In 2012, the City of Fremont installed two Tree Well Filters (TWFs) on Osgood Road to improve city aesthetics and treat urban runoff. Two distinct TWFs configurations were designed and built side-by-side so that they could be tested against one another for efficacy of pollutant removal and maintenance costs.

The San Francisco Estuary Institute monitored both Tree Well Filters over a series of storms in order to:

• Qualitatively assess whether the TWFs were treating stormwater runoff at rainfall rates up to 0.2 in/hr, estimated to be equivalent to 80% of the total annual rainfall;
• Quantitatively assess whether the TWFs reduced pollutant concentrations in water entering the storm drain system;
• Compare the effluent concentrations exiting the TWFs to findings from other studies of Low Impact Development performance.

Subsurface Loaded Tree Well Filter