Groundwater Vulnerability and Protectability to Chernobyl-Born Radionuclide - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 91

The minimum-vulnerability ( 137 Cs concentrations below 0.1mBq/dm 3 ) and
vulnerability groundwater areas correspond to relatively small sites of watershed
areas in the south and southwestern parts, respectively, of the Kyiv region and to
separate relatively clean spots. The rest of the territory, which is the largest by
area, corresponds to average-vulnerability groundwater with 137 Cs concentra-
tions in the range of 1-10 mBq/dm 3 .
To evaluate the proposed method, the results obtained were compared with
the results of the assessment of groundwater vulnerability to 137 Cs for the same
territory of the Kyiv region by the Russian method [ Belousova , 2005], which
was vulnerability described in Chapter 1. As already mentioned, we performed
it in the course of the joint Russian-Ukrainian-Belarusian project in 2003
[ Shestopalov , 2003]. A schematic map of the assessment is shown in Figure 5.7.
As can be seen in Figure 5.7, the obtained vulnerability variation over the area
is close to the actual contamination of the surface of the Kyiv region (see
Figure 2.2). Maximum values of groundwater vulnerability (very high and
high) occur in the northern part of the territory (CEZ). Conditionally invulner-
able (very low) groundwater is in the central, southern, and southeastern parts
of the region covering most of the study area. Low-vulnerability groundwater
corresponds to individual spots of increased radioactivity in the southern part
of the region.
As one would assume, the groundwater vulnerability estimated using our pro-
posed procedure (Figure 5.6) is significantly higher over the study area than that
obtained by the Russian method. It should be emphasized that in the Russian
method the vulnerability categories are determined depending on the contami-
nant travel time from the surface to the groundwater table: up to 30 years, 30-60
years, 60-100 years, and more than 100 years (see Table 1.5). As a result, for up to
30 years the radionuclides could reach the groundwater level within only a few
sites in the northern region.
However, actual data show that quite measurable radionuclide concentra-
tions (see Table 2.1) were observed already a few years after the accident (1992-
1997) not only within the CEZ area but also in the central part of the region (see
Figure 2.1).
According to the proposed methodology, the obtained vulnerability map is
drawn for a forecast period of 30 years from the onset of contamination. The map
gradations are determined by the relative concentration and expressed in absolute
units based on the value of the actual surface contamination. A separate scale (C)
shows an approximate estimate of the total groundwater vulnerability based on
the protective capacity of the rocks in the accessed aquifer. As can be seen in
Figure 5.6, unlike Figure 5.5, within almost the entire territory of the region there
is penetration of the pollutant on the groundwater table. However, the activity of
the penetration is different. It not only depends on the differences in surface con-
tamination density and the protective ability of the vadose zone but also accounts
for PFMZ distribution and activity in the study area.