United States Science Advisory EPA-SAB-EEC-94-002
Environmental Board (1400F) November 1993
Protection Agency
&EPA AN SAB REPORT: REVIEW
OF MMSOILS COMPONENT
OF THE PROPOSED RIA FOR
THE RCRA CORRECTIVE
ACTION RULE
REVIEW OF THE OSWER & ORD
DRAFT DOCUMENTATION AND.
USER'S MANUAL AND RIA OF
THE MMSOILS MULTIMEDIA
CONTAMINANT, FATE, TRANSPORT,
AND EXPOSURE MODEL
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
November 19, 1993 OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD
EPA-SAB-EEC-94-002
Honorable Carol M. Browner
Administrator
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
Re: Review of MMSOILS Component of the Proposed Regulatory Impact Analysis (RIA) for
the RCRA Corrective Action Rule
Dear Ms. Browner:
The Science Advisory Board (SAB) is pleased to submit its report on review of the Agency's
draft document entitled "MMSOILS: Multimedia Contaminant Fate, Transport and Exposure Model
Documentation and User's Manual," dated September 1992. The MMSOILS (Multi-Media
Contaminant, Fate, Transport and Exposure Model) document was developed jointly by the Office of
Research and Development's (ORD's) Office of Health and Environmental Assessment (OHEA),
Exposure Assessment Group (EAG) and the Office of Environmental Processes and Effects Research
(OEPER). This report by the MMSOILS Model Review Subcommittee (MMRS) was prepared as part
of the SAB's review of the "Draft Regulatory Impact Analysis for the Final Rulemaking on Corrective
Action for .Solid Waste Management .Units: Proposed Methodology: for Analysis.". Our report
resulted from the MMRS public reviews on April 22 and 23 and June 29, 1993.
The Agency, through the Office of Solid Waste and Emergency Response (OSWER) asked the
SAB to review specific elements of the multi-media contaminant fate, transport and exposure model,
MMSOILS, with regard to the methodology used to predict contaminant concentrations in the
environment and the resultant implications on human health and ecological risk assessments.
Specifically, the review dealt with:
a) the adequacy of methods for using a screening level model where there is substantial
subsurface heterogeneity and/or where nonaqueous phase liquids (NAPLs) are present,
b) the appropriateness of the Agency's approach for aggregating releases from solid waste
management units (SWMUs) in order to estimate concentrations at exposure points as a
function of time, and
Recycled/Recyclable
Printed on paper that contains
at least 75% recycled fiber
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c) the adequacy of the Agency's approach for developing long-term effectiveness and
failure scenarios for site remedies.
The OSW/ORD working group is to be commended for a well-coordinated and focused effort to
develop a regulatory impact analysis (RIA) that will help the Agency and the Nation better understand
the costs and benefits of the proposed rule. The Subcommittee wishes to recognize the responsiveness
and progress made by the OSW/ORD working group to many of the recommendations made at the April
22-23, 1993 meeting and candidly displayed in detail at the June 29, 1993 meeting. The Subcommittee
appreciates and recognizes the significant effort expended to date, the positive attitude and open candor
displayed by the OSW/ORD working group in their presentations and interactions during the two review
meetings. The Subcommittee considers the intraagency coordination represented by this RIA to be a
"model approach" that the Agency would do well to adopt in other programs.
On the positive side, the Subcommittee observes that MMSOILS uses simple, conservative, and
computationally efficient equations for estimating chemical transport via ground water, surface water,
soil erosion, atmospheric, and food chain pathways. Pathway documentation is well organized with
appropriate references. Applied mathematical formulae are widely used and accepted by the scientific
community for use in simple situations. Underlying assumptions have been identified, clearly stated,
and appear to be reasonable yet not overly restrictive. Given these strengths, MMSOILS, when applied
to simplified case studies, might certainly be a valid screening tool for assessing the relative risks and
costs associated with alternative regulatory options.
However, the Subcommittee notes that two problems create unquantifiable uncertainties that
seriously diminish the utility of MMSOILS relative to its use in the draft Corrective Action Regulatory
Impact Analysis (RIA), namely:
a) inaccurate input parameters; and
b) application of the model to cases outside its range of validity.
Inadequate input data are a consequence of sparse or inaccurate information, poor parameter
estimation especially relative to source terms, and suspected over-reliance upon default parameters. The
Subcommittee recommends a documented and thorough peer review of all aspects of the data base,
focusing particularly on those parameters to which the results are most sensitive.
Equally serious is the inappropriate application of the MMSOILS model to scenarios for
which it was not intended, such as sites with complex hydrogeological conditions or sites where NAPLs
are present. To some extent, as discussed in the Subcommittee's full report, the latter could be
addressed
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by means of appropriate revisions to model formulations. However, for a significant number of sites,
the Subcommittee suspects that no generic model is likely to provide answers of acceptable quality.
OSWER is generally aware of the limited usefulness of generic models for the analysis of complex
environmental settings.
The Subcommittee also observes that uncertainty analysis for the RIA is in its infancy and will
require much greater effort to meet the needs of the assessment process. Given the high stakes involved
in terms of potential commitment of national resources, defensible estimates of the uncertainties
associated with risks and benefits are critical, and the protocol followed to obtain such estimates
deserves as much forethought and careful peer review as that required to obtain the central estimate. As
a related issue, the Subcommittee is concerned that the simple protocol followed to obtain high-end risk
estimates may be inadequate in that these estimates in some cases apparently gave rise to lower
exposures than did the central tendency estimate.
Given these serious shortcomings, many of which were already recognized by the Agency, the
most basic and pressing concern of the Subcommittee is whether the use of a generic model such as
MMSOILS is appropriate as a basis for the assessment of regulatory costs and benefits at the national
level, given the fate and transport estimates that comprise the model output may be wrong by orders of
magnitude for many complex sites. We recommend that the Agency:
a) augment its RIA with cost/benefit estimates derived by alternative approaches, such as:
1) utilizing assessment data generated for Superfund sites,
2) using more sophisticated models with better-defined data to develop estimates for
representative sets of waste sites, or
3) applying site-specific models to analyze that relatively small number of facilities
which MMSOILS results indicate dominate the total costs or risks, and
b) at a minimum, expert review of the latter cases should be undertaken to judge the
reasonableness of model outputs.
This augmentation should help validate the present reliance on the screening studies that use MMSOILS
model output as a starting point.
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The SAB appreciates the opportunity to comment on the EPA's MMSOILS model. We are
gratified that the Agency has brought this issue before us and look forward to receiving a summary of
the EPA's response, particularly to the points raised in this letter to you.
Sincerely,
C,
Dr. Raymond C. Loehr, Chair Mr. Richard A. Conway, Chair
Executive Committee Environmental Engineering Committee
S ci ence Advi sory B oard S ci ence Advi sory B oard
Dr. C. Herb Ward, Chair
MMSOILS Model Review Subcommittee
Environmental Engineering Committee
Science Advisory Board
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NOTICE
This report has been written as a part of the activities of the Science Advisory Board, a public advisory
group providing extramural scientific information and advice to the Administrator and other officials of
the Environmental Protection Agency. The Board is structured to provide a balanced, expert assessment
of scientific matters related to problems facing the Agency. The report has not been reviewed for
approval by the Agency; hence, the comments of this report do not necessarily represent the views and
policies of the Environmental Protection Agency or of other federal agencies. Any mention of trade
names or commercial products does not constitute endorsement or recommendation for use.
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ABSTRACT
The MMSOILS Model Review Subcommittee (MMRS) of the Environmental Engineering
Committee (EEC) of the EPA Science Advisory Board (SAB) has prepared a report on the Agency's
Office of Solid Waste (OSW) MMSOILS Multimedia Contaminant Fate, Transport, and Exposure
Model. This model and guidance document was developed as a technical resource for estimating
potential health risks at sites contaminated by toxic wastes or spills of toxic chemicals.
The review by the SAB's MMRS dealt with the adequacy of methods for using a screening level
model where there is substantial subsurface heterogeneity or where non-aqueous phase contaminants are
present, the appropriateness of the Agency's approach for aggregating releases from solid waste
management units (SWMUs) to estimate concentration at exposure points over time, and the adequacy
of the Agency's approach for developing long-term effectiveness and failure scenarios for site remedies.
The general consensus of the MMRS was that the use of a multimedia pathway model for
screening purposes could be an appropriate approach for developing risk and cost estimates for a
national-level Regulatory Impact Analysis (RIA), as long as the input parameters are accurate and the
model is not applied outside its range of validity. Furthermore, the Agency's use of a single model, to
the extent defensible for each facility considered, was viewed by the MMRS as necessary in order to
ensure consistency among model results. The major overriding concerns of the MMRS were: a)
application of MMSOILS outside its range of validity; b) large uncertainties in input parameters; c)
consequent large uncertainties in MMSOILS results; d) clear communication of this uncertainty to
decision-makers; and e) presentation of the results in the draft RIA document in a scientifically
defensible manner that communicates the uncertainties of the calculations and their implications for the
cost/benefit analysis.
The MMRS recommended that the Agency augment the MMSOILS results with cost/benefit
estimates derived by alternative approaches, such as utilizing assessment data generated for Superfund
sites, using more sophisticated models with better-defined data to develop estimates for representative
sets of waste sites, applying site-specific models to analyze that relatively small number of facilities
which MMSOILS results indicate dominate the total costs or risks, and submission of selected case
studies to expert panel review.
