The MDU Heskett Power Plant that provides electricity to Bismarck is located along the Missouri River north of Mandan.

A mechanical failure Tuesday morning on a backhoe at Montana-Dakota Utilities' Heskett Station north of Mandan led to a small hydraulic oil spill that caused a sheen on the Missouri River.

MDU estimates that 1 gallon leaked from the excavator, which was performing dredging work to clear out sediment in a small channel where the water intake is for the power plant. Spokesman Mark Hanson said it appears a hydraulic seal was leaking.

The company has isolated the channel with booms, which are floating devices attached to netting. Booms help prevent oil from migrating in water, said Bill Suess, manager of the state Department of Environmental Quality's spill investigation program.

Hanson said Marathon Petroleum, which operates the nearby oil refinery, helped out by placing its own booms along the riverbank as a precautionary measure.

Suess does not anticipate any lasting environmental impacts from the spill. The Missouri River is flowing quickly right now, which, he said, should help dissipate any oil in the river.

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(Reach Amy R. Sisk at 701-250-8252 or amy.sisk@bismarcktribune.com.)