ASTM D5880-95(2000)
(Guide)Standard Guide for Subsurface Flow and Transport Modeling
Standard Guide for Subsurface Flow and Transport Modeling
SCOPE
1.1 This guide covers an overview of subsurface fluid-flow (ground-water) modeling. The term subsurface fluid flow is used to reduce misunderstanding regarding ground water, soil water, vapors including air in subsurface pores, and non-aqueous phase liquids. Increased understanding of fluid-flow phenomena is the combined result of field investigations and theoretical development of mathematical methods to describe the observations. The results are methods for modeling viscous fluids and air flow, in addition to water, that are practical and appropriate.
1.2 This guide includes many terms to assist the user in understanding the information presented here. A ground-water system (soils and water) may be represented by a physical, electrical, or mathematical model, as described in 6.4.3. This guide focuses on mathematical models. The term mathematical model is defined in 3.1.11; however, it will be most often used to refer to the subset of models requiring a computer.
1.3 This guide introduces topics for which other standards have been developed. The process of applying a ground-water flow model is described in Guide D5447. The process includes defining boundary conditions (Guide D5609), initial conditions (Guide D5610), performing a sensitivity analysis (Guide D5611), and documenting a flow model application (Guide D 5718). Other steps include developing a conceptual model and calibrating the model. As part of calibration, simulations are compared to site-specific information (Guide D5490), such as water levels.
1.4 Model use and misuse, limitations, and sources of error in modeling are discussed in this standard. This guide does not endorse particular computer software or algorithms used in the modeling investigation. However, this guide does provide references to some particular codes that are representative of different types of models.
1.5 Typically, a computer model consists of two parts; computer code that is sometimes called the computer program or software, and a data set that constitutes the input parameters that make up the boundary and initial conditions, and medium and fluid properties. A standard has been developed to address evaluation of model codes (see Practice E978).
1.6 Standards have been prepared to describe specific aspects of modeling, such as simulating subsurface air flow using ground-water flow modeling codes (see Guide D5719) and modeling as part of the risk-based corrective action process applied at petroleum release sites (see Guide ES 38).
1.7 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:D5880–95 (Reapproved 2000)
Standard Guide for
Subsurface Flow and Transport Modeling
This standard is issued under the fixed designation D 5880; 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.
1. Scope and fluid properties.Astandard has been developed to address
evaluation of model codes (see Practice E 978).
1.1 This guide covers an overview of subsurface fluid-flow
1.6 Standards have been prepared to describe specific as-
(ground-water) modeling. The term subsurface fluid flow is
pectsofmodeling,suchassimulatingsubsurfaceairflowusing
used to reduce misunderstanding regarding ground water, soil
ground-water flow modeling codes (see Guide D 5719) and
water, vapors including air in subsurface pores, and non-
modeling as part of the risk-based corrective action process
aqueous phase liquids. Increased understanding of fluid-flow
applied at petroleum release sites (see Guide ES 38).
phenomena is the combined result of field investigations and
1.7 This guide offers an organized collection of information
theoretical development of mathematical methods to describe
or a series of options and does not recommend a specific
the observations.The results are methods for modeling viscous
course of action. This document cannot replace education or
fluids and air flow, in addition to water, that are practical and
experienceandshouldbeusedinconjunctionwithprofessional
appropriate.
judgment. Not all aspects of this guide may be applicable in all
1.2 This guide includes many terms to assist the user in
circumstances. This ASTM standard is not intended to repre-
understanding the information presented here. A ground-water
sent or replace the standard of care by which the adequacy of
system (soils and water) may be represented by a physical,
a given professional service must be judged, nor should this
electrical, or mathematical model, as described in 6.4.3. This
document be applied without consideration of a project’s many
guide focuses on mathematical models.The term mathematical
unique aspects. The word “Standard” in the title of this
model is defined in 3.1.11; however, it will be most often used
document means only that the document has been approved
to refer to the subset of models requiring a computer.
through the ASTM consensus process.
1.3 This guide introduces topics for which other standards
have been developed. The process of applying a ground-water
2. Referenced Documents
flowmodelisdescribedinGuideD 5447.Theprocessincludes
2.1 ASTM Standards:
defining boundary conditions (Guide D 5609), initial condi-
D 653 Terminology Relating to Soil, Rock, and Contained
tions (Guide D 5610), performing a sensitivity analysis (Guide
Fluids
D 5611), and documenting a flow model application (Guide
D 4105 Test Method (Analytical Procedure) for Determin-
D 5718). Other steps include developing a conceptual model
ing Transmissivity and Storage Coefficient of Nonleaky
and calibrating the model. As part of calibration, simulations
ConfinedAquifersbytheModifiedTheisNon-Equilibrium
arecomparedtosite-specificinformation(GuideD 5490),such
Method
as water levels.
