UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON. D.C. 20460
f*ii
July 31, 1985
Hon. Lee M. Thomas TH1fiOM!
Administrator
U. S. Environmental Protection Agency
401 M Street, S. W.
Washington, D.C. 20460
Dear Mr. Thomas;
In late November, 1984, the Science Advisory Board was asked to review the
technical basis for the development of a "decision rule" for determining whe-
ther or not specific haEardous wastes should he restricted from land disposal.
This review was assigned to the Environmental Engineering Committee.
In the course of its review, the Committee examined two proposed approaches
to developing the decision rule, one proposed by the Office of Solid Waste,
and the Other by the Office of Policy Analysis in OPPE. We have already sent
you our report on the QStt version, and are pleased to now forward our review
of the one proposed by QPA.
The Committee agrees chac the QPA approach, because of its complexity and
data-intensiveness, will not be applicable to all waste-banning decisions,
The approach should be useful, however, on a waste- and site-specific basis
for comprehensive comparisons of the risks of alternative hazardous waste
disposal options.
The Committee has been particularly pleased with the cooperation extended by
the QPA staff, and we are pleased to note that they have already taken steps
to implement some of the Comtnittee's recommendations.
If you have any questions, or should you wish any-further action on our part,
please call On us.- " ' " " "' ' ' :'•" " '""
Sincerely,
Raymond C. Loehr
Chairman, Environmental
Engineering Committee
Science Advisory Board
cc: R* Morgenstern
S. Napolitano
A* Fisher
J, Briskin
A. Corson Norton Nelson
S. Bromm Chairman, Executive Committee
T! Yosle Science Advisory Board
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REPORT
of the
ENVIRONMENTAL ENGINEERING COMMITTEE
SCIENCE ADVISORY BOARD
U. S. ENVIRONMENTAL PROTECTION AGENCY
on their review of
"COMPARISON OF RISKS AND COSTS OF HAZARDOUS WASTE ALTERNATIVES;
METHODS DEVELOPMENT AND PILOT STUDIES"
July, 1985 "
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I. EXECUTIVE SUMMARY
The Committee finds that the QPPE method of comparative risk analysis has
scientific and technical merit and can provide useful information to decislon-
makets if further developed. However, we do not find the method per se useful
for the Nationwide waste banning decision on several hundred chemicals. It
is useful on a waste- and site-specific basis in that a decision can be based
on a comprehensive appraisal of comparative risks of alternatives.
The method may not have generic applicability* The method is based on
the scenario approach, the selection of a specific set of sub-models required,
and the output form, as characterized by comparative risks and costs among
the chosen scena-rios. Its generality depends on how representative the
scenarios can be made. An advantage of the method is that it provides
for an explicit statement of uncertainties, if the uncertainties of the
component parameters and models are known or estimated.
The choice of model components and the linking mechanisms to arrive at
the complete model concerns the Committee in the following ways: (1) While some
suggested sub-models are tested and accepted, others are not now verified and
may not in practice be verifiable; (2) The data base for some of the models
needs careful analysis, for both quality and quantity. Selection of para-
meter values based on quality peer-reviewed research is essential to avoid
misleading results.
The health-effects section of the model, as with other similar models,
suffers from the data-base problems already described. In addition, however,
the Committee has concerns about the methods used. Aatong these are the use
of a non-threshold model (which introduces problems when considering chemi-
cals which may have threshold effects); the ignoring of pharaacokinetic
effects and compound interactions; and inadequate lexicological evaluation
and extrapolation techniques, especially simplistic temporal, route-to-route
and specles-to-species extrapolations. The Committee notes that the modular
nature of the model does not restrict it to-the use of a non-threshold ap-
proach,
The overall OPPE method needs upgrading in the area of surface drainage
modeling and most-importantly in the risk .assessments'related-.to'the handlijog -
and transport of"wastes with respect,to fugitive emissions and probability of
leakage and spills*
Finally, the model makes no provision for evaluating non-human environ-
mental effects except for a "qualitative" evaluation. However^ we are in-
formed by OPPE that improvements are being made. •
It is important to note that OPPE has responded at length to many of
the comments and concerns expressed by the Committee in written summaries and
in discussions with the Committee, and is studying ways of improving the
method. The Committee commends OPPE for undertaking this major piece of
research and encourages further work. The basic idea, if the concerns ex-
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pressed can "be taken into proper account. Is sound for Identifying the compar-
ative risks of hazardous waste disposal options. With Agency policy interest
in risk assessment strong, a properly developed method will be of real value.
II. INTRODUCTION ASD HISTORY
At a meeting of the Environmental Engineering Committee on August 16,
1984, Mr. Alan Carson, Office of Solid Wastes, briefed the Committee on the
development of a decision rule for restricting certain hazardous wastes from
land disposal as governed by the proposed amendments to the Resource Conser-
vation and Recovery Act. Two main approaches were under way: One Incorpor-
ating a simplified predictive modeling approach (referred to as the OSW
nodel), the other a more complex modeling framework based upon comparative
risk assessment (referred to as the QPPE model).
