Uranium series disequilibrium measurements at Mol, Belgium and Whiteshell

Measurements of uranium series disequilibrium in groundwaters derived from sand layers above and below the Boom Clay formation in North East Belgium, are analysed in terms of uranium, thorium and radium isotopic geochemistries, water types, and their mixing in the regional groundwater systems. Most sampled waters are mixtures of younger shallow groundwaters from horizons above the Boom Clay lens and older waters from horizons below the lens, at depths greater than 500m. No true old water end-members have been sampled. The longest residence times of the sampled waters are found to be not much in excess of 104y. More detailed modelling is required in conjunction with groundwater hydraulic pressure and flow direction data to establish detailed mixing patterns. In a second parallel study the 228Ra/226Ra activity ratios were measured in large groundwater samples, from the Underground Research Laboratory at Pinawa, Canada. (author)