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Identification of major sources controlling groundwater chemistry from a hard rock terrain — A case study from Mettur taluk, Salem district, Tamil Nadu, India

Journal of Earth System Science (Impact Factor: 0.79). 02/2008; 117(1):49-58. DOI: 10.1007/s12040-008-0012-3

ABSTRACT The study area Mettur forms an important industrial town situated NW of Salem district. The geology of the area is mainly
composed of Archean crystalline metamorphic complexes. To identify the major process activated for controlling the groundwater
chemistry an attempt has been made by collecting a total of 46 groundwater samples for two different seasons, viz., pre-monsoon
and post-monsoon. The groundwater chemistry is dominated by silicate weathering and (Na + Mg) and (Cl + SO4) accounts of about 90% of cations and anions. The contribution of (Ca + Mg) and (Na + K) to total cations and HCO3 indicates the domination of silicate weathering as major sources for cations. The plot for Na to Cl indicates higher Cl in
both seasons, derived from Anthropogenic (human) sources from fertilizer, road salt, human and animal waste, and industrial
applications, minor representations of Na also indicates source from weathering of silicate-bearing minerals. The plot for
Na/Cl to EC indicates Na released from silicate weathering process which is also supported by higher HCO3 values in both the seasons. Ion exchange process is also activated in the study area which is indicated by shifting to right
in plot for Ca + Mg to SO4 + HCO3. The plot of Na-Cl to Ca + Mg-HCO3-SO4 confirms that Ca, Mg and Na concentrations in groundwater are derived from aquifer materials. Thermodynamic plot indicates
that groundwater is in equilibrium with kaolinite, muscovite and chlorite minerals. Saturation index of silicate and carbonate
minerals indicate oversaturation during pre-monsoon and undersaturation during post-monsoon, conforming dissolution and dilution
process. In general, water chemistry is guided by complex weathering process, ion exchange along with influence of Cl ions
from anthropogenic impact.

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