| The release of chlorinated contaminants sequestered in low-permeability strata is emerging as a critical challenge to site management, limiting remediation performance and sustaining plume longevity. An adapted version of MT3DMS, linked to MODFLOW, is used to simulate the coupled effect of sorption and back diffusion on plume tailing using an ensemble of two-dimensional realizations of a highly heterogeneous formation and corresponding DNAPL (dense nonaqueous phase liquid) source distributions. The simulation results indicate that appropriate representation of sorption processes is important for accurate prediction of plume longevity, especially once the DNAPL has been completely dissolved. The mean of the near-source plume sustained by linear sorption-controlled back diffusion is 19 years beyond DNAPL depletion, representing 6% of total plume longevity. The plumes are even more prolonged for cases with nonlinear sorption and rate-limited sorption, which are determined to be 2.7 and 3.5 times longer than the linear sorption case. A limited effect of sorption on NAPL dissolution is also observed. |
