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Second, it is important that the DOC does not change character down a flow path, which could indicate transformation of DOC along a flow path and/or addition of DOC to the groundwater.
Although specific DOC compounds could not be identified for samples collected at four sites, all four groundwater sample spectra show the same general shape over the duration of the HPLC run indicating that the DOC compound composition of groundwater does not significantly change from up-gradient to down-gradient.
Longer exposures to radiation increases amounts of helium-3 among other cosmogenic isotopes.
Information about the age of groundwater can be used to define recharge rates, refine hydrologic models of groundwater systems, predict contamination potential, and estimate the time needed to flush contaminants from ground-water systems.
Tritium decays to the stable isotope helium-3, which stays dissolved in the water below the water table.
With precise measurement, the parent and daughter isotopes can be quantified, providing a means to accurately date when water was recharged.
For more information about the use of chlorofluorocarbons for dating, see the Chlorofluorocarbons page.
The measurement of cosmogenic helium makes it possible to date rocks.
Not the date of rock formation, but dating how long a rock has sat at the Earth's surface and been exposed to cosmogenic radiation.
The bombardment of the earth by particles causes spallation within the atmosphere, and within the upper centimeters of terrestrial surfaces.
The Noble Gas lab contains a mass spectrometer system capable of precise isotopic measurements of the noble gases as well as most other common atmospheric gases.
The Environmental Tracers Lab utilizes a gas chromatography system for precise measurements of dissolved CFC's in natural waters to determine timing of recharge.
Atmospheric atomic bomb testing in the 1950's and 60's bolstered the concentration of tritium in the atmosphere where it can become incorporated into a water molecule and enter the water cycle.