ASTM D5490-93(2008)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D5490 −93(Reapproved 2008)
Standard Guide for
Comparing Groundwater Flow Model Simulations to Site-
Specific Information
This standard is issued under the fixed designation D5490; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.7 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 techniques that should be used to
responsibility of the user of this standard to establish appro-
compare the results of groundwater flow model simulations to
priate safety and health practices and determine the applica-
measured field data as a part of the process of calibrating a
bility of regulatory limitations prior to use.
groundwater model. This comparison produces quantitative
1.8 This guide offers an organized collection of information
and qualitative measures of the degree of correspondence
or a series of options and does not recommend a specific
between the simulation and site-specific information related to
course of action. This document cannot replace education or
the physical hydrogeologic system.
experienceandshouldbeusedinconjunctionwithprofessional
1.2 During the process of calibration of a groundwater flow
judgment. Not all aspects of this guide may be applicable in all
model, each simulation is compared to site-specific informa-
circumstances. This ASTM standard is not intended to repre-
tion such as measured water levels or flow rates.The degree of
sent or replace the standard of care by which the adequacy of
correspondence between the simulation and the physical hy-
a given professional service must be judged, nor should this
drogeologic system can then be compared to that for previous
document be applied without consideration of a project’s many
simulations to ascertain the success of previous calibration
unique aspects. The word “Standard” in the title of this
efforts and to identify potentially beneficial directions for
document means only that the document has been approved
further calibration efforts.
through the ASTM consensus process.
1.3 By necessity, all knowledge of a site is derived from
2. Referenced Documents
observations. This guide does not address the adequacy of any
2.1 ASTM Standards:
set of observations for characterizing a site.
D653 Terminology Relating to Soil, Rock, and Contained
1.4 This guide does not establish criteria for successful
Fluids
calibration, nor does it describe techniques for establishing
E978 Practice for Evaluating Mathematical Models for the
such criteria, nor does it describe techniques for achieving 3
Environmental Fate of Chemicals (Withdrawn 2002)
successful calibration.
3. Terminology
1.5 This guide is written for comparing the results of
numericalgroundwaterflowmodelswithobservedsite-specific
3.1 Definitions:
information. However, these techniques could be applied to
3.1.1 application verification—using the set of parameter
other types of groundwater related models, such as analytical
values and boundary conditions from a calibrated model to
models, multiphase flow models, noncontinuum (karst or
approximate acceptably a second set of field data measured
fracture flow) models, or mass transport models.
under similar hydrologic conditions.
3.1.1.1 Discussion—Application verification is to be distin-
1.6 This guide is one of a series of guides on groundwater
guishedfromcodeverificationwhichreferstosoftwaretesting,
modeling codes (software) and their applications. Other stan-
comparison with analytical solutions, and comparison with
dards have been prepared on environmental modeling, such as
other similar codes to demonstrate that the code represents its
Practice E978.
mathematical foundation.
1 2
This guide is under the jurisdiction ofASTM CommitteeD18 on Soil and Rock For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and is the direct responsibility of Subcommittee D18.21 on Groundwater and contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Vadose Zone Investigations. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Sept. 15, 2008. Published October 2008. Originally the ASTM website.
approved in 1993. Last previous edition approved in 2002 as D5490 – 93 (2002). The last approved version of this historical standard is referenced on
DOI: 10.1520/D5490-93R08. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5490−93 (2008)
3.1.2 calibration—the process of refining the model repre- 4.3.1 Comparison of general flow features. Simulations
sentation of the hydrogeologic framework, hydraulic should reproduce qualitative features in the pattern of ground-
properties, and boundary conditions to achieve a desired water contours, including groundwater flow directions,
degree of correspondence between the model simulations and mounds or depressions (closed contours), or indications of
observations of the groundwater flow system. surface water discharge or recharge (cusps in the contours).
4.3.2 Assessment of the number of distinct hydrologic
3.1.3 censored data—knowledge that the value of a variable
conditionstowhichthemodelhasbeensuccessfullycalibrated.
in the physical hydrogeologic system is less than or greater
It is usually better to calibrate to multiple scenarios, if the
than a certain value, without knowing the exact value.
scenarios are truly distinct.
