DELTAIC PROCESS CONTROL ON SPATIAL HETEROGENEITY OF ARSENIC IN GROUNDWATER: KANDAL PROVINCE, CAMBODIA

Arsenic contamination in the aquifers of the Mekong River Delta in Cambodia is spatially variable and poses a significant public health risk to the population as new wells continued to be drilled. Understanding the connection between surficial geologic characteristics and high arsenic groundwater concentrations is an essential need for providing safe drinking water wells to the people of Cambodia. Our work in the Kandal Province of Cambodia demonstrates a link between deltaic processes and arsenic contamination of groundwater. We examined two transects where arsenic concentrations range from below the WHO standard of 10 ppb to upwards of 1 ppm. We conducted well sampling, shallow coring (2-5 m), and deep drilling (40m) to examine the link between dissolved arsenic concentrations and near surface sedimentary structures. In addition, Research Development International Cambodia (RDIC) provided us with a large GIS database of wells. Using Shuttle Radar Topography Mission data in conjunction with Landsat imagery, we were able to identify areas of recent deposition including point bar sequences and recent channel avulsions. When our well data and the database provided by RDIC were overlaid, it became clear that areas of recent deposition are at a much higher risk of arsenic contamination. The increase in dissolved arsenic is likely due to the recent input of both arsenic bearing minerals, as well as organic matter, which has been demonstrated to be important in the mobilization of arsenic.