Metals in waste foundry sands and an evaluation of their leaching and transport to groundwater

Authors: ALVES, BARBARA - University Of Santa Catarina; Dungan, Robert - Rob; CARNIN, RAQUEL - Tupy Sa Rua Alban Schmidt; GALVEZ, ROSA - Laval University; DE CARVALHO PINTO, CATIA - University Of Santa Catarina

Submitted to: Water, Air, and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2014
Publication Date: 5/1/2014
Citation: Alves, B.S.Q., Dungan, R.S., Carnin, R.L.P., Galvez, R., de Carvalho Pinto, C.R.S. 2014. Metals in waste foundry sands and an evaluation of their leaching and transport to groundwater. Water, Air, & Soil Pollution. 225:1963.

Interpretive Summary: Metalcasting foundries discard vast amounts of molding and core sand, with most going to private and municipal landfills. Because the majority of waste foundry sands (WFSs) are not considered hazardous, there is ongoing interest in beneficially using them in agricultural and geotechnical applications. Diverting WFSs from landfills makes practical economic and environmental sense, since foundries can save on disposal costs, while end users decreased demand for virgin aggregate alleviates the environmental burdens associated with mining activities. Despite this fact, state regulatory agencies are generally reluctant to permit their beneficial use due to concerns over metal contamination. In this study we quantified total metals in 16 waste sands from ferrous foundries and assessed the ability of the metals to leach to groundwaters when WFSs were directly applied to land over a large area. The land application scenario was considered since unconsolidated applications represent the greatest potential risk to environmental and public health. Using a groundwater leaching model, it was determined that under a wet climate regime that some WFS metals could be transported to groundwater, causing concentrations to exceed drinking water standards. While the sands tested in this study were not hazardous, land application of WFSs in wet climates could potentially exacerbate the leaching of metals to groundwater; however, metal leaching in drier climates was greatly diminished. This modeling exercise provided valuable information with respect to metal leaching and transport, but a detailed onsite analysis should be considered before beneficially using unconsolidated WFSs in any land application scenario.

Technical Abstract: While most waste molding foundry sands (WFSs) are not hazardous in nature, regulatory agencies are often reluctant to permit their beneficial use in agricultural and geotechnical applications due to concerns over metal leaching. The objective of this study was to quantify total and Toxicity Characteristic Leaching Procedure (TCLP) metals in 16 waste sands from Brazilian ferrous foundries and assess their potential to leach metals to groundwater using a probabilistic model developed by the U.S. EPA. Total and TCLP metal concentrations in the non-hazardous sands fell within ranges as reported in the literature, although some of the leachate concentrations were found to exceed drinking water and groundwater maximum contaminant levels MCLs. Leachate values above the MCLs were then used in the model to estimate groundwater concentrations at hypothetical wells up to 400 m downgradient from the land application unit. A conservative scenario of one hectare of land applied WFS and high annual rainfall totals (> 1219 mm/year) suggested that groundwater concentrations of Ba, Hg, Mn, Ni, and Pb could potentially exceed health-based MCLs at most wells. Compared to moderate rainfall totals (813–1016 mm/year), the model demonstrated that wet climates can exacerbate the transport of metals from unconsolidated applications of WFS; however, the use of TCLP results as model input values is not considered appropriate for most byproduct beneficial use scenarios since it simulates low pH conditions within a municipal landfill.