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- Title
Numerical Modeling and Data‐Worth Analysis for Characterizing the Architecture and Dissolution Rates of a Multicomponent DNAPL Source.
- Authors
Prieto‐Estrada, Andres E.; Widdowson, Mark A.; Stewart, Lloyd D.
- Abstract
A numerical solute transport model was calibrated to a high‐resolution monitoring data set 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 SEAM3D with parameter zones including adjustable NAPL saturations and mass transfer 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 the pre‐calibration uncertainty of mass transfer coefficients. In turn, decreasing concentrations of the most soluble NAPL fraction constrained the source mass estimation. The accurate estimation of model parameters was possible by removing concentrations measured during early NAPL dissolution stages, identified as drivers of model bias using the iterative ensemble smoother PESTPP‐iES. Although uncertainty analyses highlighted model limitations for representing sub‐grid‐scale heterogeneity of NAPL distribution and mass transfer rates, final stages of NAPL dissolution measured at multilevel ports eliminated parameter bias and produced long‐term projections of multi‐stage source zone depletion. Including mass discharge rates for model calibration further improved the accuracy of estimated residual source mass, complementing multilevel monitoring constraints on the saturation distribution and mass transfer coefficients. Plain Language Summary: Predicting the persistence of groundwater contamination by dense non‐aqueous phase liquids (DNAPLs), such as chlorinated solvents, is crucial for effective environmental stewardship. The dissolution behavior of DNAPL source zones depends on the contaminant mass distribution within hydrogeologic systems, referred to as the source zone architecture, which cannot be measured directly at contaminated sites. We investigated the worth of high‐resolution monitoring of aqueous concentrations during a controlled field experiment for indirectly characterizing a multicomponent DNAPL source zone, including its architecture and dissolution behavior. Our methods coupled numerical modeling of groundwater flow and contaminant transport with parameter estimation and uncertainty analysis techniques. Parameter uncertainties were linked to the variability of DNAPL dissolution rates observed at multiple scales of monitoring resolution, including a multilevel transect and groundwater recovery wells. While early aqueous concentration peaks were identified as drivers of model bias, the depletion profile of the most soluble DNAPL component accurately constrained the estimated source architecture and dissolution behavior. Hence, our characterization approach can benefit remedial designs for managing DNAPL source zones undergoing final depletion stages at sites with monitoring histories. Key Points: Aqueous‐phase concentrations monitored in a field experiment were simulated to quantify nonaqueous phase liquid (NAPL) distribution and dissolution ratesDepletion profiles of the most soluble dense NAPL component accurately constrained the source zone architectureMultiscale heterogeneity of source zone architecture controlled the uncertainty of estimated mass transfer coefficients
- Subjects
DENSE nonaqueous phase liquids; NONAQUEOUS phase liquids; MASS transfer coefficients; GROUNDWATER monitoring; MAGNETIZATION transfer; HAZARDOUS waste sites; FOOD emulsions
- Publication
Water Resources Research, 2023, Vol 59, Issue 5, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2022WR034351