VA Aquifer Susceptibility-Methods

The environmental tracers and isotopes present in the ground-water sample were derived from an atmosphere in the past. Sample collection and analytical methods had to minimize, if not eliminate, contact of the sample water with today's atmosphere. The sampling and analytical methods for the five techniques used to determine the age of ground water are briefly described below.

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Environmental tracer/
isotope
Sampling
method
Analytical
Method

Chlorofluorocarbons
(CFCs)
Samples are flame-sealed into borosilicate-glass ampules using a special apparatus that excludes contact with air.
Purge-and-trap gas chromatography procedure with electron capture detector

Tritium
(³H)
Samples are collected in 500-mL glass bottles with polycone seals.
Enriched electrolytically and analyzed by liquid scintillation counting

Tritium/Helium-3
(³H/³He)
Tritium: Samples are collected in 500-mL glass bottles with polycone seals.

Helium-3: Samples are collected in special copper tubes fitted with stainless steel pinch-off clamps. The discharge end of the tubes are fitted with an overpressure valve to prevent gas bubble formation in the ground-water sample
Tritium: Mass spectrometrically by the helium ingrowth method

Helium-3: Mass spectrometry

Sulfur Hexafluoride
(SF₆)
Samples are collected by filling 2.5-L plastic coated glass bottles from the bottom. The bottles are sealed with screw caps with conical liners. No headspace is allowed in the bottles.
Purge-and-trap gas chromatography procedure

Carbon-14
(¹⁴C)
Samples are collected in coated-glass bottles fitted with teflon septum. Sample water is filtered to eliminate contamination from particulates containing carbonate minerals. Contact with the atmosphere is minimized by establishing a closed path from the water source. Actual sample volume is dependent upon the pH and alkalinity of the water.
Accelerator mass spectrometry (AMS)

Last Updated on 2/4/2002
By David L. Nelms

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U.S. Department of Interior, U.S. Geological Survey
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URL http://va.water.usgs.gov/va123/2meth.html
Last update: 09/15/04 12:49

Environmental tracer/ isotope	Sampling method	Analytical Method
Chlorofluorocarbons (CFCs)	Samples are flame-sealed into borosilicate-glass ampules using a special apparatus that excludes contact with air.	Purge-and-trap gas chromatography procedure with electron capture detector
Tritium (³H)	Samples are collected in 500-mL glass bottles with polycone seals.	Enriched electrolytically and analyzed by liquid scintillation counting
Tritium/Helium-3 (³H/³He)	Tritium: Samples are collected in 500-mL glass bottles with polycone seals. Helium-3: Samples are collected in special copper tubes fitted with stainless steel pinch-off clamps. The discharge end of the tubes are fitted with an overpressure valve to prevent gas bubble formation in the ground-water sample	Tritium: Mass spectrometrically by the helium ingrowth method Helium-3: Mass spectrometry
Sulfur Hexafluoride (SF₆)	Samples are collected by filling 2.5-L plastic coated glass bottles from the bottom. The bottles are sealed with screw caps with conical liners. No headspace is allowed in the bottles.	Purge-and-trap gas chromatography procedure
Carbon-14 (¹⁴C)	Samples are collected in coated-glass bottles fitted with teflon septum. Sample water is filtered to eliminate contamination from particulates containing carbonate minerals. Contact with the atmosphere is minimized by establishing a closed path from the water source. Actual sample volume is dependent upon the pH and alkalinity of the water.	Accelerator mass spectrometry (AMS)