How news of the leak at Prairie Island nuclear plant unfolded Thursday:

3:53 a.m.

Operators at Prairie Island nuclear plant declare an alert after workers discover sodium hypochlorite -- commonly known as chlorine bleach -- leaking from a tank in the screen house.

The chemical is used to treat water that is brought into the plant for cooling.

4:01 a.m.

Xcel Energy, which owns the plant, sent out an emergency notification alert at 4:01 a.m.

4:41 a.m.

The Nuclear Regulatory Commission contacts Prairie Island Indian Community Tribal Council President Johnny Johnson and the Prairie Island Indian Community immediately initiates its Emergency Response Plan.

6:30 a.m.

Ellsworth Community School District sends out a notice saying school buses will be delayed, but it is not known how long.

7:06 a.m.

Xcel Energy, owner/operator of the plant, sends out a press release regarding the chlorine leak. According to Xcel, no release of radioactive material is associated with the event and there is no danger to the public.

7:14 a.m.

The Pierce County Emergency Operations Center warns the public about the incident at the nuclear plant and suggests tuning into radio stations KCUE, KWNG and WCCO for more information.

7:27 a.m.

The Minnesota Department of Public Safety announces it has activated its Emergency Operations Center and is monitoring the nuclear plant situation.

7:50 a.m.

An update from the Ellsworth School District alerts parents that school will begin two hours late.

7:52 a.m.

The Prairie Island Indian Community uses its phone alert notification system to advise employees and community members of the chlorine leak at the plant.

7:55 a.m.

The Minnesota Department of Safety announces it will hold a news conference at 9 a.m. in its media briefing room to address the status of the nuclear plant.

8:04 a.m.

Goodhue County Emergency Operations Center repeats the alert sent out earlier by Xcel Energy.

8:41 a.m.

The federal Nuclear Regulatory Commission announces that its resident inspectors are monitoring plant workers' handling of the incident.

The leak has been isolated in a berm around the screen house and a chemical crew is on the way to clean up the leak, the NRC says.

9 a.m.

Minnesota officials and Xcel Energy hold a press conference.

10:30 a.m.

A Prairie Island nuclear plant crew is working to clean up the chemical spill of more than 500 gallons of sodium hypochlorite that occurred seven hours earlier.

2:08 p.m.

Operators at the nuclear plant officially terminate the alert that was declared at 3:53 a.m. in response to the chemical spill.