Age and provenance of groundwater in a shallow arsenic-affected aquifer in the lower Mekong Basin, Kandal Province, Cambodia

Arsenic (As) contamination of groundwaters in South/Southeast Asia is a major threat to public health. Under-standing the source and age of the groundwaters is critically important to understanding the controls on As mobilization in these aq-uifers. Utilizing a suite of isotopic tracers, we have determined various site-specific recharge mechanisms, and estimated recharge source contributions. Tritium-helium age determinations show that the groundwater in this area is modern, indicating relatively fast recharge even in the absence of large-scale groundwater abstraction. The relationship between apparent age and depth indicates a strong vertical control on hydrology, which may influence preferential flow paths and ultimately As release in these aquifers.