In response to an Agency request for review of these approaches, a Sub-
committee chaired by Dr. J. William Haun was appointed to conduct the review
on an accelerated time schedule. The Subcommittee was assisted by several
consultants (for a full list of the Subcommittee, see Appendix A), The full
Environmental Engineering Committee completed a report to the Agency on its
review of the OSW approach in April, 1985.
By letter dated January 7, 1985, and at a meeting of the Waste Banning
Subcommittee (denoted above)» on January 31, 1985, Dr* Richard D. Morgen-
stern. Director, Office of Policy Analysis, QPPE, presented the draft Final
Report on "Comparison of Risks and Costs of Hazardous Waste Alternatives;
Methods Development and Pilot Studies" (EPA Prime Contract No. 68-01-6558»
Subcontract No. 130.155, Work Assignment No. 24), which forms the basis for
the QPPE model. Dr. Nicholas Nichols, Dr, Ann Flsher» Ms. Jeanne Briskin and
several contractor representatives also provided the Subcommittee with details
of the method and background. The Subcommittee again met on February 25 and
February 27 with Dr. Fisher and other members of the OPPE project team.
As a result of this activity, responding to the urgent need of Agency
staff for a preliminary response, a Letter Report on the review to date was
issued by Dr.-Terry YosiSi. Staff Director,- SAB ^ on betialf -of the Environmental-
Engineering Committee on March 8, 1985. This report constitutes the detailed
basis for that Letter Report.
The scope of the review as originally suggested by OPPE, which focused
primarily on the reasonableness of the sub-models and their integration, is
shown in Appendix B. In addition, based on the early discussions. Dr. Loehr
developed a more general list of issues for the Subcommittee. This list is
shown In Appendix C. Both Lists were used by the Subcommittee in its conduct
of the review.
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III. DESCRIPTION AND EVALUATION OF THE MODEL
As a result of the recent (11/84) amendments to the Resource Conserva-
tion and Recovery Act (RGRA), EPA is required to establish which wastes, of
those Specified in the Act, are not to be banned from disposal in certain land
disposal facilities. It is believed that the required rule must be "generic,"
i.e., of National scope and not of a site specific nature.
The research described In the draft study report was designed to: (a)
"test the viability of comparative risk assessment for hazardous waste man-
agement alternatives," and (b) "serve as a basis for making land disposal
prohibition decisions for hazardous waste streams" (p. 1-2), The study
contributed to the development and demonstration of comparative risk assess-
ment methods by using a pilot study approach.
The model proposed is utilised for a specific waste by selecting a num-
ber of possible disposal technologies (scenarios) considered appropriate for
the particular waste. For each waste and waste treatment scenario, existing
models are used in combination to estimate waste releases, environmental
transport of the released components of concern, and to identify the poten-
tial population exposed, and estimated doses to exposed individuals in that
population. Further, the model then develops dose-response relationships for
each vaste component based on the best literature data available and, from
this estimates human health risks by combining the exposure and dose-response
information. Finally, the model is used to qualitatively evaluate ecological
Impacts of the selected scenarios. Using estimates of uncertainties in the
human health risk estimates, an explicit estimate of the uncertainty of each
overall estimate is made to peroit decision-makers to take these ranges into
account.
The Pilot Study considers for illustration three wastes, with four or
five scenarios for management of each. While its potential utility and po-
tential versatility were reasonably well represented in the pilot study,
the method as presented represents a still-preliminary approach.
IV". EVALUATION OF "THEMfiTHOD AND ASSUMPTIONS
A» General Comments
Over the next five years, the Agency must determine which, of as
many as 450,' wastes or waste streams are to be evaluated to determine if
they should not be "banned" from landfills. The OPPE states that-the
approach identified in the draft study report may be .able to consider
from 20 to 40 wastes or perhaps 5 to 10 percent of the wastes that nay
have to be evaluated. The implementation of this approach even to a
small number of wastes will require significant effort involving extensive
data-gathering and evaluation as well as significant judgmental evaluation
of input and results. The effort to apply the OPPE method to selected
wastes could be an excellent investment if it prevented suboptimal
decisions that Increase risks to human health or to the environment.
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The approach makes an important contribution by attempting to esti-
mate the relative risks in all.media, since, if the land disposal option
is banned, the wastes still have to be handled and disposed of in some
manner. The approach can provide information concerning: (a) pretreat-
merit alternatives that can be considered before land disposal, (b) the
relative impact of'other disposal alternatives on protection of human
health and the environment, (c) relative costs involved, and (d) data
and research needs that can reduce the uncertainties involved in esti-
mating the relative risks.
It will readily be appreciated that this approach is necessarily
data- and resource-intensive. Analysis of each scenario for each vstste
requires detailed knowledge of the available technologies of disposal
and detailed knowledge of the existence and use of many submodels:
fugitive emissions from landfills; solute transport in groundwater;
dispersion models for air transport; dose-response and health affects,
and many others.
OPPE is to be commended for undertaking such an important evalua-
tion, for its early judgaent to support such a detailed study, and for
its wisdom of continued support for the study. The study clearly has
had good intellectual input, the individual components appear sound, and
reasonable estimates of potential health risks appear to have been ob-
tained. The study also has considerable fallout valus. Even if not
applied solely to'the banning decision, the technique developed will be
useful in many other situations. The task of risk assessrtie.it is to make
the most credible possible statements about definable relationships,
reducing uncertainty, and making explicit whatever uncertainty rsnains.
