(CBS) — U.S. Senators Mark Kirk and Dick Durbin want a meeting with BP’s U.S. chief executive officer to discuss the latest spill at its Whiting, Ind., refinery.

They sent a letter to BP CEO John Minge as the oil giant released a statement in which it more than doubled its estimate of the amount of oil that could have been spilled.

READ MORE: State Reps LaShawn Ford And Fran Hurley To Host Crime Summit at UIC

“We are deeply concerned about this week’s oil spill,” the senators wrote in their letter, released to WBBM by Kirk’s office.

“Any unanticipated spill is cause for concern, but given the Whiting refinery’s recent expansion of its operations to double the amount of heavy oil sands being processed, this spill raises questions about the long-term safety and reliability of BP’s new, expanded production at Whiting,” they wrote.

They said they intend to speak with Minge about potential public health and environmental threats to surrounding communities.

BP spokesman Scott Dean said that the company now estimates that the spill may be up to 39 barrels — 1,638 gallons. It blames a malfunction in its oil processing unit, officials said Thursday.

READ MORE: Multiple Juveniles Arrested After Large Gathering, Fights Near Millennium Park

Dean said, in a statement obtained by WBBM, that it bases the new estimates on the oil recovered so far using vacuum trucks, oil-absorbent booms and collection of waxy, oil-laden balls from nearby beaches. Previously, it said no more than 18 barrels had spilled.

The cleanup continues.

Durbin and Kirk said they are particularly concerned about contamination of drinking water drawn from Lake Michigan by several nearby communities. The letter goes on to ask what has been done to determine if oil has settled on the floor of the lake.

“Protecting the lake must be a priority,” the letter states. “We urge you to explore every avenue to expeditiously recover any spilled oil, remediate the damage where possible and minimize future threats the Whiting refinery poses.”

MORE NEWS: Kenosha Man Shot, Killed In North Chicago

The U.S. Environmental Protection Agency has said it believes there is no effect on municipal water supplies.