Leaching Of Trace Elements From Roadway Materials Stabilized With Fly Ash

This study evaluated the leaching of trace elements from roadway materials physically stabilized with fly ash from coal combustion. Five field sites with stabilized materials and three sites with control materials used as base course or subgrade were constructed with pan lysimeters to collect leachate discharging from the bottom of the roadway layers. Pore volumes of flow from the layers was calculated from the volume of leachate collected, pH and Eh of the leachate was measured, and samples were collected for chemical analysis. Laboratory column leach tests (CLTs) and water leach tests (WLTs) were also conducted on specimens of some fly ash and base course/subgrade materials collected in the field. The type, concentration, and pattern of elemental leaching from field and laboratory specimens were determined, and concentrations were compared to those from control materials and relevant groundwater maximum contaminant levels (MCLs). The laboratory tests were compared for their utility in predicting field leaching behavior. The elements As, Cd, Cr, Mo, Ni, Pb, Se, and V exceeded MCLs and were elevated relative to control concentrations, with B, Mo, and V concentrations the most elevated from the controls, and exceeding the MCL for the longest time. Both CLTs and WLTs were similar in their utility for estimating peak field concentrations, especially when peak field concentrations were >500 μg/L.

The full thesis may be found in the following file:

Jonathan O’Donnell Master Thesis 2009