Groundwater Arsenic Contamination and Availability of Safe Water for Drinking in Middle Ganga Plain in India

Abstract

The Middle Ganga Plain (MGP) is the second largest arsenic (As) contaminated groundwater zone in south-east Asia after the Bengal Delta Plain. About 90% of the total population in the MGP depends on shallow aquifer based groundwater supply for their drinking and irrigation need. More than ten million people in the alluvial belt of MGP are exposed to elevated levels of As (more than the limit set by Bureau of Indian Standards (BIS) 2012 drinking limit of 50 μgL−1) in their drinking water. In the light of synthesis of groundwater As distribution in MGP, the availability of safe sources of water for drinking have been analyzed. The current study delineates two aquifer systems in MGP through the study of borehole lithologs (n = 27). The first aquifer system persists from below the top aquitard to up to ~87–126 m below ground level (bgl), while the second aquifer system starts at various depths ranging from ~116 to 139 m bgl and continues up to the depth of ~250 m bgl. Suitability of the deeper (second) aquifer system for As free drinking water has been assessed through analysis of pumping test data. The Newer Alluvium comprising the top aquitard and the upper 15–20 m slice of the first aquifer system hosts the contaminated aquifers for the depth of ~50 m below ground surface. The Pleistocene aquifers (the bottom three-fourth part of the first aquifer system and the entire second aquifer system) are low in groundwater As. The second aquifer system, existing in confined condition, can be used for community water supply through the installation of deep tube wells with a regulated draft. Community hand pumps in the depth range of 5–15 m below ground can be constructed in the sandy areas in the floodplain for drinking need of the local people. Large diameter dug wells can also be constructed to tap the replenished dynamic groundwater, which normally remains oxic and low in As.