Controlling Factors Affecting NAPL Residuals in Aquifers Containing Low-Permeability Lens Bodies

The presence of residual non-aqueous phase liquid (NAPL) in low-permeability lens aquifers of ten results in a “tailing” effect, ecological deterioration and poor sustainability, which is a primary factor contributing to remediation failures at NAPL-contaminated sites. This issue is largely due to the poorly understood mechanisms by which NAPL residuals interact with low-permeability lens aquifers. To elucidate these mechanisms, this study conducted a series of column experiments, varying the permeability contrast ( Kmn ), lens sizes ( ϕ ), and hydraulic gradients ( I ). Complementary techniques such as mercury intrusion porosimetry and particle size analysis were employed to characterize the aquifer and lens materials. The data obtained include the residual NAPL saturation ( Sr ), groundwater flow velocity ( V ), pore size distribution, particle size, and gradation under different experimental conditions. Sensitivity analyses using range and variance analyses identified the following order of effect on NAPL residuals in low-permeability lens aquifers: Kmn > ϕ > I . Correlation analyses further suggest that the governing mechanisms are predominantly mediated by changes in the average particle size, macroporosity (pores > 60 μm), mesoporosity (pores = 30~60 μm), and microporosity (pores = 2~30 μm), as well as abrupt changes in pore size at the interface between the lens and the aquifer, in addition to V . This study can provide a theoretical basis for green, low-carbon, and sustainable development, such as pollution remediation and ecological environment security.