Performance Monitoring of a High Flow Bioretention System in Washington for Basic and Phosphorus Treatment Under the Technology Assessment Protocol - Ecology

The City of Bellingham, Washington installed a Filterra Bioretention system in the Lake Whatcom watershed due to a phosphorus impairment and the inclusion of the lake on Ecology’s 303(d) list. The Filterra system is a flow-through stormwater bioretention treatment system manufactured by Americast, Inc. Results demonstrated significant reductions in total suspended solids (TSS) and phosphorus, and 98.9% total volume treatment. The TSS removal rate was 89% percent for influent TSS concentrations above 20 milligrams per liter (mg/L). The mean phosphorus removal rate was 73% percent for influent phosphorus concentration between 0.1 and 0.5 mg/L. In addition, discrete sampling demonstrated that flow rates in excess of 254 centimeters (100 inches) per hour well exceeded water quality requirements for both Ecology’s Basic and Phosphorus Treatment requirements. Based on this study, Washington State Department of Ecology granted General Use Level Designation through the Technology Assessment Protocol – Ecology for Basic and Phosphorus Treatment.