Hazard Ranking System Issue Analysis:
Containment Rating Factor
MITRE
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Hazard Ranking System Issue Analysis:
Containment Rating Factor
Stuart A. Haus
March 1987
MTR-86W199
SPONSOR:
U.S. Environmental Protection Agency
CONTRACT NO.:
EPA-68-01-7054
The MITRE Corporation
Civil Systems Division
7525 Colshire Drive
McLean, Virginia 22102-3481
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irmw
Department Approva
MITRE Protect Approval: /< LsCS <>J
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ABSTRACT
This report addresses issues related to the modification of the
current HRS containment factor. Advantages and disadvantages of
basing the containment factor on the RCRA Subtitle C land disposal
regulations are discussed. A number of alternative approaches for
modifying the containment factor so as to base it on evaluation
criteria other than the RCRA Subtitle C regulations are identified
and briefly examined. Two of these alternatives are recommended for
possible further development. These two alternatives are:
• The integration of evidentiary and predictive criteria in
the containment factor.
• The integration of a physical state factor into the
containment factor.
Suggested Keywords: Superfund, Hazardous waste, Hazard ranking,
Containment.
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ACKNOWLEDGEMENT
The author wishes to acknowledge Greg Vogel for his valuable
contribution in the development and analysis of the options
presented in this report.
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TABLE OF CONTENTS
LIST OF TABLES
1.0 INTRODUCTION
1.1 Background 1
1.2 Issue Description 3
1.3 Scope and Approach 5
1.4 Organization of the Report 6
2.0 REVIEW OF CURRENT HRS CONTAINMENT EVALUATION METHODOLOGY 9
2.1 Overview of HRS Containment Factor 9
2.2 Analysis of Current HRS Containment Factor 14
2.3 Issues Relevant to the Revision of the HRS Containment 19
Factor
2.3.1 Screening Out Sites 20
2.3.2 Differentiation of Sites 22
2.4 Summary of Containment Factors in Other Ranking Systems 23
3.0 CONTAINMENT EVALUATION ALTERNATIVES 27
3.1 Overview of Alternatives 27
3.2 Updating of Present RCRA-Based Criteria 30
3.3 Integration of Containment Factor With a Factor Based 32
on Waste Quantity
3.4 Development of Evidentiary Criteria With a Zero Value 33
3.5 Development of Evidentiary Criteria Without a Zero Value 36
3.6 Integration of Evidentiary and Predictive Criteria 37
3.7 Development of Time-Dependent Criteria 38
3.8 Use of Criteria Based on Waste Disposal Location 41
3.9 Development of Criteria Based on Site Drainage 44
3.10 Integration of Containment and Physical State Factors 46
3.10.1 Use of Evidentiary Criteria 48
3.10.2 Use of Predictive Criteria 49
4.0 SUMMARY AND RECOMMENDATIONS 51
APPENDIX A - REVIEW OF CONTAINMENT FACTORS IN OTHER SITE 59
RANKING SYSTEMS
APPENDIX B - BIBLIOGRAPHY 87
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LIST OF TABLES
Table Number Page
2-1 HRS Containment Factor for Ground Water Route 12
2-2 HRS Containment Factor for Surface Water Route 13
2-3 Distribution of HRS Containment Factor Values 16
for Facilities in the Automated NPL Technical
Data Base
3-1 Illustrative Containment Factor Values Based 43
on Waste Disposal Location
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1.0 INTRODUCTION
1.1 Background
The Comprehensive Environmental Response, Compensation, and
Liability Act of 1980 (CERCLA) (PL 96-510) requires the President to
identify national priorities for remedial action among releases or
threatened releases of hazardous substances. These releases are to
be identified based on criteria promulgated in the National
Contingency Plan (NCP). On July 16, 1982, the Environmental
Protection Agency (EPA) promulgated the Hazard Ranking System (HRS)
as Appendix A to the NCP (40 CFR 300; 47 FR 31180). The HRS
comprises the criteria required under CERCLA and is used by EPA to
estimate the relative potential hazard posed by releases or
threatened releases of hazardous substances.
The HRS is a means for applying uniform technical judgment
regarding the potential hazards presented by a release relative to
other releases. The HRS is used in identifying releases as national
priorities for further investigation and possible remedial action by
assigning numerical values (according to prescribed guidelines) to
factors that characterize the potential of any given release to
cause harm. The values are manipulated mathematically to yield a
single score that is designed to indicate the potential hazard posed
by each release relative to other releases. This score is one of
the criteria used by EPA in determining whether the release should
be placed on the National Priorities List (NPL).
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During the original NCP rulemaking process and the subsequent
application of the HRS to specific releases, a number of technical
issues have been raised regarding the HRS. These issues concern the
desire for modifications to the HRS to further improve its
capability to estimate the relative potential hazard of releases.
The issues include:
• Review of other existing ranking systems suitable for
ranking hazardous waste sites for the NPL.
• Feasibility of considering ground water flow direction and
distance, as well as defining "aquifer of concern," in
determining potentially affected targets.
• Development of a human food chain exposure evaluation
methodology.
• Development of a potential for air release factor category
in the HRS air pathway.
• Review of the adequacy of the target distance specified in
the air pathway.
• Feasibility of considering the accumulation of hazardous
substances in indoor environments.
• Feasibility of developing factors to account for
environmental attenuation of hazardous substances in ground
and surface water.
• Feasibility of developing a more discriminating toxicity
factor.
• Refinement of the definition of "significance" as it relates
to observed releases.
• Suitability of the current HRS default value for an unknown
waste quantity.
• Feasibility of determining and using hazardous substance
concentration data.
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• Feasibility of evaluating waste quantity on a hazardous
constituent basis.
• Review of the adequacy of the target distance specified in
the surface water pathway.
• Development of a sensitive environment evaluation
methodology.
• Feasibility of revising the containment factors to increase
discrimination among facilities.
• Review of the potential for future changes in laboratory
detection limits to affect the types of sites considered for
the NPL.
Each technical issue is the subject of one or more separate but
related reports. These reports, although providing background,
analysis, conclusions, and recommendations regarding the technical
issue, may not directly affect the HRS. Rather, these reports will
be used by an EPA working group that will assess and integrate the
results and prepare recommendations to EPA management regarding
future changes to the HRS. Any changes will then be proposed in
Federal Register notice and comment rulemaking as formal changes to
the NCP. The following section describes the specific issue that is
the subject of this report.
1.2 Issue Description
The HRS containment factor is currently a measure of the
methods (either engineered or natural) that have been employed to
minimize or prevent the migration of hazardous substances to ground
water or surface water. Examples of engineered containment methods
include landfill liners, leachate collection systems, diversion
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structures, and diking. Examples of natural containment methods
include locating waste management sites in areas where the terrain
precludes the overland migration* of hazardous substances to surface
water or in areas where there is no ground water or surface water in
the vicinity of the site.
The criteria in the current HRS containment factor are based
upon those land disposal regulations developed, as of early 1982,
under Subtitle C of the Resource Conservation and Recovery Act
(RCRA). Since that time, there have been significant changes in the
RCRA Subtitle C land disposal regulations, and further modifications
are currently being developed in response to requirements mandated
by the Hazardous and Solid Waste Amendments of 1984 (HSWA).
Consequently, concerns have been raised within EPA that the HRS
containment factor should be modified to be more consistent with the
current RCRA Subtitle C land disposal regulations.
Public commenters have not raised technical issues about the
HRS containment factor in either NCP or NPL rulemakings. Those
comments that have been received from the public have been related
to site-specific applications of the containment factor (e.g.,
whether a specific site should have been assigned a containment
factor value of 2 or 3).
*For reasons beyond the scope of this discussion, the HRS does not
assess the potential for hazardous substances to be released to
surface water via the ground water. Consequently, containment
methods relating to ground water discharges to surface water are not
included in this discussion.
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1-3 Scope and Approach
In the absence of public comments on the MRS containment
factor, the original objective of this effort was the development of
options for modifying the MRS containment factor to make it more
consistent with the current RCRA Subtitle C land disposal
regulations. This objective did not include the examination and
development of additional alternative technical approaches for
evaluating containment in the HRS. However, the analysis presented
in Chapter 2 indicates that few, if any, sites currently eligible
for the NPL are likely to have employed containment measures that
even come remotely close to meeting the requirements of the 1982
RCRA Subtitle C regulations, let alone those currently in effect.
For this reason, as well as for other reasons discussed in Chapter 2,
modification of the HRS containment factor to ensure more consistency
with the current RCRA regulations is considered to be primarily a
policy issue rather than a technical issue.
Consequently, the primary focus of this paper has been
redirected toward a discussion of the issues related to any
modification of the containment factor, rather than the development
of specific options for modifying the containment factor. Advantages
and disadvantages of basing the containment factor on the RCRA land
disposal regulations are discussed. A number of alternative
approaches for modifying the containment factor so as to base it on
evaluation criteria other than the RCRA Subtitle C regulations are
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identified. The advantages and disadvantages of each approach are
discussed. One option for the development of a containment factor
under each of the alternative approaches is briefly outlined to
illustrate the types of options possible under each of these
alternative approaches. The full development of options under
any of the alternative approaches will, however, require the
identification, by EPA, of the preferred options and the resolution
of specific issues (both policy and technical) discussed under each
alternative. For example, decisions on whether data will be
collected for determining environmental concentrations of
contaminants greatly influence the types of MRS containment
evaluation criteria that can be developed (see discussion in
Chapter 3).
The discussion in this paper is limited to the development of
containment options for the current HRS surface water and ground
water pathways because the current HRS has no air pathway
containment factor. Options for containment factors for the air
pathway are discussed in a companion paper that addresses the
development of a potential for air release factor category
(Wolfinger, 1986).
1.4 Organization of the Report
The current HRS containment evaluation criteria are presented
and analyzed in Chapter 2. Issues associated with any modifications
to the current HRS containment evaluation criteria (including
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modifications to ensure more consistency with the current RCRA
Subtitle C land disposal regulations) are discussed. Several
possible objectives to be considered in the development of
alternatives to the containment factor are identified. Important
similarities and differences between the current HRS containment
factor and the containment factors in ten other site ranking systems
and three EPA hazardous waste policy analysis models are also
summarized in Chapter 2. (Appendix A presents a detailed review of
the use of containment in these other hazardous waste site ranking
systems and the EPA policy analysis models.) Chapter 3 outlines
nine options for modifying the containment factor to meet the
various objectives discussed in Chapter 2. Advantages and
disadvantages of each option are described. Chapter 4 presents a
summary and recommendations. Appendix B contains the bibliography.
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2.0 REVIEW OF CURRENT HRS CONTAINMENT EVALUATION METHODOLOGY
This chapter presents a summary of the current HRS containment
evaluation methodology. This is followed by an analysis of the
current containment factor. The analysis identifies several issues
associated with the containment factor that need to be considered in
any modification of the containment factor. Other issues generic to
modification of the containment factor are then identified and
discussed. This chapter concludes with a summary of the important
similarities and differences between the current HRS containment
factor and the containment factors incorporated in ten other systems
used to rank hazardous waste sites and in three EPA hazardous waste
policy analysis models. A more detailed review of these systems is
provided in Appendix A.
2.1 Overview of HRS Containment Factor
The HRS migration score currently reflects the potential threat to
humans or the environment from the migration of a hazardous substance
away from a site by three possible routes—ground water, surface water,
and air. A migration score for each applicable route is calculated by
rating the site with respect to a number of factors that characterize
a) the potential for hazardous substances to migrate from the site by
that route, b) the hazardous substances present at the site, and
c) the presence and proximity of targets (e.g., human populations).
