PARTITIONING OF METALS BETWEEN SOIL AND DISSOLVED PHASES, HENRYVILLE BED, NEW ALBANY SHALE

Black shales contain significant concentrations of toxic metals that during natural weathering processes can be released into the environment. Metal-rich shales, ephemeral mineral phases and overlying soils from outcrop were obtained from two exposures of the Henryville bed, Clegg Creek Member of the Devonian New Albany Shale in south-central Indiana. The Henryville bed is unusually metaliferous and soil development on the Henryville bed has shown that Zn is enriched in the soils, but Cu, Cr, and Pb are not. Total sulfur concentrations range from 1.5 to 3.5 wt% in the shales while the soils contain less than 0.1 wt. % total S. The sulfur and trace metals are incorporated into a variety of sulfate ephemeral mineral phases and water from seeps along bedding planes and fractures that can be observed on the outcrop face in spring and early summer. The subsequent dissolution of these, later in the summer and fall, introduces these metals into local water supplies as non-point source contaminants. Many of the exposures studied have been weathering for many decades and are approaching equilibrium with the environment, however, calculations suggest that 780 mg/L Cu, Cr, and Pb can be introduced from the weathering of 1 m2 of fresh outcrop exposures of the Henryville bed. This concentration of metals suggests that remediation might be necessary around new construction to trap metals during the early stages of soil development.