Development of a laboratory procedure to evaluate the consolidation potential of soft contaminated sediments

Consolidation settlement of non-aqueous phase liquid (NAPL) contaminated sediments may trigger NAPL mitigation. The consolidation potential and resulting NAPL mobilization of the sediments should be evaluated in the laboratory; however, due to the highly compressible and weak nature of riverbed sediments, it is usually not possible to conduct conventional consolidation tests on sediment specimens. In this study, a triaxial setup was modified to work effectively under low stresses. Kaolinite was used to represent the soil solid phase and Soltrol 130 (a type of mineral oil) was used to represent the NAPL. Both oil-wetted and water-wetted regimes were analyzed. Hexane Extraction and moisture content tests results confirmed the final fluid amounts in the specimen obtained by measuring the effluent volume during consolidation. The results of the tests show that approximately 0.1 g of NAPL per 1 g of soil solids is unlikely to be mobilized by consolidation. The developed procedure could also be employed to define the mobile and immobile fractions of NAPL and the expected compression of contaminated sediments. The volume of NAPL in excess of the retained residual can be used to design NAPL collection systems or to size layers of NAPL sorbent materials such as organo-clays.