FINGERPRINTING ARSENIC CONTAMINATION IN THE SEDIMENTS OF THE HYLEBOS WATERWAY, COMMENCEMENT BAY SUPERFUND SITE, TACOMA, WASHINGTON

Two of the potential sources of arsenic in Hylebos waterway sediments are an arsenic-rich copper smelter slag and sodium arsenite (NaAsO2), an arsenic pesticide. The slag's high Pb, Cu, and Zn concentrations (> 1000 mg/kg) and distinct Pb, Cu, Zn, and As concentration ratios, in c omparison to those of sodium arsenite-contaminated sediments, are used to distinguish which of these two potential sources is most likely th e predominant source of arsenic in Hylebos sediments. Correlation anal yses indicate that among the 42 Hylebos sediment samples collected in this study and 241 sediment samples collected by the Hylebos Cleanup C ommittee, Pb, Zn, and Cu log concentrations are highly correlated with As log concentrations (R values range from 0.69 to 0.79 with signific ance levels below 0.00005), These high correlations are consistent wit h slag not sodium arsenite contamination. To illustrate this point, se diment contamination by slag and sodium arsenite was numerically simul ated to produce Pb, Cu, and Zn versus As contaminant titration curves. The results show that sediment data plot along the simulated slag con tamination curves, not the sodium arsenite contamination curves, sugge sting that slag is the predominant source of As in contaminated sedime nts. Two multivariate statistical analyses, a cluster analysis and dis criminant analysis, strongly support these conclusions.