GNS provides a number of complementary age tracer methods to date water samples.
These include tritium, CFCs, SF6, silicon-32, carbon-14, and stable isotopes, covering a range of ages from less than six months to tens of thousands of years.
However, shallow ground-water supplies are generally young (recently recharged) and, because there has been a wide variety of man-made pollutants produced in the 20th century, are more susceptible to contamination than deeper ground water.
H, half-life of 12.43 years (Unterweger and others, 1980)) has provided an excellent tracer of young waters.
Locating the position of the mid-1960s bomb peak is difficult due to the required high density of vertical sampling and, therefore, is often an impractical means of obtaining ground-water age information. Ekwurzel, B., Schlosser, P., Smethie, Jr., Plummer, L. L., Weppernig, R., and, Stute, M., 1994, Dating of shallow groundwater: Comparison of the transient tracers Kr: Water Resources Research, v.
Determination of the H in the water sample (Schlosser et al., 1988, 1989).
Young ground water in shallow ground-water systems Young ground water is typically found at depths from 0 to 100 feet in unconsolidated sediments and at depths up to 1000 feet in fractured-rock systems.
Shallow ground-water systems are commonly used for drinking water sources and they make up a large part of the baseflow in rivers and lakes.
The concentration of the tracers in the groundwater depends on the atmospheric concentration at the time of contact when the water fell as rain or snow, and the time since the last contact of the water with the atmosphere.After oxidation to HTO, it takes part in the natural water cycle.Before the full potential of natural tritium as a tracer for water movement in natural systems could be explored its distribution was masked by addition of large amounts of so-called ‘bomb tritium’ produced during the surface tests of nuclear weapons.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). It has a shapely blued-steel needle engraved N & S for clarity over a traditional paper dial incorporating eight cardinal points, with an elaborate fleur de lis denoting North.This is one of the larger examples measuring 115mm square and is in very good condition with a clean crystal and dial.These problems can be overcome by using tritium in combination with its decay product He age formally calculated from equation (1) is an apparent age.This is a very elegant mid 19th century pocket compass circa 1860, set in a hinged mahogany block with chamferred sides on the lid which is fastened by two side brass clasps.Tritium input to ground water has occurred in a series of spikes following periods of atmospheric testing of nuclear devices that began in 1952 and reached a maximum in 1963-1964. Tritium measurements alone can be used to locate the depth of the mid-1960s bomb peak, but, because of radioactive decay, many samples may need to be collected and analyzed today to locate its position. In systems younger than the mid-1960s, the bomb peak will not be present due to radioactive decay. Although unsigned, as many 19th century wood block compasses are, the concealed hinges were a feature almost exclusively used by Francis Barker & Son, and the quality is certainly in keeping with that makers reputation.In full working order, including the transit lock this is an impressive Victorian compass, with a particularly attractive compass rose.If the tritium delivery as a function of time can be reconstructed, this penetration process can be used for quantitative studies of water movement through identification of the bomb peak in certain ground water bodies.