Reserve Silica Reclamation
26000 Black Diamond Ravensdale Rd SE, Ravensdale, WA 98051


Reserve Silica Corporation (Reserve Silica) and Holcim (US) Inc. (Holcim) entered into an Agreed Order with Ecology on December 16, 2019. The Agreed Order requires Reserve Silica and Holcim to prepare a Remedial Investigation, Feasibility Study, and Draft Cleanup Action Plan for the Reserve Silica Reclamation site (Site).

The Remedial Investigation/Feasibility Study (RI/FS) Work Plan is now available. This work plan describes preliminary remedial investigation tasks that were performed during negotiation and revision of the document.

RI/FS Work Plan, Text and Tables

RI/FS Work Plan, Figures 1-1 to 2-9

RI/FS Work Plan, Figures 3-1 to 3-12

RI/FS Work Plan, Figures 5-1 to 6-4

RI/FS Work Plan, Appendix A, Historical Photographs and Maps

RI/FS Work Plan, Appendix B, Data Summary Tables

RI/FS Work Plan, Appendix C, Site Boring Logs

RI/FS Work Plan, Appendix D, Sampling and Analysis Plan

RI/FS Work Plan, Appendix E, Quality Assurance Project Plan

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The Site is generally located at 26000 Black Diamond–Ravensdale Road near Ravensdale, Washington. The initial Site boundary includes King County Tax Parcel Nos. 362206-9138, 012106-9011, and 352206-9046. The Site boundary will be determined based on the findings of the planned Remedial Investigation. The Site does not include King County Tax Parcel No. 352206-9018, which is included in the Reserve Silica Plant site located at 28131 Black Diamond-Ravensdale Road.

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Coal and sand were mined from geologic rock formations from 1924 to 2007 at the Site.

Coal Mining

Underground coal was mined from the Dale No. 4 and 7 coal seams from 1924 to 1933, and from the Dale No. 7 seam from 1945 to 1948. The underground mine continues to drain from a pipe installed in the collapsed Dale mine portal.

Surface coal mining was performed from the Dale No. 4 seam from 1946 to 1950, in an area referred to as the Dale Strip Pit (DSP).

Sand Mining

Surface sand mining operations were performed from 1968 to 2007. An area referred to as the Lower Disposal Area (LDA) was mined from the Bonneville Power Administration (BPA) transmission lines to the northwest-southeast trending fault line near the Dale No. 1 portal. The surface pit was mined until inhibited by standing water at the bottom of the pit. Sand mining was performed from additional seams between the DSP and the LDA toward the southeast.

Surface mining areas were reclaimed with fill material to re-contour the surface pits. The LDA and DSP were reclaimed using cement kiln dust (CKD) as fill material.

·         Approximately 175,000 tons of CKD were disposed in the LDA from June 1979 to October 1982. After placement, the CKD was graded, covered by a 2-foot thick layer of clayey material and a 7-foot layer of overburden from the sand mining operations, and the area was seeded with grass.

·         The DSP was reclaimed with CKD between November 1982 and 1989 with an estimated 250,000 cubic yards of fill material. The top 7 feet of the DSP was reclaimed with 4 feet of on-site clay soil and 3 feet of overburden from the sand mine, and the completed surface was seeded.

·         Additional sand-mining pits—the North Pit, Tan Sand Pit, Upper Pit, Lower Pit, and Middle Pit—were filled with inert materials. Reserve Silica continues to reclaim the Lower Pit and the Middle Pit; the remaining sand pits have been reclaimed.


Mining reclamation and landfilling activities are regulated by:

Washington State Department of Natural Resources (DNR)

DNR issued a Surface Mining Permit for sand mining and reclamation in 1971. This permit was cancelled on April 15, 2010 following King County’s request to assume primacy.

Washington State Department of Ecology (Ecology)

Ecology grants coverage under the Sand and Gravel General Permit for the discharge of surface water at the mining Site.

King County Department of Permitting and Environmental Review (DPER) (formerly Department of Development and Environmental Services)

King County issues a Grading Permit to regulate reclamation activities.

Public Health – Seattle & King County (Public Health).

·         Public Health issues a Post-Closure Maintenance Permit for the Lower Disposal Area and the Dale Strip Pit.

·         Public Health issues an Inert Waste Landfill Permit for filling of the Lower Pit and Middle Pit area.


Cement kiln dust reacts with water to form calcium hydroxide, which can increase the pH to greater than 12 standard units. Some naturally occurring metals are mobilized in high pH water. Arsenic solubility increases above pH 9 due to the formation of anionic species, and lead solubility increases above pH 11 due to the dissolution of calcium silicates.

In June 1981, Ecology became aware that caustic storm water was released from the LDA during the filling of the surface pit from June 1979 to October 1982. Industrial Mineral Products, a predecessor company of Holcim (US) Inc., alleged that the cementitious CKD would cure and harden like concrete, preventing further releases.

