TM97-04 Tritium/helium dating of ground-water samples available through contract with Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York

The National Water Quality Laboratory (NWQL) of the U.S. Geological Survey (USGS) has contracted with the Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, for the analysis of low-level tritium (3 H), total dissolved helium (He), total dissolved neon (Ne), and the helium-3/helium-4 isotope ratio (3 He/4 He) of dissolved helium for purposes of groundwater dating based on the tritium/helium-3 (3 H/3 He) method. The 3 H/3 He dating method can be used to date waters recharged within approximately the past 30 years and complements existing capabilities within the U.S. Geological Survey for age-dating young ground-water, such as by use of chlorofluorocarbons (see joint Offices of Water Quality and Ground Water Technical Memorandum No. 95.02, dated December 29, 1994).