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

Landsburg Mine Trench
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Filling In of Trench to Cover Wastes Has Begun
Cleanup that began last 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 now complete and will be part of the groundwater monitoring system.

The initial stages of filling in the northern trench will begin on June 3, 2019. A source of clean fill was identified last May. 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 will be periodically analyzed to ensure no new contamination is introduced to the site.

1,4-Dioxane Investigation
Background: Before the CD and CAP were finalized, the groundwater was analyzed for around 220 contaminants in order to detect any potential contamination coming from the waste area. Upon the request of the Department of Health in 2016, a chemical called 1,4-Dioxane was added to the CAP and was voluntarily added to the current interim monitoring. In November 2017, low levels of 1,4-Dioxane were found at several monitoring wells at the north portal area of the Site. Although these levels were low, they were above allowable levels under state standards of Washington cleanup law, the Model Toxics Control Act (MTCA). The decision was made to investigate this by installing more monitoring wells to help trace the extent of 1,4-Dioxane at the Site. Three additional northern wells were installed in November 2018 and were sampled in December 2018. Final results show no detections (see “1,4-Dioxane Alternative Source Evaluation Report” below). These preliminary results would indicate 1,4-dioxane has limited extent with no impacts to Cedar river and nearby private wells.
1,4-Dioxane Alternative Source Evaluation Report: The report on the 1,4-dioxane investigation was submitted last May (available here). In addition to reporting the results of the December 2018 sampling of additional wells installed past the north portal area towards Cedar River, the report was an alternative source evaluation to determine if these detections were from the site or from a different source. An “alternative source evaluation” is part of the process in the Cleanup Action Plan in case a contaminant  is detected at the site. The report concludes that the low level detections of 1,4-dioxane in three site monitoring wells at the north portal area indicate that it could possibly be a mine waste contaminant. However, after a year of quarterly groundwater monitoring, concentrations have decreased and three new downgradient groundwater wells show no detections. This would indicate that it is of a limited extent and has not impacted Cedar River or nearby private wells. The report concludes that the 1,4-dioxane does not present a threat to human health or the environment.

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.  On 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.

Read more about 1,4-Dioxane here.

Interim Groundwater Monitoring
The most recent groundwater monitoring at northern site wells (LMW-2, LMW-4, LMW-10, LMW-12, and LMW-13R) was conducted in March 2019. Results were somewhat similar to historical monitoring, where low concentrations of 1,4-dioxane were measured in LMW-2 (1.5 parts parts per billion, or micrograms per liter or ug/L), LMW-4 (1.7 ug/L), and LMW-12 (1.1 ug/L). The MTCA Method B cleanup level for 1,4-dioxane is 0.438 ug/L. 1,1-Dichloroethane was detected in LMW-12 at 0.21 ug/L, below the MTCA Method B cleanup level of 7.68 ug/L. No other chemicals were found above cleanup levels.

Site-wide groundwater monitoring in December 2018 showed results similar to historical monitoring (nothing above cleanup levels except for one arsenic hit at the deep interior well and 1,4-dioxane in three wells at the north portal area. Other detections (arsenic, benzene, carbon disulfide, chloroform, 1,1-dichloroethane, naphthalene, and toluene) were below MTCA cleanup levels and drinking water standards. Either lower detection limit estimates (J-flag) or well construction or sampling artifacts that are expected to go away.

Next Steps
The first phase of construction consisting of filling in the northern trench shall continue this summer. Frequent well testing will occur during this process, following the schedule and procedures in the CAP. The northern trench will only be partially filled this year in order to allow for the fill to settle. The second construction phase to completely fill in the trench and install the overlying cover will occur next year. In addition, Ecology and the Potentially Liable Persons (PLPs) will evaluate at a later time how the 1,4-Dioxane hits will be addressed in the framework of the CAP.

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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. The 1996 remedial investigation and subsequent interim, ongoing groundwater monitoring have shown no impacts to groundwater at the site or surrounding areas.

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The Washington State Department of Health (Health) worked with Ecology and the City of Kent to complete a health consultation. They wanted to learn if the work done at the Landsburg Mine site provided the information they need to determine whether there is a potential threat to drinking water supplies and surface water in the area. Health learned three things:

The waste at the site could pose a health threat to ground-water in the area, which is used for drinking water.

None of the groundwater chemicals that were evaluated, except arsenic, pose a health threat. Although the highest level of arsenic found at the site presents some risk of long-term health effects, no one is drinking thegroundwater and the level of arsenic is below drinking water standards.

There are some physical hazards at the site, including steep trench walls and possible openings into the mine. 

Ecology and the Potentially Liable Persons agreed to take actions to address many of Health’s suggestions. This is also described in the Responsiveness Summary.  A full copy of the health consultation reportand recommendations is available at

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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
3190 160th Ave SE
Bellevue, 98008-5452

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