GROUNDWATER POLLUTION OF THE MADRAS URBAN AQUIFER, INDIA

Most of the water requirement for Madras is met from surface- and ground-water supplies piped in from outside the city limits. However, as is the case for many cities, a certain proportion of the population, usually the poorest, is forced to rely on wells within the urban area. A study was therefore carried out to gain an idea of the inorganic quality of the water in the wells penetrating the shallow (< 20 m thick) alluvial aquifer below the city. Two general surveys of selected wells across the city indicated that relative to Indian domestic water standards, of the 93 ground-water samples obtained, 25% exceeded the Ca limit, 11% the Mg limit, 43% the total dissolved solids limit, 14% the SO4 limit, and 70% the NO3 limit. As an indicator of biological contamination, the high concentrations of NO3 (up to 1040 mg/1) are particularly worrying. A detailed survey of sites close to a city river was also undertaken. High heavy metal concentrations were detected, with As up to 0.42 mg/1, Hg to 0.02 mg/l, Pb to 1.82 mg/l, and Cd and 1.31 mg/l. Microbes have been found in several of the wells. It is clear that, as expected, the shallow ground water is grossly polluted.