The path to the Environmental Protection Agency’s December release of its final rule for coal-ash disposal stretched for nearly 40 years through the halls of Congress, the bureaucratic web of federal agencies, and in and out of courtrooms across the country. Here are a few key milestones:

October 1976 — Congress passes the Resource Conservation and Recovery Act (PL 94-580) to govern the management of hazardous waste from the time of generation to final disposal, a “cradle to grave” regulatory system. The law is amended in 1980 to temporarily exempt certain fossil fuel wastes from hazardous rules until a study on health and environmental risks is conducted.

Oct. 31, 1982 — The EPA misses the statutory deadline for submitting the report to Congress. Six months later, the agency also misses a deadline for making a regulatory decision on whether hazardous waste controls are warranted. The agency finally submits the report in 1988, but again skips a listing decision and is sued by a citizens group for doing so in 1991.

June 1992 — The EPA reaches a legal settlement requiring it to make the required regulatory decisions. The agency spends the next two decades painstakingly conducting additional study of the issue. New litigation by environmentalists in 2012 results in a legal settlement in which the EPA agrees to finalize a decision on coal ash.

December 2014 — The EPA finalizes non-hazardous disposal requirements for coal ash.