AN INVESTIGATION OF TRACE METAL CONCENTRATIONS IN SEDIMENT AND SURFACE WATER OF THE WOOLSEY WILDFIRE AREA, CALIFORNIA

Population pressures and climate change have pushed Southern California into a scenario in which wildfires affect people year-round, and these conflagrations leave behind toxic materials from burned structures. We investigated trace solids detectable in water and sediment in the area of the Woolsey fire, which in August 2018 destroyed 1,600 structures in Los Angeles and Ventura Counties. Bedrock geology of the region is predominantly siltstone and sandstone, with interbedded volcanics. We collected sediment and stream water samples from burned and non-burned areas, near and away from structures. The collection took place ten months post-incident. Samples were filtered, acidified and diluted, then analyzed for trace metals and dissolves solids using an ICPMS, applying the Agilent Environmental Calibration Standard.

Previous environmental inventories of trace metals in burned areas (Abraham et al., 2017, Burton et al., 2016) found elevated concentrations of Cu, Pb, Ni and Zn in ash from burned residences rather than wildland areas. Our preliminary data show elevated concentrations of Mn, Co, Zn, Cr, Ni and Pb in the burned areas compared to non-burned ten months post-incident. Although these metals are naturally abundant, it is possible that elevated concentrations were introduced by burned materials such as wiring, fencing and household items. Our sediment samples from stream beds produced at or below detection level amounts of elements compared to those from open, dry areas, suggesting that the unusual amount of precipitation in winter 2018-19 had a diluting effect.

The Woolsey fire took place in a relatively wild region close to a major metropolitan area, and affected multiple counties and stakeholders. Understanding the mobilization of trace metals and other dissolved solids through the landscape will have implications for environmental policy and urban planning.