CONTAMINANT METAL SPECIATION AND PHASE ANALYSIS: RIVERSIDE PARK, MILWAUKEE, WISCONSIN

For over a century, the North Avenue Dam regulated the flow of the Milwaukee River in Milwaukee, WI. The slow-moving waters of the dam's 2.5-mile impoundment facilitated the sedimentation of a variety of contaminants from industrial, urban, and agricultural sources. A suite of trace metals accumulated on the bottom of the impoundment. In 1990 the gates were opened, allowing the river to resume a narrower course before the dam was demolished in 1997. While this drawdown has lead to a more natural and healthier river system, it has exposed the erstwhile bed of the impoundment as a now-contaminated shore, much of which is contained within Riverside Park, Milwaukee, WI. Previous workers, in cooperation with the Urban Ecology Center at Riverside Park, performed soil analyses and reported the presence and concentrations of heavy metals in the soil. Knowledge of the abundance of metals is certainly important, however it is even more essential that we understand how these metals are contained in the soil. Studying how the metals are partitioned within and cycle through the soil will lead to a better understanding of the relative availability of the metals. A series of 12” deep punch-cores were collected at each of 5 locations along the banks of the river, including: i) saturated, ii) seasonally saturated, iii & iv) below historical waterline but above the modern high water mark, and v) above the historical high water mark. The 5 composite samples taken were divided into shallow and deep halves, totaling 10 samples. This sampling regime will help us understand trace metal speciation with varying soil saturation, location in the soil profile, and distance from the current river. Our primary analytical focus is the execution of Selective Sequential Extractions (SSEs) to determine the phase and speciation of trace metals at Riverside Park. Sequential application of selective reagents will extract metals in 5 fractions, exchangeable, organic matter, carbonates, redox sensitive elements (Fe & Mn oxyhydroxides), and a residual portion. These SSEs will allow us to better assess the bioavailability of contaminant metals. Complementary SEM-EDS analyses are employed to aid in this assessment. Metal speciation is crucial for understanding the relative danger presented by metals in these soils as well as evaluating future remediation strategies.