Stormwater Management

 More than 700 municipal water agencies around the country are updating their sewer systems, at a cost of billions. It’s an urgent task because in the 100-plus-year-old systems — built with state-of-the-art design at the time — raw sewage is spewed directly into local rivers during heavy rainstorms. The affected sewer systems are concentrated in the Northeast and in older systems in San Francisco and Chicago, among other cities.

Photo courtesy of Metropolitan Water Reclamation District of Greater Chicago

Those combined sewer overflows (CSOs) have created polluted waterways that have been the subject of at least one lawsuit and local and federal consent decrees. Water agencies are updating their systems with massive tunnels and sewage treatment plants, trying to prepare for the even greater needs — and heavier rainstorms — that climate change will bring.

 Washington, D.C.: Lawsuit Leads to Overhaul

Washington, D.C., is home to two rivers, the Potomac and the Anacostia. The city attracts millions of tourists every year, many of whom enjoy beautiful waterfront sites around the city. But the rivers have a complicated history.

In 2000, the Anacostia Watershed Society sued DC Water over the sewage in the river. The eventual result was a 2005 consent decree, a court order with the U.S Environmental Protection Agency, that requires the city to meet certain pollution standards in the river.

Photo courtesy of Anacostia Watershed Society

The elements of the consent decree have been renegotiated over the years. After a modification in 2015, the plan includes both gray and green infrastructure (GI). Gray infrastructure is what is traditionally thought of as infrastructure — tunnels, reservoirs, pumping stations and treatment plants.

“Green infrastructure uses vegetation, soils, and natural processes that mimic nature, to soak up and store rainwater water where it falls to control wet weather pollution and create healthier urban environments,” according to the EPA.

Four New Tunnels, New Treatment Plant

The bulk of the city’s consent decree requirements will be met by the construction of four large tunnels and a sewage treatment plant, all part of the city’s Clean Rivers Project. The Clean Rivers Project is a massive undertaking, the largest infrastructure project since the city’s subway system was built starting in the 1960s. The first phase was completed in 2018, as the newly built Anacostia River Tunnel was connected to the Blue Plains Tunnel.

Photo courtesy of DC Water

The two tunnels have deep shafts and large concrete structures that divert raw sewage from the Anacostia River. The tunnels deliver the combined sewer overflows to the Blue Plains Advanced Wastewater Treatment Plant, which cleans the water before discharging it to the Potomac River.

The third tunnel, the Northeast Boundary, will be completed in 2023. Once it is connected to the other two tunnels, combined sewer overflows to the Anacostia will be reduced by 98 percent, said DC Water. It should also reduce the chance of flooding in area neighborhoods from 50 percent to 7 percent.

The final phase will be completed by 2029 with construction of the Potomac River Tunnel. The consent decree sets a deadline of March 2030.

The Clean Rivers Project has been a success so far.

“The Anacostia River Tunnel dramatically reduced sewage discharge into the river,” said Phillip Musegass, vice president of programs and litigation at the Potomac Riverkeepers.

Emily Conrad is director of communications for the Anacostia Watershed Society (AWS), which filed the lawsuit against the city in 2000. Clean Rivers has exceeded expectations, she said. September 2021 saw several days of rain in a row, and the tunnels captured 100 percent of the overflow — more than five billion gallons.

The system is designed to capture 80 percent of overflow, and there have been rainstorms where it captures less than 100 percent. Construction of the Northeast Boundary Tunnel should bring the capture rate up to 98 percent, Conrad said.

How Prepared Is It for Climate Change?

The real question is how the system will do as climate change brings heavier and more frequent storms to the area.

“We have a very high degree of control compared to a lot of systems in the country,” said John Cassidy, Clean Rivers lead pollution control officer engineer at DC Water. “We’re set up for a changing climate.”

Director of Clean Rivers Moussa Wone explained.

“It’s designed to be at least 20 percent bigger than required, based on the model,” Wone said. “The pumping station and treatment system are at the end of the tunnel, so we can double the size. It’s a very practical way to expand the system without exorbitant cost.”

Musegass of Potomac Riverkeepers doesn’t think the system is adequately prepared for the future. When DC Water created the plan, it followed EPA guidelines. The plan used rainfall data from 1988 to 1990, a period with higher-than-normal rainfall.

“Now, that’s over three decades old,” said Musegass. “More recent history in this region raises concerns that data is not what we’re going to see in the future.”

The cost of Clean Rivers is primarily paid for by ratepayers, using a formula based on impervious area and generation of wastewater. Impervious area is pavement where water runs off instead of seeping into the ground underneath.

DC Water has sought federal funding but has received only $270 million of the total cost to date of $1.9 billion. When all projects are completed, the total cost is expected to be just under $3 billion, said Wone.

DC’s Stormwater Retention Credit Program

DC was the first city in the country to create a Stormwater Retention Credit (SRC) trading program. The idea is to shift the cost of retrofitting areas with green infrastructure to private developers, said Matt Johnson, branch chief for green infrastructure incentives and assessment in the DC Department of Energy and Environment.

Photo courtesy of DC Water

“Rather than build green infrastructure in the central business districts, we do it offsite when it’s cost-prohibitive to do it onsite,” Johnson said.

Under regulations the city created after the EPA consent decree, any new development project that disturbs more than 5,000 square feet of land must meet specified stormwater retention standards. One way developers can do that is by buying stormwater retention credits.

