The hydroperoxides promote decomposition of chlorinate olefins by forming a secondary liquid-phase reactive interface to the contaminants such as volatile chlorinate olefins and volatile hydrocarbons including chlorinated hydrocarbons, chlorinated olefins such as tetrachloroethylene, trichloroethylene, cis 1,2-dichloroethane and vinyl chloride and other compounds e.g., aromatic ring compounds, pro