Stillwater Holdings Chevron

Page updated October 21, 2025.

Ecology’s contractor, NWFF Environmental, is on site daily, monitoring the temporary water treatment and vapor mitigation systems in the basements of the Marcus Whitman Hotel and the 106 Building. Mitigating contaminated water and potentially harmful vapors in the Marcus Whitman Hotel and 106 Building remains the highest priority.

NWFF monitors water levels in the sumps at both buildings to ensure levels remain stable. A vacuum truck removes sump water at the Marcus Whitman as needed in the summer months when the water level is low and up to twice a week in the winter when the water level increases.

GeoEngineers is drafting an engineering design report for the permanent mitigation systems. We expect the draft report to be available by the end of 2025.

GeoEngineers completed another round of groundwater sampling at Stillwater Chevron, 106 Building, and the Marcus Whitman Hotel properties at the end of September 2025. Indoor air (vapor intrusion) sampling was completed for all three properties at the end of April. We will post the results as soon as the final reports are available.

Groundwater

September 2025 sampling results indicate concentrations of gasoline-range petroleum hydrocarbons (GRPH) and volatile organic compounds (VOCs) remain generally consistent with previous data, with continued decreases in some wells.

Petroleum contamination concentrations in the Marcus Whitman were below the Walla Walla wastewater discharge limits for the second consecutive quarter, requiring continued pretreatment before discharge.

At the 106 Building, sump petroleum concentrations were below discharge limits for the third consecutive quarter; four consecutive compliant results are required before direct discharge to the city sewer is allowed.

Soil

On September 5, 2024, Stillwater Holdings had five soil samples collected on their property while removing some old product lines and fuel pumps. Sample results showed contaminated soil near the southern fuel canopy at 300 milligrams per kilogram (mg/kg), greater than the cleanup level of 30 mg/kg. Stillwater Holdings’ consultant, Aspect, interpreted the contamination as highly weathered gasoline likely from the historical release.

Indoor air

In August 2024, Ecology sampled indoor air in the 106 Building. 106 Building sampling results showed initial indoor air was safe for adults working an 8-hour shift, but not for children or adults occupying the building for longer than a normal work shift.  

Local, state, and federal agencies, along with third-party contractors, have deemed the area safe for residents and visitors with protection measures and air quality monitoring in place. Testing of Walla Walla's municipal water and wastewater systems and nearby Mill Creek has shown no evidence of contamination.

The first deliverable required from Stillwater Holdings is a comprehensive schedule and a remedial investigation work plan, which has not been submitted to us yet. When the remedial investigation is finished, a draft of the report will be available for public comment.

Ecology received $3.5 million from the 2025–2027 state capital budget to continue cleaning up the gasoline spill. The funding will allow Ecology to complete the remedial investigation, feasibility study, cleanup action plan, implementation of a cleanup remedy, and long-term monitoring. We are pursuing recovering costs from Stillwater Holdings Chevron. In the meantime, we are using state funding to ensure the safety of the community and environment.

We held a public comment period June 18 – August 16 for the Enforcement Order and Public Participation Plan. The order requires Stillwater Holdings to continue work to reduce harmful vapors and remove contaminated water from nearby buildings until a permanent treatment system is installed. You can learn more in the public notice we mailed to the surrounding community. We responded to comments from five people and thank them for their input. Based on concerns expressed about using state funding for cleanup, we amended the Enforcement Order to require a remedial investigation and feasibility study.

On September 14, 2023, the Marcus Whitman Hotel was evacuated due to volatile organic vapors entering the building, also known as vapor intrusion. The Walla Walla Fire Department called in Ecology’s Spill Response Team to help assess the situation and identify the source.

Testing identified potentially harmful vapors and gasoline in the basement, and in two nearby buildings. The buildings were ventilated to eliminate the risk of an explosion, and the buildings’ drainage systems, also known as sumps, were pumped to reduce vapor concentrations.

An investigation found that gasoline pooling in the adjacent building sumps matched the fuel in Stillwater Holdings’ underground tank. Since then, the tank was taken out of service and emptied, product is no longer visible in the sumps, and petroleum contaminants continue to decrease in water samples from the sumps.