SEATTLE – Two new underground water reservoirs in Seattle need to be waterproofed again because of a problem with the material used to coat the lids of the concrete structures.
The waterproof coating applied to the covers of the reservoirs on Beacon Hill and West Seattle was supposed to make the structures watertight.
The projects are part of a $150 million effort to move four city reservoirs underground and build parks on top of them. The city needs the lids to be waterproof so it can build parks above the reservoirs. Officials hoped to have the reservoirs finished this spring.
No one knows why the waterproof coating is leaking, and the city isn’t sure yet how much it will cost to replace it and who will pay for it.
“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 told The Seattle Times.
The leaks were first reported by the West Seattle Blog.
The spongy rubberized coating was applied last summer according to specifications written by MWH, a Broomfield, Colo., engineering and design firm, said Carlos Balansay, the supervising construction manager for the West Seattle and Beacon Hill reservoirs.
A representative the product manufacturer, W.R. Grace & Co., made several visits to the Beacon Hill site to watch the coating application, Balansay said. The product warranty required the manufacturer to be present.
The utility had originally decided to cover the reservoirs for security reasons, but adding park space on top made waterproofing essential.
“They’ll be planting grass or shrubs, and we don’t know what sort of fertilizer they use,” he said. The drinking water below must be protected from any contaminant, including fertilizer.
Once the waterproof membrane is removed from the reservoir lids, the city will be applying a thick coating of rubberized asphalt.
“We know that works,” said utility spokesman Cornell Amaya.