This study accomplished these goals.
However, in terras of EPA needs relative to the waste banning deci-
sions, it does not appear that the 'study approach can serve as the sole
basis for the final decisions. The study approach can be used with one
or more other approaches or methods to provide a broader perspective 0:1
those major wastes that may be banned from land disposal in order to
protect human health and the envirornient. Suchjnajor wastes could be
. those .that.are of large volume,'are-of unique .characteristics'f may have."
an apparent adverse econemic impact on an industry if banned from land
disposal, and/or appear likely to cause a potential adverse human- health
and enviromiental impact if disposed of in another way. Other approaches
may be able to more quickly evaluate a larger number of wastes and iden-
tify those for which more detailed evaluation is needed.
The study approach would provide the Administrator with a richer
array of information on relative risks, intermedia transfer or costs
when making decisions about which wastes should not be banned from land
disposal.
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B. Components of the Modol aid Model Linking
1. Randan, Walk Solute Transport Model
The Rardan. Walk model was selected to predict two-dimensional
contaminant transport in groundwater aquifers, The horizontal flow
field in the aquifer is conputed using a finite difference tech-
nique. Solute transport is calculated using a population balance
technique in which many particles are released and their fate simu-
lated . The advective transport for each particle follows the flow
field and dispersion is incorporated by randan displacements. As
the number of particles released becomes large, the spatial distri-
bution of particles corresponds to the concentration profile of
the constituent. The technique produces a solute concentration
profile which should in theory (as the number of particles beccmes
large) be identical to that obtained with more traditional, two-
dimensional advective-dispersive models using finite difference
or finite elanent solution methods. Linear equilibrium adsorption
is incorporated through the use of a retardation coefficient, and
reaction is represented with a generalized half-life (i.e., multi-
ply results by e"^).
The Randan Walk model has been used in many applications and is
a well recognized tool, for example, through its use as part of the
program of the Holcanb Groundwater Research Institute. This pro-
vides confidence and credibility for its use. There are, however,
limitations to the model that should be recognized, particularly
as regards its treatment of chanical transformations of contaminants
in the soil. A detailed review of Random Walk and other groundwater
transport models was performed as part of a study sponsored by the
Electric BDVsr Besearch Institute (Kincaid and f-torrey, 1984). A
sum-nary of this Randan Walk review is included as Appendix D. • Based
on the EPRI analysis and a review of the Randan Walk Model by the
Ccmtdttee's consultants, there is a major area of concern about
the model's applicability. The model allows for a detailed char-
acterization of two-dimensional flow profiles; spatial heterogeneity
in- hydraulic conductivity,.'Storativity, etc. As mentioned.---.in • T" -•
the OPPE presentation, the model allows incorporation of pumping-
remedial action, which is useful for its intended applications.
Similarly, a careful representation of dispersion is incorporated.
As such, transport mechanisms are well represented, and the model
is very appropriate for predicting the fate of "solutes"...consti-
tuents which undergo no chemical transformation. The reaction and
adsorption components of the model, however, are much more limited.
In particulari
a. In the Randan Walk model, both the reaction rate and the
adsorption (retardation) coefficient are constant over
the aquifer study area. Heterogeneity in soil conditions
which might affect these factors is not considered.
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b. Unlike other numerical models where the chemical inter-
actions are formulated as part of the finite difference
or finite element equations, the population balance tech-
nique used in Random Walk is expressly designed for the
case of linear, equilibrium adsorption and first order
decay. The Random Walk model would require significant
rftodifieations to maKe it applicable to more complex chemi-
cal conditions. While nonlinear, non-equilibrium adsorp-
tion and higher order kinetics are not commonly incorpor-
ated in applied groundwater models today, they may be
used in the future a$ our scientific understanding advan-
ces. It will be very difficult to incorporate these
advances in the Random Walk model.
The limited representation of chemical processes relative to
the detail given to transport processes should be recognized. It
may reduce the applicability of the Random Walk model for certain
kinds of problems in certain locations, particularly when chemical
processes are non-ideal. The level of chemical representation is
no better than that provided by the OSW model (and possibly worse,
depending on the resolution of item b above). This limitation
should be recognized.
To summarize, the use of the Random walk model is acceptable,
with the limitations noted. In addition, it should be noted that
there are a number of other numerical codes which can simulate two-
dimensional advective-dispersive transport. Those models utilize
more traditional solutions of the material balance equation at a
grid point or cell, and like the Random Walk model, can allow for
non-homogeneous flow conditions, pumping wells, etc. Some users
may be more familiar with the conceptual basis for these siodels,
and they may be easier to adapt to situations where the use of more
complex chemistry is appropriate. ; As such, alternative numerical
models should be considered in future applications.
A final consideration applicable to the_use of any numerical
groundwat«x model», regards the limited, level -of -validation-, -parti-.-
eularly for complex field conditions where constituents undergo
chemical transformation. Successful attempts to verify models in
the field have been made in recent years, though validation remains
difficult and expensive. Some degree of field calibration and
verification is recommended.
