Washington Aqueduct

Washington Aqueduct. The Washington Aqueduct is a major water supply system serving the District of Columbia and portions of Northern Virginia. Authorized by an Act of Congress in 1852, its construction was a significant engineering feat of the mid-19th century. Operated by the United States Army Corps of Engineers, it draws raw water from the Potomac River and delivers treated water to the Washington Aqueduct Distribution System.

History

The urgent need for a reliable public water supply for the growing capital city was championed by Montgomery C. Meigs, a captain in the United States Army Corps of Engineers. Construction began in 1853 under the supervision of Meigs, utilizing innovative techniques for the era, including large masonry tunnels. The initial system, featuring the Georgetown intake and the Chain Bridge reservoir, was completed in 1863, crucially providing water during the American Civil War. Major expansions followed, including the construction of the Dalecarlia Reservoir and the McMillan Reservoir in the early 20th century, named for Senator James McMillan. The system was further modernized with the addition of the Great Falls intake and treatment plant in the 1950s.

Infrastructure

The aqueduct's infrastructure is an extensive network of intake structures, reservoirs, tunnels, and pipelines. Primary water sources are the intakes at Great Falls and Georgetown, which draw water from the Potomac River. The raw water is conveyed to the Dalecarlia Reservoir, which serves as the primary sedimentation basin. From there, it flows via the Washington City Tunnel to the McMillan Reservoir for additional storage. Key conduits include the Georgetown conduit and the Dalecarlia Tunnel, which distribute water to the treatment facilities. The system also includes major pumping stations that supply areas like Arlington County and the Pentagon.

Water treatment

Water treatment occurs primarily at two modern facilities: the Dalecarlia Water Treatment Plant and the McMillan Water Treatment Plant. The process begins with chemical addition, including aluminum sulfate for coagulation and sodium hypochlorite for primary disinfection. Water then undergoes flocculation and sedimentation in large basins, followed by filtration through rapid sand filters and granular activated carbon. A secondary disinfection step uses chloramine to maintain water quality throughout the extensive Washington Aqueduct Distribution System. The treatment process is designed to meet stringent standards set by the United States Environmental Protection Agency under the Safe Drinking Water Act.

Operations and management

The entire system is operated and maintained by the United States Army Corps of Engineers, specifically its Baltimore District. Day-to-day management involves monitoring intake levels from the Potomac River, controlling flow through the Dalecarlia Reservoir and McMillan Reservoir, and ensuring continuous operation of the treatment plants. The agency coordinates closely with wholesale customers, including the District of Columbia Water and Sewer Authority and the Arlington County Department of Environmental Services. System operations are guided by a formal agreement with the Interstate Commission on the Potomac River Basin to manage water withdrawals, especially during droughts.

Water quality and environmental impact

The aqueduct consistently meets all federal and local drinking water regulations enforced by the United States Environmental Protection Agency and the District of Columbia Department of Energy and Environment. Regular monitoring checks for contaminants like lead, copper, and disinfection byproducts. The system's source water protection program involves collaboration with the Interstate Commission on the Potomac River Basin and upstream states like Maryland and West Virginia to address pollution in the Potomac River watershed. Environmental stewardship efforts include projects to reduce combined sewer overflows in partnership with the District of Columbia Water and Sewer Authority and initiatives to protect the riparian zones near the Great Falls Park intake.