Geography Reference
In-Depth Information
this operation, both the vulnerability map and the DRASTIC-priorities
are reclassified, assigning to each qualitative class a numerical value
ranging from 1 (the lower class) to 5 (the higher one).
6.3.2. DRAMIC (Modified DRASTIC) Method
The DRASTIC method, originally developed for rural/agricultural lands,
had some limitations and/or required modifications while applying in urban
areas.
First, it was observed that the parameter C (hydraulic conductivity) of the
DRASTIC method is closely related to the parameter A (aquifer media). Thus,
impact of aquifer media has two-fold effect.
Second, topography of most cities in urban areas remains relatively flat
(with negligible slope), and therefore, the parameter T (topography) can be
ignored from DRASTIC method. Third, in urban areas, the ground surface is
mostly covered by built-up structures, concrete, etc. and it is quite difficult to
obtain comparable values of the parameter S (soil media). To overcome these
problems, and to improve the predictability and applicability of the DRASTIC
method, Wang et al. (2007) proposed DRAMIC method. The method is
expressed in Equation (24), where parameters of DRAMIC method and their
respective assigned weights are shown. Four parameters, i.e. D, R, A and I of
the DRAMIC method are same as in DRASTIC method; parameter T is
deleted and the parameters S and C are replaced with two new parameters, i.e.
aquifer thickness (M) and impact of contaminant (C). DRAMIC index is
described as (Wang et al., 2007):
DRAMIC
5
D
3
R
4
A
2
M
5
I
1
C
index
R
R
R
R
R
R
(24)
where, D, R, A, and I are the same as in the DRASTIC method; M = aquifer
thickness defined by media; C = parameter showing impact of contaminant;
and R = rating. The computed DRAMIC index values can be used to delineate
areas, which are more susceptible to groundwater contamination compared to
other areas. The higher the value of DRAMIC index is, the greater the
vulnerability to groundwater pollution. The hydrogeological significance,
ranges and ratings for the four factors D, R, A, and I of the DRAMIC method
are the same as in DRASTIC methods.
The ranges and ratings for the two new parameters of the DRAMIC
method, e.g. aquifer thickness and contaminant characteristics are listed in
Table 6.
