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This March 25, 2014 photo shows the BP Water Processing Facility in Whiting, Ind, where crews continue to assess and clean up crude oil that spilled into Lake Michigan following a malfunction at the facility, officials said. (AP Photo/The Times, Jim Karczewski)

WHITING, IN -- BP crews on Thursday more than doubled their earlier maximum estimate of how much oil spilled into Lake Michigan when a refinery malfunction occurred in Indiana this week.

Company representatives now estimate between 630 and 1,638 gallons of oil has been recovered since the spill at BP's Whiting Refinery on Monday, March 24. It was estimated Wednesday that between 377 and 755 gallons of crude oil had spilled. BP said the initial numbers were based off visual observation.

BP spokesperson Scott Dean said the company's updated estimate spans a wide range because of water and sand that is mixed with oil collected by vacuum trucks and rakes. Techniques to separate oil can "take a bit of time."

"We are committed to continuing to try to be more precise," Dean said. "Whenever we find evidence of oil, we can recover it and add it to our tally."

A team comprised of BP, Environmental Protection Agency and U.S. Coast Guard workers twice on Thursday combed an industrial stretch of shoreline that spans about a half-mile between a wastewater plant and steel mill. A malfunction with a crude oil distillation unit Monday afternoon sent oil into the refinery's cooling water outfall and into the lake.

Cleanup crews deploy boom along the Lake Michigan shoreline near the BP Whiting Refinery in Whiting, Ind., March 25, to recover crude oil discharged from the refinery the previous day.

Dean said the "vast majority" of oil has been collected and he was not aware of the team detecting additional oil Thursday. Crews earlier this week manually removed oil that had formed into waxy tarballs on the shore. More than 3,000 feet of boom was used to contain oily water to the cove area to be vacuumed.

U.S. Coast Guard representatives in a statement said the cleanup team will continue to examine the rocky wall of the cove to address the extent of oiling along the shore. Crews are expected to return Friday to look for potentially submerged oil by following the path of discharge.

Drinking water was not compromised, Dean said. Philip Willink, senior biologist with Chicago's Shedd Aquarium, earlier said based on information released, Lake Michigan wildlife should not suffer any long-term effects.

Angie Jackson covers public safety and breaking news for MLive/The Grand Rapids Press. Email her at ajackso3@mlive.com, and follow her on Twitter.