Evaluation of groundwater pollution potential of sewage-irrigated vegetable growing areas of the eastern fringe of Calcutta city.

In recent years recycling in agriculture is a common method of disposal or utilisation of waste. However, recycling of wastes may cause contamination of groundwater by toxic elements like heavy metals, cationic and anionic contaminants and pathogens. Groundwater of shallow and deep tubewells was collected during 1991 to 1997 from raw sewage effluent irrigated garbage farming areas on the eastern fringe of Calcutta city. In general raw sewage effluents, sludges and sewage-irrigated soils contain very high amounts of cations, anions, organics and heavy metals. It is found that most of the groundwater contained undesirable pH, total dissolved solids, total hardness, calcium, magnesium, phenolic compounds, iron and manganese and the observed values or concentrations were much above the maximum desirable limits specified by World Health Organisation (WHO) and Bureau of Indian Standards (BIS) for use as drinking water. Groundwater of that area may be used for irrigation. Dispersion by leaching of the metals, cationic and anionic contaminants from irrigated soil and from settled bottom sludge in unlined sewage channels are the principal causes of groundwater contamination. Some management plans have been suggested to control further deterioration of groundwater quality.