The potential for migration along a route may be evaluated in one
of two ways—either through direct evidence of a release (i.e.,
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an observed release) or through the use of factors that evaluate the
potential for a release in terms of route characteristics and
containment. If there is a documented observed release for any
route, a rating value of 45 is assigned for that route and the route
characteristics and containment are not evaluated. If there is no
evidence of an observed release, the observed release is assigned a
value of zero. In this case, route characteristics and containment
are evaluated for the ground water or surface water routes, but not
for the air route. The route characteristics score and the
containment score are multiplied to assign a rating to the potential
for a release; their product has a maximum value of 45, the same as
the value for an observed release. The migration score for a route
is then determined by multiplying either the observed release score
or the potential for a release score (for ground water or surface
water) by scores for waste characteristics and targets and
normalizing the product so that it ranges from 0 to 100. The
individual route scores are combined to obtain the overall migration
score for the site.
The components of the route characteristics rating category for
the ground water route are the depth to the aquifer of concern, the
net precipitation, the permeability of the unsaturated zone, and the
physical state of the waste. The components of the route
characteristics rating category for the surface water route are the
facility slope and intervening terrain, 24-hour rainfall, the
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distance to the nearest surface water, and the physical state of the
waste. For both routes, the values assigned to the component factors
of the route characteristics category are weighted and then added
prior to being multiplied by the containment factor value.
The HRS containment factor is currently a measure of the methods
(either natural or engineered) that have been used to minimize or
prevent the migration of hazardous substances to ground water or
surface water. The containment factor is assigned a value for either
route by applying criteria that are specific both to the route and to
the type of waste management method being evaluated for that route.
The specific criteria for rating containment are presented in Table 2-1
for the ground water route and in Table 2-2 for the surface water
route. The containment factor value assigned to a route is the
highest containment value (i.e., value for the least effective
containment measure) assigned to any of the containment measures
applicable to that route.
The evaluation criteria in Tables 2-1 and 2-2 are based on the
technical requirements of the RCRA Subtitle C land disposal regulations
(40 CFR 264 and 265) promulgated or proposed prior to mid-1982. Wastes
whose containment meets the specified RCRA technical requirements are
considered to pose a lesser threat to human health and the environment
than wastes whose containment does not meet the specified requirements
and are currently assigned the lowest relative containment factor value
of zero. A containment factor value of zero for a route, in the
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TABLE 2-1
HRS CONTAINMENT FACTOR FOR GROUND WATER ROUTE
Assign containment a value of 0 if: (1) all the hazardous substances at the facility are underlain by an essentially
non-permeable surface (natural or artificial) and adequate leachate collection systems and diversion systems are present; or (2)
there la no ground water in the vicinity. The value "0" does not Indicate no risk. Rather, it indicates a significantly lower
relative risk when compared with more serious sites on a national level. Otherwise, evaluate the containment for each of the
different means of storage or disposal at the facility using the following guidance.
Assigned
Value
•• Surface Impoundment
Sound run-on diversion structure, essentially non-permeable liner (natural or artificial) compatible with the 0
waste, and adequate leachate collection system
Essentially non-permeable compatible liner with no leachate collection system; or inadequate freeboard 1
Potentially unsound run-on diversion structure; or moderately permeable compatible liner 2
Unsound run-on diversion structure; no liner; or incompatible liner 3
B. Containers
Containers sealed and In sound condition, adequate liner, and adequate leachate collection system "
Containers sealed and In sound condition, no liner or moderately permeable liner 1
Containers leaking, moderately permeable liner 2
Containers leaking and no liner or Incompatible liner 3
C. Piles
Piles uncovered and waste stabilized; or piles covered, waste uns tabilized , and essentially non-permeable liner 0
Pilea uncovered, waste unstabllced, moderately permeable liner, and leachate collection system 1
Piles uncovered, waste uns tabilized , moderately permeable liner, and no leachate collection system 2
Piles uncovered, waste unstabillzed, and no liner 3
D. Landfill
Essentially non-permeable liner, liner compatible with waste, and adequate leachate collection system 0
Essentially non-permeable compatible liner, no leachate collection system, and landfill surface precludes ponding 1
Moderately permeable, compatible liner, and landfill surface precludes ponding 2
No liner or incompatible liner; moderately permeable compatible liner; landfill surface encourages ponding; no 3
run-on control
Source: 47 PR 31180, July 1982.
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TABLE 2-2
HRS CONTAINMENT FACTOR FOR SURFACE WATER ROUTE
A»lgn containment a value of 0 If: (1) all the waste at the site Is surrounded by diversion structures that are In sound
condition and adequate to contain all runoff, spills, or leaks fron the waste; or (2) Intervening terrain precludes runoff fron
entering surface water. Otherwise, evaluate the containment for each of the different Beans of storage or disposal at the site
and assign a value as follows:
Assigned
Value
A. Surface Impoundment
Sound diking or diversion structure, adequate freeboard, and no erosion evident 0
Sound diking or diversion structure. Inadequate freeboard 1
Diking not leaking, but potentially unsound 2
Diking unsound, leaking, or In danger of collapse 3
B. Containers
Containers sealed, In sound condition, and surrounded by sound diversion or containment system 0
!_. Containers sealed and In sound condition, but not surrounded by sound diversion or containment system 1
U>
Containers leaking and diversion or containment structures potentially unsound 2
Containers leaking, and no diversion or containment structures or diversion structures leaking or In danger of 3
collapse
C. Haste Piles
Files are covered and surrounded by sound diversion or containment system 0
Piles covered, waste unconsolldated, diversion or containment system not adequate 1
Piles not covered, waste unconsolldated, and diversion or containment system potentially unsound 2
Piles not covered, waste unconsolldated, and no diversion or containment structures or diversion system 3
leaking or in danger or collapse
D. Landfill
Landfill slope precludes runoff, landfill surrounded by sound diversion system, or landfill has adequate cover 0
material
Landfill not adequately covered and diversion system sound 1
Landfill not covered and diversion system potentially unsound 2
Landfill not covered and no diversion system present, or diversion system unsound 3
Sourcei 47 PR 31180, July 16, 1982.
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absence of an observed release, results in the route receiving a
migration score of zero because the other rating factor values are
multiplied by the containment factor to obtain the migration score.
Because of this multiplicative property, the containment factor is
one of the two most influential rating factors in the HRS (along with
observed release) for the ground water and surface water route scores.
Accordingly, very specific criteria have been established for assigning
the containment factor value. For example, a surface impoundment
having a sound run-on diversion structure, an adequate leachate
collection system, and an essentially non-permeable liner that is
compatible with the waste in the impoundment is assigned a zero value
for the containment factor for the ground water route. A zero value
can also be assigned for the ground water route if there is no ground
water in the vicinity. If no waste containment is attempted, the
containment factor is assigned a value of three. Containment factor
values of 1 or 2 are assigned for various intermediate levels of
containment.
2.2 Analysis of Current HRS Containment Factor
This section presents an analysis of the current HRS containment
factor. The analysis identifies several issues that need to be
considered in any subsequent modification of the containment factor.
Although data are not available to determine the actual
distribution of containment factor values that have been assigned to
all wastes sites ranked using the HRS, it is apparent from data for
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sites in the automated NPL technical data base that there is little
variation in the containment values assigned among these sites.
Table 2-3 presents the distribution of the containment factor values
(for ground water and surface water migration routes) that have been
assigned to the approximately 600 sites in the automated NPL
technical data base that do not have an observed release and for
which a containment value has been reported. Approximately
99 percent of the relevant NPL sites, 93 percent of the relevant
"other sites," and 96 percent of all such sites in the automated NPL
technical data base have been assigned the maximum containment
factor value for the ground water pathway. For the surface water
pathway, these numbers are 87, 80, and 84 percent, respectively.
Not one site has been assigned a containment factor value of zero
for either pathway. This is not especially surprising since sites
with a containment factor value of zero would have a route score of
zero; only sites with migration scores of 25 or higher are required
to be forwarded to EPA Headquarters for review.
The data in Table 2-3 illustrate that the current HRS
containment factor provides little discrimination, based on
containment practices, among those sites submitted to EPA
Headquarters for quality assurance review. For these sites,
the primary function of the containment factor appears to be the
screening out of those few sites that have relatively high levels
of containment. For example, about 65 to 85 percent of sites in the
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TABLE 2-3
DISTRIBUTION OF HRS CONTAINMENT FACTOR VALUES FOR FACILITIES
IN THE AUTOMATED NPL TECHNICAL DATA BASE*
Number of NPL Facilities**
Containment Value
0
1
2
3
Total
Ground Water
No. %
Surface Water
No. %
0 0
1 2
2 1
3 216
Total 219
0
1
1
99
100
0
19
16
252
287
0
7
6
87
100
Number of Other Facilities***
Ground Water
No. %
0 0
10 3
12 4
300 93
322 100
Surface Water
No. %
0 0
35 11
29 9
256 80
320 100
Total Number of Facilities****
Ground Water
No. %
0 00
1 12 2
2 13 2
3 516 96
Total 541 100
Surface Water
No. %
0 0
54 9
45 7
508 84
607 100
*This distribution applies to facilities in the automated NPL
technical base that do not have an observed release and for
which a containment value has been reported.
**Based on the 888 facilities listed on or proposed for NPL as of
August 1986.
***Based on facilities in the automated NPL technical data base that
have not been proposed for or listed on the NPL as of August
1986; containment values for these facilities have not all been
subjected to a quality assurance review.
****Summation of the NPL and other facilities identified above.
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automated NPL technical data base assigned a containment value of 1
for any route are not on the NPL.*
No conclusions can be drawn from the data in Table 2-3 about how
containment factor values affect the overall ability of the current
HRS to discriminate between NPL and non-NPL sites. Low scoring sites
(i.e., those with migration scores less than 25) are not generally
submitted to EPA Headquarters for quality assurance review. It is
possible that low containment factor values are much more prevalent
among these sites and do, in fact, assist in discriminating such
non-NPL sites from NPL sites. Data to prove or disprove this are not
available.
One observation possible from the data in Table 2-3 is that
wastes at many CERCLA sites are not well contained** and that the use
of technical criteria based on the RCRA Subtitle C land disposal
regulations may not provide much differentiation among containment
practices at these sites. For most sites eligible for the NPL, this
is even more likely to be true if the HRS containment factor is
modified to reflect the current RCRA regulations which are
considerably more stringent than those in effect during early 1982.
Another consideration with regard to the present containment
evaluation criteria is that the criteria may lead to the assignment
*Some of these sites are still under quality assurance review for
placement on the NPL and may ultimately be placed on the NPL.
**A containment factor value of 3, which most sites appear to receive,
indicates that there is essentially no containment provided at the
sites for at least some of the wastes present at the site.
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of containment ratings values that are based, to a large extent, on
subjective judgments. The evaluation criteria currently require a
determination of whether the relevant containment technologies
(e.g., liners) exist at a site and, if so, an assessment of the
effectiveness of each containment technology. For example, the HRS
user needs to differentiate between sound, potentially unsound, and
unsound diversion structures. Similarly, assessments are required
as to whether liners are essentially non-permeable or moderately
permeable and whether they are compatible or incompatible with
wastes. Hie adequacy of covers and leachate collection systems must
also be assessed. In light of the type of containment likely to be
present at CERCLA sites, it may be more meaningful for HRS screening
purposes just to distinguish whether a containment technology is
present at a site and not to try to make fine distinctions about how
effective it is. For example, with regard to liners, the containment
could be ranked on whether a liner is present, not on whether it is
permeable or compatible with wastes. Data to make such distinctions
are not generally available from current site inspections.
The above analysis suggests a need for examining whether
alternatives exist for modifying the current containment factor that:
• Meaningfully provide greater differentiation among sites by
including evaluation criteria other than RCRA-based technical
requirements and/or
• Reduce the subjectivity of the containment evaluation
criteria
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2.3 Issues Relevant to the Revision of the HRS Containment Factor
One issue that needs to be considered is whether the containment
factor should continue to be included in the HRS. The containment
factor currently appears to be effective in screening out sites that
have relatively high levels of containment. However, the number of
such sites appears to be relatively small, at least based on data for
the sites in the automated NPL technical data base. Of the sites in
the automated NPL technical data base that have containment values
assigned, only 4 percent do not receive the maximum factor value for
the ground water route and about 16 percent do not receive the maximum
factor value for the surface water route.
