King County developing plan for smelter metals found at Vashon Treatment Plant construction site

2005 Archived News

King County's Wastewater Treatment Division is investigating the extent of metals found Jan. 13 in soil at the construction site for upgrading the Vashon Treatment Plant on 171st Street Southwest. The county will use results of the investigation to develop a soil management plan for the site.

Like other areas on Vashon and Maury islands, a sample of the shallow surface soil at the plant site contained low to moderate levels of arsenic, lead and cadmium. Studies show that the dominant source of those metals in island soil is Asarco's former Ruston copper smelter south of Vashon. That smelter operated for more than 90 years and closed in 1986.

Soil samples taken at the plant site in 2002 contained lead and arsenic at levels under the state Model Toxic Control Act's cleanup level for unrestricted land use. But in routine soil testing during recent grading and clearing at the undeveloped construction site, scientists identified concentrations of arsenic and lead in shallow surface soil that were higher than the state level.

Plans to manage the affected soil will be consistent with guidelines of Public Health -- Seattle & King County. King County will also follow guidelines of the state Department of Ecology and the Areawide Soil Contamination Task Force for responding to low-to-moderate levels of arsenic and lead contamination in the state.

For more information about soil studies on Vashon and Maury islands, visit Public Health's Web site.

Construction plans

During the treatment plant upgrade, King County contractors will comply with Public Health's best management practices.

The county's regional wastewater treatment utility is upgrading the aging plant to increase capacity, add backup systems and move the outfall for treated wastewater farther out in Puget Sound. The plant needs these improvements to meet regulations and protect public health and the environment. The outfall extension was completed in 2004.

All work, to be done under approved permits and environmental controls, is scheduled for completion in 2006.

The Vashon Sewer District contracted with King County in 1999 to take over ownership and operation of the formerly inadequate and poorly functioning sewage treatment system. The plant had experienced more than 100 permit violations in the1990s under the U.S. Clean Water Act and National Pollutant Discharge Elimination System. The sewer district requested King County's expertise in wastewater treatment and financing to solve serious problems.

The sewer district owns and operates local systems that collect sewage and send it to the plant. The plant serves 425 customers -- mostly homes and businesses in and around the island's main business area.

After taking over plant operations, King County took many interim steps to improve the plant. Since then, the county has substantially reduced permit violations such as excessive fecal coliform levels in the plant effluent. Also, raw and lightly treated sewage no longer contaminates nearby Gorsuch Creek.

For more information, contact Jo Sullivan at 206-296-8361 or jo.sullivan@kingcounty.gov. The project also has a 24-hour hot line, 206-205-9181, and Web site.

King County's Wastewater Treatment Division protects public health and water quality by serving 18 cities, 16 local sewer agencies and more than 1.4 million residents in King, Snohomish and Pierce counties. Formerly called Metro, the regional public utility has been preventing water pollution for nearly 40 years.