Modelling groundwater pollution using visual modflow in Eloor industrial belt

Abstract

Groundwater of shallow aquifer is a good source of fresh water for drinking and irrigation for the state of Kerala. However, in some cases it is polluted by salt water intrusion and industrial pollution; Eloor municipality in the central part of Kerala is a typical example for the latter situation due to the presence of several hazardous industries. The place has been considered as one of the hot spots of the world, however, not much studies have been reported on the quantitative analysis of the area extent of the pollution and plausible remedial measures. Hence, this study has been conducted at Eloor to assess the aquifer characteristics, water quality, develop groundwater and contaminant transport models and thereby to suggest remedial measures to mitigate pollution issues of an industrial area. Resistivity survey has been conducted at five different locations and the water quality parameters of ten observation wells were tested in the laboratory. Irrigation water quality parameters viz. EC, SAR (Sodium Adsorption Ratio), RSC (Residual Sodium Carbonate, KI (Kelly Ratio) and Na% (Sodium Percentage) were computed. In addition, Irrigation Water Quality Index (IWQI) and Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI) were used to assess irrigation water and drinking water quality respectively. The study also utilized Visual MODFLOW and it’s MT3DMS add on module to simulate the groundwater movement and contaminant transport. The models were calibrated for the period 2008 to 2013 and validated for 2014 to 2015. Simulation studies were made with different scenarios to get insight into the arresting of groundwater contamination. Geophysical survey showed that, the site which was at close proximity to the contaminant disposal site gave a very low resistivity value for all depth ranges, indicating highe moisture content and concentration of ions in the subsoil possibly due to the leaching of the effluents. IWQI and CCME values indicated that the water of the wells viz. W1, W2, W3, W4, W5, W6 in the neighbourhood of the contaminant disposal sites have poor standards both from the perspectives of irrigation and drinking water qualities, plausibly due to the influence of leachates from the effluent’s disposal site. At the same time, water qualities of the other wells were within the acceptable limits. It was found that IWQI index was more reliable to classify the irrigation water quality as it includes multiple parameters in its computation. Calibration and validation of Visual MODFLOW Flex 8.0 resulted in a correlation coefficient of 0.89 and 0.87 for the calibration and validation periods respectively. The corresponding values for the MT3DMS model were respectively 0.86 and 0.85. Prediction of contaminant transport for the year 2025 by MT3DMS model showed that the presence of contaminants may spread to an area extent of 4.46 km2 lying in the wards of 1, 2, 3, 4, 5, 6, 29, 30 and 31 of Eloor municipality. Simulation of the effect of a C- shaped impermeable barrier to control this contaminant transport showed that radial movement of pollutants can be reduced to 1.46 km from the 2.43 km corresponding to no control measures. Though barrier appeared effective to check the spread of pollution to the habituation, it would turn out to be a costly measure and in addition, it might enhance the movement of pollutants into the river Periyar. Hence, as an alternative to physical barriers, the study recommends bio remedial measures in two different radial zones; one in the immediate neighbourhood of the point source with a radial distance of 0.4 km and other at 4 km as an economic and sustainable measure.