This paper describes treatability studies, design, and remediation for the stabilization of contaminated soil at two hazardous waste sites in Washington State. In both sites, the soil was contaminated with metals. The study of stabilization/solidification included bench-scale treatability studies, preparation of plans and specifications for the remediation, and monitoring stabilization remediation. This paper presents the results of the above work with focus on practical, regulatory, and performance aspects of the stabilization. The effect of stabilization agents on the leaching of metals and the relation of the leaching results to applicable regulations are discussed.
Site A was a large manufacturing facility covering about 300 000 m2 (80 acres). Soil contamination included lead, chromium, and arsenic. The soil to be stabilized contained total concentrations of up to 19 000 mg/kg lead, 1600 mg/kg chromium, and 180 mg/kg arsenic; however, bulk soil samples obtained for this study contained unexpectedly lower concentrations of these metals. Extraction procedure toxicity (EP Tox) concentrations were below hazardous waste designation levels. Stabilization will be used on soil with total concentrations greater than 8000 mg/kg lead, 600 mg/kg chromium, and 100 mg/kg arsenic. Site B covered about 10 000 m2 (2 acres) and was used to repair and store machinery. As a result, the soil was contaminated with lead. The highest lead concentration was 17 000 mg/kg, with the corresponding EP Tox concentration of 300 mg/L. The selected remedial action was to remove the soil with lead over 500 mg/kg and place it in a solid waste landfill. In order for the soil to be classified as a solid waste, the leachable lead had to be less than 5 mg/L based on the EP Tox test.
At Site A, the stabilized soil had low compressive strengths, possibly due to petroleum contamination and natural organics in the soil. Leaching tests using a monolith showed that the leachate from the soil/cement specimen unexpectedly contained higher concentrations of chromium than the leachate from untreated soil. The relative amount of lead leached from soil/cement and untreated soil varied. The results for arsenic were inconclusive because of the low arsenic concentrations in the tested soils and leachates. At Site B, proprietary stabilization agents were successfully used to reduce leachability below hazardous waste levels as measured by EP Tox.