The STB said that those shippers that had opposed BNSF’s outlines did not prove that they were unreasonable.

The decision comes after a lawsuit filed in June by the Sierra Club, Puget Soundkeeper, Columbia Riverkeeper and environmentalists in Washington state with claims that the line’s trains discharged coal, coal dust and chunks, and other pollutants into water bodies, leaving harmful mercury, arsenic and uranium concentrations.

BNSF spokeswoman Courtney Wallace told Associated Press that the STB’s judgment would ensure that coal dust remains where it belongs, in its railcars.

“We established our coal loading rule after extensive field testing, and when properly followed, our rule effectively addresses issues with coal dust,” she said.

At the same time, she called the Sierra Club’s suit a publicity stunt aimed at its major mission: stopping coal exports in the Pacific Northwest.

The railroader, which operates largely in the western US states and considers coal one of its largest carried commodities, has been working to reduce coal dust on its lines because track stability and overall line operation.

Some of that stemmed from a previous STB decision in March 2011 stating that dust emissions from open-top railcars were creating issues with track beds; in new rules issued in July 2011 the railroader said it would require coal loadings have a bread loaf shape and be sprayed a topper agent.

Wallace told AP that BNSF would continue to work with PRB shippers to ensure compliance.