State says Kent property can come off contaminated sites list

The state Department of Ecology proposes to remove a Kent property from a statewide list of contaminated sites because it has been shown to meet state cleanup standards.

The five-acre, vacant parcel at South 218th Street and 90th Avenue South contained slag from steel recycling, used as fill material. The slag imparted high pH to storm water and ground water that flowed through the material, according to a July 27 state DOE media release.

This made the water highly caustic and therefore harmful to aquatic life in ditches and streams that flow to the Green River.

The property owner has agreed to remove the slag, replace it with clean soil and plant vegetation to stabilize the replacement fill.

Based on that work, DOE officials have determined that the property no longer poses a threat to human health or the environment and is eligible for removal from the Hazardous Sites List.

Before doing so, the DOE invites public comment until Aug. 27. For details and contact information, please see Ecology's fact sheet, available at

Prior to 1984 the property was undeveloped and covered with vegetation. As part of proposed site development activities, steel slag was used to fill the site between 1984 and 1990. The placement of steel slag as fill was approved by DOE and the Seattle King County Health Department.

The steel slag was a waste product from recycling steel scrap by melting it down. The slag contained lime ash, which reacted with water to increase the water’s pH. Water flowed through the slag and emerged as seeps with an alkalinity above the regulatory limit. More simply put, DOE officials said the water flowing from the seeps was as alkaline as Drano drain cleaner, which is a caustic liquid.

Cleanup actions were conducted at the site in 1996 and 2002 to stop the discharge of surface water with high alkalinity. Although these earlier cleanup actions became less effective as time passed, in 2007, DOE confirmed that the requirements of the consent decree had been met.

But in March 2009, pH levels above regulatory limits were measured in seeps on the north and northwest sides of the site. Quick and effective actions were taken to capture the seep water. The captured water was treated and discharged under permit to the city of Kent sanitary sewer system.

The final cleanup action was excavation of the slag from the site in 2011. The excavated slag was sent to a landfill permitted and constructed to accept such material. The site was backfilled with clean soil and re-vegetated.

Restrictive covenants were originally recorded on the site limiting its use due to the presence of the slag waste. These restrictive covenants can now be removed since the slag waste is no longer present at the site.

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