Soil colloids are biotic or abiotic nano- to micron-scale particles that have the potential to migrate through the subsurface and pose risks if they are pathogenic micro-organisms, or facilitate transport of typically immobile chemicals of emerging concern (CEC, e.g. antibiotics, hormones and other pharmaceuticals used in farm operations). Several fundamental physical-chemical colloidal interaction mechanisms have been identified at the pore-scale. However, implementation of colloid transport into practically usable soil water models suitable for risk-based predictions is still at its infancy because of the complexities involved. Key questions are whether current column and field-scale models accurately represent colloid transport mechanisms that fundamentally occur at the pore-scale, but also whether all pore-scale mechanisms are relevant. Can valid simplifications be imposed that effectively enhance a soil water's model practical applicability regarding colloid transport? The proposed UA-OSU collaboration will meet the research challenges by resolving colloidal particle distributions within idealized porous systems, using near real-time 3D computed x-ray microtomography. These measurements will subsequently be analyzed with pore-scale lattice-Boltzmann modeling in which we turn on or off the various colloidal interaction mechanisms and derive column-scale transport relations. Analysis of the model results will lead to practically useful relations for colloid transport in soil water models. We subsequently carry out a number of variably saturated column-scale studies for simplified media as well as real soils and quantify the appropriateness of a range of model approaches. The novel datasets and results will be shared with practitioners who develop or carry out risk analysis relevant for farm operations.