Detailed characterization of a LNAPL-contaminated soil using X-ray microtomography and gas chromatography

Abstract

The effectiveness of remediation strategies for soils contaminated by light non-aqueous hydrocarbons (LNAPL) depends on a detailed understanding of their geological and hydrodynamic properties, as well as their spatial distribution. In this work, 3D X-ray microtomography (μ-CT) and gas chromatography (GC) are combined to characterize porosity, permeability, LNAPL saturation (S_n), and van Genuchten parameters (α and N) at a LNAPL-contaminated site. Moreover, a novel μ-CT-based method is presented to quantify LNAPL ganglia connectivity—an essential factor in understanding their spatial distribution and migration dynamics. The data obtained using this approach were employed to calculate LNAPL transmissivity. This technique, referred to as the μ-CT/GC method, was compared with LNAPL transmissivity values derived from the API-LRDM 2 hydrodynamic model (based on literature data) and from baildown test results, revealing significant discrepancies. However, the transmissivity obtained through μ-CT/GC method was more closely aligned with values measured during in-situ tests (baildown test). These findings underline the limitations of conventional transmissivity prediction approaches and pave the way for developing more effective remediation strategies. Moreover, the results highlight the significant impact of the site's strong hydrodynamic heterogeneity on pollutant retention and mobility.