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Mass Innovations, From the Beacon, November 2014
The city of Cambridge has used an innovative engineering strategy to comply with federal stormwater standards.
A key component in the project, which won an award from the American Public Works Association in July, is an enhanced 3.4-acre wetland that helps to store and treat stormwater.
“First there is a catch basin where the water flows into a retaining pond, where all the sediments, all the dirt, the gunk, the oil, will go to the bottom,” said Stephen Long, the director of government relations at The Nature Conservancy, which has been involved with the project.
The water then enters a series of ponds, each at a lower elevation, before entering the Little River, which connects with Alewife Brook. The enhanced wetland appears to be entirely the work of nature.
The city worked on the project with Salem-based Bioengineering Group, according to Catherine Woodbury, the Cambridge Public Works Department’s engineering project coordinator.
“We needed to find a way of discharging the stormwater,” she said. “And through that process, the stormwater wetland became a tool to help us achieve that.”
The project, which includes recreational and educational features, is seen as benefitting the neighboring communities of Belmont, Arlington and Somerville, all of which are close to Alewife Brook, which flows into the Mystic River and, ultimately, Boston Harbor.
Woodbury noted that the wetland was created on land owned by the state Department of Conservation and Recreation. Around the same time that Cambridge was planning the creation of the wetland, the DCR was preparing to expand its network of walking and biking trails in the area.
“Our processes overlapped,” Woodbury said. “We were basically working with DCR and their planning group.”
The DCR’s role also helped lead to a strong educational component. Embossed plaques are posted at various locations.
One, near Alewife Brook in Cambridge, explains how and why the water quality in the brook has often been impaired “due to bacteria and other pollutants from a number of sources, including combined sewer overflows (CSO) and stormwater runoff. CSO and stormwater discharges contain bacteria, oxygen-demanding pollutants and solids.”
The plaque, which dates to 2012, cites eight CSO outfalls along Alewife Brook that “discharge a mix of untreated wastewater and stormwater from overtaxed combined sewer systems” during moderate to heavy rainstorms. This is no longer the case, however, due to the enhanced wetland.
The Clean Water Act is 40 years old, but the pressure on municipalities to conform to combined sewer overflow regulations is relatively recent.
During the early period of consent orders, according to Bioengineering Group President Wendi Goldsmith, “everyone was just building big tunnels, or a series of smaller underground-lined tanks, and the whole idea was to treat it strictly as an engineering and structural-mechanic problem.
“When you are building something around living processes, you do need to be careful with construction,” Goldsmith added, noting that workers salvaged the peat-rich natural soils they extracted. Care was taken to ensure that all vegetation in the wetland is indigenous.
The wetland was also engineered to reduce the number of mosquitos. That goal, Goldsmith said, was achieved by maximizing high-quality habitat to reduce mosquito larvae. Mosquitoes, she said, thrive on lower-quality habitat.
For more information, contact Catherine Woodbury at (617) 349-4818.