Over the past decade, the use of hydrogen peroxide (H2O2) for in situ remediation of contaminated groundwater and soil has become increasingly popular. In this remedial practice, concentrated solutions of hydrogen peroxide sodium persulfate are injected into groundwater or are added to soil. Upon contact with iron- and manganese-containing minerals, the oxidants are converted into hydroxyl radical and sulfate radical. The technology is simple, easy to deploy, and effective against many contaminants normally encountered at hazardous waste sites (e.g., benzene, trichloroethylene, or polycyclic aromatic hydrocarbons). The disadvantage of using hydrogen peroxide has a very short lifetime in the subsurface, meaning that it may be consumed before it reaches contaminated zones. Persulfate offers an attractive alternative, but its reactions with minerals and organic contaminants are not well understood. In this project, we are unraveling the complex chemistry of oxidants under conditions encountered in remediation systems.