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

Abstract

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. In this work, some results regarding density-induced transport and some implications regarding the experimental study of geochemical interactions are presented. A set of alternative models incorporating different ideas on conceptualization of flow and mass-transport processes has been applied. Both sharp interface (Densflow) and fully miscible (Tough2 and Codesa-3D) models were used for simulation of the plume spreading. The major factors controlling preferential flow paths of the brine movement were investigated. The calibration of flow/transport models was based on hydrodynamic and geochemical data on regime of groundwater within the contaminated site. Preliminary long-term predictions were performed. Data from laboratory experiments on the study of radio-strontium adsorption and diffusion into porous matrix were used for modeling of the reactive component transport. In particular, a relationship between the adsorption distribution constant and NaNO3 content established under laboratory conditions has been incorporated into the transport code.