Key Words: Mathematical Models, Cleanup, Corrective Action, Regulatory Impact Analysis, RCRA
Models
11
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U.S. ENVIRONMENTAL PROTECTION AGENCY
Science Advisory Board
Environmental Engineering Committee
MMSOILS Model Review Subcommittee
CHAIR
Dr. C. Herb Ward, Professor and Director, Energy and Environmental Systems
Institute, Rice University, Houston, TX
VICE CHAIR
Dr. George F. Carpenter, Environmental Quality Manager, .Environmental
Response Division, Michigan Department of Natural Resources, Lansing MI
MEMBERS AND CONSULTANTS
Dr. Steven M. Bartell, Vice President, Center for Risk Analysis, SENES Oak
Ridge, Inc., Oak Ridge, TN
Dr. Randall J. Charbeneau, Professor and Director, Center for Research in Water
Resources, Department of Civil Engineering, University of Texas, Austin, TX
Dr. Calvin C. Chien, Principal Consultant, duPont Corporate Remediation Group,
E.I. duPont de Nemours & Company, Wilmington, DE
Dr. Rolf Hartung, Professor of Environmental Toxicology, Department of
Environmental and Industrial Health, School of Public Health, University of
Michigan, Ann Arbor, MI
Dr. Wayne M. Kachel, Corporate Environmental Management, Martin Marietta
Corporation, Oak Ridge, TN
Dr. June Fabryka-Martin, Hydrogeologist, Isotope and Nuclear Chemistry Division,
Los Alamos National Laboratory, Los Alamos, NM
Dr. Ishwar P. Murarka, Senior Program Manager, Land & Water Quality Studies,
Environmental Division, Electric Power Research Institute, Palo Alto, CA
Dr. Bernard Weiss, Professor, Department of Environmental Medicine, University
of Rochester Medical Center, Rochester, NY
Science Advisory Board Staff
Dr. K. Jack Kooyoomjian, Designated Federal Official, U.S. EPA, Science Advisory
Board, (1400F), 401 M Street, SW, Washington, DC 20460
Mrs. Diana L. Pozun, Staff Secretary
Dr. Donald G. Barnes, Staff Director, Science Advisory Board
iii
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TABLE OF CONTENTS
1. EXECUTIVE SUMMARY 1
1.1 Overall Comments 1
1.2 Response to Charge 2
1.3 Additional Observations and Recommendations 4
1.3.1 Model Selection, Development, Formulation and
Documentation 4
1.3.2 Possible Improvements to Model Formulations for
Specific Processes 5
1.3.3 Issues of Parameter Estimation 6
1.3.4 Issues of Range of Model Validity 7
1.3.5 Issues Relating to Pathway Model Verification and
Validation 7
1.3.6 Comments on Remediation Effectiveness 8
1.3.7 Issues Relating to Assessment of Uncertainty 9
1.3.8 Comments on Results for Health Risk Analysis 9
1.3.9 Comments on Use of MMSOILS in Corrective Action RIA 10
1.3.10 Other-User Groups for MMSOILS 11
2. INTRODUCTION 12
2.1 Charge for SAB Review 12
2.2 SAB Review Procedure 12
3. COMMENTS ON MODEL SELECTION, FORMULATION,
DOCUMENTATION AND APPLICATION 14
3.1 MMSOILS Selection, Development, Formulation and
Documentation 14
3.1.1 Model Selection and Development 14
3.1.2 Use of Standard Formulations 15
3.1.3 Documentation of Modeled Pathways 15
3.1.4 Documentation ;of Assumptions Underlying Multimedia
Treatment 15
3.2 Possible Improvements to Model Formulations for Specific
Processes 16
3.2.1 Additional Types of Solid Waste Management Units
(SWMUs) 16
3.2.2 Recognition of Natural Biodegradation Processes in
Ground Water Pathway 16
3.2.3 Modeling Transport through the Vadose Zone 17
3.2.4 Plume Aggregation in Groundwater Pathway 17
3.2.5 Food-Chain Module 17
3.2.6 Mass Balance 18
3.2.7 Disparity in Relevant Time and Space Scales for
Transport Mechanisms 18
3.2.8 Relevant Time Scales for Ecological Risk Assessment 18
3.3 Issues of Parameter Estimation 19
iv
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TABLE OF CONTENTS: CONTINUED:
3.3.1 Source Term Parameters 19
3.3.2 Waste Release and Solubility 20
3.3.3 Use of Default Values 21
3.3.4 Peer Review of Data Base 21
3.3.5 DataBase for Future Related Modeling Efforts 21
3.4 Issues of Range of Model Validity 21
3.4.1 Extreme Events 22
3.4.2 Complex Sites 23
3.4.3 NAPLs 23
3.4.4 Development of Guidelines for Assessing Model
Applicability to Specific Cases 23
3.5 Issues Relating to Pathway Model Calibration, Verification and
Validation 24
3.5.1 Ground Water Model 24
3.5.2 Other Pathway Models 24
3.5.3 Guidelines for Calibration, Verification and Validation 24
3.6 Comments on Remediation Effectiveness 24
3.6.1 Remediation Times 24
3.6.2 Effect of Unknown Presence of DNAPLs on Remediation
Times 25
3.6.3 Remediation Effectiveness 25
3.6.4 Inclusion of Biologically-Based Remediation Technologies 26
3.6.5 Risks of Remediation 26
3.7 Issues Relating to Assessment of Uncertainty 26
3.7.1 Uncertainty Estimation Protocol 26
3.7.2 Development of High-End Risk Estimates 27
3.8 Interpretation of Results for Health Risk Analysis 27
3.8.1 Health Risk as the Assessment Endpoint 27
3.8.2 Empirical Validation of Exposure Estimates 28
3.8.3 Inconsistent Treatment of Cancer and Noncancer Health
Risks 28
3.8.4 Inaccurate Identification of Critical Health Effects 28
3.8.5 Questionable Treatment of Different Waste Classes 29
3.8.6 Other Sources of Hazardous Wastes 29
3.9 Comments on Use of MMSOILS in Corrective Action RIA 29
3.9.1 Facility Selection Process 29
3.9.2 Use for National-Level Screening 30
3.9.3 Presentation of Results in Corrective Action RIA 30
3.9.4 Presentation of Uncertainty Analysis in RIA 31
3.10 Other User Groups for MMSOILS 31
3.10.1 Applicability to Other EPA Program Activities 31
3.10.2 Use for State-Level Screening 31
3.10.3 Other User Groups 31
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TABLE OF CONTENTS: CONTINUED:
APPENDIX A - BRIEFING AND REVIEW MATERIALS A-l
APPENDIX B - REFERENCES CITED B-l
APPENDIX C - GLOSSARY OF TERMS AND ACRONYMS C-l
VI
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1. EXECUTIVE SUMMARY
In response to a request from the Office of Solid Waste and Emergency Response (OSWER), the
Science Advisory Board (SAB) has reviewed several aspects of the draft Regulatory Impact Analysis
(RIA) prepared in support of the Resource Conservation and Recovery Act (RCRA) Corrective Action
Rule. At the October 1992 meeting, the SAB Executive Committee, recognizing the importance,
complexity, and creativity of OSWER's work and its multi-disciplinary nature, established an ad hoc
Steering Committee to assure that certain significant aspects of the RIA —both methodology and
application —received appropriate attention from the relevant SAB standing Committees.
At a public meeting on January 29, 1993, the Steering Committee concluded, based on
presentations by and discussions with OSWER staff, that four SAB committees, with appropriate inter-
committee liaison participation, should review major segments of the RCRA Corrective Action RIA as
follows: the Environmental Economics Advisory Committee (EEAC) would review the Contingent
Valuation (CV) methodology and its application in the RIA; the Environmental Engineering Committee
(EEC) would review the MMSOILS multi-media contaminant fate, transport and exposure model; the
Ecological Processes and Effects Committee (EPEC) would review the ecological risk analysis; and the
Environmental Health Committee (EHC) would review the human health risk assessment. In addition,
the Steering Committee agreed to prepare an overview report to accompany the individual committee
reports.
The MMSOILS Model Review Subcommittee (MMRS) of the EEC reviewed the Agency's draft
document entitled "MMSOILS: Multimedia Contaminant Fate, Transport and Exposure Model
Documentation and User's Manual," dated September 1992 (See Appendix B, Reference 6), as well as
the supporting RIA and Appendices (See Appendix B, References 7 & 8). The draft documentation and
user's manual was developed jointly by the Office of Research and Development's (ORD's) Office of
Health and Environmental Assessment (OHEA) arid Office of Environmental Processes and Effects
Research (OEPER). The MMRS report resulted from a review of the above draft documents and
briefing materials at meetings on April 22-23, 1993 and June 29, 1993 (See Appendix A, and Appendix
B; References 6 through 8).
1.1 Overall Comments
The OSW/ORD working group is to be commended for a well-coordinated and focused effort to
develop a regulatory impact analysis (RIA) that will help the Agency and the Nation better understand
the costs and benefits of the proposed rule. The Subcommittee wishes to recognize the responsiveness
and progress made by the OSW/ORD working group to many of the recommendations made at the April
22-23, 1993 meeting and candidly displayed in detail at the June 29, 1993 meeting. The Subcommittee
appreciates and recognizes the significant effort expended to date, the positive attitude and open candor
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displayed by the OSW/ORD working group in their presentations and interactions during the two
review meetings. The Subcommittee considers the intraagency coordination represented by this RIA to
be a "model approach" that the Agency would do well to adopt in other programs.
The consensus of the MMSOILS Model Review Subcommittee (MMRS) is that the use of a
multimedia pathway model for screening purposes could be an appropriate approach for developing risk
and cost estimates for a national-level RIA as long as the input parameters are accurate and the model is
not applied outside its range of validity. The Agency's use of a single model, to the extent defensible,
ensures consistency among model results.
The major overriding concerns of the MMRS are the application of MMSOILS outside its range
of validity; large uncertainties in input parameters; consequent large uncertainties in MMSOILS results;
clear communication of this uncertainty to decision-makers and the generation of credible guidance on
exposure, risk, costs, and benefits. Consequently, the recommendations contained in this report are
focussed at efforts to decrease the level of uncertainty, to validate the MMSOILS results by comparison
with alternative, estimation methods, and to ensure that the results of the modeling exercise are
expressed in the RIA background documents in a scientifically defensible manner that communicates the
uncertainties of the calculations and their implications for the cost/benefit analysis.
1.2 Response to Charge
The following issues were presented in the charge to the Subcommittee. (Please note that numbers
following specific observations and recommendations refer the reader to more detailed discussion in
Section 3 of this review report.):
Issue 1. The adequacy of methods for using a screening level model to characterize
situations where there is a substantial subsurface heterogeneity or where non-
aqueous phase contaminants are present.
While the Subcommittee (the MMRS) agrees that a screening-level model may be appropriate
for developing risk and cost estimates for a national-level RIA, the MMRS recommends that the current
version of MMSOILS not be applied to the characterization of contaminant distributions in ground water
in complex hydrogeological settings or where Non-Aqueous Phase Liquids (NAPLs) may be present.
For these facilities, the MMRS recommends that alternative approaches to characterization should be
used. Such approaches include modification of the MMSOILS ground water module to more accurately
model contaminant movement in complex hydrogeologic settings; utilization of assessment data
generated at Superfund sites; application of more sophisticated models with better-defined data to
develop estimates for representative sets of waste sites; application of site-specific models to analyze
that relatively small number of facilities which MMSOILS results indicate dominate the total costs or
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risks; and submission of these case studies to expert panel review to develop estimates of contaminant
migration.
Issue 2. Appropriateness of the Agency's approach for aggregating releases from solid waste
management units (SWMUs, the source terms for the contaminant modeling) to
estimate concentration at exposure points over time.
The Subcommittee is concerned that the method of aggregation used to obtain the concentration
distributions for application to individual wells may not conserve mass. Rather, it appears that the
resulting apparent mass and the average concentrations for each concentric ring downgradient from the
SWMUs will always exceed that from the untransformed plumes. Such an approach may nonetheless be
defensible for the purposes of the RIA because it is conservative; however the MMRS recommends that
the degree of conservatism be evaluated through comparison with a number of simulations which do not
use this method of aggregation. Unduly conservative estimates can cause the inappropriate prioritization
of risks. In addition, the MMRS recommends that the Agency evaluate whether movement of the
contaminant plumes could result in a decreased concentration for population wells. The required
transformations from cartesian to cylindrical coordinates should not require much computational effort
compared with that required for the model to begin with.
Issue 3. Adequacy of the Agency's approach for developing long-term effectiveness and
failure scenarios for site remedies.
The Subcommittee observes that the annual time scale for exposure estimates produced by
MMSOILS may be inappropriate for many ecological applications. Typical organisms of concern
exhibit short life spans, or critical stages in their complex life histories that occur at time scales
substantially shorter than one year. Thus, the Subcommittee recommends the modification of
MMSOILS to produce more realistically-scaled exposures for meaningful inputs to ecological risk
analysis (Recommendation #13; also Section 3.2.8). The Subcommittee recommends that the ecological
risk assessment component be constructed using the principles for ecological risk assessment as
suggested by the Risk Assessment Forum. (Recommendation #9; also Section 3.2.5; See also Appendix
B, Reference 23). The Subcommittee further recommends that ecologically relevant exposure scenarios
be modified so as to be capable of simulating acute impacts from waste sites on aquatic environments
due to surface run-off after major rain events. (Recommendation #10; also Section 3.2.5).
Issue 4. The implications of the fate and transport modeling assumptions on the ecological
and human risk assessment.
The Subcommittee observes that certain hazardous agents are not easily controlled and may pose
health risks beyond the substances discussed in the RIA. (Observation #43; Section 3.8.6). The
Subcommittee recommends that the Agency revise its practices for assessing cancer and noncancer
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health risks so as to make them more consistent with one-another (Recommendation #40; Section 3.8.3).
The Subcommittee also recommends that the Agency review its assumption of additivity of Hazard
Indices, and additivity of risks across Class A (known) and Class C (suspected) carcinogens
(Recommendation # 42; Section 3.8.5). The Subcommittee further recommends that the Agency review
its discussion of critical health effects and correct any inaccurate information (Recommendation #41;
Section 3.8.4).
The Subcommittee recommends that the Agency consider how the general validity of its
exposure estimates might be tested by comparison with empirical field data. This is being recommended
as a result of the observation by the Subcommittee that the translation of contaminant concentrations to
estimates of exposure necessarily involves a long chain of assumptions and requires the adoption of
parameter values of variable uncertainty (Recommendation #39; Section 3.8.2).
