-€&. -8 3"- * ^ 8
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       I          UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
       3
       c                        WASHINGTON, D.C.  20450
                                       July 31, 1985
       HOH. Lee M« ThomaS                                            THE ADMINISTRATOR
       Administrator
       U. S* Environmental Protection Agency
       401 M Street, S. ¥.
       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 hazardous wastes should be 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 OSW version, and are pleased to now forward our review
       of the One proposed by OF A.

       The Committee agrees that 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 OPA staff, and we are pleased to note that they have already taken steps
       to implement some of the Committee's reeomftendations •

       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. Morgeastern
           S* Napolitano
           A. Fisher
           J, Briskin
           A. Carson                                  Norton Nelson
           S. Brorom                                   Chairman, Executive Committee
           T. Yosie                                   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 decision-
makers 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 fora, as characterized by comparative risks and costs among
the chosen scenarios.  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.  Among these are the use
of a non-threshold model (which introduces problems when considering chemi-
cals which may have threshold effects)j the ignoring of pharmacokinetic
effects and compound interactions; and inadequate lexicological evaluation
and extrapolation techniques, especially simplistic temporal, route~to-route
and species-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 QPPE method needs upgrading in the area of surface drainage
modeling and most importantly in the risk assessments related ^to the handling
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.  Howevert we are in-
formed by OPPE that improvements are being made.

     It is important to note that QPPE 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 OPPS 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-
stive 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 AMD HISTORY

     At a meeting of the Environmental Engineering Committee on August 16,
1984, Mr. Alan Gorgon, 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
model), 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 aa 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, Die. Richard D. Morgen-
stern, Director, Office .of Policy Analysis, OPPE, 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 OPPE model.  Dr. Nicholas Nichols, Dr. Ann Fisher, 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 pr. Terry Yosie, Sjtaff Director, SA|i} .on behalf 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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                                 -3-
III.  DESCRIPTION AND EVALUATION OF THE MODEL

     As a result of the recent (11/84) amendments to the Resource Conserva-
tion and Recovery Act (ROM), 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 toi (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 utilized 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 concernt 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 waste 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 permit decision-makers to take these ranges into
account.

     The Pilot Study considers for Illustration three wastes, with four or
five scenarios lot management of each.  While its potential utility and po-
tential versatility were reasonably well represented in the pilot study,
the method as presented represents m still-prelimiiwty approach.


IV.  EVALUATION OF'THE METHOD'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 may
     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 QPPE 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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      Tha 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 seme
 manner.   The approach can provide information concerning:  (a) pretreat-
 tnent alternatives that can  be considered before  land disposal, (b) the
 relative impact of other disposal alternatives on protection of huoan
 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 waste
 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 judgment to  support such  a detailed study, and for
 its wisdon of continued support  for the study.   The study clearly has
 had good intellectual input, the individual cernponents appear sound, and
 reasonable estimates of potential health risks appear to have been ob-
 tained.   The study also has considerable fallout value.  Even if rot
 applied solely to the banning, decision, the technique developed will be
 useful in many other situations.   The  task of risk assessment is to make
 the most credible possible  statements  about definable relationships,
 reducing uncertainty, and making explicit  whatever uncertainty remains.
 Ihis study accomplished these goals.

      However, in terms 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 on
 those major wastes that may be banned  from land  disposal in order to
 protect human health and the envirorment.  Such  major wastes could be
. those .that-are o.f large volume,'  are of unique .characteristics, may have   •
 an apparent adverse economic impact on an  industry if banned fran land
 disposal, and/or appear likely to cause a  potential adverse human health
 and environmental 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  Mninistrator with a richer
 array of information on relative risks, intemedia transfer or costs
 when making decisions about which wastes should  not be banned from land
 disposal.

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                            -5-
B. Components o£ the Model and Model  Linking

     I, Randan Walk Solute Transport  Model

          The Random Walk model was selected  to predict  two-dimensional
     contaminant transport in groundwater aquifers,   The horizontal  flow
     field in the aquifer is computed 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 adveetive transport  for each particle follows the flow
     field ard 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 manber of particles  becomes
     large) be identical to that obtained with more  traditional, two-
     dimensional advective-dispersive models  .using finite  difference
     or finite element 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
          Ihe Random Walk model has been teed in many applications and is
     a well recognized tool, for example, through its use as part of the
     program of the Bolccmb Qroundwater 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 chemical 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 Rjwer Research institute (Kincaid and Morrey, 1984).  A
     sum-nary of this Rardcm Walk review is included as Appendix D,  Based
     on the EPRI analysis and a review of the Handera Walk Model by the
     Comdttee'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,, storatiyity, etc. ,, As mentioned. in   ,. ,^  .
     the QPPE 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 "solutes11..* consti-
     tuents which undergo no chemical transformation.  Ihe reaction and
     adsorption caoponents of the model, however, -are much more limited*
     In particular:

          a.  In the Random Walk model, both the reaction rate and the
          adsorption (retardation) coefficient are constant over
          the agaifer study area.  Heterogeneity in soil conditions
          which might affect these factors is not considered.

