Stormwater infiltration practices, namely infiltration trenches, are source control mechanisms that are implemented in urban developments with reduced natural permeable surfaces. Infiltration practices are designed to encourage infiltration of non-point source runoff into the ground as a means of water quality management and flood protection.
Conventionally, infiltration trenches are installed as storage reservoirs for urban runoff, which are comprised of an excavated trench that is backfilled with a coarse porous medium. The underlying subsoil acts as a filter to remove solid particles and associated pollutants from the fluid within the porous media, prior to discharging into the saturated zone. The limited research on the long-term performance of these systems has emphasized the role of physical filtration mechanisms within porous media filters to address ongoing concerns surrounding system failure.
A comprehensive methodology for characterizing the overall system performance of infiltration trenches was developed using a continuous macroscopic depth filtration model with respect to three different failure modes: clogging of porous material, overflow events, and groundwater contamination. Applying a probabilistic approach, this new framework combines theory from fixed-bed granular filtration of monodisperse suspensions and utilizes site specific filtration trench design, meteorological, and filtration modeling parameters.
Based on Monte Carlo simulation results using existing design criteria, stormwater infiltration facilities are shown to clog prior to the expected lifetime of 8 to 19 years and although adequate volumetric control is observed during the first several years of operation, clogging leads to early and frequent overflow events. A methodology for characterizing the mass loading of zinc and copper from the bottom of the infiltration trench was developed and shows that the mass loading of these pollutants is restricted by the gradual reduction in flow through the filter. Overall, with an improved design strategy, these infiltration facilities are not likely to operate properly after 10 years of implementation.Without proper maintenance of pre-treatment facilities and filter fabrics, earlier failure may be expected.