[en] The British Geological Survey has extensive experience in the extraction of pore-waters by mechanical squeezing using a hydraulic pump with a maximum output stress of 70 MPa. The technique, which is analogous to the natural process of consolidation but at a greatly accelerated rate, is ideal for clays and mudrocks, for which other extraction methods are generally not suitable. A wide variety of materials have been tested. Of these, only a few samples have failed to provide sufficient pore-water for chemical analysis. A lower boundary for pore-water collection appears to be between 7 % and 8 % moisture content, although the stiffness of a sample can also affect extraction. A number of typical data are presented which exemplify the range of materials tested and the scope of chemical analysis performed on extracted pore-waters. These data have been used to improve the understanding of fluid and solute movement through clays and mudrocks, assisting in the investigation of pollutant and radionuclide migration. (authors). 4 refs., 8 figs

[en] There are a number of advantages associated with argillaceous deposits as host rocks and buffer backfill materials for the deep underground disposal of radioactive waste. They include low hydraulic conductivity, high absorption of radionuclides and their mechanical properties. Although laboratory studies provide much useful information on short-term processes, they are less reliable in providing data on the longer-term processes relevant to performance assessment of the repository. Pore-water chemistry and isotope analyses provide important long-term data for modelling water and ion transport through the argillaceous rock. Solute transport mechanisms, including advection and diffusion, can be studied by comparison of the observed data with modelled distributions. The study of the pore-water chemistry of the material surrounding the repository and other natural analogues can give an insight into processes occurring over thousands or millions of years. There are a number of methods of extracting pore-water for chemical purposes from argillaceous rocks, including squeezing, distillation and, indirectly, by leaching. Squeezing provides pore-water for all types of analysis, including major and trace ions and isotopes. The squeezing method not only provides basic chemical information, but also provides information on the interactions between the pore-water solutes and the rock, buffering and ion exchange, which are important factors influencing contamination migration. Pore-water extraction by squeezing has been carried out at the BGS for over 20 years for UK NIREX and many international clients, including Andra, Nagra, SCK/CEN, JNC and GRS. This work has been carried out on borehole core and backfill mixes for a wide range of clay materials. Chemical fractionation and other trends have been apparent in the pore-water data but, because these systems are quite complex, some of these trends have been poorly understood. Early squeezing tests carried out in the 1940's and 50's by Kryukov et al. (1962) studied a range of clay materials mixed to thick pastes with sodium chloride solutions. The results of these experiments showed that chloride and sodium concentrations remained relatively constant until a certain moisture content was reached, at which point their concentration progressively reduced with decreasing moisture content. The moisture content and pressure at which this occurred depended on the properties of the clay. Building on the work of Kryukov and his co-workers, this paper describes research into reactions between natural and proprietary clays mixed with three different pore water chemistries (deionised water, potable water and sea water) to investigate in more detail the fundamental interactions between clay minerals and pore-water solutes. (authors)

[en] The hydro-chemistry of a site at Down Ampney in Gloucestershire, UK has been studied by means of conventional groundwater sampling and analysis of pore-waters collected from drill core samples of mud rocks by mechanical squeezing. The pore-waters are mainly Na-Cl dominated, except in the fault zone where Na-SO₄ waters dominate. The evidence from the geochemical data, including stable isotope compositions, suggests that modern meteoric water penetrates downwards through the mud rocks, diluting groundwaters and pore-waters that are present already, with the major fault acting as a short-circuit to groundwater flow. The hydro-chemistry of the site may also be controlled by the influx of oxidising Na-SO₄ rich waters. (author)

