Groundwater in an industrial belt (namely Upper Kodaganar River basin, Tamilnadu, India) is polluted due to discharge of untreated effluents from 80 operating tanneries. Total Dissolved Solids (TDS) measurements vary in and around the clusters of tanneries from 2,000 mg/l to 30,573 mg/l in open wells. A mass transport model was constructed to study the contaminant migration using Visual MODFLOW and MODPATH. An area of 240 km2was chosen to construct the groundwater flow model of the weathered portion of the unconfined aquifers. The shallow groundwater potential field computed through flow model was then used as input to the mass transport model. The mass transport model was calibrated with field observation. Sensitivity analysis was carried out whereby model parameters viz. transmissivity, dispersivity etc. were altered slightly and the effect on calibration statistics is observed. This study indicates that the transmissivity plays a sensitive role than the dispersivity. It shows that the migration phenomenon is mainly through advection rather than dispersion. Particle pathlines also had been computed to trace the movement of contaminants. The contaminant migration is being emanated from the tannery belt and polluted towards eastern side of the Kodaganar river. This modeling study has indicated that even if the pollutant sources were reduced to 50% of the present level, TDS concentration level in the groundwater, even after 20 years, would not be reduced below 50% of it. The study suggests immediate measures for arresting the deterioration in groundwater quality as well as augmentation for restoration of aquifer in some parts of the study area.
Key words: Unconfined aquifer, tannery clusters, groundwater pollution, mass transport model, upper Kodaganar river basin, India.
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