Department of Ecology News Release - October 30, 2018

Agreement starts cleanup process for east King County landfill

Public meeting Nov. 16; Comment through Dec. 7

A system at Reserve Silica Landfill contains and treats water that seeps from part of the site.

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.

Contact information

Larry Altose
Communications manager
Twitter: ecyseattle
Madeline Wall
Site manager