U.S. Senators Dick Durbin (D-Ill.) and Mark Kirk (R.-Ill.) have requested a meeting with oil producer BP after a newly expanded BP refinery in Whiting, Ind., spilled up to 39 barrels, or 1,638 gallons, of crude oil into Lake Michigan last week.

Although the U.S. Environmental Protection Agency indicated it's unlikely the spill poses a hazard to the lake, Durbin and Kirk are seeking assurance the refinery can operate safely now that it has doubled capacity, to 405,000 barrels per day.

“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,” wrote Senators Durbin and Kirk.

BP attributed the spill to a malfunction in a distillation unit that came on line in July, following a $4-billion upgrade that allows the facility to process more heavy Canadian crude.

Clean up has been under way for a week. “Crews have recovered the vast majority of oil that had been visible on the surface of a cove-like area of Lake Michigan and on the shoreline between the refinery and a nearby oil spill,” BP indicated in a statement last week. “They have used vacuum trucks and absorbent boom to contain and clean up the surface oil. Responders also manually collected oil that reached the shore.”

BP initially estimated nine to 18 gallons of oil were discharged into the lake. The company says it is continuing work to determine the amount discharged.

EPA is investigating potential violations of the U.S. Clean Water Act.

The Whiting facility is the nation's seventh largest oil refinery.