Megacity pumping and preferential flow threaten groundwater quality.

Area of Science:

• Hydrogeology
• Environmental Science
• Geology

Background:

• Megacities rely on complex aquifers, often over-exploited and vulnerable to contamination.
• Groundwater exploitation in Dhaka has led to significant water level declines, impacting surrounding areas.

Purpose of the Study:

• To illustrate how aquifer heterogeneity and groundwater exploitation interact to threaten regional groundwater resources.
• To evaluate the vulnerability of deep, low-arsenic groundwater in Dhaka using advanced modeling techniques.

Main Methods:

• Utilized groundwater models incorporating geostatistical simulations of aquifer heterogeneity.
• Analyzed large-scale drawdown caused by groundwater pumping in Dhaka.
• Simulated preferential flow paths in fluvio-deltaic aquifer stratigraphy.

Main Results:

• Groundwater pumping in Dhaka causes drawdown extending to areas with arsenic-contaminated shallow groundwater.
• Simulations indicate preferential flow can contaminate deep groundwater ( >150m) within a decade.
• Contamination spread is nearly a century faster than predicted by homogeneous models.

Conclusions:

• Aquifer heterogeneity significantly accelerates groundwater contamination spread, posing a regional threat.
• Complex vulnerability, extending beyond city limits, challenges sustainable megacity groundwater management.
• Simplified models and standard measurements are insufficient for predicting critical contamination pathways.