Estimation of plume persistence based on linear source depletion and aquitard characteristics

The pattern of contaminant source depletion, referred to as source strength function, and contaminant diffusion into and out of aquitards play an important role in plume longevity in the aquifer. In this study, the trichloroethene (TCE) plume persistence with linear source depletion was simulated using the 1-D analytical solutions for concentration profiles in a finite domain aquitard and flux-average concentrations caused by back diffusion to an adjacent aquifer. Three key variables (the plume history (μ), the ratio of tortuosity to retardation factor (S), and the diffusive penetration distance (ζ)) were used to assess plume persistence, respectively. The results showed that as μ increased because of more rapid source dissolution, the back diffusion initiation time (ɛBD) and relative aquifer concentration at ɛBD (χ) decreased. As S increased because of decreased sorption and simplified flowpath in the aquitard, ɛBD decreased but χ increased. As ζ increased, χ decreased with convergence to χ = 0.51, and ɛBD increased with convergence to ɛBD = 0.014. The results from this study indicate that the longest period maintained above the maximum contaminant level (ɛMCL) (MCL = 5 μg/L) following complete source removal was showed in a range of χ = 0.52 to χ = 0.56 despite the values of each variable. These results suggest that ɛBD and time at which TCE reached the no flux boundary in the aquitard occur almost simultaneously, and the relative concentration of the aquifer might be used as an indicator to determine whether the back diffusion occurs in the finite aquitard.

Acknowledgment: This research was supported by the MSIT(Ministry of Science, ICT), Korea, under the High-Potential Individuals Global Training Program) (RS-2022-00155315) supervised by the IITP(Institute for Information & Communications Technology Planning & Evaluation.