Abstract: Storm water runoff is treated by passing the runoff through a bed of high quality leaf compost material to remove pollutants from the runoff prior to discharge into a water receiving system, such as a river, lake or storm water drainage system. Apparatus for treating storm water runoff is disclosed having at least one chamber for containing compost defined by a pair of opposed side walls and a pair of opposed end walls; an influent pathway for providing storm water to the compost chamber, a drain field positioned beneath the compost chamber for receiving storm water from the compost chamber, a layer of water permeable material interposed between the compost chamber and the drain field providing fluid communication between the compost chamber and the drain field while preventing the flow of compost material into the drain field, and a storm water outlet in fluid communication with the drain field for discharging treated storm water from the apparatus.