1.3 Additional Observations and Recommendations
1.3.1 Model Selection, Development, Formulation and Documentation
Recommendation 1. The MMRS recommends that the criteria and rationale for the
selection of MMSOILS be more fully documented in the RIA so that the scientific and strategic
bases for the selection will be clear to all concerned - regulator, regulated, and scientific/risk
assessment/economic communities at large. (3.1.1)
Observation 2. The model uses simple, conservative, and computationally efficient equations
for estimating chemical transport via ground water, surface water, soil erosion, the atmosphere, and
foodchains. Mathematical formulae used to estimate transport rates for each pathway are widely used
and accepted by the scientific community for application to simple situations. Underlying assumptions
for each pathway model have been identified, are clearly stated, are reasonable and are not overly
restrictive. However, for a significant number of sites, the MMRS suspects that no generic model is
likely to provide answers of acceptable quality. OSWER is generally aware of the limited usefulness of
generic models for the analysis of complex environmental systems, including aquifers. (3.1.2)
Recommendation 3. While documentation of the formulations for individual pathway
models is well organized with appropriate references, the manual would benefit from another
round of editing. (3.1.3)
Recommendation 4. Documentation for MMSOILS would benefit from a concise and
explicit presentation of the model's basis, assumptions and limitations in a central location at the
beginning of the user's manual. (3.1.4)
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1.3.2 Possible Improvements to Model Formulations for Specific Processes
Recommendation 5. MMSOILS should be modified to make it capable of handling other,
potentially more costly, types of SWMUs such as leaky sewer systems which are currently
excluded from the RIA. Eventually these problematic SWMUs will be impacted by the proposed
corrective action rule, so an estimate of their cost contribution to the implementation of the
proposed rule should be developed. (3.2.1)
Recommendation 6. Because of the long time periods involved, the MMRS believes that it
is critical that the role of natural biodegradation processes be explicitly incorporated into the
ground water fate and transport pathway by the use of an appropriate biodegradation coefficient
value. This function is essential and provides realism for actual mechanisms taking place. Even a
small biodegradation coefficient would have a big impact. (3.2.2)
Recommendation 7. The MMRS recommends that the unsaturated-zone transport module
be replaced with a simple kinematic model in order to make its treatment consistent with the other
transport process models. (3.2.3)
Recommendation 8. The MMRS recommends that the Agency quantitatively assess the
degree of conservation introduced by its method of plume aggregation through a comparison with
simulations which do not use this method. As a part of this exercise, the Agency should
quantitatively evaluate whether movement of the plumes could result in a decreased concentration
for population wells. (3.2.4)
Recommendation 9. The MMRS recommends that the ecological risk assessment
component be constructed using the principles for ecological risk assessment as suggested by the
Risk Assessment Forum. (3.2.5)
Recommendation 10. The MMRS recommends that the ecologically relevant exposure
scenarios be modified so as to be capable of simulating acute impacts from waste sites on aquatic
environments due to surface run-off after major rain events. (3.2.5)
Observation 11. The MMRS is concerned that the MMSOILS model may not effectively
estimate long-term consequences of remediation alternatives due to a suspected breakdown of mass
balance as a result of model output post-processing. (3.2.6)
Observation 12. The MMRS notes that a major problem that must be confronted in the
development of any multimedia model, such as MMSOILS, is the forcing of differently scaled
environmental transport processes into a single model construct. Attempts to force disparate scales into
a single model by selecting a compromise in time step will necessarily result in a loss of accuracy in
model predictions. (3.2.7)
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Recommendation 13. The Subcommittee recommends the modification of MMSOILS to
produce more realistically-scaled exposures for meaningful inputs to ecological risk analysis. This
recommendation results from the observation that the annual-time scale for exposure estimates
produced by MMSOILS may be inappropriate for many ecological applications. Typical
organisms of concern exhibit short life spans, or critical stages in their complex life histories that
occur at time scales substantially shorter than one year. (3.2.8)
1.3.3 Issues of Parameter Estimation
Recommendation 14. The Subcommittee recommends that the Agency ensure that the
uncertainty estimates in the RIA fairly reflect the uncertainties in quantification of the source
term of the model input. The MMRS believes that the largest single source of uncertainty in the
risk analysis is probably that related to quantification of the source term. Problems include
sparse or inaccurate information on identification of types of wastes present (e.g., presence of
NAPLs), on quantification of waste quantities, and on estimation of waste distribution. (3.3.1)
Recommendation 15. The MMRS recommends that the Agency consider the quantity and
quality of waste information as a reasonable criterion or requirement for the inclusion of a
particular facility in the facility selection process. The Subcommittee believes that the expected
improvement of the confidence in the modeling results is obvious. (3.3.1)
Observation 16. The MMRS observes that the uncertainty of the waste transport calculations
may be increased by the fact that the existing data that have been developed for SWMUs were generally
not constructed or collected for the purpose of estimating risks to humans or to ecosystems, but rather
for the purpose of defining the extent of contamination at a site rather than defining the exposures at or
near the site. (3.3.1)
Recommendation 17. The MMRS recommends that the solubility models used for metals
and organics be submitted to peer review to assess their scientific basis and limitations. (3.3.2)
Recommendation 18. The MMRS recommends that the input data for the case studies
undergo peer review in order to evaluate a suspected over-reliance on the use of default parameter
values. (3.3.3)
Recommendation 19. The MMRS recommends a documented and thorough peer review of
all aspects of the data base, focusing particularly on those parameters to which the results are
most sensitive. (3.3.4)
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Recommendation 20. The MMRS recommends that the Agency build upon the extensive
data base it has accumulated for the Corrective Action RIA, to begin the development of an
extensive data base that could be tapped for other EPA programmatic efforts, such as for a
comparable assessment of the risks associated with NORM wastes and radiologically
contaminated sites. The intraagency modeling task force, the Ad Hoc Agency Task Force on
Environmental Regulatory Modeling (AFTERM), may be an appropriate vehicle for organizing
and coordinating such an effort in a manner that would be most beneficial to the potential users.
(3.3.5)
1.3.4 Issues of Range of Model Validity
Recommendation 21. The MMRS recommends that the Agency evaluate the validity of
each pathway model to assess the extent to which extreme events might be expected to contribute
to the bulk of contaminant releases, and the extent to which the model may under - or over-
estimate transport. (3.4.1)
Recommendation 22. For facilities in complex hydrogeological settings outside the range of
validity of the MMSOILS model, the MMRS recommends that alternative approaches to
characterization be used. Examples include the following modification of the ground water
module in MMSOILS to more accurately model contaminant movement under these conditions;
utilization of assessment data generated for Superfund sites; application of more sophisticated
models with better-defined data to develop estimates for representative sets of waste sites;
application of site-specific models to analyze that relatively small number of facilities which
MMSOILS results indicate dominate the total costs or risks; and submission of these case studies
to expert panel review to develop estimates of contaminant migration. (3.4.2)
Recommendation 23. The MMRS strongly endorses ORD's recommendation that the
Agency develop an improved screening-level model for non-aqueous phase liquid (NAIL)
transport, either by modification of the existing MMSOILS model or by conducting independent
modeling exercises. (3.4.3)
Recommendation 24. The MMRS recommends that the Agency develop guidelines -
perhaps including a requirement for peer review for key case studies -in order to assess the
applicability of MMSOILS to specific cases. (3.4.4)
1.3.5 Issues Relating to Pathway Model Verification and Validation
Recommendation 25. The MMRS recommends that the Agency prepare a documented
comparison of model predictions of chemical transport to field data that would strengthen the
scientific credibility of the results and provide a basis . for readers to evaluate the model validity
and magnitude of uncertainty. For similar reasons, the MMRS recommends that, for a subset of
SWMUs[ where ground water plume predictions are made by using MMSOILS, NATL/EPACMS
models also be exercised so as to permit comparison of plume predictions. (3.5.1)
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Recommendation 26. The MMRS recommends that documented validation exercises be
undertaken for the remaining environmental transport pathways, e.g., aerosolization,
volatilization, surface water runoff, and bioaccumulation, in order to assess the ability of these
pathways models to provide meaningful input to the RIA. (3.5.2)
Recommendation 27. The MMRS recommends that the Agency, perhaps through
AFTERM, develop generic guidelines for model calibration, verification and validation, including
criteria for judging whether or not discrepancies among alternative modeling results or between
calculated and measured field data are significant. In the case of MMSOILS, it recommends that
the Agency undertake a root-cause analysis for discrepancies, where significant, in order to
evaluate the potential for systematic bias in the modeling approach. (3.5.3)
1.3.6 Comments on Remediation Effectiveness
Recommendation 28. The MMRS recommends that the sensitivity of the RIA conclusions
to these estimated remediation clean-up times be evaluated. This recommendation is made from
the observation that experience gained from the Superfund program with respect to remediation
effectiveness and time has shown that time estimates are commonly overly optimistic for ground
water extraction systems. Because of unidentified sources, vadose zone contamination,
heterogeneities, and the unknown presence of NAPLs, remediation has gone on at a number of
sites for periods well in excess of initial estimates. (3.6.1)
Recommendation 29. The MMRS recommends that the Agency discuss the implications of
unknown presence of NAPLs in the Corrective Action RIA. The MMRS observes that NAPLs are
not always recognized during site characterization, and that this oversight may result in selection
of a remediation system that is not appropriate for NAPLs, resulting in excessive remediation
times and associated costs, and possibly in remediation goals not being achieved. (3.6.2)
Recommendation 30. The Subcommittee recommends that the Agency evaluate the
sensitivity of the RIA analysis to assumptions about remediation effectiveness. The MMRS
believes that, for some cases, especially cases in which NAPLs are present or those sites located in
fine-grained soils and fractured or karst rock, the assumed extent of remediation effectiveness
may be too high. (3.6.3)
Recommendation -31. The MMES recommends that a closer review be made of the
derivation and scientific basis of the soil-water partition coefficient (K value) used in the post-
processing of model results to calculate the change in concentrations at the exposure location.
(3.6.3)
Recommendation 32. The MMRS recommends that the suite of remediation technologies
used in the analysis be expanded to include biologically-based treatment technologies. The
Subcommittee observes that a significant advantage of these treatment technologies is that,
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where applicable, they may provide a more cost-effective treatment approach than other currently
available remedial technologies. (3.6.4)
Recommendation 33. The MMRS recommends that the risk analysis be modified to
recognize risks that may be incurred through the remediation process. (3.6.5)
1.3.7 Issues Relating to Assessment of Uncertainty
Recommendation 34. The MMRS recommends that guidance be provided in the
MMSOILS user manual concerning why and how the user should obtain qualitative or
quantitative estimates of the uncertainties associated with each pathway. (3.7.1)
Recommendation 35. The MMRS recommends that any numerical results emanating from
the RIA analysis be presented as a range. The MMRS stresses that presenting results as "a
number" tends to give the reader a false sense of accuracy which, in this instance, is particularly
dangerous given the incompleteness of the input data set and our incomplete comprehension of the
fate of hazardous constituents in the environment. (3.7.1)
Recommendation 36. The MMRS recommends that the MMSOILS model and results be
subjected to more thorough, formal and comprehensive sensitivity and uncertainty analyses in
order to identify the critical parameters associated with predictions of contaminant concentrations
along various pathways. This information can then be used to determine what the critical data
are for improving model predictions, and possibly to simplify the model structure without
sacrificing accuracy or precision of model results. (3.7.1)
Recommendation 37. The MMRS recommends that the Agency review its risk estimation
protocol. The MMRS is concerned, that the simple protocol followed to obtain high-end risk
estimates may be inadequate, in that; these estimates in some cases apparently give rise to lower
exposures than those generated using the central tendency estimate. (3.7.2)
1.3.8 Comments on Results for Health Risk Analysis
Observation 38. The MMRS observes that since health risks are the predominant focus of
current environmental protection initiatives, the adequacy of risk estimates has to serve as the ultimate
criterion of model relevance and accuracy. (3.8.1)
Recommendation 39. The MMRS recommends that the Agency consider how the general
validity of its exposure estimates might be tested by comparison with empirical field data This is
being recommended as a result of the observation by the MMRS that the translation of
contaminant concentrations to estimates of exposure necessarily involves a long chain of
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assumptions and requires the adoption of parameter values of variable uncertainty. (3.8.2)
Recommendation 40. The MMRS recommends that the Agency revise its practices for assessing
cancer and noncancer health risks so as to make them more consistent with one another. (3.8.3)
Recommendation 41. The MMRS recommends that the Agency review its discussion of critical
health effects and correct any inaccurate information. (3.8.4)
Recommendation 42. The MMRS recommends that the Agency review its assumption of
additivity of Hazard Indices, and additivity of risks across class A (known) and Class C
(suspected) carcinogens. (3.8.5)
Observation 43. The MMRS observes that certain hazardous agents are not easily controlled and may
pose health risks beyond the substances discussed in the RIA. (3.8.6)
1.3.9 Comments on Use of MMSOILS in Corrective Action RIA
Recommendation 44. The MMRS recommends that the word "random" be deleted from any
reference to the sample; the fact that various facilities were eliminated from the analysis for
various reasons, some of which are quite valid, belies, the concept of the sample being "random."
Observation 45. The MMRS agrees that MMSOILS may be appropriate to use as a screening-level
model at the national level, but observes that the model is actually used beyond screening in estimating
the fate and transport of contaminants. The MMRS observes that the acceptability of uncertainties
associated with model predictions must be evaluated in the context of model use. The model use
determines the objective of any validation effort. If the model is used; in a screening mode, then greater
uncertainties on the model outputs can be tolerated in making a coherent decision and validation efforts
should focus on how well the model screens. If the model is to be used in estimating spatial-temporal
values of contaminant concentrations, for example, to feed into a site-specific risk assessment, then
validation requires comparisons with these kinds of data which are highly likely to need greater
accuracy and precision, if the model is to effectively contribute to these estimations. Care must be taken
in not confusing the two. different uses of the model and that such a distinction be made to the model
users. (3.9.2)
Observation 46. The MMRS observes that, as an alternative to attempting to estimate a national
average by aggregating the 38 site-specific applications of MMSOILS, it might be just as valid to use as
much data as possible from the 5,800 sites to construct an "average" national waste site and apply the
model to this single hypothetical site. This approach might be particularly effective given that the
validity of each site-specific simulation is not held to be very accurate.
