Chloride migration in groundwater for a tannery belt in Southern India.

Groundwater in a tannery belt in Southern India is being polluted by the discharge of untreated effluents from 80 operating tanneries. Total dissolved solids and chloride (Cl(-)) measurements in open wells in the tannery cluster vary from 27,686 to 39,100 and 12,000 to 13,652 mg/l, respectively. A mass transport model was constructed using Visual MODFLOW Premium 4.4 software to investigate the chloride migration in an area of 75.56 km(2). Input to the chloride migration model was a groundwater flow model that considered steady and transient conditions. This model was calibrated with field observations; and sensitivity analysis was carried out whereby model parameters, viz., conductivity, dispersivity, and source concentration were altered slightly, and the effect on calibration statistics was evaluated. Results indicated that hydraulic conductivity played a more sensitive role than did dispersivity. The Cl(-) migration was mainly through advection rather than dispersion. It was found that even if the pollutant load reduced to 50% of the present level, the Cl(-) concentration in groundwater, even after 6 years, would not be reduced to the permissible limit of drinking water in the tannery belt.