Landsburg Mine
Kent Kangley Rd & 268th Ave SE, Ravensdale, WA 98051

Landsburg Mine Trench
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Ecology is amending the legal agreement, called a Consent Decree, and the Cleanup Action Plan for the Landsburg Mine Site in Ravensdale. They’re being amended because trace amounts of a compound called 1,4-Dioxane were discovered in groundwater, in a limited area of the Site outside the former coal mine. Ecology wants to ensure that it gets addressed appropriately.

We’d like your input on:

·        Cleanup Action Plan Amendment: an update to Ecology’s plan that describes the cleanup work to address contamination at the Site.

•    Consent Decree Amendment: an update to the 2017 legal agreement that was signed by Ecology and the Landsburg Mine Potentially Liable Persons (PLP) Group.

Ecology will accept public comments on these documents from May 10 through July 8, 2021. You can comment by contacting Jerome Cruz or Brad Petrovich at the contacts to the right of this page, or with Ecology's e-comment system.

Ecology will host an online public meeting to present these amendments and information about the Landsburg Mine Site. (Please note that in consideration of public health and safety, we are hosting public meetings online instead of in-person meetings).


Wednesday, May 19, 2021

6-7pm – presentation

7pm – Q & A (as needed)

Register at:

Read more about these new amendments, 1,4 Dioxane, and some history of the Landsburg Mine and Site at Ecology's Blog.

Landsburg Mine Location
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The Landsburg Mine site is a former underground coal mine located approximately 1.5 miles northwest of Ravensdale in southeast King County. The site is located directly south of the S.E. Summit-Landsburg Road and north of S.E. Kent-Kangley Road. The Cedar River is approximately 500 feet north of the site. The former mine site occupies property currently owned by Palmer Coking Coal Company and formerly by the Plum Creek Timber Company, L.P. During the late 1960s to late 1970s, industrial wastes were disposed in the trench that formed above the former mine.


Preliminary environmental investigations at the Site included a limited soil gas survey in 1990, sampling of area private wells in 1992, sampling of surface water at the former mine portals, and limited sampling of ponded surface water, drum contents, and soils for a site hazard assessment in 1991. The latter investigation detected hazardous substances in drum contents, adjacent soils, and ponded surface water within the northern subsidence trench above the former mine. Hazardous substances were not detected in groundwater discharging from the former mine and in surrounding areas.

In 1991, the Potentially Liable Persons (PPLPs) implemented an Expedited Response Action (ERA) involving the removal of the most accessible drums from the trenches and construction of a fence to restrict access to the Site. The ERA removed over 100 55-gallon drums at that time, out of an estimated 4,500 drums disposed over a period of time. In 1993, Ecology and the PLP Group entered into an Agreed Order which directed the PLPs to conduct a remedial investigation / feasibility study (RI/FS) to evaluate the need for remedial action. The 1993 Agreed Order was closed out in 2013.

The RI/FS, which consisted of a comprehensive investigation of environmental conditions at the Site and evaluations of potential remedial action alternatives, was conducted from mid-1993 to early 1996. The RI/FS report was made final after public review and comment in 1996. In May of 2004, a hydrogeologic investigation was completed at the south end of the Site (Golder 2004). This investigation was initiated to understand groundwater movement at the south end of the Rogers Seam Coal Mine (Rogers Seam).


Investigations and monitoring indicate that there are no impacts to nearby surface water (Cedar river), nearby private wells, and the Clark Springs Water Supply.
The 1996 RI/FS determined that the most significant potential contaminant migration pathway was from groundwater coming from the former mine portals. The surrounding geology and the results of remedial investigations beginning in 1994 indicate the wastes are confined to the northern trench and possibly within the mine workings beneath this area of the former mine. However, contamination from the wastes could potentially still be released from the Site and transported off-site via groundwater, despite the fact that to date, no groundwater contamination has been detected coming from the former mine.

A Consent Decree (CD) was finalized on November 2017 that would implement a Cleanup Action Plan (CAP) that included backfilling and capping the trench wastes, monitoring groundwater, and planning for a Contingent Groundwater Extraction and Treatment System (CGETS) to prevent contamination from leaving the site should any contamination be detected coming out of the former mine in the future. 

