Wan and Tokunaga's (2005) comments give us an opportunity to relate our recent findings to our initial paper (Crist et al., 2004). The main purpose of our first paper (Crist et al., 2004) was “to describe a novel pore-scale visualization technique” and “help reconcile some inconsistencies among earlier studies,” in particular by demonstrating the need to refine the widely held assumption used to explain observed breakthrough curves, namely that colloids are retained at air–water (AW) interfaces in unsaturated media. Contrary to the statement of Wan and Tokunaga (2005), attempting “to provide pore-scale insights into mechanisms...

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