A Reclaimed Hiking Trail in Seattle
Next to a hiking trail in a park near Seattle in King County, Washington, a large subsidence suddenly appeared. The 8-foot by 10-foot, 45 degree slope entry opened into abandoned coal mine workings and created a serious hazard for the public.
The OSMRE Western Region’s Abandoned Mine Lands (AML) staff rapidly responded to this emergency. Polyurethane was used to construct a bulkhead in the throat of the mine entry (Photo 1).
Next, a cone-shaped concrete plug was constructed to seal the top of the entry (Photo 2). A pipe drains water that accumulates on top of the plug into the mine and also holds a monument marker. Soil backfill is placed over the concrete and the marker identifies the location (Photo 3 – note the monument pipe near the red flagging).
The restoration was completed quickly, within 16 days of the subsidence, and the hiking trail was made safe once again for recreation with minimal disruption for those who use the trail.