Residents in an area of rural Petaluma were told to shelter in place as a precautionary measure Tuesday night while a Sonoma County hazardous materials team investigated three 55-gallon drums containing an unknown white liquid west of town.

The hazmat team was called out to the intersection of Eastman and Stadler lanes shortly after 6:30 p.m. to check out the situation, made urgent because some of the substance had leaked from one metal drum and was running toward a stream in the area, according to initial reports.

The shelter-in-place request was for all residents of Stadler Lane and residents who live from 1901 to 2155 Eastman Lane, the Sonoma County Sheriff’s Office said.

Wilmar Fire Chief Mike Mickelson said the material was running across Stadler Lane but did not appear to have reached a small creek on the other side, though firefighters had established an exclusion zone around the intersection and kept their distance, so they couldn’t be sure.

He said the barrels were found on the shoulder of Eastman Lane right at the intersection. The hazmat team had determined the leaking substance was acid, but knew nothing else as of 9 p.m., he said.

Mickelson said he expected emergency personnel to be on the scene until midnight or 1 a.m., and said residents would be alerted when the shelter-in- place order was lifted.

Along with Wilmar and Sonoma County personnel, Cal Fire firefighters were on the scene.