A Dallas sanitation truck caught fire on Northwest Highway near Bachman Lake on Friday afternoon, diverting traffic.
The truck and a huge cloud of smoke around it could be seen from a block away.
"I just saw this 18-wheeler, and flames were coming out of the hood," Nathan Tonolini said. "We watched it for a few minutes, and there was a big boom."
While putting the fire out, Dallas firefighters noticed about 40 to 50 gallons of diesel leaking from the truck. The diesel mixed with the water used to fight the fire and went down Northwest Highway toward a storm drain at Midway Road.
Firefighters immediately put up barriers but say some diesel may have gotten inside the drain.
"We are hopeful it is a very small amount," Dallas Fire-Rescue spokesman Jason Evans said.
City officials told Evans that no drinking water would be affected if some diesel got in the storm drain, he said.
Firefighters were able to offload the bulk of the truck's diesel.
The driver got out when the truck caught fire and is fine.