Transport studies were conducted to assess ocean disposal of soil contaminated with low-level natural radioisotopes. The experimental approach involved characterization of the soil for parameters affecting transport and fate of radionuclides. Radioactivity was associated with discrete soil particles up to 6,000 micrometers. Gross and most individual isotope and element activities were more concentrated on smaller particles. The median size based on gross radio-activity was 125 micrometers, while the median size based on dry mass was 350 micrometers. Particle-setting velocities measured in a 1 m settling column ranged up to 8.2 cm/s (median 2.1 cm/s). Large-scale mixed water column experiments (5 m) confirmed that settling would be the dominant verticle transport mechanism for the soil particles. Experimental results were used to calibrate a convective-diffusive transport model, which was applied to a hypothetical ocean disposal site in 4,000 m of water. The model indicated that 95 percent of the soil and associated radionuclides would impact the bottom sediment within five days and up to 40 km from the disposal point, along the mean current flow. (Copyright (c) 1992 ASCE.)