By Lucy Kates, MyRWA volunteer
Over the past year, MyRWA has worked with municipalities to build 98 infiltration trenches to reduce stormwater pollution entering our waterways. After initial success of these trenches in Arlington and Lexington, more trenches are on the way with 50 set for installation in Arlington, Medford and Winchester in the next two years, and 250 more being sited in the communities of Arlington, Cambridge, Lexington, Medford, Melrose, Everett, Reading and Woburn.
Read on to learn how infiltration trenches reduce stormwater pollution and how this innovative approach came to our watershed:
What is a stormwater infiltration trench?
Cities change rivers by paving over the landscape. Rain that falls on roofs and roads and parking lots in a storm—called “stormwater runoff”—is carried directly to rivers and streams through a system of underground stormwater pipes, carrying pollutants it picks up along the way. One surprising result in urban areas: too much of the nutrient phosphorus, which leads to excessive growth of invasive plants, poor fish habitat, and blooms of toxic cyanobacteria that are a threat to public health.
Infiltration trenches are an element of nature-based green infrastructure that contribute to runoff reduction and help keep our waterways clean by redirecting some of that stormwater to directly infiltrate the ground instead. Cost-effective and easy to install, these trenches effectively filter out phosphorous from rain and snowmelt that would otherwise sweep across impermeable paved surfaces, like roads and parking lots, and carry this pollutant directly into bodies of water like the Mystic River.
Trench construction in progress. PC: Catherine Pedemonti
The trenches are installed adjacent to a storm drain in the road. They are made by digging a trench next to the storm drain, running a perforated pipe from the storm drain’s catch basin through the trench, and then filling the trench with crushed stone. The layers of stone allow for a slow filtration of the first flush of stormwater, which carries the majority of pollutants.
Diagram of an infiltration trench. Source: Nick Naculich
In collaboration with other elements of green infrastructure, like rain gardens, infiltration trenches are a simple way to help keep our waterways significantly cleaner—for our own benefit and that of local wildlife. That’s why MyRWA has been focusing on infiltration trench installation at a regional scale and education about this method of stormwater management.
How did trenches come to the Mystic?
In spring 2020, MyRWA worked together with the town of Arlington to pilot trenches as a potential approach to strormwater, emerging from a long-term project to control phosphorus pollution in the watershed. This pilot included the design and installation of 20 infiltration trenches and 2 rain gardens, helping to prevent runoff into the Mystic River and Alewife Brook. Read more about the effort here.
In October of 2020, MyRWA was awarded nearly $500,000 in grants by the Baker-Polito administration Massachusetts Department of Environmental Protection (MassDEP), part of over 1.4 million dollars in EPA Clean Water Act grant money administered by the state to construct dozens more infiltration trenches, based off of the designs piloted in Arlington. Read more about the green infrastructure grant here.
And with the support of an additional grant from MassDEP, MyRWA is siting 250 trenches in the communities of Arlington, Cambridge, Lexington, Medford, Melrose, Everett, Reading and Woburn in the coming year. One key goal of the project is technology transfer: sharing the knowledge gained in Arlington about the power of these devices, and the knowledge of how to get them in the ground.
Each stormwater trench is small; but together, these hundreds of trenches add up to a distributed approach to stormwater management at a regional scale. With 250 site designs in the pipeline, MyRWA and its partners will be looking to secure construction funding for them in the near future.
MyRWA interns Amy Shen and Alexis Bilas-Imperial are working with cities to site 250 trenches. PC: Andy Hrycyna
