Geography Reference
In-Depth Information
the groundwater vulnerability; a rating of 10 indicating a high pollution
potential of the parameter.
Once the ratings are assigned to all classes of the parameters, the weights
ranging from one to five reflecting their relative importance with respect to
each other are assigned to seven parameters (Table 5).
The DRASTIC Index is then computed applying a weighted linear
combination of all seven parameters by multiplying each parameter rating with
its weight and adding together the resulting values according to the following
equation (Aller et al., 1987):
DRASTIC
D
D
R
R
A
A
S
S
T
T
I
I
C
C
(23)
Index
R
W
R
W
R
W
R
W
R
W
R
W
R
W
where D, R, A, S, T, I, and C are the seven parameters expressed above and
the subscripts R and W are the corresponding ratings
and
weights,
respectively.
DRASTIC provides two weight classifications (Table 5), one for general
conditions and the other one for conditions with intense agricultural activity.
The latter, called the Pesticide DRASTIC index (DRASTIC-P), represents a
specific vulnerability assessment approach. The DRASTIC-P method is the
most suitable in agricultural areas mainly due to the greater weight given to
the variables of soil and slope types (Massone et al., 2007).
In recent years, the originally developed DRASTIC method has been
modified by using additional parameters or factors and/or by ignoring the
existing unimportant parameters according to the local characteristics of the
study area (Fritch et al., 2000; Al-Adamat et al., 2003; Lee, 2003;
Thirumalaivasan et al., 2003; Babiker et al., 2005; Simsek et al., 2006; Guo et
al., 2007; Wang et al., 2007; Umar et al., 2009; Martínez-Bastida et al., 2010;
Awawdeh and Jaradat, 2010). This reflects flexibility of the DRASTIC model
to modify according to need of the study. The well-established DRASTIC
method has been applied in different parts of the world such as the United
States (e.g., Rupert, 2001; Merchant, 1994; Loague and Corwin, 1998; Wade
et al., 1998; Stark et al., 1999; Fritch et al., 2000), Canada (Murat et al., 2004),
Europe (e.g. Stigter et al., 2006; Vias et al., 2005), South America (Tovar and
Rodriguez, 2004; Herlinger and Viero, 2006), Australia (Piscopo, 2001), New
Zealand (McLay et al., 2001), Asia (Al-Adamat et al., 2003; El-Naqa, 2004;
Thirumalaivasan et al., 2003; Rahman, 2008; Kimand Hamm, 1999), and
Africa (Lynch et al., 1997; Ibe et al., 2001).
