Coffeyville ? An oil spill that damaged hundreds of Coffeyville homes during flooding four weeks ago was caused when the valve on a refinery storage tank was left open, the Kansas Department of Health and Environment said.

The refinery’s owner, Coffeyville Resources, has long acknowledged that a storage tank overflowed as the refinery was swamped by floodwaters from the nearby Verdigris River. An estimated 71,000 gallons of crude oil escaped.

But refinery officials said they are still awaiting the findings of their own inspection on what caused the overflow and declined to comment on the department’s report.

“The cause is not a relatively simple error,” said company spokesman Steve Eames. “It’s caused by an act of God … a massive flood.”

Eames said refinery staff made “heroic efforts” to shut down the plant as water flowed over the river levees. He said while securing the plant usually takes 24 hours, employees had only five or six hours before the flood forced them to evacuate.

Refineries facing floods typically partially fill their oil tanks to keep them from floating away, which is what Coffeyville Resources said it was trying to do.

The Kansas Division of Emergency Management said a storage tank sitting at a higher elevation continued to pour oil into a main storage tank at a lower level. It was that lower tank that overflowed, said Sharon Watson, spokeswoman for the Kansas Adjutant General’s Department.

Phil Myers, a California-based tank safety expert, said it would take 10 to 15 minutes to manually shut a tank valve and less if a remote-controlled shut-off system is in place. He said making sure the valves on filled tanks are closed is a key step in an emergency shutdown but can be overlooked in the chaos surrounding a disaster.