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Title: Review and selection of unsaturated flow models

Abstract

Since the 1960`s, ground-water flow models have been used for analysis of water resources problems. In the 1970`s, emphasis began to shift to analysis of waste management problems. This shift in emphasis was largely brought about by site selection activities for geologic repositories for disposal of high-level radioactive wastes. Model development during the 1970`s and well into the 1980`s focused primarily on saturated ground-water flow because geologic repositories in salt, basalt, granite, shale, and tuff were envisioned to be below the water table. Selection of the unsaturated zone at Yucca Mountain, Nevada, for potential disposal of waste began to shift model development toward unsaturated flow models. Under the US Department of Energy (DOE), the Civilian Radioactive Waste Management System Management and Operating Contractor (CRWMS M&O) has the responsibility to review, evaluate, and document existing computer models; to conduct performance assessments; and to develop performance assessment models, where necessary. This document describes the CRWMS M&O approach to model review and evaluation (Chapter 2), and the requirements for unsaturated flow models which are the bases for selection from among the current models (Chapter 3). Chapter 4 identifies existing models, and their characteristics. Through a detailed examination of characteristics, Chapter 5 presents themore » selection of models for testing. Chapter 6 discusses the testing and verification of selected models. Chapters 7 and 8 give conclusions and make recommendations, respectively. Chapter 9 records the major references for each of the models reviewed. Appendix A, a collection of technical reviews for each model, contains a more complete list of references. Finally, Appendix B characterizes the problems used for model testing.« less

Authors:
; ;  [1]
  1. INTERA, Inc., Las Vegas, NV (United States)
Publication Date:
Research Org.:
TRW Environmental Safety Systems, Inc., Las Vegas, NV (United States); INTERA, Inc., Las Vegas, NV (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
145325
Report Number(s):
DOE/RW/00134-T11
ON: DE94015954; TRN: 94:015479
DOE Contract Number:
AC01-91RW00134
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 4 Apr 1994
Country of Publication:
United States
Language:
English
Subject:
05 NUCLEAR FUELS; 54 ENVIRONMENTAL SCIENCES; GROUND WATER; FLOW MODELS; EVALUATION; RADIOACTIVE WASTE DISPOSAL; SITE SELECTION; YUCCA MOUNTAIN; Yucca Mountain Project

Citation Formats

Reeves, M., Baker, N.A., and Duguid, J.O.. Review and selection of unsaturated flow models. United States: N. p., 1994. Web. doi:10.2172/145325.
Reeves, M., Baker, N.A., & Duguid, J.O.. Review and selection of unsaturated flow models. United States. doi:10.2172/145325.
Reeves, M., Baker, N.A., and Duguid, J.O.. 1994. "Review and selection of unsaturated flow models". United States. doi:10.2172/145325. https://www.osti.gov/servlets/purl/145325.
@article{osti_145325,
title = {Review and selection of unsaturated flow models},
author = {Reeves, M. and Baker, N.A. and Duguid, J.O.},
abstractNote = {Since the 1960`s, ground-water flow models have been used for analysis of water resources problems. In the 1970`s, emphasis began to shift to analysis of waste management problems. This shift in emphasis was largely brought about by site selection activities for geologic repositories for disposal of high-level radioactive wastes. Model development during the 1970`s and well into the 1980`s focused primarily on saturated ground-water flow because geologic repositories in salt, basalt, granite, shale, and tuff were envisioned to be below the water table. Selection of the unsaturated zone at Yucca Mountain, Nevada, for potential disposal of waste began to shift model development toward unsaturated flow models. Under the US Department of Energy (DOE), the Civilian Radioactive Waste Management System Management and Operating Contractor (CRWMS M&O) has the responsibility to review, evaluate, and document existing computer models; to conduct performance assessments; and to develop performance assessment models, where necessary. This document describes the CRWMS M&O approach to model review and evaluation (Chapter 2), and the requirements for unsaturated flow models which are the bases for selection from among the current models (Chapter 3). Chapter 4 identifies existing models, and their characteristics. Through a detailed examination of characteristics, Chapter 5 presents the selection of models for testing. Chapter 6 discusses the testing and verification of selected models. Chapters 7 and 8 give conclusions and make recommendations, respectively. Chapter 9 records the major references for each of the models reviewed. Appendix A, a collection of technical reviews for each model, contains a more complete list of references. Finally, Appendix B characterizes the problems used for model testing.},
doi = {10.2172/145325},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1994,
month = 4
}

Technical Report:

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  • Under the US Department of Energy (DOE), the Civilian Radioactive Waste Management System Management and Operating Contractor (CRWMS M&O) has the responsibility to review, evaluate, and document existing computer ground-water flow models; to conduct performance assessments; and to develop performance assessment models, where necessary. In the area of scientific modeling, the M&O CRWMS has the following responsibilities: To provide overall management and integration of modeling activities. To provide a framework for focusing modeling and model development. To identify areas that require increased or decreased emphasis. To ensure that the tools necessary to conduct performance assessment are available. These responsibilities aremore » being initiated through a three-step process. It consists of a thorough review of existing models, testing of models which best fit the established requirements, and making recommendations for future development that should be conducted. Future model enhancement will then focus on the models selected during this activity. Furthermore, in order to manage future model development, particularly in those areas requiring substantial enhancement, the three-step process will be updated and reported periodically in the future.« less
  • Models of partially saturated flow and transport in porous media have application in the analysis of existing as well as future low-level radioactive waste facilities located above the water table. An extensive literature search along with telephone and mail correspondence with recognized leading experts in the field, was conducted to identify computer models suitable for studies of low-level radioactive waste facilities located in the unsaturated zone. Fifty-five existing models were identified as potentially useful. Ten of these models were selected for further examination. This report contains a statement of the ground-water flow-contaminant transport problem, a discussion of those methods usedmore » to reduce the physical problem to a computer model, a brief discussion about the data requirements of these models. The procedure used to select the ten codes for further discussion is given, along with a list of these models. Finally, the Appendices contain the data about the fifty-five codes examined. Specifically Appendix D contains the detailed discussion of each of the ten selected codes. Included in each discussion are such items which a potential user requires in determining whether the code is suitable for his applications. Appendix E contains brief summary information about each of the fifty-five codes. Included in the summaries are identification data, authors, pertinent references, and model type.« less
  • This report is the first in a series of reports that will provide critical reviews and summaries of computer programs that can be used to analyze the potential performance of a high-level radioactive waste repository. The computer programs identified address the following phenomena: saturated and unsaturated subsurface flow, heat transport, solute transport, surface water runoff, geomechanical interactions, and geochemical interactions. The report identifies 183 computer programs that can be used to analyze a repository site and provides a summary description of 31 computer programs. The summary descriptions can be used: to assist in code evaluation, to facilitate code comparison, tomore » determine applicability of codes to specific problems, to identify code deficiencies, and to provide a screening mechanism for code selection.« less
  • Capillary barriers consisting of tilted fine-over-coarse layers have been suggested as landfill covers as a means to divert water infiltration away from sensitive underground regions under unsaturated flow conditions, especially for arid and semi-arid regions. Typically, the HELP code is used to evaluate landfill cover performance and design. Unfortunately, due to its simplified treatment of unsaturated flow and its essentially one-dimensional nature, HELP is not adequate to treat the complex multidimensional unsaturated flow processes occurring in a tilted capillary barrier. In order to develop the necessary mechanistic code for the performance evaluation of tilted capillary barriers, an efficient and comprehensivemore » unsaturated flow code needs to be selected for further use and modification. The present study evaluates a number of candidate mechanistic unsaturated flow codes for application to tilted capillary barriers. Factors considered included unsaturated flow modeling, inclusion of evapotranspiration, nodalization flexibility, ease of modification, and numerical efficiency. A number of unsaturated flow codes are available for use with different features and assumptions. The codes chosen for this evaluation are TOUGH2, FEHM, and SWMS{_}2D. All three codes chosen for this evaluation successfully simulated the capillary barrier problem chosen for the code comparison, although FEHM used a reduced grid. The numerical results are a strong function of the numerical weighting scheme. For the same weighting scheme, similar results were obtained from the various codes. Based on the CPU time of the various codes and the code capabilities, the TOUGH2 code has been selected as the appropriate code for tilted capillary barrier performance evaluation, possibly in conjunction with the infiltration, runoff, and evapotranspiration models of HELP. 44 refs.« less
  • Activities 5 and 7 are part of a program to hydrologically characterize coal seams for designing effective dewatering schemes. Activity 5 evaluated the single-phase well testing methods that are used in analyzing coal seams and assessed the effectiveness of dewatering designs. Activity 7 examined stress-dependent permeability effects and discovered an intermediate, unsaturated flow regime (between single-phase flow of water and two-phase flow of gas and water), and developed appropriate testing and data analysis procedures. Examination of five cases in which single-phase test methods were used in coal seams proved that instantaneous and constant-rate methods are useful when appropriate precautions aremore » observed. A model of a stress-sensitive aquifer was developed and used to show that stress sensitivity is apparently insignificant in the case available for application. The method was applied to a drawdown test in which unsaturated flow was observed.« less