Metals Leaching from Highway Test Sections Constructed with Industrial Byproducts

Metals leaching from industrial byproducts used in highway construction was assessed in the field and laboratory. Four byproducts were evaluated: foundry sand and foundry slag from a gray-iron foundry and bottom ash and fly ash from a coal-fired power plant. Field leaching behavior was evaluated by analyzing samples from lysimeters installed beneath highway test sections constructed with the byproducts. Batch water leach tests (WLTs) and column leach tests (CLTs) were conducted in the laboratory. All leachates were analyzed for concentrations of cadmium (Cd), chromium (Cr), selenium (Se), and silver (Ag). Concentrations from the WLTs and CLTs were compared with concentrations measured in the leachate collected in the field and with groundwater quality standards stipulated in the Wisconsin Administrative Code. Leachate collected in the lysimeters commonly had Cd, Se, and Ag concentrations exceeding Wisconsin groundwater quality standards. However, application of dilution factors to account for the reduction in concentration expected between the bottom of the pavement structure and the groundwater table showed that concentrations exceeding groundwater quality standards would not occur if the byproducts layer is at least 5 m above the groundwater table. For a separation distance of 1 m, only Cd would modestly (30%) exceed the groundwater quality standard directly beneath the centerline of the pavement. Peak concentrations from the lysimeters were 4-160 times larger than the WLT concentrations. Dilution caused by the large liquid-solid ratio used in the WLTs is largely responsible for the disparity between the lysimeter and WLT concentrations. Peak concentrations from the CLTs typically were within a factor of 10 of peak concentrations from the CLTs, although peak CLT concentrations were as much as 45 times higher and 131 times lower than the peak field concentrations. The elution patterns in the field and the CLTs generally were similar, although the magnitude of the concentrations differed. An exception is the fly-ash-stabilized soil, for which both concentrations and elution patterns from the field and the CLTs were similar.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 72p

Subject/Index Terms

Filing Info

  • Accession Number: 01531749
  • Record Type: Publication
  • Files: TRIS, ATRI, USDOT
  • Created Date: Jul 18 2014 1:03PM