State health officials have been at the site of an accident along an eastern Kansas natural gas pipeline that spewed a natural gas cloud that left a dark, oily residue over now withering crops and trees.

The incident Thursday along a Panhandle Eastern pipeline near Olpe occurred as crews were trying to perform pipeline maintenance. Residents reported seeing a dark, oily plume burst from the line and spread across nearby fields and yards.

The Kansas Department of Health and Environment says the substance released was natural gas condensate. Natural gas condensate can come in various compositions, but typically contains benzene, a known carcinogen.

KDHE spokeswoman Sara Belfry says she doesn’t know how much condensate was released, but that KDHE crews are assessing the situation.