TRACE METAL CONTAMINATION IN A SAND AND GRAVEL AQUIFER (CASCADE, MICHIGAN)

Trace metal contamination of groundwater aquifers is a widespread problem that can have adverse effects on human health. To better understand trace metal bioavailability and mobility in such systems, it is important to quantify trace metal partitioning among various aqueous and solid phases. In this study, sediment was obtained while digging four monitoring wells, at depth intervals of 10 feet, from an aquifer in Cascade Township, Michigan. Ground water samples obtained from locations near the sediment samples indicate high levels of Ni (up to 51 ppb). Sediment samples were analyzed for grain size by sieving and for the surface area of fine (silt, clay, and very fine sands), medium (fine and medium grained sands) and coarse (coarse grained sands) samples from each interval. An operationally-defined sequential extraction scheme (modified from Tessier et al. 1979 Anal Chem) was used to assess the partitioning of Ni, Cu, Fe, Mn, Cr, Co, Zn, Ba, Pb, and Cd among three fractions: associated with carbonates and exchangeables, reducibles (mostly Fe and Mn oxides), and oxidizables (mostly organic material and sulfides). Ni concentrations in all sediment samples are under 15 μg/g dry sediment, and Ni is mostly extracted in the reducible step. Cu concentrations are higher than expected with a maximum level >3000 μg/g in one well, and >1000 μg/g in the second well. Cu in samples with higher concentrations is mostly extracted from the carbonates and exchangeables fraction, while the Cu from the lower concentration samples is extracted mostly from the reducibles fraction in the results currently available. Concentrations of Zinc were also high, up to 1800 μg/g, with significantly higher concentrations in the fine grained sediment. Zn was in nearly the same quantity from the carbonates/exchangeables and reducibles fractions of these sediments. The results suggest that Cu and Zn has been a significant contaminant in this aquifer, as well as Ni. Adsorption experiments are planned to assess the competitive sorption of Cu, Zn and Ni on various fractions of these sediments, both in the presence and absence of EDTA, which is another known co-contaminant in the aquifer.