SILVERTON – A truck hauling waste from a Colorado mine – the source of a 2015 spill that polluted rivers in three states- crashed into a creek on Monday, spilling at least some of its load into the water, authorities said.

The driver was not seriously injured, but about 9 cubic yards of sludge spilled into the water, officials said.

The sludge is a byproduct of a U.S. Environmental Protection Agency wastewater treatment plant cleaning up water draining from the inactive Gold King mine near Silverton in southwestern Colorado.

The agency said previously the sludge is not hazardous. An EPA spokesman didn’t immediately respond to a phone call and email after hours Monday.

Authorities said it did not appear the truck spilled any fuel.

The Gold King was the source of an August 2015 spill that released 3 million gallons of potentially toxic wastewater, polluting rivers in Colorado, New Mexico and Utah and on Native American lands. An EPA-led contractor crew inadvertently triggered the spill while excavating at the mine entrance.

The 2015 spill sent a yellow-orange plume containing arsenic, lead and other toxic metals into waterways, putting the rivers temporarily off-limits for drinking water, farming, rafting and fishing. The EPA said the water quality quickly returned to pre-spill levels.

The EPA installed a temporary treatment plant below the Gold King two months after the spill to clean up wastewater still flowing from the mine.

The plant removes metals from the water before it enters Cement Creek. The truck that crashed Monday slid off the shoulder of a mountain road and dumped the sludge back into the same creek farther downstream.

The EPA had been storing the sludge at the treatment plant but was running out of room. Trucks began hauling it to another site this summer.

The agency designated the area a Superfund site in 2016 but hasn’t announced long-term cleanup plans.