HARRIMAN, Tenn.  (AP)– A retention pond wall collapsed early Monday morning at a power plant run by the nation's largest public utility, releasing a frigid mix of water and ash that flooded 15 homes nearby.

  The 40-acre pond was used by the Tennessee Valley Authority as a containment area for ash generated by the coal-burning Kingston Steam Plant in Harriman, about 50 miles west of Knoxville, said TVA spokesman Gil Francis. An earthen wall gave way just before 1 a.m., flooding the road and railroad tracks leading to the plant.

  No one was seriously injured or needed to be taken to the hospital, said Howie Rose, the director of the Roane County Office of Emergency Management and Homeland Security. WVLT-TV reported that two people had to be rescued from their homes but had only minor injuries.

  The extent of the damage was not immediately clear. TVA experts went up in a helicopter after sunrise to assess the damage from the air.

  Crews were working to clear debris in the neighborhood on Swan Pond Circle Road, Rose said.

Rose said a train carrying coal to the plant reached the point on the tracks that is flooded and couldn't go forward or back up. He said there were no injuries and authorities were trying to assist the train.

  The Environmental Protection Agency has been notified, Francis said. Investigators are still trying to determine exactly what caused the flood, but he said heavy rains and freezing temperatures may be to blame. The National Weather Service reported it was only 14 degrees just before 6 a.m. in Harriman.

According to Francis, the area usually receives about 2.8 inches of rain in December. There's been about 4.9 inches of rain so far this month, Francis said.

Knoxville-based TVA supplies electricity to 8.8 million consumers in Tennessee, Mississippi, Alabama, Kentucky, Georgia, North Carolina and Virginia.