Groundwater Vulnerability in the Megacity of Chennai, India

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Groundwater plays a major role for municipal water-supply and for private domestic and industrial use in urban areas of developing and emerging nations. Roughly one billion inhabitants from Asia and 150 million from Latin America depend on the precious resource. According to estimates, 50 % of India’s total urban population uses groundwater for domestic purposes.

Water supply systems of rapidly growing urban areas in emerging and developing countries are mostly overwhelmed by the rising water demand, which led to drastic extension of private well development over the last decades. In the study area of Chennai City, where population increased from 1.75 million to 4.7 million over the last 50 years, 420,000 wells were estimated to be abstracting water from the groundwater reservoir in 2005, whereas this number grows continuously. This reflects the great number of inhabitants being dependent on the groundwater as a safe source of water supply.

In general, groundwater is chosen over surface water for drinking purposes, since often it is covered by rock layers of low permeability, which eliminate or at least attenuate introduced contaminants by physical, chemical or biological processes. However, in alluvial areas like Chennai City, having a shallow aquifer and being located in an area of a river system, vulnerability to contamination is enhanced as pollutants can access the aquifer easier.

These mega-urbaun areas with its high and dense population implicate a large variety and intensity of anthropogenic impacts. Many of the associated processes and structures, like sewer disposal, urban runoff, landfills, storage tanks, etc. pose hazards to groundwater contamination as the pollutants can be transported to the aquifer by infiltrating water. Actually, a study revealed that 60 % of Chennai City’s groundwater is not suitable for drinking purpose. For this, groundwater vulnerability and risk assessment methods are established as management tools providing valuable information for planning prevention of (further) groundwater quality deterioration. However, in India many chemical groundwater studies have been conducted, whereas groundwater vulnerability studies are rather rare. Therefore, within the framework of this study it was aimed at the development of a vulnerability map and a risk map for the study area.