D.C. set to tunnel its way out of sewage overflows
District's green roofs, rain gardens and stormwater upgrades make it a leader in controlling runoff
- Comments are closed for this article.
The churning brown water that surges off roads and parking lots in the District of Columbia during rainstorms is a visible sign of trouble for the Potomac and Anacostia rivers. Underground and out of sight, there's another problem.
A labyrinth of pipes beneath the city catches the stormwater and moves it toward the Potomac River. Below one-third of the District, stormwater in these pipes combines with raw sewage.
During periods of heavy rain, the system overflows with a distressing mix of untreated stormwater and sewage. The excess pours through outfall points directly into the Anacostia River, Potomac River and Rock Creek. It also overwhelms the advanced wastewater treatment plant at Blue Plains.
Now, overflows in the District of Columbia are about to meet their match.
If all goes as planned, an enormous machine will begin drilling its way under the city in 2011. Chewing away earth hundreds of feet below the city and the Anacostia River, it will create the first of three massive tunnels designed to move urban sewage safely toward the treatment plant and away from D.C.'s rivers.
The tunnels are designed to catch this rush of water and release it in an orderly way to the treatment plant. They are the most dramatic and costly element of the District's multipronged effort to counter the water quality problems from polluted stormwater and meet its requirements under the Clean Water Act.
While states and local jurisdictions struggle to reduce stormwater pollution across the Bay watershed, the District's work has won respect.
"The District, as a city, is head and shoulders above any other municipality in the Bay watershed," said Tom Schueler, with the nonprofit Chesapeake Stormwater Network.
The Stormwater Network created the first stormwater performance report card for the Bay region in 2009. The District earned the highest overall grade of B+. Others earned Cs and Ds. Schueler said the grade was based on a combination of factors.
The District has been working for years to encourage and help fund green roofs, rain gardens and other surface treatments that hold and absorb rainwater. "They have a stormwater utility fee and they've raised the rates recently so they have an adequate budget, which a number of states lack," Schueler said.
Fees for both businesses and home?owners are based on the amount of impervious surface on the property. Increasing trees and green spaces can reduce the fee.
The District has strict regulations for controlling erosion, which prevents dirt from washing away with stormwater. In general, Schueler said, staffing is able to meet the need for inspections and maintenance.
Revisions to stormwater regulations for construction projects are under way, so that portion of the grade was incomplete.
The District is also upgrading stormwater management in the two-thirds of the city that is not drained by a combined sewer system. In these areas, stormwater and sewage move through completely separate pipes, governed by a federal Municipal Separate Storm Sewer Systems (MS4) permit.
In a recent update to its permit, the District has committed to specific actions to reduce polluted stormwater runoff. For example, the permit requires measurable amounts of street cleaning, green roofs and tree planting, while the District continues to incorporate new stormwater management techniques at development sites.
"It's a progressive permit and the city has agreed to do a lot," said Josh Saks of the Chesapeake Bay Foundation's D.C. office. "We rarely see a major municipality, especially in these economic times, take on such a burden. It needs to be applauded."
Stormwater runoff is the fastest-growing source of pollution in the Bay and its rivers. The increasing presence of roads, rooftops and parking lots send water rushing into drains and streams, carrying trash, oil, dirt, pesticides and pet waste. The grit, grime and chemicals from the streets and overflowing sewage harm aquatic life and threaten human health.
The Chesapeake Bay Program estimates that 17 percent of phosphorus, 11 percent of nitrogen and 9 percent of sediment loads to the Bay originate in stormwater.
In some locations, chemical contaminants reaching waterways through stormwater runoff can equal or exceed the amount that comes from industries. The Bay Program considers the Anacostia one of the region's most toxic waterways, where high rates of tumors have been found in brown bullhead catfish.
Reducing pollution from stormwater is a challenge for state and local jurisdictions. In the District, as in all urban settings, the problem is acute. The urban landscape is a concentrated hub of hard surfaces with comparatively few trees and green spaces to trap and absorb rainfall. In rural and suburban areas, these features are more easily planned with new development. In contrast, cities have much less space available.
Cities have also inherited a vast maze of drains and underground pipes. Portions are at least 100 years old and strained by the volume of water they handle today. They are buried under countless roads and buildings, making updates costly and a logistical nightmare.
In the District, water in the combined sewer system that merges stormwater with sewage normally moves toward the sprawling complex of Blue Plains, which treats wastewater for more than 2.9 million people in the District and portions of two states.
But "normal" depends on dry weather.
The District's combined sewer system is old and overburdened. Even average storms can overflow the pipes and flush untreated sewage directly into the rivers.
