Billion-dollar tunnels aren’t the only way to clean the Anacostia. (Mark Gail/WASHINGTON POST)

It will cost $2.6 billion, and it is being paid for almost entirely by city residents, who have seen a new “impervious area charge” on their water bills in recent years.

So why are we doing this?

The utility and the District government in 2005 signed a court-enforced agreement with the federal government to address the ongoing pollution of the Anacostia and Potomac rivers by raw sewage. The oldest portion of the city’s sewer system combines the drainage from households and businesses with street runoff. So when it rains, there’s often more of that sewage/rainwater cocktail than Blue Plains can process, and the excess gets dumped straight into the rivers.

The storage tunnels present a brute-force solution: They will hold as much as 157 million gallons of sewage, allowing it all to be processed before discharge into the Potomac. But it’s also massively expensive for city residents, not to mention dangerous for the workers who will be building tunnels for the next 13 or more years. But there’s hope there might be a better, cheaper way to handle the city’s runoff problem.

Officials are contemplating ways to reduce the amount of stormwater that gets funneled into city sewers. It’s too late to mitigate the need for the tunnel that’s now underway, but two other tunnels are contemplated in the consent decree. And there’s a new hope that developments above ground can prevent expensive tunneling underground. (I wrote about some of this stuff in May.)

It tends to be called “low-impact development,” but I prefer how Christophe Tulou, the city’s environment director, puts it: “making the city spongier.” It means “green roofs,” with vegetation on top that can naturally consume storm water. It means gardens and other greenery that absorb rain rather than sending it into sewers. And it means new types of pavement and street infrastructure that rain can actually soak into.

There also appears to be a new willingness on the part of the federal government to consider this kind of stuff as part of its clean-water oversight. Last week, the Environmental Protection Agency issued the city a new permit for discharges from the newer part of its sewer system, the part with separate storm sewers. For the first time, it includes “sponginess” requirements: a minimum of 350,000 square feet of green roofs; planting at least 4,150 trees yearly; and requiring new, large developments to soak up an inch of rain per day.

“This is actually a very dramatic change in the manner for which permitting has been done in the United States for the last 40 years,” George Hawkins, D.C. Water’s general manager, said of the new stormwater permit. “The notion that the federal government would be involved in those kinds of local standards is a dramatic shift, but it’s an important shift.”

The big question is whether the federal government will be willing to renegotiate the 2005 agreement on the combined sewer system to trade tunnels for new “sponginess” criteria. Some environmental advocates are skeptical that green building standards will be able to provide the same level of protection as the tunnels, but there is some optimism. Hawkins said last week that D.C. Water will soon open formal negotiations with the EPA over modifications to the consent decrees.

It may not be easy, Hawkins said. “In order for us to not build [tunnels], we need to build at a scale much greater than what we’ve contemplated to date. But [the stormwater permit] is a good start.”