Water Technology and Sciences - July - August, 2014 - page 19

17
Water
Technology and Sciences.
Vol. V, No. 4, July-August, 2014
Paris
et al.
,
Supply Well Protection: Groundwater Quality Indicators
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
m
*
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
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