ARSENIC CONTAMINATION IN THE FLOOD PLAIN AQUIFER OF THE MEKONG DELTA, CAMBODIA

We are characterizing the spatial and temporal variation in dissolved arsenic within groundwater of the Mekong River in the Kandal Province of Cambodia, where sediments derived from the Himalayas have lead to arsenic contamination of local aquifers similar to the situation in Bangladesh. Temporal variation in surface and groundwater levels along with the geochemistry of the aquifer, and perceived inputs, are being defined in order to assess means by which arsenic is entering the aquifer. Our findings reveal that arsenic concentrations vary spatially but are high (exceeding 100 ug/L) throughout the aquifer, and groundwater levels along with recharge gradients are dominated by seasonal fluctuation of the Mekong River. The arsenic-containing groundwater is reduced, as evidenced by low Eh and dissolved oxygen and elevated ferrous iron; additionally, in some cases dissolved sulfide is detected. Our geochemical observations are similar to the conditions reported for Ganges-Brahmaputra Delta in Bangladesh, while the hydrology is unique to the local area and represents a well constrained system.