Improved DNAPL source zone architecture characterization with the use of self-potential signals and hydraulic/partitioning tracer tomography
Abstract
The characterization of dense non-aqueous phase liquid (DNAPL) distribution in the subsurface is important for optimizing remediation strategies. Hydraulic/partitioning tracer tomography (HPTT) has proven to be an effective method to identify DNAPL distributions by combining traditional hydrodynamic measurements, i.e., piezometric head and tracer concentration. However, characterization for DNAPL source zones often suffers due to the sparsity of the available data from direct sampling in boreholes. As a non-intrusive, cost-effective, and high sampling density method, time-lapse self-potential method can provide a good complement to the piezometric head data due to its sensitivity to groundwater flow. NAPL saturation determines the relative permeability kr. This relationship can be delineated by constitutive models (e.g. Brooks-Corey). In this work, we integrate hydraulic head and SP data to improve the estimation of the effective permeability. Then, partitioning tracer data are used to further map the DNAPL distribution based on the estimated permeability. The joint inversion problem is solved by the Principal Component Geostatistical Approach (PCGA). In this method, the large prior covariance matrix is truncated and replaced by its low-rank approximation, thus reducing markedly the number of runs of the hydrogeophysical forward model. The low-rank method (PCGA) is necessary for large-scale inversion problems with tens of thousands of unknown parameters, because the computational burden of the corresponding hydrogeophysical model is quite heavy. Results from large-scale synthetic cases based on 3D confined aquifer demonstrate that using HPTT alone can only provide a smooth estimation of the DNAPL distribution due to a sparsity of the available data, however, the combination of HPTT and SP techniques can significantly improve DNAPL imaging.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H11D..01K
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGY;
- 1835 Hydrogeophysics;
- HYDROLOGY;
- 1865 Soils;
- HYDROLOGY;
- 1899 General or miscellaneous;
- HYDROLOGY