Do changes in hydrology of the Mekong River affect trace element concentrations in alluvial aquifers?

Along major rivers in South and Southeast Asia, groundwater has been found to contain arsenic in concentrations that pose health risks to tens of millions of inhabitants. Anoxic conditions appear to trigger arsenic leaching from sediments, and intensive pumping for irrigation can facilitate the spread of arsenic in groundwater. Most research has focused on the occurrence of arsenic beneath the deltas of the Ganges, Brahmaputra, Mekong, and Red rivers. Less attention has been paid to arsenic beneath upstream floodplains. With colleagues at Khon Kaen University (Thailand) and Virginia Tech, I propose to collect preliminary data for a study of how seasonal variability and anthropogenic changes in Mekong River hydrology could affect concentrations of arsenic and other trace elements in upstream alluvial aquifers. I will travel to northeast Thailand in mid-November 2013 and May-June 2014 (for 2 weeks each trip) to collect water samples from ~ 15 wells and from the river at three sites in Nakhon Phanom province. If wells are open, we will determine depth to the water table using an electric water-level indicator, and we will install logging transducers in two wells to record water levels at 15-minute intervals. Water samples will be analyzed in the field and in laboratories at UK. We will use geologic and topographic maps of the area with drillers' logs from wells and borings, if available, to develop a simple framework model of the alluvial aquifer in a geographic information system (GIS). We will use measurements of river stage and water levels in wells to infer directions of groundwater flow and simulate flow during dry and wet seasons. Spatial distributions of hydrochemical parameters will be mapped in the GIS. We will interpret controls on groundwater chemistry using graphical approaches and statistical techniques. We will use geochemical modeling software to test inferences of mixing and reactions within the aquifer by modeling mass transfer between sampling points. Based on the findings from this study, we would submit a regular proposal to the NSF Hydrologic Sciences Program in June 2015, which would entail a 3-year, more spatially intensive study of groundwater flow and chemistry in the alluvial aquifer.