The Washington Aqueduct, which has carried water for the District since the mid-19th century, is undergoing $21 million in repairs.
The brick, stone and mortar aqueduct, also known as the “Old Conduit” is 10 miles beneath McCarthur Boulevard, was originally constructed by the US army to provide clean drinking water to the city. Now, according to a report by WTOP, it provides water to more than 1 million people in DC, as well as parts of Fairfax and Arlington counties in Virginia (An additional conduit was added in the 1920s).
Maga Mechanical Contractors was awarded the contract Dec. 7, 2022 by the US Army Corps of Engineers Baltimore District. The contract will allow for construction services for the repair or upgrade of mechanical equipment and infrastructure
“It’s actually an astounding piece of construction … most of the mileage of the pipe is still the original construction, and is still in very good repair. It’s only in certain locations where it’s experiencing distress,” Robin White, construction branch chief for the Washington Aqueduct told the broadcaster. “It’s a 9-foot diameter conduit. So if you can imagine that general floor to ceiling height in a residential house is 9 feet … it’s quite a big pipe.”
“One of the big challenges for this particular construction was that the pipe had to cross the Rock Creek area. And so in order for the pipe to cross, they built what’s now known as Cabin John Bridge. At the time it was called the Union Arch Bridge. And for many decades, that bridge was a record holding bridge for a masonry arch structure and is still in use for that purpose today,” White said.
However, while the pipe/conduit has held up well through many decades, traffic on the road above it has become problematic.
“This pipe is experiencing some structural distress in several spots throughout its length, primarily due to overweight vehicles traveling on MacArthur Boulevard … there is a strict weight limit for vehicles on the roadway, which not everyone adheres to … the pipe travels along MacArthur Boulevard under its centerline and it’s, in some places, only 12 inches under the roadway,” said White.
When the conduit was originally constructed, concrete reinforcing with steel (rebar) wasn’t done.
“It being unreinforced is both a bad and a good thing … the No. 1 thing that corrodes in modern structures is the steel reinforcement. So we don’t have corrosion issues, because we don’t have reinforcement. And it will actually last longer, it will last for a very long time, provided that it’s not loaded improperly,” White said.
WTOP reports that the river intakes for the Washington Aqueduct are located at Great Falls, and gravity alone moves the water down the “Old Conduit” to the Dalecarlia Reservoir.
However, the yearlong repairs require a costly pumping process since the water needs to be electrically pumpedl from Little Falls to the Dalecarlia Reservoir/
“During normal operations, it does not cost any money to send the water from the river to the reservoir, it flows naturally down the slope by gravity. When we have to pump around, that costs an extreme amount of money, because of the electricity required to run the pumps,” White said. “On average, it’s $10,000 per day.”
According electricity bills represent $4 million of the overall $21 project.
The “Old Conduit” is being repaired with Shotcrete — concrete in liquid form pumped through a hose and sprayed in thin layers onto the inside of the conduit, WTOP reported.
