Methods of Groundwater Vulnerability and Protectability Assessment - Groundwater Vulnerability: Chernobyl Nuclear Disaster - page 19

1 to 14 TU (tritium units, 1 TU = 0.119 Bq/L). The wide use of this method
requires implementation of special field works for groundwater sampling and
sample analysis for determination of isotopes Tr, δD, δ 18 O, δ 13 C, and δ 14 C.
AVI method . Among the parametric groundwater vulnerability assessment
methods, one should mention the aquifer vulnerability index (AVI), which was
developed at the National Hydrogeology Research Institute of Saskatoon
(Canada) by Van Stempvoort et al . [1995]. The authors used the total flow resis-
tance of the covering deposits taking into account the lithology:

m
k

= ∑ , r

i

(1.13)

i

i

where m i are layer thicknesses and k i are the corresponding hydraulic conductiv-
ities. The method is equivalent to the assessment using groundwater percolation
time because the total resistance r can be treated as the time of water percolation
through the whole formation at a unit vertical hydraulic head gradient.
The method was by Tovar and Rodriguez [2004] for a groundwater vulnera-
bility assessment in the area of Leon, Mexico. The hydraulic conductivities were
determined by pumping tests and direct measurements with a constant head per-
meameter. The assessment required a significant volume of initial information
that was provided by detailed GIS maps of relief, geological conditions, and con-
ditions of land use. The obtained results were compared with an alternative
assessment using the DRASTIC method. Authors noted that the AVI method
gave a higher vulnerability, particularly in zones of tectonic dislocations.
Overall, parametric groundwater vulnerability assessments by water perco-
lation time or flow often lead to underestimation or overestimation of the
potential groundwater contamination depending on whether or not the physico-
chemical interaction in the “contaminant-water-rock” system is taken into
account. The approach uses the representation of a contamination front with a
definite concentration at a definite depth below which the groundwater medium
is still considered clean at each time moment. The approach often takes no
account of areal distribution PFMZs of different dimensions (from macropores
to areal zones related with depressions, geodynamically active zones, etc.). With
an increase in the assessed area, the heterogeneities of larger dimensions should
be brought into consideration, and the assessed groundwater vulnerability should
be determined by their total “degree of openness.”

1.4. Modeling Methods

Among the modeling methods used by different authors for groundwater vul-
nerability assessments, two methods should be distinguished: deterministic and
statistical.