The concrete roofs on two of Seattle's newest underground water reservoirs showed leaks and a waterproof barrier must be replaced.

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As Carlos Balansay stood inside the cavernous new underground reservoir that would soon hold 50 million gallons of drinking water, the last thing the construction manager expected to see was water, dripping from a roof that was supposed to be watertight.

The drops, first detected last August, have triggered a massive do-over project involving the removal of waterproof coating applied to Beacon Hill’s new covered reservoir. A second new reservoir, in West Seattle, had the same orange coating applied to its concrete cover, and it, too, is being blasted off with pressure washers.

The slow work of removing the waterproof barriers is a setback for Seattle Public Utilities, which owns the reservoirs and had hoped to finish them this spring.

Despite the passage of a year, no one involved with the project can say why the waterproof membranes failed, what it will cost to replace them and who will pay for it.

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“At the end of the day, someone is going to pay for it, and it’s not going to be us,” utility spokesman Andy Ryan said.

The projects are part of a $150 million effort to underground four city reservoirs — including another one in West Seattle — and turn their concrete covers into planted parks. Problems with the coating were first reported by the West Seattle Blog.

The spongy rubberized coating, which was sprayed on and topped with a liner resembling a thick, shiny tablecloth with fuzzy backing, was applied last summer to the reservoirs at South Beacon Street, and in West Seattle at Southwest Myrtle Street.

Balansay, the supervising construction manager for both projects, said the product was applied according to specifications written by MWH, a Broomfield, Colo., engineering and design firm.

A representative of W.R. Grace & Co. — the product manufacturer — made several visits to the Beacon Hill site to watch as the waterproof coating was applied to the 6.4-acre lid, according to Balansay.

The product warranty required the manufacturer to be present, Balansay said. He said he could not recall whether a manufacturer’s rep was present for the much-smaller (about two-thirds of an acre) job at Myrtle.

The project designer, MWH, did not return phone calls. A project manager at MidMountain Contractors of Kirkland, which is doing the work, declined to comment, saying the utility asked that all calls be referred to its spokesmen.

Security reasons

The utility had initially decided to cover the reservoirs for security reasons after the terrorist attacks on Sept. 11, 2001. The city opted to replace the open-air reservoirs with concrete vaults, saying there was little cost difference between undergrounding them, and the alternative: building floating covers and beefing up security, according to the utility.

Adding new park space atop the covers made waterproofing “a big deal,” Balansay said: “They’ll be planting grass or shrubs, and we don’t know what sort of fertilizer they use.”

Protecting the drinking water from any contaminant, including fertilizer, that might seep through cracks in the 11-inch concrete cover is paramount, said Balansay.

Rather than try a second time using the waterproof membrane, the city has told the contractor that it wants to go in a new direction: Once the concrete is stripped bare, the city wants a thick coating of rubberized asphalt to be applied to the covers.

“We know that works,” said utility spokesman Cornell Amaya.

Discovering the leak

The Myrtle reservoir had already been filled and the cover topped with gravel, topsoil and grass when leaks on the Beacon reservoir, which had yet to be fully covered by landscaping, were discovered during an unusual rain last August.

Balansay said the leaks were easily spotted because the reservoir was empty, and workers had only to look up 30 feet to the ceiling to see them.

Engineers figured if the Beacon cover was leaking, there was a good chance the one at Myrtle was, too. But the Myrtle reservoir was already covered and full, and there was no way to check except to test the coating electronically. They found what utility spokesman Amaya described as “breaches” that may or may not represent leaks.

“We’re not going to take the chance” of leaks at Myrtle, Amaya said. “This is our water supply. We don’t want to mess around.”

Amaya said the choice of coating was made by MidMountain, which selected it from the four products recommended by the designer, MWH. The product, from W.R. Grace’s Procor line, has been used in other large products requiring waterproofing, he said.

The utility’s reservoir at Cal Anderson was covered with a different W.R. Grace product using different specifications, Amaya said, and tests there indicated no leaks.

Removing the spray-on coating has turned into a huge headache. While the product apparently didn’t keep the water out, it has proved difficult to remove.

MidMountain scraped some of it, but resorted to pressure washing to get to bare concrete. The utility expects to pay the extra cost of replacing it with the rubberized asphalt, said Amaya.

The cost of redoing the work will not be known until the utility’s negotiations with the contractor and designer are completed.

Removing the coating from Beacon could take as long as a month: MidMountain has been able to remove 10,000 square feet a day using three pressure washers. At that rate, removing the covering at Myrtle should take about three days.

Both projects are expected to be replanted by late November, Balansay said.

Susan Kelleher: 206-464-2508 or

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