Mechanistic insights into contaminant transport dynamics in the saturated porous system in the presence of low permeability region using numerical simulations and temporal moment analysis.

The influence of low permeability porous media (LPPM) on contaminant transport dynamics in saturated porous systems was investigated using numerical simulations and temporal moments of contaminant concentrations. Two-dimensional flow and contaminant transport simulations were conducted, considering various parameters such as longitudinal dispersivity (ranging from 15 to 60 m), the ratio of transverse to longitudinal dispersivity (ranging from 0.05 to 0.2), retardation factor (ranging from 1 to 4), and hydraulic gradient (ranging from 0.005 to 0.02) for both homogeneous and heterogeneous porous systems. The findings revealed significant differences in the transport behavior of conservative and highly reactive contaminants between the porous systems without and with the LPPM region. The center of mass of contaminant plume and peak concentration zone were observed inside the LPPM region for the heterogeneous porous system, especially during the source off-loading period. Furthermore, asymmetric distributions of the zeroth temporal moment (ZTM), mean residence time (MRT), and variance of the breakthrough curve (BTC) were observed along the longitudinal distance within the LPPM region for heterogeneous porous system, highlighting the impact of heterogeneity on contaminant plume evolution dynamics. The moment analysis results provided insights into the influence of LPPM region on time-averaged contaminant transport dynamics in adjacent porous systems. These findings can help risk managers understand the complex fate and transport dynamics in heterogeneous porous systems. Future studies could explore the modelling of multispecies contaminants in heterogeneous saturated porous systems subjected to fluctuating water table.