WASHINGTON (From news reports) -- The source of a mysterious and unpleasant odor that drew widespread concern among residents of two Pacific Northwestern states has finally been found.

Nearly two months after initial reports of the foul stench - described by residents as akin to sulfur, natural gas or burning garbage - authorities believe they have uncovered a likely contributor.

The Smurfit Westrock paper mill in Longview, Washington, 'likely contributed' to the pungent stench that wafted through southwest Washington and northwest Oregon in September, the Washington State Department of Ecology determined.

Yet, the agency is unable to say for sure that the mill was the lone contributor to the putrid odor that triggered an onslaught of complaints and widespread speculation among residents.

'Ecology's investigation identified that the WestRock facility in Longview likely contributed to the odor,' the agency wrote.

'However, based on the data, we can't conclude if this venting was responsible for all of the odor complaints across the region.'

With no clear source and mounting complaints, authorities began their investigation using any and all leads they had at the time.

Before turning blame towards the mill, authorities speculated that a nearby active stratovolcano, Mount St. Helens - just over an hour's drive from the paper mill - may have contributed to the scent.

Though after further investigation the volcano was ultimately ruled out.

'In general, odor investigations are challenging to address and are often inconclusive,' ecology department officials said as the investigation progressed.

Authorities later discovered that the Westrock paper mill vented a gas stream on September 24, that contained chemicals that cause odors.

However, the amount the mill vented was within the confines of its permit to do so, the DOE revealed.

Though not performed daily, the venting is an integral part of the mill's normal operations and is allowed under the terms of the facility's permit.

'Smurfit Westrock can confirm that no air permit violations occurred at the facility on September 24, 2024, and there is no indication the Longview paper mill was the source of odors cited in complaints,' the company said in a statement at the time.

The permit requires the company to report each round of venting as it did so on September 24.

Upon a later review of the facility's emissions data, the DOE discovered that release of the odor-causing chemicals was too small to pose a threat to human health or the environment.

The department also said its conclusions were based on air quality and meteorological data, emissions data, official odor complaints and in-person visits to assess the operational conditions at WestRock and another nearby paper mill.

The agency added that it could not conclusively say if other sources contributed to the odd smell, adding that no data is available to confirm whether or not the facility was also responsible for the odor complaints in nearby Vancouver and Portland.