The filtration models commonly used to describe colloid transport in porous media do not consider particle-particle contacts. In this work, near-neutrally buoyant microspheres visible to cone-beam x-ray were prepared to study the effects of particle-particle contacts. Packed column experiments were conducted under environmentally relevant conditions. Microsphere deposition at particle-particle contacts were determined using x-ray microtomography at various flow velocities in porous media of different particle sizes and particle shapes. Medial axis analysis was performed to allow exact characterization of the pore structures that provided quantitative basis to describe the difference in deposition at particle-particle contacts in different pore media. The impact of deposition at particle-particle contacts on colloid transport and fate are discussed. Different mechanisms (e.g. rolling upon collision with particle surfaces) and their contribution to overall deposition at particle-particle contacts were also discussed.

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