Persulfate-based in situ chemical oxidation (ISCO) involves the injection of persulfate (S2O82-) into the subsurface to remediate contaminated groundwater and soils. Although S2O82- does not react with contaminants to an appreciable extent, it can be activated into stronger oxidants (e.g., SO4• and •OH) by heat, alkaline solutions, dissolved iron and iron-containing minerals. The objective of the research described in this thesis is to explore the influence of temperature and background solutes on contaminant transformation by heat- and mineral-activated S2O82-. Through the transformation of benzoic acid (a model organic compound) and chlorendic acid (a flame retardant), it was discovered that temperature affects not only the rate of contaminant transformation but also the transformation pathway and distribution of byproducts. Solution pH, alkalinity, and chloride also influence the rates of persulfate activation and contaminant degradation. These novel understandings may help improve the design and operation of S2O82--based remedial systems.