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Analyzing the hypothetical site with the model might be more in-line conceptually with the notion of
screening. (3.9.2)
Observation 47. The MMRS commends the Agency for having drafted such a well-organized
and well-written report for such a highly complex issue as that for the Corrective Action RIA. However,
the MMRS observes that the major goal of the RIA is to provide a quantitative estimate of the cost with
incremental benefit for corrective actions, and it is commonly recognized -and accepted as a necessary
reality -that the MMSOILS model application could derive exposure estimates no better than "order(s)
of magnitude". Although the results may still be valuable for the purposes of screening, e.g., for
assessing relative clean-up costs or cost versus incremental benefits between various sites, their utility is
brought into question when the results are intended to be used for evaluating remediation costs, i.e., how
meaningful it is when a cost estimate is given with a built-in uncertainty of one or more orders of
magnitude, considering the total cost at the national level would probably involve hundreds of billions of
undiscounted dollars? (3.9.3)
Recommendation 48. The MMRS recommends that the Agency give high priority to
highlighting the uncertainties in the MMSOILS model screening effort and the propagation and
perhaps magnification of that uncertainty in the subsequent estimates of exposure, risk, costs, and
benefits, because of the critical importance of this aspect of the RIA. The MMRS observes that a
major deficiency with the draft RIA relates to an inadequate representation of the magnitude of
the uncertainties associated with the cost and benefit estimates. The MMRS further recognizes
that communication of the relevance and implications of uncertainty analysis to decision-makers is
a difficult and challenging problem. (3.9.4)
1.3.10 Other User Groups for MMSOILS
Recommendation 49. Because of the potential utility of MMSOILS for estimating
ecological risks in relation to other EPA programmatic efforts, the MMRS recommends that this
modeling construct continue to receive attention, both in terms of review and in resources, to
ensure that it has utility beyond RCRA. (3.10.1)
Recommendation 50. On a longer-term perspective, the MMRS recommends that the
Agency consider what might be its role in providing guidance to states as to the appropriate types
of models to use for state-level screening calculations. (3.10.2)
Recommendation 51. The MMRS observes that the model documentation makes clear that
MMSOILS is meant to be used by non-specialists. Consequently, the MMRS recommends that
the manual be revised to contain stronger statements that emphasize the model limitations to such
users, to recommend alternative models, and to emphasize the inapplicability of the model to site-
specific evaluations. (3.10.3)
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2. INTRODUCTION
2.1 Charge for SAB Review
In accordance with the charge to the MMSOILS Model Review Subcommittee (MMRS), [See
Appendix A, Reference 1 (memorandum dated March 26, 1993 from Richard Guimond to Donald
Barnes regarding Charge for SAB review of Regulatory Impact Analysis Supporting the Corrective
Action , Regulation), as well as Appendix A, Reference 2 (a jointly-signed memorandum dated June 26,
1992 from Richard Guimond and Peter Preuss requesting a SAB review of the RCRA Corrective Action
RIA), and Appendix A, Reference 3 (Federal Register, Vol. 58 (April 9, 1993), pg. 18395, which states
the charge to the SAB) ] the MMRS focussed on the technical aspects of the MMSOILS model. The
specific issues that the Subcommittee was asked to address include:
Issue 1. The adequacy of methods for using a screening level model to characterize, situations where
there is a substantial subsurface heterogeneity or where non-aqueous phase contaminants are
present.
Issue 2. Appropriateness of the Agency's approach for aggregating releases from solid waste
management units (SWMUs, the source terms for the contaminant modeling) to estimate
concentration at exposure points over time.
Issue 3. Adequacy of the Agency's approach for developing long term effectiveness and failure
scenarios for site remedies, and
Issue 4. The implications of the fate and transport modeling assumptions on the ecological and
human risk assessment.
2.2 SAB Review Procedure
The primary review document is the EPA/ORD report, MMSOILS: Multimedia Contaminant
Fate, Transport, and Exposure Model -Documentation and User's Manual (September 1992 draft; See
Appendix A, Reference 4, as well as Appendix B, Reference 6). The Subcommittee also relied heavily
upon the EPA/OSW Draft Regulatory Impact Analysis for the Final Rulemaking on Corrective Action
for Solid Waste Management Units: Proposed Methodology for Analysis (including its
Appendices)(March 1993 draft; See Appendix A, References 5 and 6, as well as Appendix B,
References 7 and 8). These documents were addressed at a meeting of the MMSOILS Review
Subcommittee (MMRS) of the Environmental Engineering Committee (EEC) in Arlington, VA on April
22-23, 1993, at which time the MMRS was also briefed by Agency staff on the selection, development
and application of the MMSOILS models in the RIA (See Appendix A, References 7 through 12).
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A second meeting was held on June 29, 1993 with some of the MMRS and Environmental
Engineering Committee (EEC) members and consultants who wished to focus of the MMSOILS model
and data [See Appendix A, Reference 13 (Federal Register. Vol. 58, No. 108, June 8, 1993, pg. 32122).
Also, see Appendix A, References 13 through 19, for a listing of the briefing materials for the June 29,
1993 meeting]. The specific purpose of this meeting was to further discuss with the Agency staff the
selection of the corrective action sample facilities, data sets, data acquisition and facility
conceptualization process, as well as progress by the OSW staff on verification and validation of the
MMSOILS model.
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3. COMMENTS ON MODEL SELECTION, FORMULATION,
DOCUMENTATION AND APPLICATION
3.1 MMSOILS Selection, Development, Formulation and Documentation
The Subcommittee would like to note that, while a number of recommendations are made in this
report to improve the MMSOILS model and overall approach, such an approach lends itself well toward
the context of better understanding and dealing with reducing risk concepts (See Appendix B,
References 9, 10, 14 through 17 and 19). This approach also is a systematic way of characterizing and
assessing ground water oriented and multi-media oriented approaches for grappling with the admittedly
very complex, difficult, demanding and challenging risk assessment concepts that are being applied in a
national context to deal with the Corrective Action RIA (See, for instance, Appendix B, References 1
through 5, 10 through 13 and 19 through 22).
3.1.1 Model Selection and Development
The OSW/ORD working group is to be commended for a well-coordinated and focused effort to
develop a regulatory impact analysis (RIA) that will help the Agency and the Nation better understand
the costs and benefits of the proposed rule for the final corrective action for solid waste management
units. The Subcommittee considers the intraagency coordination represented by this RIA to be a "model
approach" that the Agency would do well to adopt in other programs.
The consensus of the MMSOILS Model Review Subcommittee (MMRS) is that the use of a
multimedia pathway model for screening purposes could be an appropriate approach for developing risk
and cost estimates for a national-level RIA, as long as the input parameters are sufficiently accurate and
the model is not applied outside its range of validity. The Agency's use of a single model, to the extent
defensible ensures consistency among model results. The rationale -for the selection of MMSOILS for
the corrective action RIA was explained during a briefing to the MMRS by OSW. The MMRS
recommends that the criteria and rationale for the selection of MMSOILS as expressed in that briefing
be more fully documented in the RIA so that the scientific and strategic bases for the selection will be
clear to all concerned -regulator, regulated, and scientific/risk assessment/economic communities.
The major overriding concerns of the MMRS are: a) the application of MMSOILS outside its
range of validity; b) large uncertainties in input parameters; c) consequent large uncertainties in
MMSOILS results; d) the lack of clear communication of this uncertainty to decision-makers; and e) the
generation of credible guidance on exposure, risk, costs, and benefits. Consequently, the
recommendations contained in this report are focused at efforts to decrease the level of uncertainty, to
validate the MMSOILS results by comparison with alternative estimation methods, and to ensure that
the results of the modeling exercise are expressed in the RIA in a scientifically defensible manner that
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communicates the uncertainties of the calculations and their implications for the cost/benefit analysis.
3.1.2 Use of Standard Formulations
MMSOILS was selected by EPA for use as a screening model for simulation of contaminant
transport from waste management units through multiple environmental pathways, and for evaluation of
potential exposures and associated risks. The model uses simple, conservative, and computationally
efficient equations for estimating chemical transport via ground water, surface water, soil erosion, the
atmosphere, and foodchains. Mathematical formulae used to estimate transport rates for each pathway
are widely used and accepted by the scientific community for application to simple situations.
Underlying assumptions for each pathway model have been identified, are clearly stated, are reasonable
and are not overly restrictive. For the most part, the representations used in MMSOILS for the various
exposure pathways are consistent in their level of treatment. However, for a significant number of sites,
the MMRS suspects that no generic model is likely to provide answers of acceptable quality. OSWER is
generally aware of the limited usefulness of generic models for the analysis of complex environmental
systems, including aquifers.
3.1.3 Documentation of Modeled Pathways
Documentation of the formulations for individual pathway models is well organized with
appropriate references. However, the manual would benefit from another round of editing; a distracting
aspect of the review draft is that several terms in the equations and figures have not been defined in the
text (e.g., Cwi, Cdwi in equation 3-11, page 3-14 of the Users Manual). The MMRS recommends that
each term be defined in three places in the manual: (a) in the beginning or end of each chapter in which
it appears, (b) at the time each is first used in a given chapter, and (c) in the compilation of terms in
Chapter 12. The terms should also be reviewed for internal consistency.- In at least one case, two
different symbols have been used for the same parameter (Qm, qm). In another case, the same symbol
(DF) has been used for two different parameters.
3.1.4 Documentation of Assumptions Underlying Multimedia Treatment
Basic underlying assumptions, such as the assumption in the ground water transport model of an
"idealized homogeneous, uniform porous media," are dispersed throughout the manual. Documentation
for MMSOILS would benefit from a concise presentation of the model's basis, assumptions and
limitations in a central location at the beginning of the user's manual. The presentation should include
descriptions of key aspects of the overall model structure, such as: modeling time frames for each
pathway, whether the model assumes finite or infinite sources, whether the model is steady-state or
dynamic, and how the model deals with competing mechanisms or pathways.
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This introductory section should be sufficiently comprehensive that a knowledgeable reader
could use it to quickly assess the level of sophistication of each pathway component in the MMSOILS
model and thus develop a level of comfort with the predictions provided by the model. Chapter 2.0 of
the user manual, "Applications and Limitations of the Methodology," does not fulfill this requirement,
although it could be revised to do so. The cursory discussion presented in the section of questions that
should be asked may be interesting but does not inform the user of the assumptions that were made in
the model construction. Assumptions and their resulting model simplifications are crucial to the
evaluation of the model. The brief section on model limitations also fails to discuss what the true
limitation's are.
3.2 Possible Improvements to Model Formulations for Specific Processes
3.2.1 Additional Types of Solid Waste Management Units (SWMUs)
As currently constructed, MMSOILS is only capable of handling the more traditional SWMUS
such as landfills and surface impoundments. Other, potentially more costly, types of SWMUs such as
leaky sewer systems have been excluded from the analysis. Although they have been identified as
SWMUs, few of these less traditional SMWUs have been remediated largely because no one really
knows how to deal with them. Their remediation could be quite costly and result in disruption of
industrial operations. Eventually these problematic SWMUs will be impacted by the proposed
corrective action rule and will have to be addressed. Thus, an estimate of their cost contribution to the
implementation of the proposed rule should be developed.
3.2.2 Recognition of Natural Biodegradation Processes in Ground Water Pathway
Approximately 130 years of simulations are made using the MMSOILS model to predict the
existence, development or dissipation of ground water plumes. Because of the long time periods
involved, it is critical that the role of natural biodegradation processes, be explicitly incorporated into
the ground Water fate and transport pathway by the use of an appropriate biodegradation coefficient
value. This function is essential and provides realism for actual mechanisms taking place. Even a
small biodegradation coefficient would have a big impact. For instance, a value of only 0.0001/yr for
the degradation coefficient of organic constituents in ground water will have a very large effect on the
distribution of contaminants when taken over simulation periods much less than 130 years.
Neglecting the role of biodegradation processes in the transport model could result in
overestimation of exposure concentrations. This omission might not be critical in screening applications
where bias towards overestimation may provide appropriately conservative results. However, the
literature continues to increase in terms of estimates of biodegradation of many organic contaminants
and these data should be examined for possible use in MMSOILS. (See also comment 3.6.4 on
biologically-based remediation technologies.)