The District has already spent $140 million to add dams, tide gates and pumping stations that have cut the annual volume of overflow by 40 percent. But nearly 2 billion gallons still empty into its rivers each year. The Anacostia bears the brunt, receiving almost 1.3 billion gallons in an average year, followed by the Potomac with 639 million, and Rock Creek with 49 million.
Water that actually reaches Blue Plains during storm events overwhelms the system. Average storms can double the flow-spiking on a typical spring day from 400 million to 800 million gallons. Such high flows can't be treated effectively and can also damage the treatment system. As a result, the excess brew of stormwater and sewage receives only partial treatment and enters the Potomac without full benefit from the plant's technology.
It's a double blow for the river: pollution from stormwater and sewage laden with nutrients.
The District is one of many cities fighting overflows from combined sewer systems. But George Hawkins, general manager of the District of Columbia Water and Sewer Authority, said that a combined system can be helpful if the overflows are stopped.
That's the role of the tunnels. The tunnels will not only prevent overflows, but deliver water to Blue Plains at a pace the system can handle.
"All the crud that we see on the street will come here to Blue Plains and go through the most advanced wastewater treatment plant in the world before it gets discharged into the river," Hawkins said. "It's true that in a separate system we don't have sewage mixing with the stormwater, but it goes into the river with no treatment at all."
The new tunnels will serve about one third of the District's land area, which is drained by the combined sewer system.
The first tunnel will run along the Anacostia, which suffers the greatest amount of overflows and where people still seek edible fish. Each of the tunnels will be approximately 24 feet in diameter, but the Anacostia tunnel-at 13 miles in length-will be the longest.
"The basic notion is like a giant underground rain barrel," Hawkins said. "The tunnels will be long enough that when water enters one end, it will generally flow by gravity toward the other end. But if a storm was large enough, the tunnels could hold it like a big bathtub. When the flow drops, we have pumps that will move it back into the pipes."
The tunnels will regulate the flow of water into Blue Plains even when rain is not a factor. That's important, because treatment takes time. Water needs about 18 hours to move through the series of tanks and filters that comprise three different treatment phases at the plant, including advanced technology for removing nutrients.
The Anacostia tunnel is planned to start catching water in 2017, with those for Rock Creek and the Potomac scheduled for 2025.
The estimated cost of this engineering feat is at least $2 billion. But overflows will be slashed to a fraction of their present levels. According to the Water and Sewer Authority, the annual average of 1.3 billion gallons of overflow in the Anacostia will fall to roughly 54 million. The total annual overflow in the District should drop from nearly 2 billion gallons to 138 million.
The numbers are dramatic-and yet not enough.
Two-thirds of the District will not benefit from the tunnels. In these areas, stormwater moves through separate channels toward the river. The battle for water quality takes place above ground, not beneath it.
It's a site-by-site march for more trees, green roofs, rain gardens, pervious pavers and rain barrels.
Such projects may become requirements under the federal MS4 permit that governs stormwater discharges. The EPA has proposed revisions to the permit that include "an enforceable approach" to low-impact development. New development, redevelopment and retrofit projects at non-federal facilities would need to retain 90 percent of stormflows on site. Public comment on the proposal is open through June 4.
Other green projects are well under way.
Last spring, Mayor Adrian Fenty announced a goal to increase the District's tree canopy from 34.8 percent to 40 percent. This means adding 8,600 trees every year for the next 25 years and conserving the ones that exist.
The RiverSmart program, managed by the District's Department of the Environment, uses money as incentive. Property owners making stormwater improvements can receive up to $1,200 in assistance. Green roofs up to 4,000 square feet receive a subsidy if the project covers at least half of the available roof surface. Trees and rain barrels can be installed for a modest fee.
Nonprofit organization like Casey Trees and DC Greenworks are partners in the program.
Brent Elementary, just southeast of the Capitol, used a District grant to green its corner playground and install a rain garden. As a result, a large recurring pool of rainwater has dried up for good.
"This whole corner, out into the street, it was a mess, especially during spring and fall rainstorms. Now it just doesn't happen," said parent Heidi Johnson.
The new rain garden runs in a 7-foot band around half of the school's playground. It features native trees and shrubs and a well-defined dip that runs through its center. This dip, or swale, catches rainwater from the playground, absorbs it and makes this particular instance of street flooding a thing of the past.
It's a vanishing act that city officials hope to replicate in countless similar settings. But the effort, in its own way, will rival that of the tunnels.
"There are all sorts of challenges to it," Hawkins said. "It's decentralized; thousands of little things instead of one big thing. Silt can build up in rain gardens, and you have to maintain green roofs. It's not just turning a dial. But we are hopeful."
Plans are under way for the full-scale application of green stormwater techniques in a District neighborhood. Hawkins said the District will spend a lot more money on such projects in the years ahead and the pilot project will show how to manage the process successfully.
