One of the plants is owned by Columbia-based South Carolina Electric & Gas Co.; four belong to state-operated Santee Cooper; and Duke Energy and Progress Energy own the other two.
Details about the sites, results of inspections and histories of any spills or leakage have to be furnished by the utilities to the Environmental Protection Agency.
The request follows the failure in December of a dike at a Tennessee power plant that released tons of toxic coal ash, which ruined area residences and killed millions of fish.
Chances of such a catastrophe are remote, said Laura Varn of Santee Cooper.
The walls are built with sound science, and we perform routine dike inspections and employ solid maintenance practices throughout the year, Varn said.
About 61 percent of electric power consumed by S.C. homes, businesses and industries is generated by coal-fired generating plants.