Brumfield Twidwell

Environmental cleanup is complete at the Site and the periodic review completed in 2020 shows the cleanup work remains effective in protecting the health of people and the environment.

After cleanup, concentrations of petroleum hydrocarbons above cleanup levels in soil and groundwater were left in place, so an environmental covenant was attached to the property in 2006.

When an environmental covenant exists for a cleanup site, Ecology reviews site conditions about every five years to ensure the long-term effectiveness of the cleanup action. 

Ecology inspected the Site on January 10, 2020. The current condition of the the building, parking lot, and pavement at the Site continues to eliminate possible exposure of people and the environment to the contaminated soil and groundwater. 

From November 19 to December 20, 2020, Ecology held a comment period to give the public an opportunity to comment on conditions at the Site. No comments were received and Ecology finalized the periodic review report.

Periodic Review Report - Final

The Brumfield Twidwell cleanup Site is located at 301 East Pioneer Avenue in downtown Montesano. Records indicate the property was originally developed by the Shell Oil Company as a gasoline service station and garage in 1927.

In 1966, several parcels were consolidated into the Brumfield Twidwell car dealership. The building on the Site was consistently used as an auto service station, auto repair, and auto sales shop. In 1997, the property was sold a new owner who leased the building to various tenants until 2005, when the structure was demolished for new development. 

Currently the Site is used for commercial purposes and this use is not likely to change in the future.

During Site operation, four underground storage tanks (USTs) were present at the Site. Three USTs (5,000-gallon, 10,000-gallon, and one of unknown size) were used to store gasoline and one 500-gallon UST was used to store waste oil. Releases from some of these USTs had affected the soil and groundwater at the Site. In 1991, three tanks were closed in place by filling with a sand or concrete slurry,  and the fourth tank (10,000-gallon) was removed.

In 2005, Ecology found gasoline-range petroleum hydrocarbons (TPH-G) in soil and groundwater at the Site. This was discovered during the the area-wide downtown Montesano groundwater study.

From 2005-2006, the owner removed about 2,079 tons of petroleum-contaminated soil and disposed of it off-site. During the excavation, a 10,000-gallon UST was discovered that was used for waste oil. The tank was removed.

Groundwater monitoring confirmed that TPH-G and benzene, toluene, ethylbenzene, and xylenes (BTEX) were above state cleanup levels. Additional monitoring wells were installed. 

In 2006, Ecology and the owner entered into an agreed order to investigate the full extent of contamination remaining on the site and to evaluate options for final cleanup. 

The remedial actions conducted at the Site included the source removal and disposal, groundwater treatment, and long-term groundwater monitoring for natural attenuation. Some of the cleanup actions were completed before the Agreed Order was signed with Ecology.

The cleanup included the following actions.

• Removal of two 10,000-gallon USTs  
• Closure of three USTs (one 5,000 tank and two 500-gallon tanks).
• Excavation and off-site disposal of about 2,079 tons of petroleum-contaminated soil.
• In-situ bioremediation that involved injecting an oxygenating compound into the groundwater wells. 
• Groundwater monitoring.

The bioremediation enhances microbial degradation of the remaining petroleum hydrocarbons in soil and groundwater.

In 2012-2013, quarterly groundwater monitoring began about three months after bioremediation was completed and continued for at least one year.

The petroleum hydrocarbon concentrations decreased during the monitoring period. Results showed contaminant concentrations were either below state cleanup levels or were not detected above the laboratory detection limits.

Based on investigations in the downtown area and knowledge of the presence of other contaminant sources near the Site, it was concluded that the remaining petroleum contamination was from off-site sources. Groundwater monitoring was discontinued and long-term monitoring was not required at the Site.

In 2013, Ecology determined the cleanup was complete. Ecology issued a satisfaction letter to show the requirements in the Agreed Order were met and no further groundwater monitoring was required. In 2014, the Site was removed from the Hazardous Sites List.

The 2006 Environmental Covenant remains in force on the property. Among the covenant's restrictions, groundwater cannot be taken from the site for drinking, agriculture, commercial, or industrial use. The structures on the Site may not be altered or modified in a way that might result in release or exposure of contaminants to the environment, or create a new exposure pathway without approval of Ecology.