The decision came when a resident called to report a home that appeared to have been affected by the oil spill but was not listed within the identified area.

"The boundary lines are not absolutes," said Scott Harris, group supervisor for the Murphy Oil incident at the U.S. Environmental Protection Agency. "We continue to do visual assessments and sampling, so the boundaries are subject to change."

About 1,800 residents and an undetermined number of other buildings were affected when a partially filled 250,000-barrel storage tank reportedly was lifted off its foundation by floodwater and shifted several feet. More than 1 million gallons of oil was released into the floodwater, environmental officials said.