A warning sign at Dominion Virginia Power's Possum Point power station in Dumfries, Va., in June 2015. (Steve Helber/AP)

Virginia student environmental activists refused to leave the lobby of the state environmental regulatory agency for three hours Monday as part of a protest against Dominion Virginia Power’s plans to release treated coal-ash water into waterways.

It’s the latest backlash to Dominion’s plans to get rid of coal-ash residue held in five ponds at the utility’s power plant at Possum Point in Dumfries in Northern Virginia.

Dozens of students from campuses across Virginia, organized by a student environmental coalition, traveled to Richmond two days ahead of a discharge permit taking effect Wednesday.

About 30 students entered the lobby of the Department of Environmental Quality’s Richmond office Monday morning, while others stood outside with banners accusing the utility of poisoning waters with the agency’s help.

Three hours later, about half of the students inside the blocked-off building left voluntarily. The others left holding court summonses on trespassing charges.

Prince William County and the state of Maryland are trying to block a permit issued by Virginia regulators in January to release about 215 million gallons of treated coal-ash water into Quantico Creek, a Potomac River tributary.