Mechanisms controlling the distribution and transport of {sup 14}C in a clay-rich till aquitard
The distribution and transport of radiocarbon in dissolved inorganic carbon (DIC) in a thick clay-rich till aquitard was investigated. Radiocarbon activities decreased with depth from 109 percent modern carbon (pmC) in the surficial oxidized and fractured zone through the thick underlying unoxidized and nonfractured aquitard, reaching minimum values of between 3 and 5 pmC at between 29 and 37 m depth. Numerical simulations of diffusive transport of radiocarbon from the oxidized zone into the unoxidized zone during the Holocene closely approximated the measured values and showed that diffusive transport and radioactive decay fully described the transport of radiocarbon in the aquitard. The lack of geochemical reactions involving DIE permitted the age of DIC in the pore water deposited with the till to be estimated at 25 to 31 ka BP. Results of this study showed that the use of radiocarbon in the study of solute transport in aquitards provides age information that cannot be obtained from natural conservative tracers such as {delta}{sup 2}H and {delta}{sup 18}O. Their results also showed that the application of conventional radiocarbon age-dating models based on piston-flow transport assumptions, is inappropriate in diffusion-dominated environments and considerably overestimates the age of the ground water.
- Research Organization:
- National Water Research Inst., Saskatoon, Saskatchewan (CA)
- OSTI ID:
- 20080435
- Journal Information:
- Ground Water, Vol. 38, Issue 3; Other Information: PBD: May-Jun 2000; ISSN 0017-467X
- Country of Publication:
- United States
- Language:
- English
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