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 9

product dissolves and leaches the micasious minerals which contribute F − to the
groundwater (Raju et al. 2012 ). The anionic dominance patterns is in the order of
HCO 3 − >Cl − >SO 4 2− > F − >PO 4 3− inpre-monsoonandHCO 3 − >SO 4 2− >Cl − > F − >PO 4 3−
inpost-monsoon.Formostwells,HCO 3 − is the only anion that exceeds the domi-
nance level (meq/l>50 %) except sample number 2 (Cl − dominance) and sample
number 9 (mixed type) in the study area.
Groundwaterinthesemi-aridregionsisgenerallycharacterizedbyhighioncon-
centrations and the dominant anion species of the water changes systematically
fromHCO 3 − toSO 4 2− toCl − as water flows from the recharge area to the discharge
area (Ronit et al. 1997 ).AnthropogenicCO 2 gas should be considered as a potential
sourceofbicarbonateinthestudyarea.PotentialsourcesofCO 2 gas are municipal
wastes within unlined landfill sites, due to the oxidation of organic material leaked
fromoldlatrinesandopensewagesystemsanddissolvedHCO 3 − ion from sulphate
reductionoforganicmaterialsintheaquifer(ClarkandFritz 1997 ). Few groundwa-
ters of high bicarbonate concentrations are likely to be influenced by anthropogenic
carbondioxide.Inordertoobtainmoredetailonitssource,pCO 2 in groundwater
samples was calculated using WATEQ4F program (Ball and Nordstrom 1992 ). The
computedpCO 2 values in the study area ranges from 3.7 × 10 −3 to 7.4 × 10 −2 atm with
a mean of 1.9 × 10 −2 atm and 6.8 × 10 −3 to 5.6 × 10 −2 atm with a mean of 2.2 × 10 −2 atm
in pre- and post-monsoon seasons, respectively (Table 1 ). The common range of
CO 2 pressures of 10 −1.5 -10 −2.5 atm is found in open system soil layers (Appelo and
Postma 1993 ).CO 2 is generated in soils by decay of organic material and by root
respiration. In case of CO 2 pressure <10 −2.5 atm, CO 2 gas was consumed through
mineral dissolution in a closed groundwater system.
Hydrochemical Facies and Processes
Hydrochemical facies are water masses that have different geochemical attributes and
arehelpfulforcomparingtheoriginsanddistributionofgroundwatermasses(Lloyd
and Heathcote 1985 ; Raju 2012a , b ). Hydrochemical facies are a function of the
lithology, solution kinetics, and flow patterns of the aquifer. Based on the relative
dominance of major cations and anions in terms of their reacting values, nine ground-
watersampleshavebeenclassiiedintothreehydrochemicalfacieswhichareCa 2+ -
Na + -HCO 3 − (three in pre- and four in post-monsoon); Na + -Ca 2+ -HCO 3 − (four in
pre- and three in post-monsoon) and Na + -Ca 2+ -Cl − (two each in pre- and post-mon-
soon) (Table 3 ). Sodium dominated facies are most widely distributed in the study
area. The average chemical composition and percent content of masses of different
hydrochemical facies are presented in Table 3 .Ca 2+ -Na + -HCO 3 − , Na + -Ca 2+ -HCO 3 − and
Na + -Ca 2+ -Cl − each represent 33 % in pre-monsoon and 45 % in post-monsoon; 45 %
in pre-monsoon and 33 % in post-monsoon; 22 % in both the seasons of the total
numberofwatersamplesanalyzed,respectively.Na + -Ca 2+ -HCO 3 − type water is domi-
natedinpre-monsoonwhereasCa 2+ -Na + -HCO 3 − type of water is dominated in post-
monsoon season in most part of the studied area. In the Na + -Ca 2+ -HCO 3 − facies Na +
valuesrangesfrom1.57to5.83meq/l(pre-)&3.13to5.13meq/l(post-),andCa 2+