Characterization and treatment of the soil of an industrial site contaminated with chromium(VI)

The surface and soil of an industrial site, which was used for 80 years to manufacture porcelain enamel signs for California highways, was characterized to determine any contamination due to toxic metals. Although surface concrete samples showed hazardous concentrations of lead, cadmium, nickel and zinc, the soil samples were found to be free of any contamination for these metals. However, soil samples collected at certain depths from certain locations were found to contain hazardous concentrations of both total chromium and hexavalent chromium. These chromium concentrations were found to vary with depth, maximizing at 20 ft and decreasing below that. Total volume of the contaminated soil was estimated and a soil treatment process which involves reduction of Cr(VI) to Cr(III) using meta bisulfate as the treatment reagent was developed in the laboratory, and then tried on contaminated soil samples. Greater than 90% reduction of Cr(VI) to Cr(III) was observed. The treatment process developed was then used to design a remedial action plan for on-site treatment of the contaminated soil.