[en] A Jurassic sequence of mudrocks, siltstones and limestones, at Down Ampney, Gloucestershire, was investigated. The aim was to evaluate the importance of faults in mudrocks as conduits for direct groundwater flow, and the influence of such faults on solute transport. Chemical analysis of porewaters and groundwaters are reported. Porewaters were obtained for analysis by squeezing mudrock core samples, yielding 18.1-34.5% of the total porewater. The solutions were analysed for major and trace elements and stable O/H isotope compositions. These analyses are compared with analyses for conventional groundwater samples. Samples were taken from a borehole array which crossed a prominent east-west trending fault, with a northerly downthrow of c.48 m. Comparisons are made between pore- and ground- water samples from each side of the fault, and from the fault zone itself. Sulphate concentrations are greatly increased in porewaters from the fault zone in comparison with sulphate concentrations in porewaters remote from the fault. The concentrations of porewater cations are related to pH, which in turn can be related to sulphate concentrations, probably controlled by sulphide oxidation. Cation concentrations are controlled mainly by carbonate dissolution and cation exchange reactions, largely dependent upon pH. Porewater concentrations of Cl and Br increase downwards but away from the fault zones the concentration gradients with depth are twice those in the vicinity of the fault. This suggests that meteoric waters are conducted by the fault, although they also penetrate downwards throughout the area. Groundwater compositions bear no simple relationship to porewater compositions, except in the case of sulphate. In the fault zone this is invariably more dilute in groundwaters than in porewaters. (author)

[en] This work is performed under contract with the Commission of the European Communities in the framework of its research programme on Management and Storage of Radioactive Wastes. The importance of faults in mudrocks as groundwater conduits, and as a control on solute transport, was assessed in a Jurassic mudrock, siltstone and limestone sequence at Down Ampney, Gloucestershire. Samples were taken from a borehole array crossing an east-west trending fault, of approximately 48 m northerly downthrow. Squeezing mudrock samples yielded 18.1 to 34.5% of total porewater, which was analyzed for major/trace elements and stable O/H isotope compositions. Fault-zone porewaters have greatly increased sulphate concentrations relative to those remote from the fault. Porewater cation concentrations are related to pH, which is correlated with sulphate concentrations, probably controlled by sulphide oxidation. Control of cation concentrations is largely by pH-dependent carbonate dissolution and cation exchange reactions. Porewater C1 and Br concentrations increase downwards, but at twice the rate away from the fault as near the fault, suggesting that although meteoric waters penetrate throughout the area, they are preferentially conducted by the fault. Comparisons are made between pore- and groundwater samples from each side of the fault, and from the fault zone. Pore- and groundwater compositions are not simply related, except in the case of sulphate which, in the fault zone, is more diluted in groundwaters. 14 refs. 20 figs., 17 tabs

[en] Full text: New data prepared by the Forum of European Geological Surveys (FOREGS) show the variation of baseline levels of uranium in soil and stream sediments and water over Europe. In this paper we evaluate the application of such data in uranium exploration with particular reference to the identification of uranium provinces. The samples have been collected and analysed according to the protocols established for the International Union of Geological Sciences/International Association of Geochemistry and Cosmochemistry (IUGS/IAGC) Working Group on Global Geochemical Baselines. The baseline levels of U vary between <0.2 to 53 mg kg-1 in topsoils, <0.20 to 30 mg kg-1 in subsoils and <1 to 59 mg kg^-1 in stream sediments. There is generally good agreement between the levels of U in the three sample types, and the median concentration in all three media is approximately 2 mg kg^-1. The baseline levels of U in water range from <0.002 μg/l to 21 μg/l with a median of 0.32 μg/l. The most anomalous baseline levels of U occur over the Variscan orogen, including remnants of the Variscan Gondwana of the Iberian Peninsula and Southern France and the Moldanubian Saxo-Thuringian and Rheno-Hercynian zones Variscan Terranes. Anomalies are especially associated with areas into which late-post orogenic radiothermal high heat production (HHP) granites were emplaced Spiderdiagrams based on trace element levels and rare earth element (REE) plots, confirm the association between the highest U anomalies and evolved radiothermal granites. High values are also associated with parts of the Alpine terrain especially in Slovenia, where there are historical U workings, and Southern Italy, where high values of U reflect contemporary volcanism. In contrast, much of the Caledonides of North West Europe and the Precambrian of the Baltic Shield and East European craton and its overlying sedimentary cover have very low values, generally <4 mg kg^-1. Uranium in water data are evaluated including in relation to residence time and complexation using parameters such as conductivity HCO₃^-, F and DOC. The results indicate that high quality systematic geochemical data not only identify prospective uranium provinces but can also be of value in understanding ore genesis. The provision of such data at the global scale will be of considerable value in future uranium exploration and resource evaluation programmes. The study also indicates the value of multielement data in distinguishing between anthropogenic and naturally occurring anomalies. (author)