2* Modeling of Onsaturated Zone Transport
In the analysis presented in the QPPE report, the McWhorter-
Nelson model is used as a basis for modeling transport in the
unsaturated zone. The McWhorter-Nelson model, however, computes
only a water recharge rate - no contaminant transport mechanisms
are included. Contaminant transport is calculated in the OFFE
\
\
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examples by considering only the hydraulic residence time in the
unsaturated zone associated with the computed recharge rate. This
results in a step break-through profile, with no consideration for
the effects of dispersion, adsorption (retardation), or reaction.
Significant adsorption or reaction may considerably alter the
pollutant washout profile from the unsaturated zone. An analysis
which ignores these processes is not consistent with either the
current state-of-the-art of unsaturated zone modeling, or the level
of sophistication used in other components of the risk assessment.
As noted in the QPEE report and the supporting MR! documents, there
are models available for the unsaturated zone, such as the analy-
tical PEgTAN model, which incorporate dispersion, retardation, and
decay, These should be utilized to generate more realistic esti-
mates of the temporal breakthrough profile from the unsaturated
zone.
3. Atmospheric Transport/Dispersion Models
Air pollution impacts are simulated using Gaussian plume mo-
dels incorporating wind speed and direction, transverse and verti-
cal diffusion (as a function of atmospheric stability class),
terrain adjustment in certain cases, and plume-depletion and par-
ticle deposition processes. The selection of the Industrial Source
Complex CISC) Long-Term Model for area sources and the ATM model
for point sources appears to be based on a careful and credible
review of the current state-of-the-art of air modeling, and a full
consideration of the capabilities of existing models, The ability
to link the ATM model to population exposure estimates through the
Graphic Exposure Modeling System (GEMS) is particularly beneficial.
It is worthwhile to note that long-term average concentration pro-
files are sought (rather than short-term "event" concentrations),
therefore, long-term versions of the models are utilized. The
long-term versions use integrated forms of the Gaussian plume
model based on the joint frequency- distribution of wind speed,
stability class, and wind direction.
' Although .the models,selected-represent the state—of-the—art -"
in Gaussian plume modeling, there has been concern expressed among
SftB members that the level of validation for this class of models
has been limited.
4« Uncertainty Analysis
The propagation-of-error technique for evaluating uncertainty
is formulated on the basis that links between model components
occur in a multiplicative fashion. The assessment may effectively
be represented by an equivalent, simplified model of the fora:
Risk = Pollutant x Transport x Exposure x Response x Health Effects
Release Factor Dose Factor
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Uncertainties in each component are assumed to be independent and
are routed logarithmically. The method is correctly developed and
implemented, assuming the multiplicative assumption is adequate.
The technique has a number of desirable features, including its
simplicity and direct use with "order-of-magnitude" judgments of
uncertainty bounds. There may, however4 be a need for a wore care-
ful consideration of the implications and limitations of the multi-
plicative assumption* This discussion is relevant as well to the
integration issue (Appendix B» 2j Have the models been integrated
(combined) without violating scientific principles? Is the integra-
tion consistent with the state-of-the-art?).
Two issues may be raised to illustrate possible difficulties
with the multiplicative assumption for model linking. The first
arises if and when thresholds are incorporated in the dose-response
functions for health effects. A more sophisticated uncertainty
routing procedure would then be required to account for the proba-
bility of eero impact (e.g., below threshold). The second issue
relates to the temporal aspects of the analysis resulting from the
stochastic nature of pollutant release in the Pope-Reid landfill
liner failure model. (We were asked not to review the Pope-Reid
model itself, but the incorporation of the model in the overall
framework is important.) In the OPPE report, the results of repli-
cations of the Pope-Reid model are averaged to obtain a nominal
temporal profile of pollutant release. It is then assumed that
the use of a multiplicative uncertainty factor can capture the
full range of uncertainty in both the amount of pollutant released
and its temporal distribution. The validity of this assumption is
not intuitively obvious, and needs to be demonstrated with a more
detailed set of example simulations. In particular, it would be
useful to evaluate transport simulations for each of the Pope-Reid
replication outputs. The resulting "exact" distribution of concen-
tration-exposure can then be compared to the lognormal distribution
derived from the multiplicative assumption. This analysis is com-
putationally intensive and should not be performed for all cases.
Rather,'the ..comparison should-be/demonstrated once to-evaluate the
adequacy of the simplified integration assumption; to build confi-
dence in its use (or provide guidance for a better alternative).
The use of "one standard .deviation" in the uncertainty analy-
sis results in an 84 percentile concentration. This is fine so
long as the scenarios are considered only in a comparative sense.
If, however, the absolute level of impact is also evaluated (as is
apparently the case from the OPPE report), then 84% seems too low
for ah "upper limit." The OPPE has indicated that it concurs with
this suggestion and intends to use a wider confidence interval.
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C. Toxlcologicsl Risk Assessment
Conceptually, the methods of health risk assessment as outlined in
the OPPE report are appropriate tools. Quantitative risk assessment and
quantitative uncertainty analyses are both desirable approaches- The
dose/response assessment proposed by OPPE is innovative in that it
estimates dose response functions for a spectra of adverse effects.
