Of concern is potentially migrating dioxins from pentachlorophenol (PCP), a wood preservative that was used at the mill site before being banned in the mid-1980s.
In response, the California Department of Toxic Substances Control (DTSC) has hired an engineering firm to do a new round of testing at the site.
The agency has taken various actions over the years to try to prevent contamination reaching the water table. At one point, soil was removed and a concrete cap was placed at the mill鈥檚 main operations area to prevent rain from seeping into the ground and becoming contaminated.
The old mill site is about a mile upstream from Humboldt Bay Municipal Water District intake wells. The district鈥檚 service area includes Eureka, Arcata and the entire Humboldt Bay area.
When the county held hearings on cannabis manufacturing permitting at the site鈥檚 former lumber storage area, district officials voiced strong opposition, saying the dioxin issue has to be addressed first.
The new round of sampling will include groundwater and a ditched tributary of Hall Creek, which flows into the Mad River.
The Humboldt Baykeeper water quality advocacy group has also been pressuring the state for action. Jen Kalt, Baykeeper鈥檚 executive director, described the new round of testing as a turning point. She said the state鈥檚 response is a 鈥渞eally huge鈥� advance in the contamination saga and testing will determine the scale of a clean-up.
鈥淲e expect there will be a public process later on down the road, once they develop the next clean-up plans,鈥� she continued.
The DTSC declared the site to be remediated in 2003. But in 2018, conditions dramatically changed. The agency found that dioxins had seeped into groundwater, whose levels had risen by 15 feet.
鈥淭hat could be pushing the plume of dioxin contamination toward the Mad River,鈥� said Kalt.
Results of the sampling are expected this spring. Timing of a clean-up plan is uncertain but Kalt said Humboldt Baykeeper will continue to press for action.
鈥淚t鈥檚 been a fairly long time that this site has been threatening the drinking water supply in the Mad River and there鈥檚 just no excuse for any additional delays,鈥� she continued.