Coal trains release an average of 100 million small particles of coal dust per second. That's according to an expert witness for environmental groups suing the company for coal pollution in Washington waterways.

BNSF Railway heard testimony from Robert Breidenthal on Monday. The professor at the University of Washington specializes in aeronautics. He testified about the discharge of coal from rail cars and the aerial trajectory he believes carries coal particles into Washington’s waterways.

During testimony to which BNSF unsuccessfully objected at least three times, Breidenthal told the court that coal trains, on average, release about 100 million small particles of coal dust per second. When asked about his degree of certainty, he replied, “I’d bet my life on it.” He also said “the loss of small particles is essentially continuous,” and “a conservative estimate would be 99% of the time.”

Environmental groups like Puget Soundkeeper Alliance have banded together to stop what they believe to be regular and widespread violations of the federal Clean Water Act by BNSF. Coal's toxic ingredients, they say, are harming fragile ecosystems in important bodies of water like Puget Sound and the Columbia River.

BNSF claims the way they load the rail cars, along with the use of a special adhesive spray, keeps coal from discharging into the air or water. However, Breidenthal says the membrane deteriorates as the train travels. Because of the deteriorated shape of the coal load, small particles of coal are more susceptible to being blown away by minimal wind speeds, far less than a mile per hour.

In addition to coal leaving the top of rail cars, Breidenthal told the court that reports show that each car loses about 10lbs of coal per hundred miles through holes in the bottom called “weep holes” that are designed to allow for water discharge when it rains.

During testimony, BNSF's attorneys grimaced as Breidenthal wrote a physics equation for the court. They asked the judge to strike the information from court record because it's "unreasonable" to require them to respond to such information with no prior knowledge. The judge denied their request. During court recess, one of BNSF's attorneys expressed concern over the case.

It is possible the parties will reach a settlement.