Washington Aqueduct releases year-long plan for repairs to the District’s original water conduit

U.S. Army Corps of Engineers, Baltimore District
Published Nov. 21, 2023

Washington Aqueduct crews will be conducting repairs to deteriorated sections of the utility's First Conduit, commonly referred to as the "Old Conduit", located under MacArthur Boulevard in Montgomery County, Maryland, starting late November 2023. Repair work will take place Monday-Friday, 7:00 a.m. to 5:30 p.m., at various locations along the conduit which may result in lane closures along MacArthur Boulevard.

Old Conduit Map.

The Old Conduit is a 12-mile-long circular tube structure carrying water from the Potomac River near Great Falls to the Dalecarlia Reservoir, which serves as the primary source of drinking water for approximately 1 million citizens living, working, or visiting in the District of Columbia, Arlington County, Virginia, and other areas in northern Virginia, including portions of Fairfax County.

Aqueduct staff conducted a visual inspection of the Old Conduit in March 2022 and determined that repairs and maintenance work were required to address compromises to the conduit's structural integrity caused by violations of imposed vehicle weight restrictions on MacArthur Boulevard.

Commuters are urged to remain aware of signage throughout work zones along MacArthur Boulevard that can indicate reduced speeds, lane changes, and other important information. Repairs are expected to continue through December 2024.

Originally appropriated by Congress in 1853, the conduit was built of brick, stone, and mortar and is 9 feet in diameter. It was the largest single structure involved in the construction of the Washington Aqueduct, directed by Corps of Engineers Lieutenant Montgomery C. Meigs, who also played a role in building a number of other well-known Washington landmarks including the Cabin John Bridge, Arlington National Cemetery and the extension and dome of the U.S. Capitol. The conduit design was based upon the early New York and Boston aqueducts, completed a decade earlier in the 1840’s. Water from the Potomac River was first introduced into the conduit in December 1863.

Construction of the Washington Aqueduct conduit. Library of Congress. 

The Washington Aqueduct, a division of the Baltimore District, U.S. Army Corps of Engineers, is a federally owned and operated public water supply agency that yields an average of 135 million gallons of water per day at two treatment plants in the District of Columbia. For more information on the Washington Aqueduct, go to http://www.nab.usace.army.mil/Missions/Washington-Aqueduct/.

Baltimore District delivers vital engineering solutions in collaboration with its partners to serve and strengthen the Nation, energize the economy, and reduce disaster risks. Headquartered near Baltimore’s Inner Harbor, Baltimore District provides design, engineering, construction, environmental and real estate expertise to a variety of important projects and customers. This support spans across five states, the District of Columbia, overseas, and across the Susquehanna, Potomac, and Chesapeake Bay watersheds. These civil and military missions and diverse engineering services support communities and warfighters while addressing the ever-growing list of emerging national security requirements and ultimately protecting the Nation.


Cynthia Mitchell
443-240-5019 (cell)
Robin White
202-510-4013 (cell)

Release no. 23-013