For centuries, the Potomac River has helped fuel the nation. Winding 405 miles from West Virginia to the Chesapeake Bay, the river beloved by George Washington has been a source of everything from fish and drinking water for the nation’s capital to a channel for commerce, a defense against the Confederate Army and a backdrop for a thousand tourist photos of Washington, D.C. 

But this March, something new emerged from its waters—or, perhaps more accurately, from the earth beneath them. Her name was Hazel. She had been working for 16 months to dig a 2.2-mile-long tunnel beneath the Potomac and the oldest part of the Virginia city of Alexandria to hold sewage. 

The city was so excited that it proclaimed April 13 a local holiday in her honor: Hazel the Tunnel Boring Machine Day. Over 1,000 people turned out to celebrate. 

If that seems like an odd holiday to observe, it shouldn’t. The massive tunnel engineered by Hazel is just one of the solutions hundreds of communities across the United States have adopted to deal with a relic of the 19th century: combined sewer systems. 

“They are pretty prevalent,” said Dana Hales, a wastewater expert for the U.S. Environmental Protection Agency’s Mid-Atlantic region. “Newer systems typically wouldn’t be constructed to be combined.” 

In a combined sewer system, sewage and runoff from storms flow through the same pipes. In dry weather, all the flows are directed to wastewater plants for treatment. But heavy rainstorms can overwhelm the system, causing overflows of stormwater as well as sewage into rivers and creeks. That pollution poses a threat to both human health and aquatic life, frequently spurring cities to shut down or restrict access to their waterways. 

“A lot of Alexandrians have a goal in their mind of: One day my family, my kids, can fish, swim, recreate in the river. And they don’t feel like they can right now, always,” said Matt Robertson, director of communications for AlexRenew, the wastewater treatment authority that in 2018 took the helm of the city’s combined sewer rehabilitation. 

In Virginia, the legislature has in recent years set aggressive deadlines for both Alexandria and the state capital, Richmond, to address those overflows. Alexandria’s work must be done by 2026, after a one-year reprieve by legislators to account for delays linked to the COVID-19 pandemic and the war in Ukraine. Richmond’s project, which has a much larger footprint, must be finished by 2035. 

But while much of the political pressure to fix the remaining combined sewer systems in Virginia has centered on clean water concerns and the state’s need to meet federal Chesapeake Bay cleanup targets, climate change is ramping up officials’ concerns in both Virginia and cities across the nation. 

Data shows both the frequency and intensity of rainfall are increasing in most of the U.S., making combined sewer overflows more likely. For cities like Alexandria that sit on tidal rivers, sea level rise can also complicate the climate picture by raising groundwater levels. 

Those changes also pose an engineering challenge for officials. Alexandria’s primary solution to its overflows is the tunnel dug by Hazel. In this approach, instead of spilling from outfalls directly into waterways, overflows are routed into holding areas where they can be confined until treatment is possible. But how the tunnel and the connections to it should be designed depends on how much precipitation Alexandria expects to get on average in the coming years—numbers that are very much in flux. 

“You have to select a typical year or design storm,” said Justin Carl, general manager and CEO of AlexRenew. “When the city was looking at the program back in 2016, they were using 1984 as a typical year. It was a relatively dry year, average rainfall.” 

Community members, he said, flagged that metric, urging officials to consider more recent rainfall records. 

“We ended up looking at the years 2000 through 2016, which was the most recent rainfall period that we had data for,” said Carl. “It did reflect the increased rainfall that we are seeing with change in climate.” 

AlexRenew then used those figures to model expected precipitation for the city through the year 2100, and designed its new system in light of those predictions to ensure it could handle the number and intensity of storms likely to occur over the next decades. 

Today, Alexandria sees an average of between 37 and 70 overflows at each of its four combined sewer outfalls annually. Under the new system, those numbers are expected to drop to anywhere between less than one and 2.3 annually. 

Carl said Alexandria is one of the first communities in the country to incorporate climate change planning into its combined sewer control plans. But others are likely to follow. In February, the EPA came out with new draft guidance for how states should issue permits for combined sewer systems that recommends officials “consider the impacts of climate change on the performance of existing and future systems.” The agency also urged states to consider how remaining outfalls and investments could impact “underserved or overburdened” communities. 

“Because the intensity and the volumes of precipitation events is increasing in many areas across the United States, they’re saying that those typical years and those design conditions upon which the [combined sewer overflow] controls are based might need to be reconsidered,” said Hales. 