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                           -6-
     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
     modifications 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 groundwatei: models today, they may be
   .. used in the future as 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 recognised.  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 adveetive—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 models,
arri 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
groundwater mode 1,_ regards the limited lev^l of validation, j?arti-
cuiarly 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 Unsaturated 2one 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 OPPE

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examples by considering only the hydraulic residence time in the
unsaturated zone associated with the computed recharge rate.  Shis
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*
&s noted in the OPPE report and the supporting MRl documents, there
are models available for the unsatnrated zone, such as the analy-
tical PESTAN 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 eases, and plume-depletion and par-
ticle deposition processes.  The selection of the Industrial Source
Complex (ISC) 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 i$ 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
in Gaussian plume modeling, there has been concern expressed among
SAB 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 form:

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-taagnitude" judgments of
uncertainty bounds.  There may, however, be a need for a more 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, 2;  Have the models been integrated
(combined) without violating scientific principles? Is the integra-
tion consistent with the state-of-the-art?}*

     Two issues taay 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 zero 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 OPFS 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 QPPE report), then 84% seems too low
for an "upper limit."  The OPPE has indicated that it concurs with
this suggestion and intends to use a wider confidence interval.

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                            -9-
C. Toxicologies! 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 asses$«nt 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 (Jose/response
functions for only a single effect, usually cancer» or are restricted
to the estimation of an acceptable exposure limit (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 OPP1 methodology include:  The use of a.
non-threshold model for all effects, the use of maximum likelihood esti-
mates, and simplistic temporal, route~to-rotite, 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 (matheraatic 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 pharnacoklnetlcs and compound interactions will 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 OPPE study attempts to address the risks from 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, OPPE 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 transported, 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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                                -10-
E. Application of the Model

     The Committee is concerned that many of the specialized models (ot
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. 0, Box 8361 (770/3423
South Charleston, WV  25303

Dr. Benjamin C. Dysart, III
Environmental Systems Engineering Department
401 Rhode? Engineering Research Center
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 s Robert
llth Floor
St. Paul, MN ' 55144

Dr. Raymond C. Loehr
Civil Engineering Department
8.614 ECJ Hall
University of Tfexas
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
D£, Marc Anderson
Water Chemistry
660 North Park Street
University of Wisconsin
Madison, WI  53706

Dr. Paul £. Brubaker, Jrt
Paul E. Brubaker Associates, Inc
3 Halstecwl Road
Mendham, NJ  07945

Mr. Allen Cywin
Consultant
1126 Areturus Lane
Alexandria* VA  22308
Dr. Patrick R,
Syracuse Research Corporation
Merrill Lane
Syracuse, NY  13210

Dr. Charles F. Reinharctt
Haskell Laboratory for Toxicology &
 Industrial Medicine
I. I* du Pont <3e 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
O.S. Environmental Protection Agency
Science Advisory Board  (A-101 F)
Washington, D.C,  20460

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                                                               APPENDIX B
jjuestions for _SAB

     1.  Because of the many steps in the health risk assessment process,
         several models were used.  Is the tige 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 ground-water movement;

          c.  The Industrial Source Coaplex Bong-Term model for dispersion
              of air emissions from area
          d.  The ATM component of GEMS for dispersion of air emissions from
               point sources;

          s.  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 acceptable "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 OPP! Method

Following are basic questions to which the Subcommittee can respond or comments

 1 .  Specific questions related to the specific model/approach with respect
     to its scientific, fundamental credibility (basically, is the approach
     scientifically sound}.

 2.  Is this model/approach likely to address the important questions facing
        , i.e. will the correct need be
Generally, the SAB is asked to respond to type (1) questions.  Shis 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 :

     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/QC, 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 landfilj.?

It seems that these types of questions also should be addressed by the Sub-
committee.

