Site-specific characterisation of hydrogeological parameters for low-level solid radioactive waste disposal facility at Tarapur, India

Site-specific hydrogeological parameters are a prerequisite to investigate the migration of radionuclides in groundwater due to leaching from low-level solid radioactive waste disposal facility (SRWDF) site. The leaching event is a low probability event due to all the engineered safety features provided in SRWDF, but the impact assessment, even due to this low probability event of leaching is a regulatory requirement. The present study focuses on SRWDF located in Tarapur, India. Hydrogeological parameters such as radionuclide specific distribution coefficient ( K d ), hydraulic conductivity (HC) and porosity are estimated for a watershed area in and around the SRWDF. Values of HC and porosity for soil samples collected from the disposal site are found to be in the range 0.006–0.15 cm/s (average 0.059 cm/s) and 25.64–32.62% (average 29.19%), respectively. Average hydraulic gradient is found to be 0.007. Using the estimated values of hydraulic gradient, porosity and HC in Darcy’s law, groundwater velocity is calculated as 0.13–3.22 m/day. The distribution coefficient of caesium, the most prevalent radionuclide in low-level solid radioactive waste, is estimated to be ranging between 116.73 and 393.54 ml/g. Physical and chemical characteristics of soil like pH, electrical conductivity, organic matter content, moisture content, CaCO 3 content and effective cation exchange capacity (ECEC) are determined experimentally. Correlation among the estimated parameters is also studied. The K d of caesium is found to be positively correlated with porosity, ECEC, clay and silt fraction of the soil and negatively correlated to sand fraction. The site-specific parameters estimated in this study would be useful for carrying out the radiological impact assessment (RIA) of the SRWDF at Tarapur through the terrestrial pathway. Research Highlights The values of site-specific distribution coefficient ( K d ) of the soil samples range from 116.73 to 393.54 ml/g. Hydrogeological parameters like hydraulic conductivity, porosity, groundwater velocity have been estimated, and the values range from 0.006 to 0.15 cm/s, 25.64 to 32.62% (average 29.19%), 0.13 to 3.22 m/day, respectively. Physico-chemical properties like pH, electrical conductivity, organic matter content, moisture content, CaCO 3 content, and effective cation exchange capacity have been estimated. Correlation among estimated parameters is studied. Site-specific K d is found to be positively correlated with porosity, effective cation exchange capacity, clay and silt fraction of the soil and negatively correlated to sand fraction.