D 5447 Guide for Application of a Ground-Water Flow
1.4 Model use and misuse, limitations, and sources of error
Model to a Site-Specific Problem
in modeling are discussed in this standard. This guide does not
D 5490 GuideforComparingGround-WaterFlowModelto
endorse particular computer software or algorithms used in the
a Site-Specific Problem
modeling investigation. However, this guide does provide
D 5609 Guide for Defining Boundary Conditions in
references to some particular codes that are representative of
Ground-Water Flow Modeling
different types of models.
D 5610 Guide for Defining Initial Conditions in Ground-
1.5 Typically, a computer model consists of two parts;
Water Flow Modeling
computer code that is sometimes called the computer program
D 5611 Guide for Conducting a Sensitivity Analysis for a
or software, and a data set that constitutes the input parameters
Ground-Water Flow Model Application
that make up the boundary and initial conditions, and medium
D 5718 Guide for Documenting a Ground-Water Flow
Model Application
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 GroundWater and
Vadose Zone Investigations. Annual Book of ASTM Standards, Vol 04.08.
Current edition approved Dec. 10, 1995. Published February 1996. Annual Book of ASTM Standards, Vol04.09.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5880–95 (2000)
D 5719 Guide to Simulation of Subsurface Air Flow Using equations using moving particles as reference points. Also
Ground-Water Flow Modeling Codes known as the particle-in-cell method.
E 943 Terminology Relating to Biological Effects and En- 3.1.13 model—an assembly of concepts in the form of
vironmental Fate mathematical equations that portray understanding of a natural
E 978 Practice for Evaluating Mathematical Models for the phenomenon.
Environmental Fate Models of Chemicals 3.1.14 numerical methods—in subsurface fluid flow model-
ES 38 Guide for Risk-Based Corrective Action Applied at ing, a set of procedures used to solve the equations of a
Petroleum Release Sites mathematical model in which the applicable partial differential
equationsarereplacedbyasetofalgebraicequationswrittenin
3. Terminology terms of discrete values of state variables at discrete points in
space and time.
3.1 Definitions:
3.1.14.1 Discussion—There are many numerical methods.
3.1.1 analytical model—in subsurface fluid flow, a model
Those in common use in ground-water models are the finite-
that uses closed form solutions to the governing equations
difference method, the finite-element method, the boundary
applicable to ground-water flow and transport processes.
element method, and the analytical element method.
3.1.2 boundary condition—a mathematical expression of a
3.1.15 numerical model—in subsurface fluid flow modeling,
state of the physical system that constrains the equations of the
a model that uses numerical methods to solve the governing
mathematical model.
equations of the applicable problem.
3.1.3 calibration (model application)—the process of refin-
3.1.16 output—in subsurface fluid flow modeling, all infor-
ing the model representation of the hydrogeologic framework,
mation that is produced by the computer code.
hydraulic properties, and boundary conditions to achieve a
3.1.17 random walk—in subsurface fluid flow modeling,a
desired degree of correspondence between the model simula-
methodoftrackingalargenumberofparticleswiththenumber
tion and observations of the ground-water system.
of particles proportional to solute concentration, and each
3.1.4 conceptual model—an interpretation or working de-
particle advected deterministically and dispersed probabilisti-
scription of the characteristics and dynamics of the physical
cally.
system.
3.1.18 sensitivity—in model application, the degree to
3.1.5 computer code (computer program)—the assembly of
which the model result is affected by changes in a selected
numerical techniques, bookkeeping, and control language that
model input representing hydrogeologic framework, hydraulic
represents the model from acceptance of input data and
properties, and boundary conditions.
instructions to delivery of output.
3.1.19 simulation—in ground-water flow modeling, one
3.1.6 deterministic process—a process in which there is an
complete execution of a ground-water modeling computer
exact mathematical relationship between the independent and
program, including input and output.
dependent variables in the system.
3.1.20 sink—in subsurface fluid flow modeling, a process
3.1.7 fidelity—the degree to which a model application is
whereby, or a feature from which, water is extracted from the
designed to be realistic.
ground-water flow system.
3.1.8 finite-difference method—in subsurface fluid flow,a
3.1.21 steady-state flow—a characteristic of a flow system
numerical technique for solving a system of equations using a
where the magnitude and direction of specific discharge are
rectangular mesh representing the aquifer and solving for the
constant in time at any point.
dependent variable in a piece wise manner.
3.1.22 stochastic—in subsurface fluid flow, consideration of
3.1.9 finite-element method—in subsurface fluid flow,a
subsurface media and flow parameters as random variables.
numerical technique for solving a system of equations using an
3.1.23 stochastic model—in subsurface fluid flow, a model
irregular triangular or quadrilateral mesh representing the
representing ground water parameters as random variables.
aquifer and solving for the dependent variable in a continuous
3.1.24 stochastic process—a process in which the depen-
manner.
dent variable is random (so that prediction of its value depends
3.1.10 ground-water flow model—application of a math-
on a set of underlying probabilities) and the outcome at any
ematical model to represent a site-specific ground-water flow
instant is not known with certainty.
system.
