WALLA WALLA — Efforts to remove groundwater contaminated with gasoline from sumps below the Marcus Whitman Hotel and Conference Center and another vacant building in downtown Walla Walla yielded about 20,000 gallons of the mixture as of Thursday, Sept. 28.

It is estimated that 1,500 to 3,000 gallons of that recovered fluid was gasoline, according to the state Department of Ecology, the agency overseeing the investigation and cleanup of the gasoline leak traced back to the Chevron station at 7 E. Rose St.

Officials found an additional sump in the basement of the Marcus Whitman Hotel on Thursday, according to a news release from Ecology.

Stephanie May, spokesperson for Ecology, said the sump is collecting groundwater and gasoline.

Clean Harbors, a private contractor brought in by the hotel, began the process of extracting contaminated water from that sump Thursday, while Ecology supervised the pumping operations from the sump in the building at 106 N. Second Ave., the release said.

The extraction work will continue until officials can control the source of the plume or move to extract contaminated fluids from the monitoring wells, the release said.

“Three of the monitoring wells drilled around the Chevron station are being explored as possible candidates for this extraction,” according to the release said.

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May said Ecology is using a frac tank treatment system to filter out contaminants and discharge clean water to the Wastewater Treatment Plant.

Clean Harbors is working to stage another frac tank filtering system in the area. May said the second system is expected to be set up by Sept. 30.

The systems use granulated active carbon, also called carbon filters, to filter the water.

City employees have been monitoring the wastewater treatment system throughout the investigation and have found no evidence of gasoline entering the system, according to the news release. There is also no evidence of contaminants in Mill Creek.

Ecology received the fingerprint analysis of gasoline samples collected earlier in the investigation, according to a Sept. 29 news release.

The release did not include the results but said the analysis is being shared with affected parties to determine next steps.

The Sept. 29 press release also said the Walla Walla Fire Department detected no trace of unsafe conditions in regular air monitoring of buildings in the affected area and was going to suspend its air monitoring of those buildings.

May said the fire department had been monitoring the air in all of the buildings in the area for elevated levels of volatile organic compounds.

The release said air monitoring would continue at the Marcus Whitman Hotel and at the building at 106 N. Second Ave. May said air monitoring would also continue above the drilled wells.