Lehigh Cement Company Closed CKD Pile

The Lehigh Cement Company (Lehigh) owned and operated a cement-processing plant at this site from 1914 until the plant closed in 1989. Cement kiln dust (CKD), a by-product of cement production, was collected from the plant and disposed of in a landfill on the site.

In 1996, Lehigh closed the CKD landfill, which is now known as the closed CKD pile.

Groundwater sampled at the site were strongly alkaline and contained arsenic, chromium, lead, and manganese that were greater than allowed by state standards set to protect human health and the environment.

In 1996, Ecology approved Lehigh’s plan to close the CKD landfill. Lehigh constructed an impermeable cover over it and installed a stormwater management system. Because CKD remained in place at the site, Ecology issued an administrative order later in 1996, requiring Lehigh to submit and enact a plan for monitoring groundwater for two years around the closed CKD pile.

Lehigh submitted the monitoring plan in 1997 and collected groundwater samples monthly between December 1996 and December 1998. They also maintained and repaired the landfill cover and stormwater management system during this time.

Lehigh submitted the monitoring data to Ecology in 1999, which showed that contaminants had continued to seep from the closed CKD pile and reach groundwater under and down-gradient from the landfill on properties owned by three other parties. The contaminated groundwater was also reaching the surface in a series of springs that discharge to Sullivan Creek.

Because the groundwater contamination was not safely contained, Ecology signed an agreed order with Lehigh in 1999, requiring them to complete a remedial investigation and feasibility study. The purpose of the remedial investigation was to determine the extent and locations of contamination, and the feasibility study evaluated cleanup options.

Following these studies, Ecology and Lehigh signed a consent decree in 2006 requiring Lehigh to:

• Install, operate, and maintain a groundwater treatment system between the CKD pile and Sullivan Creek.
• Install, operate, and maintain a gravity drain on the edge of the Closed CKD Pile to direct groundwater away from it.
• Continue groundwater monitoring.
• Provide and maintain restrictive covenants, fences, and signs to keep people away from the contamination.
• Operate and maintain the existing landfill cover and stormwater system.

In 2015, Ecology proposed to stabilize the bank of Sullivan Creek to prevent erosion near the groundwater treatment system. The enhancements included installing boulders and logs to redirect water flow along the left bank to protect Sullivan Creek from potential contamination and the treatment system from damage. The project was completed in August 2015.

We are continuing to monitor groundwater, its treatment system, the stability of the stream bank, and the cap over the CKD pile.

2025 Periodic Review

When Ecology visited the site October 7, 2025, the treatment system was running. When water levels are high enough, treated water is discharged to Sullivan Creek, and discharges are reported to Ecology. The site is vacant except for the building containing treatment system components such as carbon dioxide tanks, the computer interface, and materials for sampling and analysis of groundwater. The CKD pile remains fenced, and the cap appears to be in good condition.

We also reviewed records and monitoring data. The environmental covenant is still in place to document the remaining contamination and prevent activities that would expose it. Groundwater monitoring data showed pH is not decreasing in the northern plume of contaminated groundwater. Because of this, we are requiring the parties responsible for cleanup, now known as Heidelberg Materials US Cement LLC, to complete more work to lower the groundwater pH in this area. Learn more in the Periodic Review report.

In September 2017, Seattle City Light started removing the Mill Pond Dam, which is on Sullivan Creek upstream of the Lehigh Cement Co site. The project finished at the end of 2019. The dam was removed in phases, so that water and sediment that was trapped behind it didn't all wash down the creek bed at once and potentially damage the groundwater treatment system at Lehigh or any other downstream features. For more information on this project, please visit the Mill Pond Dam Removal and Habitat Restoration website.