Disclosed are a process and a system for treating contaminated soil. The process includes introducing a contaminated soil to an agitation unit. Ozone is supplied to the agitation unit thereby forming a soil-gas mixture, and the soil-gas mixture is agitated for sufficient time for the ozone to contact the contaminants thereby forming an ozone-treated soil and a residual gas-particulates mixture. The ozone-treated soil and the residual gas-particulates mixture are removed from the agitation unit. If necessary, remaining ozone is then flushed from the soil. The process occurs under negative pressure to prevent ozone from being released to the atmosphere.