Environmental Engineering Reference
In-Depth Information
Base Exchange Indices (
r
1
) and Meteoric Genesis Indices (
r
2
)
The changes in the chemical composition of groundwater during its travel in the
subsurface must be understood (Sarin et al.
1989
). Base Exchange Indices (
r
1
) and
MeteoricGenesisIndices(
r
2
) are proposed to indicate the ion exchange between the
groundwater and its host environment. Base Exchange Indices (
r
1
) is determined by
using the equation which could be applied for the further classification of ground-
water given as follows:
(
)
)
(
r
1
=
Na
+
−
Cl
−
/
SO
2
−
where
allions in meql
/
4
The groundwater can be grouped as Na
+
-HCO
3
−
type if
r
1
> 1 and Na
+
-SO
4
2−
type if
r
1
< 1 (Soltan
1998
). Majority of samples in both the seasons are of Na
+
-HCO
3
−
type.
Based on Base Exchange Indices, 89 % and 11 % of samples are Na
+
-HCO
3
−
type and
Na
+
-SO
4
2−
type waters in both the seasons, respectively (Fig.
4
). The dissolution of
gasesandminerals,particularlyCO
2
andCO
3
2−
related compounds in the atmosphere
and in the unsaturated zone during precipitation and infiltration, would impart the
observedHCO
3
−
water type (Shanyengana et al.
2004
; Singh et al.
2006
).
ThegroundwatersourcescanalsobeclassiiedbasedonMeteoricGenesisIndex
and can be computed using following equation (Soltan
1999
):
{
(
)
−
}
)
(
r
2
=
K
+
+
Na
+
Cl
−
/
SOwhere
2
−
allions in meql
/
4
The groundwater source is of deep meteoric water percolation type, if
r
2
< 1
while
r
2
> 1 indicates that it is of shallow meteoric water percolation type. No sig-
nificant variations were noticed within this category. Based on
r
2
indices, 89 % and
11 % of samples are shallow meteoric water and deep meteoric water type in both
the seasons, respectively (Fig.
5
). The groundwater samples are showing shallow
meteoricwatersduetolessutilizationofborewellwatersaswellashardbasement
rock in the study area.
Pre-monsoon
Post-monsoon
4
3
2
1
0
0
2
4
6
8
10
−
1
−
2
−
3
−
4
Sample Numbers
Fig. 4
Scatter plot of base-exchange indices
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