If the Subcommittee decides to address some 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-
derations

     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-$pecific
         situation?

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                                -2-
3.  To what extent have the models been verified, cheeked 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 sbout the
    models needs to be provided to the Subcommittee.

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                                                      APPENDIX D
        TRANS - A Random Walk Solute Transport Model
                            for
          Selected Grouiidwater Quality Evaluations
                        described in



        GEOHYDRQCHEM1CM, MODELS FOR SOLOTE MIGRATION

Volume 2: Preliminary Evaluation of selected Computer Codes-


                     EA-3417, VOluiae 2
              Research Projects 2485-2r 1619-1

                Final Report, November 1984


                        prepared by
          Battelle, Pacific Northwest Laboratories
                     Battalia Boulevard
                Richland, Washington  99352
                        prepared for
             Electric Power Research Institute
                    3412 Hillview Aventte
               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  S1801

Thomas A. Prickett
Thomas A. Prickett and  Associates
8 Monte!air Road            "      .
Urbana, IL  61801          "   •

Thomas S. 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 where water'flow is typically
           horizontal. ' [The code addresses temporal variations
           in two-dimensional (x-y) flow for a variety of"
           boundary conditions and arbitrary x-y geometry.]

      *    Adygctio_n. of a chemical contaminant in a saturated
           groundwater system released from a variety of  typical
           sources.	

      *    Hydrodynamic Dispersion-(both  lateral and transverse)
           and diffusion of  a chemical contaminant  ;n a
           saturated groundwater  system.              -  -

      *    Retardation of a  chemical contaminant when it  can be
           characterized by  i constant IC^ and the assumptions of
           instantaneous and reversible adsorption ire adequate.

      *    Radioactive decay of a "-chemical contaminant.
 There, are  two :m in  parts  to _the_.TRANS  code: 7 flow calculations  and..-  :
 transport  calculations.

 Provisions for  aqyifer  flow  {potential  or head)  calculations  are  per-
 formed  in  four  ways.  Two methods  {subroutines  HSOLY2  and  HSOLV4)
 compute heid  distributions for simple,  analytical  problems.  The third
 method  is  through the K50LYE  subroutine,  which  1s a  subroutine  fona'
 of  the  Prickett and Lonnquist* flow model.  This model  1s  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 §rid 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 55,  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)-

              where
                    V - interstitial velocity
                    K * hydraulic conductivity
                    I » hydraulic gradient
                    n - effective porosi.ty.

              Velocity at  my other  position in the system is Interpolate using
              Chapeau-basis  functions  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  HSQLV4 are analytical solutions*
              but  one must 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, MlADl, to solve  for  head distribution to a specified -
              level of convergence  at  each  timestep.  Adequacy of a spatial 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 TRAHS 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 these particles Is moved  according to-the advec-
               tive velocity and dispersed according to random walk- theory.  The
               miss assigned to each particle represents a fraction of the total
               mass of chemical  constituents involved*  In the limit,"as the number
               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 "timestep that  can be taken
               for both a time-dependent and spatially dependent  problem*  Tiroesteps
               for particles are limited such that advective plus dispersive move-
               ment 1s no  greater than  the  spacing between velocity (head) nodes.

APPLICABILITY              ,               •
ASPECTS:       The TRANS model allows 'the user  to investigate groundwater 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 in  infinite
                         aquifer without  dispersion  or  dilution

                    2,   Pumping  from  a well near  a  line source  of  contami-
                          nated water,  with  dilution  but without  dispersion

                    3,    Longitudinal  dispersion in  a uniform one-dimensional
                          flew with continuous injection at X = 0
                                         A-68

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 SECONDARY
 CONSIDERA-
TIONS;   -
                    4.    Longitudinal  dispersion in uniform one-dimensional  •
                          flow with a slug tracer injected at X = 0

                    5,    Longitudinal  dispersion in a radial 'flow system
                          produced by an injection well

                    6.    Longitudinal  and transverse dispersion in a uniform
                          one-dimensional  flow with a slug of tracer injected
                          at X = 0

                In addition, the documentation illustrates the use of the model for a
                real  field-scale contaminant problem at Merodosia, Illinois.
Purpose and Scope

The purpose of this code  fTRANS), as stated by- the  authors,  is  to
provide a generalized computer code that can  simulate a  large class .
of problems Involving convection and dispersion  of  chemical  contami-
nants associated with fertilizer applications, hazardous waste  leaeh-
ate from 1andf111ed and'Other sources,  and injection of  chemical
waste into the subsurface using disposal wells.   TRANS does  not
address density-induced convection.  Concentration  distribution in
the aquifer represents a-  vertically averaged  value  over  the  saturated
thickness of  the aquifer.

