Long-term radiostrontium interactions and transport through sediment.

Radioactive strontium is one of the most common radiological contaminants in groundwater and soil. Objectives of this study were to (1) evaluate Sr transport through an 11-year-long field lysimeter study and (2) quantify secondary aging effects between Sr and sediment that may need to be considered for long-term transport modeling. Batch sorption/desorption tests were conducted with (85)Sr, (88)Sr, and (90)Sr using a sediment recovered from a field lysimeter containing a glass pellet amended with high-level nuclear waste for 24 years. Sr was largely reversibly and linearly sorbed. (85)Sr sorption coefficients (Kd, concentration ratios of solids/liquids) after a 23-day contact period were about the same as the (90)Sr desorption Kd values after a 24-year contact period: sorption Kd = 32.1 ± 3.62 mL g(-1) and desorption Kd = 43.1 ± 11.4 mL g(-1). Numerical modeling of the lysimeter (90)Sr depth profile indicated that a Kd value of 32 mL g(-1) fit the data best. The Kd construct captured most of the data trends above and below the source term, except for immediately below the source where the model clearly overestimated Sr mobility. (90)Sr desorption tests suggested that the overestimated mobility may be attributed to a second, slower sorption reaction that occurs over a course of months to decades.