At the District’s Blue Plains Advanced Wastewater Treatment Plant, city contractors are clawing into the ground to install huge pipes along the Anacostia River, wider and deeper than anything operated by Metrorail.

They are not for trains. They are meant to end a scourge that has plagued the District for decades: raw sewage mixed with polluted storm water that overwhelms the Civil War-era combined sewer system that serves a third of the city and overflows into local waterways.

The pipes will form a tunnel that will run 50 feet below Metro’s Navy Yard station in Southeast. It will cost $2.6 billion, paid for in large part by a major rate increase to home and business owners.

When the Anacostia tunnel of the Clean Rivers project is finished in 2025, it will snake 13.1 miles north to Rhode Island Avenue NE and capture 98 percent of storm water, which can slowly be pumped into Blue Plains and treated.

But the tunnel isn’t the only remedy DC Water has in mind. Even as workers dig at Blue Plains in Southwest and another area near RFK Stadium, DC Water officials talked to representatives of Region III of the Environmental Protection Agency last week about another ambitious undertaking that could transform the appearance of several District communities and dramatically change how the city manages storm-water runoff.

DC Water’s general manager, George Hawkins, asked the EPA’s permission to spend $10 million to place grass on rooftops, put flower gardens at curbsides, and lay sidewalks made of porous stone along the Potomac River leading into Georgetown and neighborhoods in the Piney Branch area.

Several cities moved forward with major green projects some time ago. An aerial view of a neighborhood in Philadelphia, for example, shows carpets of green across building tops, and in Portland, water authority officials claim that street planters, rain gardens and permeable pavement soaked up 60 percent of storm-water runoff.

A green project could reduce the cost of the Clean Rivers project, which also calls for building a pair of tunnels near the areas where officials envision the green makeover.

Hawkins has staked part of his legacy on creating a green project that works. “This is one of the reasons I was hired. I’m probably pushing it more than anyone else. It was one of the things I presented when I was being interviewed for this job,” Hawkins said.

The solution holds appeal for environmentalists, but some want to see proof of the green solution’s effectiveness. Last year alone, more than a billion gallons of wastewater gushed into the Anacostia River. It is among the dirtiest rivers in the nation, and every inch of the Potomac River that runs through the city is “impaired,” according to EPA criteria.

“It’s pretty disgusting,” said Rebecca Hammer, an attorney for the Natural Resources Defense Council. “There’s no question that that needs to stop, one way or the other.”

Hammer said “green” water management techniques must prove as successful as “gray” cement pipes to gain acceptance. “Assuming they can stop the same number of sewer overflows, we would be very supportive,” she said.

“It has a lot of benefits that the underground tunnel doesn’t have,” Hammer said. “Increased vegetation can improve air quality. It makes neighborhoods more beautiful. Jobs will last into the future because of maintenance.”

Residents in Seattle became believers in green water management when their property values shot up, said Nathan Gardner-­Andrews, general counsel for the National Association of Clean Water Agencies, which represents about 280 public utilities, including DC Water, covering 80 percent of households hooked to sewers nationwide.

“When you use the green, you see it,” Gardner-Andrews said. “There’s a real aesthetic value. Homeowners want to be the community to get the next green makeover.”

For now, DC Water is focused on a 13.1-mile “gray” cement tunnel makeover. Project director Carlton Ray said it will go as deep into the ground as a skyscraper and store 157 million gallons of combined sewage and storm water.

“We’ll start pumping it” into wastewater treatment as soon as it starts filling up, Ray said.

The District operates two types of sewers, separate and combined. Separate sewers in two-thirds of the city receive sewage and storm water in different tunnels, but outdated combined sewers that mix the two quickly fill during rains.

DC Water is trying to plug 53 sources of sewage overflows that vary in volume along the Anacostia and Potomac rivers and Rock Creek, contaminating them with harmful bacteria. Last year, about 2.3 billion gallons of combined wastewater entered the Anacostia and Potomac.

“These discharges from combined sewer overflows are illegal,” said Ken Kirk, executive director of the Clean Water Agencies group. “Simply addressing the problems doesn’t mean you’re going to be home free.” Also, tunnels cost a lot of money to maintain, he said, particularly in a recession.

The upgrade to the combined sewer is being covered by a rate increase. Starting in 2008, the water bill for the average single family jumped from $40 a month to $65, Hawkins said. But it won’t stop there: A proposed budget calls for another monthly increase to $72, he said.

A separate program to remove nitrogen as part of an aggressive EPA effort to limit pollution in the Chesapeake Bay, already underway, adds $900 million to the cost. A third project to create a marketable class-A fertilizer and produce energy that would power part of the plant costs $450 million, covered by municipal bonds.

In addition to the 13-mile Anacostia tunnel, construction is set to begin soon on a separate tunnel along M Street SE that will divert sewage from other areas to the 13-mile Anacostia tunnel.

One additional tunnel is planned to run 100 feet deep past the Kennedy Center and the Watergate Hotel into Georgetown along the Potomac, and a second will run along Piney Branch Road in Upper Northwest. Those tunnels and their costs could be downsized or eliminated if the green pilot program promises to remove storm water as effectively.

“I certainly applaud DC Water and George Hawkins . . . for thinking creatively on how to address polluted runoff when it rains,” said Hedrick Belin, president of the Potomac Conservancy. But whatever DC Water does needs to work for the Potomac, he said.

“There’s clearly something wrong when the DC Triathlon can’t do the swimming portion in the Potomac River if it rains the night before,” which happened in September, Belin said.