Warden City Water Supply Wells No. 4 and 5

Ecology issued the Cleanup Action Plan in May 2020, which requires Simplot to complete the following actions to clean up the pesticide ethylene dibromide (EDB) in soil and groundwater:

• Excavating as much contaminated soil as is technically possible.
• Cleaning excavated soil onsite by extracting contaminated vapors from it.
• Filing an environmental covenant on the property restricting drilling any new water wells into the contaminated groundwater.

Soil excavation, treatment, and monitoring

Cleanup contractors hired by Simplot excavated about 3,000 cubic yards of contaminated soil from March through May 2021. The soil is stockpiled and covered at the site. Treatment is scheduled to begin in summer 2022. Soil samples will be collected and tested for EDB until soil meets state standards.

Groundwater monitoring

Groundwater samples are collected twice a year to detect any EDB movement off property and track the rate of EDB reduction. With contaminated soil removed, Simplot’s consultant estimated it will take 3 to 5 years for EDB concentrations in groundwater to reduce to 0.05 micrograms per liter, the federal standard for drinking water.

In 1989, the City of Warden tested their public water wells in response to changes in Washington Department of Health monitoring guidelines and found wells 4 and 5 contained EDB at levels exceeding safe drinking water standards.

Further investigation found EDB in soil on property owned by Simplot, the party responsible for cleanup. From 1971 to 1992, Simplot stored, blended, and transported agricultural chemicals, including the pesticide EDB, at the site. Contaminated soil at the Simplot property was found to contain EDB at levels that are a potential risk for groundwater contamination and consistent with EDB levels in groundwater.

The city notified residents that the EDB levels were not likely to affect the general population, but recommended that pregnant women and children not drink the water. To temporarily fix the problem, the city stopped using the most contaminated well and blended the less contaminated water with clean water to reduce contaminants to meet drinking water standards.

In 2011, Ecology entered into an Agreed Order with Simplot, requiring them to complete a remedial investigation and feasibility study to identify all contaminated areas and propose cleanup options.

The remedial investigation and feasibility study became final after undergoing public comment July 30 through August 28, 2018. We responded to comments from one person. You may read a summary of the investigation findings and four cleanup options in the notice that was mailed to local residents.

We used public input and the information Simplot gathered to develop a cleanup proposal. The following draft documents were available for public review and comment February 3 through March 4, 2020, before becoming final:

• Cleanup Action Plan — explains our proposed cleanup plan for the site
• Agreed Order — legal agreement requiring J.R. Simplot Company (Simplot), the party responsible for funding and completing cleanup, to follow the Cleanup Action Plan to remediate ethylene dibromide (EDB) contamination in soil and groundwater
• State Environmental Policy Act (SEPA) documents — we have reviewed the cleanup actions using the SEPA checklist, and decided they won’t adversely affect people or the environment