Chapter 3 examines several alternative approaches for evaluating
containment in the HRS. A further alternative is to replace or
integrate the current containment factor with another factor that
addresses the retardation (e.g., geochemical removal) of containments
in the subsurface environment and in surface water. The development
of options for considering retardation in the HRS is currently being
examined in two companion studies (Sayala, 1986; Wang, 1986). Once
the development of these options is completed, it will be possible to
assess how they could most effectively be used in the HRS.
Assuming that containment is to remain a component of the HRS and
that the HRS is to remain a screening tool, there are several other
important issues that are generic to any modification of the current
HRS containment factor. These issues are reviewed in this section.
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The first issue that needs to be resolved is the specification
of the primary function that a containment factor is to serve in the
HRS. There are two different functions that a containment factor can
provide. It can be used primarily to screen out (assign low rating
values to) those relatively few sites that have adequate containment*
or it can be used primarily to provide differentiation among all sites
without an observed release, through modifications designed to provide
a more uniform distribution of containment rating values. Based on the
data presented above, it is unlikely that any single containment factor
(especially one based on technical requirements for containment
structure design)** can be developed to do both effectively. For
those sites in the automated NPL technical data base, the current HRS
containment factor appears to be serving the former function rather
than the latter function. Data are not available to determine which
function it actually serves for all sites ranked with the HRS; however,
for reasons discussed above, it is likely to serve the former function.
2.3.1 Screening Out Sites
Because containment is currently one of only two multiplicative
factors in the HRS (the other is observed release), it can be
extremely effective as a factor for screening out sites that exhibit
*Issues related to the definition of adequate containment are
discussed below.
**Technical requirements for containment structure design include such
requirements as covers, liners, and leachate collection systems
rather than the specification of performance objectives for the
containment structure.
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specified levels of containment. If it is decided to use the
containment factor primarily to screen out those sites that have
adequate containment, the basic structure of the containment factor
would likely be:
• No containment—assign maximum value
• Limited containment*—assign intermediate value
• Adequate containment—assign minimum value
The main issue that would need to be resolved is how the concept
of adequate containment is to be defined and evaluated for HRS
purposes. Ideally, it would be defined such that, at sites meeting
the definition, there would be little or no potential for hazardous
substances to migrate from the site via the route being evaluated.
This would tend to argue for basing the definition of adequate
containment on RCRA technical requirements since they provide, for
screening purposes, the clearest definition of adequate containment.
However, to be effective, the definition must also be consistent
with the site characteristics that would actually be encountered in
the universe of sites being evaluated for the NPL. If no sites meet
the definition of adequate containment, then there is likely to be
little or no benefit, for ranking purposes, to such a definition.
Chapter 3 identifies and examines several possible alternatives that
*There could be one or more levels of limited containment defined,
depending on how fine a distinction can realistically be developed
from available data.
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could be further developed for screening out sites, if this is the
desired approach.
A further issue that needs to be considered is whether or not the
minimum value to be assigned for adequate containment should be zero.
With a multiplicative containment factor, a zero value would result in
a zero score for that migration route. A non-zero (but relatively low
value) would result in a low score for the migration route and would
reflect the fact that almost no containment is likely to be 100 percent
effective over a sufficiently long period of time. This issue is
primarily a policy issue, not a technical issue.
2.3.2 Differentiation of Sites
If, on the other hand, a primary objective is to provide greater
differentiation within the types of containment practices likely to be
present at most sites eligible for the NPL, the issues are more
technical in nature. (One reason for such an objective might be to
provide some greater differentiation among those sites whose scores
are high enough for placement on the NPL.) The primary issue in this
case is the definition of containment characteristics that meaningfully
delineate actual, but likely small, differences in containment
effectiveness and that at the same time are representative of the
containment technologies likely to be present at most sites eligible
for NPL listing. Based on Tables 2-1 through 2-3, most sites in the
automated NPL technical data base have no containment for at least a
portion of the wastes present at the site. Thus, it is unlikely that
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any useful definition could be based solely on technical requirements
for land disposal. Chapter 3 identifies and examines several possible
alternatives for non-RCRA based criteria that could be further
developed for differentiating among sites, if this is the desired
approach.
2.4 Summary of Containment Factors in Other Ranking Systems
In addition to the above analysis, ten ranking systems that
consider containment in rating the threat posed by hazardous waste
sites have been identified along with three EPA hazardous waste policy
analysis models that also account for waste containment. The
containment factors in these systems have been reviewed. The review
focuses on how containment is used in the various systems and how
containment effectiveness is defined and evaluated. Important
similarities and differences between these factors and the HRS
containment factor have been identified. The findings of this review
are presented in Appendix A and are summarized below. The ten ranking
systems reviewed are:
• HARM • S.P.A.C.E. for Health
• HARM II • PERCO
• GSR • Illinois Rating Scheme
• ADL • Rating Methodology Model
• SAS • Dames and Moore Methodology
The three EPA hazardous waste policy analysis models reviewed are:
• Liner Location Risk and Cost Analysis Model
• Hazardous Waste Tank Failure Model
• RCRA Risk-Cost Analysis Model
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Of the 10 ranking systems reviewed, one (S.P.A.C.E. for Health)
has a containment factor that is identical to the HRS containment
factor and four (HARM, HARM II, CSR, and ADL) have multiplicative
containment factors that are very similar to the HRS containment factor
in concept and application. There are two major differences between
these latter four systems and the HRS. Three of these systems (HARM,
HARM II, and CSR) have a non-zero lower limit for the containment score
to indicate that no containment is likely to be 100 percent effective.
Three of the systems (HARM, CSR, ADL) also employ fewer intermediate
containment levels (either one or none) than the HRS to avoid making
fine distinctions about the degree of containment present at a site.
Two other ranking systems (SAS and PERCO) do not explicitly use
containment in rating a site. SAS uses containment only as a means of
evaluating waste quantity. PERCO uses containment only for identifying
sites similar to the site being evaluated.
One other ranking system (Illinois Rating System) considers
operational history, rather than containment effectiveness, in the
ranking of sites. This approach does not appear practical to apply to
CERCLA sites where information about the operational history of the
site is extremely limited and often unavailable.
The remaining two ranking systems (Rating Methodology Model and
Dames and Moore Methodology) have containment factors that are additive
rather than multiplicative and that are rated on the same scale
(0 to 3) as the HRS containment factor. These factors were considered
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in the original development of the HRS and were judged not to be
comprehensive, nor well defined.
Consequently, we have concluded that these other ranking systems
do not provide any further basis for developing modifications to the
HRS containment factor.
The three EPA hazardous waste policy analysis models address
containment in a very different manner than the HRS. Two of the models
(the Liner Location Risk and Cost Analysis Model and the Hazardous
Waste Tank Failure Model) use fault tree analysis and Monte Carlo
simulation (see Appendix A) to estimate both the probability and timing
of containment failure events that lead to releases of hazardous
substances and the release volumes associated with the failure events.
The failure and release components of the two models are currently
developed for application to a limited number of facility designs
(e.g., several specified containment configurations) and operating
conditions, most of which are not likely to be representative of CERCLA
sites.
The third model (RCRA Risk-Cost Analysis Model) is a more
deterministic model than the other two with regard to the
consideration of containment failure. In this model, all synthetic
liners are assumed to fail within 35 years and to have a linear failure
rate over this 35-year period; leachate collection systems are assumed
to release a fixed fraction of the leachate they handle; and surface
releases from storm-water management units and surface impoundments are
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assumed to occur solely from overtopping during storm events, and
overtopping is assumed to have a constant probability of occurrence in
any year.
As currently structured, these three models are intended primarily
for use in analyzing the risks and costs associated with alternative
regulatory strategies (e.g., alternative standards for waste
containment). They are not meant for, nor are they applicable to,
site-specific comparisons of containment effectiveness among different
facilities, especially among abandoned, uncontrolled waste disposal
sites. Consequently, we have concluded that the models themselves do
not provide any further basis for developing modifications to the HRS
containment factor.
However, some results from regulatory analyses conducted with
these models may be useful in developing portions of various
containment rating scales to be incorporated in the HRS containment
rating factor. This will depend, in part, on the nature of the
containment rating factor alternatives that are developed. (Chapter 3
identifies various alternative approaches for evaluating containment
in the HRS.) Limitations in the release pathways and facility types
and designs accounted for in the three models will, however, limit any
such application.
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3.0 CONTAINMENT EVALUATION ALTERNATIVES
Nine alternative approaches for evaluating containment in the
HRS are identified and examined in this chapter. These alternative
approaches have been developed to collectively illustrate ways that
the current HRS containment factor could be modified to:
• Increase its consistency with RCRA Subtitle C land disposal
regulation
• Include criteria other than RCRA-based technical requirements
• Provide greater differentiation among sites, or
• Reduce the subjectivity of the current containment
evaluation criteria
No one alternative approach does all four. However, depending on
data availability, several of the alternative approaches could be
combined to encompass various objectives.
One option for the development of a containment factor under
each alternative approach is briefly outlined to illustrate the
types of containment options possible under each alternative. The
advantages and disadvantages of each alternative are discussed, and
issues that need to be resolved before more complete options can be
developed under the alternative are identified.
3.1 Overview of Alternatives
The nine alternatives are as follows:
1. Modify the present criteria to incorporate changes in the
RCRA technical requirements since 1982 (Section 3.2).
2. Integrate the containment rating factor with a rating
factor based on waste quantity (Section 3.3).
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3. Revise the evaluation criteria to be evidentiary rather
than predictive, and retain the zero factor value
(Section 3.4).
4. Revise the evaluation criteria to be evidentiary rather
than predictive, and eliminate the zero factor value
(Section 3.5).
5. Integrate evidentiary and predictive criteria (Section 3.6).
6. Develop time-dependent evaluation criteria to replace the
present criteria (Section 3.7).
7. Develop evaluation criteria based on waste disposal
location rather than on waste management technology
(Section 3.8).
8. Develop evaluation criteria based on site drainage to
replace the present criteria (Section 3.9).
9. Integrate the containment rating factor with the physical
state rating factor (Section 3.10).
The first alternative provides an illustration of the criteria
that would be developed if the containment factor was modified to be
more consistent with current RCRA Subtitle C land disposal
regulations.
Two other alternatives examine methods for providing a more
uniform distribution of containment values. One of these
alternatives (Alternative 9) considers the integration of the
current HRS physical state factor into the containment factor. As
discussed in Section 3.10, most sites in the automated NPL technical
data base have been assigned values of 3 for both of these factors.
This approach seeks to provide a more uniform distribution of
assigned values by integrating these factors into a revised
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containment factor. The other alternative (Alternative 2) considers
the integration of the current containment factor with a factor
based on the quantity of waste present in the various waste
management areas at a site. The current HRS containment value
assigned to a route is the highest rating value assigned to any
waste management area for that route. This alternative attempts to
define a more representative containment value by weighting the
containment value for each waste management area by the portion of
the waste at the site that is present in that waste management unit.
Two additional alternatives (Alternatives 3 and 4) examine the
use of evidentiary criteria, instead of RCRA-based criteria, in
evaluating containment. The criteria in the present HRS containment
factor, which are based on RCRA requirements, are predictive,
equating the application of good containment technology to the
existence of good containment. These two alternatives consider
criteria based on evidence of containment efficiency at a site
rather than on the predictive technical requirements. Such
evidentiary criteria would equate the visual or analytical evidence
of hazardous substances in contact with the environment with the
existence of poor containment. Good containment would also need to
be proven through analytical evidence. A third alternative
(Alternative 5) then considers the integration of evidentiary and
predictive criteria in evaluating containment.
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Another alternative (Alternative 6) addresses the use of
time-dependent criteria, rather than RCRA-based criteria, in
evaluating containment. This alternative examines whether
containment values could be assigned based on the time elapsed since
waste deposition, recognizing that no containment is likely to be
100 percent effective over time.
