Field Evaluation of a Stormwater Bioretention Filtration System

A field evaluation of the Filterra® Stormwater Bioretention Filtration System was performed to: 1) determine removal efficiency information based on field data, which is inherently more variable than laboratory data, and 2) to compare the observed field efficiency with the efficiency determined in the laboratory. Inlet and outlet pollutant concentrations from a Standard 6' x 6' Filterra® System were monitored between October 19, 2004 and November 22, 2005. The pollutants of interest were Total Suspended Solids (TSS), Total Phosphorus (TP), Total Kjeldahl Nitrogen (TKN), and the heavy metals cadmium, copper, lead and zinc. Monitoring data were then evaluated to determine appropriate Efficiency Ratios. Raw data were first evaluated to determine if they were normally distributed. If so, the Efficiency Ratio was determined based on the Event Mean Concentrations of the influent and effluent samples. If the raw data were not normally distributed, the Efficiency Ratio was calculated using the Event Median Concentrations. Results show the following average efficiency ratios: TSS 85%; TP 55%; TKN 20%; Cu 16%, and Zn 50%. Statistical significance and seasonal variations of the removal efficiency were also examined.