New Plan for ‘Perceived Odor’

New Plan for ‘Perceived Odor’

On a hot dry day, the stench assaults hikers along the towpath, residents of Cabin John along the C&O Canal and drivers of convertibles on the Clara Barton Parkway.

But the smell does not come from slow-moving water in the canal.

The stink is in fact just what it smells like: raw sewage baking in the heat.

The smell wafts from vents in the Potomac Interceptor, a sewage pipeline carrying 50 million gallons of “wastewater” a day. The sewer pipe, which has 50 vents, originates near Dulles Airport and runs to the Blue Plains Advanced Wastewater Treatment Plant in D.C. for treatment before discharge into the Potomac River.

The interceptor runs along the canal on Maryland side of the Potomac River with a series of vents running from Great Falls to the District, and another series of vents for several miles above Swains Lock.

The DC Water and Sewer Authority refers to the problem as “perceived odor.” Their website says the problem began in the hot, dry summer of 1999.

Residents in Cabin John say they have been perceiving the odor for somewhat longer than that.

"I've been smelling it for 23 years," said Cabin John resident Reed Martin, who said he is frustrated by slow progress by the National Park Service and WASA in addressing the issue. "I've given up on them totally."

Now relief may be in the works.

The DC Water and Sewer Authority (WASA) began a study of the issue in 1999, when low wastewater flows combined with high temperatures resulting in “increased odor potential,” according to the Potomac Interceptor's website.

A new proposal calls for a combination of active blower units, sealed vents and intake-only vents with passive carbon filters to control the odor problems.

"[At first], I just thought the smell was due to stagnant water in the canal," said Burr Gray, president of the Cabin John Citizens Association. "You don't notice that the vents are what it's emanating from unless you're particularly observant."

Vents near locks 8 and 10, both part of the "Seven Locks" portion of the canal near Cabin John, are especially noticeable, said Gray. The odor by these vents "gets going pretty well in the summer."

Congress authorized the design and construction of the Potomac Interceptor in 1960. Several jurisdictions discharge into the system, including Loudoun County and Fairfax County in Virginia, Montgomery County and the District of Columbia.

The National Park Service released the results of an environmental assessment of long-term odor control. The long-term plan proposes four facility sites within the C&O Canal National Historic Park and the George Washington Memorial Parkway.

Gray said he was told a public comment period would run through Oct. 18, with a public meeting planned for Oct. 2 or 9 in Glen Echo.

Martin suggested a different location.

"If there are any meetings of public interest they should hold them under the Chain Bridge," said Martin. "That would make it clear to anybody what the problem is. … Just don't light a match."

Officials at the Water and Sewer Authority did not return calls by presstime.

The environmental assessment is available for review at Potomac Library, Great Falls Tavern in the C&O Canal National Historic Park, Little Falls Library in Bethesda, and Clara Barton House in Cabin John. The environmental assessment is also available online at