Two other alternatives examine ways to reduce the subjectivity
in the current containment evaluation criteria and to make the
criteria more applicable to the differences in containment likely to
be present at CERCLA sites. One alternative (Alternative 7) examines
the use of containment factors based on waste location (i.e., above
ground or below ground) rather than on the type of waste management
unit in which the wastes are placed. The second alternative
(Alternative 8) equates good containment with good site drainage and
bases the evaluation criteria on site drainage.
3.2 Updating of Present RCRA-Based Criteria
HSWA imposes additional technical requirements for RCRA
Subtitle C hazardous waste management facilities, particularly land
disposal units. The containment evaluation methodology could be
revised to incorporate these additional requirements, as well as
additional requirements promulgated under RCRA in the period after
1981. For example, HSWA requires double liners, leachate collection
systems, and ground water monitoring at surface Impoundments,
disposal piles, and landfills, although waivers are allowed. The
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revised evaluation criteria applicable to surface impoundments for
the ground water route might be the following:
Rating* Criteria
0 = Sound run-on diversion structure, non-permeable and
compatible double liners, functioning leachate
collection and ground water monitoring systems, sound
diking with cover, adequate freeboard, weekly
inspection.
1 = Sound run-on diversion structure, non-permeable and
compatible liner, no leachate collection or ground
water monitoring systems, sound diking, adequate
freeboard.
2 = Potentially unsound run-on diversion structure or
diking, liner installed but integrity unknown, or
inadequate freeboard.
3 = Unsound or no run-on diversion structure, no liner, or
unsound diking.
Similar criteria could be developed for landfills, waste piles, tanks
and containers under both the ground water and surface water routes.
These revisions would have similar characteristics to the
present methodology. Specifically, they may not result in
differentiation among sites considered for placement on the NPL.
Hie major advantage of using these criteria is that for screening
purposes they do provide a clear definition of adequate containment,
and sites that are well engineered to contain the wastes would
likely be assigned very low scores.
*Note the rating values indicated here and throughout the remainder
of Chapter 3 are meant only to illustrate relative rankings of
containment. They are not specifically being recommended for use
in the HRS.
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3.3 Integration of Containment Factor With a Factor Based on Waste
Quantity
In the current HRS each containment area is assigned a
containment factor value for each of the two water routes. The
containment value for each route is the highest rating value assigned
to any waste management area for that route.
A more representative measure of containment at the site may be
obtainable by weighting the containment factor rating value for each
waste management area by the portion of the hazardous waste at the
site that is present in that waste management area. This weighted
value could then be used to assign the overall containment rating
value to the route. In addition to providing a more representative
containment value, this approach would also provide increased
differentiation among sites that have some degree of containment for
at least some of the wastes at the site.
However, this alternative does not appear to be practical to
implement unless current data acquisition problems can be overcome.
Presently, hazardous waste quantity estimates cannot be derived for
about 20 percent of the sites in the automated NPL technical data
base (Kushner, 1986). For many of the remaining sites, waste
quantity estimates can be derived only for a fraction of the
hazardous wastes deposited at the site. Unless more complete
estimates of hazardous waste quantities can be obtained for CERCLA
sites, this is not a viable alternative. To derive more complete
estimates of hazardous waste quantity, the current site inspection
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program would have to be expanded considerably. (A companion report
[Wolfinger, 1986] discusses issues involved in the collection of waste
concentration data which could be used to estimate waste quantity at
CERCLA sites.) Because of the data limitations, this alternative is
not developed further in this report.
3.4 Development of Evidentiary Criteria With a Zero Value
The present containment evaluation criteria are based on the
presumption that if a waste is contained using technology specified by
the RCRA regulations, it poses a lesser threat to human health and the
environment than waste not contained using such technology; this level
of containment is currently assigned a value of zero. Reductions in
the containment technologies present at a site or in their operating
efficiencies result in higher containment factor values being assigned.
Several subjective evaluations are presently required to assign a
containment factor value, such as liner permeability, diversion
structure soundness, and container condition. The information required
to make these evaluations may be difficult to obtain. For example,
the presence of a liner may be established through design drawings or
site inspections, but the condition or permeability may be difficult
to determine without laboratory testing or on-site monitoring that
disturbs the site.
The approach under this alternative is to base the containment
factor value primarily on criteria that can be evaluated through
observation and limited site sampling and analysis, such as the
following:
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Rating Criteria
0 = Demonstrated compliance with current RCRA waste
containment requirements, such as impermeable and
compatible double liners, covers, functioning diversion
and leachate collection systems, and non-leaching waste
stabilization.
1 = Evidence of waste containment measures, efficiency
unknown, no evidence of uncontained waste.
2 = Evidence of waste containment measures and presumptive
evidence of uncontained waste.
3 = Visual or analytical evidence of uncontained waste, or
no evidence of waste containment present.
The above criteria for assigning a zero value are similar to the
present criteria for assigning a zero containment value, except that
they reflect the current RCRA regulations. If compliance with RCRA
requirements cannot be documented, but waste containment measures of
unknown efficiency exist, a higher value (e.g., 1) could be assigned
under this alternative. This category would include sites at which
a liner or cover is installed but at which the liner's compatibility
and integrity were not evaluated, or at which a diversion structure
or leachate collection system is present, but at which its operating
efficiency was not determined.
A still higher value (e.g., 2) could be assigned when there
is analytical evidence of uncontained waste, even if some waste
containment measures exist. The analytical evidence could include
contaminated soil, ponded water, or leachate where the contaminants
can be attributed to the wastes disposed at a site. While this
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analytical evidence would be insufficient to score an observed
release, it does indicate that containment is poor and that waste
constituents have a higher potential for entering the environment.
The criteria for assigning the highest value (e.g., 3) are
similar to the present containment factor criteria. Sites at which
no waste containment measures are evident, or at which waste contact
with the environment can be visually observed, would be assigned
this highest value.
This alternative illustrates the use of evidentiary criteria,
rather than RCRA-based technical criteria, to rate most levels of
waste containment. RCRA-based criteria, not evidentiary criteria
are, however, used to rate the highest level of containment because
the lack of analytical evidence of uncontained waste does not
necessarily indicate that a release has not or will not occur. It
may just mean that the evidence has not been found. For example,
where monitoring has been done, the lack of such evidence may be
the result of temporal or spacial variations in environmental
concentrations or faulty monitoring procedures. It may also mean
that substances being released were not those tested for in the
sample analysis. This is discussed further in Wolfinger (1986).
Consequently, it is possible for sites with identical wastes and
identical containment measures to be assigned different containment
ratings under this alternative because evidence has been found at
one site but not at the other.
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It should be noted that this evidentiary approach may be more
applicable to the surface water route than to the ground water route,
Certain types of evidence that would be of extreme importance in the
ground water route (e.g., leachate or soil samples from below
landfills, surface impoundments, etc.) are not easily obtainable or
have risks inherent in their collection (e.g., drilling through a
landfill could open conduits for waste migration). The collection
of these additional data would likely require an expansion of the
current site inspection program. Without further analysis, it is
not possible to determine whether the data required to use the above
criteria or the data required to use the current ground water
containment factor are more costly to obtain.
This approach is not likely to result in any significant shift
in the distribution of containment factor scores. The highest and
lowest evaluation criteria under this alternative are essentially
the same as those of the current containment factor. As a result,
there would likely be little change in the distribution of these two
values. There would be some limited shift in the distribution of
the two intermediate values, but probably almost no shift in the
absolute number of sites being assigned an intermediate value.
3.5 Development of Evidentiary Criteria Without a Zero Value
This alternative is the same as that in Section 3.4, except
that the zero rating value is eliminated. The following evaluation
criteria illustrate this approach:
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Rating Criteria
1 = Waste containment measures evident, no evidence of
uncontained waste.
2 = Waste containment measures evident with presumptive
evidence of uncontained waste.
3 = No waste containment present, or visual or analytical
evidence of uncontained waste.
The zero rating value has been eliminated both to remove
dependence of the criteria on RCRA land disposal requirements and
to indicate that complete waste containment over time cannot be
absolutely assured even with measures that comply with RCRA
requirements. (This latter consideration could also be incorporated
in the alternative in Section 3.4 by assigning a value of 1, not
zero, to containment that meets RCRA requirements and by adjusting
all other values accordingly.) The advantages and disadvantages of
this alternative are essentially the same as those discussed in
Section 3.4. However, no differentiation is made for different
levels of containment when there is no evidence of uncontained
wastes. This is addressed in Section 3.6.
3.6 Integration of Evidentiary and Predictive Criteria
This alternative illustrates the integration of evidentiary
and predictive criteria in the rating of containment. Under this
approach, sites at which there is evidence that hazardous substances
have been released from a containment area would be assigned a
higher value than sites at which there is no evidence of release.
Where there is no evidence, the rating would be based on predictive
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technical requirements. It is anticipated that the type of evidence
that would be used under this alternative would be evidence that
shows migration from a waste containment area, but which is not
adequate for demonstrating an observed release to surface or ground
water (e.g., contaminated soil, leachate, erosion trails).
This alternative would have essentially the same advantages and
disadvantages as the alternative presented in Section 3.4. However,
it would have the added advantage of being able to differentiate
among sites at which there was no evidence of uncontained waste.
One possible option under this alternative is illustrated below (for
the ground water route for a landfill):
Rating Criteria
0 = Demonstrated compliance with RCRA-based land disposal
requirements.
1 = No evidence of uncontained waste; single liner and
functioning leachate collection system.
2 = No evidence of uncontained waste; single liner, no
functioning leachate collection system.
3 = Presumptive evidence of uncontained waste.
4 = Visual or analytical evidence of uncontained waste, or
no evidence of waste containment present.
3.7 Development of Time-Dependent Criteria
Since the physical, chemical, and biological processes that
result in contaminants being released from waste sites are
continuous, the duration of time these processes have been in
operation affects the integrity of containment structures at the
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site, the quantity of any constituents released from the site, and the
nature of the wastes that remain at the site. The longer wastes are
at a site, the greater the overall potential for there to be a release
from the site, especially if the site is abandoned or not maintained.
The approach under this alternative is to use criteria that are
based on the elapsed time since waste deposition to evaluate the
containment at a site. Such criteria would likely result in a more
uniform distribution of containment values. The following evaluation
criteria are an example of criteria that could be developed (they are
presented solely for illustration purposes; they are not based on an
analysis of containment failure data):
Rating Criteria
0 = Less than two years elapsed time since the initial
disposal of hazardous substances.
1 ™ At least two years, but less than ten years, since
initial disposal.
2 = At least ten years, but less than twenty years, since
initial disposal.
3 = Twenty years or more since initial disposal or no
evidence of waste containment.
The use of time-dependent criteria would, by its very nature,
tend to differentiate sites on the basis of the timing of a potential
release (i.e., how soon is it likely to occur). For example, under
this approach, older sites would be assigned higher rating values
than those newer sites where releases are equally likely to occur
within the same period of time from waste deposition. Consequently,
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newer sites would, in general, tend to have lower HRS migration
scores than older equivalent sites. The net effect would be that
sites that are close to (or are already) releasing hazardous
substances would be more likely to be placed on the NPL than sites
that are equally likely to, but further away in time from, releasing
hazardous substances. The desirability of such an impact is a
policy issue.
Furthermore, there would be several drawbacks to the application
of time-dependent criteria. First, it would be necessary to define
a viable measure of time. Documentation of the wastes managed at a
site has proven difficult (see Section 3.3); documentation of the
dates of deposition would be even more difficult. Disposal dates
are often unavailable because of poor or non-existent recordkeeping.
Further, wastes were often deposited at different times and in
different amounts and mixtures at a site. Surrogate measures, such
as years since site opening or site closing, suffer from similar
information collection problems and may differ significantly from
the actual years since waste deposition.
