Elliot, TrevorBonotto, Daniel Marcos [UNESP]Andrews, John Napier2015-03-182015-03-182014-11-01Journal Of Environmental Radioactivity. Oxford: Elsevier Sci Ltd, v. 137, p. 150-162, 2014.0265-931Xhttp://hdl.handle.net/11449/116598Natural, dissolved U-238-series radionuclides (U, Ra-226, Rn-222) and activity ratios (A.R.s: U-234/U-238; Ra-228/Ra-226) in Continental Intercalaire (Cl) groundwaters and limited samples from the overlying Complexe Terminal (CT) aquifers of Algeria and Tunisia are discussed alongside core measurements for U/Th (and K) in the contexts of radiological water quality, geochemical controls in the aquifer, and water residence times. A redox barrier is characterised downgradient in the Algerian Cl for which a trend of increasing U-234/U-238 A.R.s with decreasing U-contents due to recoil-dominated U-234 solution under reducing conditions allows residence time modelling similar to 500 ka for the highest enhanced A.R. = 3.17. Geochemical modelling therefore identifies waters towards the centre of the Grand Erg Oriental basin as palaeowaters in line with reported C-14 and Cl-36 ages. A similar U-234/U-238 trend is evidenced in a few of the Tunisian CI waters. The paleoage status of these waters is affirmed by both noble gas recharge temperatures and simple modelling of dissolved, radiogenic He-4-contents both for sampled Algerian and Tunisian CI and CT waters. For the regions studied these waters therefore should be regarded as "fossil" waters and treated effectively as a non-renewable resource. (C) 2014 The Authors. Published by Elsevier Ltd.150-162engUranium isotopesRadiogenic heliumNoble gas recharge temperaturesGroundwater agesContinental Intercalaire & ComplexeTerminal aquifersAlgeria & TunisiaArtigo10.1016/j.jenvrad.2014.07.003WOS:000343628100021Acesso abertoWOS000343628100021.pdf7430102726026121