Advanced oxidation treatment processes involve powerful and indiscriminate radical intermediates, including hydroxyl radicals (•OH) and sulfate radicals (SO4-•). Inefficiency in radical-driven treatment systems involves scavenging reactions where radicals react with non-target species in water and solids. Radical scavenging studies have been focused on soluble scavengers in the water and have not assessed radical scavenging by solids which are also present in oxidation treatment systems. The objective of this study was to quantify radical scavenging by solid surfaces. •OH were produced in iron (Fe)- and UV-activated hydrogen peroxide (Fe-AHP, UV-AHP) systems where the loss of rhodamine B (RhB) dye served as an indicator of •OH activity. The basis used to estimate the •OH surface scavenging rate constant (k≡S) were comparisons of treatment results between simple solids-free oxidation systems and more complex systems containing mineral solids. The solids-free system was based on Fe-AHP and UV-AHP reactions; the solids-amended systems were identical but contained different mineral species. Therefore, differences in the loss of RhB were attributed to •OH scavenging by the solid surfaces in the Fe-AHP and UV-AHP treatment systems. Alumina (Al₂O₃), silica (SiO₂), and montmorillonite (Al₂H₂O₁₂Si₄) (MMT) are solid minerals found in soil and aquifers. These minerals were used in this study to assess the solid surface scavenging rate constants. Preliminary results in the Fe-AHP system indicated that k≡S for silica (2.85×10⁶ 1/m²×s) was not statistically distinguishable from alumina (3.92×10⁶ 1/m²×s). k≡S values in the UV-AHP system for silica (4.50×10⁶ 1/m2×s) and alumina (7.45×106 1/m2×s) were greater than estimates in the Fe-AHP system and may be due to pH. k≡S,MMT (≤ 4.22×10⁵ 1/m²×s) was much less than k≡S for silica and alumina indicating k≡S is mineral-specific. A critical analysis suggests that radical scavenging by solid surfaces in aquifer systems is orders of magnitude greater than scavengers in the water.