Abstract:
Groundwaters of the coastal region are significant
and serve as a fragile ecosystem in the sedimentary
terrain. The Pondicherry region is characterized by different
geological formations of distinct geological epochs
Cretaceous, Tertiary and Quaternary. Ninety-three samples
were collected from specific aquifers with respect to spatial
distribution [Alluvium (31), Upper Cuddalore (13), Lower
Cuddalore (13), Other Tertiary (7), Cretaceous (24) and
Mixed—multiple completion aquifer (5)]. The collected
samples were analyzed for major ions Ca2?, Mg2?, Na?,
K?, HCO3
-, Cl-, PO4
2-, SO4
2-, F and DOC. Stables isotopes
of d18O, dD and d 13C were also analyzed along with
heavy metals like Al, Ba, Fe, Sr, Cd and Zn. The d18O
ranges between -6.85 and -2.15 %, and dD ranges
between -43.94 and -19.41 %. The distribution of these
environmental isotopes in groundwater of this layered
aquifer sequence was also attempted. A comparison of the
isotopic data with the rainfall, Local Meteoric Water Line
with a equation of dD = 7.398 * d18O ? 5.067, Indian
Meteoric Water Line and Global Meteoric Water Line was
performed. The d13C values for groundwater ranges from
-5.3 to -18.1 %. The result indicates that the groundwater
in the study area is mainly meteoric in origin, and
few samples show evidence of evaporation. The dissolved
organic carbon (DOC) is a very important component in
biogeochemical cycling of elements characterized by high
susceptibility to leaching. The range of the DOC in the
study area is 0–16 mg/L. Factor analysis was applied to
classify the groundwater samples and to identify geochemical
processes controlling groundwater geochemistry.
The Alluvium aquifers show a complex hydrogeochemistry
than the older aquifers. The major factor influencing the
hydrogeochemistry of the region is rock–water interaction
and anthropogenic processes. Hence, metal mobility of the
groundwater shows the correlation of metal bonding and
DOC. The relation between the DOC and heavy metal
concentration in the aquifers was also identified.