Most other approaches used by the Agency either estimate dose/response
functions for only a single effect, usually cancer* or are restricted
to the estimation of an acceptable exposure liadt (e.g.* ADI, ambient
water quality criteria, drinking water criteria). For the purposes of
comparing risks with costs of hazardous waste alternatives, the esti-
mation of dose/response functions for all significant effects should be
encouraged if it leads to more fully and clearly using the available
toxicity data. With several significant modifications, the OPPE ap-
proach could serve as a useful decision-making tool, As currently
written, however, it has some serious flaws and could mislead rather
than assist the decision-maker.
Concerns related to the OPPE methodology include; The use of a
non-threshold model for all effects, the use of maximum likelihood esti-
mates, and simplistic temporal, route-to-route, and species-to-species
extrapolations. In addition, several areas in the methodology and
application of the methodology require clarification. These include:
the rationale for combining effects (i.e., independent vs. graded series);
how quantitative estimates of uncertainty are made (atathematie or
judgmental) as well as the validity of such estimates; details of how
effects on which incidence data are not available will be handled in
the risk assessment (in the case studies, such effects are ignored),
and how data on pharmacokinetics and compound interactions «ill be
used (in the case studies, such data are not considered).
These concerns have been discussed with OPPE personnel and their
contractors. OPPE has indicated a willingness to alter their approach
to constructively address these issues.
D. Fugitive Emissions, Leaks and Spills
The OPPI study attempts to address the risks frou production of
fugitive emissions, transportation over interstate highways and atmos-
pheric emissions from capped landfills. Each of the primary refer-
ences is based on a minimum of information. Indeed, OPPI shares in these
SAB concerns (stated in a follow-up letter to the EEC). In addition,
as off-site landfill and deep-well injection alternatives force more
chemical wastes to be stored, transported and re-stored before ultimate
disposal, the probability of risks will be magnified over previous
experience. The inclusion of small-generator wastes, all of which will
have to be transportedj will further exacerbate the problem. The OPPE
methodology needs a major' effort to gather the Information to adequately
address these issues and their ramifications.
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E. Application of the Model
The Committee is concerned that many of the specialized models (or
submodels) required to apply the method may not be adequately verified
or even verifiable. An example is the estimation of exposures resulting
from handling of wastes in transportation, which both the Pilot Study
and one's intuition would indicate as a major route of population expo-
sures. One advantage of the OPPE framework is that its modular nature
permits the substitution of improved models and data as they become
available.
*
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APPENDIX A
U.S. ENVIRONMENTS, PROTECTION AGENCY
SCIENCE ADVISORY BOARD
ENVIRONMENTAL ENGINEERING SUBCOMMITTEE
WASTE BANNING SUBCOMMITTEE
CHAIRMAN
Dr. J. William Haun
Engineering Policy (4SW)
General Mills, Incorporated
P. O. Box 1113
Minneapolis, MN 55440
MEMBERS
Mr. Richard A. Conway
Corporate Development Fellow
Union Carbide Corporation
P. O. Box 8361 (770/342)
South Charleston, wv 25303
Dr. Benjamin C. Dysart, III
Environmental Systems Engineering Department
401 Rhodes Engineering Research Centet
Clemson University
Clemson, SC 29631
Mr. George Green
Public Service Company of Colorado
P.O. Box 840, Room 820
Denver, CO 80202
Dr. Joseph T. Ling
3M Community Service Executive Office
Minnesota Mutual Life Center
6th fi Robert
llth .Floor - - .-.. . . ^
St. Paul, MN 55144
• ?
Dr. Raymond C. Loehr
Civil Engineering Department
8.614 ECJ Hall
University of Texas
Austin, TX 78712
Dr. Donald J. O'Connor
Professor of Environmental Engineering
Environmental Engineering Science Program
Manhattan College
Manhattan College Parkway
Bronx, NY 10471
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CONSULTANTS
Dr. Marc Anderson
Water Chemistry
660 Horth Park Street
University of Wisconsin
Madison, wi 53706
Dr. Paul E. Brubaker, Jr.
Paul E. Brubaker Associates, Inc.
3 Halstead Road
Mendham, NJ 07945
Mr. Allen Cywin
Consultant
1126 Arcturus Lane
Alexandria, VA 2230S
Dr. Patrick R. Durhin
Syracuse Research Corporation
Merrill Lane
Syracuse, NY 13210
Dr. Charles F. Reinhardt
Haskell Laboratory for Toxicology &
Industrial Medicine
S. I. du Pont de Nemours and Company
Elkton Road
Newark, DE 19711
Dr* Mitchell Small
Department of Civil Engineering
Carnegie-Mellon University
Schenley Park
Pittsburgh, PA 15213
Dr. Leonard Greenfield
6721 Southwest 69 Terrace
South-Miami, Florida ..33143.
Executive Secretary
Mr. Harry C. Torno
Executive Secretary, EEC
U.S. Environmental Protection Agency
Science Advisory Board (A-101 F)
Washington, D.C. 20460
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APPENDIX B
Cgj-estions for _SAB Review
1. Because of the many steps in "the health risk assessment process,
several models were vsed» is the use of each of the following
reasonable?
a* The Farmer et al* equation for fugitive emissions from land-
fills,*
b» The Random Walk Solute Transport model for groundwater movement;
c. The Industrial Source Complex Long-Tern model for dispersion
of air emissions from area sources;
d* The AIM component of GEMS for dispersion of air emissions from
point sourcesi
e. The multistage model, with the one^hit model as a backup when
data are limited, for dose-response functions;
f. The Carcinogen Assessment Group potency factors, Wiebull model,
and modified ac'ceptable-daily-intake approach as sensitivity
checks for the dose-response function selected} and
g. The propagation-of-errors approach for evaluating uncertainty
in the health-risk estimates.
