New paper: Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence
- Release of arsenic to deep groundwater in the Mekong Delta , Vietnam , linked to pumping-induced land subsidenceLaura E. Erban, Steven M. Gorelick, Howard A. Zebker, and Scott FendorfProceedings of the National Academy of Sciences. 110 (34): 13751-13756.AbstractDeep aquifers in South and Southeast Asia are increasingly exploited as presumed sources of pathogen- and arsenic-free water, although little is known of the processes that may compromise their long-term viability. We analyze a large area (>1,000 km2) of the Mekong Delta , Vietnam , in which arsenic is found pervasively in deep, Pliocene–Miocene-age aquifers, where nearly 900 wells at depths of 200–500 m are contaminated. There, intensive groundwater extraction is causing land subsidence of up to 3 cm/y as measured using satellite-based radar images from 2007 to 2010 and consistent with transient 3D aquifer simulations showing similar subsidence rates and total subsidence of up to 27 cm since 1988. We propose a previously unrecognized mechanism in which deep groundwater extraction is causing interbedded clays to compact and expel water containing dissolved arsenic or arsenic-mobilizing solutes (e.g., dissolved organic carbon and competing ions) to deep aquifers over decades. The implication for the broader Mekong Delta region, and potentially others like it across Asia , is that deep, untreated groundwater will not necessarily remain a safe source of drinking water.