O’Hare’s ‘Hot Tap’

Diverting Water for A Half-Million People

by Steve Kaelble

It takes a huge volume of water to supply 600,000 customers, and when all that water flows through one massive pipeline, it’s a big job to move the pipeline without shutting off the water.

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That was the challenge of a $25 million utility project linked to the massive modernization at Chicago’s O’Hare International Airport. The solution was to tap into the live water main and temporarily divert the water away from the section that needed to be moved.

The 9-ft-wide pipeline, 90 in. across on the inside, is owned by the North Suburban Municipal Joint Action Water Authority. The water main serves customers in seven northwest suburbs, and its original course took it 5 ft below grade across a piece of land needed for construction of O’Hare’s eighth runway. Building a runway over a massive water main would not be wise because servicing the line would require shutting down and digging up the runway.

“We had to get it out of the way,” says Rosemarie Andolino, executive director of the O’Hare Modernization Project. “There was no other option.”

The old alignment cut diagonally across the planned runway. The pipe now parallels the runway and is about 1,000 ft from the centerline of the runway.

Keeping the Spigot Open

One thing was clear: It would not be reasonable to shut down water service for so many customers, not even for a short time.

The solution involved technology from pipeline-maintenance manufacturer T.D. Williamson Inc. to “hot tap” into the water main, diverting the water into a temporary bypass line so that workers could connect a new permanent section of pipeline running around the north end of the runway expansion area.

“It was essentially like performing bypass surgery,” Andolino adds.

There simply was no way to make a permanent connection to a new, full-sized section of pipeline while water was running through it. The bypass allowed the water to keep flowing to customers on the other end, while giving contractors a dry section of pipeline for making the permanent connection.

The process may sound relatively simple, but it required careful planning and meticulous execution. Water inside a main this size creates a tremendous amount of pressure.

“You have to work with no mistakes,” says Wes Brazas, senior resident project representative in Chicago for Muscatine, Iowa-based Stanley Consultants, designer of portions of the project. “You check everything and double-check everything before you do it.”

Tapping In

An initial step was to locate sections of pipeline suitable for tapping on each end of the project.

Patrick Armstrong, who served as project manager for T.D. Williamson, says the prestressed concrete pipe includes a layer of steel, but the thickness of the steel varies from one point of the pipeline to another. Because the job required chipping away at the concrete outside of the steel layer before tapping into the pipe itself, it was necessary to find places with steel at least 5/16 of an in. thick thick enough to handle the water pressure even with the outer concrete removed.

Once the tapping locations were determined, Stanley had to design thrust-restraining systems to keep the pipeline from shifting during the project, Brazas says.

This was critical because of the massive force exerted when stopping the water flow in the main pipeline and diverting it into the bypass line, basically turning the column of water 90 degrees to bring it up to ground level where the temporary line traversed the construction site.

Thrust blocks secured by 4-ft-diameter caissons prevented all lateral and vertical movement and maintained the 90-in. pipeline’s integrity, Brazas says.

The hot-tapping process involved installing custom-fabricated “saddle” fittings onto the 90-in. line, two at each end of the project. Onto those fittings went shutoff valves, and on the other side of those valves T.D. Williamson attached special closed-system cutting equipment.

The cutting equipment then sliced into the water line, creating openings but no leaks, because the cutting equipment was located inside a closed-system environment. Once holes were created, the valves were shut again, allowing workers to remove the cutting equipment and attach the 48-in. bypass line from one end of the project to the other.

With the bypass line in place, the contractor then installed specially designed stopples at the other two valve locations.

Armstrong says that the stopple equipment was attached to the remaining valves on each end that were located just inside the bypass connections. Like the cutting equipment, the stopples were housed inside a closed system so that when the water valve was opened, the pipeline retained its seal.

T.D. Williamson’s stopples were designed to drop through a 60-in. hole in the pipeline, then expand to plug the entire 90-in. water line. With that flow stopped, the water diverted into the 48-in. bypass, he says.

That allowed the middle section of the permanent pipeline to be drained, and workers began connecting it to a new section of 90-in. pipe that had been laid along a course outside of the runway construction area. Once that connection was complete, the stopples were removed to bring the new section of pipe online, and the bypass line was shut off and removed.

Shoot for the Moon

The time that the bypass was actually in use wasn’t all that long 42 days but the overall planning took much longer, Armstrong says.

“We started working with the city nearly five years ago, talking to them about this option,” he adds. A full-scale simulation was constructed to demonstrate the stopple system, to verify its functioning and to ensure the system was tailor-made for the O'Hare project.

T.D. Williamson got the go-ahead in March 2006, and by the middle of the summer the locations to tap were identified and the thrust blocks were in place, but the tap could not commence until a separate contractor finished constructing the new 90-in. pipeline around the north end of the runway construction site.

T.D. Williamson’s crew performed the hot taps in early February, and toward the end of March installed the stopples that diverted the flow of water into the bypass pipes. The bypass remained in place until the permanent pipeline connection was complete in early May.

Brazas says the timing of the operation was critical because the plan was to take water from a large pipeline and divert it into a smaller bypass. That required picking a time when water use would be comparatively low, such as early spring.

“Water demand is a lot higher in the summer,” he adds.

The careful preparation paid off, and the hot tap and bypass were performed without incident.

“It was kind of like going to the moon,” Brazas says. “You get one shot at it, and we did it right.”

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