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.