70193-Influence of Clastic Dikes on Vertical Migration of Contaminants in the Vadose Zonde at Hanford

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The purpose of this study was to examine the hypothesis that clastic dikes could form a preferential flow path through the vadose zone to the water table at the Hanford Site. Clastic dikes are subvertical structures that form within sedimentary sequences after deposition and cut across the original sedimentary layers. They are common throughout the Hanford Site, often occurring in organized polygonal networks. In the initial phase of the project, we analyzed the large-scale geometry of the clastic dikes and developed an algorithm for simulating their spatial distribution. This result will be useful in providing maps of the potential distribution ... continued below

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39 pages

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Murray, Christopher J; Ward, Anderson L. & Wilson, John L. April 7, 2004.

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Description

The purpose of this study was to examine the hypothesis that clastic dikes could form a preferential flow path through the vadose zone to the water table at the Hanford Site. Clastic dikes are subvertical structures that form within sedimentary sequences after deposition and cut across the original sedimentary layers. They are common throughout the Hanford Site, often occurring in organized polygonal networks. In the initial phase of the project, we analyzed the large-scale geometry of the clastic dikes and developed an algorithm for simulating their spatial distribution. This result will be useful in providing maps of the potential distribution of clastic dikes in areas where they are not exposed at the surface (e.g., where covered by windblown sand or construction of facilities like tank farms at the surface). In addition to the study of the large-scale distribution of the dikes, a major focus of the project was on field, laboratory, and modeling studies of the hydrogeological properties of the clastic dikes and the effect that they have on transport of water through the vadose zone. These studies were performed at two field locations at the Hanford Site. We performed an extensive series of field and laboratory measurements of a large number of samples from the clastic dikes, linked with infrared (IR) and visual imagery of the clastic dikes and surrounding matrix. We developed a series of correlations from the sample data that allowed us to estimate the unsaturated hydraulic conductivity of the dike and matrix at an extremely high resolution (approximately 1 mm). The resulting grids, each of which measured several meters on a side and included nearly four million grid nodes, were used to study the distribution of moisture between the clastic dike and surrounding matrix, as well as the relative velocities that moisture would have through the clastic dike and matrix for a number of different recharge scenarios. Results show the development of complex flow networks that depend on input flux rates and boundary type and that may sometimes mask the underlying heterogeneity. The networks occupy two complementary states: a high-permeability region in the fine-textured media at low fluxes and a high-permeability region in the coarse-textured media at high fluxes. Transition between the two states occurred at an input flux of about 100 mm yr{sup -1}. At this input flux, preferential channels essentially disappear with the dike and host matrix conducting at similar rates. This suggests that clastic dikes might serve as a conduit for more rapid movement of moisture and mobile contaminants to the water table, but only under a restricted set of recharge (or leak) conditions. However, owing to the relatively high content of reactive minerals, especially clay, that is found in the clastic dikes, the movement of reactive contaminants like heavy metals and radionuclides may be restricted. The field site developed for this project, as well as the data and numerical models, are now the focus of several ongoing studies funded by the Hanford Groundwater Protection Program's Science and Technology (S&T) Project. These studies focus on collecting datasets to support conceptual model development and model calibration, the development and use of advanced scaling methods to facilitate inverse modeling of heterogeneous systems, and the identification of appropriate parameters for predictive modeling of field-scale reactive transport.

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39 pages

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INIS; OSTI as DE00823359

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  • Other Information: PBD: 7 Apr 2004

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  • Report No.: DOE/ER/62890
  • Grant Number: FG07-99ER62890
  • DOI: 10.2172/823359 | External Link
  • Office of Scientific & Technical Information Report Number: 823359
  • Archival Resource Key: ark:/67531/metadc779318

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  • April 7, 2004

Added to The UNT Digital Library

  • Dec. 3, 2015, 9:30 a.m.

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  • Dec. 16, 2016, 4:27 p.m.

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Murray, Christopher J; Ward, Anderson L. & Wilson, John L. 70193-Influence of Clastic Dikes on Vertical Migration of Contaminants in the Vadose Zonde at Hanford, report, April 7, 2004; United States. (digital.library.unt.edu/ark:/67531/metadc779318/: accessed December 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.