Groundwater Vulnerability and Protectability to Chernobyl-Born Radionuclide - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 81

5 . Groundwater Vulnerability and Protectability
to chernobyl-born radionuclide
5.1. upper Groundwater
Let us consider the methodology described in Chapter 4 assessment of
groundwater vulnerability and protectability as related to contamination by
Chernobyl-born radionuclide 137 Cs in the study area of the Dnieper River basin
within the borders of the Kyiv region.
According to the developed methodology (see Chapter 4), we have performed
preliminary zoning of the study area into three landscape types: (1) the southern
areas of black soils and loess-like loams; (2) the central (Kyiv) areas of loamy and
sod-podzolic soils and sandy-loamy composition of the unsaturated zone; and
the (3) northwestern areas of Polesye, the first and second Dnieper floodplain
terraces and sandur plains.
In accordance with the methodology described in Chapter 4, for each of these
typical landscapes we obtained representative vertical distributions of the relative
concentration of the radionuclide to a depth of 20 m (upper part of the Quaternary
aquifer) for the 30 year period (the half-life for 137 Cs). In the majority of the area,
this period corresponded to the achievement of real measurable concentrations of
the radionuclide in the groundwater. The typical vertical distributions of the pre-
dicted relative concentration were calculated using the vertical transport model
(4.1)-(4.4) after the corresponding model calibration for each of three characteristic
landscape types described above.
During the model calibration, the infiltration velocity w and storage coeffi-
cient n = θ + k d [see equation (4.3)] were determined using the available observation
and experimental data for the sites within the characteristic landscape areas
[ Shestopalov , 2001]. The values of w varied for different landscape types: from
50 mm/year (landscape type 1) to 75 mm/year (landscape type 2) to 100 mm/year
(landscape type 3). The values of n are determined mainly by the distribution coeffi-
cient k d characteristic for the given radionuclide ( 137 Cs) because it is usually several
orders of magnitude higher than the effective porosity or moisture content, θ ,