Treatment performance of gravel filter media: Implications for design and application of stormwater infiltration systems

Stormwater infiltration systems are widely used to address the flow and water quality impacts of urbanization. However, their pollutant removal performance is uncertain, with respect to varying filter depth, and over time. Seven simulation experiments were conducted on a laboratory-scale gravel infiltration system to test the pollutant removal under a range of water level regimes, including both constant and variable water levels. Gravel filters were found to be very effective for removal of sediment and heavy metals under all water level regimes, even as the system clogged over time. Despite the sediment particle size distribution being much smaller than the filter media pore size, sediment and its associated pollutants were effectively trapped in the top of the gravel filter, even when the water level was allowed to vary. A media depth of 0.5 m was found to achieve adequate pollutant removal. Breakthrough of pollutants may not be of concern, since physical clogging occurred first (thus determining the lifespan of the filter media). However, gravel filters were less effective at nutrient removal, particularly for dissolved nutrients.