2. Have the models been integrated without violating scientific princi-
ples? Is the integration consistent with the state of the art?
3« How can this approach be improved to better estimate risks
for each management strategy for a given hazardous waste stream?
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APPENDIX C
QUESTIONS RAISED BY DR, RAYMOND C. LOEHR
on
Proposed QPPE Method
Following are basic questions to which the Subcommittee can respond or comment?
1. Specific questions related to the specific tnodeI/approach with respect
to its scientific, fundamental credibility (basically, is the approach
sci entifically sound).
2. Is this model/approach likely to address the important questions facing
EPA, i»e. will the correct need be addressed?
Generally, the SAB is asked to respond to type (1) qo.estions. This generally
skirts the real basic issue and we should attempt to address the type (2)
ques tions.
Therefore, in addition to the questions that have been placed before the
Subcommittee, the Subcommittee should also consider addressing the following
questions s
1 * To what extent does the Subcommittee feel that this approach can be
used for the banning decision - i.e., from the scientific or engi-
neering basis and not from the policy aspects?
2, Are the'nodels that are proposed to be used the appropriate ones
for the intended use? Have they been adequately peer-reviewed
and verified by independent data?
3. Is the data base to be used adecuate from the standpoint of accu-
racy, OA/OC, etc.? Is there sufficient data that can be used with
this approach?
4. Are there adeouate other models that can be used for other land
disposal approaches, such as land •treatment, waste piles, surface
impoundments and all land disposal approaches listed in the RCRA
amendments, i*e., really address whether the model/aproach can be
used for other land disposal methods besides" landfill? ~ ;• -~ -
It seems that these types of questions also should be addressed by the Sub-
committee.
If the Subcommittee decides to address so»e of the above issues, then at a
future meeting it would be helpful-if OPPE could address the following
questions (or provide detailed discussion on these items) - it would be
helpful to hear their explicit thoughts on these subjects for our consi-
deration;
1. How would this approach be useful for the "banning" decision?
2. TO what extent is it possible for the OPPE approach to be used for
a generic situation, rather than on a waste-specific/site-specific
situation?
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-2-
3. To what extent have the models been verified, checked or peer-
reviewed? Details should be provided on models such as the Pope-Reid
model, or the Random-walk model, as used in their approach.
4. if the Subcommittee is to review/comment on applicability of certain
models (see questions asked), then detailed information shout the
models needs to be provided to the Subcommittee.
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APPENDIX D
TRANS - A Random Walk Solute Transport Model
for
Selected Groundwater Quality Evaluations
described in
GEOHYORQCHSMICAI, MODELS FOR SQLQTE MIGRATION
Volume 2: preliminary Evaluation of Selected Computer Codes
"L
EA-3417, Volume 2
Research Projects 2485-2, 1619-1
Final Report, November 1984
prepared by
Battelle, pacific Northwest Laboratories
Battelle Boulevard
Richland, Washington 99352
prepared for
Electric Power Research Institute
3412 Hillview Avenue
Palo, Alto, California 94304
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CODE:
SPONSOR:
AUTHORS:
PROCESS'AND
INTERACTIONS:
OPERATIONAL
ASPECTS.*
TRANS - A Random Walk*Solute Transport Model for Selected"Groundwater
Quality Evaluations
Illinois Department of Energy and Natural Resources
State Water Survey Division
Champaign, IL 61801
Thomas A. Prickett
Thomas A. Prickett and Associates
8 Hontclair Road
Urbana, tL 61801 ' -
Thomas G. Naymik, and Carl G. Lonnquist . •
Illinois Water Survey ,
Champaign, IL 61801
The processes .and interactions addressed by this code are:
* Saturated groundwater flow in a singled confined or
unconfined aquifer wnere water flow is typically
horizontal. " [The code addresses temporal variations
in two-dimensional U-y) flow for a variety of
boundary conditions and arbitrary x-y geometry.]
» Advectlon of a chemical contaminant in a saturated
groundwater system released from a variety of typical
sources,
* Hydrodynamlc Dispersion-(both lateral and transverse)
and diffusion of a chemical contaminant in a
saturated groundwater system, - ~ '
• Retardation of a chemical contaminant when it can be
characterized by a constant K^ and the assumptions of
instantaneous and reversible adsorption are adequate.1
* Rad1oaet1ve_decay of a -chemical contaminant.