[en] This report represents the conclusion to Phase III of the Maqarin Natural Analogue Study. The main thrust was to establish the origin and chemistry of the Western Springs hyper alkaline groundwaters (Na/K enriched Ca(OH)₂ type) and to study their interaction with rocks of different compositions, as natural analogues to key processes that might occur at an early stage within the 'alkali disturbed zone' of cementitious repositories in different host rocks. Whilst earlier studies at Maqarin were very much site-specific and process-oriented, Phase III provided a regional perspective to the geological evolution of the Maqarin region. This was made possible by greater field access which allowed a more systematic structural and geomorphological study of the area. This has resulted in a greater understanding of the age and spatial relationships concerning formation of the cement zones through spontaneous combustion of the Bituminous Marls, and the subsequent formation of high pH groundwaters at the Eastern and Western Springs locations. At the Western Springs locality, hydrochemical and hydrogeological evaluation of new and published data (plus access to unpublished data), together with detailed mineralogical and geochemical studies, helped to clarify the very earliest stage of cement leachate/host rock interaction. The data were used also to test coupled flow/transport codes developed to assess the long-term evolution of a cementitious repository. Additional objectives addressed include: a) rock matrix diffusion, b) the occurrence and chemical controls on zeolite composition, e) the occurrence and chemical controls on clay stability, and d) the role of microbes, organics and colloids in trace element transport. The Maqarin site now provides a consistent picture explaining the origin of the hyperalkaline groundwaters, and is therefore a unique location for the examination of the mechanisms and processes associated with cementitious repositories. Application of these mechanisms and processes to repository performance assessment are listed and described

[en] This report represents the conclusion to Phase III of the Maqarin Natural Analogue Study. The main thrust was to establish the origin and chemistry of the Western Springs hyper alkaline groundwaters (Na/K enriched Ca(OH)₂ type) and to study their interaction with rocks of different compositions, as natural analogues to key processes that might occur at an early stage within the 'alkali disturbed zone' of cementitious repositories in different host rocks. Whilst earlier studies at Maqarin were very much site-specific and process-oriented, Phase III provided a regional perspective to the geological evolution of the Maqarin region. This was made possible by greater field access which allowed a more systematic structural and geomorphological study of the area. This has resulted in a greater understanding of the age and spatial relationships concerning formation of the cement zones through spontaneous combustion of the Bituminous Marls, and the subsequent formation of high pH groundwaters at the Eastern and Western Springs locations. At the Western Springs locality, hydrochemical and hydrogeological evaluation of new and published data (plus access to unpublished data), together with detailed mineralogical and geochemical studies, helped to clarify the very earliest stage of cement leachate/host rock interaction. The data were used also to test coupled flow/transport codes developed to assess the long-term evolution of a cementitious repository. Additional objectives addressed include: a) rock matrix diffusion, b) the occurrence and chemical controls on zeolite composition, e) the occurrence and chemical controls on clay stability, and d) the role of microbes, organics and colloids in trace element transport. The Maqarin site now provides a consistent picture explaining the origin of the hyperalkaline groundwaters, and is therefore a unique location for the examination of the mechanisms and processes associated with cementitious repositories. Application of these mechanisms and processes to repository performance assessment are listed and described