Chernobyl-Born Radionuclides In Geological Environment - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 33

12

8
4
0

3

2.75

2.5

2.34
2.09

2.12

.2

1.93
1.61

1.89

1.69

1.5

1.54

1.32

1.04

1

0.7 0.71
0.5
0.29

0.69

0.5

0.5

0

0 200 400 600 800 1000 1200

Distance, m

Figure 2.5 Distribution of 137 Cs (Bq/kg) in Kyiv marls (depth 80 m) plotted by sampling
data obtained during drilling of tunnels for the Kyiv subway between Zoloti Vorota and
Dorogozhichi stations. Upper curve shows the relief elevation.

with a linear geodynamic zone and characterized by increased permeability of the
deposits. Previously an increased content of pesticides had also been discovered
at this location [ Shestopalov , 1988].
The separate available data on the real rock contamination with radionu-
clides and more abundant data on groundwater contamination enable to obtain a
preliminary average assessment for contamination of the geological environment.
With this purpose, the average distribution coefficient K d (dm 3 /kg) was used,
determined as the ratio of a radionuclide concentration in the solid (rock) phase
M (Bq/kg) to its concentration in the liquid phase (groundwater) C (Bq/dm 3 ):

KMC

d = /.

(2.1)

The K d values for 137 Cs vary in a wide range over the section from 3 to 500 dm 3 /
kg. In close vicinities of the Chernobyl NPP it varies from several dm 3 /kg to several
thousand dm 3 /kg depending on the rock properties, radionuclide migration forms
(solute or colloid), groundwater chemical composition, and other factors. For this
reason a reliable forecast of radionuclide concentrations in the geological environ-
ment can be obtained only after proper study of the regularities of interactions in
the “soil-water-rock” system with account of its main influencing factors.