The U.S. Environmental Protection Agency is expected to announce its rule on regulating fly ash from coal-based power plants, Friday, Dec. 19. Currently, the North Dakota Department of Health regulates fly ash. The state has also been supportive of efforts to turn this byproduct from a waste into something beneficial.
About 40 percent of the fly ash from North Dakota's eight power plants is sold, rather than landfilled. Much of the fly ash is used as replacement for Portland cement. Some of it can be found in the parking lots and highways in and around Bismarck and other North Dakota towns.
Fly ash is composed of 80 to 90 percent glass particles that are formed when clays, shales, limestone and dolomite found intermixed with coal burned in the huge boilers at power plants. These small particles combine with calcium hydroxide to form calcium silicate hydrate, which is the principal binder in cement.
Underground coal mines are a part of North Dakota's history. Now lignite is removed by surface mining techniques but prior to the 1940s, much of the coal was used for home heating purposes and was mined underground. The mined coal seams were often less than 150 feet below the surface. Once the coal was removed, voids were created. The collapse of these voids can lead to the formation of sink holes. Towns with abandoned underground coal mines, including Beulah, Dickinson, Garrison, Hazen. Scranton and Wilton, have seen the resulting sink holes.
From 1995 through 2014, the PSC has spent more than $15 million to pump grout with fly ash into boreholes drilled into abandoned underground coal mines to help stabilize the surface.