CHERNOBYL-BORN RADIONUCLIDES: GROUNDWATER PROTECTABILITY WITH RESPECT TO PREFERENTIAL FLOW ZONES

摘要

The available data of groundwater contamination with Chernobyl-born ra-dionuclides (~(139)Cs and ~(90)Sr) within the CEZ and Kyiv region have proven the reality of measurable concentrations of these radioisotopes not only in the soil solutions and upper groundwater, but practically in regional aquifers down to a depth of 100 m and more. Experimental and modeling studies have shown that groundwater contamination mainly enters the upper groundwater aquifer by subvertical preferential pathways of different scales and activities. The depression-related PFZs, which occur widely in floodplain terraces of the Dnieper and Ukrainian Polesye region, have been studied in detail. Their role in the penetration of Chernobyl-born radionuclides through the soil-unsaturated zone barrier into the aquifer system is very important, although it is different for different parts of the area studied. An experimental study of radionuclide distribution in deposits and ground-water also revealed the influence of other types of preferential flow zones on the total contamination of the geological environment. As a result, a conclusion was drawn about the insufficiency of considering only the lithological and thickness parameters of the unsaturated zone, and the necessity of considering the preferential flow zones in order to obtain a more reliable assessment of possible groundwater contamination and protectability. A new concept has been proposed for the assessment of groundwater protectability and vulnerability based on field experimental assessments and modeling. Application of this methodology enabled maps to be drawn of groundwater protectability and vulnerability for ~(137)Cs within the Kyiv region of the Dnieper basin giving consideration to preferential flow zones.