The amount of oil spilled also wasn't known by Saturday afternoon, Williams said, but he added that officials hoped to have a better idea once they're able to reach the derailed oil tankers.
Some of the cars soon began leaking crude oil into the Little Rock River floodwaters, prompting an evacuation of nearby houses and sparking fears of drinking water contamination.
Gov. Kim Reynolds visited the derailment site Saturday as part of a tour of areas hit by recent flooding.
BNSF railroad spokesman Andy Williams said workers have unloaded oil from 10 of the oil tank cars that did not leak after the derailment approximately 15 miles south of the Minnesota border. Sheriff Stewart Vander Stoep (VAN'-dur stoop) in neighboring Lyon County says the train derailed between 5 and 5:30 a.m. Friday just south of Doon.
About 100,000 gallons had been hemmed off using booms out of the estimated 230,000 gallons spilled, BNSF said in a statement on Saturday. "We had a large supply in our water towers and we are using our interconnection with rock valley rural water to recharge our water supply".
A major part of the cleanup work includes building a temporary road parallel to the tracks to allow in cranes that can remove the derailed and partially-submerged oil cars.
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Cleanup of an oil spill caused by the derailment of almost three dozen oil tankers in northwestern Iowa has begun.
Metropolitan Utilities District, which provides the Omaha metro area's drinking water, said it was monitoring the spill.
Some officials have speculated that floodwaters eroded soil beneath the train track. In the meantime, the city is getting its water from the nearby Rock Valley Rural Water system, which Olson says is not in danger of being contaminated by the spill. The Little Rock River rose rapidly after heavy rain Wednesday and Thursday.
The city, with a population of almost 3,400, will stay on the rural water system until testing by the Iowa Department of Natural Resources confirms the safety of the city's drinking water, Olson said.
Four homes near the site have been evacuated.
The Rock River had already carried some oil to Rock Valley by midmorning, said Ken Hessenius with the Iowa Natural Resources Department.