Occasionally, helicopters can be seen over the Potomac River rescuing people stranded on the rocks, but it’s rare see a helicopter putting people on them. That’s exactly what is happening this week just north of Great Falls in Virginia.
D.C. Water is dropping crews and a 14-ton drilling rig to gather samples for a future sewer project.
In the cold dawn hours Monday morning, helicopters dangling pairs of workers made several trips, dropping them onto the uneven and frozen rocks in the middle of the Potomac River.
They were followed by a specialized drill that can punch out 2.5-inch rock samples.
They will use that drill to dig 50 feet into the rocks that jut out near the Washington Aqueduct to gather core samples that will help inform them on the future project, but the work this week will be harrowing.
“(It’s) kind of challenging when you’ve got on the river and the water level fluctuates a little bit,” said Brad Murray, a geotechnical engineer with Delve Underground.
He said most of the time, drilling is fairly easy with work trucks traveling to the exact spot, but when the project will travel underneath the Potomac River, things are a little more challenging.
“We’ll take these samples, send them to a lab and actually do some scientific testing of their strength,” Murray said.
This is the very first step in a rehabilitation of the 3,000-plus feet of Potomac Interceptor pipe that runs underneath the river.
The Potomac Interceptor is a 54-mile pipe that runs from Dulles Airport to D.C. Water’s Blue Plains wastewater treatment plant. There are 84 different connections from contributing municipalities, including the cities of Herndon and Vienna, as well as Fairfax and Loudoun counties; all contribute to the 60 million daily gallons that run through the sewage pipe.
The Potomac Interceptor was built back in the ’60s. They are now looking to rehab or even possibly build a redundant pipe that can be used if the current pipe is ever damaged.
“We’ll look at the samples to understand the fracturing of those samples, looking at how watertight the rock is,” said Eric Lienhard, deputy program manager of the Clean Rivers team which works on the Potomac Interceptor.
Moussa Wone, vice president of D.C. Water said, “This investigation is basically to get some geological data to inform us in the design of the alternative.”
Crews will be out all week boring into five different spots to gather those rock samples before they are sent off to be analyzed.
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