Greening sewers saves environment, money



By Liz Pacheco

Afternoon rainstorms do more than keep the grass green in Detroit. Heavy rainfall often overflows sewers, dumping untreated human and industrial waste, toxic materials and other debris into streets and waterways.

Inadequate sewer systems have caused problems in the River City since 1701, when raw sewage flowed through open channels and into nearby waterways. The city built a closed tunnel in 1836, but it continued dumping untreated waste into the waterways, causing outbreaks of typhoid and cholera.

Wastewater treatment plants were eventually added, but the biggest problem remains. Stormwater and sewage flow together into a treatment facility.

And during heavy rainfall or snowmelt, the system overflows.

Detroit planned to separate the systems, but construction was costly and the timeline long. Instead, the city is greening the system.

While environmentally friendly technologies can’t replace combined systems, they can soak up stormwater, keeping it out of sewers. Green techniques also look nicer and cost less than steel pipes and concrete reservoirs.


Combined sewer systems date back to the late 19th century when collecting water in a joint system was easier for growing American cities.

“In a small enough storm event, all the water goes to the treatment system,” says Jon Hathaway, a North Carolina State University professional engineer in the Department of Biological and Agricultural Engineering. “The issue with this type of system, obviously, is if you have a big rain event, your whole system can get overwhelmed.” Instead, untreated stormwater is discharged to the surface, never reaching the treatment system.

Even in systems where waste and stormwater are separated, similar problems can happen, Hathaway says. Cracks or crumbling pipes in older systems leak stormwater into the sewer line and overflow.

Crews work on the installation of porous pavement in front of the Macomb County Public Works Office in Michigan. Photo courtesy of Macomb County Public Works

While water contamination no longer results in typhoid and cholera, cities are finding germs and pollutants in their drinking and recreational water sources.

In July 2010, Chicago area beaches were closed for two days when heavy rain forced the city to direct overflow into Lake Michigan. The Chicago Tribune reported the closing as routine; the system frequently must divert sewage into the lake.

In old cities like Detroit and Chicago, the combined systems aren’t necessarily responsible for the overflow; it’s the development of grass into concrete and asphalt.

“The capacity of the system has remained the same, while the amount of runoff increased as the ity developed over the last decades,” says Kelly Karll, a senior civil engineer for the Southeast Michigan Council of Governments, a regional planning partnership for seven Michigan counties. “If you’re increasing paved surface … you’re increasing the amount of runoff that enters the combined system.”

Simply put: “You pave over the [grass] and you get more rainwater entering the pipes,” Karll says.


Cities have traditionally relied on separating the sewers or building giant concrete tunnels and huge underground retention basins to collect excess wastewater.

These options are becoming difficult for cities like Detroit, which have limited funding, Karll says.

What’s important about green controls is that the stormwater is still managed, but more naturally and in pieces. It is not in one place with a large tank or pipe.

“For example, you can use green roofs,” Karll says. “Rather than shingles or asphalt you actually construct green roofs using sedum, a low growing plant material, and so, plant material soaks up a certain amount of the rainwater.”


Before considering green controls, Detroit followed a 1996 plan to prevent the sewer system from overflowing into the Rouge River. Construction on a multi-million dollar tunnel had started in 2008.

“[The] contracting for that project had been hired and begun,” says Charles Hersey, the environment manager for the Southeast Michigan Council of Governments.

Then, the economic crisis hit.

Detroit’s population shifted and fewer were living in the overflow area. High poverty and unemployment rates plus the project’s construction costs and estimated debt made the tunnel unaffordable.

The plan was abandoned.

Hersey, along with others in the Detroit Water and Sewerage Department, started looking to other solutions.

They visited Philadelphia where green controls will help improve air quality, reduce greenhouse gases and beautify communities and streets, says Joanne Dahme, a civil engineer with the Philadelphia City Water Department.

“We wanted to make sure we were making the best investment with our repair dollars,” Dahme says.

One aspect of Philadelphia’s plan that Detroit hopes to mimic is the community participation. “Whenever we do any of these projects, we reach out to the civic association first and have public meetings,” Dahme says. “We have strong civic partners and are invited into the neighborhood instead of doing a project and not explaining it.”

Community involvement also plays a role in Cincinnati, another city they looked at, Hersey says.

The Metropolitan Sewer District of Greater Cincinnati created Project Groundwork, an enabled impact program that recruits willing participants to implement green controls.

The objective is to establish and monitor different projects so participants can see stormwater level reduction in the combined system. The projects are all sizes and use different types of green controls.

The Cincinnati Zoo is the largest program participant. They have three projects, one of which is replacing the asphalt in their Africa exhibit with ornamental grasses and a material that better absorbs stormwater,

The smallest participant is the city of Wyoming, who is using rain barrels to collect stormwater.


Detroit skyline seen from Windsor, Ontario, across the Detroit River. Photo: Bernt Rostad, Flickr

Detroit also plans to use rain barrels, starting with a project to disconnect downspouts from the sewer system. Instead of water flowing from downspouts and into sewers, it is directed onto grass to be absorbed or into a rain barrel to be reused on lawns and in gardens.

Demolishing abandoned and vacant homes and greening these properties will be another method used to help water soak into the soil, Karll says.

The city will also use bioswales. These wide ditches are typically filled with native plants whose root systems will absorb the stormwater.

Paved areas, like roadways and parking lots, will get green makeovers as well. These changes will be site specific and can include tree planter boxes, rain gardens and bump outs – vegetated areas that extend out from the original curb to help absorb and direct water overflows.

Planting trees along roadways and open spaces is another management method. The trees will refresh properties and simultaneously take up water through their root systems.


Planting trees to soak up rainwater isn’t a new idea for Detroit.

A few years ago, the Greening of Detroit, a 20-year-old urban forestry group, started pushing trees as stormwater controls.

“It’s kind of easy to get folks to understand trees as good for beauty and shade, making your neighborhood a nice place to live … but there’s not an innate understanding of trees as good infrastructure,” says Rebecca Salminen, Greening of Detroit president.

With so much vacant space in Detroit, the organization started thinking about returning that land to forest to help with storm reclamation and improve soil and water quality.

“When an opportunity came forward to change strategy on the Rouge River, we approached [the water department] with our idea for storm water reclamation,” Salminen says. “Fortunately, they were thinking along the same lines.”

The organization started a pilot project in early 2010. Sites will be chosen with help from Detroit’s recreation departments. Some are unused parks; others are vacant lots or former industrial sites. All are within the combined sewer overflow area the 1996 plan addressed.

A variety of species will be densely planted and in all different types, sizes and ages. “We’re going for the look of a classic forest,” Salminen says.

Like all of Greening of Detroit’s projects, the community will be a part of the pilot. Sites will only be selected after a community planning process. Volunteers will plant the trees.


While the cost to add green controls is still much less than building concrete tunnels and retention basins, Hersey says a few million dollars still will be needed each year.

In September 2010, his regional planning agency received a $308,000 grant strictly for planning.

The hope is to implement green controls wherever the city can. But it will take time, Hersey says.“The needs are massive, you can’t do this overnight.”

Editors note: This is part of a series of stories about Great Lakes sewer system issues.

Related story: Sprawl, climate change, carp control hinder Chicago sewer solution.

This story initially appeared in the Fall 2010 issue of EJ Magazine.

Comments are closed.