Arsenic-contaminated groundwater in Holocene sediments from parts of Middle Ganga Plain, Uttar Pradesh, India.

Abstract

Groundwater survey in Ghazipur, Varanasi and Mirzapur districts of Uttar Pradesh (UP) in Middle Ganga Plain shows that people in these areas are drinking arsenic-contaminated groundwater. Moreover, 60% of tubewells have arsenic concentration above the WHO guideline value of 10 μg/l and 20% is above 50 μg/l, the Indian standards for arsenic in drinking water. Depth information of 68 tubewells indicates that 85% tubewells are from shallow aquifers (10-42 m). Most of the arsenic-contaminated tubewells have a depth of 25-45 m. The iron content in tubewells varies from 0.1 to as much as 7.6 mg/l and 83% tubewells have iron more than 1 mg/l. The correlation between dissolved arsenic and iron in tubewell waters is positive. Arsenic-contaminated tubewells in UP are located in Holocene Newer Alluvium entrenched channels and floodplains which are characterized by grey to black coloured organic-rich argillaceous sediments. Saidpur, Varanasi, Chunar and Mirzapur towns have arsenic-safe groundwater because their positions on the Pleistocene Older Alluvium upland surfaces are made up of oxidized yellowish-brown coloured sediments with calcareous and ferrugenous concretions. However, deeper tubewells (> 60 m) in Pleistocene Older Alluvium aquifers in arsenic-contaminated areas would be a better option for arsenic-safe groundwater. Dugwells would be another source for arsenic-safe groundwater in arsenic-affected areas. The arsenic in groundwater in Middle Ganga Plain, UP is getting released from associated sediments which were mainly deposited from the Himalayan hill ranges and minor inputs from peninsular India.