TRANS addresses only  a  single aquifer.  Spatial  and temporal distri-
bution of head  in  the aquifer can be calculated  by  four  methods;

     1.   Analytic (HSOLV2) solutisi for  a uniform  1-ft/d flow
          in  the x direction                             '   '

     2.   Analytic (HSOLY4) solution to the  Tneis formula cen-
          tered at node (IS, 15)

     3.   Numerical  finite  difference  solutionCHSOLVE)  to the
          two-dimensional (x-y)  vertically  averaged groundwater
       •  '  flow equation*  {this solution  is  for transient or
           steady-state  flow)

     4*   User-supplied subroutine  for reading or calculating
           head"on  the finite-difference grid used in the TRANS
           transport model.

 The TRANS code was designed to solve real  pollution problems and to
 address only single contaminants-  TRAMS can also handle (with  slight
 changes in subroutine calls! radioactive decay and chemical  retarda-
 tion.   The modifications required for decay are clear but those
 required for retardation are unclear.   The code can handle  contami-
 nant source or sinks at  every node as well  as a variety of  special
 sources, which include points, rectangles, circles, and lines.   The
 flow model  can handle impermeable boundaries {no flow), leaky
  * Priekett, T. A., T. G- Namik, and C. 5- Lonhnquist,  "A Random-Walk Solute
  Transport Model for Selectee! Groundwater Quality Evaluations."  Illinois State
  water Survey Bulletin 65, 1981.

                                          A-S9

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              artesian  source,  induced Infiltration {I.e.,, streams, lakes, and
              rivers),  held-head boundary conditions, flow from springs, and evapo-
              transpiration from 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 Dig1- .
              tal Equipment Corporation VAX 11/780,  Other, than.changes to the pro-
              gram header, logical' unit checker, and formatted character strings
              (which were §11 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-175.  TRAKS 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 may be encountered because
              Instructions for  increasing dimensions-are not specifically discussed
              in the documentation.

              Input Requirements

              Input reqyresents for,the:code are explained with both appropriate
              text and  in  pictorial  form (Figures  9, 10t  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  timesteps  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 .and .permeability  for  leaky-  ....      _. -
                          . artesian aquifers "
                         —Simulations
                         —Artesian and water  table storige coefficients
                    »    Pumping and recharge  well  locations  and temporal
                         rites
                    *    Stream {river.or lake)  node locations,  surface-water
                         elevations, stream or lake bed thickness and  pensea-.
                         bility* fraction of node area  available for transfer
                    *    Constant head node locations and elevation for held
                         head
* Prickett,, T, A.» T, G. Naiwik, and C. S. Lonnquist.  "A Random-Walk Solute
Transport Model for Selected Groundwater Quality Evaluations."  Illinois State
water Survey Bulletin 65, 1981.
                                        A-70

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     *    Locations of springs, elevation  at  which  spring flow-
          begins» and slope of the  spring  flow  versus  ground-
          water head for the spring production  line
     »    Locations of nodes where  evapotranspiration  from the
          water table is to be considered  and the slope of the
          fate versus head Hne and the  water-table elevation
          at which evapotranspiratIon  effects are to be
          ignored.

FOP the transport model, additional .Input  requirements include:

          Longitudinal dlspersivity
          Lateral dispersivity
          Effective.porosity
          Actual porosity
          Retardation factor or K^
          Bulk mass density of.porous  medium
          Location  and concentration of  sources, description of
          source geometry,  and1 selection- of method for release
          of particles
     •    Sink  locations  arid  grouping of sink locations for
          sujwnarizing: outflow  versus time results.

The  model contains  no checking of input  for consistency and automatic
termination  for  faulty  or  inconsistent inputs.

Output  Results    '  •   '   -   x.

