Treatment of arsenic-contaminated soils. I: Soil characterization

Industrial sites frequently have arsenic-contaminated soils as a result of repeated applications of arsenic herbicides. Four such sites were investiga ted to determine the suitability of cement-based solidification/ stabilizat ion (S/S) for in situ soil treatment. Arsenic concentrations ranged up to a bout 2,000 ppm in the soil, although leachability was relatively low. No to xicity characteristic leaching procedure leachates showed As concentrations as high as 5 mg/L. The low leachability appears to be due, at least in par t, to iron present in the soil. Although soils with higher As concentration s generally showed greater leachability, a somewhat stronger relationship e xisted between the percentage of As in the soil that was leached and the ir on concentration in the soil. Another factor working in favor of the succes s of S/S in the present cases is the sandy character of the soils with litt le clay or organic content. Thus, the quartz sand will serve as an aggregat e and should not offer any interferences to cement hydration. A third favor able circumstance is afforded by the oxidizing character of the soils. The weathered arsenic present in the soils should be in the form of As(V), and arsenate salts present a wider range of possibilities for precipitation of insoluble arsenic species than arsenite salts. A significant variable with the potential to affect S/S is the soil moisture content, which varied grea tly among the four sites due to differing water table depth.