"They were able to find nothing to indicate there is a bigger problem," Gibson said.
Downstream past the Clarks Fork's confluence with the main branch of the Yellowstone River, water suppliers in the Billings area were on watch for contamination coming getting into their intakes.
Woody Woods, manager of the Lockwood Water and Sewer District, said no signs of the chemical had turned up by late Tuesday. He said workers will continue daily checks to monitor the water, but added that after Wednesday any potential threat likely will have passed.
The truck was operated by Lynch Trucking of Riverton, Wyo., according to the Montana Highway Patrol, which issued the driver a citation for reckless driving. The company could not be reached for comment.
Any potential water pollution violations will be investigated by the Montana Department of Environmental Quality.