Vol. V, No. 4, July-August, 2014

Paris

,

Figure 9. Evolution of EC and SO

4

=

in well e17 and its relation with the determined associations.

be proposed. The definition of the indicator

should consider the natural base, that is, the

values characteristic of the natural composition

of the water, based on which the state of the

system will be demonstrated —the pressures

to which it is submitted and its response.

Manzano, Custodio andNieto (2003) define this

natural base of the quality of groundwater as

the range of concentrations of a given element,

species, or substance in the dissolved phase

and derived from natural geological, biological

or atmospheric sources. The same authors

also mention that the BaSeLiNe (Natural

BaSeLiNe Quality in European Aquifers)

project decided to operationally adopt the

median as the parameter most illustrative of

the value that is characteristic of the natural

base of groundwater and the percentiles 2.3%

and 97.7% to illustrate the range of variation.

This ensure that 95.4% of the population

studied is within the range. Nevertheless, the

same authors indicate that if the statistical

distribution is normal or lognormal, the mean

or median could be considered characteristic

values, though this often does not occur because

the quality of the water is the result of more

than one process. Investigations performed

by Blarasin, Damilano, Cabrera and Matteoda

(2006) indicate that the f1 distribution presents

a better fit to the empirical distribution and

determined an estimator

for the natural

base, which results from a linear combination

of the mean and the median. Nevertheless, they

report that the distributions that correspond to

the different components need to be studied

in more depth if the objective is to determine

the natural base using the parametric estimate

of the typical concentrations (localization

parameters) of each component and its

distribution related to these values. The

SEO Version