[en] This paper is an introduction to some of the issues of hydrochemical characterization in argillaceous rocks which are being evaluated as potential repository hosts. The hydrochemical characterisation must be fit for purpose. Data are required for a number of objectives, including conceptual modelling, defining geochemical baseline and palaeohydrogeology. All methods have limitations and the uncertainties are likely to be minimized by integrating data from a range of methods. geochemical modelling of the clay-water system from first principles is also a necessary tool to improve understanding. Uncertainties in the hydrochemical characters and processes of argillaceous rocks include: quantification of pH and Eh and their controlling factors, significance of spatial heterogeneity, models for solute exchange (including radionuclides) between fissure water, pore waters and the clay surfaces, and the effects of stress changes on the hydro chemistry in the vicinity of an excavation. (J.S.). 39 refs., 10 figs

[en] The palaeoclimatic influences on recharge form an important part of the evaluation of aquifer resources, particularly in arid and semi-arid areas where the magnitude of present recharge may not be well understood. Initially the factors affecting the isotopic composition of groundwater in temperate areas are examined, and it is clear that the isotopic relationship between precipitation and recharge is not yet fully understood. Palaeogroundwater studies in the United Kingdom illustrate phenomena such as mixing that require the application of several isotopic and chemical techniques to resolve the age and composition of palaeo-recharge. Studies in northern African regional aquifers have demonstrated the significance of episodic recharge as a function of climatic change and also the importance of carbon isotope data on dissolved and solid phases. In contrast, the recharge history of southern African aquifers is not well understood, in particular the magnitude of the active recharge component and its isotopic composition. (author)

[en] Short communication

[en] The authors assess the current state of knowledge which will mould future radioactive waste repository sites. Particular attention is paid to the technological aspects of site investigation and characterisation, and to the methodology which needs to be applied to future field investigations at potential deep repository sites. 30 refs.; 5 figs

No abstract available

[en] Published in summary form only

[en] The estimation of groundwater residence times from ¹⁴C data for dissolved carbonates relies on the use of one of a number of geochemical and physical models to take account of the exchange of carbon, by precipitation and dissolution between the groundwater and the aquifer rock. Such exchange results in a dilution of the ¹⁴C content of the dissolved carbon by rock carbonate. In this preliminary study, the ¹⁴C content of different fractions of CO₂ evolved by acid dissolution of a rock core from the East Midlands Triassic Sandstone aquifer has been measured using the Harwell small-sample ¹⁴C measurement facility. As much as 20 pmc ¹⁴C has been found on the secondary carbonate phase of the rock and this compares with a ¹⁴C level of 37 pmc measured in groundwater. The measured amount of ¹⁴C present is approximately two orders of magnitude more than that predicted from precipitation, using the Reardon and Fritz geochemical model, indicating that much greater exchange processes could occur, possibly sorption or atomic exchange. The effect of this large 'sink' of ¹⁴C is discussed generally in relation to the estimation of groundwater residence times from ¹⁴C data. It is concluded that further work is required to substantiate the presence and distribution of ¹⁴C on aquifer rocks. (author)

[en] Results of chemical and isotopic analyses of Altnabreac groundwaters are presented. They are used to define the origin and maturation scheme of groundwaters to depths approaching 300 m in crystalline rocks (granites and metasediments). Samples are derived from packer-isolated zones in 3 deep (approx. 300 m) boreholes, temporal monitoring of 17 shallow boreholes (less than 41 m deep) and about 60 springs and other surface waters as well as from 1981-82 aggregated monthly rainfall. Stable oxygen and hydrogen isotope ratios show all waters to be wholly meteoric in origin and the precipitation input to be well mixed. ³H (tritium) contents suggest that recharge occurs on discrete upland areas where there tends to be downward movement with essentially horizontal flow, resulting in slight discharge, under the remaining ground. Samples abstracted from boreholes frequently contain significant levels of ³H indicating a component of post-1953 recharge. This results from hydraulic connection to the borehole water column in deep boreholes or directly to the surface storage in the case of shallow boreholes. On the basis of ¹⁴C and ⁴He contents, details of which are being reported separately, the oldest analysed water (from 259 to 281 m in borehole A1B) has an age of about 10⁴ years. The results are discussed. (author)

[en] A detailed geochemical study (elemental, isotopic and dissolved inert gases) of unconfined and confined sections of the Triassic non-marine sandstone aquifer in Eastern England has been undertaken. Aspects of the recharge history of this aquifer over the past 40 000 years are revealed by examination of the data. (orig./HK)

[en] Hydro-geochemistry is central to the planning, design and construction of a long-term repository for the disposal of radioactive wastes. The criteria for measurement of hydrochemical and isotopic parameters (e.g. pH, Eh, salinity, isotopes, trace elements etc.), in terms of accuracy, spatial detail and spatial coverage, should be determined by how they will be used. Their use should be based on two major (and closely interrelated) categories of application recognised in repository development: 1) safety and performance assessment of the repository, and 2) characterisation of the potential repository site and support for groundwater flow modelling. Hydrogeochemical investigations are a necessary component of site characterisation since they test the applicability of many of the principles on which conceptual models of groundwater systems are based. Such principles include changes of salinity and Eh with depth, the control of pH by geochemical reactions and the importance of present and past boundary conditions in groundwater movement. In conclusion, it is suggested that there are two main avenues of improvement to be considered in deriving the maximum benefit from integrating hydrogeochemical data with groundwater flow models for performance assessment. (K.A.)