Changes in River-Aquifer Exchange Induced by Groundwater Pumping, and Their Effect on Arsenic Contamination in the Red River Delta, Vietnam

At least two billion people in the world, including an estimated 40 million in the United States, use domestic wells for potable drinking water. The quality of this groundwater can have a large impact on human health, yet we know little about how extensive groundwater pumping, primarily for agricultural and urban water supplies, impacts groundwater quality. This project studies the effect of groundwater pumping on the sustainability of water quality in aquifer systems affected by arsenic, a naturally occurring carcinogen. In South and Southeast Asia, extensive pumping has influenced the spatial extent and concentration of arsenic contamination in groundwater. This field-based project examines how hydrological changes impact the biogeochemistry of aquifers and, subsequently, the arsenic levels in groundwater. Specifically, this project investigates how urban water use in Vietnam is changing aquifer hydrology and river-groundwater interactions that mobilize arsenic. The results of this study will provide generalizable insights leading to more effective management of groundwater resources impacted by naturally occurring contaminants in other settings. The research activities will involve undergraduate and graduate students from Columbia University, Barnard College, and Massachusetts Institute of Technology and engage underprivileged high school students in New York City.

In northern Vietnam, the reversal of groundwater flow along the western bank of the Red River has been induced by groundwater pumping for the city of Hanoi. This flow reversal draws high-As groundwater from a gray Holocene aquifer into an adjacent low arsenic, orange Pleistocene aquifer, and the orange Pleistocene sands are turning gray as iron oxyhydroxides are reduced by advected dissolved organic carbon (DOC). This project examines how pumping influences the source and composition of aquifer recharge at the riverbank, where labile arsenic is available and high levels of DOC are released by freshly deposited sediments. To quantify the impact of urban pumping, the hydrology and biogeochemistry of the western bank aquifers of the Red River influenced by pumping are compared to the eastern bank aquifers that are insulated from the effects of pumping. This controlled study quantifies the extent to which human perturbations have affected the chemical composition of groundwater and aquifer sediments.