There are two-ma in parts to .the TRAMS code:
transport calculations. ,
flow calculations and
Provisions for aquifer flow (potential or head) calculations are per-
formed in four ways. Two methods (subroutines HSOLV2 and HSOLY4)
compute head distributions for simple analytical problems. The third
method is through the HSQLYE subroutine, which 1s a subroutine fonrr
of the Prickett and Lonnquist* flow model. This model Is a.well.-
documented, finite difference, groundwater flow model for simulating
transient or steady-state groundwater flows in a water table or leaky
confined aquifer. The fourth method supplies the aquifer's head dis-
tribution through a user-supplied program. Any other acceptable
method or model can be used as long as head values are supplied for
the same finite difference grid used in TRANS and for the same
* Prickett, T, A. and C, G. Lonnquist. "Selected Digital Computer Techniques for
Groundwater Resource Evaluation," Illinois State Water Survey Bulletin SS, 1971.
A-67
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hydraulic conductivity and effective porosity distributions supplied
to TRANS. Velocity at every finite difference grid is calculated by:
V * KI/(7,48 n) . " " (A.4),
V = interstitial velocity
K = hydraulic conductivity
I * hydraulic gradient
n * effective porosity.
Velocity at any other position in the system is interpolate using
Chapeag-basis function* and the values at the finite difference grid
points. Stability requirements for the flow portion of the model
depend on the method chosen to develop the head (and subsequently the
• , • velocity) distribution. HSOLV2 and HSOLV4 are analytical solutions,
but one roust still ensure that adequate spatial, sampling of these
analytical solutions has been selected, HSOLVE uses a finite dif-
ference numerical scheme and a modified interative alternating direc-
tion method, MIADI, to solve for head distribution to a specified
level of convergence at each timestep. 'Adequacy of a soatial and
temporal time spacing can be checked in the same manner as for any
finite difference or finite element scheme, by reducing grid spacing
or timesteps and comparing results.
The transport model portion of TRAKS uses a direct simulation tech-
nique, The concentration of a chemical constituent in a groundwater
system Is assumed to be represented by a finite number of discrete
particles. Each of thest particles 1s moved according to the advec-
tlve velocity and dispersed according to random walk- theory. The
mass assigned to each particle represents a fraction of the total
mass of chemical constituents involved. In the limit, 'as the numoer
of particle approaches the molecular level, an exact solution to the
actual situation Is obtained. This kind of transport model is
inherently mass conservative. Convergence can be checked by increas-
ing the number of particles. There are restrictions, as with any
numerical method, which limit the size of Yimestep that can be taken
for both a time-dependent and spatially dependent problem, Timesteps
for particles are limited such that adjective plus dispersive move-
ment 1s no greater than the spacing between velocity (head) nodes.
APPLICABILITY ' ' ' '. /
ASPECTS: The TRAKS model allows the user to investigate growndwater pollution
problems from a vertically averaged viewpoint for contamiants
injected Into wells, leaching fom landfills or arising from surface-
water sources such- as ponds, lakes, and rivers. The documentation
for the TRANS program illustrates comparisons with theory for six '
problems: • ' .
1. Divergent flow from an injection well in an infinite
aquifer without dispersion or dilution
2. Pumping from a well .near a lint source of contami-
nated water, with dilution but without dispersion
3. Longitudinal dispersion in a uniform one-dimensional
flow with continuous Injection at X * 0
A-68
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Longitydinal dispersion in uniform one-dimensional
flow with i slug tracer Injected lt°JVo 10Ml
5" nJUSS??1 d1!P!rSion in * radial 'flow system
produced by an injection well
6.
at X - 0
longitudinal and transverse dispersion in a
one-dimemional.flw with a slug of tracer i
flv A - U
»,iittdj]t!!nt *?e ^"'"en^tibn illustrates the use c
real fleld-scale contaminant problem at Merodosia! 1
SECONDARY
COKSIDERA-
'TIONS:^ • Purpose mi Seooe
ite fhM Unfilled and other £,££ "nl ?nJec??L of.H^ each'
4.
Numerical finite difference solution(HSOLY£} to the
two-diroensional x-y) vertically averaged
1S S°1Uti0n iS '- ?
User-supplied subroutine for reading or
A-69
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artesian source, Induced infiltration {I.e., streams, lakes, and
rivers), held-head boundary conditions, flow from springs, and evapo-
transpiration front the water table.
Operational Characteristics
The TRANS code is written in FORTRAN and run by the authors on a CDC
CYBER-175.* The code, for purposes of this study, was run on a Digi-
tal Equipment Corporation VAX 11/780. Other, than changes to the pro-
gram header, logical1 unit checker, and formatted character strings
{which were all CDC-specific practices); conversion to the VAX '
required access to a system specific random number generator. A
similar but not equivalent-random number scheme was Implemented. The
authors indicate that, the test problems included in the documentation
examples took no more than a few seconds of CPU time, including com-
piling and loading on their CDC CYBER-17S. TRANS used 140,800 bytes
of virtual memory on the VAX; 10,363'central processing seconds were
needed to perform the test problem simulation.. The code, as docu-
mented, is dimensioned for.a 29 x 30 finite difference grid and
5000 particles. These dimensions can be changed* however, to accom-
modate larger problems.- Some difficulties nay be encountered because
instructions for increasing dimensions-are not specifically discussed
in the documentation.
Input Requirements
Input requrentents for.thercode are explained with both appropriate
text and in pictorial form' {Figures 9, 10, 11, and 12 of Prickett
et al.*). Input requirements for the code are those typically avail-'
able from standard field or laboratory -measurements. For- the flow
portion of the model they include:
« A variable finite difference grid description
• Timestep and number of tfmesteps to be run
* Areal distributions of
—Permeability
—Source aquifer potential for leaky artesian
simulations
—Aquifer bottom elevations .
