by John Stang June 29th, 2012
The next tweak in fixing Seattle Gas Works Park’s contamination problem will likely occur next fall when a half-acre tarp will be buried in the site’s northeast corner. This will be the latest measure to ensure more pollution, in this case toxic and carcinogenic polycyclic aromatic hydrocarbons, won’t ooze from the park into Seattle’s Lake Union. Ultimately, all this effort will lead to cleaning up underwater sediment contaminated by old wastes from the park. In the first half of the 20th century, gas companies operated on the north shore of today’s 20-acre park site a plant that converted coal and oil into gas. The byproducts of that plant were used for a tar refinery at the same location.
A public comment period ended Friday on the latest fix-it measure, meaning the Washington Department of Ecology will review comments and plans for the next few months. John Keeling, the state’s manager for this project, speculated a contract will be signed by next fall to lay out a half-acre geofabric sheet – a plastic-like material commonly used in landscaping that will stop rainwater from seeping through – and to cover that tarp under a foot-thick layer of soil.
That measure is to prevent soil contaminated with polycyclic aromatic hydrocarbons, or PAHs – toxic and carcinogenic – from eroding into Lake Union. Here is a more detailed breakdown of the contaminants beneath park’s surface. This project will also modify the site’s drainage.
In 2000 and 2001, the state supervised putting a tarp-like covering under two feet of topsoil over much of the park to combat the rainwater that carries pollutants in the soil to the lake. The new project will tackle a spot where the extra work will slow down the seeping contaminants some more.
Meanwhile, state experts found high levels of pollutants from Gas Works Park already extending roughly 200 yards off Lake Union’s northern shore. A study is underway to determine the extent of the contamination in the lake’s sediment. The state expects actual work to begin on the new Gas Works Park soil project by October, Keeling said. A cost estimate is till up in the air.