The deep groundwater aquifers around Dhaka, Bangladesh, may become contaminated with arsenic within a decade, according to a study published in Nature Communications this week. A new model demonstrates how contaminated shallow water may flow into groundwater sources in cities and surrounding areas.
Many of the world’s largest cities are reliant on groundwater from aquifers that are over-exploited and threatened by contamination. However, the effect of over-pumping of water in cities on groundwater quality in the regions outside the city and surrounding areas is poorly understood. This is largely due to the use of simplified aquifer models in examining how groundwater flows. Natural aquifers are made up of layers of rocks which naturally enclose water; the composition of these layers may affect the flow of water and distribute contaminants.
Holly Michael and colleagues examine how differences between aquifers and over-exploitation of groundwater affect regional ground resources by developing a complex aquifer model based on regional data from Dhaka, Bangladesh. They show that over-pumping of water in the city has lowered groundwater levels regionally (around Dhaka) and is encouraging the downward flow of contaminated shallow waters into the deeper part of the aquifer. The model predicts that preferential groundwater flow from the shallow aquifers with contaminated waters containing arsenic could contaminate deep (>150 m) aquifers in the surrounding region within a decade as opposed to a century as previously thought.
The study demonstrates the importance of using complex aquifer models in assessing groundwater flow in cities. The authors note that effective remediation measures and proper management of aquifer exploitation may mitigate against future arsenic contamination of groundwater in the region.