Colorado's richest oil field — the Denver-Julesburg Basin — is buried in floodwaters, raising operational and environmental concerns, as state and industry officials work to get a handle on the problem.

Thousands of wells and operating sites have been affected — some remain in rushing waters, officials said.

"The scale is unprecedented," said Mike King, executive director of the Colorado Department of Natural Resources. "We will have to deal with environmental contamination from whatever source."

Any pollution from oil fields likely will be mixed with a stew of agricultural pesticides, sewage, gasoline from service stations and other contaminants, King said.

"As far as we know, all wells affected by flooding have been shut," said Tisha Schuller, president of the Colorado Oil and Gas Association, a trade group.

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