3.2 For definitions of other terms used in this guide, see
3.1.11 mathematical model—mathematical equations ex-
Terminology D 653 and Terminology E 943.
pressing the physical system and including simplifying as-
sumptions. The representation of a physical system by math-
4. Summary of Guide
ematical expressions from which the behavior of the system
4.1 Modeling is a tool that can be used to evaluate many
can be predicted.
ground-water problems. Models are useful for reconnaissance
3.1.12 methodofcharacteristics—insubsurfacefluidflow,a
studies preceding field investigations, for interpretive studies
numerical method to solve solute transport equations by
following the field program, and for predictive studies to
construction of an equivalent system of ordinary differential
estimate future field behavior. In addition to these applications,
models are useful for studying various types of flow behavior
by examining hypothetical aquifer problems.
4.2 Models can be described many different ways. In this
Annual Book of ASTM Standards, Vol 11.05.
Discontinued; see 1994 Annual Book of ASTM Standards, Vol 11.04. guide they are differentiated by flow in porous versus karst or
D5880–95 (2000)
fracturedmedia,flowinsingleormultiphase,function,fidelity, solve problems concerning water supply, ground-water/surface
construction, and method of solution. water interactions, capture zones, and dewatering.
6.4.1.2 SoluteTransport—Solutetransportissimulatedwith
5. Significance and Use
an equation in addition to the flow equation to solve for
5.1 Subsurfacefluidflowmodelingisawellestablishedtool
concentrationsofthechemicalspecies.Solutetransportmodels
that can aid in studying and solving soil and ground-water
are often used to solve problems concerning aquifer restora-
problems.
tion, waste injection, sea-water intrusion, and underground
5.2 Evaluation of more complex problems has been allowed
storage tank releases.
as a result of advances in computing power and numerical
6.4.1.3 Models have been developed to describe chemical
analysis, yet confusion and misunderstanding over application
transformations due to interactions between the fluid(s) com-
of models still exists. As a result, some inappropriate use
position and media composition. These models, called hydro-
occurs and some problems which could be readily addressed
geochemical models, do not consider the transport processes,
are not.
and can be subdivided into three major categories: thermody-
5.3 The purposes of this guide are to introduce the basic
namic codes, distribution-of-species codes, and reaction
concepts of subsurface fluids modeling and to show how
progress codes (2). Several geochemical codes have been
models are described and categorized.
described by van der Heijde and Einawawy (3).
5.4 This guide should be used by practicing ground-water
6.4.1.4 Heat Transport—In a simple form heat flow is
modelers, purchasers of modeling services, and by those
simulated with an equation in addition to the ground-water
wishing to understand modeling.
flow equation, similar to the solute transport equation, but in
6. Model Types terms of temperature. In a more rigorous manner, heat flow is
coupled with fluid flow. The equation for fluid flow must
6.1 Simulation of a ground-water system refers to the
account for variable density and an additional equation is
constructionandoperationofamodelwhosebehaviorapproxi-
required to represent conduction of heat through the rock and
mates the actual aquifer behavior. Models can be described in
its pores. Heat transport models are often used to solve
many different ways. Model description in this guide provides
problems with thermal storage, and thermal pollution. For
logical groupings to illustrate similarities and differences
evaluating geothermal energy development multiphase flow
between models.
equations are required to consider the presence of water and
6.2 Models of subsurface flow can first be segregated into
steam.
flow in porous medium flow and non-continuum (fractured and
karst) flow. Flow can then be subdivided into single phase and 6.4.1.5 Deformation—Aquifer deformation is simulated by
multiphase flow. Single phase flow includes flow of water in combining a ground-water flow model with a set of equations
the unsaturated and saturated zone. Multiphase flow includes that describes the stress/strain relation of the soil and rock
unsaturated zone flow where water and air that occupy the media. Deformation models are often used to solve problems
pores flow independently or where two or more immisible with land subsidence, soil settlement, or compaction.
fluids flow independently. Models of subsurface fluid flow then
6.4.2 Model Fidelity—Three general classifications of real-
can be further subdivided for handling special cases, such as
ism are described; screening, engineering calculation, and
variable density of the fluid.
aquifer simulator (4).
6.3 Most modeling is performed using porous medium flow
6.4.2.1 Screening—A screening model is least representa-
codeswherethegoverningequationsarebasedonDarcy’slaw.
tive of the real system and is used to assess generalities and
Insomesettingsandforsomeproblems,flowthroughfractures
functions of processes. These applications may be useful with
may be represented with equivalent porous media behavior,
alowdegreeofcorrespondencebetweenthesimulationandthe
however,themodelermustevaluatewhetherthi
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