Second, the interactions between site age, containment structure
integrity, and contaminant mobility are very complex. It is not
clear that they could be adequately defined or be simplified enough
to be incorporated in the HRS. Site-specific and waste-specific
characteristics would be very important and would have to be
considered. For example, buried drums in a desert environment
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generally corrode more slowly than those buried in locations with
high ground water tables where the drums are continually in contact
with water and quickly corrode. Furthermore, waste characteristics,
such as corrosivity and reactivity, also strongly affect the drum
life.
For these reasons, time-dependent criteria do not appear to be
a viable alternative for use in the HRS containment factor.
3.8 Use of Criteria Based on Waste Disposal Location
This alternative illustrates the use of criteria that are based
on waste location rather than on the type of waste management unit
in which wastes are deposited. For each water route, the criteria
are differentiated by whether the wastes are deposited below the
ground surface or deposited at or above the ground surface. The
assumption is that waste containment requirements are similar for
wastes deposited in similar locations (i.e., above or below ground),
regardless of the type of unit in which they are placed. For
example, for the surface water route diking is important for wastes
deposited above ground, but is not important for wastes deposited
below ground.
For each pathway under this alternative, containment is
evaluated for both locations using predictive criteria similar to
those in the current containment factor. The criteria are modified,
however, to make them more applicable to the differences in
containment likely to be present at CERCLA sites and to remove some
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of the subjectivity that results from use of current site inspection
data. For example, under this alternative distinctions are made as
to whether or not liners are present, not on how permeable the liners
are or whether they are compatible with the wastes at the site. Such
distinction may not be appropriate for CERCLA sites since it appears
that the vast majority of these sites do not have liners. Further,
based on current site inspection data, asssessments of liner
integrity, permeability, and compatibility are often subjective.
Illustrative criteria for this alternative are presented in
Table 3-1. It should be noted that the values listed in Table 3-1
are based on engineering judgments, not an analysis of modeling
results or site data. Such analysis may be necessary if this
approach is to be considered further. In using the criteria in
Table 3-1, it is recommended that evidence of properly functioning
waste containment measures be required to assign values corresponding
to excellent or good containment. A lack of evidence would result
in a rating of poor containment if containment measures were present.
When both types of disposal locations are present at a site, rating
values would be assigned to each and the highest rating value would
be used to compute the route score.
One advantage of this approach is that it can be applied to any
type of waste containment unit at a site; it is not limited to the
four types in Tables 2-1 and 2-2. It also eliminates some of the
subjectivity present in the current containment factor. Further, it
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TABLE 3-1
ILLUSTRATIVE CONTAINMENT FACTOR VALUES BASED ON
WASTE DISPOSAL LOCATION
Rating Value
Criteria
Ground
Water
Surface
Water
Below-Grade Disposal
Excellent containment
(4 of 5 technologies functioning)
Good containment
(2 of 5 technologies functioning)
Poor containment
(1 of 5 technologies functioning
or efficiency unknown)
No containment
Above-Grade or Surface Disposal
Excellent containment
(4 of 5 technologies functioning)
Good containment
(2 of 5 technologies functioning)
Poor containment
(1 of 5 technologies functioning
or efficiency unknown)
No containment
2
3
2
3
0
0
1
2
2
3
Containment Technologies
• Engineered Cover • Leachate collection
• Double liner
• Run-on diversion
Diking with adequate
freeboard
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may provide a somewhat more uniform distribution of containment
values since only one containment technology needs to be present to
achieve a value of 1.
One major disadvantage of this approach is that it assumes that
each containment technology in Table 3-1 is of equal importance.
This may not be the case. For example, leachate collection may be
more important than run-on diversion. A further disadvantage of the
approach is that the five listed containment technologies may not be
applicable, nor even meaningful, for every type of waste management
unit. For example, surface impoundments are not likely to have
covers, while almost all landfills would have some limited cover.
Additional refinements would thus be necessary if this approach was
deemed to warrant further investigation.
3.9 Development of Criteria Based on Site Drainage
This alternative represents a further simplification of the
approach in Section 3.8. The simplification is directed at providing
a more uniform distribution of containment values and further
i
reducing subjectivity in the evaluation of containment. To do this,
the evaluation criteria are based on those containment technologies
more likely to be present at CERCLA sites (i.e., some type of cover
material or cap and drainage or diversion structures). Technologies
(e.g., liners, leachate collection systems) not likely to be present
or whose evaluations are likely to be subjective are not included.
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Under this alternative, the level of waste containment could be
equated with good site drainage using criteria similar to the
following:
Rating Criteria
0 = Cap or cover, functioning drainage or diversion
structure with collection system.
1 = Cap or cover, functioning drainage or diversion
structure.
2 = No or non-functioning drainage or diversion structure,
no ponding observed.
3 = No or non-functioning drainage or diversion structure,
ponding observed.
These criteria are similar to the current surface water route
containment evaluation methodology and, except for liner and leachate
collection system evaluations, they are also similar to the ground
water criteria.
This approach eliminates the evaluations of liner permeability
and leachate collection system operation from the present HRS
criteria because accurate information on their effectiveness is
difficult to obtain without extensive monitoring programs. For
example, the presence of a clay or synthetic liner is not by itself
evidence that the waste is contained. The synthetic liner may be
torn or the clay may be cracked or channeled such that the liner is
quite permeable. There is no way of making this determination
without more extensive monitoring data than is presently available
from site inspections.
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The primary advantage of this approach is that it would provide
a more uniform distribution of site scores, if this is desired. In
addition, the proposed criteria should be simpler to implement than
the existing criteria because they are not specific to each waste
management technology. The necessary evaluations could be based on
visual evidence; evaluations of liner permeability or compatibility
are not required. The criteria could also be integrated with the
evidentiary criteria discussed in Sections 3.4 to 3.6 to obtain a
more uniform distribution among containment values than presently
exists and to incorporate other factors affecting waste containment.
The major disadvantage with this alternative is that it ignores
elements (e.g., liners) that are important to good containment. It
is structured to provide a more uniform distribution of values, not
to meaningfully evaluate the overall effectiveness of containment at
a site.
3.10 Integration of Containment and Physical State Factors
The physical state of a waste is included as a rating factor
under the current HRS route characteristics category. It is
evaluated when there is no evidence of an observed release for the
ground water or surface water routes. The following criteria are
presently used to assign a value to physical state:
Rating Criteria
0 = Consolidated or stabilized solid.
1 = Unconsolidated or unstabilized solid.
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Rating Criteria
2 = Powder or fine material.
3 = Liquid, sludge or gas.
The physical state of a waste affects the potential for the
waste (or its hazardous constituents) to migrate from a site or
alternatively for it to be contained at a site. Physical state can
thus be used as a measure of either waste containment or waste
migration potential. It is currently used as a measure of waste
migration potential in the ground water and surface water route
characteristics factor category of the HRS. Physical state could,
however, be integrated with the current containment factor (or a
revised containment factor) and deleted from the route
characteristics factor category. The advantages and disadvantages
of this are discussed below.
Most of the sites in the automated NPL technical data base for
which there are physical state and containment values have a value
of 3 assigned to both factors, indicating that there are at least
some uncontained liquids, sludges, or gases present at most of these
sites.* Of the 698 sites in the automated NPL technical data base
for which a value was assigned to the physical state factor, 617 of
the sites (88 percent) received a value of 3. Eighteen sites
*The physical state factor value assigned to a route is the highest
physical state factor value assigned to any of the substances at the
site that can migrate along that route. Thus, there could be solids,
in addition to liquids, sludges, or gases, present at a site that
receives a factor value of 3.
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(3 percent) were assigned a value of zero, 32 sites (5 percent) a 1,
and 31 sites (4 percent) a value of 2.
Based on the above data, it appears that the primary function
that physical state currently serves in the HRS is to assist in
screening out (i.e., lowering scores) of sites that do not contain
at least some liquids, sludges, or gases. If this is the objective,
it could most likely be carried out more effectively by integrating
physical state into the containment factor, since this would place
greater weight on physical state in the overall route score. Under
this approach for each waste management unit, both the type of
containment and the physical state of the wastes in that unit would
be considered in assigning a rating value to that waste management
unit. This integration could at the same time provide some further
differentiation among the vast majority of CERCLA sites at which
uncontained liquids, sludges, and gases are present in some, but not
all, waste management units at the site. This would, however, have
to be verified by further analysis if this alternative was deemed to
warrant further investigation.
There are numerous ways in which physical state could be
integrated into the containment factor. Two examples are illustrated
below, using both evidentiary and predictive approaches.
3.10.1 Use of Evidentiary Criteria
The physical state and containment factors could be integrated
for each waste management unit using evidentiary criteria similar to
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those presented in Section 3.4. The following criteria illustrate
this approach for rating a waste management unit:
Rating Criteria
0 = Evidence of only stabilized or contained solid in the
waste management unit
1 = Unstabilized, contained solid in the waste management
unit with presumptive evidence of containment failure,
or containment efficiency unknown
-or-
Evidence of contained liquid or sludge in the waste
management unit
2 = Uncontained solid in the waste management unit
-or-
Contained liquid or sludge in the waste management unit
with presumptive evidence of containment failure, or
containment efficiency unknown
3 = Uncontained liquid, sludge, or gas in the waste
management unit
The effective use of these criteria focuses on the determination
of containment. For example, a solid must be stabilized or contained
for the waste management unit to be assigned a zero value.
Containment or stabilization must be supported by evidence similar to
that discussed in Section 3.4. The advantages and disadvantages of
this approach would be similar to those advantages and disadvantages
discussed for the evidentiary approach in Section 3.4.
3.10.2 Use of Predictive Criteria
The physical state and containment rating factors could also be
integrated for each waste management unit using predictive criteria
similar to those of the current containment factor or to those
illustrated in the alternatives. The following criteria illustrate
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how some of the waste location criteria in Section 3.8 could be
integrated with the physical state factor:
Rating Criteria
0 = Stabilized solid, or solid disposed with four of the
five functioning containment technologies.*
1 = Unstabilized solid disposed with two of the five
functioning containment technologies
-or-
Liquid or sludge disposal with four of the five
functioning containment technologies
2 = Unstabilized solid disposal with one of the five
functioning containment technologies
-or-
Liquid or sludge disposal with two of the five
functioning containment technologies
-or-
Analytical evidence of leaking containment
3 = No waste containment for solids, liquids, sludges, or
gases
Evidence of functioning containment technologies, similar to that
discussed in Section 3.8, would be required to ensure consistent
evaluation. The advantages and disadvantages of the above criteria
would be similar to those discussed in Section 3.8.
*From Section 3.8, the five containment technologies are:
dike with adequate freeboard, run-on diversion structure, double
liner, engineered cover, and leachate collection system.
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4.0 SUMMARY AND RECOMMENDATIONS
The current HRS containment factor uses evaluation criteria
that are based on the requirements of the RCRA Subtitle C land
disposal regulations as of early 1982. The analysis in Chapter 2
indicates that many wastes at CERCLA sites are not well contained
and that the use of evaluation criteria based on the RCRA Subtitle C
regulations may not provide much differentiation between sites.
This is even more likely to be true if the HRS containment factor is
modified to reflect the current land disposal regulations.
Furthermore, the current HRS containment evaluation criteria may be
more complex and subjective than is warranted. In light of the type
of containment likely to be present at CERCLA sites, it may be more
meaningful for HRS screening purposes just to distinguish whether a
containment technology is present at a site and not to try to make
fine distinctions about how effective it is.
Based upon the analysis in Chapter 2, several issues that need
to be considered in any modification of the HRS containment factor
have been identified. One issue is whether the containment factor
should continue to be included in the HRS. While the containment
factor appears to be effective in screening out sites that have
relatively high levels of containment, the number of sites receiving
less than the maximum containment factor value appears to be small.
Assuming that containment is to remain a factor in the HRS, the
primary issue that needs to be addressed is whether the containment
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factor is to be used primarily to screen out those relatively few
sites that have adequate containment or to provide increased
differentiation among all sites without an observed release. For
reasons discussed in Chapter 2, it is unlikely that any single
containment factor can be developed to do both effectively.
