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By October 19, 2019 No Comments

Today Mayor Martin J. Walsh was joined by the Massachusetts Department of Environmental Protection (MassDEP), the Charles River Watershed Association (CRWA), and Boston Groundwater Trust (BGwT) for the ribbon cutting of Boston’s newest green, porous alley in the South End. The reconstructed alleyway will be a living laboratory, helping reduce pollution from stormwater runoff while addressing groundwater issues in the neighborhood.

“Stormwater pollution and groundwater do not understand our municipal or property boundaries, and we must work together to address these challenges,” said Mayor Martin J. Walsh. “I applaud the Charles River Watershed Association for their vision, MassDEP for helping fund this work, and the City’s Department of Public Works for implementing the new Porous Alley.”

So how does it work?

The porous pavement “recreates nature by capturing rainwater and filtering it back into the ground,” said Bob Zimmerman, CRWA Executive Director. The South End is a great location for this project for three reasons. First, the area is served by combined sewers, which carry both sewage and stormwater. During heavy rainstorms, the sewers can become overwhelmed, causing untreated sewage and stormwater to overflow into local waterways. By capturing stormwater, this porous alleyway is actually preventing overflows!

Secondly, buildings in the South End, just like other places in Boston, are supported by wood pilings that can rot when exposed to air. Since most land is now paved over, groundwater levels are declining because water cannot seep back into the ground. This new porous pavement filters stormwater into a large gravel-filled storage area below, where it slowly seeps into the ground, recharging groundwater levels. This helps maintain the structural integrity of the buildings. Lastly, the location was perfect because of the nearby connection to the storm drain, where both runoff volumes and water quality can be adequately monitored. The project will be monitored by CRWA, in coordination with BGwT for improvements in water quality and groundwater levels.

(Underground wood pilings form the structural support for buildings constructed on fill especially before the 1920’s. These pilings are structurally sound if they are completely submerged in water. Source: Boston Groundwater Trust)

The Department of Public Works will also monitor the maintenance needs and durability of the pavement. If it holds up and is cost effective, it could be used in other areas of the city.

Engineered by Vanasse Hangen Brustlin, Inc. (VHB) and completed this summer, the porous alley is located in Public Alley 543 between West Canton and Holyoke Streets.The project was funded in part by a 319 Nonpoint Source Grant from MassDEP. The City of Boston provided the construction cost for the Alley as a project match.

The South End Porous Alley is the City’s second “green alley,” the first of which was completed in partnership the Boston Architectural College in the Back Bay. The Porous Alley Project is part of CRWA’s Blue Cities Initiative, a water-centric urban design and planning approach that promotes the use of green infrastructure to restore the natural hydrology to the urban environment. Learn more at