Clay layers and distant pumping trigger arsenic contamination in Bangladesh groundwater

To avoid arsenic contamination, many Bangladeshi households access water via private wells drilled to 300 feet or less, beneath impermeable clay layers. Such clay layers have been thought to protect groundwater in the underlying aquifers from the downward flow of contaminants. However, a new study suggests that such clay layers do not always protect against arsenic, and could even be a source of contamination in some wells.