Bothell Riverside HVOC

The Bothell Riverside HVOC Site is generally located at NE 180th Street & Woodinville Drive (SR 522) in Bothell, WA. The Site formerly housed a strip mall, restaurants, and historic gas stations along the Sammamish River. 

One property, two cleanup sites

In 2008, the City acquired the larger triangle-shaped property (see Figure 1) as part of the Highway 522-Woodinville Drive realignment and downtown revitalization effort. This property was called the Riverside Cleanup Site. The City entered into an Agreed Order (AO) with Ecology to investigate contamination on the site and found that there were two separate areas of contamination.

The property was then divided into two cleanup sites:  the Riverside TPH Site and the Riverside HVOC Site. 

Riverside TPH (Total Petroleum Hydrocarbons) site
The Riverside TPH site was cleaned up by Ecology and the City in 2019. The TPH contaminated soil was excavated and disposed of offsite at a permitted facility. 

Riverside HVOC (Halogenated Volatile Organic Compounds) site 
In 2013, Ecology and the City agreed to amend the 2009 AO to allow the City to conduct an interim cleanup action to prevent the contaminants from discharging into the Sammamish River. The City installed six extraction wells to collect HVOC-contaminated groundwater and discharge it into the sanitary sewer system.

Contamination
Operations at a former machine maintenance shop are believed to have released HVOCs into the soil and groundwater within the HVOC area at levels higher than allowed under the Model Toxics Control Act (MTCA). 

Proposed cleanup
Samples of contamination collected during preparations for the cleanup of the Site showed a decrease in concentrations of HVOCs. The proposed cleanup method is being modified using direct-push injections, instead of continuous injection, extraction, and recirculation treatment to address the remaining contamination in soil and groundwater.

• Direct-Push Injections: Throughout the Site, a mixture of soluble organic carbon and Dehalococcoides (a type of bacteria that breaks down HVOC contamination) will be injected into the ground. This mixture will contain different amounts of zero-valent iron (ZVI) depending on contamination levels throughout the Site. This type of treatment breaks down contamination into a nontoxic form.  
• In Situ Groundwater Treatment Barrier: An underground treatment barrier will be installed along the southeastern part of the Site. This barrier will contain soluble organic carbon, Dehalococcoides bacteria, zero-valent iron (ZVI), and colloidal activated carbon to treat contaminated groundwater that would otherwise flow into the river. As the contamination passes through the barrier, it will be captured and broken down before leaving the Site.
• Monitoring: A series of new and existing monitoring wells at the Site will be used to see how well the injections are reducing contaminant concentrations in the soil and groundwater. Monitoring will be ongoing at the Site. 

State Environmental Policy Act (SEPA) Checklist
The City is the lead agency for the Site’s SEPA Determination and has completed the SEPA checklist. The SEPA process  identifies and analyzes environmental impacts associated with this cleanup and other government decisions.

The Model Toxics Control Act (MTCA) is Washington’s environmental cleanup law. It provides requirements for contaminated site cleanup and sets standards that protect human health and the environment. Ecology is responsible for administering MTCA, including oversight of cleanups. The MTCA cleanup process is completed in steps over a variable timeline.

Next steps: Ecology will consider all comments received and may amend the documents based on your comments. After that, the documents will be finalized, and the final stages of cleanup will begin (see MTCA diagram). If significant changes to the plan are needed, a new draft of the plan and another public comment period may occur.