Plan required to prevent further discharges of power boiler ash slurry into a ditch.
The leak comes as the Nebraska Public Service Commission is set to vote on the Keystone XL sequel.
Propane fuelled forklift was the origin of the carbon monoxide that sent two to hospital.
Crews were working to clean up the release, contained in an excavation pit.
Sulfolane leaked into well water supplies as far as two kilometres from the plant.
Up to 250,000 litres leaked from a pipeline into the North Saskatchewan River.
Four workers were killed at La Porte works in Houston area.
Spikes in radiation levels in seawater samples taken at Fukushima nuclear plant.
Enbridge restarts pipeline system following 750-barrel leak in June.