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 investigated to determine the suitability of cement-based solidification/ stabilization (S/S) for in situ soil treatment. Arsenic concentrations ranged up to about 2,000 ppm in the soil, although leachability was relatively low. No toxicity characteristic leaching procedure leachates showed As concentrations as high as 5 mg/L. The low leachability appears to be due, at least in part, to iron present in the soil. Although soils with higher As concentrations generally showed greater leachability, a somewhat stronger relationship existed between the percentage of As in the soil that was leached and the iron concentration in the soil. Another factor working in favor of the success of S/S in the present cases is the sandy character of the soils with little clay or organic content. Thus, the quartz sand will serve as an aggregate and should not offer any interferences to cement hydration. A third favorable 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 greatly among the four sites due to differing water table depth.