Chapter 14
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on August 24, 2015 | http://pubs.acs.org Publication Date: November 14, 1996 | doi: 10.1021/bk-1996-0651.ch014
Isotopic Characterization of Humic Colloids and Other Organic and Inorganic Dissolved Species in Selected Groundwaters from Sand Aquifers at Gorleben, Germany 1,4
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M. Ivanovich , M. Wolf , S. Geyer , and P. Fritz 1
Atomic Energy Authority Technology, B551 Harwell, Oxfordshire OX11 ORA, United Kingdom Gesellschaft für Strahlen und Umweltforschung, Institut für Hydrologie, Ingolstadter Landstrasse 1, D-85764 Neuherberg, Germany Umweltforschungzentrum Leipzig Halle GmbH, Permoser Strasse 15, D-07050 Leipzig, Germany 2
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The aim of this work was to determine the significance of groundwater colloids in far-field radionuclide migration. To this purpose, isotopic data presented in this paper were obtainedfromseveral selected Gorleben groundwaters as part of the colloid characterisation programme. The contents of major and minor ions, light isotopes ( H, H, C, C, O and S), and the U/Th isotopes were measured. Radiocarbon and C were measured in dissolved inorganic carbon (DIC), ion the humic acid (HA -colloids) and fulvic acid (FA-solution)fractionsof dissolved organic carbon (DOC). The O and S were also determined in dissolved sulphate phase. The U/Th isotope measurements were carried out on total and surface solid phases, colloidfraction(1-1000 nm particle size, HA) and solution (30 ka BP) whereas, some of the FAfractionscontain higher yielding model groundwater ages more consistent with post-glacial recharge (3', and electrical conductivity). The sampling was carried out under anaerobic conditions (N2 + 1% CO2 atmosphere) in order to prevent significant changes in the physical and chemical characteristics of the colloids through interaction with air. Sample processing in thefieldcomprised the concentration of 500 £ of 1 μηι prefiltered groundwaters using an Amicon DC10-LA ultrafiltration systemfittedwith a 10,000 MW cut-off hollowfibretangentialflowcartridgefilter(-1.5 nm cut-off pore size) having an effective surface area of 5 m (12). This system was used to produce 20 £ of colloid concentrate giving a concentration factor of about 25 and colloidal size distribution between 1000 and -1 nm. Twenty litre samples of ultrafiltrate (thefractionrepresenting 'solution' that passed through the 10,000 MW ultrafilter) were also collected. Two 501 unfiltered groundwaters samples were also collected and stored anaerobically in Al-containers with a special coating (Sigma Coating 9255-0300) to prevent contamination during transportation and storage. Further samples included 25 i of 1 μηι prefiltered and acidified water for U/Th isotopic analysis and 1 μηι prefilters preserved for the U/Th analysis of particulates. 2
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Measurement Techniques. Light isotopes Concentrations of H were determined radiometrically after synthesis of propane (13) in a proportional counter after about twenty-fold electrolytical enrichment of H (14), The C content of large samples (£0.5 g C) were determined by liquid scintillation counting after synthesis of benzene (15)fromCO2 which was extractedfromthe water sample after acidification. The content of small samples (