The first SRC trade was in 2014. A nonprofit group, Building Hope, leased the site of a closed elementary school and started an extensive renovation of the building. The school’s modest size and structural limits made it hard for it to install green infrastructure onsite.

To meet the city’s stormwater retention standards, the school bought credits from the Westchester, a co-op apartment complex in another part of town. The Westchester had installed rain gardens that generated the stormwater credits. Selling those credits to the school enabled the Westchester to recoup a large portion of its investment installing the rain gardens. The transaction also allowed the school to meet its stormwater retention obligations.

The stormwater credit program also has a purchase price guarantee, called the Price Lock Program. It allows stormwater credit generators to sell the credits to the city’s Department of Energy and Environment at fixed prices, without losing the option to sell to another buyer. If the participant sells to another buyer, DOEE pays a portion of the purchase price on behalf of the buyer.

“[Large-scale] development is the main driver of green infrastructure,” said Johnson of DOEE. “The Price Lock Program is DOEE’s way of putting our thumb on the scale.”

Part of the goal of the Price Lock Program is to make it easier to generate stormwater credits on land owned by nonprofits, such as churches, cemeteries and schools. Such projects get funding priority.

Currently, 13 percent of development is taking on some voluntary off-site stormwater retention. Because the stormwater retention credits have to be generated in areas of the city where untreated sewage goes into the river, DOEE hopes to generate more green infrastructure there to help clean the waterways, Johnson said. The long-term success of the program depends on large-scale developers opting to buy stormwater credits, he added.

Bioretention, Permeable Pavement

For other green infrastructure, the city has four River- Smart programs: Communities, Homes, Rooftops and Schools. The Communities and Schools programs are administered by the Anacostia Watershed Society. For both programs, nonprofit groups can apply for a grant to install green infrastructure, and the AWS hires contractors. Examples of GI projects are permeable pavement, rain gardens and bioswale.

Photo courtesy of Metropolitan Water Reclamation District of Greater Chicago

Permeable pavement allows rainwater to seep through the pavement and gradually disperse underground instead of just running off, as it would with a conventional concrete sidewalk. Rain gardens are planted with native vegetation that allow rain runoff to be absorbed into the soil. Bioswale are vegetated or mulched channels that convey stormwater runoff while removing dirt and silt.

Green roofs are planted with vegetation and, in some cases, a drainage and irrigation system.

The Alliance for the Chesapeake Bay works with the city to run RiverSmart Homes. Under the Rooftops program, property owners can get a rebate of $15 per square foot if they voluntarily install green roofs. To be eligible, the property must be in a Municipal Separate Storm Sewer System (MS4) area, one where sewage is discharged directly into the river.

Chicago: Nation’s Largest Reservoirs

The Chicago sewer system, while sharing DC’s outdated design and combined sewer overflows, has some important differences. Chicago was not sued, but it entered into a consent decree with the federal and state EPA.

“The motivation was to get us on an enforceable schedule to complete our project,” said Kevin Fitzpatrick, assistant director of engineering at the Metropolitan Water Reclamation District of Greater Chicago (MWRD). “The federal government began cracking down on CSOs.” Chicago’s deadline is December 31, 2029.

Chicago’s Tunnel and Reservoir Plan (TARP) is designed to reduce flooding and improve water quality by capturing stormwater and sewage before it goes to area waterways. The four tunnels total 109 miles and service Chicago and 51 suburbs. MWRD adopted the plan in 1972.

“During a storm, pumping stations are trying to clean as much water as they can from tunnels,” said Fitzpatrick.

During very big rainstorms, the tunnels and reservoir may completely fill up and spew combined sewer overflows (CSOs) into the waterways. The two TARP systems that are completely built capture at least 99 percent of CSOs, Fitzpatrick said.

How prepared is Chicago’s system for increased rains in the future from climate change?

“Unfortunately, the design is based on data from decades ago,” Fitzpatrick said. “The size is pretty much maximized.” At 10 billion gallons, TARP’s reservoir has more storage capacity than anywhere in the country. The original reservoir, built in partnership with the Army Corps of Engineers, held 7 billion gallons.

“MWRD expanded it on our dime to 10 billion,” said Fitzpatrick. “There are no additional plans to expand it.”

MWRD paid for the first part of the project with EPA grants, then with state revolving funds and low-interest loans. To build the reservoirs, MWRD partnered with the Army Corps of Engineers, which shared the cost. MWRD raises most of its share of the cost through real estate taxes. It can also sell bonds.

MWRD has also worked with the Chicago Department of Water Management to install different types of green infrastructure. They partner with Transportation Departments, park districts and Chicago public schools to provide permeable pavements, bioswales and green alleys planted with native vegetation.

Photo courtesy of Metropolitan Water Reclamation District of Greater Chicago

The city also has a program to provide all Cook County residents with rain barrels at a discounted price of $22, or half price for residents over 65. Since 2008, the city has distributed 148,000 rain barrels. Rain barrels are a type of green infrastructure that capture rainwater from roofs and save it for when a resident may need it. By keeping this water out of the sewer system, rain barrels help prevent sewer overflows and flooding. As a local example, much of the rain that falls on the Chicago Center for Green Technology’s roof flows into four 3,000-gallon cisterns and is later used to water the landscape. According to the EPA, rain barrels can save a homeowner 1,300 gallons of water per year and is another tool to assist communities with stormwater and rainwater control.