WA DOT Rimrock Maintenance Site 1

The Washington State Department of Transportation Rimrock Maintenance Site 1 is located near the intersection of State Highway 12 and 410, west of the City of Naches. In May 1991, petroleum contamination was discovered in the soil and groundwater during the decommissioning of two underground storage tanks (USTs). Both tanks (one 5,000-gallon and one 500-gallon) had leaked. The piping had leaked as well. 

In March 1994, the site was added to Ecology’s Hazardous Sites List with a ranking of “5”.  This ranking was updated in August 1994 to a ranking of "3". Sites on the Hazardous Sites List are a priority for Ecology, and have completed a Site Hazard Assessment (SHA). A SHA provides information about the environmental risk of the site. Risk is based on the amount of contaminants, how toxic they are, and how easily they can come in contact with people and the environment. Sites are ranked relative to each other on a scale of “1” to “5”; with a rank of “5” being the lowest.

In June and July 1991, a limited amount of petroleum contaminated soil was excavated and more sampling was conducted. In 1995, the maintenance building was demolished because of work on the highway intersection. This allowed for more petroleum contaminated soil to be removed in 1995 and 1996.

About 1,200 cubic yards of soils were removed. Sampling confirmed all contaminated soil was either removed or stockpiled and treated onsite. Groundwater monitoring was started in October 1997 with four groundwater monitoring wells. After monitoring quarterly for a year, no groundwater showed contaminants above state cleanup levels.

Based upon cleanup activities, Ecology has determined the site is no longer a threat to human health and the environment. Ecology made a no further action determination in June 2014. The site has been removed from the Hazardous Sites List.