If it is decided to use the containment factor to screen out
sites with adequate containment, there are two basic issues that
need to be addressed:
• How adequate containment is to be defined and evaluated for
HRS purposes.
• Whether the rating assigned for adequate containment is to
be a zero or a non-zero value.
If it is decided to use the containment factor to differentiate
among all sites without observed releases, the primary issue is more
technical. The primary issue is defining containment characteristics
that meaningfully delineate actual, but likely small, differences
in containment effectiveness and that at the same time are
representative of the containment technologies likely to be present
at most sites eligible for NPL listing. For reasons discussed in
Chapter 2, it is unlikely that any useful definition could be based
solely on technical requirements for land disposal.
Nine alternative approaches for evaluating containment in the
HRS are identified and examined. These alternatives have been
developed to collectively illustrate ways that the current HRS
containment factor could be modified to:
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• Increase its consistency with RCRA Subtitle C land disposal
regulations
• Include criteria other than RCRA-based technical requirements
• Provide greater differentiation among sites, and/or
• Reduce the subjectivity of the current containment
evaluation criteria
No one alternative approach does all four. One option for the
development of containment factors under each alternative approach
is briefly outlined to illustrate the types of containment options
possible under each alternative. The advantages and disadvantages
of each alternative are discussed, and issues that need to be
resolved before more complete options can be developed under the
alternative are identified.
As part of the development of the alternatives, ten existing
ranking systems that consider containment in rating the threat posed
by hazardous waste sites were reviewed along with three EPA hazardous
waste policy analysis models that also account for containment. Five
of the ranking systems were found to have containment factors that
are very similar in concept and application to that of the HRS. Two
ranking systems were found not to explicitly evaluate containment in
ranking a site. The other three ranking systems were found to have
containment factors that are not comprehensive nor well defined. The
three EPA hazardous waste policy analysis models were found not to be
applicable for use in making site-specific comparisons of containment
effectiveness.
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Of the nine alternatives developed, one focuses on updating the
current RCRA-based containment evaluation criteria. One examines the
use of time-dependent, rather than RCRA-based, criteria. Two others
examine the use of evidentiary criteria rather than RCRA-based
criteria. Three others examine the integration of waste quantity,
physical state, or evidentiary criteria into the containment factor.
The remaining two examine ways to reduce the subjectivity in the
current evaluation criteria and to make the current criteria more
applicable to the differences in containment likely to be present at
CERCLA sites.
It is recommended that two of these alternatives be considered
for possible further development and that six others be eliminated
from further consideration. Further development of the ninth
alternative, Updating of the Current Containment Factor, is entirely
a policy issue.
The two alternatives that are recommended for possible further
development are the following:
• Integration of Evidentiary and Predictive Criteria in the
Containment Factor.
• Integration of the Physical State Factor Into the Containment
Factor.
The integration of evidentiary and predictive criteria offers
several possible advantages. First, it could be used to assign
higher rating values to sites at which there is evidence that
hazardous substances are leaving waste management areas than to sites
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at which there is no detected evidence that hazardous substances are
leaving the waste management area. Such evidence is currently not
considered in the HRS unless it can be used to document an observed
release. Second, where there is no detected evidence of a release,
predictive criteria could also be used to assign containment factor
values based on differences in containment technologies. For reasons
previously discussed, it is recommended that such criteria only
distinguish whether a technology is present and not whether there are
differences in the effectiveness of the technology. Third, this
approach would likely result in a slightly more uniform distribution
of containment values; however, any such change is not expected to be
large. The major disadvantage of this approach is that sites that
have releases that are not detected, due for example to environmental
variations in concentrations, would receive a lower rating than they
should. However, the same problem can also occur with the current
observed release factor.
From the analysis presented in Section 3.10, it appears that
there is not much differentiation of sites based on the current
physical state factor. Instead, the physical state factor appears
to assist in screening out sites that do not contain at least some
liquids, sludges, or gases. Regardless of which containment
alternative, if any, is selected for further development, it is
recommended that the integration of the physical state and
containment factors be evaluated further. Such an integration may
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increase the effectiveness of the HRS in screening out those sites
that have an adequate level of containment for the types of wastes
present at the site. It may also increase the differentiation among
the vast majority of CERCLA sites that have at least some uncontained
liquids, sludges, or gases.
The other six alternatives are not recommended for further
development for a variety of reasons. The integration of the waste
quantity and containment factor is not recommended for further
development because of significant problems with data availability.
If these could be resolved, this alternative would be the preferred
approach because it could be used to both screen out sites with
adequate containment and to provide a considerably more uniform
distribution of containment values.
The use of time-dependent criteria is not recommended because
it is unlikely that the complex relationships between site age,
containment integrity, and contaminant mobility could be adequately
defined or simplified for effective use in the HRS. This approach
also suffers from data acquisition problems.
The two evidentiary approaches that are not integrated with
predictive criteria are not recommended because the integrated
approach offers several advantages over these two.
The other two approaches are not recommended because many of
their simplifications either ignore or equate differences in
containment that may be significant for certain types of containment
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structures. Further, some of the more meaningful simplifications
can still be incorporated into whatever containment factor is
ultimately used in the HRS. However, it should be noted that, if it
is decided to modify the containment factor to provide a more uniform
distribution of containment values, these latter two approaches are
the only ones identified that are likely to be able to achieve this.
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APPENDIX A
REVIEW OF CONTAINMENT FACTORS IN OTHER SITE RANKING SYSTEMS
This appendix reviews the containment factors that have been
incorporated in other systems. Ten ranking systems that consider
containment in rating the threat posed by hazardous wastes sites have
been identified along with three EPA hazardous waste policy analysis
models that also account for containment. The review of these systems
focuses on how containment is used in each system and how containment
effectiveness is defined and evaluated. Important similarities and
differences between these factors and the HRS containment factor are
identified. The ten ranking systems reviewed are:
• HARM • SAS
• HARM II • PERCO
• GSR • Illinois Rating Scheme
• ADL • Rating Methodology Model
• S.P.A.C.E. for Health • Dames and Moore Methodology
The three EPA hazardous waste policy analysis models reviewed are:
• Liner Location Risk and Cost Analysis Model
• Hazardous Waste Tank Failure Model
• RCRA Risk-Cost Analysis Model
Before reviewing these systems, it should be noted that the HRS
containment factor is a multiplicative factor that is rated on a
scale of 0, 1, 2 or 3. Since it is a multiplicative factor, if it
were to be divided by three and the divisors used to normalize the
corresponding HRS pathway scores were also to be divided by three,
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there would be no change in the HRS pathway scores. In this case, the
HRS containment factor would be rated on a scale of 0 to 1 and would
have values of 0, 0.33, 0.67- and 1.
A.I HARM
Hie Hazard Assessment Rating Methodology (HARM) is used by the
U.S. Air Force to rank hazardous substance sites for priority attention
for follow-on site investigations and confirmation activities under
Phase II of the Air Force's Installation Restoration Program (IRP).
HARM is designed to use data developed during the Record Search
(Phase I) portion of the IRP (Engineering-Science, 1983). Record
Searches are essentially equivalent to EPA Preliminary Assessments.
The HARM score is developed from four subscores: Receptors,
Pathways, Waste Characteristics, and Waste Management Practices. A
total risk score is determined by averaging and normalizing the first
three subscores. The total risk score is then multiplied by the Waste
Management Practices subscore to produce the HARM score.
The Waste Management Practices subscore is a measure of the
containment at the site and ranges from 0.1 to 1 as follows:
• No containment 1.0
• Limited containment 0.95
• Fully contained and in full compliance 0.10
Table A-l shows the guidelines for a determination of fully
contained. These guidelines are quite similar to those used to
assign a zero rating to the current HRS containment factor.
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TABLE A-l
FULLY CONTAINED SITES—HARM GUIDELINES
Landfills;
• Clay cap or other impermeable cover
• Leachate collection system
• Liners in good condition
• Adequate monitoring walls
Surface Impoundments;
• Liners in good condition
• Sound dikes and adequate freeboard
• Adequate monitoring wells
Spills;
• Quick spill cleanup action taken
• Contaminated soil removed
• Soil and/or water samples confirm total cleanup of the spill
Fire Protection Training Areas;
• Concrete surface and berms
• Oil/water separator for pretreatment of runoff
• Effluent from oil/water separator to treatment plant
Source: Engineering-Science, Comparison of U.S. Air Force Hazard
Assessment Rating Methodology (HARM) with U.S. Environmental
Protection Agency Hazard Ranking System (HRS) at Four Air
Force Bases Evaluated under the Phase I Installation
Restoration Program, Engineering-Science, Atlanta, GA,
April 1983.
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The HARM Waste Management Practices subscore is thus very
similar in concept and application to the HRS Containment Factor.
The main differences are that its lower limit is 0.1, rather than
zero, and that it has one, rather than two, intermediate rating
categories. The primary disadvantage of the HARM factor is that
it does not address route-specific differences in containment.
A.2 HARM II
The Hazard Assessment Rating Methodology II (HARM II) is a
modification and extension of the HARM system that is intended to
permit the use of site-specific monitoring data in setting
priorities. HARM II is used by the U.S. Air Force in Phase II of the
IRP program to set priorities for detailed site investigations and
possible remedial action (Barnthouse et al., 1986).
HARM II has a Waste Containment Effectiveness factor that is
based on the HRS containment factor (Barnthouse et al., 1986) and
that is consequently very similar in concept and application to the
HRS containment factor. The Waste Containment Effectiveness factor
is a multiplicative factor used to determine surface water or ground
water pathway subscores. Tables A-2 and A-3 present the Waste
Containment Effectiveness factor for the surface water and ground
water pathways, respectively. Again, the main difference compared
to the HRS, is that the lower limit is 0.1, not zero.
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TABLE A-2
HARM II WASTE CONTAINMENT EFFECTIVENESS
FACTORS FOR SURFACE WATER PATHWAY
Containment Structure Score
Landfills
Clay or other cover in sound condition without evidence 0.1
of severe erosion; if in floodplain, diked effectively
to prevent floodwater encroachment
Some problems with cover or dike/diversion systems; 0.5
no wastes exposed
Problems with both cover and dike/diversion system; 0.8
or serious problem with one of these; no exposure of
wastes yet
Cover and/or diking system (if needed) absent; wastes 1.0
exposed
Surface Impoundments
Sound dikes, adequate freeboard, and no erosion evident 0.1
Inadequate freeboard 0.5
Potentially unsound dike 0.8
Dikes unsound, leaking, or in danger of collapse, or 1.0
evidence of past spillover
Spills
Contaminants material apparently removed completely; 0.1
but possible occurrence of a spill
Contaminated area covered with impervious material 0.5
Contaminants completely covered with soil, area 0.8
revegetated
No cleanup action or covering done 1.0
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TABLE A-2 (Concluded)
Containment Structure Score
Tanks
Tanks in sound condition and inspected regularly; tank 0.1
area effectively bermed to contain any spills (and
subsequent rainfall)
Tanks in sound condition and bermed, but berm system 0.5
or inspection system possibly insufficient
Tanks in sound condition, but not bermed 0.8
Tanks unsound 1.0
Fire Protection Areas
Berms; oil-water separator for treatment of runoff; 0.1
oil-water separator effluent to treatment plant
Some deficiency in the above 0.8
None of the above 1.0
Source: Barnthouse, L.W. et al., Development and Demonstration of a
Hazard Assessment Rating Methodology for Phase II of the
Installation Restoration Program, (ORNL/TM-9857), Oak Ridge
National Laboratory, TN, 1986.
