Flow and transport modeling of liquid radioactive waste injection using data from the Siberian Chemical Plant Injection Site

The focus of our investigation was simulating pre-injection and post-injection subsurface conditions at the waste disposal site of liquid radioactive wastes at the Siberian Chemical Complex (SCC). The main environmental and human safety concern posed by this site is related to the potential radionuclide discharge into the nearby Tom River and into the existing public-water-supply well fields located 10–13 km away. Even though (within the site) the two lower injection aquifers are isolated from the upper aquifers by a relatively continuous aquitard, in terms of regional flow they represent one hydrogeologic system that is affected by injection as well as by groundwater withdrawal from the upper aquifers and groundwater discharge into the river. Groundwater flow and transport models were developed to simulate regional flow and waste migration. Even after 1,000 years, none of the simulations indicated that there is any serious potential of high-concentration contamination of water supply wells and the discharge zone. In that time frame, simulation indicated a potential for upward movement of some amounts of contaminants through the heterogeneous sandy-clay aquitard. That is why a conceptual model incorporating heterogeneity of the clay aquitard with the possibility of preferential flow via sandy windows needs to be developed. Additional field characterization of the aquitard properties should be performed along the potential contaminant migration pathways that lead to the groundwater discharge zone.