—Aquifer top elevations
—Head .{initial conditions)
—Aquitard thickness *nd permeability for leaky: -
. artesian aquifers "
—Simulations
—Artesian and water table storage coefficients
* Pumping and recharge well locations and temporal
rates
« Stream (river .or lake) node locations, surface-water
elevations, stream or lake bed thickness and permea-
bility, fraction of node area available for transfer
* Constant head node locations and elevation for held
head
Pnckett, T, A., T. G. Namik, and C. G. Lonnquist, "A Random-Walk Solute
Transport Model for Selected Sroundwater Quality Evaluations," Illinois State
Water Survey Bulletin 65, 1981.
A-70
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f ?PHft9s* elevation at which spri
s-pnng Production line
water if *!° Jes*here evapotranspi ration from the
water table is to be considered and the slope of the
rate versus head line and the water-table elevation
evapotransP1>ati^ «"•«. areto be
For the transport model', additional input requirements include:
Longitudinal dispersivity
lateral dispersivity
iffectlve.porosity
Actual porosity
Retardation factor or KH
Bulk mass density of,porous medium
Location and concentration of sources, description of
ennr'^a rtn««.,',•_.. i. » , , *•« ^vj, wcsui I p L i Un OT
of
Output Result
you concise and
Hne ppintr ots S L» C°K6 BChOS input P^^ters and produces
The c£l^lI0Pi£2 •?! S*d* "U1ISberS Of P^^1"- a"d concentrations.
and or2nnc 15 !P?r%S the Concerttrat1on of water entering sink nodes
Numerical Approximation^
The general flow problem solution available with this
solves for head distribytiorj in a leal^y artesian
-aquifer for t heterogeneous, inlsdtVopIc |iopouf
«ods b«,d«
K2S nasrs-i
oCtvH " 9f1d blocks is *"1n«'. ^ * ««
velocity midway between each grid b1ock is aiculatefl by
A-5)
A-71
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where
V * Interstitial velocity
K = hydraulic conductivity
I = hydraulic gradient
n * effective porosity.
The raidgrid- block X and Y direction velocities are then used in a
bilinear interpolation scheme to estimate the velocity at any
arbitrary location (x,,y).
Transport is simulated by a direct simulation technique which-
involves movement of contaminant mass particles according to the con-
nective velocity as Interpolated from the conveetive velocity field-
described above, ' Dispersion ts simulated by random walk methods, 'In
the ,nmn, as the number of particles gets extremely large (I.e.,
when the number of particles approaches the level at .which each
particle represents a molecu-le), an exact" solution to the actual
situation 1s obtained.
As sufflptl ons and Si mo 1 i f 1 cat i on
We address the flow and transport separately. The principal assump-
tions regarding flow are;
* Darcian flow is assumed.
« Flow In the aquifer ,1s horizontal and controlled only
by hydraulic head- gradients.
» Leakage between the simulated aquifer, rivers, lakes,
other aquifers, and springs is a 1-inear function of
head difference with the slope of this relationship
determined from the leakance -parameter, K/m, where K
is the permeability of the aquitard (or stream bed)
and m is the thickness.
9 Storage in the stream, lake, or river beds and
aquitards is ignored.
The principal assumptions regarding contaminant transport are:
• The ad vection-d1f fusion equation for selute transport
is assumed valid*
» ._ els-person in porous media is a random -process ,-•:
» Retention of a contaminant (or retardation of a con-
centration front) may be represented by an instantan-
eous and reversible sorption process.
st.l c or Statistical Aspects
The code solves i deterministic problem. .
Available Documentation
McDonald, M. G., and W. B. Fleck. -"Model Analysis of the Impact OR
Sroundwiter conditions of the Husktgon County Waste-Witer Disposal
System, Michigan." U.S. Geological Survey Ooen-File Report 78-79,
1978. '
A-72
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Water Survey
PHckett, T. A., T. G, Namik, and C, S. Unnquist. "A
Solute Transport Model for Selected Gr.oundwater Quality
minors State Water Survey Bulletin 65, 1981.
Software Quality
Sref XnSlS? ^"^ *»••*'" V™W** 20 subroutines, and "
" 1$ "*" ««not«ted and the documen
GENERAL . '
CRITIQUE: The documented verification ten cases we're easy to set up and
repeat; however, direct checking of the results is no? pSsSle
as-
g.c
explains the vertically avenged solution for transient or steady
flow. From an applfcatfan point of view, the TRANS documents are
difficult to follow. Examples are weak and the MrrattvedSertS.
™L3rf "°* stff fhtforward. However, excellent code anSout Sn
compensates for limitations of the user's manuals*
?4ost of the data required by TRANS fs typical groundwater survey
information. The exception 1s the source term for the transport
simulation, which needs a parcel release rite. This rate may be dif
ficult to quantify for someone unfamiliar with 'random walk' models.
TRANS Js very flexible with respect to problem configuration- thus
no modifications to- the specified geometry were necessary. There *
were no, problems encountered while- running t*e code.
A-73
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