Grid Resolution Study of Ground Water Flow and Transport

Three-dimensional grids representing a heterogeneous, ground water system are generated at 10 different resolutions in support of a site-scale flow and transport modeling effort. These grids represent hydrostratigraphy near Yucca Mountain, Nevada, consisting of 18 stratigraphic units with contrasting fluid flow and transport properties. The grid generation method allows the stratigraphy to be modeled by numerical grids of different resolution so that comparison studies can be performed to test for grid quality and determine the resolution required to resolve geologic structure and physical processes such as fluid flow and solute transport. The process of generating numerical grids with appropriate property distributions from geologic conceptual models is automated, thus making the entire process easy to implement with fewer user-induced errors. The series of grids of various resolutions are used to assess the level at which increasing resolution no longer influences the flow and solute transport results. Grid resolution is found to be a critical issue for ground water flow and solute transport. The resolution required in a particular instance is a function of the feature size of the model, the intrinsic properties of materials, the specific physics of the problem, and boundary conditions. The asymptotic nature of results related to flow and transport indicate that for a hydrologic model of the heterogeneous hydrostratigraphy under Yucca Mountain, a horizontal grid spacing of 600 m and vertical grid spacing of 40 m resolve the hydrostratigraphic model with sufficient precision to accurately model the hypothetical flow and solute transport to within 5% of the value that would be obtained with much higher resolution.

[1]  Georges Voronoi.  Nouvelles applications des paramètres continus à la théorie des formes quadratiques. Deuxième mémoire. Recherches sur les parallélloèdres primitifs. , 1908 .

[2]  H. Haitjema,et al.  Selecting MODFLOW Cell Sizes for Accurate Flow Fields , 2001, Ground water.

[3]  Mark de Berg,et al.  Computational geometry: algorithms and applications , 1997 .

[4]  Hydrogeology of the unsaturated zone, North Ramp area of the Exploratory Studies Facility, Yucca Mountain, Nevada , 1999 .

[5]  George A. Zyvoloski,et al.  Finite element methods for geothermal reservoir simulation , 1983 .

[6]  Mary C. Hill,et al.  Hydrogeologic evaluation and numerical simulation of the Death Valley regional ground-water flow system, Nevada and California , 1997 .

[7]  Peter A. Forsyth,et al.  A Control Volume Finite Element Approach to NAPL Groundwater Contamination , 1991, SIAM J. Sci. Comput..

[8]  C. C. Faunt,et al.  Status of understanding of the saturated-zone ground-water flow system at Yucca Mountain, Nevada, as of 1995 , 1996 .

[9]  Hari S. Viswanathan,et al.  A reactive transport model of neptunium migration from the potential repository at Yucca Mountain , 1998 .

[10]  P. Reimus,et al.  The saturated zone at Yucca Mountain: an overview of the characterization and assessment of the saturated zone as a barrier to potential radionuclide migration. , 2003, Journal of contaminant hydrology.

[11]  H. Trease,et al.  Geological applications of automatic grid generation tools for finite elements applied to porous flow modeling , 1996 .

[12]  Atsuyuki Okabe,et al.  Spatial Tessellations: Concepts and Applications of Voronoi Diagrams , 1992, Wiley Series in Probability and Mathematical Statistics.

[13]  S. S. Hughes,et al.  Evaluation of a groundwater corrective action at the Chem-Dyne Hazardous Waste Site using a telescopic mesh refinement modeling approach , 1987 .

[14]  George A. Zyvoloski,et al.  FEHMN 1.0: Finite element heat and mass transfer code , 1991 .

[15]  Larry S.K. Fung,et al.  Hybrid-CVFE method for flexible-grid reservoir simulation , 1994 .

[16]  Peter A. Forsyth,et al.  A Control Volume Finite Element Method for Local Mesh Refinement , 1989 .

[17]  George A. Zyvoloski,et al.  On the development of a three-dimensional finite-element groundwater flow model of the saturated zone, Yucca Mountain, Nevada , 1996 .

[18]  B. Robinson,et al.  MILESTONE SP25BM3: THE SITE-SCALE UNSATURATED ZONE TRANSPORT MODEL OF YUCCA MOUNTAIN , 1997 .

[19]  C. Zheng,et al.  A dual‐domain mass transfer approach for modeling solute transport in heterogeneous aquifers: Application to the Macrodispersion Experiment (MADE) site , 2000 .

[20]  B. Robinson,et al.  The site-scale saturated zone flow model for Yucca Mountain: calibration of different conceptual models and their impact on flow paths. , 2003, Journal of contaminant hydrology.

[21]  Y. Saad,et al.  GMRES: a generalized minimal residual algorithm for solving nonsymmetric linear systems , 1986 .

[22]  D. George,et al.  The X3D grid generation system , 1996 .

[23]  G. A. Zyvoloski.  Calibration of the Site-Scale Saturated Zone Flow Model , 2001 .