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3.2.3 Modeling Transport through the Vadose Zone
The finite element numerical model used for the partially saturated zone is adequate for the job,
but it may not necessarily be consistent with the precision of other model components. This is
especially true in light of other assumptions made in the RIA. For example, only a single layer (or small
number of layers with only roughly estimated properties) was used to represent the unsaturated zone and
the net infiltration rate was taken as piece-wise constant. Given these assumptions, simple kinematic
models are appropriate and consistent with the rest of the transport process models. Kinematic models
for flow and transport will conserve mass, can address step-wise constant infiltration rates, and will
provide simple algebraic equations for use in the model.
3.2.4 Plume Aggregation in Groundwater Pathway
The method of aggregation used to obtain the concentration distributions for application to
individual wells does not conserve mass. Rather, it appears that the resulting apparent mass will always
exceed that from the untransformed plumes. While this approach is conservative, the degree of
conservation should be evaluated through comparison with a number of simulations which do not use
the method of aggregation. In addition, the question of whether movement of the plumes could result in
a decreased concentration for population wells should be evaluated. The required transformations from
cartesian to cylindrical coordinates should not require much computational effort compared with that
required to operate the model.
3.2.5 Food-Chain Module
The food-chain module in MMSOILS is very synthetic and unrealistic. Food chains are highly
site-specific and depend upon the gathering of the contaminant into the receptor environment, the
structure of the ecological community, and the ultimate receptor of interest (humans or eagles or
others). It makes considerable difference in the risk estimate whether the ecological community is
terrestrial or aquatic and to what extent the contaminated food contributes to the total food in each
trophic level. Furthermore, the efficiency of contaminant transfer from one trophic level to the next
varies, and is dependent in part upon the octanol-water partition coefficient (Kow) and molecular size of
specific organic compounds.
The ecological risk assessment component should be constructed using recommendations
structured in the SAB's report of the Ecology and Welfare Subcommittee of the Relative Risk reduction
Strategies Committee of the SAB [See Appendix B, Reference 10 in particular, as well as Appendix B,
References 9, 11 and 12, and the principles for ecological risk assessment as suggested by the Risk
Assessment Forum, Appendix B, Reference 23.]
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3.2.6 Mass Balance
The effectiveness of the model for estimating long-term consequences of remediation
alternatives appears to be weakened by the breakdown of mass balance as a result of post-processing of
model outputs (See also Section 3.2.4 regarding issues related to the method of aggregation and
conservation of mass). The exponential decay of ground water contaminants as described represents one
particular example of this apparent breakdown. Similar concerns for overall mass balance in MMSOILS
remain. For example, if the combined degradation or transport along all pathways accounts for more
contaminant mass than is available, the flux along each pathway is merely normalized according to the
"demand." This procedure may provide results of questionable accuracy given the different time scales
applied to contaminant flux along different pathways.
3.2.7 Disparity in Relevant Time and Space Scales for Transport Mechanisms
One major problem that must be confronted in the development of any multimedia model, such
as MMSOILS, is the forcing of differently scaled environmental transport processes into a single model
construct. For example, the temporal dynamics of volatilization of organics may vary on the order of
hours or less, given changes in microclimatic conditions that drive this process (e.g., temperature, wind
velocity). Surface water runoff leading to transport of soils and dissolved contaminants is strongly
event-driven, that is, local precipitation patterns and strong storms can move significant amounts of
chemicals in time scales of hours. These dynamics contrast markedly with the slow movement of
contaminants in ground water, where years to decades may be the relevant time scale.
Attempts to force the above disparate scales into a single model by selecting a compromise in
time step will necessarily result in a loss of accuracy in model predictions. Parallel considerations apply
in the spatial domain. Representing the spatial distribution .of ground water plumes of contaminants
may allow a comparatively coarse spatial description of the waste site and surrounding region. To
achieve comparable accuracy in estimating atmospheric transport, a more detailed spatial representation
of the system may be necessary. Again, attempting, to force disparate spatial scales into a single model
can produce inaccuracies in model results. Finally, the combination of time and space scale selections
required in establishing a single model can compound problems outlined above.
3.2.8 Relevant Time Scales for Ecological Risk Assessment
At present the ecologically relevant exposure scenarios are inadequate. The known major source
for acute impacts from waste sites on aquatic environments is surface run-off after major rain events.
The MMSOILS model cannot simulate this in its present version. On a long-term basis, major effects
can be due to biomagnification, changes in biodiversity, etc.
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Methods for estimating ecological risk continue to evolve, e.g., the EPA Framework for
Ecological Risk Analysis. Nonetheless, it is quite apparent that the methods will surpass simple
multiplicative models of food chain accumulation and comparison of exposure concentrations to acute
or chronic toxicity benchmarks. The annual time scale for exposure estimates produced by MMSOILS
seems inappropriate for many ecological applications. Typical organisms of concern exhibit short life
spans, or critical stages in their complex life history that occur at time scales substantially shorter than
one year. Thus, an average annual concentration is not particularly useful as an input to many
ecological risk assessments. Strong seasonal constraints are typically important, especially for
temperate surface waters, e.g., streams and lakes. Thus, MMSOILS may have to be modified to produce
more realistically-scaled exposures for meaningful inputs to ecological risk analysis.
3.3 Issues of Parameter Estimation
The MMRS notes that the use of inaccurate input parameters is a suspected major source of
unacceptable errors and unreasonable magnitudes of uncertainties in MMSOILS results relative to their
use in the draft Corrective Action RIA. Inappropriate input data are a consequence of sparse or
inaccurate information, poor judgement in parameter estimation, and suspected overreliance upon
default parameters. Regardless of the high quality of the model formulation, the quality of the outputs
will retain the deficiencies of the inputs, and may well amplify them further. Agency personnel are
clearly aware of problems in this area. Below are highlighted some of the parameters of greatest
concern.
3.3.1 Source Term Parameters
Most members of the MMRS believe that the largest single source of uncertainty in the risk
analysis was probably that related to quantification of the source term. Problems include sparse or
inaccurate information on identification of types of wastes present (e.g., presence of NAPLs), on
quantification of waste quantities, and on estimation of waste distribution. Given the time and budget
constraints under which it is operating, it is highly questionable whether the Agency could significantly
improve upon the extensive and thorough job it has already done in compiling the source-term data.
Nonetheless, at a minimum, the Agency should ensure that the uncertainty estimates in the RIA fairly
reflect the uncertainties in this aspect of the model input.
The MMRS believes that consideration of the quantity and quality of waste information should
be a criterion for the inclusion of a particular facility in the facility selection process. As explained by
the Agency in its presentations, the 79 sites were selected randomly from approximately 5,800 sites
nation-wide; for many of these sites, information on the wastes is often sketchy or non-existent.
Because a computer model cannot provide results that are any more precise or accurate than the input
data used, there may be no issue more important than ensuring that the model input has the most
accurate information possible on waste characteristics and history.
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An appropriate criterion for facility selection might be a requirement for "waste information with both
reasonable quality and quantity." Evaluation of the waste information against such a criterion should
not take much additional effort or affect the purpose of the statistical selection process, particularly
when less than 2% of the sample sites are chosen from 5,800 sites. The expected improvement of the
confidence in the results from this study is obvious.
Another problem that may increase the uncertainty of the waste transport calculations is that the
existing data that have been developed for SWMUs were generally not collected for the purpose of
estimating risks to humans or to ecosystems. The data were collected to define the extent of
contamination at a site, rather than defining the exposures at or near the site. The data are often
deficient in providing information on environmental properties that influence the dynamics of releases to
air, surface water, or ground water. In addition, the structure (dimensional distribution of materials,
physical characteristics) and processes occurring at a site are only partial understood. These short-
comings significantly affect the utility of input data.
3.3.2 Waste Release and Solubility
Predictions of ground water contamination and future growth in the plume are directly
proportional to the mass of leachate assumed to be released to the subsurface from a SWMU. The
release models used for metals and organics, while being good starting points, could be improved.
With regard to metals release, the model's use of the maximum observed concentrations near
known source terms might over- or underestimate metal solubility depending on the environmental
context of the waste site, e.g., pH, redox, aerobic/anaerobic, soil type, organic content of soils and
ground water, etc. Perhaps some of the chemical speciation models e.g., MINEQL, might be examined
to see if they can provide more meaningful estimates of the solubility, complexed, adsorbed, etc.
fractions of metals for use in MMSOILS calculations.
With regard to organics release, it appears that using a multiplier of 100 to estimate organic
leachate concentration is arbitrary at best. The choice of the 100 value incidently corresponds to the
generic Dilution Attenuation Factor (DAF) of 100 used in the Toxicity Characteristic (TC) rule
promulgated by the Agency in 1991. The ideal or the most reliable method for choosing leachate
concentrations might involve choosing the most important solid phases for metals and perhaps aqueous
solubilities based on Raoult's Law for most of the organic compounds. It is also recommended that only
a fraction of the total mass of a chemical in the SWMUs be allowed/available for leaching instead of the
entire 100%. [NOTE: It is recognized that there should be significant attention paid to what the fraction
of total mass that would be allowed to leach might be.]
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3.3.3 Use of Default Values
The MMRS suspects that the modelers relied more heavily than warranted on the use of default
values, although this aspect is difficult to judge from the information provided by the Agency. Clearly,
the OSW/ORD working group needs to address the issue of use of default values, making it very clear
when they are used and why the default value makes sense for the particular application, in the absence
of better data.
3.3.4 Peer Review of Data Base
The MMRS recommends a documented and thorough peer review of all aspects of the data base,
focusing particularly on those parameters to which the results are most sensitive. Such a peer review
does not need to involve the SAB, but occasional consultation with the SAB or the interagency
modeling task force, ATFERM, on the approach and issues to be grappled with might be a useful
exercise.
3.3.5 Data Base for Future Related Modeling Efforts
The MMRS recommends that the Agency build upon the extensive data base it has accumulated
for the Corrective Action RIA, to begin the development of an extensive data base that could be tapped
for other EPA programmatic efforts, such as for a comparable assessment of the risks associated with
NORM wastes and radiologically contaminated sites. The intraagency modeling task force, AFTERM,
may be an appropriate vehicle for organizing and coordinating such an effort in a manner that would be
most beneficial to the potential users.
3.4 Issues of Range of Model Validity
MMSOILS was not designed to estimate contaminant transport and fate for chemicals in sites
With complex hydrology, nor to assess: the environmental behavior of non-aqueous phase contaminants
in ground water. However, these limitations should not necessarily be considered as weaknesses of the
model. Complex sites and Non-Aqueous Phase Liquids (NAPLs) need to be addressed for the RIA; but
remain outside the domain of applicability of the current; MMSOILS construct. The solution lies either
in developing separate models to examine these issues or modifying the current MMSOILS so as to
extend its applicability. Given the current state-of-the-art in our understanding and ability to model
either complex hydrogeology or NAPLs, it may be some time before these aspects can be realistically
introduced into MMSOILS. For example, stochastic modeling of ground water may contribute toward
addressing the complex hydrogeology issue. The literature on this subject continues to grow; however,
the complexity of these kinds of models may preclude their easy incorporation into a scheme such as
MMSOILS. This is not to undermine the importance of these issues, but merely to emphasize that we
are at the cutting edge of science in the development and applications of MMSOILS (albeit that
MMSOILS deals with simple, conservative
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and computationally efficient equations for estimating chemical transport) and progress may be slow.
Some additional questions about model validity and some suggestions for how the Agency might deal
with this issue are provided below.
The Subcommittee offers the following comment on use of stochastic models and Monte Carlo
models. Stochastic models are usually for simple hydrogeology, but with complex parameterization,
and it is doubtful that they are or will be considered useful for a screening analysis. Further, these (the
stochastic models) should be distinguished from Monte Carlo models which generally are simple
deterministic models with random input data. The later are appropriate for uncertainty analysis with a
screening model.]
3.4.1 Extreme Events
How well does the model deal with processes that are event-driven? These applications may be
outside the range of validity of the model. Two examples are offered. First, the water-balance approach
is not expected to work well for sites in arid regions in which average precipitation and
evapotranspiration are approximately equal. Use of the balance approach would lead one to expect no
recharge. While some infiltration and recharge in arid regions does occur as a result of extreme rainfall
events, extreme rainfall events are typically associated with flash flooding. Recharge is more likely due
to confluence of flows along arroyos, and can occur with "normal" rainfall events. Such recharge is
localized, and probably should not be considered in the screening model calculations, unless a facility is
placed along the ephemeral stream.]
