Washington Aqueduct | |
 TheUnion Arch Bridge carries the Washington Aqueduct acrossCabin John Creek in 2008 | |
  Dalecarlia Reservoir & Treatment Plant | |
| Location | 5900 MacArthur Blvd., NW Washington, D.C. |
|---|---|
| Coordinates | 38°56′15″N77°6′51″W / 38.93750°N 77.11417°W /38.93750; -77.11417 |
| Built | 1853-1864 |
| Architect | Montgomery C. Meigs |
| NRHP reference No. | 73002123 |
| Significant dates | |
| Added to NRHP | September 8, 1973 |
| Designated NHL | November 7, 1973 |
TheWashington Aqueduct is anaqueduct that brings water from thePotomac River toWashington, D.C., and parts of its suburbs.
One of the first major aqueduct projects in the United States, it was commissioned by theU.S. Congress in 1852, and construction began the following year under the supervision ofMontgomery C. Meigs and theU.S. Army Corps of Engineers. Portions of the aqueduct began operation on January 3, 1859, and the full pipeline began operating in 1864.[1]: 68 It has been in continuous use ever since.
Owned and operated by the Corps of Engineers, the aqueduct is part of the system that supplies thepublic water systems that serve D.C. and nearby Virginia locations, includingArlington County,Falls Church, and part ofFairfax County.
It is listed as aNational Historic Landmark. TheUnion Arch Bridge, which carries a portion of the aqueduct, is also listed as aHistoric Civil Engineering Landmark.
The centerpiece of the Aqueduct is a 12-mile (19 km)pipeline that connects the system'sdam atGreat Falls with theDalecarlia Reservoir on the border withMontgomery County, Maryland. Portions of the Aqueduct went online on January 3, 1859, and the full pipeline began operating in 1864.[1]: 68 The pipeline runs along what is nowMacArthur Boulevard, traversing some of the higher cliffs along the Potomac River.
TheUnion Arch Bridge carries the pipeline and MacArthur Boulevard overCabin John Creek and theCabin John Parkway near the community ofCabin John, Maryland. This bridge was the longestmasonryarch bridge in the world for 40 years.[2][3]
The Dalecarlia Reservoir serves as a primarysedimentation basin. A portion of the water from the reservoir is treated at the nearby Dalecarlia Water Treatment Plant and distributed to municipal water mains. The remainder of the water from the reservoir flows to theGeorgetown Reservoir in thePalisades neighborhood of Washington. This facility serves as an additional sedimentation basin, and then the water flows through theWashington City Tunnel to the treatment facility at theMcMillan Reservoir, after which it is pumped through city mains. The Dalecarlia Reservoir was modified in 1895 and 1935 to improve water quality and increase water supply.[1]: 99
The Aqueduct originally used a single pipe to deliver water. It lackedwater purification plants, relying instead on the reservoirs to act as settling basins. By the turn of the 20th century, Washington's growth and the high amount ofsediment in the Potomac's water kept the reservoirs from doing their jobs well. In 1905, the first treatment plant, a massiveslow sand filter bed system, was completed at McMillan Reservoir .[4]: Ch.4 Improvements in the early 1900s were planned and supervised by Army engineerHenry C. Newcomer.[5] The regular use ofchlorine as adisinfectant began in 1923 at the McMillan plant. The McMillan plant was not replaced until 1985, when arapid sand filter plant was opened next to it.[1]: 124–125
In the 1920s, a second pipe was added from Great Falls to Dalecarlia, along with several new reservoirs and a pumping station. A rapid sand filter plant at Dalecarlia Reservoir went online in 1927.[4]: 204–205 A 1950s upgrade made the Dalecarlia plant larger than the McMillan plant; it is the one that serves theVirginia communities that draw water from the Aqueduct.
In 1926, Congress approved selling water from the aqueduct toArlington County, Virginia.[1]: 105 A new water supply pipe atChain Bridge enabled service to Arlington to begin in 1927. More pipes were built as Arlington grew, including one under the Potomac River. In 1947, Congress approved adding the city ofFalls Church, Virginia, to the aqueduct system, and nearby portions ofFairfax County, Virginia, were added in the 1960s.[1]: 129–130
In 1959, the U.S. Army Corps of Engineers builtLittle Falls Dam, a new intake, and a pumping station.[4]: 256 This intake provides about 15 to 20 percent of the river water used by the aqueduct, and up to 30 percent during drought conditions.[6]
The Aqueduct is a wholesale water supplier to utilities that bill customers and manage water mains. The service area is:
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