Assessing preferential fluxes in deep vadose zones using a source-responsive modeling approach
Abstract
Radionuclide contamination in the deep vadose zone at both the Idaho National Laboratory (INL) and the Nevada National Security Site (NNSS) (formerly the Nevada Test Site) poses a potential threat to the water quality of the underlying aquifers. The high uncertainty associated with quantifying preferential flow and contaminant transport processes through the heterogeneous, fractured volcanic rocks at both INL and NNSS presents a considerable challenge. Unsaturated flow models that simulate diffuse-flow require extensive site characterization that is rarely available for deep vadose zones and typically underestimate fluxes in situations where preferential flow is significant. Less data-intensive alternatives that are sensitive to preferential flow are therefore needed to inform management decisions. A recently developed source-responsive model, which incorporates film-flow theory with conservation of mass, was designed specifically to estimate unsaturated zone preferential fluxes with minimal data inputs. The term source-responsive is used to describe the sensitivity of preferential flow in response to changing conditions at the source of water input. At INL, characterization of temporal variations in water source at the land surface and the corresponding subsurface response were sufficient to parameterize the source-responsive model and examine the capacity for preferential flow along connected fractures. For NNSS, the limited availability of source and response data at temporal resolutions relevant to preferential flow led to the use of indirectly related information (e.g., fracture density) to provide a physical basis for constraining model parameter values. Results for both INL and NNSS suggest that the parsimonious source-responsive model could be a useful supplement to traditional approaches, particularly as part of a model ensemble in situations where preferential flow is an important process.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H41A1066M
- Keywords:
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- 1803 HYDROLOGY / Anthropogenic effects;
- 1847 HYDROLOGY / Modeling;
- 1875 HYDROLOGY / Vadose zone