Utility Gets Drone's-Eye View of Inflow and Infiltration

Minneapolis takes advantage of drone technology to more effectively monitor rooftop vents during annual smoke testing.

Utility Gets Drone's-Eye View of Inflow and Infiltration

The City of Minneapolis Surface Water and Sewers Division has employed drones in its smoke testing program to get a better look at the tops of buildings without having to send workers onto private property.

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Pump smoke into a sanitary sewer system and observe. It’s a common method municipalities use to identify illicit sewer connections. But even a fairly straightforward process has room for improvement, as the city of Minneapolis has shown.

For the past two years, the city’s Surface Water and Sewers Division has experimented with using a drone in its annual smoke testing in hopes of improving efficiency as well as worker safety. Smoke testing in residential neighborhoods presented no problems, says Katrina Kessler, director of the Surface Water and Sewers Division, but when the environment shifted to industrial and commercial areas, it wasn’t as easy.

“The smoke testing primarily involves city staff standing in the middle of the right-of-way and looking at the top of buildings,” Kessler says. “That works fine if it’s a residential neighborhood with shorter buildings, but when it’s a large commercial building where you actually need to have someone go up on the roof in order to check if the smoke is venting in the right places, there can be complications. You have to find the right person who knows how to access the roof of these buildings, and then you may come to find that the vents are in difficult places and it’s unsafe to be up on top of the roof.”

The city decided that a drone could potentially be an answer to eliminating those complications while still getting a proper view of the rooftops of Minneapolis’ largest structures. The smoke testing program began in 2007, and the city dedicates the months of August through October to it. A drone was first brought in for 2017’s round of testing.

“The city has worked with a consulting firm that has one drone,” Kessler says. “The firm operates the drone with a two-person crew, and we have two people from the city there as well, watching the video footage as it’s being shot, because the consultant doesn’t have as much experience knowing what to look for.”

In 2017, the city conducted smoke testing for 717 total blocks, with the drone being used on 118 of those. The drone footage was able to identify 13 illicit connections. In 2018, the drone was again used on 118 of a total of 654 blocks that were smoke tested. No illicit connections were identified by the drone from this most recent go-around of testing.

“Overall we’re very pleased with the results,” Kessler says. “We did get good images and were able to view and identify illicit connections. We definitely gained efficiencies. We estimate that for each larger building we smoke tested with the drone, it took us 15 to 30 minutes less than it would have getting in the building, talking to people and walking around on the roof. Using the drone required fewer city staff, but we still had the consultant. That was kind of a wash, but without the drone, it would have taken longer and we would have gotten less done. And it’s definitely a win in the safety column.”

However, something extra the city had to be cognizant of by using a drone was the issue of privacy. Kessler says her division made sure to communicate with the public to inform them that the drone would be limited to commercial areas and large buildings with flat roofs and would only be operated from the public right-of-way. And the crew was careful with how exactly the drone was operated.

“Essentially what would happen is the staff would be in the middle of the street, fly the drone up above the building, turn it to look at the top of the building and bring it back down,” Kessler says. “They weren’t flying over the roof. We wanted to make sure we weren’t infringing on private property.”

There are about three more years of smoke testing left to cover the entire city, but in the meantime, Kessler says the city is looking at potentially procuring its own drone for other beneficial uses within the Public Works Department. Stormwater outfall inspections is one of those possibilities.

“A lot of the city ultimately outfalls to the Mississippi River, and some of those outfalls are high up on bluffs or in difficult areas that you can’t really access except by boat and only when the conditions are safe to do so,” Kessler says. “That’s one thing we thought about going forward.”

Acquiring a drone would require Federal Aviation Administration licensure for employees to be able to operate it, and privacy would continue to be a concern if the city ends up going that route.

“We want to make sure we have the support of the elected officials and that we’re following the right legal processes if we go and get a drone ourselves. So we’re not there yet, but we’re exploring the option,” Kessler says.

For any other municipalities contemplating using a drone to aid day-to-day operations, Kessler emphasizes the vital role of communication.

“I would say that communication is really important, both with elected officials and the city attorney’s office as well as citizens.”


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