To protect the city of Alameda’s water supply from potentially crippling damage during an earthquake, the East Bay Municipal Utility District recently completed a highly complex project: replacing a vulnerable underwater, cast-iron water main with a 3,300-foot-long, high-density polyethylene pipe.

The project, which cost $26 million, was completed in January after about a decade of planning. It dramatically improves the resiliency and reliability of the transmission system, which carries water under the harbor from Oakland to Alameda, a city on an island in San Francisco Bay, via four pipelines — the new earthquake-resistant line and three older lines, says Raffi Moughamian, an associate civil engineer in the utility’s pipeline-infrastructure division.

The engineering feat was achieved by using horizontal directional drilling technology. A 44-inch-diameter bore hole was drilled about 155 feet below the harbor floor. This particular pipeline, which can carry approximately 25 million gallons of water per day, was installed first because it is Alameda’s primary water feeder.

“The city has no reservoirs or water-storage tanks to hold emergency water supplies, so they’re completely dependent on the water lines,” he says, underscoring the project’s importance.

The project also included the open-trench installation of 11,000 feet of 24-inch steel pipe in both Oakland and Alameda to connect the new pipeline to the existing transmission system.

During the next decade or so, two more of the aging, cast iron water mains will be replaced with earthquake resistant HDPE pipes to further protect the city’s roughly 80,000 residents from potential water-service interruptions stemming from seismic activity. The fourth main will not be replaced, Moughamian notes.

“We looked at all the data and determined that three new pipelines, which will be as large or slightly larger in diameter than the existing lines, would be sufficient to meet Alameda’s future water needs,” he says.

EBMUD supplies water to approximately 1.4 million people in a 332-square-mile area across the bay from San Francisco; the service area covers 20 incorporated communities — including Oakland and Berkeley — and 15 unincorporated communities.

The utility gets its water from 90% from snowmelt in the western Sierra Nevada mountains. The water is stored in two up-country reservoirs. EBMUD also owns and operates five water reservoirs, six water treatment plants and about 4,200 miles of pipelines. In addition, the utility operates wastewater collection and treatment infrastructure.

UNSTABLE SOIL

The new underwater pipelines are needed because the original lines, some of which date back to the 1940s, weren’t laid deep enough. For example, the recently replaced pipeline was buried only 50 feet below the inner harbor floor.

Furthermore, the soil surrounding them was too liquefiable, or unstable, which raised the risk of pipe failures due to inadequate support for the brittle cast iron pipeline, Moughamian explains.

“It was a huge problem … that required a proactive approach,” Moughamian says. “We avoided that liquefiable layer of soil by installing the new line deeper than the original line.” 

Pipeline construction began in summer of 2022. About half of the bore was drilled from the Oakland side of the harbor and the other half was drilled from the Alameda side.

The underwater portion of the project culminated in early April 2023 when the pipeline was pulled through the bore hole — an operation that took contractor Michaels Corp. about a day to complete, he says.

“The pull of the new pipe under the estuary was a remarkable feat of engineering and construction,” said Doug Linney, the director of the EBMUD board. “This work will benefit the residents of Alameda for decades to come with a more resilient and reliable water distribution pipeline.

“We are extremely grateful and proud of this effort, the crews who performed it and our customers for their patience and support.”

COMPLEX PROCESS

The pipeline was created by fusing together 63 sections of HDPE pipe, a process that took about three months to complete. When completed, the pipeline was laid out along a little more than a half-mile stretch of Mitchell Avenue in Alameda.

Before it was pulled through the borehole, it was pressure tested to detect leaks, Moughamian says.

“Laying out more than 3,000 feet of pipe in a highly urban, densely populated area was a challenge,” he notes. “We had to do a lot of community outreach and develop plans to minimize the impact on residents and businesses, including traffic-control strategies.”

The pipe was pulled from Alameda to Oakland at a rate of between 3 to 4 feet per minute. The pipe rested on more than 100 pipe rollers. These small metal stands feature rollers that enable the pipe — which weighed a whopping 457,000 pounds (about 228,500 tons) — to move throughout the pull.

Even with years of planning, was it nerve-wracking to watch the process unfold?

“Yes – I’m not going to lie,” Moughamian says. “It definitely was a big day. But everything went very smoothly, with no major issues.”

MAJOR INFRASTRUCTURE UPGRADES

The underwater pipeline replacements are just a small part of a sprawling and ambitious $2.8 billion, five-year infrastructure upgrade program underway at EBMUD, marking one of the utility’s most capital-intensive periods since its establishment in 1923.

The program includes rehabilitation of water treatment plants, pumping plants, reservoirs, pipelines, wastewater facilities and sewer interceptors.

“Water infrastructure is the very lifeline of society,” says Jimi Yoloye, the utility’s engineering and construction director. “We cannot delay investing in this system. We must bring projects like the Oakland Inner Harbor Crossing to fruition. The coming years will be exciting and vital for our region’s future.”

During the last two fiscal years, the utility replaced about 45 miles of water mains.

“Our goal is to replace at least 20 miles of pipe a year, mostly aging cast iron mains, and we beat that goal by a few miles last year,” says Nelsy Rodriguez, a media spokesperson for  EBMUD.

In addition, the second underwater water main replacement is currently in the design phase. The approximately 2,050-foot-long HDPE pipeline will be installed via horizontal directional drilling on the south end of Alameda’s island. It will travel about 120 feet below the floor of San Leandro Bay.

After that project is completed, the third HDPE pipeline, which will be an estimated 1,300 feet long, also will be installed via horizontal directional drilling. It will be located about halfway between the first two pipelines and will pass about 100 feet below the bottom of a tidal canal.

Moughamian says that when the three projects are completed, Alameda will be better prepared for future population growth and economic development.

“These pipelines will help ensure that Alameda continues to receive high-quality water without service disruptions,” he says. “They will better position the city to meet its future water needs.

“As a utility, we’re always trying to proactively plan for an uncertain future.”