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 6

Results and Discussion
Chemical Quality of Groundwater
Understanding the groundwater quality is important as it is the major factor determining
its suitability for drinking, domestic, agricultural and industrial purposes. In order to
know the chemical quality of groundwater, nine water samples have been collected
fromtheborewellssituatedintheJNUinstitutionalarea.Thesummarizedresultsof
chemical analysis of major ions are presented in Table 1 .Overall,thegroundwaterof
the study area is slightly alkaline in nature in pre-monsoon (6.9-7.5) and post-mon-
soon(6.7-7.7)seasons.TheECrangesare481-2,430 ʼS/cm (mean: 1,113 ʼS/cm) in
pre-monsoon and 589-2,220 ʼS/cm (mean: 1,052 ʼS/cm) in post-monsoon season.
TDS varies from 207 to 1,002 mg/l (mean: 509 mg/l) in pre-monsoon and 260-
965mg/l(mean:462mg/l)inpost-monsoon.Groundwatersamplesinpre-andpost-
monsoon contain freshwater, since the TDS values are <1,000 mg/l, except one
location in pre-monsoon (Davis and De Wiest 1966 ), and all groundwater evaluated is
therefore suitable for drinking and irrigation purposes (Table 2 ).
The low TDS content observed could be either a result of the slow decomposition
ofmetamorphicrocks,sincetheterrainisunderlainbymostlyquartziterocks,or
due to the short residence time of the groundwater. Seasonal variation in the TDS,
ECandionicconcentrationsinthegroundwatermaybeattributedtogeochemical
processes and anthropogenic activities (Raju et al. 2011 ). Among the cationic con-
centrations in pre- and post-monsoon seasons: Na + is the dominating ion with mean
valuesof125.44and106.65mg/l,respectively,followedbyCa 2+ (means: 63.46 and
64.08 mg/l), Mg 2+ (means: 8.95 and 12.84 mg/l), and K + (means: 2.54 and 2.18 mg/l)
(Table 1 ). In this groundwater system, in both the seasons, there is no dominant
cation that exceeds the threshold of dominance (i.e. meq/l > 50 %) except sample
number 2 where Na + is dominating cation. Since overall no one cation constitutes as
much as 50 % of totals in the pre- and post-monsoon seasons, the water is recog-
nizedasamixedcationtypeexceptsamplenumber2.Thehydrochemistryofcat-
ionic dominance pattern is in the order of Na + >Ca 2+ > Mg 2+ > K + in pre- and
post-monsoon seasons. In general, weathering, dissolution and base-exchange pro-
cesses control the levels of cationic concentrations in groundwater.
Amongtheanionicconcentrationsinpre-andpost-monsoonseasons:HCO 3 − is
the dominating ion, ranging from 176 to 420 mg/l (mean: 307 mg/l) and 224-
376 mg/l (mean: 288 mg/l), respectively, followed by Cl − (means: 130.27 and
118.55mg/l),SO 4 2− (means: 47.57 and 47 mg/l), F − (means: 0.90 and 1.08 mg/l) and
PO 4 3− (means: 0.30 and 0.04 mg/l) (Table 1 ). The concentration of fluoride in the
groundwater of the area varies from 0.4 to 2.0 mg/l and 0.7 to 2.0 mg/l in pre- and
post-monsoonseasons,respectively.Twogroundwatersamples(i.e.KoyanaLawn
andMahiMandviLawn)outofninesamplesanalyzedinthestudyareaexceedthe
maximum permissible limits of fluoride (1.5 mg/l) set by WHO (Table 1 ). The
weatheringactivitycharacterizedbyalternatewetanddryconditionsisresponsible
for leaching fluoride from the micasious minerals present in the soils and rocks (Jal
Nigam Report 2006 ). Easy accessibility of circulating water to the weathered