CS(AR)-2/2011 : Modelling of pesticide transport in groundwater: a case study of metropolitan city - Vadodara

Abstract

An extensive field survey in and around Vadodara city was carried out and identified six wastewater drains viz; Nandesari Drain, Gujarat Alkalies and Chemicals Limited (GACL) Drain, Gujarat Refinery Drain, Indian Petrochemicals Corporation Limited (IPCL) Drain, Kamati Bagh Drain, Gujarat Industrial Development Corporation (GIDC) Drain, and two rivers namely river Jambua and river Vishwamitri through which mixture of different kind of untreated/partially treated/treated wastes are being discharged. Wastewater samples from these drains and rivers and thirty five groundwater samples from open wells, tubewells, piezometric wells, bore wells and hand pumps in and around Vadodara city were collected in pre- and post-monsoon seasons during 2008-09 and 2009-10 and analysed for physico-chemical parameters and organochlorine pesticides. Very high concentrations of isomers of SHC pesticides (>1.0 pg/L) were observed in drains, rivers and in few of the groundwater samples specially in the southern part of the city. Identification of contamination sources was carried out by studying chemographs of drains, rivers and groundwater. Correlations were developed between the chemistry of drains, rivers and groundwater. Further cause and effect relationship for groundwater contamination was attempted using cluster analysis, which utilizes pattern recognition from statistical presentation of data and heuristic relationships have been obtained by carrying out correlation analysis for various data set combinations. It may be inferred that the groundwater chemistry is mainly influenced by the Nandesari drain, GACL drain and IPCL drain. For transport of pesticides in unsaturated zone of the study area, optimized conditions for adsorption of Lindane on soil of Vadodara city were maintained in the column of length 25 cm and diameter 4 inch. The soil of Vadodara was characterized by analyzing physical and chemical parameters. The column was packed with the slurry of weighted soil. A 10 ppm concentration of Lindane was loaded on the top of the soil in the column. The maximum concentration of Lindane was observed in 12th fraction after transporting through the soil column and maximum amount of transportation of Lindane through the soil in the column was 3.434 ng/g.

Migration pattern of Lindane in the groundwater in space and time for prediction purposes was attempted using Visual MODFLOW Premium Version 2009.1 (MODular 3- dimensional finite difference groundwater FLOW model) MT3D. The groundwater flow model has been constructed upto a depth of 60 in considering a three layer structure. The general groundwater flow direction is from northeast to south and southwest. The river Vishwamitri and river Jambua form natural hydrologic boundary. The predictions of the mass transport model for next 50 years indicated advancement of containment of plume size both spatially and depthwise as a result of increasing level of pesticide in river Vishwamitri. The restoration of the aquifer system may take a very long time as seen from slow improvement in the groundwater quality from the predicted scenarios for different years. This may be due to very low groundwater velocities prevailing in the area because of clay predominant formations. It is recommended that all the industries working in the study area should install efficient Effluent Treatment Plants (ETPs) to abate this pollution problem.