Selecting Bioretention Media to Treat Stormwater to Meet Very Low Numeric Permit Limits for Emerging Contaminants

Bioretention has been promoted for stormwater management to reduce the loads of solids, heavy metals, and nutrients to surface waters. Many researchers have reported the treatment effectiveness of bioretention for these pollutants, typically as percent removals. No studies, however, have evaluated the ability of carefully-selected bioretention media to treat pollutants to meet specific numeric effluent limits for certain organic toxicants and radionuclides. This project focused on the selection of a bioretention media mixture from pre-selected components – a granular activated carbon (GAC), two zeolites, two sands, and a peat moss – to treat numerous constituents, including dioxins, mercury, perchlorate, oil and grease, and radioactive components. Two series of column tests, one focusing on long-term pollutant removal behavior and the other on the effect of depth/contact time on removal, showed that a media containing a virgin coconut-hull granular activated carbon (GAC) could treat these constituents to the very low permit limits under a wide range of likely site conditions.