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D.C. Water will deploy lidar-equipped drones along the 54-mile Potomac Interceptor following a sewer collapse that sent more than 240 million gallons of sewage into the Potomac River.
Flights are scheduled for weekdays from March 26 through April 3, weather permitting, between 8 a.m. and 3 p.m. The interceptor carries wastewater from Loudoun and Fairfax counties through Montgomery County to the Blue Plains Advanced Wastewater Treatment Plant.
The aerial surveys will document above-ground conditions and topography along the sewer line. Crews will use the resulting maps to identify locations with rocks or boulders that may require additional inspections using equipment such as ground-penetrating radar.
The data will also guide D.C. Water’s ongoing 10-year, $625 million rehabilitation of the Potomac Interceptor.
The inspection follows the Jan. 13 collapse of the sewer line near Clara Barton Parkway. Large rocks and boulders used as backfill when the interceptor was built in the 1960s blocked the damaged pipe, causing an unusual overflow. Sewage poured into the river for several days.
The drones will carry lidar, or light detection and ranging, equipment that produces detailed three-dimensional maps of vegetation, buildings and ground surfaces. Because the equipment makes the aircraft larger than typical recreational drones, they will need to land repeatedly for battery changes.
The drones will operate at elevations of roughly 300 to 350 feet and display flashing navigation lights. D.C. Water coordinated the flights with the Federal Aviation Administration because portions of the route inside the Capital Beltway cross restricted airspace.
People using the C&O Canal may see the aircraft overhead. Sherri Lewis of D.C. Water described the work as a routine inspection and said the drones do not emit harmful beams or present a public health or safety risk.
Crews will place temporary yellow-and-black ground markers throughout the survey area to ensure the flights and collected data remain accurate. Officials are asking the public not to touch or move them.