In the neighboring watershed of Delaware Bay, officials in Philadelphia decided tunnels weren't feasible. Instead, they aim to address all of the city's stormwater problems with an aggressive application of rain gardens, trees, green roofs and rain barrels.
"I hugely favor those ideas, but I'm not convinced," Hawkins said of the Philadelphia experiment. "Some cavern systems are needed, because they give you clear performance. Combined with an above surface, aggressive greening program, you have a system that will work better than either by itself."
Hedrick Belin, president of the Potomac Conservancy, said that scale and funding are key.
"We are confident that low-impact solutions such as cisterns and green roofs, when implemented thoroughly and thoughtfully, are effective in reducing the runoff from stormwater," Belin said. "However, these projects have to be funded and implemented on an appropriate scale. Half measures won't do the job."
The District is seeking federal funds to help pay for its stormwater program. Hawkins said it's a fair request, and ratepayers will share the burden. But without a significant influx of federal money, ratepayers could see their bill double or triple over the next 15 years.
"Are we greatly concerned about the funding? Absolutely," Hawkins said. "The question becomes, how do we have a joint funding system that, of course, D.C. residents participate in, along with residents in the suburbs and the federal government?"
District officials might take some comfort in their track record-advancing a suite of expensive and complicated stormwater initiatives that have stalled elsewhere in the Bay watershed.
"We have to be as aggressive in marketing and outreach as Nike," Hawkins said. "I think it's a sell we can make."
Aggressive stormwater absorption plans key to Anacostia cleanup
Stormwater management is the keystone of a sweeping new plan announced in April by the U.S. Army Corps of Engineers to clean and restore the Anacostia River.
The Anacostia Watershed Restoration Plan includes more than 3,000 specific projects to improve water quality, enhance fish habitat and increase parkland. More than half of these projects-approximately 1,800-target stormwater.
The restoration plan, called "Turn It Around," recommends the aggressive use of low-impact techniques that capture and absorb stormwater where it falls. Solutions such as rain gardens, bio-swales and green roofs are especially important in older developed areas that suffer from failing drain systems or lack any existing features to control runoff.
The plan resulted from a two-year, $2.8 million effort to identify specific projects that will collectively reduce pollution in the river. The Corps developed the plan with support from the state of Maryland, Montgomery and Price George's counties, the District of Columbia, and the Metropolitan Washington Council of Governments.
Local watershed groups helped to pinpoint needs and opportunities.
"We relied heavily on 10 subwatershed groups to help identify the projects," said Dana Dunmire Minerva, executive director of the Anacostia Watershed Restoration Partnership.
Stormwater is the largest source of pollution in Anacostia's heavily developed watershed, which covers 176 square miles in portions of Maryland and the District. Much of the land was developed before requirements were in place for managing stormwater.
As a result, approximately 64 percent of the impervious surface in the Anacostia watershed has no stormwater controls of any kind. The regular surge of water off roads, rooftops and parking lots damages stream banks and fouls the water with trash, dirt, toxics and nutrients from fertilizer and pet waste.
Elected officials from Maryland and the District celebrated the plan as a clear path forward with an unusual amount of regional cooperation, accountability and federal support.
"Today, we are taking a giant step toward a new life for the Anacostia River and watershed," said Maryland Gov. Martin O'Malley. "When plan implementation is complete, a healthier and cleaner river will mean continued economic investment along its banks and throughout the Anacostia River watershed."
Along with stormwater retrofits, the plan calls for reducing trash and removing 125 major barriers to fish passage. Restoration projects will help offset the tremendous amount of woods and wetlands that have been lost in the river system, as well as stabilize eroding stream banks.
These projects are designed to complement the work of local watershed groups and public agencies. The District, for example, breaks ground next year on a large stormwater-sewage tunnel that travel along the Anacostia, which will reduce sewage overflows to the river.
The full scope of projects described in the Anacostia plan is estimated to cost $1.7 billion dollars over a 10-year period.
Minerva said the funds will come from a combination of county, state and federal sources. While the funding package has yet to be fully identified, some of the work dovetails with projects that Maryland counties are already required to conduct as part of their federal permits for stormwater.
"We're optimistic that we can put together a patchwork of funding sources, including some new federal funds," Minerva said.
Minerva believes the payback will be felt in neighborhoods as well as the river. "These projects aren't just good for the river and the watershed, but they are really good for people, too, because they green the community and make our lives better."
By submitting a comment, you are consenting to these Rules of Conduct. Thank you for your civil participation. Please note: reader comments do not represent the position of Chesapeake Media Service.
Comments are now closed for this article. Comments are accepted for 60 days after publication.