| Title: |
Apparent 85Kr Ages of Ground Water Within the Royal Watershed, Maine, USA.
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| Resource Type: |
document --> technical publication --> journal article
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| Country: |
USA
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| Year: |
2006 |
| Availability: |
Journal of Environmental Radioactivity. 91:113-127
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| Author 1/Producer: |
Sidle, W.C.
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| Author / Producer Type: |
University research group / research institute
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EUGRIS Keyword(s): |
Contaminated land-->Site investigation-->Sampling and analysis
Contaminated land-->Soil and groundwater processes-->Hydrogeology
Contaminated land-->Soil and groundwater processes-->Soil and groundwater processes overview
Groundwater protection-->Groundwater protection overview
Water and sanitation-->Water and sanitation Overview
Water resources and their management -->Water resources and their management Overview
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| Short description: |
From NRMRL.
Most people are familiar with the use of radiocarbon dating to place once-living objects in their historical period. In a parallel approach, NRMRL
hydrologists are pioneering the measurement of naturally occurring radioactive isotopes to determine the age (that is, the residence time) of ground
water in support of watershed contamination studies.
While age-dating of young ground water (ground water that's less than 50 years old) is a frontier field in watershed studies, it has long been realized
that very young ground water could be a more significant source of contamination than older water. This is true because a shorter residence time
means that ground water moves 'faster.' Thus, contamination will get to the drinking well from the recharge area (point of entry) faster if the ground
water is younger.
However, it has been difficult to measure the exact age of young ground water. The conventional indicator has been tritium, a radioactive form of
hydrogen, but its usefulness has nearly ended because of a short half-life combined with its last significant input to the atmosphere from
thermonuclear tests of the early 1950s. NRMRL isotope hydrologists believe that dissolved krypton gas (in the isotope form of 85 Krypton) may be the best
indicator, among the other potentially useful isotopes tested, of young recharge water.
85Kr is ideal for several reasons:
- It has increased in precipitation since the 1950s at a relatively constant rate.
- It has an appropriately short half-life.
- It is almost uniformly distributed in the northern hemisphere.
Furthermore, because it is chemically inert, it retains its unique isotope characteristics while it decays as predictably as the unwinding of a clock.
Until recently, the chief shortcoming of this method was the daunting task of collecting voluminous water samples to measure traces of the rare 85Kr
isotope. Finally, a breakthrough in field collection and laboratory measurement has permitted the new 85Kr isotope method to detect ground water as
young as 2 years and as old as 50 years.
For the first time, the widespread economical use of the new 85Kr method has been applied to selected watersheds where elevated natural
occurrences of arsenic and lead have prompted hydrologists to ask whether, and how, the ground water will flush these materials out over time.
Recent research in Maine, for example, suggests that a vulnerability map can be plotted using the new 85Kr technique, either alone or through
integration with conventional hydrology investigations. In cooperation with the State of Maine and rural ground water supply districts, NRMRL
researchers are using this innovative approach to help diagnose prospective contamination areas so that water supply managers can effectively plan
well fields to ensure a stable supply of clean drinking water.
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Submitted By:
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Professor Paul Bardos WhoDoesWhat?
Last update: 13/02/2007
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