title: Dissolved uranium, radium and radon evolution in the Continental Intercalaire aquifer, Algeria and Tunisia.
abstract: Natural, dissolved (238)U-series radionuclides (U, (226)Ra, (222)Rn) and activity ratios (A.R.s: (234)U/(238)U; (228)Ra/(226)Ra) in Continental Intercalaire (CI) 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 CI for which a trend of increasing (234)U/(238)U A.R.s with decreasing U-contents due to recoil-dominated (234)U solution under reducing conditions allows residence time modelling ∼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 (14)C and (36)Cl ages. A similar (234)U/(238)U 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 (4)He-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.
authors: Environmental Tracers Laboratory (ETL), School of Planning, Architecture & Civil Engineering (SPACE), Queen's University Belfast, David Keir Building, Stranmillis Road, Belfast BT9 5AG, Northern Ireland, UK. Electronic address: t.elliot@qub.ac.uk.
authors: Trevor
authors: T
authors: Elliot
authors: Departamento de Petrologia e Metalogenia, IGCE-UNESP, Av. 24-A, 1515, CP 178, CEP 13506-900 Rio Claro, São Paulo, Brazil. Electronic address: danielbonotto@yahoo.com.br.
authors: Daniel Marcos
authors: DM
authors: Bonotto
authors: School of Chemistry, University of Bath, Bath, UK.
authors: John Napier
authors: JN
authors: Andrews
mesh_terms: D000462:Algeria; D060587:Groundwater / Q000032:analysis*; D011834:Radiation Monitoring; D011883:Radium / Q000032:analysis*; D011886:Radon / Q000032:analysis*; D014416:Tunisia; D014501:Uranium / Q000032:analysis*; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D014875:Water Pollutants, Radioactive; D014501:Uranium; D011886:Radon; D011883:Radium
keywords: Algeria & Tunisia; Continental Intercalaire & Complexe Terminal aquifers; Groundwater ages; Noble gas recharge temperatures; Radiogenic helium; Uranium isotopes