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Annapolis Business Park

Anne Arundel County, Maryland, United States


Bay Engineering 


June 2015

A small commercial flex-office development in Anne Arudel County, MD, was built in 2003. Surface bioretention facilities were constructed to collect stormwater runoff from impervious surfaces and provide water-quality control. Despite ongoing maintenance, by 2015, the largest bioretention system had begun to demonstrate several failure modes. These failures resulted in reduction of aesthetic quality and would have required extensive rebuilding of the facilities, at a large expense, to correct the appearance and restore the water quality function.

The consulting firm, Bay Engineering, proposed an innovative solution to repairing and replacing the bioretention unit. Bay Engineering chose Filterra high-flow bioretention systems to provide water quality control. The Filterra technology is a high-flow bioretention system used to directly collect and filter Stormwater runoff from pavement, building rooftops, and other pollution-generating impervious surfaces. It consists of a proprietary filter media placed in a prefabricated tank and planted with vegetation. Runoff is directed into the tank, to be quickly and completely discharged through an exit pipe at the bottom of the unit as contaminants are captured. This approach also allowed the existing bioretention facility to be abandoned and replaced with more traditional landscaping.

In most applications the Filterra unit is simply placed as an opening in the curb and gutter and located at the appropriate collection point in terms of specific area of drainage to the facility. The discharge from the Filterra exists via an integral underdrain pipe, and bypass flows enter the existing riser overflow from the original bioretention facility.

Speed and cost control were of the highest priority in terms of installing the two Filterra units. Installing the two Filterra units was quick and easy. Being completely prefabricated, including the internal piping and filter media, the units were simply trucked to the site and offloaded into place like any standard inlet. Filterra has cost-effective installation and maintenance requirements. The entire process for both units was completed in a few hours. Once the final paving and site stabilization took place, a crew from the supplier of the Filterra systems performed the “activation” of each facility, which included planting the selected vegetation, placing the 3-inch mulch layer and rock cobble scour protection. Grass and trees were planted as landscaping inside the curbed area. A clean, pleasing look was achieved successfully. 

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