Mass transport modeling of an industrial belt using visual MODFLOW and MODPATH: A case study

Abstract

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 km2 was 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.