Geology of Washington - Puget Lowland . WA state DNR .
Tertiary sedimentary rocks that contain significant coal resources are exposed along the eastern margin of the Puget Lowland . In the northeastern Puget Lowland, coal was mined as early as 1853 from the Chuckanut Formation at Bellingham and nearby localities. During the period 1900-1918, when coal was the major source of fuel for heating and locomotives, numerous underground mines produced as much as 4 million tons of coal annually. In King County, underground coal mining was carried out under Renton only 10 miles from downtown Seattle.
However, I am rock solid sure that the folks at the state dept of ecology will be able to differentiate between coal exposed to local ground water and sea water for eons, from natural formations, as opposed to the evil, baby killing coal dust coming off train cars - yes ?