Hydraulic and Mineralogical Characterization of Organoclay Before and After Reaction with Non-Aqueous Phase Liquid (NAPL)

Sediment capping—a method used to stabilize and remediate contaminated subaqueous sediment in lakes or river shores by covering the contaminant with multiple layered materials— is a more effective, economic, and durable in situ treatment compared to ex situ methods such as dredging. The caps are typically composed of porous geomaterials such as gravels, sands, Reactive Core Mat (RCM), including reactive soils (e.g., organoclay) and geosynthetics (e.g., geotextiles). The designed caps are regarded as water-permeable so as not to disturb the sediment; however, the caps become unsaturated state because of trapped gas generated from the decomposition of organic matter. Most of the past studies have emphasized only permeability when it is saturated; however, the contaminant transport aspect of the RCM and the mechanical integrity of this cover system under unsaturated condition has not been studied. In this study, to manage coal-tar creosote, a non-aqueous-phase liquid (NAPL) consisting primarily of polynuclear aromatic hydrocarbons (PAHs), the unsaturated hydraulic properties of organoclay was investigated. The water retention properties of organoclay before and after contact with NAPL by using unsaturated soil testing apparatus were experimentally evaluated. The data was modeled and analyzed by using van Genuchten (vG) and Brook-Corey (BC) fitting models. Furthermore, the mineralogical properties measured by X-Ray Diffraction (XRD) were analyzed with water retention properties. The higher the air entry (ΨA) the lower the hydraulic conductivity and permeability of the sample. The hydraulic conductivity drops dramatically as air enters the samples with the unleaded gasoline organoclay sample exhibiting the lowest permeability. The unsaturated hydraulic conductivity obtained from the vG and BC models are far apart and the reason is the pore interaction parameters not being suitable for organoclay. The trend of fitting parameters and smectite content and therefore degree of reaction, demonstrate unsaturated properties changing from coarse to finer WRC behavior. The results can be used in later studies to address the effects of bulging on the performance of RCM and the need to protect against this phenomenon in the sediment capping system. Under the Supervision of Professor Jongwan Eu