Arsenate breakthrough in column studies with a porous granular ferric hydroxide (GFH) was investigated in model waters and groundwaters. In this study, the use of rapid small-scale column tests (RSSCTs) initially designed for simulating the removal of organic compounds by granular activated carbon was extended for arsenate adsorption onto GFH. Adsorption kinetic studies and a comparison of laboratory RSSCT performance versus pilot-scale performance suggests that proportional diffusivity (PD) RSSCT scaling approaches are more valid than constant diffusivity (CD) approaches for arsenate onto GFH. Adsorption densities from column tests ( qcolumn ) were calculated at the point in the breakthrough curve when arsenate equaled 10 μg/L in the column effluent. For a simulated 2.5 min empty-bed contact time (EBCT), a model water (pH=8.6) had qcolumn values of 0.99 to 1.5 mgAs/gGFH versus 0.02 to 0.28 mgAs/gGFH with a comparable pH and EBCT in a natural groundwater. The differences were attributed to the silica, pho...