ASTM D6170-97e1
(Guide)Standard Guide for Selecting a Ground-Water Modeling Code
Standard Guide for Selecting a Ground-Water Modeling Code
SCOPE
1.1 This guide covers a systematic approach to the determination of the requirements for and the selection of computer codes used in a ground-water modeling project. Due to the complex nature of fluid flow and biotic and chemical transport in the subsurface many different ground-water modeling codes exist, each having specific capabilities and limitations. Furthermore, a wide variety of situations may be encountered in projects where ground-water models are used. Determining the most appropriate code for a particluar application requires a thorough analysis of the problem at hand and the required and available resources, as well as detailed description of the functionality of candidate codes.
1.2 The code selection process described in this guide consists of systematic analysis of project requirements and careful evaluation of the match between project needs and the capabilities of candidate codes. Insufficiently documented capabilities of candidate codes may require additional analysis of code functionality as part of the code selection process. Figs. 1- is provided to assist with the determination of project needs in terms of code capabilities, and, if necessary, to determine code capabilities.
1.3 This guide is one of a series of guides on ground-water modeling codes and their applications, such as Guides D 5447, D 5490, D5609, D5610, D 5611, D 5718 and D 6025.
1.4 This guide offers a series of options and considerations, but does not specify a course of action. It should not be used as a sole criterion or basis of comparison, and does not replace or relieve professional judgment.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.6 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word "Standard" in the title of this document means only that the document has been approved through the ASTM consensus process.
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Designation: D 6170 – 97
Standard Guide for
Selecting a Ground-Water Modeling Code
This standard is issued under the fixed designation D 6170; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Paragraph 1.4 was added editorially January 1999.
1. Scope 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This guide covers a systematic approach to the determi-
responsibility of the user of this standard to establish appro-
nation of the requirements for and the selection of computer
priate safety and health practices and determine the applica-
codes used in a ground-water modeling project. Due to the
bility of regulatory limitations prior to use.
complex nature of fluid flow and biotic and chemical transport
in the subsurface many different ground-water modeling codes
2. Referenced Documents
exist, each having specific capabilities and limitations. Further-
2.1 ASTM Standards:
more, a wide variety of situations may be encountered in
D 653 Terminology Relating to Soil, Rock, and Contained
projects where ground-water models are used. Determining the
Fluids
most appropriate code for a particular application requires a
D 5447 Guide for Application of a Ground-Water Flow
thorough analysis of the problem at hand and the required and
Model to a Site-Specific Problem
available resources, as well as detailed description of the
D 5490 Guide for Comparing Ground-Water Flow Model
functionality of candidate codes.
Simulations to Site-Specific Information
1.2 The code selection process described in this guide
D 5609 Guide for Defining Boundary Conditions in
consists of systematic analysis of project requirements and
Ground-Water Flow Modeling
careful evaluation of the match between project needs and the
D 5610 Guide for Defining Initial Conditions in Ground-
capabilities of candidate codes. Insufficiently documented
Water Flow Modeling
capabilities of candidate codes may require additional analysis
D 5611 Guide for Conducting a Sensitivity Analysis for a
of code functionality as part of the code selection process. Figs.
Ground-Water Flow Model Application
1- is provided to assist with the determination of project needs
D 5718 Guide for Documenting a Ground-Water Flow
in terms of code capabilities, and, if necessary, to determine
Model Application
code capabilities.
D6025 Guide for Developing and Evaluating Ground-Water
1.3 This guide is one of a series of guides on ground-water
Modeling Codes
modeling codes and their applications, such as Guides D 5447,
D 5490, D 5609, D 5610, D 5611,D 5718 and D 6025 .
3. Terminology
1.4 This guide offers an organized collection of information
3.1 Definitions of Terms Specific to This Standard:
or a series of options and does not recommend a specific
3.1.1 analytical model—in ground-water modeling, a model
course of action. This document cannot replace education or
that uses closed form solutions to the governing equations
experience and should be used in conjunction with professional
applicable to ground-water flow and transport processes.
judgement. Not all aspects of this guide may be applicable in
3.1.2 code selection—the process of choosing the appropri-
all circumstances. This ASTM standard is not intended to
ate computer code, algorithm, or other analysis technique
represent or replace the standard of care by which the
capable of simulating those characteristics of the physical
adequacy of a given professional service must be judged, nor
system required to fulfill the modeling project’s objective(s).
should this document be applied without consideration of a
3.1.3 computer code (computer program)—assembly of
project’s many unique aspects. The word “Standard” in the
numerical techniques, bookkeeping, and control language that
title of this document means only that the document has been
represents the model from acceptance of input data and
approved through the ASTM consensus process.
instructions to delivery of output.
This guide is under the jurisdiction of ASTM Committee D-18 on Soil and
Rock and is the direct responsibility of Subcommittee D18.21 on Ground Water and
Vadose Zone Investigations. Annual Book of ASTM Standards, Vol 04.08.
