sentences:  Additionally some of these ponds have had structural failures, causing massive ash spills into rivers, such as the 2014 Dan River coal ash spill.Federal design standards for ash ponds were strengthened in 2015, although various provisions of the new regulations are on hold as of 2019, pending ongoing litigation and revisions to the regulations.About 43 percent of CCPs in the U.S. were recycled for "beneficial uses" in 2008, according to the American Coal Ash Association.