3.1.3.1 Discussion—For example, if a well is dry, then the
4.3.3 Assessment of the reasonableness or justifiability of
potentiometricheadatthatplaceandtimemustbelessthanthe
the input aquifer hydrologic properties given the aquifer
elevation of the screened interval of the well although its
materials which are being modeled. Modeled aquifer hydro-
specific value is unknown.
logic properties should fall within realistic ranges for the
3.1.4 conceptual model—an interpretation or working de-
physical hydrogeologic system, as defined during conceptual
scription of the characteristics and dynamics of the physical
model development.
system.
5. Significance and Use
3.1.5 groundwater flow model—an application of a math-
ematical model to represent a groundwater flow system.
5.1 During the process of calibration of a groundwater flow
model, each simulation is compared to site-specific informa-
3.1.6 hydrologic condition—a set of groundwater inflows or
tion to ascertain the success of previous calibration efforts and
outflows, boundary conditions, and hydraulic properties that
to identify potentially beneficial directions for further calibra-
cause potentiometric heads to adopt a distinct pattern.
tion efforts. Procedures described herein provide guidance for
3.1.7 residual—the difference between the computed and
making comparisons between groundwater flow model simu-
observed values of a variable at a specific time and location.
lations and measured field data.
3.1.8 simulation—in groundwater flow modeling, one com-
5.2 Thisguideisnotmeanttobeaninflexibledescriptionof
plete execution of a groundwater modeling computer program,
techniques comparing simulations with measured data; other
including input and output.
techniques may be applied as appropriate and, after due
3.1.8.1 Discussion—For the purposes of this guide, a simu-
consideration, some of the techniques herein may be omitted,
lation refers to an individual modeling run. However, simula-
altered, or enhanced.
tion is sometimes also used broadly to refer to the process of
modeling in general.
6. Quantitative Techniques
3.2 For definitions of other terms used in this guide, see
6.1 Quantitative techniques for comparing simulations to
Terminology D653.
site-specific information include calculating potentiometric
headresiduals,assessingcorrelationamongheadresiduals,and
4. Summary of Guide
calculating flow residuals.
6.1.1 Potentiometric Head Residuals—Calculate the residu-
4.1 Quantitative and qualitative comparisons are both es-
als(differences)betweenthecomputedheadsandthemeasured
sential. Both should be used to evaluate the degree of corre-
heads:
spondence between a groundwater flow model simulation and
site-specific information.
r 5 h 2 H (1)
i i i
4.2 Quantitativetechniquesforcomparingasimulationwith
where:
site-specific information include:
r = the residual,
i
4.2.1 Calculation of residuals between simulated and mea-
H = the measured head at point i,
i
sured potentiometric heads and calculation of statistics regard-
h = the computed head at the approximate location where
i
ing the residuals. Censored data resulting from detection of dry
H was measured.
i
or flowing observation wells, reflecting information that the
If the residual is positive, then the computed head was too
head is less than or greater than a certain value without
high; if negative, the computed head was too low. Residuals
knowing the exact value, should also be used.
cannot be calculated from censored data.
4.2.2 Detection of correlations among residuals. Spatial and
NOTE 1—For drawdown models, residuals can be calculated from
temporal correlations among residuals should be investigated.
computed and measured drawdowns rather than heads.
Correlations between residuals and potentiometric heads can
NOTE 2—Comparisons should be made between point potentiometric
be detected using a scattergram.
heads rather than groundwater contours, because contours are the result of
4.2.3 Calculation of flow-related residuals. Model results
interpretation of data points and are not considered basic data in and of
themselves. Instead, the groundwater contours are considered to reflect
should be compared to flow data, such as water budgets,
features of the conceptual model of the site. The groundwater flow model
surface water flow rates, flowing well discharges, vertical
gradients, and contaminant plume trajectories.
4.3 Qualitative considerations for comparing a simulation
Cooley, R. L., and Naff, R. L., “Regression Modeling of Ground-Water Flow,”
with site-specific information include: USGS Techniques of Water Resources Investigations , Book 3, Chapter B4, 1990.