High pH seepage continues to be released on the northwest side of the LDA, and elevated pH and arsenic and lead concentrations have been observed in surface water and groundwater at the Site. Ecology issued a Notice of Violation on June 29, 2016 for the release of high pH surface water. Seepage of hazardous constituents from the LDA led to the regulation of the Site under the state cleanup law, the Model Toxics Control Act .


Early attempts to control leachate from the Lower Disposal Area:

• 1979-1980: Industrial Mineral Products allowed caustic surface water to flow unconfined to a borrow pit along Black Diamond-Ravensdale Road, about a 1,000 feet from the seepage face. The impacted surface water was allowed to percolate to groundwater in the advance outwash formation.

• 1981: Ecology requested that the caustic discharge be neutralized with acid at its point of origin. Industrial Mineral Products dismissed acid neutralization due to the absence of power needed for a metering pump, and concerns about spillage and vandalism.

• 1981: Industrial Mineral Products collected the caustic discharge and conveyed it through a corrugated pipe to mix with purported acid mine drainage from the Dale mine portal. The drainage pipe was routed along an old drainage ditch adjacent to the mine road. The relatively large flow of weakly acidic mine drainage (pH 6.6) was reported to neutralize the relatively small flow of strongly caustic leachate (pH 12.4) to a pH of 8.1, which met the state discharge criteria (pH 6.5–8.5). The mixed discharge then flowed overland to the borrow pit.

In 2002, Reserve Silica executed an Agreement to allow Holcim to conduct monitoring and remediation activities for the CKD landfills. The investigation and remediation activities for the CKD include:

• 2002: Developed a monitoring well system and reported data quarterly to Ecology and Public Health.

• October 2006: Submitted post-closure plan for the LDA and DSP. Evaluated remediation alternatives for the LDA, including construction of a clay cap and a shallow leachate collection interceptor trench. Evaluated leachate treatment options, including wetlands, onsite chemical treatment, and discharge to an offsite wastewater treatment plant.

• September to October 2007: The cover of the LDA was upgraded to reduce infiltration. A minimum 2-foot thick low permeability soil cover was constructed. The soil cover was graded to drain stromwater and then seeded with grass.

• September 2008: Constructed and monitored two test trenches to collect high pH seepage from the LDA.

• 2009 to 2013: Performed hydrogeological studies for the LDA. The studies included test trenches and borings, seismic refraction to evaluate depths to bedrock, electromagnetic imaging to evaluate interconnected porosity, moisture content, and dissolved ion concentrations, and groundwater tracer studies to evaluate groundwater flow.

• November 2010 to July 2011: The DSP soil cover was upgraded. The cover was regraded to promote drainage and a minimum 2-foot thick low permeability soil cover was a constructed and vegetated with grass to reduce infiltration.

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• February 2013: Constructed an approximate 400-foot long surface water collection ditch and concrete catch basin to collect seepage and surface water runoff from the LDA and divert the flow to the infiltration pond.

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• September 2013: Installed a gravel-filled trench to intercept and divert groundwater flowing into the southeast portion of the LDA.

• April 2015: The approximate 1,000-foot long, 4-inch diameter seepage diversion pipe was replaced with a 12-inch diameter pipe to alleviate plugging problems associated with carbonate precipitation.

Please click on the photo for a larger view

• December 2017: Extended the surface water collection trench approximately 100-feet to capture additional seepage from the LDA.

• September 2018: Constructed a seepage treatment system to neutralize the pH and lower the concentration of arsenic before discharge to the infiltration pond. The treatment system includes a carbon dioxide sparging system to lower the pH and concentration of dissolved arsenic and steel filings to adsorb residual arsenic before discharge. The treatment system began operation on September 18, 2018.

• Chain-link fencing has been installed to restrict access to high pH surface water, including the seepage collection trench, the south pond, and the infiltration pond.


Ecology identified Reserve Silica Corporation, Holcim (US) Inc., and BNSF Railway as potentially liable persons (PLPs) for the Site in September 2017 and March 2018. Reserve Silica and Holcim entered into an Agreed Order with Ecology on December 16, 2019 to prepare a Remedial Investigation, Feasibility Study, and Draft Cleanup Action Plan in accordance with Model Toxics Control Act (MTCA).


View Electronic Documents in the right-hand column. Click for instructions on how to submit a public records request.

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Map showing site location as King County, WA SITE INFORMATION


View Electronic Documents

Cleanup Site Details Report

Facility Site ID: # 2041

Cleanup Site ID: 4728

Ravensdale, King County

Status: Cleanup Started   Get definitions of Status terminology

Alan Noell
Site Manager
(425) 213-4803

Document Repositories:

Northwest Regional Office
15700 Dayton Ave N
Shoreline, 98133

Maple Valley Public Library
21844 SE 248th Street
Maple Valley, 98038