WA DNR Webster Nursery

In 2018, pesticide (heptachlor epoxide) contaminated soil at the Webster Forest Nursery was excavated from an area on the southeast corner of the site near where a former leaking underground storage tank (UST) was located.  Since then, groundwater has been monitored to evaluate conditions at the site.

Monitoring wells located along the property line indicate that contamination has not migrated off the property and the contaminated area is centered around the location where the former UST was located.

Ecology received results of groundwater sampling events completed after the cleanup work in August 2018. Results indicate heptachlor epoxide is present above cleanup levels in groundwater located near the former UST.  Additional groundwater sampling is needed to determine if the excavation of contaminated soil will significantly reduce the concentration of pesticides in groundwater over time.  

Ecology will continue to monitor groundwater at the site to evaluate the effectiveness of removing the contaminated soil.

RELEVANT DOCUMENTS

• August 2018 Groundwater Monitoring Report 
• November 2018 Groundwater Monitoring Report
• February 2019 Groundwater Monitoring Report

Webster Nursery is a tree nursery run by the Washington State Department of Natural Resources (WA DNR). The nursery is 300 acres and produces 10-15 million seedlings per year, which they sell to fund the nursery operation. Herbicides and fungicides are applied to soils and plants in early spring, summer, and early fall to control weeds and protect seedling from disease. 

On the southeast corner of the property, soil and groundwater were contaminated by a historical release of organochlorine pesticides from a leaking UST, which was located next to the warehouse building.    

1978: The pesticide storage warehouse was built with a system of floor drains plumbed to a concrete underground storage tank (UST). During normal operations, pesticide was rinsed and washed into the tank.

1982: The concrete UST was replaced with a steel UST.

1996: The steel UST was full, found to be leaking, and removed along with 70 cubic yards of contaminated soil (about 7 dump trucks full).  Not all the contaminated soil could be removed because groundwater kept seeping in and filling the hole. Excavating more soil threatened the structural stability of the warehouse. Contaminated soil and water were taken offsite for proper recycling and disposal. Soil around the drains and pipes were tested and did not have any contamination.

1998: Ecology and WA DNR entered into an agreement to investigate the extent of contamination, consider cleanup alternatives, and develop a cleanup plan.

2001: Ecology and WA DNR entered into an agreement to finalize the cleanup plan, monitor the site, and prevent water from moving through the contaminated area.

2001-2016: Yearly groundwater monitoring showed heptachlor epoxide concentration in groundwater in the vicinity of the former UST was above the state cleanup level.

2014: WA DNR tested soil and groundwater to find the extent of contamination.

2016: Ecology and WA DNR entered into an agreement to remove more contaminated soil and monitor groundwater. Due to the lack of approval of a state capital budget, the cleanup action was  delayed.

2018: WA DNR removed about 145 cubic yards of contaminated soil, backfilled with clean soil, and covered it with grass. Not all of the contaminated soil could be removed due to structural constraints.

2018-present: Groundwater was monitored quarterly to determine the effectiveness of the cleanup action.