The model appears to under-estimate waste transport via surface runoff. Net infiltration is
calculated from precipitation less runoff and evapotranspiration. Runoff is calculated using the curve
number method, which is based on daily rainfall amounts. Precipitation is provided through monthly
rainfall amounts. Daily rainfall amounts are calculated by dividing the monthly rainfall by the average
number of days with rainfall greater than 0.01" per month; .The "wet" days are then distributed
uniformly though the month to calculate infiltration and runoff. This approach increases the likelihood
of infiltration and decreases the potential for runoff. Runoff tends to occur when storms of greater than
normal precipitation occur, or when storms occur on consecutive days. The approach may be
conservative because the ground water pathway appears to dominate the exposures and risks. However,
it is not clear that this was the intent. Actual daily rainfall data should be used for specific locales and
regions where available.
The MMRS recommends that the Agency evaluate the validity of each pathway model to assess
the extent to which extreme events might be expected to contribute to the bulk of contaminant releases,
and the extent to which the model may under- or over-estimate transport.
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3.4.2 Complex Sites
The Subcommittee observes that applicability of MMSOILS is limited by its inability to deal
with complex sites. It is likely that critical investigations of the applicability of MMSOILS will turn up
other complex sites beyond karst (e.g., a limestone region marked by sinks, abrupt ridges, irregular
protuberant rocks, caverns and underground streams) and fractured rock. Sites in glacial till, such as
former gravel pits, may also exhibit more complexity than MMSOILS could reasonably address.
For complex sites, the MMRS recommends that the Agency pursue alternative approaches and
should develop a strategy that combines MMSOILS with an appropriate monitoring strategy. The
outputs from such an effort can also be used to modify and improve the MMSOILS model.
3.4.3 NAPLs
The MMRS strongly endorses ORD's recommendation that the Agency conduct a separate
modeling exercise and obtain expert opinion to develop an improved screening-level modeling of
NAPLs. For dense non-aqueous phase liquids (DNAPLs), a possible modification might be to locate the
source term in the saturated zone: For light non-aqueous phase liquids (LNAPLs), a possible
modification might be to use an alternative volatilization model. Four volatilization models are
available, representing two conceptualizations of the process. One approach is based on Pick's first and
second law, and gives classical solutions to the diffusion equation. The second approach combines
Pick's first law with a moving boundary model for continuity. This is the "Landfarming Equation" of
Thibodeaux and Hwang. A comparison between these approaches shows that the moving boundary
model predicts fluxes that are smaller than the classical diffusion model by a factor of about 0.8 (square
root of 2 divided by pi).
Given the level of accuracy expected from a screening model, these approaches provide
essentially the same result. By choosing the moving boundary model, one can represent cases with a
finite region of contamination, both with and without a cover, using simple algebraic equations. Use of
an effective diffusion coefficient in soil along with appropriate partitioning relationships will also allow
one to account for the presence of air, NAPLs, and water within the pore space, and partitioning of the
constituent within the air, water, soil, and NAIL system.
3.4.4 Development of Guidelines for Assessing Model Applicability to Specific Cases
The MMRS recommends that the Agency develop guidelines in order to assess the applicability
of MMSOILS to specific cases.
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3.5 Issues Relating to Pathway Model Calibration, Verification and Validation
3.5.1 Ground Water Model
The ground water flow module has been verified by comparison of results to those of numerical
models. However, documented comparison of model predictions of chemical transport to field data
would strengthen the scientific credibility of the results and provide a basis for readers to evaluate the
model validity and magnitude of uncertainty.
Another possible means to provide a limited validation of the ground water pathway component
of MMSOILS is to compare its output to that of other peer-reviewed EPA models. The EPA Office of
the Solid Waste (OSW) has developed and used EPA Composite Model for Landfills (NATL)TEPA
Composite Model for Surface Impoundments (EPACMS) model for ground water transport and fate of
contamination for the purpose of regulating RCRA wastes on the national level. MMSOILS is similar in
many respect to the NATL/EPACMS models. Therefore, the MMRS recommends that, for a subset of
SWMUs where ground water plume predictions are made by using MMSOILS, NATL/EPACMS
models also be exercised so as to permit comparison of plume predictions.
3.5.2 Other Pathway Models
The MMRS strongly recommends that documented validation exercises be undertaken for the
remaining environmental transport pathways, e.g., aerosolization, volatilization, surface water runoff,
and bioaccumulation, in order to assess the ability of these pathway models to provide meaningful input
to the RIA.
3.5.3 Guidelines for Calibration, Verification and Validation
The MMRS recommends that the Agency, perhaps through. AFTERM, develop generic
guidelines for model calibration, verification and validation, including criteria for judging whether or
not discrepancies among alternative modeling results or between calculated and measured field data are
significant. In the case of MMSOILS, it recommends that the Agency undertake a root-cause analysis
for discrepancies, where significant, in order to evaluate the potential for systematic bias in the modeling
approach.
3.6 Comments on Remediation Effectiveness
3.6.1 Remediation Times
As part of the RIA process, experts have estimated the time for clean-up of contaminated sites.
Experience cited in EPA's "19 Sites" (a 1989 publication; See Appendix B, References 24 and 25) and
"24 Sites" (a 1992 publication; See Appendix B, References 26 and 27) documents has shown that these
time estimates may be overly optimistic for ground water extraction systems. Even less is known about
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the operation and efficiency of other remedial systems. Because of unidentified sources, vadose zone
contamination, heterogeneities, and the unknown presence of NAPLs, remediation has gone on at a
number of sites for periods well in excess of initial estimates. In addition, for a number of these sites,
the remediation goal has changed from site clean-up to plume containment. The impact of
underestimating the clean-up time is that the clean-up costs will be underestimated, and the benefits
associated with clean-up will be overestimated. The sensitivity of the RIA conclusions to these
estimated remediation clean-up times should be evaluated.
3.6.2 Effect of Unknown Presence of DNAPLs on Remediation Times
MMSOILS and the RIA do not adequately address the presence of NAPLs. It is well recognized
that NAPLs are not always recognized during site characterization. This may result in selection of a
remediation system that is not appropriate for NAPLs, resulting in excessive remediation times and
associated costs, and possibly in remediation goals not being achieved. NAPLs strongly influence the
source term. Effective solubility and partition coefficients are far different when NAPLs are present,
compared to their absence. The degree and timing of contamination events are different when NAPLs
are mobile, as compared to cases with only dissolved phase contamination. These issues should be
addressed in the Corrective Action RIA.
3.6.3 Remediation Effectiveness
According to the RIA documentation, most of the risk is associated with the ground water
pathway. To calculate the benefits of corrective action, the MMSOILS model is run for each site to
develop the extent and concentration of the plume over the time period of interest. The plumes are then
aggregated to obtain the baseline or pre-remediation conditions. For sites requiring clean-up, a remedial
action, plan is identified, and the effectiveness of each remedial scheme is assumed. The extent of
remediation is applied to each plume, and the plumes are aggregated to provide the post-remediation
concentration distributions. Exposures and risks are then calculated for the two conditions to evaluate
the benefits of corrective action.
At least two questions arise with regard to this procedure. The first concerns the assumed level
of remediation achieved with each applied technology. For some cases, especially NAPLs, the assumed
extent of remediation may be too high. In fine-grained soils and fractured or karst rock, it is doubtful
that complete remediation of LNAPLs is achievable. For DNAPLs the assumed levels of containment
and remediation are also in question. The sensitivity of the RIA analysis to these assumed levels of
remediation should be evaluated.
The remediation effectiveness predictions are, at times, made by using the MMSOILS model
directly. But at other times the Agency has used post-processing through the use of a decay or a percent
removed value. For simplicity reasons, several assumptions regarding failure of caps, liners and barriers
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etc., have been used. A simplified decay rate coefficient (K) has been employed to calculate the change
in concentrations at the exposure location. In the case of ground water pump and removal remedy, it is
very unclear as to how the K value is derived or how realistic this approach is in representing the
appropriator of the response. It is recommended, therefore, that a closer review of the K value for
choosing the quantitative number for sites be made.
3.6.4 Inclusion of Biologically-Based Remediation Technologies
The suite of remediation technologies used in the analysis -should be expanded to reflect the
realities of emerging technologies. The principal defect is the parsimonious use of biologically-based
treatment technologies. Although these may not at this time be considered as proven technologies, the
scientific principles upon which the technologies are based are sound. It is therefore entirely reasonable
to assume that over the 128-year time frame spanned by the analysis that these technologies will become
widely used. The magnitude of uncertainty associated with these technologies is certainly no greater
than that associated with the data base of source terms and transport parameters upon which the EPA has
based its analysis.
A significant advantage of the biologically-based treatment technologies is that they will likely
provide a more cost-effective treatment approach than other currently available remedial technologies.
3.6.5 Risks of Remediation
The MMRS recommends that the risk analysis be modified to recognize risks that may be
incurred through the remediation process. It is conceivable that the very act of remediation could incur a
higher level of risk than what would be reduced through remediation. This potential trap should be
avoided by estimating the risks of remediation and including them in : the analysis.
3.7 Issues Relating to Assessment of Uncertainty
3.7.1 Uncertainty Estimation Protocol
No guidance is provided to the user as to how one can obtain a qualitative or quantitative
estimate of the uncertainties associated with each pathway. Given the high stakes involved in terms of
potential commitment of national resources, such an estimate is as important as, or possibly even more
important than, the final result.
The MMRS recommends that any numerical results emanating from the RIA analysis must be
presented as a range. Presenting results as "a number" tends to give the reader a false sense of accuracy
which in this instance is particularly dangerous given the incomplete level of the input data set and our
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incomplete comprehension of the fate of hazardous constituents in the environment. Adding on the
uncertainties associated with risk analysis even further expands the error bands.
The model should be subject to formal, comprehensive sensitivity and uncertainty analysis.
Some initial efforts have been completed by the Agency, emphasizing the ground water pathway.
Similar analyses should be completed for the other pathways in the model, and finally for the entire
model.
Sensitivity analyses can be used to identify the critical parameters associated with predictions of
contaminant concentrations along various pathways. This information can be used to determine what
the critical data are for improving model predictions, and to simplify the model structure without
sacrificing accuracy or precision of model results. Both applications of sensitivity results are important
in increasing the capabilities of the model for site-specific use and in improving its utility in the RIA
process.
3.7.2 Development of High-End Risk Estimates
The MMRS is concerned that the simple protocol followed to obtain high-end risk estimates may
be inadequate in that this estimate in some cases apparently gave rise to lower risks than did the central
tendency estimate. The Subcommittee recommends that the Agency review its protocol.
3.8 Interpretation of Results for Health Risk Analysis
3.8.1 Health Risk as the Assessment Endpoint
The model produces outputs which estimate concentrations in various environmental media over
time. These concentrations in various media are then applied to various exposures gathered as an initial
phase of risk assessment for the protection of humans and ecosystems. The result of the risk
assessments comparing no-action and remedial action scenarios are then used as major inputs into a
cost-benefit analysis. The use of various assumptions in exposure assessments as part of the risk
assessment process has been highlighted previously as a major source for uncertainties in risk
assessments.
Three documents refer to health risk assessment implications: MMSOILS (Documentation and
User's Manual, the Corrective Action RIA draft, and appendices for the latter. See Appendix B;
References 1 through 3). These implications are drawn from exposure analyses based on applying the
models described in MMSOILS. Because health risks are the predominant focus of current
environmental protection initiatives, the adequacy of risk estimates has to serve as the ultimate criterion
of model relevance and accuracy.
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3.8.2 Empirical Validation of Exposure Estimates
Section 9.0 of the MMSOILS document (See Appendix B; Reference 6) provides equations for
determining exposure due to inhalation, ingestion, and dermal contact. (Section E of the RIA document
addresses some of these as well.) The relevant variables come from the list on page 9-4, and includes 21
parameters, some of which are given default values in tables. These values, however, are simply guides
to translating air, water, and soil concentrations into exposure estimates. These presumed concentrations
are connected to human exposures through a long chain of assumptions. Because of this lack of direct
coupling, questions arise about how the chain might be shortened. Are there any empirical data by
which the models might be tested? Is there any way in which they might be acquired? Measures as
simple as uptake by plants might be useful, for example. Or, analyses of animal carcasses at particular
sites to which the modeling has been applied. Is empirical validation, the process by which theories and
models are tested in science, out of the question?
3.8.3 Inconsistent Treatment of Cancer and Noncancer Health Risks
The other aspect of health risk assessment treated in these documents is described in the draft
report on Regulatory Impact Analysis (See Appendix B; Reference 7) in the chapter on human health
benefits (Chapter 7). Here, the ingenuity of the modeling effort encounters barriers that the
Environmental Health Committee has noted in some of its reports, the most recent of which is entitled
Superfund Site Health Risk Assessment Guidelines. February, 1993 (See Appendix B; Reference 20).
