The owner of the Reserve Silica Landfill in eastern King County and the owner of a cement producer that deposited material there have agreed to undertake the state’s cleanup process at the former mining site.
A draft legal agreement between the companies and the Washington Department of Ecology would require them to study the site’s contamination, evaluate cleanup alternatives, and develop a cleanup plan.
Ecology is seeking public comment on the agreement, called an agreed order, with Reserve Silica Corporation and Holcim US, Inc. from Nov. 6 through Dec. 7, 2018. And, people can attend a public meeting on Friday, Nov. 16, to learn more and ask questions about the agreement.
Place: Maple Valley Fire Station, 22225 SE 231st St. (intersection with SR-169)
Time: Open house – 7 p.m. Presentation/questions – 7:30 p.m.
Pit mines became landfills
Coal and sand were formerly mined at the site – located at 28130 Black Diamond-Ravensdale Road – from several large pits. State mining law requires re-filling the pits, and the company has done so by operating a construction waste landfill, licensed by Public Health – Seattle & King County.
In the 1970s and 80s, a corrosive material called cement kiln dust (CKD) was placed in the landfill by a company now owned by Holcim in two of the pits. Groundwater that seeps to the surface from one of these former pits contains high pH – a measurement of corrosiveness – and metals, including arsenic and lead.
Contaminated water receives treatment
Holcim has installed a system to contain and treat the seepage, under an Ecology water quality permit and the landfill’s Public Health permit. A trench captures the water, which drains into a treatment system that lowers the pH and removes metals. The treated water is released into ponds where it infiltrates into the ground.
The cleanup process will begin with a study, called a remedial investigation, which will evaluate the location and extent of contamination at the site.
Ecology will consider public comments before finalizing the agreement and a public participation plan, which outlines how the community will be kept informed about the cleanup process.
Get information and make comments
The agreements and public participation plan are available at:
In addition to using Ecology’s online comment form, people can mail comments to Madeline Wall, Site Manager; Department of Ecology; 3190 160th Ave. S.E.; Bellevue, WA 98008.
The agreement is part of the cleanup process outlined under the state Model Toxics Control Act.