Removal and thermal desorption of coal tar contaminated soils from former manufactured gas plant (MGP) sites has proven to be a cost and environmentally effective treatment technology. Additional cost and environmental benefits can be accrued by using the thermally desorbed soil to backfill the excavation created by the removal action rather than disposing of the soil in a landfill and purchasing backfill. For example, Klimek et al., 1998, reported savings of approximately $205,000 in backfill costs for a multi-site thermal desorption project. Heating of the soils in the primary unit to over 650°C (1200℉) during the thermal desorption treatment process could, however, affect both their physico-chemical and geotechnical engineering properties, which could limit their use as an engineered fill and thus future construction on the site. This paper presents the results of an extensive physico-chemical and geotechnical engineering characterization program carried out on thermally desorbed soils from five former MGP sites in Iowa. Results of geotechnical index and engineering classification tests, including specific gravity, particle size distribution, and Atterberg Limits, compaction tests, permeability tests, shear strength tests, collapse potential tests and physico-chemical characterization tests are presented. In addition, implications of the test results on the reuse of thermally desorbed soils as engineered fills are discussed.
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