Assessment of environmental impact of dredged material disposal in deep ocean water calls for predictions of water column concentration, exposure time as well as the impacted area of the bottom (footprint). Predictions based on vertical settling and horizontal advection of single particles ignore the effects of bulk properties of the disposed material, vertical and horizontal diffusion, and material dilution due to entrainment of ambient water during descent. The paper highlights the spatial and temporal changes in the particle exposure fields for the water column and bottom at a hypothetical deep-ocean disposal site within the two-day period following instantaneous release of barged dredged material. The model incorporates a proposed mechanism for differential internal mixing for various size classes, and a mechanistic approach to calculating detachment of material from the main cloud.