ELKO, Nev. — The Nevada Highway Patrol is continuing to investigate a hazardous materials spill that shut down part of U.S. Interstate 80 east of Elko for a day and a half.

The patrol says a Montana truck driver hauling ammonium bisulfite admitted falling asleep before the tractor trailer went into the median and overturned about 20 miles east of Elko at 5:25 a.m. Wednesday.

Thousands of gallons of the material that poses an inhalation hazard leaked onto the highway so authorities shut down the interstate in both directions and set up a detour.

The westbound lanes reopened at 11:15 p.m. Wednesday but the eastbound lanes remained closed until 1:45 p.m. Thursday.

The patrol says the hazmat crews that cleaned up the mess concluded about 3,100 gallons spilled on the ground and 1,000 gallons remained in the truck. The driver wasn’t hurt.