Legacy Lead Isotopic Signature in Riverine Sediments in Everett, Washington

Highly industrialized areas near sensitive estuarine environments are a perennial focal point of environmental studies concerning releases of hazardous materials, including trace heavy metals. This study focuses on determining the heavy metal distribution legacy at a demolished ASARCO smelter site in north Everett, WA near the mouth of the Snohomish River. This site has been the target of recent remedial actions under the Model Toxics Control Act (MTCA) Cleanup Regulation developed by the Washington Department of Ecology (WA DOE) due to widespread arsenic and lead contamination in the early 1900s. Previous research has shown evidence of a correlation between heavy metal concentrations in benthic sediment of Possession Sound and proximity to industrial sites, while suggesting heavy metal concentrations varied with changes in Snohomish River discharge. Overall, lead concentrations were shown to be higher at sites closer to the mouth of the river. Therefore I hypothesize that the suspended solids in runoff from the ASARCO site is traceable down river from the site, perhaps into Possession Sound, and deposits correlate with river discharge. Future research will seek to establish the extent of dispersion of anthropogenic lead derived from the ASARCO site through lead isotope fingerprinting (Pb-204, Pb-206, Pb-207, Pb-208). Lead tracing as a geochemical indicator from one specific source will further demonstrate heavy metal distribution in a highly complex riverine system with many potential point and non-point sources of contaminants. Slag samples from WA DOE will be used to determine the isotopic signature of the site. Three one-meter benthic sediment core samples collected near the mouth of the Snohomish River, near the ASARCO site, and up river will be analyzed using a specialized MC-ICP-MS instrument at the University of Washington in January and February of 2014. Analyzing multiple layers of a core sample will demonstrate a temporal trend based contaminated sediment thickness at the sampling sites. Results will be analyzed in conjunction with Ecology Site Hazard Assessment data. This research will emphasize both the spatial and temporal aspects by demonstrating the relationship between coherent structures in a tidally influenced fluvial system and lead deposition