A Costly Challenge

Nationwide, about 700 municipalities had combined sewer systems in 2022—down from roughly 1,100 communities in 1994, when the federal government issued its first major policy for controlling overflows. Almost half of those systems are found in the Great Lakes region, with the Mid-Atlantic following. Washington, D.C., which lies just across the river from Alexandria, is one major example: In recent years, the nation’s capital has been systematically tackling its sewage problem by constructing massive tunnels for overflows.  

“As you move west across the United States, you don’t see as many combined systems,” said Hales.

Curbing the pollution that stems from these systems is a daunting task, one that takes not only engineering on a massive scale, but money in the tens to hundreds of millions of dollars. In Virginia, Alexandria’s project comes with a price tag of $615 million. Richmond has spent roughly $300 million over the past 35 years and expects to pony up an additional $600 million to meet the state’s 2035 deadline. And while grants are available from the federal government—and sometimes states—many municipalities rely heavily on borrowing to get their work done, meaning officials must balance the need to reduce pollution and the ability of residents to absorb the cost increases on their monthly bills.  

“I don’t know if there’s an awareness of how much time and financing it takes for communities to invest in the solutions to reduce the discharges,” said Hales. “It really takes a huge effort. It takes a long time, a lot of planning, a lot of coordination and a lot of money to get done.” 

For cities that embarked on work around the time of the pandemic, COVID-19 may have provided a helping hand. The American Rescue Plan Act allowed municipalities to tap into a flood of grants, while historically low interest rates drove down financing costs. 

“It really takes a huge effort. It takes a long time, a lot of planning, a lot of coordination and a lot of money to get done.” 

In Alexandria, $140 million in ARPA grants “reduced the amount of loans that we would need to take to fund the program and help reduce the rate shock,” said Carl. Furthermore, he noted, “we locked in interest rates down around 1.3, 1.8 percent … and that really helped us as well.” 

While Alexandria initially projected the average monthly household bill would rise between $20 to $40 as a result of the combined sewer work, increases have so far topped out at between $17 and $18. 

“It’s still significant given that it’s been done in a six-year period,” he said. “But the timing of the program given the General Assembly date kind of demanded that.” 

Costs have also dominated debates over combined sewer fixes in Richmond, where poverty rates outstrip the national average. A financial capability assessment commissioned by the city as part of a long-term control plan submitted to the state this July found that rate increases required to pay for the upgrades could push typical monthly wastewater bills from around $76 to between $160 and $180 by 2040. 

“Significant funding from the state level will be necessary to not further worsen the affordability of wastewater services for a meaningful portion of the city’s customer base,” the report concluded.  

Inflation, too, is squeezing many local governments as the costs of materials and labor for combined sewer work remain high. In Alexandria, Carl said AlexRenew saw a roughly 30 percent increase in materials and commodities costs over the course of the project, although he said a financial cushion built into the contracting meant customers were not further impacted. 

“This project, it’s pretty unique,” he said. “During the planning phase, we had a government shutdown, which was followed by a nationwide pandemic and a war that then delayed our [tunnel boring] machine coming from Germany. And we’re still close to getting the thing done on time, on a schedule that is unprecedented in the rest of the United States for a program of this magnitude.” 

SCOTUS Will Weigh in on Combined Sewers

Despite their size and cost, combined sewer fixes have often flown below the radar for the public. But that may change as a new case brought by San Francisco against the EPA is scheduled to go before the U.S. Supreme Court during its next term. 

In the city’s petition, backed by groups including the Chamber of Commerce, National Mining Association and American Petroleum Institute, San Francisco argues that the EPA wastewater permit governing outfalls from its combined sewer system is too vague. While the permit sets specific numeric limits on discharges during dry weather, it offers only “a set of comprehensive management requirements” for operating the system during wet weather, the city says. 

“San Francisco is not the only permittee facing this predicament,” attorneys for the city wrote. “Permitholders across the country must attempt to operate under permits containing generic water quality prohibitions that do not tell them their pollution control obligations.”

EPA in turn has argued that the limits laid out in the permit are clear that discharges cannot violate the Clean Water Act. 

However the high court rules, Hazel’s work is poised to land Alexandria on the list of cities that, after years of work and millions of dollars, have finally halted flows of sewage into their waterways—even as the storms that precipitate overflows elsewhere intensify. With a 2026 state completion deadline and the project 70 percent finished, any ruling weakening current federal law would likely have little effect on the city’s cleanup. 

“Watching Alexandrians rally around the project is really unique,” said Robertson. “We’ve seen tremendous support, not a lot of naysayers.” 

And the results, he and Carl said, will be clear to residents.

“This project is a contributor to cleaning up the river and making it swimmable and fishable for future generations of Alexandrians,” said Robertson.