TOUGHREACT V1.0 modeling was used to reproduce laboratory tests involving sandstone samples collected from a deep radionuclide repository site at the Siberia Chemical Plant, Seversk, Russia. Laboratory tests included injection of alkaline fluids into sandstone samples at 70°C. Some minerals were constrained in the model to precipitate or dissolve, according to laboratory test results. Modeling results were compared with observed test data (mineral phase changes, transient concentration data at the outlet of a sample column). Reasonable agreement was obtained between calculated and measured mineral phases (Na-smectite and kaolinite precipitation, quartz, microcline, chlorite, and muscovite dissolution). After a cation exchange option was used in the model, the most abundant secondary mineral generated was dawsonite, which corresponds to sodium carbonates observed in the sample after an injection test. Time-dependent chemical concentrations (transient chemical concentration data) at the outlet of the sample column qualitatively matched the data observed.