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TABLE A-3
HARM II WASTE CONTAINMENT EFFECTIVENESS
FACTORS FOR GROUND WATER PATHWAY
Containment Structure Score
Landfills
Liner essentially impermeable, intact, and compatible 0.1
with waste; cover of low permeability, and intact;
leachate collection system; adequate monitoring wells
Physical containment system suitable; no monitoring 0.5
Deficiencies in physical containment system (e.g., 0.8
moderately permeable liner, no leachate collection,
or defective cover)
Cover and/or diking system (if needed) absent; wastes 1.0
exposed
Surface Impoundments
Liner essentially impermeable and compatible with 0.1
waste; double liner or leakage detection system
System essentially sound, but no double liner or 0.5
leakage detection system
Liner moderately permeable or in deteriorating condition 0.8
No liner or incompatible liner; soil contaminated 1.0
by leakage from impoundment
Spills
Contaminated material apparently removed completely; 0.1
but possible occurrence of a spill
Contaminated area covered with impervious material 0.5
No cleanup action or covering done 1.0
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TABLE A-3 (Concluded)
Containment Structure Score
Tanks
Tanks in sound condition and inspected regularly; tank 0.1
area lined adequately
Tanks in sound condition; no liner 0.5
Tanks leaking 1.0
Fire Protection Areas
Concrete surface 0.1
No concrete surface 1.0
Source: Barnthouse, L.W. et al., Development and Demonstration of a
Hazard Assessment Rating Methodology for Phase II of the
Installation Restoration Program, (ORNL/TM-9857), Oak Ridge
National Laboratory, TN, 1986.
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A.3 GSR
The Confirmation Study Rating (GSR) model is used by the U.S. Navy
in the Navy Assessment and Control of Installation Pollutants (NACIP)
Program to assign priorities for further study to hazardous substance
sites. The GSR model is based on the HARM system (Luecker, 1982).
In the GSR model, Receptor, Pathway, and Waste Characteristics
rating factors are multiplied by a Waste Management factor to obtain
the site score. The Waste Management factor is a measure of the
containment at the site and is identical to the Waste Management
Practices subscore of HARM, with one exception. The one difference is
that limited containment is given a value of 0.8 in the CSR model
rather than 0.95 as in HARM.
A.4 ADL
The Arthur D. Little, Inc. (ADL) system is an adaption of the
HRS that was developed for the Chemical Manufacturers Association
(Arthur D. Little, Inc., 1981).
Like the HRS, the ADL system contains a multiplicative containment
factor that is used only when there is no observed release for the
ground water or surface water pathway. The containment factor is
scored as either a 0 or a 1. For both pathways, it is scored 0 if the
site is certified to have an impermeable liner (natural or artificial),
the high water table is below the liner, and an impermeable cover has
been installed. Otherwise, it is scored 1.
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The major difference between the HRS containment factor and the
ADL containment factor is that the ADL containment factor does not
attempt to evaluate intermediate levels of containment. It is based
on the assumption that the rater should not try to make fine
distinctions in the degree of containment present at a site. The
site is scored as either being contained or not contained.
A.5 S.P.A.C.E. for Health
The System for Prevention, Assessment, and Control of Exposures
and Health Effect from hazardous sites (S.P.A.C.E. for Health) was
developed by the Centers for Disease Control (CDC) for use in public
health assessments of hazardous sites (French et al., 1984; Kay and
Tate, 1984). The system is used to assign priorities to sites,
based on the potential of the site to endanger human health.
Site Characteristics is one of four factors used in S.P.A.C.E.
for Health for determining the site priority. There are seven
elements used to rate Site Characteristics. One element, Site
Management and Containment, provides a measure of the containment at
the site. Site Management and Containment is evaluated through the
use of criteria that are identical to those of the HRS containment
factor (see Tables 2-1 and 2-2).
A.6 SAS
The Site Assessment System (Michigan, 1983) is used to assess
and prioritize release sites for further investigation and possible
remedial action.
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SAS considers containment through a Release Potential
Category. All containment structures (e.g., landfill) are first
rated for each pathway as to whether their containment effectiveness
is unquestionably adequate, inadequate, or unknown for that
pathway. A rating of unquestionably adequate containment for a
pathway must be based on information that indicates the structure
was designed, constructed, and is operating so that emissions of
hazardous substances are effectively prevented from entering the
environment through that pathway. Limited guidelines are provided
for this determination.
The Release Potential Category is scored for each containment
structure that is not rated unquestionably adequate. This is done
by first determining the fraction of the total waste quantity at the
site that is present in each containment structure (this results in
a value between 0 and 1 for each structure). The physical state of
the waste in each containment structure without unquestionably
adequate containment is then scored as follows: solid—1.0,
semi-solid—1.5, liquid or gas—2.0. The quantity fraction and the
physical state score are then multiplied to give a release potential
score for each structure. The release potential scores for each
structure without adequate containment for a specific pathway are
then summed to obtain the release potential score for the pathway.
The aggregated pathway release potential scores may not exceed 2.
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The aggregated pathway release potential score is then used as a
multiplicative factor in determining the overall pathway score.
SAS thus differs from the HRS in that it uses the concept of
containment strictly as a means of measuring the quantity of waste
that can migrate along a pathway and not as a measure of the
relative effectiveness of the containment structure at a site. In
the HRS containment is used for both purposes. Any waste in a
containment structure receiving an HRS containment score of zero for
a pathway is not considered in the rating of the HRS waste quantity
factor for that pathway.
A.7 PERCO
The Prioritization of Environmental Risks and Control Options
(PERCO) model (Arthur D. Little, Inc., 1983) was developed for the
Massachusetts Department of Environmental Quality Engineering for
use in ranking contaminated sites in terms of immediate and
long-term environmental and human health hazards. The ranking is
used to provide a rationale for allocation of state remedial action
funds.
Containment is not explicitly considered in ranking a site with
PERCO. Rather containment is used in the following manner. PERCO
contains a multiplicative factor called contaminant severity. It is
calculated based on the measured concentrations of contaminants in
the environment of a site and acceptable ambient levels of those
contaminants, using relationships defined in PERCO. Contaminant
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severity is assigned a value ranging from zero to 100. If monitoring
data are not available for a site, then the contaminant severity is
approximated for the site, using information from other similar
sites for which monitoring data are available. To do this, at least
ten similar sites, whose contaminant severity scores fall within an
acceptable range, are identified; the contaminant severity scores
for those sites are then averaged. This average contaminant
severity score is used as the contaminant severity score for the
site.
As one option, similar sites may be identified through
professional judgment. For two pathways (air and surface water),
there is also an option for identifying similar sites through the
calculation of a similarity score. One of the factors used to
calculate the similarity score is containment integrity. Containment
integrity is a measure of the potential for leakage from three types
of containment structures: drums; tanks; and pools, pits, or
lagoons. Drum integrity is scored as follows: many drums
leaking—8; a few widely separated drums leaking—4; all drums
intact—2; no drums on surface—0. Tank integrity is scored as
follows: at least one tank leaking—10; all tanks intact—6; no
tanks on site—0. Pools, pits and lagoons are scored as follows:
large pools or lagoons evident, but not associated with leaking
drums or tanks—10; no such pools evident—0.
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For the air pathway, there is one further option for calculating
similarity scores to identify similar sites. This involves
calculating a release potential score for sites that may be similar.
The release potential score is calculated for each site, based on
the condition of drums and tanks at the site; the volume of liquids
in pools, pits, and lagoons at the site; and the areal extent over
which liquid wastes are buried at the site. The condition of drums
is scored on a scale of 0 to 40, primarily based on the percent of
drums present that are corroded, damaged, have loose covers, or are
otherwise capable of leaking contents to the environment. The
condition of tanks is scored for each tank on a scale of 0 to 7,
based on whether the tank is leaking, has air vents to the outside,
and/or has an open top. The liquid volume, the surface area, and
the two scores for drum and tank condition are manipulated
mathematically and then added to obtain the release potential score.
PERCO thus differs from the HRS in that it does not consider
waste containment in the rating of a site. Each site is rated
solely on monitoring data obtained either from that site or from at
least ten similar sites. Containment is considered only in the
identification of the sites that are similar to the one being
rated. The containment evaluation factors used in PERCO are
appropriate only for this purpose; they are not intended for, nor
are they appropriate for, rating the relative effectiveness of
containment structures.
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A.8 Illinois Rating Scheme
The Illinois Rating Scheme is used by the State of Illinois as
a screening tool, for regional planning, to identify and prioritize
sites or areas potentially affecting ground water for more detailed
study and evaluation (Gibb et al., 1983).
The Illinois Rating Scheme consists of four additive factor
categories, each of which is made up of several additive elements.
One of these factor categories, Health Risk of Waste and Handling
Mode, contains an element that is a measure of site containment.
This element, Recorded Management of Waste, is evaluated differently
for active industrial sites, active landfills, and abandoned sites
as indicated in Table A-4. In using the criteria in the table, no
guidance is provided as to what constitutes controlled or
uncontrolled operation, a violation, or a site being well operated.
The Illinois Rating Scheme differs from the HRS (and the nine
other ranking systems reviewed) in that it considers limited features
of a site's operational history (e.g., source of waste, types of
violations) rather than its waste management characteristics in the
ranking of the site. While containment effectiveness is related to
operational history to a limited extent, this kind of approach does
not appear practical to apply to CERCLA sites where information
about the operational history of the site is extremely limited and
often unavailable.
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TABLE A-4
ILLINOIS RATING SCHEME RATING RECORDED MANAGEMENT OF WASTE
Criteria Rating
Active Industrial Sites
Principal On-site Storage or Disposal Method
Incineration 0
Secure Containers 2
Treatment/Discharge 4
Land Application 6
Landfill 8
Surface Impoundments 10
Active Landfills
Operational History
No violations whatsoever; operated up to best 0
expectations
No violations; generally well operated 2
No violations of a serious nature; generally well 4
operated
Some violations of a serious nature; history doubtful 6
Selected violations of a serious nature; past history 8
unknown
History of serious violations; essentially 10
uncontrolled for periods of time
Abandoned Waste Sites
Operational History
Controlled operation; solely municipal wastes 0
involved
Controlled operation; predominantly municipal wastes 2
involved
Controlled operation; municipal and industrial wastes 4
involved
Uncontrolled operation; municipal and industrial 5
wastes involved
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TABLE A-4 (Concluded)
Criteria Rating
Operational History (Concluded)
Uncontrolled operation; predominantly industrial 8
wastes involved
Uncontrolled operation; wastes of all types probably 10
present
Source: Gibb, J. et al., Hazardous Waste in Ogle and Winnebago Counties;
Potential Risk via Groundwater Due to Past and Present
Activities, Illinois Department of Energy and Natural Resources,
Document No. 83/26, Springfield, Illinois, 1983.
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A. 9 Rating Methodology Model
The Methodology for Rating the Hazard Potential of Waste
Disposal Sites (Rating Methodology Model) was developed for use by
the EPA Office of Enforcement and the Oil and Special Materials
Division in setting priorities for sites based upon preliminary
assessment data (JRB Associates, Inc., 1980).
The Rating Methodology model consists of four rating areas
whose scores are added to obtain an overall site score. One of the
four rating areas is Waste Management Practices which consists of
eight rating factors, four of which are related to waste containment.
These four rating factors are:
• Use of liners
• Use of leachate collection systems
• Use of gas collection systems
• Use and conditions of containers
The criteria and rating scales used to evaluate each of these four
rating factors are shown in Table A-5. The eight Waste Management
Practices rating factors are weighted and summed to determine the
score for the Waste Management Practices rating area.
The rating factors in the Rating Methodology model were
considered in the original development of the HRS. The rating
factors for containment were found not to be suitable for inclusion
in the HRS, in part because they were not comprehensive enough, nor
well enough defined, for use in evaluating site containment.
