AUBURN – It wasn’t gasoline and it wasn’t oil. It wasn’t glue or any kind of noxious solvent.

The source of a phantom odor that disrupted a New Auburn neighborhood Thursday afternoon may never be known.

One woman went to the hospital with a headache and several others were evacuated from homes and businesses when a powerful aroma was reported at about 1 p.m.

Fire officials who investigated the stink said heavy rains may have been the culprit. Sludge on its way through underground pipes may have moved along quicker and settled in the pipes, in the New Auburn area, the odor wafting up in a busy section of the city.

“Everything kind of collects in one area on the way to the treatment plant,” said Auburn Assistant Fire Chief Ray Lussier. “It’s one of those strange events. We call it a slug.”

Residents at an apartment house on Mill Street were cleared out of their homes as were employees and customers at the Happy Days Diner. Fire crews began searching for a source for the odor, checking a local gas station and other businesses for leaks.

“We didn’t find anything dumped or spilled,” Lussier said. “All the obvious sources were ruled out almost immediately.”

The treatment plant was also checked for unusual substances and nothing was found, Lussier said. Later in the day, officials from the sewer department were ventilating the New Auburn neighborhood.