Evaluation and optimization of engineered media amendments for contaminant removal in stormwater runoff filtration systems

Various contaminants exist in stormwater runoff, including nutrients, metals, pathogens and organic compounds. Filtration systems built with engineered media are used to manage stormwater runoff, but NCDOT’s current standard filtration media mix specification does not take the optimization of contaminant removal into consideration. To better meet regulatory compliance, it is beneficial for NCDOT to explore different material selections and mixing options to build filtration systems with better capacity of contaminant removal, while maintaining desirable support for plant growth and water infiltration. The objective of this project is to evaluate a variety of affordable media materials that can remove multiple contaminants simultaneously and maintain high performance in runoff filtration measures under various natural conditions. Up to 25 different filter materials identified from an extensive literature review will be screened to select the ones with the highest contaminant removal rate and capability. These materials will be tested with different mixing strategies to identify media mixtures that allow stormwater infiltration at a reasonable rate and have enough organic matter and water retention to support plant growth. The selected media mixtures will be tested in bench-scale columns for contaminant removal performance under various natural conditions, such as alternating concentrations, antecedent drought period, low temperature and presence of deicing agents. The best performing media mixture(s) will be recommended for future field tests, then be applied in NCDOT stormwater management systems. Information gained through this project will enable NCDOT to improve the performance of its stormwater filtration systems to effectively remove contaminants including nutrients, metals, pathogens, and organic contaminants. Such improvement will help NCDOT comply with the NPDES permit, state nutrient load reduction rules, future dissolved metals TMDLs, and potential regulations on organic contaminants in future.