SAN JUAN, Puerto Rico - Inside a small concrete pump station by the side of a freeway, a Quality Assurance team from the U.S. Army Corps of Engineers and a crew of government contractors labor over a large orange generator. The station is part of a complex flood control system that helps keep San Juan and neighboring towns dry. It is just one of hundreds of sites Corps teams are visiting as part of a unique mission to repair local generators and keep critical infrastructure functioning in the aftermath of Hurricane Maria.

The mission, known as Non-Federal Generator Operation and Maintenance, focuses on repairing and maintaining the electrical generators that already exist in Puerto Rico. In a typical disaster response, the Corps of Engineers, in conjunction with the Federal Emergency Management Agency (FEMA), delivers emergency generators to provide temporary power to essential facilities such as hospitals and water treatment plants.

By fixing pre-existing generators at those facilities, the Corps can free up the federal emergency generators for use at additional sites. To date, the operation and maintenance mission has assessed nearly 400 generators to see which ones are repairable and what parts they need. The teams have repaired more than 100 generators.

"Every generator that we are able to keep running is one less generator that another agency has to push out," said Zach Taylor, Mission Manager for the Savannah Emergency Power Planning and Response Team, which runs the operation and maintenance mission in Puerto Rico. "Everything we do, is less that they have to do."

The operation and maintenance mission is a response to the large scale of destruction in Puerto Rico, as well as the logistical challenges of getting temporary emergency generators here from the mainland United States. It complements both the grid restoration work conducted by the Corps of Engineers and the Puerto Rico Electric Power Authority (PREPA), and the emergency temporary generator mission.

"It's a way to relieve the pressure of getting generators here, and it's a way to fast track providing power to the island," Taylor said.

The mission has its own challenges. The majority of the generators assigned for maintenance are owned and operated by the Puerto Rico Aqueduct and Sewer Authority (PRASA). They power flood control systems, water purification plants and sewage treatment plants, and many were installed decades ago. In some cases, the generators were flooded during the hurricane or sucked in debris that was stirred up by the storm, and they require maintenance.

When the Quality Assurance teams and contractor crews first head out to a site to assess how well the generator is functioning, they must be prepared to troubleshoot and repair a vast array of generator types. The generators are often unique, older models and may require odd parts that are not easily available. For example, one team encountered an old submarine engine that was powering a generator.

"When we go out to [assess] these generators, we never know what size the generator is going to be, and we never know what it's going to need. We're running into unusual things, unusual matchings on generators -- as far as the motor and generator -- and unusual control panels," said Michael Kunkel, the owner and founder of Automotive Experts, one of the contractors working on the operation and maintenance mission. "Some of them are a conglomeration of things, and so finding parts and preparing them is challenging to say the least."

The effort is well worth it, said Mike Bauman, a Quality Assurance technician from the Corps of Engineers' Honolulu District. He described a situation in one town where residents were desperate to get the generator working at a wastewater plant.

"When I first got here, the wastewater treatment plants weren't working, and sewage was backed up in homes. The next day we got it running. That's always rewarding, being able to help and give back to these communities," he said.