Numerical modeling and data-worth analysis for characterizing the architecture and dissolution rates of a multicomponent DNAPL source

Abstract

A numerical solute transport model was history matched to a high-resolution monitoring dataset to characterize a multicomponent source of nonaqueous phase liquids (NAPLs) and evaluate the uncertainty of estimated parameters. The dissolution of NAPL mass was simulated using the SEAM3D solute transport model with spatially-varying NAPL saturations and mass transfer rate coefficients, representing the heterogenous architecture of the source zone. Source zone parameters were simultaneously estimated using PEST from aqueous-phase concentrations measured in a multilevel monitoring transect and from mass recovery rates measured at extraction wells during a controlled field experiment. Data-worth analyses, facilitated by PEST ancillary software, linked maximum aqueous-phase concentrations of all compounds to reductions in prior uncertainty of mass transfer coefficients. In turn, transient concentrations of the most soluble NAPL fraction constrained the source mass estimation. Accurately estimating the source mass and reducing prior uncertainties was possible by removing concentrations measured during early NAPL dissolution stages, identified as prior-data conflicts using the iterative ensemble smoother PESTPP-iES. Prior-based Monte Carlo analyses highlighted model limitations for representing sub-grid-scale heterogeneity of source zone architecture and NAPL dissolution, yet history-matching of final dissolution stages measured at multilevel ports eliminated parameter bias and produced long-term projections of source depletion with multistage behavior. Including mass discharge constraints further improved the accuracy of source mass estimation, complementing multilevel monitoring constraints on the source architecture and mass transfer coefficients