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Last month, crippled one of the largest pipes feeding water to urban Honolulu, stymying an already slow westbound commute across Oahu for about two weeks as local officials scrambled to fix the vital link as soon as possible.

The crews had been digging a new sewer line for the Army under the Moanalua Freeway near Fort Shafter when the accident happened. They knew the Board of Water Supply’s 42-inch diameter main, which feeds some 15 million gallons each day to customers from Kalihi to Hawaii Kai, was in the area.��

Still, they thought they were in the clear.

“Our plans and specifications indicated that we were going to miss the water main by quite a bit,” Todd Barnes, U.S. Army Corps of Engineers Engineering and Construction Division chief, said at a two days after the accident. “We weren’t anticipating this.”

It was precisely the type of that local officials want to avoid once heavy rail construction moves eastward down Dillingham Boulevard, where a separate 42-inch water main plus numerous other utility lines snake beneath the narrow, crowded street.

Combined, the two large mains — the one that runs near Fort Shafter and the other beneath Dillingham — supply about half of urban Honolulu’s water supply, piping it in from wells around Pearl Harbor and Halawa. The rest of the city’s water comes from wells in town, according to the Board of Water Supply.

Yet Oahu has a problem: The locations of the island’s vital utility lines often don’t match what’s in utility companies’ own drawings.

“Underground construction, wherever you do that on this island, can be challenging,” BWS Manager and Chief Engineer Ernest Lau said at the same media briefing as Barnes. “There are a lot of utilities underground and sometimes the plans or designs are not perfect.”

Sometimes the discrepancies are found prior to construction through testing methods such as sonar and ��Other times the mismatches are discovered the hard way: during construction.

For rail, that’s been happening regularly during the preliminary construction in town, according to Honolulu Authority for Rapid Transportation officials. At one point, crews were finding utility lines where they didn’t expect them several times a week, Marc Gravel, a former HART project director, .

When heavy construction reaches Dillingham, it’s not a matter of if but when crews will encounter the same problems, Gravel and others at HART have said.

Meanwhile, BWS cannot guarantee that its drawings outlining the path of the 42-inch main under Dillingham are 100% accurate, according to Lau. It all depends on how well his predecessors at the water agency recorded the pipe’s precise location when it was built, he said.

Some parts of that giant main at the west end of Dillingham are about 50 years old, Lau told the Honolulu City Council last year.��

“It’s a possibility during places of intense construction that things can happen,” Lau added during an interview Thursday, referring to utility line damage. “When they come close to where our pipe is located, then yeah, that does cause us concern.”

Lau said the trench work planned for the rail construction on Dillingham is less risky than the Army-contracted horizontal tunnel work that crippled the 42-inch main at the freeway on June 18.

Still, even the slightest chip or leak in the giant steel pipe beneath Dillingham would have a huge impact on Honolulu’s water supply, Lau added. It would force the BWS to shut down the main entirely until repairs could be completed.��

“The bigger the pipe, the greater the effect on the water system,” Lau said Thursday.

The 42-inch mains are the largest in the BWS system.��

Running The Utility Gauntlet

The existence of the large main under Dillingham has vexed HART officials for years as they try to figure out how to fit the future transit system’s elevated guideway down that narrow street.��

It’s a big reason why the rail agency has been unable to solve the puzzle of how to properly relocate all the water, sewer, drainage, gas, electrical and telecommunication lines that run along that tight, crowded corridor, plus get the design approvals needed from the city and the utility companies.��

That failure, in turn, is a big reason why the largest public works project in the state’s history now faces a more than 10-year delay — the full 20-mile line isn’t slated to open until 2031 — plus a renewed budget deficit of around $3.6 billion.

HART will further have to avoid hitting the numerous smaller water lines that connect to the 42-inch main and branch out across both sides of Dillingham.

Lori Kahikina, the agency’s interim executive director, was unavailable Thursday to discuss the challenges posed by the main, according to HART spokesman Joey Manahan. He did not respond to follow-up requests to discuss the matter Friday.

Last year, several city department heads, including Kahikina, who was then serving as the city’s environmental services director, rejected HART’s request for special utility-clearance design exemptions, or “variances.” They would have allowed the rail agency to squeeze utilities closer together than what’s normally allowed at some 31 different choke points along Dillingham.

Although Kahikina has rejected design variances, she’s also acknowledged that final designs will be based on flawed drawings and information.

It’s inevitable that the rail project will still need utility clearance variances — but they’ll come once heavy construction starts and crews encounter unforeseen circumstances under the road, she and other rail officials say.

“To have to stop and redesign the whole system because a pipe is not where it’s supposed to be, that’s going to be difficult,” Kahikina . “So before we do shovel-to-ground, we’re going to have to meet with the agencies to understand what would be allowed once we encounter something like that.”

Meanwhile, the 42-inch main that ruptured last month next to the freeway required crews to dig a garbage truck-sized trench to make the repairs, Lau said. The effort required closing up to two westbound freeway lanes at some times.

When the June 18 accident occurred, BWS wasn’t sure how long those repairs would take. The agency tried out a new welding-repair method to help speed things up and managed to have the main fixed on June 30, Lau said. BWS��expects to have the road re-striped by next week.��

Had the incident occurred in August or September, which is when Honolulu sees its peak water demand, the BWS likely would have asked customers to conserve water, Lau said.

Lau added, incidentally, that the pipe that was damaged last month carries water from the aquifer near Red Hill, where BWS worries that continued leaks from the Navy’s underground fuel storage tanks could eventually contaminate Honolulu’s drinking water supply.