Reserve Silica Asarco Soil Disposal Site

The Site is located at 26000 Black Diamond–Ravensdale Road near Ravensdale, Washington. The Reserve Silica Asarco Soil Disposal site is located on King County Tax Parcel No. 012106-9010 (Lot 2). This site is distinguished from the Reserve Silica Reclamation site, whose initial Site boundary is confined to King County Tax Parcel Nos. 362206-9138 (Lot 6), 012106-9011 (Lot 5), and 352206-9046 (west of Lot 6). The parcels are identified on King County’s iMap and Parcel Viewer websites.

Reserve Silica Corporation (Reserve Silica) performed grading operations on Lot 1 (Parcel No. 362206-9065) and Lot 2 (Parcel No. 012106-9010) following timber harvesting after June 2021. In May 2023, Reserve Silica inadvertently accepted 33 truckloads of soil that were generated during development activities at the former Asarco Tacoma Smelter Facility portion of the Commencement Bay Nearshore/Tideflats Superfund site in Ruston, Washington. The estimated 500 cubic yards of soil contain arsenic and lead at concentrations above the unrestricted soil cleanup levels. Reserve Silica commingled and mixed the Asarco soils with approximately 49,500 cubic yards of other imported clean soil during their grading operations.

The Environmental Protection Agency became aware of the soil excavation and disposal work in July 2023 and notified Ecology. Reserve Silica investigated the nature and extent of soil contamination in September 2023. The investigation and disposition of the Asarco soil is described in the Former Asarco Soil Nature and Extent Investigation Report and the Cleanup Requirements Evaluation for Former Asarco Soil Report.

Ecology’s Toxics Cleanup Program reviewed the reports and prepared an Initial Investigation Field Report on January 2, 2024. The Asarco soil was effectively diluted with the imported clean soil. Arsenic and lead concentrations are statistically in compliance with the Model Toxics Control Act (MTCA) Method A cleanup levels. 

Based on the information provided, Ecology determined that there was a release of a hazardous substance, but the release does not pose a threat to human health or the environment. Ecology issued a determination that no further action is necessary related to this release under MTCA and issued a No Further Action letter on February 16, 2024. In this letter, Ecology noted that this determination does not preclude Reserve Silica from complying with other Ecology or local jurisdiction requirements under other authorities, including but not limited to, performing monitoring to confirm the long-term effectiveness of the soil management actions.

The mining history and reclamation activities are described on the Reserve Silica Reclamation site webpage. The surface mining and mine reclamation activities are confined to Parcel No. 362206-9138 (Lot 6) and Parcel No. 012106-9011 (Lot 5).

Mining reclamation and landfilling activities are regulated by the King County Department of Local Services, Public Health – Seattle & King County (Public Health), and Ecology’s Water Quality Program. The permits include:

• King County Department of Local Services issues Grading Permit No. GRDE15-0011 for the Reserve Silica fill site. The Reserve Silica fill site is associated with reclamation activity to restore specific areas of the property to pre-mining elevations.
• Public Health issues Post-Closure Care and Maintenance Permit No. PR0015708 for the closed cement kiln dust landfills—Lower Disposal Area and the Dale Strip Pit—on Parcel No. 362206-9138 (Lot 6).
• Public Health issues Inert Waste Landfill Permit No. PR0082027 for disposal of inert waste in reclamation fill on Parcel No. 012106-9011 (Lot 5).
• Ecology grants coverage under the Sand and Gravel General Permit for the discharge of surface water at the mining Site. Ecology provides details for Permit No. WAG503029 on the PARIS database.

Southwest Region