Groundwater Vulnerability and Protectability to Chernobyl-Born Radionuclide - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 84

and 3, respectively). As is seen, the predicted concentration values at definite
depths increase successively with changes in the characteristic landscape type
from 1 to 3. The increase is not prominent when changing from plot 2 to plot 3.
This can be explained by the relatively similar sandy-loamy composition structure
of the aeration zone in these two subregions. However, in correlation with the
surface contamination density, the dimensional 137 Cs concentrations in Bq/dm 3 in
the upper groundwater may increase 1-2 orders of magnitude with changes in the
landscape type from 1 to 2 and from 2 to 3. To obtain refined groundwater vul-
nerability and protectability maps accounting for depression-related PFMZs, a
similar modeling was performed using data for typical depressions within the
CEZ and Kyiv regions. The corresponding vertical profile of the dimensionless
concentration in floodplain areas (subregion 3) is shown in Figure 5.2, plot 4.
The calculated characteristic profiles for the above three typical areas are
used to prepare the preliminary (“background”) groundwater vulnerability and
protectability maps for 137 Cs within the Dnieper basin.
Following the zoning of the study area into three typical subareas and obtain-
ing the typical vertical concentration distributions, the assessment depths z 1 * have
been specified according to available data for the upper groundwater table depth
and the values of the predicted relative 137 Cs concentrations for a 30 year period
taken at these depths from the typical vertical distributions. The obtained area
distribution of the relative concentration at depths of the groundwater table char-
acterizes the background cover vulnerability of the upper Quaternary aquifer
(still with no account of PFMZs).
Further on, the refinement stage accounting for depression-related PFMZs
has been performed according to the typical vertical distribution of relative 137 Cs
concentrations (curve 4, Figure 5.2).
By the available observation data for the infiltration rate w at a groundwater
table depth and the obtained predicted concentration of 137 Cs, the approximate
input of depression-related PFMZs into the total infiltration recharge and their
possible share in the total contamination of the Quaternary aquifer have been
determined.
To this end, a cartographic analysis of depression occurrence was performed
using topographic maps on scales of 1:50,000 and 1:20,000 and separate local
areas on a scale of 1:10,000. The analysis shows that the number of contoured
depressions per unit area increases significantly with increasing detail of the
map. However, even the less detailed scale of 1:50,000 enabled more than 2000
depressions to be discovered per standard map sheet on the scale 1:50,000. Using
these data, the coefficient K c = S 10 / S 50 determined by the ratio of the total depres-
sion area identified by the map on a scale of 1:10,000 to that identified by the
map on the scale 1:50,000 was found, and its dependence on the total number of
depressions per standard map sheet on the scale 1:50,000 was plotted (Figure 5.3).
Using this plot and a sheet-by-sheet calculation of the depression area of
this scale, a map of the relative area density of depressions (in percentage of a