Deep groundwater in coastal Bengal basin remains uncontaminated

Groundwater pumped from depths below 150 m in the coastal regions of the Bengal basin is thousands of years old, and generally secure from the contamination by salinity and arsenic found in shallow groundwater.

Such deep groundwater provides an invaluable source of drinking water for over 80 million people in coastal areas of Bangladesh and West Bengal, India. In the early 1990s the discovery of arsenic contamination in shallow groundwater led to various mitigation strategies, including the rapid development of deep groundwater resources. Nevertheless, serious concerns remained about the security of such resources from arsenic and saline pollution by shallow groundwater.

In a new study, published in Geophysical Research Letters on 19 July, a team of scientists from the UK, Bangladesh and India analysed chemical tracers of groundwater age, including radiocarbon and chlorofluorocarbons (CFCs), in samples of wells.

Dan Lapworth (British Geological Survey and UCL Geography) concludes:

“Results reveal no modern components in deep groundwater with ages ranging from 1,000 to 10,000 years. Traces of modern groundwater are, however, evident in a few pumping wells where they are associated with short-circuiting of vertical leakage within inadequately sealed boreholes.”

The implications for the coastal Bengal Basin may apply in other deltaic environments in south and Southeast Asia, where deep groundwater provides a critical supply of drinking water to tens of millions of people.

Professor Richard Taylor (UCL Geography) concludes:

“This study supports the case for continued but carefully monitored development of deep groundwater for domestic water supply in the coastal region of the Bengal basin. Monitoring needs to capture both short-circuiting of contaminated water through poorly constructed wells … over a timescale of years in pumped sites, and vertical leakage … which may take much longer (many decades).”

See

• Security of deep groundwater in the coastal Bengal Basin revealed by tracers