Protection of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 196

3 VULNERABILITY, HAZARDS, RISKS
3.1 Vulnerability
The vulnerability of aquifers is by defi nition (Zwahlen et al. , 2003) a relative
property, non-measurable and adimensional, based on the supposition
that the environment can provide protection for groundwater against
anthropogenic impacts, particularly those caused by pollutants entering
the subterranean environment. Vulnerability is therefore an evaluation of
the lack of this natural protection.
There is a distinction between intrinsic vulnerability, which is inherent
to the geologic environment and to the local climatic conditions, and specifi c
vulnerability, which is linked to the properties of the contaminant.
Intrinsic vulnerability is therefore the extreme case of specific
vulnerability for a tracer that is entirely conserved (for example a chloride)
between its entry point and its target (aquifer or catchment point). In the
opposite case, an organic substance with low mobility and a high ease of
adsorption or degradation will not pass all the way from entry to exit.
Specifi c vulnerability is, in the great majority of cases, smaller than
intrinsic vulnerability.
3.2 Hazards and risks
An environmental hazard is defined as an instantaneous event or a
continuous process which, when it occurs, results in the possibility of
degradation in the quality of the environment, directly or indirectly.
A risk is the combination of a hazard and a vulnerable environment;
as a result, a hazard only presents a risk if it is likely to affect something
valuable (the target), in this case, groundwater (Figure 103). The risk over
an aquifer is the effect of a hazard, for example, leakage of an industrial
pollutant, on the vulnerability of the environment, without overlooking
the fl ow of the aquifer, which can displace impacts.
The origin-path-target conceptual model depicts the transfer of a
hazard towards the aquifer (vulnerability of the resource), then towards
its catchment points (springs, wells, boreholes).