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.

The basin, one of the most promising onshore oil plays, has been the target of an estimated $4 billion of oil industry investment, with about 48 rigs operating when the flood hit.

Companies are using boats and helicopters to check sites not accessible by road, Schuller said.

“As water levels recede, operators are assessing any damage and addressing it,” she said.

The major public health risks will come from contaminated water and sediments, said Miriam Rotkin-Ellman, a Natural Resources Defense Council staff scientist.

“The aim is to find where there may be significant pollutants and where they are heading,” said Rotkin-Ellman, who studied industrial contamination in New Orleans after Hurricane Katrina.

The Colorado Oil and Gas Conservation Commission is setting up a clearinghouse to log the status of every well and operation, said Matt Lepore, the commission’s executive director.

The commission also is using its mapping technology to identify well sites along the South Platte River for inspection.

“Mapping is a really good first step — it locates where the problem could be,” said NRDC’s Rotkin-Ellman.

The commission is forming teams — including inspectors, engineers and environmental specialists — to focus on locations north and south of the South Platte.

Still, the specter of pollution has raised concerns among environmentalist and community groups.

“With the Texas Gulf Coast, they know in advance a hurricane is coming,” said Irene Fortune, a retired chemist who worked for British Petroleum and is now running for the Loveland City Council.

“To have something this inland, this level of flooding in an area with high oil and gas development, it’s new territory,” Fortune said.

Gary Wockner, Colorado Program Director for Clean Water Action, said, “Every flooded well needs to get inspected.

“The COGCC needs to pass new regulations for drilling in floodplains to better protect people and the environment.”

There are more than 20,000 wells in th e DJ-Basin and surrounding areas and 3,200 permits for open pits in Weld County, according to state data.

A review of the pit permits, however, found a significant number are old permits that may not be operating — most were to hold produced water that contains salts and metals from wells.

Major operators in the basin said they were able to shut all the wells hit by the flood.

Encana Oil & Gas (USA) has shut about one-third of its 1,241 wells, the company said.

“We have plans in place to inspect all of our facilities,” Doug Hock, an Encana spokesman, said in an e-mail. “We’re using (geographic information systems) to help prioritize lower-lying facilities that may likely have greater impacts.”

Anadarko Petroleum Corp., the second-largest operator in the basin, shut wells and stopped drilling activity.

“The majority of our drilling, completions and workover activities in the affected areas of the field have been shut down,” the company said on its website.

“Restarting the activities is expected to be significantly delayed due to road and location conditions,” the company said.

The well sites are designed to withstand harsh weather, said William Fleckenstein, a professor of petroleum engineering at the Colorado School of Mines.

“The actual wells are meant to hold pressure on the inside. They’re designed to be fluid-tight,” Fleckenstein said.

Concern arises when tanks are knocked over or damaged, Fleckenstein said.

The “worst-case scenario,” however, would be damage to a high-pressure gas line, which would leak hydrocarbons in the air and be “very explosive,” Fleckenstein said.

The impact of the flood waters has been uneven in the basin, said the oil and gas association’s Schuller. Some areas are untouched, and some facilities are still surrounded by flowing water, Schuller said.

“It may take some operations a week to get back up,” Schuller said. “It may take a year for others.”

Pictures of flooded well and drilling sites and damaged or floating tanks have been appearing on several social-media sites.

“We’ve seen the pictures but don’t know the locations,” Schuller said. “If people provide the locations, we will check them.”

Mark Jaffe: 303-954-1912, mjaffe@denverpost.com or twitter.com/bymarkjaffe