Kouli_etal_2008_Groundwater modelling_BOOK.pdf - Pantelis ...

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Maria Kouli, Nikos Lydakis-Simantiris and Pantelis Soupios
ensures the best representation of the hydrogeological setting. The numerical ratings and
weights, which were established using the Delphi technique (Aller et al. 1987), are well
defined and are used worldwide. This makes the model suitable for producing comparable
vulnerability maps on a regional scale. The necessary information needed to build up the
several model parameters is, in general, available for the study area or it can easily be
inferred.
Several studies have used the DRASTIC model within a GIS environment although few
attempts have been made to apply the DRASTIC methodology in arid and semi-arid
environments (Fritch et al. 2000, GVM in Texas, USA).
Modifications of DRASTIC Model
Many modifications of DRASTIC model have been proposed by several authors, according to
data availability and problem singularity.
Evans and Myers (1990) used a GIS-based approach to evaluate the potential for regional
groundwater pollution with a modified DRASTIC approach in southern Delaware, USA.
Three DRASTIC parameters were not used in this research, namely net recharge, impact of
the vadose zone and the aquifer media. Instead, the authors added new parameters to the
DRASTIC index: the land use/land cover and septic tank system density. The authors claimed
that their approach could generate groundwater-related information for large geographical
areas that was sufficiently detailed for use by government agencies involved in protecting
groundwater.
Secunda et al. (1998) integrated the impact of extensive land use (risk) data over long
periods of time upon aquifer media as an additional parameter in the DRASTIC model, again
integrated into a GIS, to assess the potential level of groundwater vulnerability to pollution in
Israel’s Sharon region. The methodology employed empirical means to integrate aquifer
media and extensive agriculture land use data. Thus, the final assessment incorporated both
the natural state of the vadose zone and aquifer media (vulnerability) as well as the potential
danger posed by the long term effect upon the media of existing extensive land usage (risk) to
the region’s groundwater.
Piscopo (2001) used DRASTIC and GIS to produce a groundwater vulnerability map for
the Castlereagh Catchment in Australia. In this research, the author excluded hydraulic
conductivity from the final DRASTIC calculation due to the lack of data. Furthermore,
Piscopo (2001) replaced the recharge parameter (net recharge) as defined by the US EPA by
the potential of an area to have a recharge based on the rainfall amount, slope and soil
permeability.
Panagopoulos et al. (2006) proposed an optimization procedure of the original DRASTIC
method using various modifications and transformations on the basis of the statistical
parameters of a pollution index distribution. The pollution index which was used was the
nitrates concentration (expressed as mg/L NO 3− ) and the selection was based not only on the
fact that it constitutes the main contaminant that human activities introduce into the
environment of the study area, but also because it has been proposed as a representative
indicator of groundwater quality degradation (US EPA 1996). The DRASTIC parameters
were imported in a simple linear equation after they had been converted from the physical
range scale to a ten-grade relative scale. Each parameter is multiplied by a weighting
coefficient which had been determined with qualitative, not quantitative criteria, based on the