Tritium/Helium-3 Method of Dating Recent Groundwater in Hydrogeoecology
Tech Area / Field
- OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences
8 Project completed
Senior Project Manager
Tyurin I A
VNIIEF, Russia, N. Novgorod reg., Sarov
- IGE (Institute of Geoecology) / Institute for Geoecology (Saint-Petersburg Branch), Russia, St Petersburg
- Istituto di Geoscienze e Georisorse, Italy, Florence\nTU Bergakademie Freiberg / Institut für Mineralogie, Germany, Freiburg
Project summaryProcesses caused by negative effects of changes of the groundwater resources and quality under the influence of anthropogenic factors require new effective approaches to solving environmental problems. Assessment of the current state and predictions concerning the groundwater regime, particularly in areas of insufficient humidity level and in regions with industrial enterprises, which are potential high-risk sources, are the hydrogeological problems of the highest priority. Under such conditions, the value of groundwater as a source of drinking water supply, on the one hand, and the material migration environment, on the other hand, is ever increasing.
The methods of quantitative assessment of hydrogeological parameters and development of models commonly used in hydrogeology have some drawbacks. First, there is a persistent insufficiency of hydrogeological data that is hard to fill up without many-fold increase of the scope of works and extension of the work periods. Second, there are difficulties in taking into account large-scale effects. For example, extrapolation of data obtained for short-term periods within relatively small areas of detailed investigations requires a legitimacy of using them for evaluation of long-term processes and processes that take place in vast areas of geological structures to be specially proved.
Analysis of the modern trends shows that new approaches, which are free, to a high enough extent, of the problems above, must be based on radioisotope methods. Use of isotope systems including noble gases is a very promising line in this field. Such methods could allow quantitative assessment of a) the time of water stay in subsurface hydrosphere; b) the real flow rates; c) the flow and transport parameters of the environment – in combination with other data.
The tritium/helium-3 method of ground water dating (Tolstikhin I.N. and Kamensky I.L., 1969) is the one that meets the requirements of studying the effect of anthropogenic factors on groundwater in the scale above to the highest extent. The idea of this method is that the ratio of the current concentrations of tritium (3H) and “tritigenous” helium-3 (3He) uniquely determines the time period beginning from water inflow to subsurface hydrosphere. Main advantages of the 3H/3He method (against the tritium dating method) are the following: (a) there is no need in specifying the input tritium-concentration function and (b) there is a possibility to diagnose and calculate proportions of mixing with tritium-free water. Besides, helium is absolutely inert in nature and its concentration in the earth atmosphere is insignificant. These facts determine its extremely low background.
The proposed project participants made a noticeable contribution to the development of radioisotope dating methods owing to
- development of original testing techniques and extension of the spectrum of isotopes and isotope ratios that can be measured;
- development of new mathematical models of transport of noble gases’ isotopes in subsurface hydrosphere and original methods for calculation of hydrogeological parameters basing on these models.
The project goal is to develop an efficient tritium/helium-3 method of groundwater dating to allow calculation of flow and mass transport parameters in subsurface hydrosphere.
The following main tasks will be carried out during the project implementation period.
- Development of the unified technique for water sampling and preparing the samples for isotope mass-spectrometric analysis. These efforts suppose designing and manufacturing a pilot set of vacuum equipment for water sampling and preparing the samples for examination.
- Development of physico-mathematical models of flow and isotopic mass transport and creation of software for numerical simulation of tritium and noble gas migration in subsurface hydrosphere. The task includes formulation of a physical model and development of software that would allow taking into account time-dependent tritium inflow to subsurface hydrosphere, as well as accumulation, transport and losses of helium in groundwater. The tritium/helium-3 age will be dated at any point of the model.
- Elaboration of criteria of the dating method applicability to solving the environmental problems. This task will be carried out based on numerical experiments on simulating basic flow and transport schemes with regard to isotope systematization of noble gases.
- Development of techniques to estimate flow and mass transport parameters in subsurface hydrosphere basing on the data obtained during the process of dating. Comparison between the experimentally obtained data on isotopes and the results of numerical simulations for real geological objects would allow matching the methods of quantitative assessment of flow and mass transport parameters with respect to isotope data.
The project methodology is based on the use of most recent results of investigations of isotope systems in subsurface hydrosphere and relies upon the advanced experimental and technological base and wide application of computer simulation.
The project goal will be achieved basing on a comprehensive approach including
- Unification of various isotope analysis stages;
- Improvement of the method of groundwater dating based on simultaneous numerical simulation of noble gas geochemistry, flow and mass transport;
- Application of the developed methods to research of real entities.
Scientists from Russian Federal Nuclear Center–VNIIEF and St.-Petersburg Branch of RAS Institute of Geoecology will participate in the project. Such cooperation allows combining the unique experience of nuclear scientists - mathematicians and physicists - in computer simulation and studying isotopes of chemical elements with the advanced theoretic and experimental methods of investigation of natural isotope systems developed in RAS IGE SPB.
Experimental investigations of the isotope geochemistry will be carried out using the newly created equipment for water sampling and preparation of the samples for examination. Theoretical studies will rely on the mathematical apparatus developed by VNIIEF specialists as a result of their efforts under the ISTC Projects #714 and #1565, in particular, NIMFA code package developed during the development of a continuously functioning model of the Satis river basin.
The project has no direct prototypes, it includes the methods and techniques previously not used by anyone:
- the method for calculation of helium contribution from water sources of various origin, which is based on studying a number of noble gas isotopes (helium-3, helium-4, neon-20, argon-36, and argon-40);
- the original technique of locating test points in space;
- the methods for numerical simulation of isotope mass transport in regional scale with taking account of irregular inflow of tritium to subsurface hydrosphere and diffusion losses of helium.
The project falls into the category of applied studies, because it creates a methodological basis for using in practice the tritium/helium-3 dating method to solve the environmental problems. The project efforts can be further developed in the following directions:
- vacuum equipment designing and development of the unified technique of sampling and preparing the samples for gas isotope analysis;
- development of a commonly used method hydrogeology experts for groundwater dating, assessment of the status of water resources and groundwater quality;
- making conclusions on the appropriateness of certain geological structure areas for highly toxic and radioactive waste storage facilities.
As for fundamental studies, the results could be used for the following purposes:
- determination of the age bounds for areas of active and slow water exchange of the earth’s crust and studies of real scales of their interaction;
- assessment of the paces of global climatic changes (in combination with data on other isotope systems, for example, deuterium/oxygen-18 and 234U/238U systems).
The project meets the ISTC goals in all aspects:
- it gives RFNC-VNIIEF weapons scientists and engineers an opportunity to re-orient to civil activities related to solving urgent environmental problems;
- the project is based on the advanced scientific achievements in the area of simulation of processes of the isotope hydrochemistry in subsurface hydrogeology and, therefore, promotes integration of weapons scientists within the international scientific community;
- the project has a certain commercial potential, because it creates a scientific and methodological basis for further development of application commercial code packages and fabrication of the unified equipment for isotope investigations.
Main achievements of the project will be published both in some leading scientific periodicals, both Russian and foreign.
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