The increasing national and international demand for water has led to increasing reliance on subsurface storage, both for naturally and artificially recharged water.
This increased reliance on the groundwater in concert with the strict regulation on water quality has led to a need by water managers and regulators to understand: Characterization of mean groundwater age and recharge temperature through the use of noble gas techniques provides information that is relevant to answering these questions and that is not accessible through traditional hydrogeologic approaches.
These tests which were mainly performed in the early 1960s, led to an increase of tritium in precipitation over the continents of the northern hemisphere from roughly 5 TU to levels of the order of 1000 TU.
One TU (Tritium Unit) means a tritium to hydrogen ratio of 10.
As these substances are virtually inert in ground water, unaffected by ground-water chemistry and unaffected by contamination from most anthropogenic sources, He dating complements existing capabilities within the U. Geological Survey for dating of young ground water, such as, uses of chlorofluorocarbons and sulfur hexafluoride, and can be applied to dating water recharged since about 1965. B., 1993, Chlorofluorocarbons (CCl) as Dating Tools and Hydrologic Tracers in Shallow Ground Water of the Delmarva Peninsula, Atlantic Coastal Plain, United States: Water Resources Research, v.
Several conditions are necessary to permit solving the helium isotope mass balance for ), after correction for dilution with old (low tritium) water, should be consistent with possible tritium-age relations for surface water or meteoric infiltration water of that age (see for example Figure 14 in Dunkle and others, 1993; Figure 7 in Ekwurzel and others, 1994; and Figure 7 in Plummer and others, 2000).
Tritium is produced naturally in the upper atmosphere by interaction of nitrogen, and, to a lesser extent, oxygen with cosmic rays.
C value between the gas-strip and precipitation methods was assumed to be caused by the contamination of modern carbon in the Na OH solution used in the precipitation method.
The contamination of modern carbon derived from the Na OH solution during precipitation was found to range from less than 1 mg/L to about 1 mg/L.
The data generated by the Groundwater Dating Laboratory are being used throughout the USGS in hydrologic studies.
The lab's staff work together in research to refine the use of groundwater dating techniques and to develop new groundwater dating methods.