Activated persulfate (PS) is a common method used to generate sulfate radicals (SO4•-), a powerful oxidant capable of degrading a broad array of environmental contaminants. The reaction of SO4•- with nontarget species (i.e., scavenging) contributes significantly to treatment inefficiency. Radical scavenging in this manner has been quantified for nontarget chemical species in the aqueous phase but has never been quantified for solid phase media. Kinetic analysis and laboratory methods were developed to quantify the SO4•- scavenging rate constant (k≡S) for alumina, a naturally occurring mineral in soil and aquifer materials. SO4•- were generated in UV and thermally activated persulfate (UV-APS, T-APS) batch systems, and the loss of rhodamine B (RhB) served as an indicator of SO4•- activity. k≡S for alumina was 2.42 × 104 and 2.03 × 104 m-2 s-1 for UV-APS and T-APS oxidative treatment systems, respectively. At [alumina] >5 g L-1, the reaction of SO4•- with solid phase media increased over the aqueous phase reactions with RhB and aqueous scavengers. SO4•- scavenging by solid surfaces was orders of magnitude greater than the reaction with the target compound and scavengers in the aqueous phase, underscoring the significant role of solid surfaces in scavenging SO4•-.