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Chris, the underground boring machine that dug the NEBT

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Posted on: November 9, 2023

By Paul Ruffins

Most Prince George’s County residents don’t realize that they’ve recently become the beneficiaries of a huge, five-year, $580 million-dollar environmental upgrade that will keep 90 million gallons of raw sewage and stormwater out of the Anacostia River, Washington Harbor and the Chesapeake Bay. The new Northeast Boundary Water Tunnel (NEBT), in operation this fall, is part of a massive $2.7 billion Clean Rivers Project that will benefit the entire region. But why did most people in the District and the bordering suburbs miss seeing or hearing a giant construction project five miles long and 23 feet wide? That’s because the entire project is hidden 90 to 180 feet underground.

The NEBT was dug using a 25-ton, hydraulically powered underground boring machine with a rotating cutter face that is 23-feet in diameter. The tunnel runs 26,700 feet, from just south of Robert F. Kennedy Stadium to the intersection of Rhode Island Avenue, NW, and 6th Street NW.  The machine started in September 2018 and slowly and steadily chewed its way across the city at a rate of about 28 feet a day. The resulting circular hole was lined with 31,000 sections of waterproof reinforced concrete.

According to John Lisle, DC Water’s vice president for marketing and communication, “The completion of the NEBT and the entire Anacostia River Tunnel System is delivering on one of the major commitments of the 2005 consent decree signed with the District, EPA, and the Justice Department. The combined sewer system (CSS) that serves about a third of the District dates back to the late 1800’s and the tunnel system will reduce combined sewer overflows to the Anacostia by 98% in an average year.”

The CleanRivers Project, arising out of that consent decree,  has several major components. These include the NEBT and the 2.4-mile Anacostia River Tunnel, which was completed in 2016 and connects the NEBT to the Blue Plains Advanced Wastewater Treatment Plant. There will also be the 5.8 mile $819 million Potomac River Water Tunnel, scheduled to be completed in 2030, which will capture the sewer overflows polluting the Potomac and Rock Creek on the west side of the District. 

Like the NEBT, the Potomac River Tunnel will function as a giant underground storage tank, holding millions of gallons of sewage and stormwater and sending it to Blue Plains rather than into the Potomac or Rock Creek. The NEBT will also help reduce local flooding due to undersized storm drains in Northeast D.C.

The region’s water pollution problem is over 200 years old. Around 1810, the swampy District of Columbia began to build  culverts and ditches that drained into the nearest waterway. Because of  its huge expansion during the Civil War and the increasing popularity of piped-in water for indoor plumbing, the city began constructing a combined sewer system that carried both untreated sewage and stormwater into approximately 19 outfalls along the Potomac and Anacostia rivers. 

In 1890, a presidential commission linked the combined sewer system to a single outfall point at Blue Plains, the southernmost spot in D.C., where the tides wouldn’t carry the waste back upstream. There was no water treatment facility, but at least all new sewers built as D.C. expanded would have separate pipes to send sewage to Blue Plains and only divert stormwater into the rivers. These are known as municipal separate storm sewer systems, or MS4s, and are now standard.

However, between 1890 and 1910, the rapid development of Prince George’s and Montgomery counties, both north of the District, created new problems. Towns such as College Park and Hyattsville built water systems for indoor plumbing and fire hydrants but also developed sanitary sewer systems that simply dumped untreated waste into the Potomac and Anacostia rivers and Rock Creek, which all flow south. 

When the District threatened to sue Montgomery and Prince George’s Counties, the resulting agreement created the Washington Suburban Sanitary Commission (WSSC) in 1918. WSSC took over all the local systems and piped most of their sewage to the outfall at Blue Plains, in southwest D.C., where an actual water treatment plant was built in 1937. (WSSC also operates several smaller treatment plants.)

Today, DC Water’s Blue Plains Advanced Wastewater Treatment Plant  is one of the largest and most advanced water treatment facilities in the world, but it still can’t solve the area’s water problems by itself. Heavy rains often overwhelm the District’s old combined system, leading to raw sewage spills in both rivers. However, partly because the Anacostia is much slower-moving than the Potomac, it remains more polluted. In 1971, fecal bacteria levels were so high that the District made it illegal to swim in the Anacostia. Few residents of Mount Rainier or Bladensburg risk swimming in the river, either. The river is tidal and rises and falls about three feet at the Bladensburg Marina, which means that sewage could possibly flow about 1,000 feet upstream.  The Anacostia’s pollution problems also threaten the Chesapeake Bay.

Maureen Mitchell, water quality project manager for Anacostia Riverkeeper, explained that the District’s combined sewer outflows aren’t the only problem. She wrote, “The MS4S of D.C. and the upper watershed in Montgomery and Prince George’s [County] lead to continuous challenges from point and nonpoint pollution from roadways (fuel/oil, byproducts from tires), lawns (excess nutrients from overfertilization and other treatments), construction projects (sedimentation and illicit dumping) and more.”

Nevertheless, the successful completion of the NEBT will eliminate 98% of the flow of fecal bacteria into the Anacostia, according to DCWater. It also means that much of the stormwater from Northeast D.C. will now be purified at Blue Plains rather than flowing untreated into Fort Washington, Washington Harbor and other Prince George’s County communities downstream.

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