Current edition approved Sept. 10, 1997. Published January 1998. Annual Book of ASTM Standards, Vol 04.09.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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FIG. 1 Checklist for Ground-Water Modeling Needs and Code Functionality (continued)
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3.1.4 conceptual model—an interpretation or working de- require extensive modeling, or where costly decisions are
scription of the characteristics and dynamics of the physical based, in part, on the outcome of modeling-based analysis.
system. 4.3 Systematic and comprehensive description of project
3.1.5 functionality—of a ground-water modeling code, the requirements and code features provides the necessary basis for
set of functions and features the code offers the user in terms of efficient selection of a ground-water modeling code. This
model framework geometry, simulated processes, boundary standard guide is intended to encourage comprehensive and
conditions, and analytical and operational capabilities. consistent description of code capabilities and code require-
3.1.6 ground-water modeling code—the non-parameterized ments in the code selection process, as well as thorough
computer code used in ground-water modeling to represent a documentation of the code selection process.
non-unique, simplified mathematical description of the physi-
5. Code Selection Process in Ground-Water Modeling
cal framework, geometry, active processes, and boundary
5.1 Code selection in ground-water modeling is a crucial
conditions present in a reference subsurface hydrologic system.
step in the application of ground-water models (see Guide D
3.1.7 mathematical model—(a) mathematical equations ex-
5447). Each ground-water project in which computer-based
pressing the physical system and including simplifying as-
modeling is performed should include a code selection phase.
sumptions; (b) the representation of a physical system by
5.2 Code selection is in essence the process of matching a
mathematical expressions from which the behavior of the
project’s modeling needs with the documented capabilities of
system can be deduced with known accuracy.
existing computer codes.
3.1.8 model construction—the process of transforming the
5.3 Selecting an appropriate code requires analysis and
conceptual model into a parameterized mathematical form; as
systematic description of both the modeling needs and the
parametrization requires assumptions regarding spatial and
characteristics of existing ground-water modeling codes.
temporal discretization, model construction requires a-priori
5.4 A perfect match rarely exists between desired code
selection of a computer code.
characteristics or selection criteria and the capabilities or
3.1.9 model schematization—simplification of a conceptu-
functionality of available codes. Therefore, the selection crite-
alized ground-water system for quantitative, model-based
ria are divided into the following two groups: essential code
analysis commensurate with project objectives and constraints.
capabilities; and non-essential code capabilities. If a candidate
3.1.10 numerical model—in ground-water modeling,a
code does not include the essential capabilities, it should be
model that uses numerical methods to solve the governing
removed from consideration.
equations of the applicable problem.
5.5 The relative importance of the non-essential code capa-
3.1.11 semi-analytical model—a mathematical model in
bilities needs to be assessed. This may be done by assigning
which complex analytical solutions are evaluated using ap-
weighting factors to the considered capabilities (for example,
proximate techniques, resulting in a solution discrete in either
using weights from one to five according their relative impor-
the space or time domain.
tance). Although such weighing factors are often not explicitly
3.2 For definitions of other terms used in this guide, see
mentioned in the code selection process, candidate codes are
Terminology D 653.
often ranked implicitly using some kind of weighting of the
4. Significance and Use non-essential capabilities. Assigning weighting factors is a
rather subjective procedure; if a match is difficult to obtain,
4.1 Ground-water modeling has become an important meth-
reassessment of these factors may be necessary. Hence, code
odology in support of the planning and decision-making
selection may turn out to be a rather iterative process requiring
processes involved in ground-water management. Ground-
a significant level of professional judgement and experience.
water models provide an analytical framework for obtaining an
5.6 Selecting the right code is critical in ensuring an optimal
understanding of the mechanisms and controls of ground-water
trade-off between effort and result in a modeling project. The
systems and the processes that influence their quality, espe-
result can be expressed as the expected effectiveness of the
cially those caused by human intervention in such systems.
modeling tasks in terms of prediction accuracy. The effort is
Increasingly, models are an integral part of water resources
basically represented by the modeling costs such as incurred in
assessment, protection and restoration studies and provide
becoming familiar with the code, model schematization and
essential and cost-effective support for planning and screening
model construction, and model-based scenario analysis. Such
of alternative policies, regulations, and engineering designs
4 costs should not be considered independently from those of
affecting ground water.
field data acquisition, especially those required for the model-
4.2 Many different ground-water modeling codes are avail-
ing effort. For a proper assessment of modeling cost, consid-
able, each with their own capabilities, operational characteris-
eration should be given to the choice of developing a new code
tics and limitations. Furthermore, each ground-water project
(or modifying an existing one) versus acquisition of an existing
has its own requirements with respect to modeling. Therefore,
code, the implementation and maintenance of the code, com-
it is important that the most appropriate code is selected for a
puter platform requirements, and the development and main-
particular project. This is even more important for projects that
tenance of databases.
NOTE 1—The availability of or familiarity with a particular code, or
both, may lead to modeling overkill by using a pre-chosen code requiring
National Research Council (NRC), Committee on Ground Water Modeling
significant more preparation in data gathering and model construction than
Assessment, Water Science and Technology Board, Ground Water Models: Scientific
and Regulatory Applications, National Academy Press, Washington, DC, 1990. necessary for the project. Such modeling overkill may also result from the
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D 6170 – 97
user’s inability to limit the number of “essential” code features, or to
variables and parameters required to run the selected code
discriminate between non-essential code features.
should be available).
NOTE 2—The belief that use of the “best” or most mathematically
6.4 The conceptual model, no matter how complex will
advanced codes will automatically provide predictive reliability and
always be a simplified representation of the ground-water
scientific credibility is false. The technical capability of the modeler or the
system. Furthermore, current limitations in scientific theories
modeling team involved in the modeling project has the greatest impact on
(and their mathematical representation) and computer capabili-
the overall results.
ties may require additional simplifications in the conceptual
5.7 If different project questions need to be addressed, more
model to facilitate computer modeling. Combining the de-
than one code might be needed, or different combinations of
scription of the conceptual model with the level of modeling
functions of a single code may be utilized. This is often the
required, while taking into considerations these scientific and
case when models are used in d
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