One of these barriers is the EPA practice of adopting radically different approaches to cancer and
noncancer risk assessment. Cancer risk is given as a probability; systemic endpoints are described by
Reference Doses (RfDs). One example of the confusion this causes appears on page 7-15. Footnote 21
notes that cancer risk is calculated by averaging intake over a lifetime; that is, dose distribution is
ignored. For noncancer risk, intake is averaged over exposure duration, with an averaging time of 9
years.
These assumptions can be disputed and might even be reversed in some instances. Perhaps more
important, the averaging of assumptions could easily distort risk. For example, for both categories of
risk, exposure during early and prenatal development might be the crucial values, and exposure peaks
the major source of adverse consequences.
3.8.4 Inaccurate Identification of Critical Health Effects
Some of the other material also arouses suspicion about the adequacy of the modeling effort.
The table in Exhibit 7-19a (See Appendix B; Reference 7) lists some of the agents driving noncancer
effect levels. The critical health effects noted there are perplexing. For example, the critical health
effect for chromium VI is given as central nervous system effects, which is contrary to the commonly
known effects ascertained by neurotoxicologists; for nickel, it is reduced body and organ weight rather
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than hypersensitivity reactions; for toluene, a prototypical neurotoxicant, it is given as liver and kidney
pathology. There are several other peculiar entries.
3.8.5 Questionable Treatment of Different Waste Classes
Another difficult problem is how to handle the kinds of mixtures found at RCRA sites. The
properties of the Hazard Index, offered as a solution, cannot be applied automatically. For example, if
101 agents are identified, each with a Hazard Quotient of 0.01, the additivity assumption will yield a
Hazard Index above 1.0. Would such a situation really present a bothersome risk?
Another additivity problem arises with cancer agents. The MMRS disagrees with the treatment
noted on pages 7-56 to 7-57 (See Appendix B; Reference 7), in which agents with different weight-of-
evidence classes are combined by adding risks, because the MMRS feels that it is misleading to add
risks across class A (known) and class C (suspected) carcinogens. Despite the warning contained within
the RIA that such a procedure may overstate the true cancer risk, the presentation of such combined
results is bound to have an impact.
3.8.6 Other Sources of Hazardous Wastes
Finally, going beyond the contents of the current documents, it would be useful to point out, not
just the intrinsic limitations of this rather ingenious and extensive modeling effort, but also where it
might coincide with the full scope of EPA's responsibilities. Certain agents are not easily controlled and
may pose health risks beyond the substances discussed in these reports. Methylmercury, for example, is
partially a product of fossil fuel combustion. Inorganic mercury is discharged when coal and oil are
burned, ascends into the atmosphere!, travels in a global mercury cycle, returns to earth in rain, and is
transformed to the toxic methyl form by organisms in the bottom sediment of bodies of water.
Methylmercury travels up the food: chain in a continuous cycle of bioconcentration to lodge in fish that
then reach human consumers. In keeping with the spirit of Reducing Risk (See Appendix B; References
9 through 12, and particularly Reference 10), such scenarios should be included in efforts such as the
current reports.
3.9 Comments on Use of MMSOILS in Corrective Action RIA
3.9.1 Facility Selection Process
The facility sample used for the analysis is incorrectly characterized as being a "stratified,
random sample." The fact that various facilities were eliminated from the analysis for various reasons,
some of which are quite valid, belies the concept of the sample being "random." The MMRS suggests
that the word "random" be deleted from any reference to the sample.
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3.9.2 Use for National-Level Screening
The model is emphasized as a screening tool. However, it is also clear that the model is used
beyond screening in estimating the fate and transport of contaminants. If the model is used in a
screening mode, then validation efforts should focus on how well the model screens. If the model is to
be used in estimating spatial-temporal values of contaminant concentrations, then validation requires
comparisons with these kinds of data. Care must be taken in not confusing the two different uses of the
model. Similarly, the uncertainties associated with model predictions must be evaluated in the context
of model use. If screening is the emphasis, then perhaps greater uncertainties on the model outputs can
be tolerated in making a coherent decision. If detailed characterizations of contaminant concentrations
are needed, for example, to feed into a risk assessment, then it is likely that greater accuracy and
precision will be required if the model is to effectively contribute to these estimations. The SAB has
given modeling-related advice in a number of instances to the Agency, and the Subcommittee refers the
staff to this (See Appendix B; References 11, 12, 13, 18, 19, 21, and 22).
Instead of attempting to estimate a national average by aggregating the 38 site-specific
applications of MMSOILS, it might be just as valid to use as much data from the 5,800 sites to construct
an "average" national waste site and apply the model to this single hypothetical site. This may be
particularly effective given that the validity of each site-specific simulation is not held to be very
accurate. Analyzing the hypothetical site with the model in this fashion might be more in line
conceptually with the notion of screening. The Subcommittee wishes to remind and caution the Agency
that a screening model can estimate the spatial-temporal values of concentrations; however, it is limited
in the scenarios it can consider. Further, it (the screening model) is not suitable for site-specific
applications where site details should be included in the model.
Subject to the reservations stated above, the MMRS agrees that MMSOILS may be an
appropriate to use as a screening-level model at the national level.
3.9.3 Presentation of Results in Corrective Action RIA
The Agency is to be commended for having drafted such a well-organized and well-written
report for such a highly complex issue as that for the Corrective Action RIA.
The MMSOILS model adopted for the study, as clearly stated by the Agency, was intended to be
used as a screening tool. The assumptions made and approaches followed in the development of this
model make the use of it appropriate for the screening exercise, but the current data base needs
significant improvement. However, the major goal of the RIA is to estimate the cost with incremental
benefit for corrective actions. Therefore a quantitative result is required from the study. It is commonly
recognized -and accepted as a reality - that the MMSOILS model application could derive exposure
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estimates no better than "order(s) of magnitude". Although the results may still be valuable for the
purposes of screening, e.g., for assessing relative clean-up costs or cost versus incremental benefits
between various sites, their utility is brought into question when the results are intended to be used for
evaluating remediation costs, i.e., how meaningful it is when a cost estimate is given with a built-in
uncertainty of one or more orders of magnitude, considering the total cost at the national level would
probably involve hundreds of billions of discounted dollars. In other, words, how can results at this
level of confidence be used in the policy/regulation decision making process?
3.9.4 Presentation of Uncertainty Analysis in RIA
The major concern of the MMRS with respect to the contents of the RIA relate to an inadequate
representation of the magnitude of the uncertainties associated with the cost and benefit estimates. For
the RIA, how much uncertainly can you live with and still make an intelligent decision regarding the
efficacy of RCRA clean-up. This issue again pertains to the use of MMSOILS as a screening model,
versus a realistic process model for estimating exposure and fate concentrations.
3.10 Other User Groups for MMSOILS
3.10.1 Applicability to Other EPA Program Activities
The utility of MMSOILS for estimating ecological risks may loom in future importance, for
example in relation to CERCLA. Therefore, the MMRS recommends that this modeling construct
should continue to receive attention, both in terms of review and in resources, to ensure that it has utility
beyond RCRA.
3.10.2 Use for State-Level Screening
On a longer-term perspective, the MMRS recommends that the Agency consider what might be
its role in providing guidance to states as to the appropriate types of models to use for state-level
screening calculations.
3.10.3 Other User Groups
The documentation makes it clear that MMSOILS is meant to be used by non-specialists. The
manual needs stronger statements to emphasize the model limitations to such users, to recommend
alternative models, and to emphasize the inapplicability of the model to site-specific evaluations. With
regard to model limitations, the MMRS recommends that each pathway model include a summary table
listing assumptions, and clearly stating the known parameter sensitivity alongside site characteristics
which might invalidate model results or which would be expected to lead to results with order-of-
magnitude uncertainties.
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APPENDIX A - BRIEFING AND REVIEW MATERIALS
Review Materials for the April 22. 1993 SAB/EEC/MMRS Review Meeting:
1) U.S. EPA/OSWER, A memo entitled "Charge for SAB Review of Regulatory Impact Analysis
Supporting the Corrective Action Regulation," signed by Richard J. Guimond, Assistant Surgeon
General, U.S. Public Health Service and Deputy Assistant Administrator, Office of Solid Waste
and Emergency Response to Dr. Donald G. Barnes, Director, Science Advisory Board, March
26, 1993
2) U.S. EPA/OSWER & ORD, A jointly signed memo entitled "Request for SAB Review of RCRA
Corrective Action RIA," from Peter W. Preuss, Director, Office of Technology Transfer and
Regulatory Support, and Richard J. Guimond, Assistant Surgeon General, U.S. Public Health
Service and Deputy Assistant Administrator, Office of Solid Waste and Emergency Response to
-: Dr Donald G. Barnes, Director, Science Advisory Board, June 26, 1992
3) U.S. EPA/SAB, Environmental Engineering Committee, MMSOILS Model Review
Subcommittee, Notice of Subcommittee Open Meeting, Federal Register, Vol. 58, No. 67,
Friday, April 9, 1993, p. 18395
4) U.S. EPA, "MMSOILS: Multimedia Contaminant Fate, Transport, and Exposure Model:
Documentation and User's Manual," Office of Research and Development [Prepared by the
Exposure and Assessment Group, Office of Health and Environmental Assessment and the
Office of Environmental Processes and Effects Research], Washington, D.C. 20460, EPA
XXX/XXX/XXX draft document dated September 1992
5) U.S. EPA, "Draft Regulatory Impact Analysis for the Final Rulemaking on Corrective Action for
Solid Waste Management Units: Proposed Methodology for Analysis," Office of Solid Waste,
March 1993.
6) U.S. EPA, "Draft Regulatory Impact Analysis for the Final Rulemaking on Corrective Action for
Solid Waste Management Units: Proposed Methodology for Analysis," APPENDICES, Office of
Solid Waste, March 1993
Briefing Materials from the April 22. 1993 SAB/EEC/MMRS Review Meeting:
7) U.S. EPA/OSW briefing entitled "Overview: Corrective Action Regulatory Impact Analysis,
Proposed Methodology," Presented to the MMSOILS Model Review Subcommittee (MMRS) of
the Environmental Engineering Committee (EEC), Science Advisory Board (SAB), by the Office
of Solid Waste (OSW),. April 22, 1993
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APPENDIX A - BRIEFING AND REVIEW MATERIALS: CONTINUED
Briefing Materials from the April 22. 1993 SAB/EEC/MMRS Review Meeting:
Continued:
8) U.S. EPA/OSW, briefing entitled "Application of the MMSOILS Model in the Corrective Action
Regulatory Impact Analysis," Presented to the MMRS of the SAB's EEC by the Office of Solid
Waste (OSW), April 22, 1993
9) U.S. EPA/OSW briefing entitled "Risk Assessment in the Corrective Action Regulatory Impact
Analysis," Presented to the MMRS of the SAB's EEC by the Office of Solid Waste (OSW),
April 22, 1993
10) U.S. EPA/OSW briefing entitled "Simulation of Remedy Effectiveness in the Corrective Action
Regulatory Impact Analysis," Presented by the Office of Solid Waste (OSW) to the MMRS of
the SAB's EEC, April 22, 1993
11) U.S. EPA/ORD briefing entitled "RCRA Corrective Action RIA: ORD Input on Significant
Technical Issues," Prepared and Presented by Stephen G. Schmelling of the Robert S. Kerr
Environmental Research Laboratory to the MMRS of the SAB's EEC, April 22, 1993
12) U.S. EPA/ORD briefing entitled "RCRA Corrective Action RIA: ORD Participation (Fate &
Transport), Presented to the MMRS of the SAB's EEC, April 22, 1993
Briefing Materials from the June 29. 1993 SAB/EEC/MMRS Review Meeting:
13) U.S. EPA/SAB, Environmental Engineering Committee (EEC), MMSOILS Model Review
Subcommittee, Notice of Subcommittee Open Meeting for June 29,. 1993 on MMSOILS Review,
-as well as EEC Open Meeting of June 30 -July 1, 1993, Federal Register. Vol. 58, No. 108,
Tuesday, June 8, 1993, p.32122
14) U.S. EPA/OSW briefing entitled "Model Selection for the Corrective Action Regulatory Impact
Analysis," Presented to the MMRS and selected specialists of the SAB's EEC by the Office of
Solid Waste (OSW), June 29, 1993
15) U.S. EPA/OSW briefing entitled "Sample Selection for the Corrective Action Regulatory Impact
Analysis," Presented to the MMRS and selected specialists of the SAB's EEC by the Office of
Solid Waste (OSW), June 29, 1993
A-2
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APPENDIX A - BRIEFING AND REVIEW MATERIALS: CONTINUED
Briefing Materials from the June 29. 1993 SAB/EEC/MMRS Review Meeting:
Continued:
16) U.S. EPA/OSW, an untitled summary sheet, which lists SAB Recommendations and the
OSW/ORD Next Steps, one page, both sides, June 29, 1993
17) U.S. EPA/OSW briefing entitled "Facility Characterization in the Corrective Action Regulatory
Impact Analysis," Presented to the MMRS and selected specialists of the SAB's EEC by the
Office of Solid Waste (OSW), June 29, 1993
18) U.S. EPA/ORD briefing entitled "SAB Presentation on Corrective Action RIA: MMSOILS
Model Validation and RIA Uncertainty Assessment," a presentation by Mr. Gerry Laniak of
ORD-Athens, June 29, 1993
19) U.S. EPA/ORD untitled briefing comparing site-specific parameters by modeling teams, using
central tendency and high-end estimates, and plots comparing the results of monitoring and
modeling data by concentration (ppm), as well as plots on modeling and monitoring minimum
curve and maximum error, a presentation by Mr. Gerry Laniak of ORD-Athens, June 29, 1993
A-3
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APPENDIX B - REFERENCES CITED
1) Keely, J.F., "The Use of Models in Managing Ground-Water Protection Programs," EPA/600/8-
87/003, ORD Ada, OK, 1987, 72p.
