It sounds like something straight out of an action-adventure movie: an intense, hours-long struggle to close a stubborn valve succeeds at the last minute, saving thousands from impending disaster.

Although the real-life threat—a high-pressure water main on the verge of failure—may not have the panache of say, an alien invasion or nuclear meltdown, the Washington Suburban Sanitary Commission (WSSC), in suburban Washington, DC, will gladly take the alls-well-that-ends-well outcome over its original plan to implement a multi-day service outage affecting than 100,000 customers during the hottest stretch of weather the area has seen so far this year.

The drama unfolded around a 54-inch diameter reinforced concrete high-pressure transmission line that delivers 10-15 million gallons of water daily to a large portion of Prince George’s County, Md., including residences, Andrews Air Force Base, and businesses such as the 300-acre National Harbor mixed-use complex adjacent to the Potomac River.

Installed in 1966 near the Capital Beltway, the pipe is part of WSSC’s 350-mile network of high-pressure mains that has experienced multiple failures in recent years. The most dramatic occurred in 2008, when a sudden burst of a 66-in diameter main inundated the main road through a semi-rural part of Montgomery County, Md., requiring helicopter rescues of several trapped motorists. A 2011 failure just north of the current problem pipeline left more than 400,000 users without water for the better part of a week.

WSSC blames the failures on pipes manufactured using the once-acceptable practice of tightly-wrapped steel wire for reinforcement. The companies that supplied the pipe in the 1960s and 70s have since gone out of business. The agency notes says that although less than 2% of the concrete pipes are affected, the estimated total repair cost is just under $3 billion.

After a 60-inch pipe fitted with failure detection sensors unexpectedly exploded earlier this year, WSSC decided to take no chances when acoustical tests of the Prince Georges County pipe indicated that 37 strands of the reinforcing wire had broken over a five-day period last week.

“The pipe would likely have failed in the form of an explosion,” WSSC CEO and GM Jerry Johnson told reporters. “It would have been a public service disaster.”

Although a nearby valve could divert water to a smaller main, requiring only a smaller section of the transmission line to be shut down, years of corrosion due to exposure to acidic soil had frozen the gears.

Estimates from local repair shops were far longer than WSSC could afford to wait, leaving the more extensive shutdown as the only practical option. A fast-tracked public awareness campaign urged customers prepare for an outage that could last up to five days, during which daytime heat indices are expected to regularly top 100º.

Meanwhile, WSSC employees Brad Destelhorst and Tom Ecker volunteered to attempt one last-ditch repair of the valve. Starting Saturday, July 13, Destelhorst and Ecker took turns standing in a partially flooded, phone booth-sized vault using a hand grinder, chisels, scrapers, and a lot of elbow grease to reform the valve’s gears.

By late Tuesday, July 16, they had managed to close the valve, allowing water to be diverted to other sections of WSSC’s water supply network. Once the bypass system’s ability to meet demand was confirmed, the agency cancelled the outage alert, although customers were asked to conserve water use until the transmission line repairs are completed this weekend.

A visibly relieved Johnson praised the employees for persevering despite the constraints and doubts.

“This was something that had never been done before,” he told reporters. “The workers went well beyond call of duty.”