Civil Engineering Reference
In-Depth Information
2 . Chernobyl-born radionuClides
in GeoloGiCal environment
The questions of radionuclide migration assessment in the geological medium
(groundwater and water-bearing rocks) after the Chernobyl accident are
complicated, from one side, because of essentially inhomogeneous degree of
contamination of landscapes and, from the other side, the high complexity and
variability of the structure of the geological environment within the studied
region, which are complicated by different human-induced factors influencing
the migration processes in the active water exchange zone.
One of the main objectives of groundwater vulnerability and protectability
assessment is obtaining a preliminary forecast of vertical penetration of radioac-
tive contaminants into the multi-layered aquifer system through the unsaturated
zone.
The preferential downward radionuclide transport within the CEZ and Kyiv
region is explained by several reasons, primarily the following:
1. Presence of low relief zones within the contamination source area, that is, the
CEZ with rather small surface runoff into the river network (river Pripyat
and its tributaries)
2. Good vertical permeability of the unsaturated zone because of preferentially
sandy rocks with presence of turf insertions
3. Presence of active vertical preferential flow pathways caused by specific
conditions within numerous closed relief depressions accumulating local
surface runoff and contamination
4. Existing climatic conditions characterized by intensive precipitation and
moderate evaporation
The role of the vertical flow component remains to be primary also for
prediction assessments of contamination of deeper aquifers. This conclusion is
obvious because of relatively small lateral flow velocities as compared to vertical
ones if taken relative to corresponding dimensions of the aquifer system.
Nevertheless, for assessments of the contamination of deeper confined aquifers
in the presence of vertical preferential flow pathways, the determination of
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