2) Kezsbom, A. and A.V. Goldman, "The boundaries of groundwater modeling under the law:
Standards for excluding speculative expert testimony," Tort & Insurance Law Journal, Vol.
XXVII, No. 1,1991, pp. 109-126
3) Konikow, Leonard F. and John D. Bredehoeft, "Ground-Water Models Cannot be validated,"
Advances in Water Resources 15, 1992, pp. 75-83
4) National Research Council, "A review of ground water modeling needs for the U.S. Army,"
Washington, D.C., 1992
5) National Research Council, Ground Water Models; Scientific and Regulatory Applications,
National Academy Press, Washington, D.C., 1990, 303 pp.
6) U.S. EPA, "MMSOILS: Multimedia Contaminant Fate, Transport, and Exposure Model:
Documentation and User's Manual," Office of Research and Development [Prepared by the
Exposure and Assessment Group, Office of Health and Environmental Assessment and the
Office of Environmental Processes and Effects Research], Washington, D.C. 20460, EPA
XXX/XXX/XXX draft document dated September 1992
7) U.S. EPA, "Draft Regulatory Impact Analysis for the Final Rulemaking on Corrective Action for
Solid Waste Management Units: Proposed Methodology for Analysis," Office of Solid Waste,
March 1993
8) U.S. EPA, "Draft Regulatory Impact Analysis for the Final Rulemaking on Corrective Action for
Solid Waste Management Units: Proposed Methodology for Analysis," APPENDICES, Office of
Solid Waste, March 1993
9) U.S. EPA, Expert Panel on the Role of Science at EPA (Loehr, Goldstein, Nerode and Risser),
"Safeguarding the Future: Credible Science!, Credible Decisions," EPA/600/9-91-050, March
1992
10) U. S. EPA, Memorandum entitled, "EPA Definition of Pollution Prevention," from F. Henry
Habicht II, Deputy Administrator, to all EPA Personnel, May 28, 1992
B-l
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APPENDIX B - REFERENCES CITED: CONTINUED:
11) U.S. EPA/SAB, "Review of the EPA Office of Solid Waste's (OSW) Unsaturated Zone Code for
the OSW Fate and Transport Model (FECTUZ)," Report of the Unsaturated Zone Code
Subcommittee of the Environmental Engineering Committee (EEC), Science Advisory Board
(SAB), EPA-SAB-EEC-88-030, July 12, 1988
12) U.S. EPA/SAB, "Resolution on Use of Mathematical Models by EPA for Regulatory Assessment
and Decision-Making," Report of the Modeling Resolution Subcommittee of the Environmental
Engineering Committee (EEC), Science Advisory Board (SAB), EPA-SAB-EEC-89-012,
January 13, 1989
13) U.S. EPA/SAB, "Review of the CANSAZ Flow and Transport Model for Use in EPACMS,"
Report of the Saturated Zone Model Subcommittee of the Environmental Engineering
Committee (EEC), Science Advisory Record (SAB), EPA-SAB-EEC-90-009, March 27, 1990
14) U.S. EPA/SAB, "Reducing Risk: Setting. Priorities and Strategies for Environmental
Protection," The report of the Science Advisory Board (SAB), Relative Risk Reduction
Strategies Committee, EPA-SAB-EC-90-021, September 1990
15) U.S. EPA/SAB, "Relative Risk Reduction Project: Reducing Risk, Appendix A," The Report of
the Ecology and Welfare Subcommittee of the Relative Risk Reduction Strategies Committee
(RRRSC) of the Science Advisory Board (SAB), EPA-SAB-EC-90-021A, September 1990
16) U.S. EPA/SAB, "Relative Risk Reduction Project: Reducing Risk, Appendix B," Report of the
Human Health Subcommittee of the Relative Risk Reduction Strategies Committee (RRRSC) of
the Science Advisory Board (SAB), EPA-SAB-EC-90-021B, September 1990
17) U.S. EPA/SAB, "Relative Risk Reduction Project: Reducing Risk, Appendix C," Report of the
Strategic Options Subcommittee of the Relative Risk Reduction Strategies Committee (RRRSC)
of the Science Advisory Board (SAB), EPA-SAB-EC-90-021C, September 1990
18) U.S. EPA/SAB, "Review of OSWER's Draft Report on Usage of Computer Models in the
Hazardous Waste/Superfund Programs and Proposed Pilot Study," Report of the Modeling
Project Subcommittee of the Environmental Engineering Committee (EEC), Science Advisory
Board (SAB), EPA-SAB-EEC-91-016, September 6, 1991
B-2
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APPENDIX B - REFERENCES CITED: CONTINUED
19) U.S. EPA/SAB, 'Teachability Phenomena: Recommendations and Rationale for Analysis of
Contaminant Release," A Self-Initiated SAB Report on teachability Phenomena by the
Environmental Engineering Committee (EEC), EPA-SAB-EEC-92-003, October 29, 1991
20) U.S. EPA/SAB, "Superfund Site Health Risk Assessment Guidelines: Review of the Office of
Solid Waste and Emergency Response's (OSWER) Draft Risk Assessment Guidance for
Superfund Human Health Evaluation Manual," A report of the Environmental Health Committee
(EHC) of the Science Advisory Board (SAB), EPA-SAB-EHC-93-007, February 22, 1993
21) U.S. EPA/SAB, "Review of the Office of Solid Waste and Emergency Response (OSWER)
Assessment Framework for Ground-Water Model Applications," A report of the Modeling
Project Subcommittee of the Environmental Engineering Committee (EEC), Science Advisory
Board (SAB), EPA-SAB-EEC-93-013, June 21, 1993
22) U.S. EPA/SAB, "Review of Draft Agency Guidance for Conducting External Peer Review of
Environmental Regulatory Modeling," A letter report of the Modeling Peer Review
Subcommittee of the Environmental Engineering Committee (EEC), Science Advisory Board
(SAB), EPA-SAB-EEC-LTR-93-013, August 12, 1993
23) U.S. EPA, Risk Assessment Forum, "Framework for Ecological Risk Assessment, EPA/630/R-
92/001, February 1992
24) U.S. EPA, "Evaluation of Ground-Water Extraction Remedies,"Office of Emergency and
Remedial Response (OERR), EPA/540/2-89/054, Volume 1: Summary Report, 1989
25) U.S. EPA, "Evaluation of Ground-Water Extraction Remedies," Office of Emergency and
Remedial Response (OERR), EPA/540/2-89/054b, Volume 2: Case Studies 1 -19, 1989
26) U.S. EPA, "Evaluation of Ground-Water Extraction Remedies: Phase II, Office of Emergency
and Remedial Response (OERR), Publication 9355.4-05, Volume 1: Summary Report, 1992
27) U.S. EPA, "Evaluation of Ground-Water Extraction Remedies: Phase II, Office of Emergency
and Remedial Response (OERR), Publication 9355.4-05A, Volume 2: Case Studies and Updates
(on 24 Sites), 1992
B-3
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APPENDIX C - GLOSSARY OF TERMS AND ACRONYMS
ATFERM
CANSAZ
Class A
Class C
Cwi
Cdwl
cv
DAF
DF
DNAPLs
BAG
EEAC
EEC
EHC
EPA
NATL
EPACMS
EPEC
FECTUZ
K
Kd
KQW
LNAPLs
MMSOILS
MINEQL
MMRS
NAPLs
NORM
OEPER
(Ad Hoc) Agency Task Force on Environmental Regulatory Modeling
Combined Analytical-Numerical Saturated Zone (Flow and transport model for
use in EPACMS)
Known Human Carcinogen
Suspect Human Carcinogen
Concentration of Chemical in Waste Layer (milligrams/kilogram)(For instance,
see Section 3.1.3)
See Kdwi, below
Contingent Valuation Methodology
Dilution and Attenuation Factor (For instance, see Section 3.3.2)
Fraction of Day During Which Exposure Occurs (hours/24 hours)(For instance,
see Section 3.1.3)
Dense Non-Aqueous Phase Liquids
Exposure Assessment Group (U.S. EPA/ORD/OHEA)
Environmental Economics Advisory Committee (SAB/EEAC)
Environmental Engineering Committee (SAB/EEC, also referred to as "The
Committee")
Environmental Health Committee (SAB/EHC)
U.S. Environmental Protection Agency (U.S. EPA, or "The Agency")
EPA Composite Model for Landfills
EPA Composite Model for Skirface Impoundments
Ecological Processes and Effects Committee (SAB/EPEC)
Finite-Element Code for Simulating Water Flow and Solute Transport in the
Unsaturated Zone (Variably saturated porous media)
First order Coefficient, Which Measures Losses of Contaminant Due to
Pumping (Also referred to as Simplified Decay Rate Coefficient) (For instance,
see Section 3.6.3)
Decay Rate/Distribution Coefficient. Also Referred to as Soil-Water Partition
Coefficient (milliliters/gram)
Solid-Water Partition Coefficient Between the Solid Waste and the Liquid
Leachate (liters/kilogram). (Also referenced as Cdwi) (For instance, see Section
3.1.3)
Water-Phase Mass Transfer Coefficient. (Also referred to as the Octanol-Water
Partition Coefficient.) (For instance, see Section 3.2.5)
Light Non-Aqueous Phase Liquids
Mathematical Model for Spoils (A Multi-Media Contaminant, Fate, Transport
and Exposure Model.)
A Chemical Speciation Model (For instance, see Section 3.3.2)
MMSOILS Model Review Subcommittee (U.S. EPA/SAB/EEC; Also referred
to as "the Subcommittee")
Non-Aqueous Phase Liquids
Naturally-Occurring Radioactive Material
Office of Environmental Processes and Effects Research (U.S. EPA/ORD)
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APPENDIX C - GLOSSARY OF TERMS AND ACRONYMS: CONTINUED
OHEA
ORD
OSW
OSWER
pH
Qm
qm
RCRA
RfDs
RIA
SAB
SWMUs
TC
U.S.
Office of Health and Environmental Assessment (U.S. EPA/ORD)
Office of Research and Development (U.S. EPA)
Office of Solid Waste (U.S. EPA)
Office of Sk)lid Waste and Emergency Response (U.S. EPA)
Negative Log of Hydrogen Ion Concentration
Monthly Net recharge (cubic meters/month)(Also Referenced as qm) (For
instance, see Section 3.1.3)
Monthly Net Recharge (cubic meters/month)(Also Referenced as Qm) (For
instance, see Section 3.1.3)
Resource Conservation and Recovery Act
Reference Doses
Regulatory Impact Analysis
Science Advisory Board (U.S. EPA)
Solid Waste Management Units
Toxicity Characteristic
United States
C-2
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DISTRIBUTION LIST
Deputy Administrator
Assistant Administrators
EPA Regional Administrators
EPA Laboratory Directors
Deputy Assistant Administrator for Office of Research and Development (ORD)
Director, Center for Environmental Research Information (CERI)
Director, Office of Environmental Processes and Effects Research (OEPER)
Director, Office of Health and Environmental Assessment (OHEA)
Director, Exposure and Assessment Group (EAG)
Deputy Assistant Administrator for Office of Solid Waste and Emergency Response
(OSWER)
Director, Office of Emergency and Remedial response (OERR)
Deputy Director, OERR
Director, Office of Solid Waste (OSW)
Deputy Director, OSW
EPA ATFERM Co-Chairs (Agency Task Force on Environmental Regulatory
Modeling)
EPA Headquarters Library
EPA Regional Libraries
EPA Laboratory Libraries
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