bomb tritium values), as well as distributions and quality from this unique tritium/³He data resource.