WALLA WALL — Walla Walla officials said Sunday, Sept. 17, the likely source of the chemical odor that caused the evacuation of the Marcus Whitman Hotel and Conference Center was a 10,000-gallon underground tank at the Chevron gas station across the street.

According to a city news release, Clean Harbors Environmental Services — a contractor brought in by the hotel — found “what appears to be pure gasoline present in a 10-foot-deep sump in the basement” of the hotel.

Officials said the gasoline is suspected to have come from the tank, containing regular unleaded fuel, belonging to the Chevron gas station across the street at 7 E. Rose St.

“There is no pipeline connecting gas station equipment to the hotel,” according to the release. “There is no indication any gasoline has entered Walla Walla’s underground utility infrastructure or waterways.”

A crew worked the night of Sept. 16 to empty the suspected tank so it can be “tightness tested to detect any leaks once a contractor can be secured to perform the testing. A timeline for this testing has not been identified at this point,” according to the news release.

The following morning, a Clean Harbors crew began pumping the gasoline out of the hotel’s basement sump and transporting it to a tank located on the north portion of the hotel property, the release said.

Throughout the process, air-quality monitors in the hotel and outside on the street level will be used to detect concentrations of volatile organic compounds and lower explosive limit.

“Readings in the basement are currently virtually zero due to the ventilation system installed by Clean Harbors,” according to the release.

Walla Walla Fire Department officials and Washington State Department of Ecology staff are present to monitor the situation and to provide technical assistance as needed, the release said.

There is no estimated timeline for how long all the procedures will take.

Meanwhile, Second Avenue between Cherry and Rose streets will remain closed to vehicles and pedestrians. U.S. Postal Service customers can use the sidewalk on the south side of Sumach Street to access the Post Office.

The release said there is no immediate risk to the community, but WWFD and Walla Walla Police Department personnel will be sure no one enters the closed area.