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EDGAR (Extraction of Dissolved Gases for Analysis of Radiokrypton) is a field device that extracts dissolved gases from groundwater samples.The gas is then sent to Zheng-Tian Lu, a scientist at Argonne National Laboratory, who calculates groundwater age from Krypton-81 concentration.“In very old groundwater, when you’re extracting water you should realize that that water took a long time to get into that location, so it would take a long time to replace that water.So knowing the age of aquifers would give you an idea of how long it took and how valuable that resource is.” An evolving technique, initiated in the late ’90s by a team of scientists at Argonne National Laboratory in Argonne, Ill., could help groundwater professionals like Dennehy calculate the age of groundwater much older than currently used methods allow.
The instrument is able to report krypton-81 concentrations within a few hours.
In light of groundwater management and regulation, a reliable tool for dating the older aquifers of the world is invaluable, he says.
“When we drill a well and we get water out, we can pump as much as the pump will allow us to withdraw.
As that water seeps underground, so does a small amount of krypton-81. Krypton-81 stays in groundwater for around a million years before completely decaying, and can be tracked as it moves through aquifers.
Every 230,000 years, the isotope’s concentration decreases by a factor of two. Samples of the isotopes are pumped from water wells into a specialized gas collection machine, called EDGAR (Extraction of Dissolved Gases for Analysis of Radiokrypton), that separates krypton from the rest of the gases present in the water.