Clearing and Capping the Waste Area
Cleanup that began in November 2018 consisted of: clearing and grubbing of trees and vegetation at the northern subsidence trench (where wastes are located); building access roads and the south contingent treatment system gravel pad, and installing sentinel wells. Sentinel well installation is complete and will be part of the groundwater monitoring system. The filling in and capping of the northern trench occurred from June 3, 2019 to November 9, 2020. The trench area where the wastes are located have been filled in with clean backfill, covered with an impermeable geomembrane liner to prevent further infiltration of rainwater, and a stormwater conveyance system and infiltration pond was constructed to handle stormwater flow at the capped areas. A source of clean fill was identified in May 2020. Extensive chemical testing required for the first batch of fill showed no contamination (results may be found here). All throughout the filling in of the trench, the source of clean fill was periodically analyzed to ensure no new contamination is introduced to the site.

Groundwater Monitoring
Sentinel well installation is complete and will be part of the groundwater monitoring system. Interim groundwater monitoring was conducted periodically from 1994 to 2003, quarterly in 2004, and semi-annually from 2005 to 2017. Recently, more frequent groundwater monitoring has been conducted as required under the cleanup action plan and to investigate the 1,4-dioxane detections. 1,4-dioxane monitoring began in November 2017 and continues to the present. Wells for 1,4-Dioxane groundwater investigation were installed in late November 2018. In the summer of 2008, the infrastructure components for the contingent groundwater treatment system were installed at the Site. The infrastructure included a gate access road, a treatment facility area pad surrounded by a security fence, underground power and telephone lines to the treatment pad, and a discharge pipe extending from the treatment facility pad to the west along Summit-Landsburg Road. The treatment system itself will be designed, built, and operated only if groundwater from the Site exceeds predetermined levels at sentinel wells or at the established points of compliance.

1,4-Dioxane is a man-made industrial chemical that is mixable in water. It is used as a stabilizer for chlorinated solvents, and is a byproduct in many products, including paint strippers, dyes, greases, antifreeze and aircraft deicing fluids. It is also common in consumer products such as deodorants, shampoos, and cosmetics. 1,4-Dioxane is a likely human carcinogen. Low level exposure to 1,4-Dioxane over a lifetime can increase the risk of cancer. However this would mean about a 1/1 million chance of getting cancer if someone drank 2 liters of water per day containing 1,4-Dioxane at 0.35 parts per billion for 70 years.  One part per billion is about one half teaspoon of water in an Olympic-size swimming pool. While the risk from 1,4-Dioxane is low, it is a contaminant found at the Site at levels above allowable MTCA levels and must be addressed. It has low aquatic toxicity since it does not accumulate, magnify, or concentrate biologically in the food chain.

Read more about 1,4-Dioxane here.

In response to public comments received on the draft CAP in 2013, Ecology added the compound 1,4-dioxane to the suite of analytes. 1,4-dioxane is a chemical that was not routinely investigated at contaminated sites until laboratory methods were able to achieve lower detection limits. Groundwater monitoring for 1,4-dioxane that began last November 2017 to September 2020 - around three years of collected data - indicate that the 1,4-dioxane hits remain at low concentration ranging from 1.1 to 2.3 µg/L (or parts per billion).  Furthermore, the hits are isolated and limited to three wells at the north portal area (LMW-2, LMW-4, LMW-12). 1,4-dioxane has not been detected in any other site wells or portal surface waters. Investigations and monitoring indicate that there are no impacts to nearby surface water (Cedar river), nearby private wells, and the Clark Springs Water Supply. Analyses of groundwater samples collected during quarterly monitoring did not detect any other contaminants that would indicate mine waste contaminants were migrating from the mine.

Due to the presence of industrial wastes in the northern trench above the former coal mine and despite the lack of any detected contaminants prior to 2017, the CAP took the precautionary approach that the wastes or their leachates could migrate out of the former coal mine in the future. Under the existing CD and CAP, if a contaminant is discovered that was beginning to come out of the former mine in groundwater monitoring wells above a certain trigger amount, then the PLP Group would implement a Contingent Groundwater and Extraction Treatment System (CGETS) at the Site. The CGETS would pump groundwater to contain, treat, and safely dispose of the pumped water in order to prevent contaminated groundwater from leaving the Site.

