Cleanup efforts at a Milton landfill contaminated with arsenic from the former Asarco smelter could wrap up this fall after nearly two decades of remediation.
Work on the final phase of the cleanup started recently at the B&L Woodwaste site east of Interstate 5. Crews will be removing contaminated soil from drainage ditches on three sides of the 11-acre site and testing a new system to remove high levels of arsenic from the groundwater.
“Those should be the last things that we do,” said Dom Reale, a state Department of Ecology site manager.
The site once was a dumping ground for slag from the former Asarco smelter and wood chips from Commencement Bay log yards. After a high concentration of arsenic was discovered, the state began regulating cleanup efforts in 1992.
This latest phase is scheduled to run through mid-October. It must be done while water in the ditches is low.
Testing shows arsenic remains in shallow sediment so contractors will use heavy equipment to scrape out 6 to 18 inches of soil in the drainage ditches. Dump trucks then will remove it from the area.
Crews also will begin using a treatment system built last year to extract contamination from the groundwater. Wells and pipes were installed under and around the site that will pump out groundwater to be cleaned. The wetlands surrounding the landfill also will be treated for lower levels of arsenic.
Although a 50-foot-high mound of contaminated material on the site leaked two separate times over a 12-year span, Ecology officials said the arsenic is not a threat to plants, animals or drinking water.
“The arsenic in the water that has escaped in the wetland doesn’t seem to be moving very far,” Reale said. “We think we can pump it out of there before it gets anywhere like Hylebos Creek.”
Workers will remove the arsenic and then reverse the groundwater flow away from Hylebos.
“We may have to pump it forever inside to keep groundwater flowing inward to keep it sealed off,” Reale said.
That maintenance will be paid with a $22 million trust managed by the state.
Asarco filed for bankruptcy in 2005 but the state sought to hold it liable for damage to the environment.
In the end, Asarco paid most of the tab but landowner Murray Pacific Co., the Tacoma timber company that produced some of the wood waste, also chipped in.
Efforts started in 1992 to control the contamination at B&L Woodwaste.
Crews created the 11-acre grassy mound made of 29,000 tons of toxic wood debris and capped it to prevent rain from washing arsenic into the rest of the property.
Then a clay slurry wall stretching 32-feet underground was installed to block the arsenic from leaching into the groundwater.
stacia.glenn@thenewstribune.com
253-597-8653
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