Leaks Found in Subway Tunnel Lining : Metro Rail: $2.5 million in repairs are planned to seal punctures in plastic that keeps out dangerous gases.

Plastic liners designed to keep explosive methane and poisonous hydrogen sulfide gases out of Metro Rail subway tunnels leaked more water than expected during the March rains, prompting transit officials to order $2.5 million in repairs while searching for a better sealant.

The leaks, which were not apparent until the rains briefly broke the five-year drought, are not a safety problem because detection and ventilation systems would prevent any gas from reaching dangerous levels, said Ed McSpedon, executive director of the Rail Construction Corp.

Nonetheless, the RCC, the construction subsidiary of the Los Angeles County Transportation Commission, has promised to have an improved liner ready for the second phase of the project, part of which will extend west from MacArthur Park toward the methane-rich Fairfax District.

A spectacular 1985 explosion and fire at a discount clothing store in the Fairfax District led to several changes in the original Metro Rail project, including rerouting the subway out of the most heavily saturated methane zone and the addition of the 0.1-inch-thick polyethylene liner for the whole system, which also runs through gas-pocketed soil downtown.

The Fairfax explosion was caused by methane gas seeping out of the oil-laden ground in unusually high volumes. Questions immediately were raised about the safety of plans to tunnel the subway through the densely populated area.

McSpedon said gas detectors and giant ventilation fans originally designed into the system could have handled any gas problem by themselves, but the liner was added as a backup to reassure federal officials and bolster public confidence.

Despite public perceptions that the liners would be airtight, they were not intended to be so. Construction contracts set a maximum allowable amount of water leakage in plastic-wrapped tunnels at one-tenth of a gallon per hour in any 100-foot section of tunnel. Station-building contracts did not specify allowable leakage, but some was always expected, McSpedon said.

“You are never going to get a 100% perfect seal on any system like this,” McSpedon said. “But if you get a 99.9% seal, you get 99.9% additional redundant protection.”

Actual leakage exceeded the allowable standard in several locations, leading to the growth of slender stalactites on some tunnel ceilings and crusty formations on some walls. Tom Tanke, vice president of the Rail Construction Corp., said he has people reviewing inspection records and interviewing workers to try to find out why the leaks are greater than expected.

Tanke said most of the leaks are in the stations, where design and construction methods made it easy for contractors to accidentally puncture or tear a seam in the liner.

“No matter what you do, how careful you are, you’re going to punch holes in this thing,” he said of the liner. “We are not happy about it, but we’re going to fix it. We are getting those leaks we have detected stopped. We can guarantee the integrity of the system. And we’re trying to prevent it from happening in the future.”

Repair crews are already drilling holes into the concrete and injecting single-component polyurethane grout under high pressure in an effort to make the structure more watertight. It is hoped that the grout will spread through cracks and along the face of the liner and plug any holes.

“It could be a pinhole or could be larger. We just don’t know,” Tanke said. “We’ll just keep pumping grout in ‘til we can’t pump it in any more.”

He estimated the cost of repairs at $500,000 per station; five stations have been built so far.

RCC has already agreed to pay $1.3 million to the company that built the stations, a joint venture called Tutor-Saliba-Perini, because acceptable leakage rates for the stations was not defined in the construction contract.

The company that built the tunnels, a joint venture called Shank-Ohbayashi, was ordered to plug the heaviest tunnel leakage at its own expense, which manager Mike L. Shank estimated at $50,000 to $100,000. He said the joint venture was paid another $20,000 to fix leaks below the allowable rate.

Tanke and McSpedon said Rail Construction Corp. will eventually try to recover some or all of the repair costs from those companies.

“We just wanted to get the cash flowing to get the job done without being bogged down,” McSpedon said. “When it’s all done, we’ll go back and try to settle with the contractors. Who is accountable to who is something that is just going to have to be sorted out.”

To prevent leaks in new stations, Tanke said, the structures will be redesigned to reduce the sharp angles that apparently contribute to the problem. A different liner also is being developed, he added. Consultants are studying a “self-sealing” design composed of alternating layers of high-density polyethylene and bentonite, an absorbent clay that swells when wet.

A new liner should be ready in 60 to 90 days, before tunneling is scheduled to start on the second leg of the subway, Tanke said. Station shells and tunnels for the first segment, from Union Station through the Civic Center and downtown to the Westlake District, are finished and the last rails are scheduled to be laid next week.

Before construction began, Tanke said, tests showed that the original liner would safely do its job.

“Obviously, the system was not foolproof,” he said. “Something happened between testing and final construction,” perhaps when temporary piles were removed from behind finished station walls.

McSpedon said the nature of heavy construction is such that “you have to expect (a liner) is going to be breeched” eventually. “It is unrealistic to expect that you are going to have an airtight environment in this situation,” he added.

As the primary defense against gas, designers added automated gas detectors that Tanke said can recognize odorless methane in concentrations as low as 15 parts per million; at that level, ventilation fans as tall as a man will be switched on to vent the gas to the surface.

Tanke said methane is not flammable until it is in concentrations of 50,000 p.p.m.--2,500 times the alarm point. He added that the plans have been approved by the city and county fire departments, both of which provide full-time liaisons to the Rail Construction Corp.

TROUBLE IN THE TUNNELS

Heavy spring rains revealed leaks in the concrete tunnel walls on the first (Phase One) segment of the Metro Rail Red Line subway.

Engineers are scrambling to plug the leaks as construction pushes west (Phase Two) toward soil saturated with explosive methane gas.

Transit officials want to extend the Wilshire corridor subway (Phase Three) westward, which is near the methane-laden soil.

Also under study are routes to Westwood that skirt the edge of the risk area.