Study of groundwater contamination by radioactive brine: the Lake Karachai case

Major hydrodynamic and hydrogeochemical mechanisms governing subsurface transport of radioactive brine released from a waste-disposal site known as Lake Karachai are investigated on the basis of field and laboratory data analysis and numerical modeling. This study presents results regarding density-induced transport and implications of geochemical interactions. We applied a set of alternative models incorporating various conceptualizations of flow and mass-transport processes, using both sharp interface (Densflow) and fully miscible (Tough2 and Codesa3D) models for plume spreading simulation. The investigation focused on major factors controlling preferential flow paths of brine movement. Calibration of flow and transport models was based on hydrodynamic and geochemical data related to groundwater regime at the contaminated site, along with preliminary long-term predictions. Laboratory experiments concerning radio-strontium adsorption and diffusion into porous matrices informed our modeling of reactive component transport, highlighting the established relationship between adsorption distribution constants and NaNO3 content under laboratory conditions, which was incorporated into the transport code.