D5490−93 (2008)
should be true to the essential features of the conceptual model and not to
6.1.2.4 Second-Order Statistics—Second-order statistics
their representation.
give measures of the amount of spread of the residuals about
NOTE 3—It is desirable to set up the model so that it calculates heads at
the residual mean. The most common second-order statistic is
the times and locations where they were measured, but this is not always
the standard deviation of residuals:
possibleorpractical.Incaseswherethelocationofamonitoringwelldoes
not correspond exactly to one of the nodes where heads are computed in
n
thesimulation,theresidualmaybeadjusted(forexample,computedheads 2
~r 2 R!
( i
i51
may be interpolated, extrapolated, scaled, or otherwise transformed) for
H J
s 5 (4)
use in calculating statistics.Adjustments may also be necessary when the
~n 2 1!
times of measurements do not correspond exactly with the times when
where sisthestandarddeviationofresiduals.Smallervalues
heads are calculated in transient simulations; when many observed heads
are clustered near a single node; where the hydraulic gradient changes
of the standard deviation indicate better degrees of correspon-
significantlyfromnodetonode;orwhenobservedheaddataisaffectedby
dence than larger values.
tidal fluctuations or proximity to a specified head boundary.
6.1.2.5 If weighting is used, calculate the weighted standard
6.1.2 Residual Statistics—Calculate the maximum and
deviation:
minimum residuals, a residual mean, and a second-order
n
statistic, as described in the following sections.
w ~r 2 R!
( i i
i51
6.1.2.1 Maximum and Minimum Residuals—The maximum
s 5 (5)
n
residual is the residual that is closest to positive infinity. The
5 6
~n 2 1! w
( i
i51
minimumresidualistheresidualclosesttonegativeinfinity.Of
NOTE 6—Other norms of the residuals are less common but may be
two simulations, the one with the maximum and minimum
5,6
revealing in certain cases. For example, the mean of the absolute values
residuals closest to zero has a better degree of correspondence,
of the residuals can give information similar to that of the standard
with regard to this criterion.
deviation of residuals.
NOTE 7—In calculating the standard deviation of residuals, advanced
NOTE 4—When multiple hydrologic conditions are being modeled as
statistical techniques incorporating information from censored data could
separate steady-state simulations, the maximum and minimum residual
be used. However, the effort would usually not be justified because the
can be calculated for the residuals in each, or for all residuals in all
standard deviation of residuals is only one of many indicators involved in
scenarios, as appropriate. This note also applies to the residual mean (see
comparing a simulation with measured data, and such a refinement in one
6.1.2.2) and second-order statistics of the residuals (see 6.1.2.4).
indicator is unlikely to alter the overall assessment of the degree of
correspondence.
6.1.2.2 Residual Mean—Calculate the residual mean as the
arithmetic mean of the residuals computed from a given
6.1.3 Correlation Among Residuals—Spatial or temporal
simulation:
correlation among residuals can indicate systematic trends or
n
bias in the model. Correlations among residuals can be
r
( i identified through listings, scattergrams, and spatial or tempo-
i51
R 5 (2)
ral plots. Of two simulations, the one with less correlation
n
among residuals has a better degree of correspondence, with
where:
regard to this criterion.
R = the residual mean and
6.1.3.1 Listings—List residuals by well or piezometer, in-
n = the number of residuals.
cluding the measured and computed values to detect spatial or
temporal trends. Figs. X1.1 and X1.2 present example listings
Oftwosimulations,theonewiththeresidualmeanclosestto
of residuals.
zero has a better degree of correspondence, with regard to this
6.1.3.2 Scattergram—Use a scattergram of computed versus
criterion (assuming there is no correlation among residuals).
measured heads to detect trends in deviations. The scattergram
6.1.2.3 If desired, the individual residuals can be weighted
is produced with measured heads on the abscissa (horizontal
to account for differing degrees of confidence in the measured
axis) and computed heads on the ordinate (vertical axis). One
heads. In this case, the residual mean becomes the weighted
point
...