Leaching Behavior of Green Sands from Gray-Iron Foundries Used for Reactive Barrier Applications

Water leach tests (WLTs) and total elemental analyses were performed on 12 green sands, zero-valent iron (ZVI) and two aquifer materials to determine their leaching characteristics for reuse applications in Wisconsin (USA). Results of the WLTs and TEAs show that none of the materials, including the ZVI and the aquifer materials, meet criteria in Wisconsin for placing industrial byproducts below the groundwater table (GWT). Concentrations of As, Cd, Mn, Pb, Sb, and F from WLTs on the green sands exceeded Wisconsin's maximum permissible concentrations (MPCs). However, the concentrations exceeded the MPCs by a small amount and similar concentrations were obtained from the ZVI, a material that is commonly placed below the GWT for groundwater remediation. Al concentrations exceeded the MPC for three green sands, and Fe concentrations exceeded the MPC for 10 of the green sands and the ZVI. TEAs showed concentrations exceeding MPCs for As and Be for all materials (including the ZVI and aquifer materials) except one green sand, Cr concentrations appreciably above the MPC for two of the green sands and ZVI, and concentrations slightly above the MPC for two polycyclic aromatic hydrocarbons for several green sands. Column tests showed that Cr, Pb, and Fe leach from green sands under flow-through conditions at concentrations comparable to ZVI. Overall review of the data indicates that using green sand as a reactive barrier medium should pose no greater risk than ZVI, provided the green sand does not leach Al at elevated levels and is not contaminated with other byproducts that may contain organic contaminants.