Performance Assessment of Underground Stormwater Treatment Devices

Proprietary underground devices are often used for stormwater treatment in urban areas due to tight space constraints. Most of these devices are designed to remove suspended solids from stormwater runoff prior to discharge into lakes, rivers, and streams via the physical separation process of sedimentation. Data on the performance of installed devices are limited and existing data are questionable because of the problems associated with assessment via monitoring. The objectives of this research were to: (1) investigate the feasibility and practicality of field testing for assessing the performance of underground devices, (2) evaluate the effects of sediment size and stormwater flow rate on the performance of four devices from different manufacturers, and (3) develop a universal approach for predicting the performance of a device for any given application. For the field testing, a controlled and reproducible synthetic storm event containing sediment of a fixed size distribution and concentration is fed to a pre-cleaned device. The captured sediment is then removed, dried, sieved, and weighed. Universal performance models were developed from the results of this work and parallel laboratory testing of two other full-scale devices using the Peclet number, which explains two major processes in performance: (1) advection or settling of particles and (2) turbulent diffusion or resuspension of particles. The universal performance models will improve the selection and sizing of these devices and their overall performance after installation.