Microbial Contamination in the Groundwater of Aligarh City

Aligarh city is a part of the central Ganga Plain. The Quaternary alluvium in the area has been deposited on a faulted and eroded surface of upper Vindhyan shale which comprises sand, silt and clay with occasional calcrete beds. There are three levels of aquifer in the alluvium of the area. The top aquifer lies at a depth of 9-66 m and is highly vulnerable to microbial and chemical pollution. The present paper evaluates the microbial contamination of groundwater, which was analysed using water samples from shallow (hand pumps) and deep aquifers (tube wells) at different sites during the summer season. Samples were examined for total aerobic heterotrophic bacterial load by the plate count method and the multiple tube dilution method for determining the most probable number (MPN) index of total coliform and faecal coliform bacteria. Microbiological analysis showed that microbial (heterotrophic bacterial) contamination in groundwater was maximum in wells with hand pumps (private) and least in tubewell water. Total coliform and faecal coliform contamination are also found comparatively more in wells with hand pumps than tubewells. It indicated that those who drink groundwater from hand pump (India Mark) may be at increased risk of infection and disease from pathogenic bacteria. The level of contamination is expected to increase in the rainy season. Immediate attention is hence needed to monitor all public drinking water systems for total coliform and faecal coliform contaminations and to assess the pathogenic potential of microbial contaminants.