Capitol Highway is a major driving route in Portland, serving local residents as well as retail outlets located at the Hillsdale Shopping Center. Street improvements were planned for various locations along Capitol Highway starting in 2005. Several existing catch basins discharged directly to local creeks and waterways. A solution was needed to capture and treat a variety of stormwater pollutants conveyed from street runoff to these local waterways. Reducing Total Suspended Solids ( TSS) was important.
The City of Portland Bureau of Environmental Services (BES) was tasked with identifying appropriate runoff control measures to treat runoff from newly improved roadway locations without impacting existing retail business owners and local residents. In addition, BES was tasked with reducing and preventing major pollutants of concern from entering local waterways, such as TSS, Oil and Grease, Trash, Phosphorus, and Metals.
After reviewing several stormwater treatment options, BES staff chose the Filterra Biofiltration System as the solution to treat street runoff at two locations where significant concentrations of pollutants could be captured and treated. Filterra harness the power of nature to capture, cycle and immobilize stormwater pollutants to treat urban runoff. The combination of landscape vegetation and a specially designed filter media allows metals, nutrients and total suspended solids (TSS) to be removed naturally.
Filterra was also chosen due to its compact design and aesthetic features, preferred over larger, more intrusive stormwater treatment systems. Filterra was able to meet the challenge of a very shallow stormwater system by using modified depth units.
Two modified 8x4 Filterra units were installed on opposite sides of Capitol Highway. Local plants such as Heavenly Bamboo were installed to complement existing landscaping and accommodate line of sight traffic safety regulations. Decorative tree grates were also used to match existing street tree grates and enhance appearance.