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TABLE A-5
CONTAINMENT RATING FACTORS IN THE RATING METHODOLOGY MODEL
Rating Factors
Criteria
Rating
Scale
Levels
Use of Liners
Use of Leachate
Collection Systems
Use of Gas
Collection Systems
Use and Condition
of Containers
Clay or other liner resistant to organic 0
compounds
Synthetic or concrete liner 1
Asphalt-base liner 2
No liner used 3
Adequate collection and treatment 0
Inadequate collection or treatment 1
Inadequate collection and treatment 2
No collection or treatment 3
Adequate collection and treatment 0
Collection and controlled flaring 1
Venting or inadequate treatment 2
No collection or treatment 3
Containers are used and appear to be 0
in good condition
Containers are used but a few are leaking 1
Containers are used but many are leaking 2
No containers are used 3
Source: JRB Associates, Inc., Methodology for Rating the Hazard
Potential of Waste Disposal Sites (Draft Final Report),
McLean, VA, 1980.
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Furthermore, the use of an additive containment factor was judged
unsuitable because with an additive factor, a site could have total
containment and still receive a high score. This is not the case
with a multiplicative containment factor.
A. 10 Dames and Moore Methodology
The Dames and Moore Methodology was developed to evaluate waste
disposal sites with respect to their potential for ground water and
surface water contamination (Dames and Moore, undated).
The Dames and Moore Methodology was adapted from the Rating
Methodology model and consists of four rating areas. One of these
rating areas is Spill Potential. Spill Potential applies only to
landfills and consists of ten rating factors, four of which are
related to waste containment. These four rating factors are:
• Cover condition
• Leachate management
• Gas management
• Personnel training
The criteria and rating scales used to evaluate each of these four
rating factors are shown in Table A-6. The ten Spill Potential
rating factors are weighted and summed to determine the score for
the Spill Potential rating area.
These four rating factors have the same limitations as the
rating factors in the Rating Methodology model from which they were
derived.
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TABLE A-6
CONTAINMENT RATING FACTORS IN THE DAMES AND MOORE METHODOLOGY MODEL
Containment
Rating Factors
Rating
Scale
Multiplier Criteria Levels
Cover Condition
Leachate Management
10 Well contoured, no cracking or
vigorous vegetative cover, no
signs of subsidence
Signs of cover failure
visible at 25% of site area
Signs of cover failure
visible at 50% of site area
Large areas of subsidence,
poor contouring, no vegetative
cover in most of the site,
exposed waste
8 Arid region; or leachate
monitors installed but none
detected
No leachate monitoring, but
leachate generation unlikely
(arid weather, good cover, etc.)
Some evidence of leachate
generation at only certain
portions of the site
No leachate monitoring, or
positive proof of leachate
generation
0
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TABLE A-6 (Concluded)
Containment
Rating Factors
Multiplier
Criteria
Rating
Scale
Levels
Gas Management
Personnel Training
No gases are generated or
generated gases are
successfully managed.
Inadequate information. Gas
generation anticipated. Some
venting measures Installed.
Inadequate information. Gas
generation anticipated. No
venting measures installed.
Gas generation is evident or
anticipated. Signs of cap
distress visible.
All waste disposal related
personnel are formally trained
in safety and environmental
control.
Only waste disposal supervisory
personnel are formally trained
in safety and environmental
control.
Some informal training of waste
disposal supervisory personnel.
None
0
Source: Dames and Moore, Overview of Methodology for Rating Potential
for and Significance of Ground and Surface Water Contamination
from Waste Disposal Sites, Bethesda, Maryland, Undated.
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A.11 Liner Location Risk and Cost Analysis Model
The Liner Location Risk and Cost Analysis Model is designed
to be used by EPA to investigate cost/risk and cost/effectiveness
implications of the land disposal of hazardous wastes under different
technology, location, and waste stream scenarios. The model
estimates the relative chronic risk to human health from land
disposal facilities with different design technology, location, and
waste stream characteristics. The model also estimates the cost of
facilities with differing technologies and sizes. The model uses a
series of submodels to predict contaminant releases, subsurface and
atmospheric transport, human exposure, and health risk based upon
dose-response factors (U.S. Environmental Protection Agency, 1985).
Containment is taken into account within the Failure and Release
Submodel of the Liner Location Model. For land disposal facilities
(i.e., landfills, surface impoundments, waste piles, and land
treatment), this submodel estimates both the probability of various
types of failures (i.e., release of leachate) at selected times for
different facility designs in different climates and the quantity of
leachate released by the failures. Various combinations of liners
and cover types and materials are used to define the different
facility types. The model does not consider failure events that
result in overland surface run-off releases.
The Failure Analysis Submodel utilizes a "fault tree" approach
to evaluate the frequency of occurrence of a failure event at a
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facility due to various elementary failure events (e.g., liner aging,
infiltration of liquid, drum failure, cover consolidation, liner
breach due to rise of ground water table). The fault tree approach
traces a failure event backwards to identify all relevant elementary
failure events which could combine to cause the failure. Each
elementary failure event is given a probability distribution based
upon theoretical and empirical data. The volume of liquid entering
or exiting the facility if the elementary failure event occurs is
also given a probability distribution. (Each elementary failure
event is assumed to occur at random and is given either a triangular,
binomial or time-dependent binomial distribution. The volume of
liquids associated with an event is given a uniform distribution.)
This submodel uses the fault tree structure to compute the
probabilities of failure events which occur if some sequence of
prerequisite elementary events have occurred.
Monte Carlo simulation* is then used to estimate the cumulative
probability of occurrence of each failure event for each facility
type and climate and to estimate the volume of leachate released by
the failure event. The volume of leachate released is estimated by
incorporating a series of hydrologic inputs (e.g., infiltration from
*Monte Carlo simulation consists of sampling from the probability
distribution of the elementary events. The sampling is done through the
use of a random number generator. After all the elementary failure
events in a fault tree are evaluated, the model determines whether a
failure event occurs and the volume released if it occurs. This process
is repeated a large number of times using a computer to obtain an
estimate of the relative frequency of occurrence of each failure event.
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precipitation) in the elementary failure events and tracking them with
a mass balance analysis.
The Liner Location Risk and Cost Analysis Model thus addresses
containment in a very different manner than the HRS. However, as
currently structured, it is not meant for, nor is it applicable to,
site-specific comparisons of containment effectiveness. Rather it is
intended primarily for use in analyzing the risks and costs associated
with alternative regulatory strategies (e.g., alternative standards
for waste containment at land disposal facilities).
A.12 Hazardous Waste Tank Failure Model
The Hazardous Waste Tank Failure (HWTF) Model is one of the models
being used by the EPA Office of Solid Waste to support the development
of regulations for hazardous waste tanks (IGF Incorporated and
Pope-Reid Associates, Inc., 1986; Pope-Reid Associates, Inc., 1986).
The HWTF model uses fault trees and Monte Carlo simulation (see
Section A.11) to predict the timing of failure events (e.g., leaks,
ruptures) for hazardous waste tank systems and to estimate release
volumes associated with these failure events over a 20-year operating
life.
The HWTF model is currently designed to analyze four types of
tanks: RCRA-permitted treatment tanks, RCRA-permitted storage tanks,
accumulation tanks (storage for less then 90 days), and small-quantity
generator tanks. For each type of tank, the HWTF estimates the timing
of failure events and the magnitude of associated releases for five
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regulatory (containment) scenarios: a baseline scenario that assumes
all tanks are managed and operated in compliance with existing RCRA
Subtitle C regulations and four alternatives that are more stringent
than the baseline scenario.
As structured, the HWTF model is not meant for, nor is it
applicable to, site-specific comparison of containment effectiveness.
Rather it is intended for use in analyzing alternative regulatory
strategies.
A. 13 RCRA Risk-Cost Analysis Model
The RCRA Risk-Cost Analysis Model is used by the EPA Office of
Soild Waste to support the development of regulations under RCRA. The
model produces relative risk and cost estimates for different
management configurations of waste streams; waste transportation,
treatment and disposal technologies; and environments. The model
estimates human health, ecosystem and sensory risks from steady state
releases of RCRA contaminants (and selected other contaminants) to
ground water, surface water, and air. The model also calculates the
costs of each technology in a management configuration as an annual
revenue requirement. The model treats each management configuration
in a generic fashion employing standard risk assessment methods (e.g.,
emissions estimates coupled with transport and fate models aligned
with dose response models) and numerous simplifying assumptions (ICF
Incorporated, 1984; Males, 1984).
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Containment is taken into account in the RCRA Risk-Cost Analysis
Model in the Waste Disposal Technologies component of the model.
This component contains six kinds of disposal technologies:
landfills, surface impoundments, waste piles, land treatment,
incineration, and deep well injection. To represent a wide range
of designs, the model includes a number of different configurations
for each kind of disposal technology. For landfills and surface
impoundments, the configurations differ primarily in the type of
liner system used, ranging from unlined to double liners. Except
for the unlined configuration, all configurations include leachate
collection, monitoring wells, and collection of surface run-off. A
number of the configurations that employ liners comply with the RCRA
Subtitle C requirements for landfills and surface impoundments.
With regard to the other four disposal technologies, the various
configurations in the model all comply with the RCRA Subtitle C
regulations appropriate to the technology.
In general, the model accounts for leachate migration to ground
water by first estimating leachate generation rates over time and
combining these with estimates of liner failure probabilities and
saturated flow limitations imposed by underlying clays and soils.
Synthetic liners are assumed to have a life of 35 years and to have
a uniform failure rate over this period. When a synthetic liner
fails, it is assumed to disintegrate (i.e., leak everywhere). Clay
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liners are assumed to retain their integrity and low permeability over
the operating life of the waste disposal technology.
Leachate collection and treatment systems are assumed to release
a fixed portion of the leachate they handle. All leachate released by
the system is assumed to be lost to the environment. The leachate is
distributed among air, surface water, and ground water by first
estimating the amount of constituents that evaporate (based on
volatility), and then assuming that 70 percent of the remainder moves
toward surface water and 30 percent moves toward ground water.
Overland run-off to surface water is also assumed to occur from
storm events exceeding the holding capacities of surface impoundments
and/or storm water run-off management systems. Overtopping is assumed
to have a constant probability of occurrence in any year. The model
does not account for other overland run-off release mechanisms (e.g.,
leaks or dike failures). The model also does not account for the
transport of contaminants by ground water to surface water.
As structured, the RCRA Risk-Cost Analysis Model is not meant
for, nor is it applicable to, site-specific comparisons of containment
effectiveness. Rather it is intended for use in analyzing alternative
regulatory strategies.
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APPENDIX B
BIBLIOGRAPHY
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Arthur D. Little, Inc., Cambridge, MA, September 12, 1983.
Barnthouse, L.W. et al., Development and Demonstration of a Hazard
Assessment Rating Methodology for Phase II of the Installation
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Dames and Moore, Overview of Methodology for Rating the Potential
for and Significance of Ground and Surface Water Containment from
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French, Jean G. et al., A System for Prevention, Assessment, and
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Gibb, J., Barcelona, M., Schock, S., and Hampton, M., Hazardous
Waste in Ogle and Winnebago Counties; Potential Risk via
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of Energy and Natural Resources, Document No. 83/26, Springfield,
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ICF Incorporated, The RCRA Risk-Cost Analysis Model Phase III Report
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ICF Incorporated and Pope-Reid Associates, Inc., Hazardous Waste
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JRB Associates, Inc., Methodology for Rating the Hazard Potential of
Waste Disposal Sites (Draft Final Report), McLean, VA, 1980.
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Kay, Robert L., Jr. and Chester L. Tate, Jr., "Public Health
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Luecker, Elizabeth B., "Navy Assessment and Control of Installation
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Males, E., RCRA Risk-Cost Analysis Model, presented at the AICHE
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Michigan Department of Natural Resources, Site Assessment System (SAS)
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Sayala, D., Hazard Ranking System Issue Analysis; Subsurface
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U.S. Environmental Protection Agency, Liner Location Risk and Cost
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Wang, M., Hazard Ranking System Issue Analysis; Alternative Methods
for Ranking the Persistence of Hazardous Substances in Surface Water
(Draft Report), MTR-86W172, The MITRE Corporation, McLean, VA. 1986.
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Revising the AirTathway (Draft Report), MTR-86W53, The MITRE
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