In March, as part of Scott Pruitt’s aggressive campaign to roll back federal regulations, the Environmental Protection Agency proposed relaxing standards for storing potentially toxic waste produced by coal-burning power plants. EPA officials cited a study indicating that forcing utilities to get rid of unlined coal ash ponds too quickly could strain the electrical grid in several regions of the country.But when environmental advocates scrutinized the specifics, they discovered a problem: The evidence cited was not established scientific research. Instead, the agency was relying on a four-page document by the utility industry’s trade association, the Edison Electric Institute, which has acknowledged that its conclusions were not “part of or a summary of a larger study.”Lisa Evans, a lawyer for the group Earthjustice, was among the advocates who seized on that omission, as well as on gaps in technical data and other evidence, to argue that the agency’s action was ill-advised and legally flimsy.