Hydro-geochemical Investigation and Quality Assessment of Groundwater for Drinking and Agricultural Use in Jawaharlal Nehru University (JNU), New Delhi, India - Management of Natural Resources in a Changing Environment - page 18

Pre-monsoon Post-monsoon

4
3
2
1

0

0 2 4 6 8 10

− 1
− 2
− 3
− 4

Sample Numbers

Fig. 5 Scatter plot of meteoric genesis indices

Saturation Index

The saturation indices (SI) describe the quantitative deviation of water from
equilibrium with respect to dissolved minerals (Sandow et al. 2011 ; Raju 2012b ).
The variation in chemical composition of groundwater in an area is controlled by the
evaporation, rainfall, climate, minerals present in geological formations and hydro-
geochemical processes such as dissolution, precipitation, sorption and ion-exchange
and anthropogenic activity (Raju et al. 2009 , 2011 ). The changes in the saturation
state can be used to distinguish the different hydrochemical evolution stages as well
as to identify the pertinent geochemical reactions that determine the water chemistry
(Stumm and Morgan 1981 ;Guleretal. 2002 ). By using the SI approach, the subsur-
face reactive mineralogy can be obtained from groundwater data without the need to
collectsolid-phasesamples,andthemineralogycanbeanalyzed(Deutsch 1997 ).
The calculated SI values range for anhydrite −2.516 to −1.919 (mean: −2.226)
and −2.382 to −2.044 (mean: −2.233); aragonite −0.413 to 0.136 (mean: −0.114)
and −0.613 to 0.32 (mean: −0.196); calcite −0.269 to 0.28 (mean: 0.029) and −0.469
to 0.464 (mean: −0.053); dolomite −1.679 to −0.654 (mean: −1.015) and −1.844 to
1.357 (mean: −0.704); fluorapatite −1.549 to 3.483 (mean: 1.342) and −3.923 to
0.91 (mean: −1.342); goethite 2.224-5.025 (mean: 3.542) and 1.631-5.234
(mean: 3.405); gypsum −2.296 to −1.699 (mean: −2.006) and −2.162 to −1.824
(mean: −2.014); halite −8.826 to −5.499 (mean: −6.797) and −8.622 to −5.561 (mean:
−7.158); magnesite −1.44 to −0.862 (mean: −1.076) and −1.406 to −0.523
(mean: −0.983); and siderite −1.785 to −0.685 (mean: −1.191) and −1.997 to −0.467
(mean: −1.265) for pre- and post-monsoon season, respectively. Variation of satura-
tion index for different minerals of both pre- and post-monsoon is shown in Fig. 6 .
Study of saturation indices reveals that all groundwater samples are undersaturated
with respect to anhydrite, gypsum, dolomite, halite, magnesite and siderite minerals,
whereas supersaturated with goethite mineral in pre- and post-monsoon seasons.
56 %, 44 % and 22 % samples show undersaturation and 44 %, 56 % and 78 %
samples show supersaturation in pre-monsoon, whereas 78 %, 67 % and 78 %