Washington Aqueduct Old Conduit Repairs Project

MacArthur Blvd between Goldsboro Road and Walhonding Road, as well as between Clara Barton Pkwy and Persimmon Tree Road: single-lane closures will be required along the aforementioned sections of MacArthur Blvd during non-peak hours, 9 a.m. to 3 p.m., Monday through Friday, June 10 to June 21, 2024 (Goldsboro to Walhonding) and June 17 to July 12 (Clara Barton to Persimmon).  Click here to view map of roadway sections that will be impacted.

Project Overview

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.

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.


Old Conduit Map

Old Conduit History

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.

Construction of the Washington Aqueduct. Library of Congress photo. 

Construction broke ground for the conduit in November 1853, with a force of 300 to 400 men at any given time. Labor was intensive but plentiful. The only machine available for construction purposes during that time was the steam-driven hoist. Aqueduct historical reports include mention of a steam-operated rock drill trial, which led to a determination that drilling by hand was far superior and faster.

Water from the Potomac River was first introduced into the conduit in December 1863. The conduit was placed in regular service in July 1864 and thanks to the qualified professionals that have overseen its operations and maintenance throughout the past 159 years, remains a vital component of ensuring that the approximately one million citizens living in, working in, or visiting the Nation’s capital can access safe water, a key component to public health and safety.


Contact Us

For questions regarding this project, contact us via email