Age Dating Old Groundwater
Physics and Chemistry of Water
Published Online: 15 APR 2005
Copyright © 2005 by John Wiley & Sons, Inc.
How to Cite
Kazemi, G. A. 2005. Age Dating Old Groundwater. Water Encyclopedia. 4:388–390.
- Published Online: 15 APR 2005
First, two closely interrelated terms, groundwater age and groundwater residence time, need to be explained and differentiated. Groundwater age is the amount of time that has lapsed since the water molecule, whose age is of concern, was recharged into the system till this molecule is sampled for age-dating. Groundwater residence time is the time it takes for a single molecule of water to travel from the recharge area to the discharge area of the aquifer, the time interval between infiltrating into, and exfiltrating out of, the subsurface media. Groundwater age and residence time are comparable to the age and lifetime of a person, respectively.
Old groundwaters may be defined as those that are too old to be dated using techniques like 3H, CFCs, 85Kr, 36Cl/Cl and 3H–3He. These techniques are specifically applied to age-date young groundwater. Four methods have been in use for dating old groundwaters. In the order of the age range they can measure, these include (1) 39Ar, (2) 14C, (3) 36Cl, and (4) 4He.
The 14C method is the most extensively used method for dating old groundwater. 14C, also known as radiocarbon, has a half-life of 5730 years; it can enter groundwater systems by various geochemical and biological processes.
- groundwater age;
- groundwater residence time;