An iron containing bioreactor for treating explosive compounds and other organics in contaminated surface water is disclosed. The bioreactor can be located either on-ground or in-ground at a location across which contaminated surface water flows. In one configuration the reactor is made up of (i) indigenous microbes, (ii) acetate, (iii) a low density iron-containing bed, and contains anaerobic zones in at least one portion of the flowpath. The reactor reduces the concentration of explosive compounds to below 10 ppb and also maintains this explosive compound reduction level for a period of at least one year without replenishing the microbes or iron.