However, the situation with 1,4-dioxane did not conform to the original scenario and design for implementing the CGETS. This is not a situation where contaminants are beginning to come out of the former mine, requiring pump and treat to contain and treat contamination and safely dispose treated groundwater. 1,4-Dioxane was not expected to be found outside of the former mine, in keeping with the historical lack of any detections of contaminants in groundwater at the Site. Ecology requested the PLPs to take initial steps to implement the CGETS, but given the low concentrations and isolated nature of the 1,4-Dioxane detections, the PLPs requested that Ecology consider the disadvantages and impracticality of implementing the CGETS in this situation and assess more feasible and protective alternative actions. 

The PLP Group provided Ecology with a “White Paper” on why an extraction and treatment system may not be the most appropriate response under the circumstances and how an alternative approach may be more appropriate based on site-specific conditions. The April 10, 2020 White paper concluded that implementing an extraction and treatment system would have significant environmental impacts and financial costs, with “minimal to no reduction in risk” based on low levels and limited extent of the 1,4-dioxane. Ecology reviewed the White Paper and agreed with its conclusion – the CAP should be amended to change the approach only to 1,4 dioxane at the northern end of the Site. However, the contingent groundwater extraction and treatment system plan will continue to be strictly enforced for all other contaminants of concern (including 1,4-dioxane) at the rest of the site, should it be needed in the future. 

The CAP revisions will include:

(1) revisions to the geomembrane cover system and surface water management system to control stormwater on the Site,
(2) increased groundwater monitoring frequency,
(3) adding 3 off-site groundwater monitoring wells north of the Site, between the Site and Cedar River (already installed and tested), to the monitoring program,
(4) complete installation of a discharge pipeline to the Soos Creek sewer line for treatment at the King County South Plant treatment system, which would increase the ability to respond rapidly if conditions change and groundwater impacts observed at the Site trigger implementation of the Contingency Plan, and
(5) evaluate the potential for use of an in situ bioremediation treatment for 1,4 dioxane, conduct studies, and implement bioremediation if feasible.

In order to address the 1,4-Dioxane situation at the northern area wells of the Site, the amendments to the  CAP and Consent Decree will be made final after Ecology has reviewed all the public comments and determined that no significant changes to the documents are necessary.

Please click on the photo for a larger view


The Environmental Protection Agency (EPA) developed an Environmental Justice (EJ) tool for mapping and screening a community, called EJ Screen. Ecology uses this tool to learn about the demographics of communities around cleanup sites. By doing this we can better design a cleanup and communication strategy that works for the community. The EJ Screen tool is based on nationally consistent data and an approach that combines environmental and demographic indicators in maps and reports. See below for information about demographics in the area of the Landsburg Mine Site.

EJSCREEN Census Block Map - This shows the Census Blocks used to generate the reports below.

EJSCREEN ACS Summary Report Landsburg Mine Site – This shows the demographic information about the population of the area.

EJScreen Report Landsburg Mine Site – This report shows the values for environmental and demographic indicators and EJSCREEN indexes. These percentiles provide perspective on how the selected block group or buffer area compares to the entire state, EPA region, or nation.

What's in My Neighborhood?
In addition to EPA's EJ Screen tool, Ecology developed a tool you can use to see what other cleanups are happening in any neighborhood you're interested in. You can view it by going to What’s in My Neighborhood .



Map showing site location as King County, WA SITE INFORMATION


View Electronic Documents

Cleanup Site Details Report

Facility Site ID: # 2139

Cleanup Site ID: 60

Ravensdale, King County

Status: Cleanup Started   Get definitions of Status terminology

Jerome Cruz
Site Manager

Brad Petrovich
Project Planner and Public Involvement Coordinator
(425) 649-4486

Document Repositories:

Northwest Regional Office
15700 Dayton Ave N
Shoreline, 98133