The Oregon Department of Environmental Quality will begin the removal of contaminated soil along the Willamette River in downtown Portland on Monday.
The DEQ and NW Natural will remove about 5,000 cubic yards of contaminated sediment and tar-like material at the former Portland Gas Manufacturing site. The cleanup is part of the Willamette River Downtown Reach project. It is the last significant legacy contamination from gas manufacturing operations from the mid-1800s to the early 1900s.
When it was operating, Portland Gas Manufacturing produced gas from coal, mixed water and oil to fuel the first street lamps in downtown Portland.
DEQ hydrogeologist Dan Hafley said there was a significant amount of waste associated with gas manufacturing in those years, with some of the byproducts being sent down the west bank and into the Willamette River.
“We believe the tar used to be along the riverbank of the river, but when they built the Portland seawall back in the early 1920s it appears that they dredged material along the river bank and cast it out into the river,” Hafley said.
The cleanup will be divided into two parts: removing the contaminated material, and placing over a blanket of clean materials like sand and gravel in activated carbon.
“What the activated carbon does is act like a sponge. There will be residual contamination left in place in the river below this clean blanket. So if any of that were to move through this clean blanket, it would be absorbed through this carbon,” Hafley said.
Work will be completed using barges and small boats in an area between the Steel and Burnside bridges, offshore of Tom McCall Waterfront Park. Dredging will take place within an enclosure, called a moon pool, to isolate and prevent the release of contaminants to the river. The contaminated sediment will be taken to landfills for disposal. Water quality will be monitored throughout both dredging and placement of clean fill.
Hafley said this project is not related to the Portland Harbor Superfund Site downriver from the DEQ cleanup. The Superfund project is being overseen by the U.S. Environmental Protection Agency.
Some areas near the waterfront will be blocked off to the public. About 800 feet of the Tom McCall Waterfront Park walkway adjacent to the seawall will be fenced to protect the public from construction underway. A narrowed portion of the pathway will remain open to allow pedestrian access.
The cleanup is estimated to last through October.