Construction of new bioretention basins at the intersection of Egerton Road and Herbert Road in Arlington is now complete. This green infrastructure project, built in partnership between Mystic River Watershed Association and the Town of Arlington, will help collect stormwater runoff and reduce pollutants discharged into Alewife Brook, thereby improving water quality. An added benefit–the plantings will beautify the streetscape and slow the traffic to make the road safer for pedestrians.
So what is stormwater runoff and why should we prevent it? Stormwater runoff is rainfall that falls on the roads, parking lots, rooftops and other paved surfaces that do not allow rain to soak into the ground. As the rain moves over the lawns and streets, it takes trash, oil, fertilizers—and anything else on these surfaces—directly into our streams and rivers without being treated. Untreated stormwater runoff is the leading cause of pollution in urban streams like Alewife Brook, and green infrastructure projects like bioretention basins are an effective manner to reduce pollution.
“Stormwater is the largest source of pollution in Arlington and will continue to impact our waterways until we begin to educate our residents of the problem and decide it is time to address it,” said Wayne Chouinard, Arlington Town Engineer. “We are very happy with the results here – the water infiltrates well and the aesthetics are great. We hope to implement this type of green and sustainable solutions for stormwater at other locations in Town.”
What is the impact of the Egerton improvement on stormwater? The designed improvements for Egerton and Herbert will divert runoff into new bioretention basins on each side of the street. This location was selected as there was significant runoff, presence of permeable soils and the intersection was wide providing opportunities to build out curbs. Beyond reducing stormwater runoff in this location, the project can serve as a model for additional green infrastructure improvements.
The sizing of these bioretention devices is designed to target the ‘first flush.’ First flush is the concentration of pollutants mobilized off of pavement and other surfaces at the beginning of a storm. Designing the structures to capture the first flush is a much more cost effective approach to reducing nutrients than designing to capture every drop of water in a storm. The basins are capped with native plants, and each year will treat and remove 20%-70% of a range of pollutants (see table below).
“These bioretention basins are really effective at removing the pollutants from the first flush of stormwater–keeping these nutrients out of our local waterway,” said Patrick Herron, Executive Director. “We are excited to continue building green infrastructure solutions in collaboration with the Town of Arlington.”
The project was designed by Hatch and built by the D’Ambrosia Construction. Beyond pollutants, vehicle passage was considered when planning this project, and the layout incorporates designs for improved vehicle movement around the sharp turn.
Wayne Chouinard, Arlington Town Engineer monitoring progress and performing field engineering.
One of the completed biorention basins filtering water during a rain storm.
This project was funded by the Environmental Protection Agency (EPA) through the Massachusetts Department of Environmental Protection (MassDEP).