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Robert Renaud, I. D. Clark, T. G. Kotzer, G. M. Milton, D. J. Bottomley

The mobility of anthropogenic ¹²⁹I in a shallow sand aquifer at Sturgeon Falls, Ontario, Canada

The transport and partitioning of ¹²⁹I has been examined for a shallow groundwater flow system at Sturgeon Falls in northeastern Ontario. Recharge into a sandy surficial postglacial deltaic aquifer occurs in the vicinity of a seasonally-wet boreal forest. Concentrations of stable iodine, ¹²⁹I, tritium, radiocarbon, stable isotopes and major ions were measured on samples of groundwater and precipitation. The present-day tritium profile delineates the position of the early 1960´s above-ground nuclear weapons pulse at a depth of approximately 12 m.
The concentrations of stable iodine for groundwaters above, near and below the above-ground nuclear weapons pulse range from 0.07 to 1.7 ppb. Over that same interval ¹²⁹I concentrations decreased from 1.9×10⁶ atoms/L at 9 m, to approximately 1.9×10⁵ atoms/L in tritium-depleted waters at 35 m, below the present-day depth of the recharging above-ground nuclear weapons peak at approximately 12.7 m. No substantial increases in the levels of ¹²⁹I were evident in waters sampled near the location of the above-ground nuclear weapons peak.
The ¹²⁹I values in the lower aquifer are 1 to 2 orders of magnitude greater than published estimates of pre-bomb ¹²⁹I (10³ to 10⁴ atoms/L), and indicate contribution of ¹²⁹I from the fissiogenic decay of ²³⁸U in the basal granite bedrock or from leaching of ¹²⁹I from the aquifer grains.
A precipitation sample collected at Sturgeon Falls had concentrations of stable iodine and ¹²⁹I of 0.2 ppb and 8.5×10⁷ atoms/L, respectively. Concentrations of ¹²⁹I in Sturgeon Falls groundwaters are lower than those reported in other studies in central Canada, suggesting that the levels of ¹²⁹I in these groundwaters may have been attenuated by complexation or ion exchange with organic materials in the near-surface soil horizons. Such processes have been documented during a previous study on the behavior of ¹²⁹I in a shallow aquifer near a low-level, radioactive waste management area.
Along a 30 cm soil profile at piezometer nest 28 at the Sturgeon Falls study site, the concentrations of ¹²⁹I ranged from approximately 4.3×10⁸ atoms/g in the uppermost soil litter layer to 5.6×10⁷ atoms/g in the siltier bottom soil horizons. Over that same profile, stable iodine varied from 4.7 ppm in the upper layers to 3.9 ppm in the lower layers.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 93, 06/2005
Pages: 363 - 371

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