Groundwater Radiation Monitoring in the Republic of Belarus. G. I. Ilkevich, L. A. Polivko, and H. F. Bondareva, Geological Service "Belgeologia" Hydrogeological Expedition, Post code: 220138 Minsk, Geological str.115; Belarus, fax +375.172.238.05.15, telephone +375.172.268.13.00
The Geological Service of the Republic of Belarus is responsible for the groundwater quality control. The control of the groundwater radiation conditions has been carried out since the accident at the Chernobyl NNP In 1986 on the basis of the general monitoring network. By 1990 a target-oriented environmental monitoring system was created. This system permits a complex description of the groundwater radiation state and dynamics under various geological-hydrogeological, landscape-geochemical, natural and disturbed environmental conditions with different soil Pollution density.
Strontium-90 and caesium-137 are components under observation. The radiation monitoring system works at the regional and local levels. The regional observation level is based on a rather sparse system of representative water sites scattered all over the territory of the technogenic halo created as a result of the Chernobyl accident. The local level observations are aimed at studying some regular features noted in the formation of the groundwater radiation conditions. Basins of "small" rivers treated as single water exchange system are used to develop an empirical model of radionuclides migration in a cycle "soil-groundwater-surface water".
Ten years, observations have revealed a considerable increase of strontium-90 and caesium-137 activity in groundwater as compared to their pre-accident background values. The highest concentrations fall within a period between 1988 and 1989. Zater on there is a well-defined tendency for the caesium-137 activity decrease. Strontium-90 was found to increase since 1994 in groundwater and surface water along with its general decrease against its values determined. During the anomalous period. caesium-137 activity shows minor variations under different landscape geochemical conditions. The strontium-90 distribution pattern is much more differentiated. Parameters controlling the groundwater radiation conditions is the surface contamination density and a time elapsed after the accident. In the recent years the radiation conditions were determined to be dependent on the runoff regime and existed geochemical barriers.
In general, specific activities of strontium-90 and caesium-137 are below the standards accepted in Belarus by one or two orders of magnitude (0.37 Bg/l for Sr-90 and 18,5 Bg/l for Cs-137). The higher radionuclide inventories exceeding the above said standards were noted in the evacuation zone only, where the highest values of soil contamination by radionuclides were determined.
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