Preferential Flow and Migration Zones in Geological Environment - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 39

3 . Preferential flow and Migration Zones
in geological environMent
3.1. state of Problem study
In spite of a large number of research works on the formation of ground-
water resources [ Heath , 1984; Fetter , 2000; Vsevolzhskiy , 1983; Shestopalov , 1979,
1981, 1988] and the processes of contaminant migration in the subsurface
hydrosphere [ Bear , 1972; Fried , 1975; Freeze and Cherry , 1979; Schnoor , 1992;
Lukner and Shestakov , 1986; Mironenko et al ., 1988; 1999; Pashkovskiy , 2002],
not enough attention has been paid to preferential pathways of groundwater flow
and migration.
The results of studies of preferential flow and migration pathways described
below show that these pathways play an important role in the groundwater
recharge and contamination. Their ignoring leads to a substantial underestimation
of groundwater vulnerability. Therefore, it is very important to characterize in
more detail the preferential pathways that we associate with PFMZs.
Under PFMZ we define the sites (in plane) or volumes (in space) of the
geological medium, which, by their lithological composition, physicomechanical
and geochemical properties, and other characteristics, reveal a higher aquife
permeability and the corresponding transport of mobile substances (radionuclides,
heavy metals, pesticides, etc.) with velocities essentially exceeding the background
values. These zones can be of different size, origin, and evolution and can have
varying water exchange characteristics and transport mechanisms for substances.
In groundwater resource assessments, insufficient attention to zones
with abnormally high vertical water exchanges leads to underestimation of
calculated forecast resources and is justified in definite conditions, for
example, in view of diminishing expenses for research. However, when study-
ing possible groundwater contamination and vulnerability and protectability
to contaminants, such approaches may lead to significant underestimates of
predicted risks as compared to their real values.