Exploring Mass Flux Response to Local Source Zone Properties Using a Coupled-Process Adjoint Sensitivity Method
Abstract
Contaminant plumes emanating from DNAPL source zones pose substantial risks to the general population by transporting pollutants to receptor points. Thus, to assess potential risk, the quantification of down gradient mass flux and mass discharge has been identified as a critical component of source zone characterization. These metrics, however, are difficult to measure directly and are typically controlled by the complex interplay of a number of transport mechanisms. In an effort to improve the accuracy and efficiency of site characterization, this work employs an adjoint sensitivity method to quantify the importance of local system properties, given some initial site characterization information, on down gradient mass flux and plume persistence. Local properties that are considered in this research include: permeability, DNAPL saturation, and dissolved and sorbed contaminant mass concentrations. The utility of the adjoint sensitivity method is examined using, numerically generated, 3D heterogeneous DNAPL source zones. Conditioned spatial distributions of the four properties are generated using a joint probabilistic model associated with texture simulations based on field borehole measurements. An existing modular three-dimensional transport simulator, MT3DMS, is applied to solve the transport equation considering both DNAPL dissolution and linear and rate-limited sorption. Consistent with this process coupling, a subroutine is added to the code to solve the adjoint states, which evolves backward in time. Sensitivity analyses are developed to investigate the down-gradient plume response to the perturbation of the four local system properties. In addition, sensitivities corresponding to these four properties at different times are also compared, to explore the influence of DNAPL dissolution and desorption over time. Results demonstrate that the initial aqueous phase concentration will have a larger impact on downstream mass flux at early times after a DNAPL release, while the influence of the field heterogeneity, initial sorbed mass, and initial DNAPL saturation will be significant at later periods. Computed sensitivities can provide guidance on the selection of future measurement locations and types, enhancing our ability to characterize source zones under realistic field conditions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H11A1280T
- Keywords:
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- 1805 Computational hydrology;
- HYDROLOGYDE: 1846 Model calibration;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGYDE: 1873 Uncertainty assessment;
- HYDROLOGY