Results ire  printed in1 a~'132-eharacter format w.ith a concise and
readable  output  layout.   The  code echos  input parameters and produces
line printer plots  of head,  numbers "of particles, and concentrations.
The  code  also  reports  the concentration  of water entering • sink nodes
and  groups  of  sink  nodes versus time.  The code produces no contour
maps or output  fields  that can be passed on to other computer system
programs  for plotting and produces no mass balance summaries for
water flow  or  transport,

Numerical Approximations

The  general  flow problem solution  available with this code  (HSQL-VE)
 solves for head distribution in a  leaky artesian or water-tabT_e
 aquifer for a heterogeneous, anisotropie -porous medium with irregular
 boundaries.   The ac*-«al system" is  approximated by finite difference
 methods based on a block-centered,  variable  finite difference grid,
 Hedium properties in each grid block  are assumed to be uniform.
 Approximation of the partial differential equation at each  grid block
 by finite difference methods results  In N equations 1n N unknown,
 where N is the number of grid blocks  representing the aquifer.. Time
 derivatives are estimated by an implicit finite difference  method* '
 and the water-table problem that results  in  nonlinear equations is
 solved by the modified iterative alternating direction implicit
 (MIAO!) equation-solving method.

 Once head distribution at the N  grid  blocks  is  obtained,  the X and Y
 direction velocity midway'between  each  grid  block  is  calculated by

                    .                                            (A-5)
                           A-71

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where

      V = interstitial  velocity
      K. = hydraulic conductivity
      1 = hydraulic gradient                .              "        t
      n - effective porosity,                                    "  •

The midgrid-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-
vective  velocity  as interpolated  from  the convective velocity fie-ld-
described above,  "Dispersion is simulated by random walk methods. In
the .limit,  as the number of particles  gets extremely large (i.e.,
when  the  number of particles approaches the level at .which each
particle  represents  i molecule),  an exact' solution to the actual
situation is ^obtained.

Assumptions and Simplification

We address  the flow and transport separately*  The principal assump-
tions regarding flow  are:

      *    Darcian flow ts 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  14near 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.
      »    Storage in the stream,  lake, or  river  beds and
           aquitards is ignored,

 The  principal  assumptions  regarding contaminant  transport are;

      »    The  advection-diffusion equation  for solute transport
           is assumed valid.
      »    Dispersion in porous media. 1s  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.

  Probabilistic  or  Statistical Aspects

  The  code solves  a deterministic  problem.

  Aval 1able  Documentation

  McDonald,  M. G.»  and W. B. Fleck.  '"Model  Analysis  of  the  Impact on
  Sroundwater conditions of the Huskegon County Waste-Water  Disposal
  System,  Michigan."   U.S.  Geological Survey Open-File Report  78-79,
  1978.
                           A-72

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              Priekett,  T.  A.,  and  C. 6* Lonnquist.  "Selected Digital "Computer
              Techniques for Groundwater Resource Evaluation."  Illinois State
              Water Survey  Bulletin 55, 1971.

              Prickett,  T.  A,,  T« G. Namik, and C. G. Lonnquist,  "A Randoo-Walk  .
              Solute Transport Model for Selected Groundwater Quality  Evaluations."
              Illinois State Water Survey Bulletin 65, 1981.

              Software Quality

              The modular code consists of a-main program, 20 subroutines,  and
              three functions.  The code listing- Is well annotated  and the  documen-
              tation report contains a complete  description of each modulet  along
              with flow diagrams-.  Transfer of this program from  one machine to
               another should be fairly easy.  The code lacks any  graphical  output
              capability other than line printer plots.  In addition,  no routines
               are supplied to dump model output  to disk files for use  with
               generally available computer system plotting routines*

GENERAL     .
CRITIQUE:      The documented verification  test cases we're easy to set  up and
               repeat; however, direct  checking of the results is  not possible
               because a different random number  generator is used on our computer
               system.  The  code'does  not produce any mass balance summaries.
                    *' •

               In order  to  use the generated  flow option of  the TRANS code,  one  roust
               obtain  Bulletin 55  from the^Illinois  State Water Survey, which
               explains  the vertically averaged solution for transient  or steady
               flow.   From  an  application point of view, .the, TRAMS documents are
               difficult to follow.   Examples are weak and the narrative descrip-
             '  tions  are  not straightforward. However,  excellent  code  annotation
               compensates  for  limitations  of the user's manuals.       - .

               Most of the  data  required by TRANS is  typical groundwater survey
               information.  The  exception is the source term  for  the  transport
               simulation,  which  needs a parcel  release  rate.  This  rate may be  dif-
               ficult to quantify for someone unfamiliar with  'random walk'  models.

               TRAMS is  very flexible with respect to problem  configuration; thus,
               no modifications  to-the specified  geometry were  necessary,   There
               were no problems  encountered while running  the  code.
                                         A-73

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